Loading...
HomeMy WebLinkAboutPD 2020-0047; HARLE RESIDENCE; GEOTECHNICAL UPDATE REPORT; 2016-07-25Geotechnical Update Report Proposed Residential Duplex Development Existing Pad (Lot .1) 4547 Cove Drive Carlsbad, California July 25, 2016 Prepared For: Mr. Kyle Stephens Kyle Stephens & Associates 1350 Columbia Street, Suite 702 San Diego, California 92101 Prepared By: SMS GEOTEC1-INiCAL SOLUTIONS, INC. 5931 Sea Lion Place, Suite 109 Carlsbad, California 92010 Project No. GI-16-06-128 RC ELVED DEC 01 2020 LAND DEVELOPMENT ENGINEERING SMS GEOTECI-INiCAL SOLUTIONS, INC. Consulting Geotechnical Engineers & G-ologists 5931 Sea Lion Place, Suite 109 Carlsbad, California 92010 Office: 760-602-7815 smsgeosol.inc@gmail.com Project No. GI-16-06-128 July 25, 2016 Mr. Kyle Stephens Kyle Stephens & Associates 1350 Columbia Street, Suite 702 San Diego, California 92101 GEOTECHNICAL UPDATE REPORT, PROPOSED RESIDENTIAL DUPLEX DEVELOPMENT, EXISTING PAD (LOT 31), 4547 COVE DRIVE, CARLSBAD, CALIFORNIA Pursuant to your request, SMS Geotechnical Solutions, Inc. has completed the attached Geotechnical Update Report for the proposed single-family residential development at tFe above- referenced project property. The following report summarizes the results of our research and review of the previous pertinent geotechnical reports, documents, and current grading plan, and provides update conclusions and amended recommendations for the proposed development, as understood. From a geotechnical engineering, standpoint, it is our opinion that the property is considered substantially suitable for the planned residential development and associated improvements, provided our recommendations presented in this report are incorporated into the design and implemented during the construction phase of the project. The property is underlain by soft to loose saturated fills and lagoonal deposits, and special ground stabilization method(s) and foundation support system will be required for the planned development as presented herein. The conclusions and recommendations provided in this. study are consistent with the indicated site geotechnical conditions and are intended to aid in preparation of final construction plans and allow more accurate estimates of associate costs. If you have any questions or need clarification, please do not hesitate to contact this office. Reference to our Project No. GI-16-06-128 will help to expedite our response to your inquiries. We appreciate this opportunity to be of service to you. Solutions, Inc. - No. 283S 19' Exp. I2/31I6 idi S. Shariat #2885 TABLE OF CONTENTS I. INTRODUCTION ......................................................1 II. SITE DESCRIPTION ...................................................2 III. PROPOSED DEVELOPMENT ...........................................2 IV. SITE INVESTIGATION ..................................................3 V. GEOTECHNICAL CONDITIONS ........................................3 Earth Materials .....................................................3 Groundwater and Surface Drainage ....................................4 Seismic Ground Motion Values ........................................4 Geologic Hazards ....................................................5 VI. FIELD AND LABORATORY TESTING ...................................9 VII. SITE CORROSION ASSESSMENT ......................................10 VIII. STORM WATER BMPs ................................................10 Bio-Rentention ......................................................10 Permeable Interlocking Concrete Payers (PICP) .........................11 IX. CONCLUSIONS ......................................................12 X. PROS AND CONS OF LIQUEFACTION MITIGATION ALTERNATIVES .... 15 XL RECOMMENDATIONS ................................................17 Ground Stabilization, Remedial Grading and Earthworks .................17 Post-Tensioned Rigid Raft Foundation Slab .............................28 Soil Design Parameters ..............................................30 Inter-Locking Payers ................................................31 GENERAL RECOMMENDATIONS .....................................32 GEOTECHNICAL ENGINEER OF RECORD (GER) .......................34 LIMITATIONS .......................................................34 4 TABLE OF CONTENTS (continued) FIGURES GeotechnicalMap ............................................................1 GeologicCross-Sections ........................................................2 Fault-Epicenter Map ..........................................................3 TsunamiInundation Map ......................................................4 FEMAMap ..............................................................5&6 Typical Bio-Retention Detail ....................................................7 Typical Permeable Paver Detail .................................................8 Typical Ground Stabilization, N-S Direction ......................................9 Typical Ground Stabilization, E-W Direction ....................................10 Settlement Plate Schematic ....................................................11 Typical Foundation Plan ......................................................12 Typical Interior Stiffener Detail ................................................13 Typical Retaining Wall Back Drainage Detail ....................................14 ATTACHMENTS I & II Prior Geotechnical Reports by Vinje & Middleton Engineering, Inc. ATTACHMENT III USGS Seismic & Design Maps Summary Report GEOTECIJMCAL UPDATE REPORT PROPOSED RESIDENTIAL DUPLEX DEVELOPMENT EXISTING PAD (LOT 31) 4547 COVE DRIVE CARLSBAD, CALIFORNIA I. INTRODUCTION The project property is an existing small bay-side lot adjacent to Agua Hedionda in the coastal areas of the City of Carlsbad. A Conceptual Grading Plan, prepared by Florez Engineering, Inc. is reproduced herein as Geotechnical Map, Figure 1. The approximate site location is depicted on a Vicinity Map included on Figure 1. The approximate site coordinates are 33.1457'N latitude and -ll7.3245W longitude. We understand that the site is planned for the support of a duplex residential structure which will occupy much of the lot surface. The project property was the subject of prior detailed geotechnical studies performed by Vinje & Middleton Engineering, Inc. (VME) dating from 2004 to 2008 (initial boring explorations were completed in late 2003), completed in connection with a development very similar to the current development scheme shown on Figure 1. Their findings and development recommendations were provided in the following written technical report: "Drilled Caisson Foundations, Proposed LBC Condominium Project, 4547 Cove Drive, Carlsbad, California," prepared by Vinje & Middleton Engineering, Inc. Job #03-348-P, dated February 2008 (an unsigned draft copy was obtained and is included with this report as an Attachment I). "Foundation Plan Review, Proposed Three-Story Twin Homes, Lot 31, Tract 5162, Cove Drive, Carlsbad, California," prepared by Vinje & Middleton Engineering, Inc., December 13, 2006, "Update Geotechnical Report and Remedial Grading Ground Stabilization Recommendations, Lot 31, Tract 5162, Cove Drive, Carlsbad, California," prepared by Vinj e & Middleton Engineering, Inc. Job #03-348-P, dated September 25, 2006 (included herein as Attachment II). "Foundation Plan Review, Proposed Three-Story Twin Homes, Lot 31, Tract 5162, Cove Drive, Carlsbad, California," prepared by Vinje & Middleton Engineering, Inc. Job #03-348- P, dated July 14, 2006 (included herein as Appendix A of Attachment II). "Preliminary Geotechnical Investigation, Lot 31, Tract 5162, Cove Drive, Carlsbad, California," Prepared by Vinje & Middleton Engineering, Inc. Job #03-348-P, dated March 3, 2,004 (included herein as Appendix B of Attachment II). S Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 2 6. "Addendum Geotechnical Report, Lot 31, Tract 5162, Cove Drive, Carlsbad, California," prepared by Vinje & Middleton Engineering, Inc. Job #03-348-P, dated November 19, 2003 (included as Appendix C of Attachment II, the printed date is suspected to be incorrect, and year 2004 is considered more reasonable for the actual report date). The referenced report is on file with our office and was reviewed in conjunction with this submittal. Selected references are attached to this report as Attachments I and II. The purpose of this effort was to update the referenced reports (Attachments I and II) and confirm their compatibility with the most current Grading Plan (Figure 1) with the indicated site geotechnical conditions. Revised and/or amended conclusions and recommendations consistent with the attached plan, current applicable codes and engineering standards are also provided in the following sections, and will supplement or superseded those given in the referenced report, where applicable. Our effort in connection with the preparation of this update report also included a recent site visit. However, added subsurface explorations, soil sampling, or laboratory testing were determined not necessary, and the prior work completed by the previous consultant in this regard was considered acceptable to us. Pertinent geotechnical data generated by the pervious consultant (see Attachments I and II) were also relied upon and utilized herein, where appropriate. II. SITE DESCRIPTION Site surface conditions are delineated on the attached Figure 1, and remain substantially unchanged from those described in the referenced report(s). In general, the project site is a small, roughly 40 feet wide by 117 long, nearly level lot between two developed residential buildings to the north and south. Cove Drive provides access and marks the front (western) boundary. A small rock-armored graded slope (shore protection rock revetments) marks the rear (eastern) boundary which descends approximately 10 feet into the adjacent lagoonal waters. The lot chiefly consists of dirt surfaces. Site drainage is indistinct with no evidence of scouring or runoff erosion. IlL PROPOSED DEVELOPMENT The project development scheme is shown on Figure 1, and remains very similar to the prior development concept used a basis for the preparation of referenced reports by the prior consultant. As, shown, the project property is planned for the support of two narrow, connected side by side duplex-type residential development with associated improvements. The buildings will likely be two- story structures and will occupy much of the lot surface. Major grade alterations or creation of large graded slopes is not planned in connection with the project development with finish pad grades (13.15 feet MSL) established at or very near the existing ground surfaces. Project earthwork is expected to mainly consist of remedial grading ground stabilization operations. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 3 Building construction and foundation designs are also not yet completed. Conventional wood-frame buildings with exterior stucco are anticipated. Several ground stabilization and foundation support options including utilizing deep drilled (CIP) caissons, driven piles, and mat and grade beam foundations with raised structural floor slabs were recommended by the prior consultant and still remain viable. However, we understand a structural rigid raft post-tensioned slab with perimeter and interior stiffening beam type foundation supported on stabilized bearing soils is also being considered due to site constrains and limitations, and based on relative ease of contraction, cost feasibility, and acceptable levels of risk and future building performance. SITE INVESTIGATION The original site investigation by Vinje & Middleton Engineering, Inc. (VME) included two exploratory test borings drilled with a truck-mounted rotary drill. Approximate location of exploratory test borings are shown on Figure 1. Logs of the test borings are included as Plates 5 and 6 of Appendix B in the enclosed Attachment II. Laboratory test data and engineering properties of underlying soils are also summarized in Appendix B (Pages 6 through 9) of Attachment II. GEOTECHINICAL CONDITIONS Geotechnical conditions at the project property remain largely as reported in detail in the referenced reports (see Attachment I). In general, the property consists of a nearly level graded pad apparently created in the 1960's as a part of the surrounding development by placing imported fill soil over natural lagoonal areas adjacent to Agua Hedionda. Depths of existing fills vary underneath each lot. Grading records for engineering observations and compaction testing of the existing fills are unavailable. A. Earth Materials Overall site subsurface conditions are described in the referenced reports. As established by the prior consultant, the project lot is underlain by a section of silty to clayey fill soils to a depth of nearly 15 feet that were placed atop natural lagoonal deposits. Formational siltstone rocks occur at an approximate depth of 49 feet below existing ground surfaces (BGS) underneath the lagoonal deposits. Added details of the site underlying earth materials are presented on the project exploratory boring logs (Plates 5 and 6, Appendix B of Attachment II) and further described in the referenced reports. Geologic Cross-Sections based on current topography and proposed finish grades are included as Figure 2. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 4 Groundwater and Surface Drainage Subsurface groundwater was encountered at depths of approximately 5 to 7 feet (BGS) at the time of original field explorations (August 2003), High groundwater levels are expected to be mostly on the order of 5 feet (BGS). The water reflects lagoonal water which has saturated the site underlying soils. The indicated levels are expected to fluctuate slightly with changing tide levels. Project over-excavations for ground stabilization and remedial grading operations are expected to encounter subsurface groundwater and light to heavy water intrusion into the excavations, depending on the seasonal and tidal conditions at the time of grading. Consequently, dewatering will likely be required and should be completed at each local quartered/phased rock mat placement and remedial grading sections, as specified below. Dewatering shall not be allowed to adversely impact the nearby buildings, structures and improvements. Completing grading during the dry seasons of the year and low tidal conditions should be considered to minimize difficulties associated with dewatering operations. Some pre-dewatering may also be considered appropriate for this project. Any dewatering technique(s) suitable to the field conditions which can effectively remove the intruding water and allow soil removals and rock mat/fill placement is considered acceptable provided it is approved by the project engineer. Dewatering should continue until completion of remedial grading operations and should be discontinued only upon approval of the project geotechnical engineer. Groundwater should be lowered below the specified bottom of over-excavation, toe of temporary slope or trench excavations unless otherwise approved or directed in the field. As with all developed properties, the proper control of flood waters and site surface drainage is a critical component to overall stability of the graded building pad. Surface water should not pond upon graded surfaces, and irrigation water should not be excessive. Over-watering of site vegetation may also create perched water and the creation of excessively moist areas at finished pad surfaces and should be avoided. Seismic Ground Motion Values Seismic ground motion values were determined as part of this investigation in accordance with Chapter 16, Section 1613 of the 2013 California Building Code (CBC) and ASCE 7-10 Standard using the web-based United States Geological Survey (USGS) ground motion calculator. Generated results including the Mapped (Ss. Si), Risk-Targeted Maximum Considered Earthquake (MCER) adjusted for site Class effects (SMS, SMI) and Design (SDs, SDI) Spectral Acceleration Parameters as well as Site Coefficients (Fa, F) for short periods (0.20 second) and 1-second period, Site Class, Design and Risk-Targeted Maximum Considered Earthquake (MCER) Response Spectrums, Mapped Maximum Considered Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 5 Geometric Mean (MCEG) Peak Ground Acceleration adjusted for Site Class effects (PGAri) and Seismic Design Category based on Risk Category and the severity of the design earthquake ground motion at the site are summarized in the enclosed Attachment lii. D. Geologic hazards Conditions which could result in potential geologic hazards are known in areas of San Diego County. The following geotechnical factors are evaluated herein: Seismicity / Faulting: A significant geotechnical factor which could impact the project site relates to ground shaking during an earthquake event along an active fault. Moderate to locally heavy levels of ground shaking can be anticipated during rare events over the lifetime of the development. The location of significant faults and earthquake events relative to the study site is depicted on a Fault - Epicenter Map enclosed herein as Figure 3. Faults or significant shear zones are not indicated within the project site. The project is not located in proximity to Aiquist - Priolo earthquake fault zone areas associated with active faults discussed above. Tsunami: A significant tsunami impacting the project property would be a very rare event. As indicated on a Tsunami Inundation Map for Emergency Planning (San Luis Rey Quadrangle), included herein as Figure 4, the project site is located on the tsunami inundation line. Consequently, potential tsunami risks are similar to the adjacent and nearby properties, and developments. Inhabitants of the residence should be aware of local evacuation routes as well as tsunami preparedness provided by the California Geological Survey on their web site. Flood Inundation: Lot 31 is located in lower hillside terrain along the west flank of agoonal waters off of Agua Hedionda. Therefore, flooding hazards risks due to remote Tsunami inundation will require inhabitants' awareness and preparedness for such a rare condition. In order to further evaluate general site flooding potential, we obtained a pertinent copy of the available Flood Insurance Rate Map produced by the Federal Emergency Management Agency (FEMA). As shown on the attached FEMA map, the project property is located on panel 764 of 2375 with eastern margins on the line with Special Flood Hazard Areas Subject To Inundation By The 1% Annual Change Flood, as depicted on the enclosed Figures 5 and 6. Flooding hazard risks for coastal flood zones with velocity hazards (wave action) will be similar to the adjacent and nearby properties and developments requiring inhabitants' awareness and preparedness for such a condition. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 6 4. Liquefaction and Seismically Induced Settlement: Liquefaction analyses were performed as a part of original site study performed by the previous consultant (VME report dated March 3, 2004, Appendix B of Attachment II). Their analysis (Page 5, Plates 8 and 9 of referenced report) concluded that "saturated site fills and natural lagoonal deposits are highly liquefiable (safety factors of less than 1)." Appropriate mitigation measures and foundation support system alternatives consistent with the site indicated geotechnical conditions were provided which included deep drilled (CIP) caissons or driven piles with raised structural floor slabs, and ground stabilization in conjunction with mat and grade beam foundations. Soil softening and liquefaction of the underlying deposits during a major seismic event along a nearby active fault remain the most significant geotechnical concern at the project building site, and appropriate mitigation measure shall be implemented. As presented in the referenced reports, several mitigation alternatives are available. The choice of alternative will depend on site constraints and ease of construction, economic feasibility, and acceptable levels of risk and future building performance. Our research (USGS & OCOF) also indicates that projected sea level rise (SLR), estimated based on various climate scenarios for the next 75-years, may range from approximate average low of 2 feet (0.6m) to average high of 4 feet (1.25m). Considering the finish pad grade elevation at roughly 13 feet (MSL), the projected SLR will not be a significant factor in our analysis nor influence ourmitigation design recommendations. Impacts of future SLR will be similar to the adjacent and nearby properties, developments and public improvements requiring current and future owners' awareness and preparedness. Seismically induced total and differential settlements are accepted to be similar to the adjacent properties, nearby public improvements and existing surrounding developments, and may be estimated to be on the order of 13 and 6.5 inches for total and differential settlements respectively, for a rare 7.5 magnitude earthquake event. Smaller seismically induced total and differential settlements, on the order of 2 and 1 inch, respectively may be estimated for more frequent low magnitude seismic events. In the case of the rock mat ground stabilization option with remedial grading using reinforced 95% compacted fill, the recommended procedures are provided to alleviate differential settlements and limit total settlements to uniform conditions throughout the mitigated building pad areas. Design parameters for rigid raft post-tensioned type foundation support system is also provided to further withstand the approximate design estimates. However, the risk level of seismically induced total and differential settlements impacts after a major large magnitude seismic event requiring future mitigation measures will remain similar to the adjacent properties, neighborhood developments and nearby public improvements, and require awareness by the current and future homeowners. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 7 Lateral Spread: Lateral spread of the existing eastern rock-face slopes during an earthquake event is also a major geotechnical concern. Liquefiable soils can create planes of weakness and sliding on the nearby graded slope posing a potential for failure. Details of the existing slope construction is not known, however, it was likely provided with a rock face to prevent erosion due to waive action and perhaps a filter layer and core materials to provide confinement and disallow large displacement due to lateral spread. Lateral spread of liquefied soils adjacent to the channel with breaks on ground surfaces creating blocks separated by fissures may be roughly estimated to be on the order of one foot. However, very large lateral spread is not expected under the liquefaction mitigated building pad surfaces, constructed as specified herein, with indicated minimum 15 feet building setback from the top of the rear channel slope. Houses and small buildings supported on deep CIP caissons/driven piles, or rigid raft post-tensioned type foundations are also expected to typically perform well with respect to potential lateral spread. The risk level of lateral spread outside the mitigated areas and possible future mitigation/repair measures will be similar to the adjacent properties and neighborhood developments and requires awareness by the current and future homeowners. Slope Stability: The rear slope is a continuous shore protection embankment feature extending well beyond the limits of the project property and is thought to have been created along the edge of the entire waterway as part of the original manmade cove and existing surrounding bayside developments. Disturbance of the rock-armored slope for investigative purposes, or by the planned development at the project property can result in costly mitigation and repairs, and in our opinion, shall be avoided. Details of the existing shore protection slope construction including thickness of the rock revetment, filter layer and core materials are not known. The man-made rock revetment-faced slope currently occurs at safe gradients ranging from 3:1 to 2:1 with the planned building adequately setback from the top of slope. The project portion of the slope is currently performing well with no indication of imminent or impending instability. In our opinion, detail slope stability analysis of the rear slope is not considered warranted, nor trenches or disturbance of the existing slope should be carried out to further confirm stability of the currently performing rear shore protection slope. Modeling of existing rear shore protection slopes with a rock armored face, which may include a filter layer and a core section, is also difficult and will include numerous uncertainties and redundant assumptions, which can result in misleading over or under estimation of the safety factor, and is not recommended by this office. The projected SLR will not be a significant factor in slope stability with inside and outside slope groundwater levels expected to be very similar. [I S Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 8 The risk level of potential instability of rear slopes, which is a small portion of a continuous embankment feature extending well beyond the limits of the project property, and possible future mitigation/repair measures will be similar to the existing surrounding bayside developments and require awareness by the current and future homeowners. 7. Settlement: Settlement of foundation bearing soils is a geotechnical concern at the project construction site. Existing soft to very soft fills and lagoonal deposits will likely experience short and long term settlements. Treatment of upper sections of these deposits by means of removal and recompaction remedial grading will be necessary in order to construct more stable building surfaces for the support of the planned building and associated improvements, as recommended in the following sections. Rock mat stabilization method and reinforced earth compacted fill bearing soils are also recommended herein to alleviate very large differential settlements. Actual total and differential settlements will be measured by the installing geotechnical instrumentation devices (settlement plates) during the remedial grading efforts and surcharging the deeper lagoonal deposits with at least 5 feet of minimum 95% compacted fills. Monitoring is recommended here by means of field surveying shots periodically taken at each monitoring site as the backfill placement progresses, and continuing after completion of remedial grading. Data reduction and establishing settlement patterns and soil compression characteristics due to surcharge loading pressures by heavy construction equipment, compaction efforts, and earthwork activities are also recommended. Foundation trenching can only begin after data reduction and approval of the project geotechnical consultant (differential settlements on the order of 0.01-foot or 0.12 inches between at least three consecutive post-grading readings per the monitoring schedule, unless otherwise noted or required by the project geotechnical consultant). The need for awaiting a period up to approximately 6 to 12 weeks after the completion of rough pad grading and before proceeding with utility and foundation trenching maybe required for this purpose. Post-tensioned rigid raft type foundation option recommended herein is also specified for an allowable foundation pressure limited to 1000 psf. The specified foundation contact pressure is typically less than surcharge loading pressures induced by heavy construction equipments for achieving 95% compaction level within the fill mat. As a result, the majority of the expected total and differential settlements due to the anticipated foundation loads are expected to occur and recorded by the monitoring of the installed settlement plates during the pad construction phase and specified monitoring period thereafter. However, secondary post construction settlement is expected to continue to occur after building construction. Total post-construction settlements may be anticipated to be uniform throughout the mitigated building pad areas and may be roughly estimated to be Geotechuical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 9 on the order of approximately 2 inches. Large differential settlements are not anticipated and the magnitude of post construction differential settlements, as expressed in terms of angular distortion, may be estimated to be approximately on the order of I-inch. Post- tensioned rigid raft type foundation slabs, as specified, should be designed to withstand the expected secondary total and differential settlements. The risk level of requiring related future mitigation is expected to be mostly similar to like construction types in neighborhood developments, and require awareness by the current and future homeowners. Collapsible Soils: Buildings and improvements founded on collapsible soils may be damaged by sudden and often large induced settlement when these soils are saturated after construction. Collapsible soils are typified by low values of dry unit weight and natural water content. The amount of settlement depends on the applied vertical stresses and the extent of the wetting and availability of water. Existing upper fill soils at the site may locally be prone to collapse potential and will require remedial grading mitigation as recommended herein. Expansive Soils: Based upon our field observation, available laboratory testing, and experience with local soils, onsite shallow soils are expected to range from low to medium expansive. Clayey expansive bearing and subgrade soils are also considered a geotechnical concern at the project construction site. Adverse effects of the site potentially expansive clayey soils should be considered in the project designs and effective mitigation measures implemented during the construction of the project as specified in the fallowing sections. Utilizing good quality sandy (D.G.) import soils used to complete remedial grading and cap the building pad within the upper grades will help to mitigate adverse effects of site expansive soils and enhance engineering properties of foundation bearing and subgrade soil. Saturated silty to clayey soils are also more difficult to process and achieve 95% compaction levels, and utilizing sandy granular (D.G.) import soils will increase remedial grading production levels. VI. FIELD AND LABORATORY TESTING Field and laboratory testing was performed by the previous consultant (VME) and presented in the referenced report dated March 3, 2004 (Appendix B of Attachment II). All field and laboratory testing provided in the referenced report is acceptable to us and were utilized herein, where applicable and as appropriate. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 10 VII. SITE CORROSION ASSESSMENT Based on results of available laboratory testing, close proximity of the site to saltwater and our experience with similar soils, the project site is considered highly corrosive. The amount of water soluble sulfate (SO4) was repoiled to be 0.268 percent by weight which is considered severe according to AC! 318 (S2 Exposure Class with Severe severity). Due to the expected concrete exposures to external seawater sources, chloride exposures should also be considered severe (C2 Exposure Class with Severe severity). Consequently, special high strength, Type V cement concrete with a minimum 28 days compressive strength (f's) of 5,000 psi and a maximum water cement ratio of 0.40, as well as epoxy coated reinforcing steel (post-tensioning tendons) and greater reinforcement cover should be considered, as determined and confirmed by the project corrosion/structural engineer. A qualified corrosion engineer may be consulted in this regard. VU!. STORMWATER BMPs A. Bio-Retention An infiltration bio-retention basin is planned along the eastern property near the top of the eastern shore protection rock revetment slope. The top of the eastern armored shore protection slope will be disturbed or modified (removed) to accommodate the proposed bio- retention, as shown on Figure 1. Depth (thickness) of the bio-retention from adjacent pad grades and extent of top of slope disturbance or modification should be shown on the project plans. Details of the existing shore protection slope construction including thickness of rock revetment, filter layer, and core materials are not known. The shore protection slope is a continuous feature extending well beyond the limits of the project property and is thought to have been created along the edge of the entire waterway as part of the original manmade cove and existing surrounding bayside developments. Significant disturbance of the rock- armored slope by the planned development at the project property can result in costly mitigation and repairs, and should be avoided. The subsurface high groundwater table occurs at the anticipated depth of approximately 5 feet (BGS) and should be considered in the proposed bio-retention designs. Typically, a minimum 10 feet clear distance from bottom of infiltration bio-retention to high groundwater levels is required. In our opinion, the project property is not suitable for an infiltration bio- retention BMP considering the depth and potential groundwater level fluctuations. A self- contained system with an imperious liner on the sides and bottom and perforated underdrain pipe is recommended herein. The self-contained bio-retention facility may also be designed as a concrete containment structure with an adequately designed deepened edge along the building side to further enhance building pad stability against potential lateral spread along the top of the adjacent channel and disallow flotation (hydrostatic uplift pressure) in the Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 11 event of a sea level rise. The system should be properly sized for adequate storage capacity with filtrations completed not more than 72 hours. Vegetation, if incorporated into the designs, carefully managed to prevent creating mosquito and other vector habitats. A schematic concept of a self-contained bio-retention is shown on the attached Typical Bio- Retention Detail, Figure 7. Periodic inspections, upkeep, and continued maintenance of the project bio-retention BMP will be required to assure proper functioning and uninterrupted continuous discharge flow of the captured runoff water. Prolonged ponding of water in the proposed bio-retention can adversely impact the proposed new improvements and building performance, or potentially result in failures, and shall be avoided. In our opinion, a well-established maintenance program which includes careful management of bio-retention vegetation and testing for proper functioning of the underdrain/outlet pipes should be set in-place and followed by the current and future home owners. As a minimum, a maintenance schedule consisting of at least two times a year, before and after the annual rainy season, should be considered. In the event unfavorable conditions appear to be developing as noted during the scheduled maintenance program, appropriate repairs and mitigation should be carried out as necessary. B. Permeable Interlocking Concrete Payers (PICP) Permeable Interlocking Concrete Payers (PICP) in combination with the bio-retention are used as a part of the project stormwater quality treatment BMP, as shown on the attached Figure 1. Project stormwater BMP permeable interlocking payers should also consist of a self-contained filtration system. In general, PICP pavement structural section should consist of 31/8-inch, traffic rated PICP over a minimum of 2 inches of ASTM No.. 8 bedding course/choke stone over a minimum 8 inches of ASTM No. 57 stone base course over a minimum of 12 inches of 95% compacted subgrade. A minimum 4-inch diameter perforated underdrain pipe (sch. 40 or greater) placed at suitable location for collection and disposal of infiltrated water through the CICP payers should also be provided in the ASTM No. 57 stone base course section. A schematic concept of a self-contained permeable paver section is shown on the attached Typical Permeable Paver Detail, Figure 8. Subgrade soils below the base course should be compacted to at least 95% compaction levels (perASTM D- 1557). Bedding course/choke stone and base course stone should also be well compacted, consolidated and interlocked (avoid crushing the underdrain pipes) with heavy construction equipments. ASTM No. 8, No. 9 or No. 89 should be used for joint materials depending on the joint size and per manufacturer recommendations. Gradation requirements for ASTM No. 57, No. 8, No. 89 and No. 9 are as follows: Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 12 Sieve Size Percent Passing j ______ No. 57 No.8 No 89 No. 9 100 V 95to100 'N' 25 to 60 100 100 85 to 100 90 to 100 100 No.4 OtolO 10to30 20to55 85to100 No.8 0to5 OtolO 5to30 10to40 No. 16 0to5 OtolO OtolO No. 50 0to5 0to5 IX. CONCLUSIONS Based on our review of the attached referenced reports (Attachments I and II), and our understanding of the project, development of Lot 31 for residential purposes is considered substantially feasible from a geotechnical viewpoint. However, the site is underlain by a section of soft to very soft saturated fills over thick saturated lagoonal deposits which will require special geotechnical engineering development techniques. Subsurface geotechnical conditions presented in the referenced reports remain unchanged, and all conclusions provided therein remain valid, unless otherwise amended and/or superseded below. The project site is not located within or near Alquist - Priolo earthquake fault zone established by the State of California. The project property is located on the tsunami inundation line with potential tsunami risks similar to the adjacent and nearby properties and developments. Although a significant tsunami Impacting the project property would be a very rare event, the current and future owners of the residence should be aware of local evacuation routes as well as tsunami preparedness provided by the California Geological Survey on their web site. The eastern margins of the project property are also located on the line with Special Flood Hazard Areas Subject To Inundation By The 1% Annual Change Flood, as designated by FEMA Flood Insurance Rate Map. Flooding hazards risks for coastal flood zones with velocity hazards (wave action) at the project site will be a very rare event and similar to the adjacent and nearby properties and developments, requiring awareness and preparedness by the current and future owners of the residence. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 13 4. Liquefaction and soil softening of the underlying deposits during a major seismic event along a nearby active fault are considered the most significant geotechnical concern at the project building site. Secondary effects such as ground spreading and lurching, and large seismically induced settlements are also a major concern at the study site. Ground stabilization techniques and special foundation designs will be required for the support of proposed building to withstand seismically induced vertical and lateral ground displacements to reasonably acceptable risk levels, and construct improved pad surfaces. Several ground stabilization methods and foundation options are available to alleviate impacts of liquefaction and potential loss of strengths of the underlying liquefiable soils. In general, the most effective design method includes utilizing deep foundations which penetrate the liquefiable soils and are supported into the formational bearing strata below. Other alternatives are also available and may be considered depending on economic feasibility, ease of construction and the acceptable risk level. Most commonly used mitigation alternatives and techniques available for the project site, as well as pros and cons of each alternative are briefly discussed below. Potential impacts of lateral spread of the existing eastern rock-face slope on the proposed new building during an earthquake event is also a major geotechnical concern. In order to alleviate potential impacts of ground displacement due to lateral speared of the eastern slope, adequate building and improvement setback from the top of slope shall be maintained, and special building foundations design(s) as well as stabilized reinforced compacted fill mat under the site improvement will be required for achieving a reasonably acceptable risk level and tolerances, as specified in the following sections. The existing slope shall not be impacted, disturbed or modified by the planned constructions and proposed new building development with related ground stabilization and construction works maintaining adequate set backs from the top of slope, as specified in this report. 6. The underlying soft clayey fills and lagoonal deposits are highly compressible. The most effective design method to mitigate impacts of large settlements in case of very thick compressible, saturated clays, is utilizing deep foundations which penetrate the unsuitable soils and are supported into the formational bearing strata below. Other options such as shallow ground stabilization and surcharging with compacted fill overburden are also commonly used to create uniform post-construction total settlement throughout the mitigated building pad areas, and limit differential settlements, considering acceptable risk levels. For this purpose, higher levels of fill compaction (minimum 95%) and installations of settlement plates placed at the bottom of the over-excavations will be required to monitor settlement of the surcharged lagoonal deposits, as specified in the following sections. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 14 The project site is an existing nearly level graded lot and significant grade alterations or construction of new large grade slopes is not anticipated. Earthwork operations necessary in connection with the planned development will chiefly consist of remedial grading and ground stabilization work, Groundwater was encountered in both exploratory boring excavations drilled in 2003 at the depths of approximately 5 to 7¼ feet (BGS) below the surface. High groundwater conditions are expected to be at about 5 feet (BGS) at the project site and expected to fluctuate with tidal conditions. Dewatering will likely be required in case of rock mat stabilization and remedial grading options, and should be completed at each local quartered/phased remedial grading section, as specified below. Dewatering should lower the groundwater levels below the bottom of excavation and should continue as rock mat and fill placement progresses. Dewatering shall not be allowed to adversely impact the nearby buildings, structures and improvements. Completing grading during the dry seasons of the year and low tidal conditions should be considered to minimize difficulties associated with dewatering operations. Some pre-dewatering may also be considered appropriate for this project. Site excavations and earthwork shall not impact the adjacent properties, structures, improvements, and underground utilities within public right-of-ways. Initially, attempts may be made to complete ground stabilization by remedial grading in local quartered/phased sections with 1:1 laid back construction slopes. However, excavation shoring consisting (drilled concrete piles reinforced with steel beams with wood lagging) should be anticipated and will be required for developing a safe excavation and protect the adjacent building foundations, structures and improvements, as recommended below. Shoring designs are provided in the following sections. Earth materials generated from the site excavations, stripping, removals and over- excavations will chiefly consist of marginal quality, wet to saturated plastic silty to clayey deposits. All site organic soils, deleterious matter and unsuitable materials encountered during the excavations, stripping, removals and over-excavations should be properly removed and exported from the site using select grading techniques. Good quality sandy granular (D.G.) import soils should then be used as site new fills and backfllls to complete grading and achieve final design grades. Based on select grading recommendations specified herein, final bearing soils are expected to chiefly consist of silty sand (SM/SW) deposits with very low expansion potential (expansion index less than 20) based on ASTM D-4829 classification. Consequently, expansive soils will not be a factor in the project development. However, the rigid raft post- tentioned foundation support system, if considered, should be designed for the minimum specified center lift and edge lift differential swells provided in the following sections. Ceotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 15 X. PROS AND CONS OF LIQUEFACTION MITIGATION ALTERNATIVES Special foundation designs and ground stabilization techniques will be required to improve site stability against potential liquefaction, soil softening, lateral spread, ground displacement and settlements, and enhance building performance. Several ground stabilization methods and building/foundation support options are available. The choice of alternative will depend on economic feasibility, ease of construction, acceptable risk levels and future building performance. A few of the most common techniques, in our opinion, suitable to the project property are briefly discussed below: Option (i) Driven concrete piles with grade beams and structural floor foundations were recommended by the previous consultant (VME report dated March 3, 2004, Appendix B of Attachment Ii). This method is still a viable option from our standpoint, and may be considered. Specific design parameters are given in the referenced report and remain valid. In this case, 15 inches square prestressed concrete piles adequately driven to competent bearing strata, until allowable design pile capacity is developed will be required. This method will require large pile driving equipments, may be more difficult to carry out due to site constraints, generate vibrations that can be damaging to the very closely located neighboring buildings, and could also be very costly. A speciality contractor(s) is required to complete this work. Option (ii) Cast-In-Place (CIP) concrete piles with grade beams and structural floor foundations were also recommended by the previous consultant (\TME report letter dated February 27,2008, Attachment I). This method is still a viable option from our point of view, and may be considered. Specific design parameters are given in the referenced letter and remain valid. In this case, 2-feet-10 inches diameter CIP piles, drilled to a minimum depth of 57.5 feet (BGS) will be required. This method will require large equipment for pile shaft drilling below the water table to the required depth, potential pile shaft caving and appropriate stabilization, handling of large amounts of spoil soils generated from shaft drilling, steel cage fabrication, placement and splicing, and concrete pour in a tight construction area that could be very costly. A speciality contractor(s) is required to complete this work. Option (iii) Compaction (pressure) grouting of lagoonal deposits and remedial grading of the foundation bearing soils with stiff grade beam footings and structural slab-on-ground mat type foundations. For this purpose, compaction grouting will be used to densify site liquefiable/soft soils from the depth of nearly 49 feet to approximately 3 feet below the final pad grade. The upper 3 feet will then be removed and recompacted using conventional remedial grading techniques. Compaction (pressure) grouting may adversely impact nearby shore protection slope, adjacent neighboring buildings, improvements and underground utilities, and could be very costly. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 16 Hardening (mixing) techniques by introducing grout materials through permeation, mixing may also be considered for treatment of soft fills and lagoonal soils. In this case, in-situ conformation testing of the treated soils by performing SPT sampling (ASTM D- 1586) will be required to verify adequate densification within the treated deposits. A speciality contractor(s) is required to complete this work. Option (iv) Vibro-replacement (vibro-stone column) with a rock mat and compacted soils in the foundation zone, in combination with grade beam footings and structural slab-on- ground mat type foundations may also be considered. In this case, a vibroprobe penetrates to a minimum depth of 49 feet by vibration and jetting of air. Gravels are then added through a tremie pipe alongside the vibroprobe to create a stone column. A rock mat is then placed over the top of the installed stone columns at about 3 feet below the final pad grades. Finally, compacted soils will be used in the foundation zone and achieving pad grads. This method utilizes large equipment, generating driving vibrations potentially impacting the very closely located neighboring buildings and could be very costly. A speciality contractor(s) is required to complete this work. Option (v) Rock mat stabilization with remedial grading using reinforced, 95% compacted fill, in combination with grade beam and structural mat type foundation were also recommended by the previous consultant (VME report dated November 19, 2003, Appendix C of Attachment II). This method is still a viable option, and may be considered. Rigid raft post-tensioned type foundations with perimeter grade beams and interior stiffening beams can also be considered in lieu of mat foundations. In this case, the upper bearing soils are removed and bottom of excavation stabilized with a rock mat, with groundwater level lowered below the bottom of excavation. Upon achieving stable bottom conditions, compacted fills using reinforced earth will be placed to achieve pad grades. Excavation shoring along the north and south margins adjacent to the neighboring building foundations will likely be required to complete this technique. Geotechnical instrumentation and settlement monitoring will also be required for this method to record behavior of the compacted reinforced fill mat support prior to utility and foundation trenching. This option, however, is similar to conventional remedial grading techniques, and with the exception of the excavation shoring, a speciality contractor(s) is not required to complete the work. Relative ease of the contraction method (compare to the other available techniques), site suitability with respect to existing constrains and access limitations, and construction costs feasibility are considered the "pro" attributes of this option. However, although this option is generally expected to alleviate major geotechnical concerns within reasonable risk levels, it is not considered in the same Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 17 higher mitigation level ("cons") as some of the other options, such as vibro- replacement (vibro-stone column), and driven or drilled CIP pile foundations alternatives. The property owner(s) should carefully evaluate the pros and cons, and cost-benefit aspects of each alternative for choosing a specific mitigation technique, with the selection of a desired alternative and mitigation procedure passed on to the future homeowner(s). The final choice of an option will depend on site limitations, acceptable levels of risk and building performance, economic feasibility and ease of construction. Specific recommendations and design parameters for prestressed driven and drilled CIP concrete piles with grade beams and structural floor foundations, provided in the referenced reports(VME reports, Attachments I and II) are acceptable to us and remain unchanged. Rock stabilization with remedial grading, and mat and grade beam foundations (Option "V") were also provided in the referenced reports(VME reports, Appendix C of Attachment II) and are also generally acceptable to us, except where specifically amended to superseded below. It should be noted, however, that in some cases,site conditions developed during excavations for rock stabilization and remedial grading work, such as excessive uncontrollable groundwater intrusions, large bottom of excavation heaving (boiling), large caving and undermining or impacting adjacent buildings and improvements may not allow implementing Option V, as determined in the field, requiring selection of an alternative method as determined at that time, and cannot be ruled out. Specific recommendations for any other options can be provided upon request. XI. RECOMMENDATIONS All recommendations provided in the referenced reports (Attachments I and II) remain valid and should be considered in the final designs and implemented during the construction phase, where appropriate and as applicable. The following modified rock stabilization with remedial grading in combination with rigid raft post-tensioned type foundations with perimeter grade beams and interior stiffening beams recommendations (Option "V"), however, will supersede those given in the referenced reports and should be considered in final designs and implemented during the construction phase: A. Ground Stabilization Remedial Grading and Earthworks The project property is underlain by a relatively modest section of soft clayey fills over thick lagoonal soil deposits. As discussed herein, a more conventional method, generally expected to alleviate major geotechnical concerns within reasonable risk levels, consists of removal and recompaction of upper soils, and surcharging the underlying untreated soils using special remedial grading ground stabilization techniques. Remedial grading ground stabilization of the upper foundation soils should construct safe and stable building surfaces as specified herein. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 18 Recommended remedial grading concept and associated earthworks details are schematically illustrated on the enclosed Typical Ground Stabilization, N-S Direction and Typical Ground Stabilization, E-W Direction, Figures 9 and 10 respectively. All excavations, grading, earthworks, constructions and bearing soil preparations should be completed in accordance with Chapter 18 (Soils and Foundations) and Appendix "J" (Grading) of the 2013 California Building Code (CBC), the Standard Specifications for Public Works Construction, City of Carlsbad Grading Ordinances, the requirements of the governing agencies and following sections, wherever appropriate and as applicable: Underground and Utility Mark-Outs: All existing underground waterlines, sewer lines, storm drains, utilities, tanks, structures and improvements at or nearby the project construction site should be throughly potholed, identified and marked prior to the initiation of actual ground stabilization works, excavations, remedial grading operations, trenching and earthworks. Specific geotechnical engineering recommendations may be required based on the actual field locations and invert elevations, backfill conditions and proposed grades in the event of a grading conflict. Utility lines may be needed to be temporarily redirected, if necessary, prior to earthwork operations, and reinstalled upon completion of the constructions. Alternatively, permanent relocations may be appropriate as shown on the approved plans. Abandoned lines, irrigation pipes and conduits should be properly removed, capped or sealed offto prevent any potential for future water infiltrations into the site fihls/backfills, foundation bearing and subgrade soils. Voids created by the removals of the abandoned underground pipes, tanks and structures should be properly backfihled with compacted fills in accordance with the requirements of this report. Site Preparation and Clearing: Remove existing surface improvements, vegetation and other unsuitable/deleterious materials from all areas of the planned new structure and improvements plus 3 horizontal feet minimum outside the perimeter where possible, and as directed in the field. Vegetation, debris, grasses, trees, roots, stumps, and other deleterious or unsuitable materials should be thoroughly removed and cleared from the construction site to the satisfaction ofthe project geotechnical consultant. Debris and site vegetation should not be allowed to occur or contaminate new fills and backfills. The prepared ground should be inspected and approved by the project geotechnical engineer or his designated representative. Removals and Over-Excavations: Site upper soft and compressible soils in the building envelope areas plus a minimum of 3 feet in the north/south ends and 5 feet along at the east-west ends, outside the perimeter and as directed in the field, should be removed to a minimum uniform depth of 6 feet below the existing grades (BGS) or at Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 19 least 4 feet below the bottom deepest footing(s), whichever is more (also see Typical Ground stabilization Figures 9 and 10). In the front paving improvement areas plus minimum 18 inches outside the perimeter, where possible and as directed in the field, removal depths should extend a minimum of 2.5 feet below the existing grades or a minimum of 12 inches below the bottom of deepest utility, whichever is more. Locally, deeper removals may be necessary based on the actual field exposures and should be anticipated. Actual depths should be established by the project geotechnical engineer at the time of ground stabilization work and remedial grading operations. 4. Excavations, Temporary Construction Slopes and Shoring: Excavation shoring consisting of drilled concrete piles reinforced with steel beams and wood lagging will most likely be required for developing a safe excavation and protect the adjacent building foundations, structures and improvements, as recommended below. However, initially attempts maybe made to complete removals/over-excavation, bottom stabilization and pad reconstruction to rough finish grades with compacted fills in limited quartered/phase sections as delineated in the enclosed Geotechnical Map, Figure 1. Attempting Temporary Construction Slopes: Preliminary excavation setbacks and temporary construction slope development concept are depicted on the enclosed Figures 9 and 10. In general site geotechnical conditions are not favorable for temporary laid back construction slopes. However, initially attempts may be made to develop laid back excavations only in limited quartered sections not exceeding approximately one-fourth of total length of the project ground stabilization areas. Developed temporary construction slopes shall maintain the required set backs and initially laid back at 1:1 gradient maximum, unless otherwise noted or directed. A limited section of 1:1 of the temporary slope can then be cut at near vertical condition within the excavation areas, if the exposed section is immediately backfilled with stabilization rocks and compacted fills in a same day operation, with the groundwater lowered below the bottom of excavations. Vertical excavation left exposed over- night or for an extended period of time shall not be allowed. Any suspected or potential unfavorable exposures and excavation stability conditions (such as caving and/or development of tension cracks along the top of excavation), as determined in the field, shall result in abandoning this procedure and implementing shoring support, as discussed below. Monitoring of site excavations and adjacent buildings are also recommended herein (see following sections). In the event construction works requires prolonged (overnight) temporary slope exposures, or field observations and monitoring indicates a potential for failure and possible movements causing damage to the neighboring building, shoring protection of nearby structures shall be required. Any continuous shoring technique which can allow safe and stable excavations, and Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 20 protect adjacent buildings, properties and nearby structures and improvements may be considered. A qualified design/build shoring contractor should be consulted in this regard. Excavation Shoring Support: Anticipated prolonged unsupported excavation exposures during construction, excavations resulting in steeper than 1:1 maximum gradients, excessive groundwater intrusions or excessive deflections/deformations (greater than 1-inch) of site excavations, and monitoring results of adjacent buildings will necessitate installation of excavation shoring support, and most likely be required and should be anticipated. Shoring will also allow development of larger excavations, thereby increasing production levels, however, due to site constraints and groundwater intrusions, excavations larger than one-half of the total length of the project ground stabilization areas are not recommended. Approximate locations requiring excavation shoring are delineated in the enclosed Geotechnical Map, Figure I. Typical Excavation Shoring detail is shown on Figure 9. In general, any temporary continuous shoring system which can adequately support adjacent building foundations, underground utilities and nearby improvements along the northern and southern property margins (see Figure 1), and provide safe and stable excavation conditions may be considered. An effective temporary shoring support suitable to the site subsurface conditions may consist of drilled reinforced cast-in-place (CIP) concrete piles with wood lagging system (Figure 9). Any other shoring system, if considered, should be reviewed and approved by the project geotechnical consultant. The following soil design parameters are appropriate for shoring design: Design point of fixity should be assumed 2 feet below the specified bottom of over-excavations. Design maximum deflection should be limited to I-inch unless otherwise noted or approved. Protection of existing buildings, foundations, pipes, utilities, conduits, and underground improvements and nearby structures located within the zone of influence of planned vertical excavation is one of the most important criteria in determining a shoring support system and shall be considered in the project designs and constructions. The shoring wall system stiffness, and sequence of excavations shall limit horizontal and vertical deflections within allowable tolerances. The project shoring contractor should evaluate the structural capacity of existing nearby foundations, buildings, pipes, utilities, conduits and underground structures and determine the allowable acceptable tolerances for his considerations in implementing in a given shoring system. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 21 - Shoring piles should be at least 24 inches in diameter. Maximum pile spacing should be not exceed 8 feet. A design apparent lateral soil pressure of 40 pcf (EFP, for heights above the water table) may be considered for temporary shoring conditions. A design apparent buoyant lateral soil pressure of 22 pcf (EFP), in combination with a 62 pcf (EFP) hydrostatic pressure, should be considered for temporary shoring conditions below water tables. Water table is recommended herein to be lowered below the bottom of excavations with dewatering efforts. An additional 640 lbs./ft. resultant lateral force acting at the depth of 2.9 feet (BGS) caused by surcharge loading of nearby building foundations should also be considered for temporary shoring design, unless otherwise determined by the project design/build consultant. Design apparent passive resistance of 200 psf/fi maybe considered for temporary shoring for the portion embedded below the point of fixity. The passive resistance may be increased by the indicated value for each additional foot of depth to a maximum 3000 pounds per square feet. - Additional soil design parameters are provided in the following sections of this report. General Excavation Requirements: Top of excavations and temporary slopes shall maintain adequate set backs from adjacent neighboring buildings, existing on and offsite improvements and structures as approved and directed in the field. Undermining and/or damages to adjacent buildings, existing improvements, structures, underground utilities and within public right-of-way or adjacent easements and properties shall be avoided. Face of temporary slopes should be protected from excessive runoff or rainfall and stockpiling the excavated materials near the top of construction embankments should be disallowed. Construction should be also completed in a timely manner minimizing unsupported slope conditions for prolonged period of time. Bottom of over-excavations will be approximately 12 inches below the anticipated high groundwater levels and moderate to heavy groundwater intrusions into the site excavations should be expected. Groundwater should be lowered to below the bottom of excavations using dewatering techniques. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 22 Site excavations and temporary shoring support will require continuous geotechnical observation during the earthwork operations. Additional recommendations should be given by the project geotechnical consultant at that time as necessary, based on actual field exposures. The project contractor should also obtain appropriate excavation permits, as needed, and conform to the Cal-OSHA and local governing agencies' requirements for open cut and trenching excavations, and safety of the workmen during construction. Commencing site excavations may also require obtaining permits from the adjacent property owners or public agencies, as appropriate and applicable. 5. Excavation Monitoring and Adjacent Neighboring Buildings: Monitoring ofthe site excavations and adjacent neighboring buildings will be required during the ground stabilization work and pad reconstruction phase. For this purpose, an appropriate excavation monitoring program should be incorporated into the project plans and implemented during site construction. We recommend an excavation monitoring program which include the following: * Pre-construction conditions of all existing nearby buildings, structures, improvements and utilities within 100 feet minimum from the top of excavation or twice the excavation depth, whichever is more, should be well documented and recorded (photographed and video taped). * Elevations and horizontal position of all existing nearby buildings, structures, improvements and utilities within 100 feet minimum from the top of excavation (or twice the excavation depth, whichever is more) should be established prior to initiation of actual excavation works. Survey and monitoring points should be established on the nearby buildings, structures, improvements and utilities at intervals less than 25 feet maximum and identified on the project grading or a separate Monitoring Plan. Monitoring data should be recorded to 0.01 -foot accuracy. * Benchmarks and reference locations for the survey and monitoring points should be established outside the influence zone of the excavations and construction equipment vibrations (minimum 100 feet or at least twice the excavation depths, whichever is more) as shown on the project grading or Monitoring Plan. * Record elevations and horizontal position of each survey and monitoring point before and after any major event, phased excavation, changes in excavation exposures (such as development of ground cracks near top of excavations or side caving), and any suspected or observed movements, as well as change in geologic units and unexpected groundwater impacts. Survey weekly during shoring, excavations, and backfihling activities. Survey at least on a monthly basis thereafter until terminated by the project geotechnical consultant. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 23 * Data generated from the monitoring program may establish new conditions requiring reconsideration into the temporary slope and shoring designs resulting in field revisions including but not limited to smaller excavation exposures or installations of additional or an intermediate shoring support system. 6. Ground/Bottom of Over-Excavation Rock Stabilization: Bottom of removals/over- excavations at the specified depth is anticipated to expose very soft to soft yielding conditions overall not suitable for receiving new fills or backfllls. Consequently, a stabilization rock mat will be required and should be placed over the exposed bottom of excavation, as conceptually depicted on the enclosed Typical Ground stabilization, Figures 9 and 10. The stabilization rock mat should initially consist of placing one-foot minus crushed angular rocks over the entire bottom of over-excavations and tracking the rocks with heavy construction equipment as directed in the field. Rock placement and tracking should continue until soft to loose soils at the bottom of removals are sufficiently displaced and rocks are fully interlocked achieving a non-yielding condition as determined in the field. Dewatering shall be carried out, as specified herein, to remove the intruding and displaced water and accelerate the bottom stabilization work. Subsequently, an approximate 6-inch thick layer of 11/2 to 3/4-inch crushed rocks should be placed over the larger rocks at the bottom and then tracked with heavy construction equipment to adequately in-fill larger rocks, enhance interlocking and provide a stable surface non-yielding conditions suitable for receiving fill. A layer of Mirafi 5 OOX (or greater from the same series or approved equal) soil separation geotextile should then be provided neatly placed over the top of the rock mat as directed in the field. Placement of reinforced fill and backfilling can then proceed until final pad grades are achieved. The actual rock mat thickness needed to achieve an unyielding bottom will depend on the in-place characteristics of the site exposures at the time of grading. Variables which will influence the rock mat thickness include specific engineering properties of the underlying soil conditions at the exposed over-excavation depths and the type of the heavy equipment used to track-walk the rock. Based on our experience with similar projects, a consolidated rock thickness on the order of 3 feet will be required. Added recommendations and field modifications for the stabilization rock mat including larger or a thicker rock section may be required depending on the site and groundwater conditions at the time of constructions and should be anticipated. Dewatering and lowering of groundwater (removal of displaced water) below the bottom of over- excavation shall be continued during rock mat and subsequent fill placement. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 24 In the on-grade improvement areas outside the building envelop only, such as driveways, a rock mat may be not necessary as determined in the field. However, fills can only be placed upon non-yielding bottom of over-excavations as determined by the project geotechnical engineer or his designated field representative. A minimum removal depth of 2.5 feet below finis pad grades or 12 inches below the bottom of deepest utility, whichever is more, is considered adequate in these areas unless otherwise noted. However, due to the expected unsuitable and yielding bottom of removals, a layer of TerraGrid RX- 1200 (or greater) stabilization geogrid earth reinforcement should be neatly placed over the exposed surfaces prior to backfihling as directed in the field. 7 Groundwater and Dewatering: High groundwater is expected at the depth of approximately 5 feet (BOS), subject to fluctuation with tidal conditions. Dewatering and removal of intruding/displaced water will be required for successful completion of site stabilization, rock mat placement, allowing remedial grading operations to progress. Dewatering should be completed at each local quartered/phased remedial grading section, with groundwater levels lowered below the bottom of excavation and should continue as rock mat and fill placement progresses. Any dewatering technique which can effectively remove the intruding/displaced water and lower the groundwater below the bottom of excavation may be considered. Sump and pump method consisting of an excavation of a two-foot deep hole backfihled with 3,4 inch crushed rocks at a low point in the over-excavated areas to act as a sump, and dewatering using a submersible pump is usually a common procedure. More specific recommendations should be provided by the project geotechnical consultant at the time of trenching and excavation inspections based on actual field exposure. Dewatering shall not be allowed to adversely impact the nearby buildings, structures and improvements. Completing grading during the dry seasons of the year and low tidal conditions should be considered to minimize difficulties associated with dewatering operations. Some pre-dewatering may also be considered appropriate for this project to facilitate excavations and ground stabilization work. 8. Underdrain: A subsurface underdrain system consisting of a minimum 6-inch diameter perforated pipe (SDR 35) surrounded with crushed rocks ('4-inch) and wrapped in filter fabric (Mirafi 140 N) installed within the I Y2"-Y4 crushed rock layer maybe required as determined and directed in the field. The need for a subsurface underdrain will most depend on conditions of site excavations, rock stabilization performance under track walking and groundwater intrusions. Actual underdrain construction details should be provided by the project geotechnical engineer, if it becomes necessary. The underdrain should be installed at suitable elevations above the "historic high tides" sea level to provide minimum 2% fall via a non-perforated out on eastern rock face slope, or other approved discharge location. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 25 9. Fill Materials and Import Soils: In general, soils generated from the site excavations will chiefly consist of marginal to very poor quality, plastic, wet to saturated silty to clayey deposits. Generated deposits are not suitable for reuse as site new fills and backfills, and should be removed and exported from the site. Good quality sandy granular (D.G.) soils should then be imported and used as new fills and backfills for completing remedial grading and achieving final pad grades. Import soils should consist of very low expansive non-corrosive sandy (D.G.) granular deposits (100% passing I- inch sieve, more than 50% passing #4 sieve and less than 18% passing #200 sieve with expansion index less than 20) tested and approved by the project geotechnical engineer prior to delivery to the site. Import soils should also meet or exceed the engineering properties of site soils as specified in the following sections. Backfilling/Reiuforced Fifi Mat: Upon completion of stabilization rock mat placement and approval of the project geotechnical consultant, building pad reconstruction to design finish grade with reinforced compacted import fills can begin. An initial fill lift on the order of 6 to 8 inches thick should be carefully and neatly placed atop the Mirafi 500X soil separation geotextile and compacted as specified herein. A layer of TerraGrid RX- 1200 (or greater) earth reinforcement geogrid should then be placed over the initial fill lift, followed by the second fill lift also on the order of 6 to 8 inches thick compacted as specified herein. Settlement plates can then be installed in accordance with requirements of this report. Backfilling and compaction should subsequently proceed with a second layer of TerraGrid RX-1200 (or greater) placed within the compacted fill mass approximately 12 below the bottom of deepest footing(s) or a minimum of 6 inches below the deepest underground utility and plumbing trenches, unless otherwise approved. Details of a reinforced compacted fill mat are conceptually shown on the enclosed Figures 9 and 10. A minimum of 18 inches overlap should be considered for Mirafi 500X soil separation geotextile and TerraGrid RX-1 200 earth reinforcement geogrid when completing remedial grading is limited quartered/phased sections. Uniform and stable well-compacted fill mat support should be constructed underneath the proposed building pad areas by the earthwork operations. For this purpose, site new fills and backfills should be adequately processed, thoroughly mixed, moisture conditioned to slightly (2%) above the optimum moisture levels, placed in thin (6 to 8 inches maximum) uniform horizontal lifts and mechanically compacted to a minimum of 95% of the corresponding laboratory maximum dry density per ASTM D-1557. Minimum 95% compaction levels shall be required for all site fills and backfills including, storm drains, utility and plumbing trench backfills, unless otherwise approved or.directed in the field by the project geotechnical consultant. Instrumentations and Settlement Monitoring: Geotechnical instrumentation devices consisting of two settlement plates should be installed at the project building site, as schematically shown on the enclosed Typical Ground Stabilization Figures 9 and 10. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 26 Settlement plates should be placed near the bottom of the over-excavations, at selected locations not to interfere with the project grading and post grading construction phases, in order to monitor settlement of the underlying surcharged natural lagoonal deposits. Preliminary locations of settlement plates are shown on the attached Geotechnical Map, Figure 1. A typical detail and installation concept of a settlement plate are shown on the enclosed Settlement Plate Schematic, Figure 11. Geotechnical instrumentation should be installed by or under direct supervision of the project geotechnical consultant. Monitoring should be performed by means of field surveying shots periodically taken at each monitoring site as the fill and backfill placement progresses approximately once every two to three days, unless otherwise approved. At the completion of remedial grading, monitoring should continue on a biweekly and/or monthly basis, per the monitoring schedule developed by the project geotechnical consultant. Monitoring should be carried out by surveying methods provided by the project civil engineer/surveyor or contractor. Survey records (vertical and horizontal positioning) should then be reduced by the project surveying consultant soon after field measurements and provided to the project geotechnical consultant to establish settlement patterns and soil compression characteristics with respect to surcharge loading pressures, compaction efforts and earthwork activities (vertical deflection versus time plot). Foundation trenching can only begin after data reduction and approval of the project geotechnical consultant (0.01-foot or 0.12 inch differential between at least three consecutive post-grading readings per the monitoring schedule, unless otherwise noted or required by the project geotechnical consultant). A waiting period between 6 to 12 weeks maybe anticipated after the completion of rough pad grading to proceeded with foundation trenching and constructions. Foundation recommendations provided in the following sections should be also confirmed and / or revised based upon the settlement monitoring data compiled at the completion of monitoring period, as necessary and appropriate. 12. Surface Drainage and Erosion Control: A critical element to the continued stability of the graded building pads is an adequate storm water and surface drainage control. This can most effectively be achieved by appropriate storm water control and drainage structures, vegetation cover and the installation of the following systems: * Flooding, soil erosion, scouring and sediment transport should not be allowed at the site. Erosion prevention facilities as well as flooding and runoff control drainage structures should be installed and constructed as shown on the approved drawings. * Concentrated flow should not be allowed. Lined concrete drainage facilities should be considered for directing stormwater and surface runoff to appropriate discharge facilities. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 27 * Building pad and improvement surface runoff should be collected and directed away from the planned buildings and improvements to a selected location in a controlled manner. Area drains should be installed. * Temporary erosion control facilities and silt fences should be installed during the construction phase periods and until landscaping is established as indicated and specified on the approved project grading or erosion control plans. 13. Engineering Observations and Testing: All ground stabilization work, remedial grading and earthwork operations including excavations and removals, dewatering efforts, shoring procedures and temporary excavation slopes, rock and earth reinforcement geogrid placement, instrumentation, suitability of import soils used as site new compacted fills and backfills, fill/backfill placement and compaction procedures should be continuously observed and tested by the project geotechnical consultant and presented in the final as-graded compaction report. The nature of finished bearing and subgrade soils should be confirmed in the final compaction report at the completion of grading. Geotechnical engineering observations should include but are not limited to the following: Initial observation - After clearing limits have been staked but before ground stabilization and remedial grading starts. * Shoring/excavation observation -During shoring installations and site excavation but before the vertical depth of excavation is more than 3 feet. Local and Cal-OSHA safety requirements for open excavations apply. * Removals, dewatering and bottom of over-excavation observation - After removals/over-excavations to the specified depths and installation of dewatering facilities, but before placing stabilization rocks are placed. * Fill/backfill observation - After the fill/backfill placement is started but before the vertical height of fill/backfill exceeds 2 feet. A minimum of one test shall be required for each 100 lineal feet maximum in every 2 feet vertical gain, with the exception of wall backfihls where a minimum of one test shall be required for each 30 lineal feet maximum. Site new fills and backfihls should consist of good quality sandy granular D.G. import soils and mechanically compacted to a minimum of 95% compaction levels unless otherwise specified or directed in the field. Finish rough and final pad grade tests shall be required regardless of fill thickness. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 28 * Foundation trench and subgrade soil observation - After the foundation trench excavations and prior to the placement of steel reinforcing for proper moisture and specified compaction levels. * Geotechnical foundation/slab steel observation - After the steel placement is completed but before the scheduled concrete pour. Underground utility, plumbing and storm drain trench observation - After the trench excavations but before placement of pipe bedding or installation of the underground facilities. Local and Cal-OSHA safety requirements for open excavations apply. Observations and testing of pipe bedding may also be required by the project geotechnical engineer. Underground utility, plumbing and storm drain trench backfill observation - After the backfill placement is started above the pipe zone but before the vertical height of backfill exceeds 2 feet. Testing of the backfill within the pipe zone may also be required by the governing agencies. Pipe bedding and backfill materials shall conform to the governing agencies' requirements and project soils report if applicable. Trench back fills shall consist of good quality sandy granular D.G. import soils, mechanically compacted to a minimum of 95% compaction levels, unless otherwise specified. Plumbing trenches more than 12 inches deep maximum under the floor slabs should also be mechanically compacted and tested for a minimum of 95% compaction levels. Flooding or jetting techniques as a means of compaction method should not be allowed. * Improvement subgrade observation - Prior to the placement of concrete for proper moisture and specified compaction levels. B. Post-Tensioned Rigid Raft Foundation Slab As a minimum, the proposed residential dwelling maybe supported on a shallow stiff rigid raft post-tensioned type foundations. Other foundation system alternatives, as presented in the referenced reports, still remain valid and are also available for considerations. The choice of appropriate option will depend on acceptable levels of future building and improvement performance, economic feasibility and ease of constructions. Geotechnical concept designs (not for construction) of the recommended rigid raft post- tensioned type foundations are depicted on the enclosed Typical Foundation Plan and Typical Interior Stiffeners Detail, Figures 12 and 13 respectively. Added or modified recommendations may also be necessary and should be given at the time of foundation plan review phase and completion of the monitoring period, as specified herein. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 29 Actual rigid raft post-tensioned type foundation designs should be completed by the project structural engineer or design/build contractor. However, the following soil design parameters and minimum requirements are appropriate and should be considered in the final designs and implemented during the construction phase: * The rigid raft type foundation design should consider a post-tensioned slab with perimeter exterior beams and interior stiffeners (ribbed foundation), as conceptually shown on the enclosed Figures 12 and 13. * All designs shall conform to the latest addition of the California Building Code (CBC), specifications of the Post-Tensioning Institute (PTI), local standards, and the specifications given in this report. * Foundation bearing soils should be inspected and tested as necessary prior to trenching and actual construction by the project geotechnical engineer. The required foundation bearing soils in-place densities, and specified moisture contents should be confirmed prior to the foundation pour. * A well-performing vapor barrier/moisture retardant (minimum 15-mil Stego) should be placed over the compacted subgrade and overlain by 4 inches of good quality well-graded clean sand. Alternatively, a 4-inch thick base of '/2 inch clean aggregate and a vapor barrier (minimum 15-mil Stego) in direct contact with concrete, and a concrete mix design, which will address bleeding, shrinkage and curling (ACI 302.2R-06) may also be considered per California Green Building Standards Code (4.505.2). * At the completion of ground and subgrade preparation as specified, and approval of the project geotechnical engineer, the rigid raft post-tensioned type foundations should be constructed as detailed on the structural/construction drawings. * Based on our experience on similar projects, available laboratory testing and analysis of the test results, the following soil design parameters are appropriate: - Design predominant clay mineral type .....................Montmorillonite. - Design percent of clay in soil .....................................60 %. - Design effective plasticity index ....................................45. - Design depth to constant soil suction ..............................7 feet. - Design constant soil suction ......................................Pf 3.6. Design velocity of moisture flow .........................0.70 inch/month. - Thomwaite Moisture Index for edge lift ...............................0. - Thornwaite Moisture Index for center lift ............................ -20. - Design edge moisture variation distance for center lift (em) ...........8.0 feet. - Design edge moisture variation distance for edge lift (em) ............3.5 feet. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 30 - Design differential swell occurring at the perimeter of slab for center lift condition (Ym) ................................1.0 inch(es). - Design differential swell, occurring at the perimeter of slab for edge lift condition (Ym) .................................2.25 inches. - Design soil subgrade modulus (k) ...............................100 pci. - Design net allowable bearing pressure for post-tensioned foundations ...................................1000 psf. Notes: Internal net allowable foundation pressure within the perimeter of the post-tension slab should be considered 1000 psf for a minimum embedment depth of 12 inches, and may be increased 20% for each additional foot of embedment or a portion thereof to a maximum of 3000 psf. The net allowable foundation pressure provided herein applies to dead plus live loads and maybe increased by one-third for wind and seismic loading. * Provide a minimum 18 inches wide by 24 inches deep exterior beams and interior longitudinal stiffeners reinforced with at least 245 continuous bars near the bottom and #3 ties at 18 inches on centers maximum (see Figures 12 and 13). Provide additional minimum 15 inches wide by 18 inches deep interior transverse stiffeners reinforced with at least 245 continuous bars near the bottom and #3 ties at 30 inches on center maximum. Stiffeners spacing shall not exceed 12 feet maximum center to center in both directions, as shown in the enclosed Typical Foundation Plan, Figure 12. Final design dimensions and spacing of interior stiffening beams should be furthered confirmed or revised as necessary based on the recorded settlement monitoring data at the completion of pad construction. Perimeter beams and interior stiffener embedment depths are measured from the lowest adjacent ground surface, not including the sand/gravel beneath the slabs. Exterior beams shall also enclose the entire building circumference. * The rigid raft post-tension type foundation slab shall not be less than 6 inches in thickness minimum. We recommend considering pre-tensioning in order to preclude early concrete shrinkage cracking. Also, see Site Corrosion Assessment section of this report for concrete type and strength. C. Soil Design Parameters Soil design parameters provided in the referenced reports are still valid and may be considered where appropriate and as applicable unless superceded below. Good quality sandy granular D.G. type import soils are also recommended herein placed within upper pad grades. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 31 The following soil design parameters are based upon on our past experience with similar projects in close vicinity of the study site, and available test results performed on representative samples of onsite and import earth materials: * Design soil unit weight = 124 pcf. * Design angle of internal friction of soil = 26 degrees. * Design active soil pressure for retaining structures = 40 pcf (EFP), level backfill, cantilever, unrestrained walls. * Design at-rest soil pressure for retaining structures = 60 pcf (EFP), non-yielding, restrained walls. * Design soil passive resistance for retaining structures = 200 pcf (EFP), level ground surface on the toe side. * Design coefficient of friction for concrete on soil = 0.25. * Net allowable foundation pressure for 95% compacted fills = 2000 psf. * Allowable lateral bearing pressure (all structures except retaining walls) for on-site compacted fill = 100 psflft. Notes: Use a minimum safety factor of 1.5 for wall over-turning and sliding stability. However, because large movements must take place before maximum passive resistance can be developed, a minimum safety factor of 2 may be considered for sliding stability particularly where sensitive structures and improvements are planned near or on top of retaining walls. When combining passive pressure and frictional resistance, the passive component should be reduced by one-third. * The allowable foundation pressures provided herein apply to dead plus live loads and may be increased by one-third for wind and seismic loading. * The lateral bearing earth pressures may be increased by the amount of designated value for each additional foot of depth to a maximum 1500 pounds per square foot. D. Inter-Locking Payers Flexible interlocking concrete payers are proposed as shown on the enclosed Figure 1 and should be installed in accordance with the manufacturer's recommendations. Subgrade preparation and compaction procedures will remain the same as specified herein, unless otherwise approved. Also refer to Stormwater BMPs/Permeable Interlocking Concrete Payers (PICP) section of this report, and the attached Figure 8 for typical geotechnical design and construction recommendations. Some repairs and period maintenance of interlocking Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 32 payers may be required depending on subgrade behavior, as wells as design and installation/construction procedures and should be anticipated. XII. GENERAL RECOMMENDATIONS The minimum foundation design and steel reinforcement provided herein are based on soil characteristics and are not intended to be in lieu of dimensions and reinforcement necessary for structural considerations. Adequate staking and grading control are critical factors in properly completing the recommended remedial and site grading operations. Grading control and staking should be provided by the project grading contractor or surveyor/civil engineer, and is beyond the geotechnical engineering services. Staking should apply the required setbacks shown on the approved plans and conform to setback requirements established by the governing agencies and applicable codes for off-site private and public properties and property lines, utility easements, right-of-ways, nearby structures and improvements, and graded embankments. Inadequate sOtaking and/or lack of grading control may result in illegal encroachments or unnecessary additional grading which will increase construction costs. Open or backfihled trenches parallel with a footing shall not be below a projected plane having a downward slope of I-unit vertical to 2 units horizontal (50%) from a line 9 inches above the bottom edge of the footing, and not closer than 18 inches from the face of such footing. Where pipes cross under-footings, the footings shall be specially designed. Pipe sleeves shall be provided where pipes cross through footings or footing walls, and sleeve clearances shall provide for possible footing settlement, but not less than 1-inch all around the pipe. Expansive clayey soils should not be used for backfilling of any retaining structure. All retaining walls should be provided with a 1:1 wedge of granular, compacted backfill measured from the base of the wall footing to the finished surface and a well-constructed back drain system as shown on the enclosed Figure 14. Planting large trees behind site retaining walls should be avoided. All underground utility and plumbing trenches should be mechanically compacted to a minimum of 95% of the maximum dry density of the soil unless otherwise specified. Care should be taken not to crush the utilities or pipes during the compaction of the soil. Very low expansive, granularD.G. type import backfill soils should be used. Trench backfill materials and compaction beneath pavements within the public right-of-way shall conform to the requirements of governing agencies. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 33 7. Onsite soils consist of expansive and moisture sensitive silty to clayey soils. These deposits can experience movements and undergo s volume changes upon wetting and drying. Maintaining a uniform as-graded soil moisture during the post construction periods is essential in the future performance and stability of site structures and improvements. Excessive irrigation resulting in wet soil conditions should be avoided. Surface water should not be allowed to infiltrate into the underlying bearing and subgrade soil. Site drainage over the finished pad surfaces should flow away from structures in a positive manner. Care should be taken during the construction, improvements, and fine grading phases not to disrupt the designed drainage patterns. Roof lines of the buildings should be provided with roof gutters. Roof water should be collected and directed away from the buildings and structures to a suitable location. Final plans should reflect preliminary recommendations given in this report. Final foundations and grading plans may also be reviewed by the project geotechnical consultant for conformance with the requirements of the geotechnical investigation report outlined herein. More specific recommendations may be necessary and should be given when final grading and architectural/structural drawings are available. All foundation trenches should be inspected to ensure adequate footing embedment and confirm competent bearing soils. Foundation and slab reinforcements should also be inspected and approved by the project geotechnical consultant. The amount of shrinkage and related cracks that occur in the concrete slab-on-grades, flatwork and driveways depend on many factors, the most important of which is the amount of water in the concrete mix. The purpose of the slab reinforcement is to keep normal concrete shrinkage cracks closed tightly. The amount of concrete shrinkage can be min:mized by reducing the amount of water in the mix. To keep shrinkage to a minimum the following should be considered: * Use the stiffest mix that can be handled and consolidated satisfactorily. Use the largest maximum size of aggregate that is practical. For example, concrete made with %-inch maximum size aggregate usually require about 40-lbs. more (nearly 5-gal.) water per cubic yard than concrete with 1-inch aggregate. * Cure the concrete as long as practical. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 34 The amount of slab reinforcement provided for conventional slab-on-grade construction considers that good quality concrete materials, proportioning, craftsmanship, and control tests where appropriate and applicable are provided. 12. A preconstruction meeting between representatives of this office, the property owner or planner, city inspector as well as the grading contractor/builder is recommended in order to discuss grading and construction details associated with site development. GEOTECHNICAL ENGINEER OF RECORD (GER) SMS Geotechnical Solutions, Inc. is the geotechnical engineer of record (GER) for providing a specific scope of work or professional service under a contractual agreement unless it is terminated or canceled by either the client or our firm. In the event a new geotechnical consultant or soils engineering firm is hired to provide added engineering services, professional consultations, engineering observations and compaction testing, SMS Geotechnical Solutions, Inc. will no longer be the geotechnical engineer of the record. Project transfer should be completed in accordance with the California Geotechnical Engineering Association (CGEA) Recommended Practice for Transfer of Jobs Between Consultants. The new geotechnical consultant or soils engineering firm should review all previous geotechnical documents, conduct an independent study, and provide appropriate confirmations, revisions or design modifications to his own satisfaction. The new geotechnical consultant or soils engineering firm should also notify in writing SMS Geotechnical Solutions, Inc. and submit proper notification to the City of Carlsbad for the assumption of responsibility in accordance with the applicable codes and standards (1997 UBC Section 3317.8). LIMITATIONS The conclusions and recommendations provided herein have been based on available data obtained from the review of pertinent prior documents, reports and plans, available subsurface explorations and laboratory testing, as well as our experience with the soils and formational materials located in the general area. The materials encountered on the project site and utilized in our laboratory testing are believed representative of the total area; however, earth materials may vary in characteristics between excavations. Ofnecessity, we must assume a certain degree of continuity between exploratory excavations and/or natural exposures. It is necessary, therefore, that all observations, conclusions, and recommendations are verified during the grading operation. In the event discrepancies are noted, we should be contacted immediately so that an inspection can be made and additional recommendations issued if required. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 35 Several stabilization and project development options with their "pros" and "cons" of each option are presented herein. The final choice of an option will depend on site limitations, acceptable levels of risk and future building performance, economic feasibility and ease of construction. It is the responsibility of the property owner(s) to carefully evaluate the pros and cons and cost-benefit aspects of each alternative with a risk level acceptable to them for choosing a specific mitigation and development technique. The selection of a desired development alternative and mitigation procedure, considered with the risk level acceptable to current owners/developers should be passed on to the future homeowner(s). The recommendations made in this report are applicable to the site at the time this report was prepared. It is the responsibility of the owner/developer to ensure that these recommendations are carried out in the field. It is almost impossible to predict with certainty the future performance of a property. The future behavior of the site is also dependent on numerous unpredictable variables, such as earthquakes, rainfall, and on-site drainage patterns. The firm of SMS Geotechnical Solutions, Inc., shall not be held responsible for changes to the physical conditions of the property such as addition of fill soils or changing drainage patterns which occur without our inspection or control. This report should be considered valid for a period of one year and is subject to review by our firm following that time. If significant modifications are made to your tentative construction plan, especially with respect to finish pad elevations final layout, this report must be presented to us for review and possible revision. This report is issued with the understanding that the owner or his representative is responsible for ensuring that the information and recommendations are provided to the project architect/structural engineer so that they can be incorporated into the plans. Necessary steps shall betaken to ensure that the project general contractor and subcontractors carry out such recommendations during construction. The project geotechnical engineer should be provided the opportunity for a general review of the project final design plans and specifications in order to ensure that the recommendations provided in this report are properly interpreted and implemented. If the project geotechnical engineer is not provided the opportunity of making these reviews, he can assume no responsibility for misinterpretation of his recommendations. SMS Geotechnical Solutions, Inc., warrants that this report has been prepared within the limits prescribed by our client with the usual thoroughness and competence of the engineering profession. No other warranty or representation, either expressed or implied, is included or intended. Geotechnical Update Report, Proposed Residential Duplex Development July 25, 2016 Existing Pad (Lot 31), 4547 Cove Drive, Carlsbad, California Page 36 Once again, should any questions arise concerning this report, please do not hesitate to contact this office. Reference to our Project No GI-16-06-128 will help to expedite our response to your inquiries. We appreciate this opportunity to be of service to you. SMS Geotechnical Solutions, Inc. di S. Shariat AL AAY Steven J. Meizer CERTIFIED CEG#2362 ENGINEERING GEOLOGIST Distribution: Addressee (5, e-mail) 4 &6GE01'ECHN1CAL SOLUTIONS, INC. REFERENCES - Annual Book of ASTM Standards, Section 4 - Construction, Volume 04.08: Soil and Rock (1); D420 - D5876, 2016, - Annual Book of ASTM Standards, Section 4- Construction, Volume 04.09: Soil and Rock (II); D5877 - Latest, 2016. - Highway Design Manual, Caltrans. Fifth Edition. - Corrosion Guidelines, Caltrans, Version 1.0, September 2003. - California Building Code (CBC), California Code of Regulations Title 24, Part 2, Volumes 1 & 2, 2013,, International Code Council. - "The Green Book" Standard Specifications For Public Works Construction, Public Works Standards, Inc., BNi Building News, 2015 Edition. - California Geological Survey, 2008 (Revised), Guidelines for Evaluating and Mitigating Seismic Hazards in California, Special Publication 11 7A, 108p. - California Department of Conservation, Division of Mines and Geology (California Geological Survey), 1986 (revised), Guidelines for Preparing Engineering Geology Reports: DMG Note 44. - California Department of Conservation, Division of Mines and Geology (California Geological Survey), 1986 (revised), Guidelines to Geologic and Seismic Reports: DMG Note 42. - EQFAULT, Ver. 3.00, 1997, Deterministic Estimation of Peak Acceleration from Digitized Faults, Computer Program, T. Blake Computer Services and Software. - EQSEARCH, Ver 3.00, 1997, Estimation of Peak Acceleration from California Earthquake Catalogs, Computer Program, T. Blake Computer Services and Software. - Tan S.S. and Kennedy, M.P., 1996, Geologic Maps of the Northwestern Part of San Diego County, California, Plate(s) 1 and 2, Open File-Report 96-02, California Division of Mines and Geology, 1:24,000. - "Proceeding of The NCEER Workshop on Evaluation of Liquefaction Resistance Soils," Edited by T. Leslie Youd and Izzat M. Idriss, Technical Report NCEER-97-0022, Dated December 31, 1997. - "Recommended Procedures For Implementation of DMG Special Publication 117 Guidelines For Analyzing and Mitigation Liquefaction in California," Southern California Earthquake Center; USC, March 1999. S 1S REFERENCES (continued) - "Soil Mechanics," Naval Facilities Engineering Command, DM 7.01, - "Foundations & Earth Structures," Naval Facilities Engineering Command, DM 7.02. - "Introduction to Geotechnical Engineering, Robert D. Holtz, William D. Kovacs. - "Introductory Soil Mechanics and Foundations: Geotechnical Engineering," George F. Sowers, Fourth Edition. - "Foundation Analysis and Design," Joseph E. Bowels. - Caterpillar Performance Handbook, Edition 29, 1998. - Jennings, C.W., 1994, Fault Activity Map of California and Adjacent Areas, California Division of Mines and Geology, Geologic Data Map Series, No. 6. - Kennedy, M.P., 1977, Recency and Character of Faulting Along the Elsinore Fault Zone in Southern Riverside County, California, Special Report 131, California Division of Mines and Geology, Plate 1 (East/West), 12p. - Kennedy, M.P. and Peterson, G.L., 1975, Geology of the San Diego Metropolitan Area, California: California Division of Mines and Geology Bulletin 200, 56p. - Kennedy, M.P. and Tan, S.S., 1977, Geology of National City, Imperial Beach and Otay Mesa Quadrangles, Southern San Diego Metropolitan Area, California, Map Sheet 24, California Division of Mines and Geology, 1:24,000. - Kennedy, M.P., Tan, S.S., Chapman, R.H., and Chase, G.W., 1975, Character and Recency of Faulting, San Diego Metropolitan Areas, California: Special Report 123, 33p. - "An Engineering Manual For Slope Stability Studies," J.M. Duncan, A.L. Buchignani and Marius De Wet, Virginia Polytechnic Institute and State University, March 1987.. - "Procedure To Evaluate Earthquake-Induced Settlements in Dry Sandy Soils," Daniel Pradel, ASCE Journal of Geotechnical & Geoenvironmental Engineering, Volume 124, #4, 1998. - "Minimum Design Loads For Buildings and Other Structures," ASCE 7-10, American Society of Civil Engineers (ASCE).