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Home My WebLink AboutMS 05-10; EUCALYPTUS LANE; GEOTECHNICAL RESPONSE TO THE NV5 REVIEW COMMENTS, PRELIMINARY GEOTECHNICAL INVESTIGATION; 2018-12-14Inland Engineering Technologies I nc. December 14, 2018 Mr. Guy Oliver 4992 Eucalyptus Lane Carlsbad, CA 92008 41655 Reagan Way Ste. E Murrieta, CA. 92562 Ph: (951) 894-6464 Fax: (951) 894-6491 Project No. 16-3319 Subject: Geotechnical Response to the NV5 Review Comments, Preliminary Geotechnical investigation for the Proposed Single-Family Residence Located at 4984 Eucalyptus Lane, City of Carlsbad, County of San Diego, California References: NV5, 2018, Review of Geotechnical Reports, Project No. 226816-00101.35, City Project MS 05- 10, dated July 13 Introduction JET, 2018, Preliminary Geotechnical Investigation for the Proposed Single-Family Residence Located at 4984 Eucalyptus Lane, City of Carlsbad, County of San Diego, California, Project No. 16-3319, Dated May 11 Land Mark, 2018, Grading Plans/or 4984 Eucalyptus Lane, 3 Sheets, GR 2018-0021, dated May 24 Inland Engineering Technologies, Inc. (IET) has prepared this response to the NV5 review comments on the referenced IET, 2018 preliminary geotechnical investigation report. The review comments are attached with this report. The following changes and clarifications should be considered part of and attached to the above referenced IET, 2018 report. Response 1: Based on the review of the referenced Landmark, 2018 plan the subject site will be divided into three parcels. Each parcel will be developed with two-story single-family home. The proposed homes will be wood frame structures. The geotechnical findings, conclusions and recommendations presented in the referenced IET, 2018 report are valid and applicable to all three parcels except for modified herein. Response 2: As stated in the original report, the subject site is located at 4984 Eucalyptus Lane, City of Carlsbad, County of San Diego, California. The general location of the site is shown on Figure 1 -Site Location Map. IET's site reconnaissance indicated the subject site currently vacant. Associated improvements at the time of the investigation included drive way, landscaping, a 6-foot-high retaining wall at the north side of the property, and utilities. The property has a slight rise in elevation from the south side at Eucalyptus Lane rising at approximately 9: 1 at the street elevation of 80 feet above mean sea level to a maximum elevation of approximately 106 feet above mean sea-level at which point the topography descends at approximately 2: 1 to the north to an elevation of approximately 92 feet behind the north retaining wall. Previous grading has occurred at the site; however, there is no documentation known for the fill previously placed. It is IET's understanding that this grading was done with a permission of the City of Carlsbad's. IET recommends that all existing fill within building pad areas be removed and replaced with compacted fill during grading. Drainage of the site occurs both to the south and to the north. The development consists of three parcels ascending from Eucalyptus Lane with pad elevations of 91.0 feet above mean sea Level, 96.5 feet above mean sea Level, and 100.0 feet above mean sea level. Building pad setbacks are in accordance with 2016 California Building Code. Response 3: 1. A geotechnical map is attached (Plate A). Regional Geology Carlsbad is within the coastal portion of the Peninsular Ranges Geomorphic Province, a region characterized by northwest-trending structural blocks and intervening fault zones. Typical lithologies in the Peninsular Ranges include a variety of igneous, intrusive rocks associated with the Cretaceous-age Southern California Batholith. The Coastal Plain region includes most of western San Diego County and consists primarily of Mesozoic crystalline rocks underlain by marine and non-marine sedimentary rocks. In this region, drastic land and sea fluctuations have preserved ancient marine rocks up to elevations around 900 feet and ancient river deposits up to 1,200 feet. Topographically, the Peninsular Ranges Province is composed of generally parallel ranges of steep- sloping hills and mountains separated by alluvial valleys. More recent uplift and erosion has produced the characteristic canyon and mesa topography in western San Diego County, as well as the deposition of surficial materials including Quaternary-age alluvium, colluvium and topsoil. The geology from the Draft Program Environmental Impact Report for the Carlsbad General Plan Update, adopted from the Oceanside Quadrangle has been prepared as Plate A. The site is underlain by sedimentary rocks of Eocene-age marine deposits. Regional dips within the Eocene marine deposits are shallow, between 3 to 15 degrees southwest to northeast. A cross section, A-A', shown on Plate B, shows the geologic relationships at the site. Earthquake Faults There are no active faults that run directly through Carlsbad and, the California Geological Survey has not included Carlsbad on its list of cities affected by Alquist-Priolo Earthquake Fault Zones. The nearest fault to the city is the Newport-Inglewood-Rose Canyon Fault, and the Coronado Bank Fault, which runs offshore of the western edge of the city and are considered active. Inland major faults include sections of the Elsinore Fault, and sections of the San Jacinto Fault. Fault activity has the potential to result in ground shaking, which can be of varying intensity depending on the intensity of earthquake activity, proximity to that activity, and local soils and geology conditions. Carlsbad is located within a seismically active region, and earthquakes have the potential to cause ground shaking of significant magnitude. Although located near fault lines, Carlsbad lies within a medium-low probabilistic peak ground acceleration zone. IET has updated the recommended seismic parameters to the 2016 CBC. Project No. 16-3319 Page2 December 14, 2018 Landslides Landslides can be the results of earthquakes, undercutting by streams, and heavy rainfall, and human activities. Activities contributing to instability include extensive over irrigation, poorly maintained drainage, groundwater withdrawal, removal of stabilizing vegetation, and over-steepening of slopes. Landslide risk is determined by steep slopes that have 25% or greater incline, soil series data, and soil- slip susceptibility. According to the Draft Program Environmental Impact Report for the Carlsbad General Plan Update, Carlsbad does not include any areas identified as being susceptible to landslides and the overall risk oflandslides is low. The site will not have any slopes over 30 feet or steeper than 2:1 gradient, and slope stability analyses are not considered necessary. Liquefaction Liquefaction is a process in which clean, loose sandy, and silty sediments below the water table temporarily lose strength during an earthquake and behave as a viscous liquid rather than a solid. Liquefaction is restricted to certain geologic and hydrologic environments, primarily recently deposited sand and silt in areas with high groundwater levels. As stated in IETs report the absence of shallow groundwater and the dense nature of the subsurface soils, the potential for liquefaction at the site is considered negligible. 2. A geotechnical cross-section is attached (Plate B). 3. It is IET's professional opinion that the development of the site has no adverse impact on adjacent properties. 4. Acknowledged. Response 4: The seismic design parameters provided in the referenced IET, 2018 report comply with 2016 CBC. Response 5: Corrosion testing was performed on a representative soil sample and the results are provided below: Soluble Sulfates: The soluble sulfate contents of selected samples were determined by standard geotechnical methods (CTM 417). The test results are presented in the table below: SAMPLE LOCATION SAMPLE DESCRIPTION SULFATE CONTENT SULFATE (%) EXPOSURE* Bag-1 @0-5' Brown Sandy CLAY 0.01 Negligible * Per ACI 3 I 8R-05 Table 4.3.1 Minimum Resistivitv and pH Tests: Minimum resistivity and pH tests were performed with CTM 643. The results are presented in the table below: SAMPLE LOCATION SAMPLE DESCRIPTION pH MINIMUM RESISTWITY (o' . \ --7 Bag-1 ~ 0-5' Brown Sandy CLAY 6.8 3,600 Project No. 16-3319 Page3 December 14, 2018 Chloride Content: Chloride content was tested with CTM 422. The results are presented below: SAMPLE LOCATION SAMPLE DESCRIPTION CHLORIDE CONTENT (ppm) Bag-1 @0-5' Brown Sandy CLAY 55 Based on testing performed within the project site, the onsite soils are classified as having a negligible sulfate exposure condition in accordance with ACI 318R-05 Table 4.3.1. It is also our opinion that onsite soils should be considered moderately corrosive to buried metals due to low resistivity. The onsite soils also have negligible amount of Chloride content from corrosion point of view. Response 6: The proposed foundation should have a minimum width of 12 inches and be reinforced with at least two #4 bars, top and bottom. Response 7: The descending slope at the rear of the property is approximately 2: l and descends from approximately 106 feet to 92 feet above mean sea level. After grading the top of this slope will be lowered to 100 feet above mean sea level. As stated in the report "No slopes more than 30 feet in height and steeper than 2: 1 (h:v) in inclination is anticipated, therefore, it is our conclusion that no slope stability analysis is needed at this time." IET stands by this recommendation. Response 8: IET prepared only one geotechnical report -IET, 2018. This comment was referred to the project Civil Engineer. Response 9: IET anticipates low expansive soils are to be used as compacted fill. An Expansion Index testing should be done after the grading because the site will be significantly cut to achieve the designed grade. As stated in Section 4.5 of the IET, 2018 report, positive drainage of surface water away .from structures is very important. No water should be allowed to pond adjacent to structures. Positive drainage may be accomplished by providing drainage away .from structures at a gradient of at least 2 percent for a distance of at least 5 feet, and further maintained by a swale or drainage path at a gradient of at least 1 percent. Where necessary, drainage paths may be shortened by use of area drains and collector pipes. Planters with open bottoms adjacent to structures should be avoided. Planters should not be designed adjacent to structures unless provisions for drainage, such as catch basins, liners, and/or area drains, are made. Over watering must be avoided. If proper drainage practice is implemented in accordance with the above recommendation, IET does not anticipate water to accumulate beneath the proposed structures; therefore, the potential for "bath tub effect" is very remote. Project No. 16-3319 Page 4 December 14, 2018 Additional Recommendation: Cut/Fill Transition and Fill Differentials To mitigate distress to structures related to the potential adverse effects of excessive differential settlement, cut/fill transitions should be eliminated from all building areas where the depth of fill placed within the "fill" portion exceeds proposed footing depths. The entire structure should be founded on a uniform bearing material. This should be accomplished by overexcavating the "cut" portion of the building pad area and replacing the excavated materials as properly compacted fill. Recommended depths of overexcavation are provided in the following table: DEPTH OF MAXIMUM FILL DEPTH OF OVEREXCAVATION ("cut" portion) ("fill" portion) Up to 5 feet Equal Depth 5 to 10 feet 5 feet Greater than 10 feet One-half the maximum thickness of fill placed on the "fill" _portion (20 feet maximum) Overexcavation of the "cut" portion should extend beyond the perimeter building lines a horizontal distance equal to the depth of overexcavation or to a minimum distance of 5 feet, whichever is greater. LIMITATION IET's services were performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable engineers and geologists practicing in this or similar localities. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. The samples taken and submitted for laboratory testing, the observations made and the in-situ field testing performed are believed representative of the entire project; however, soil and geologic conditions revealed by excavation may be different than IET' s preliminary findings. If this occurs, the changed conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted as required or alternate design(s) recommended. This report is issued with the understanding that it is the responsibility of the owner, or of his/her representative, to ensure that the information and recommendations contained herein are brought to the attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are taken to see that the contractor and/or subcontractor properly implements the recommendations in the field. The contractor and/or subcontractor should notify the owner if they consider any of the recommendations presented herein to be unsafe. The findings of this report are valid as of the present date. However, changes in the conditions of a property can and do occur with the passage of time, whether they be due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards may occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside IET's control. Project No. 16-3319 Page5 December 14, 2018 CLOSURE The opportunity to be of service is appreciated. Should you have any questions or require further clarification, please contact this office at your convenience. Sincerely, INLAND ENGINEERING TECHNOLOGIES, INC. I Expires June 30, 2020 Tom Smith, CEG Project Geologist Attachments: Soils Report Review Letter Plates A and B References: 0"$ Yogi Pirathapan, GE 2834 Geotechnical Engineer California Geological Survey, 2007, Geologic Map of the Oceanside 30' x60' Quadrangle, California City of Carlsbad, 2014, Draft General Plan & Drcift Climate Action Pl and Draft Environmental Impact Report, Section 3. 5. County of San Diego, 2011, General Plan Update, Environmental Review, Section 2.6. USGS, 1965, Geologic Map of California, Santa Ana Sheet Project No. 16-3319 Page 6 December 14, 2018 ,, ,,, "'' -- j ~ -l_ ,\ \ '!)JD\! ""'r,--- ~ :y ~ ., ~ ' \ ~i\ ,-:, i ~ I 1 Fleure 3.5-1 PROPOSED GENERAL PLAN Geologic Map of the Oceanside Quad rangle Alluvium Ctt-aceous mam Eocene marine e 1.11dllrlded Mese<ol<: granitic rocks Upper Crettceous marine Mese<olc ><>lcaniC and . mctavolcank Pliocene marine WatH -Highways = MajorS11'1'C:t ===== Planned Street -• -Railroad LJOtyUmlts Plate A ... w TRQL BtttP TABLE EA7Ml;NT CON , REQUIRED JR,;;;;.,_,_ I -····-' I I Percc:11 """"'"'' ., .... ,"...-.. --,-1·-~-~, Euc, __ ,._ -,. TlhU~• Fjll/ Cut 1 .. -•-- A' ,. ,,. ,. Legend ___,.i,._ Boring Location TB-3 CL ML SM at·1on Contact Form Clay Silt Silty Sand 1" Scale as drawn Adapted from Grading rk Consulting Plan by Landma Plate B