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HomeMy WebLinkAboutPUD 2021-0001; CDP 2021-0003; PRELIMINARY GEOTECHNICAL REPORT; 2020-12-09----------- ----- - • - -- --- - REPORT OF PRELIMINARY GEOTECHNICAL INVESTIGATION Proposed Garfield Street Homes 4008 Garfield Street Carlsbad, California JOB NO. 20-12942 09 December 2020 Prepared for: Rincon Homes ; •• .i-.-~ .,/;-r1 ... , ••-' .. ..:: .... JAN 14 2011 U.-,~;ARL.SBAD f-·, 1-1,-.,J!.1.iC~ DIVISiO:~ Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 4 been prepared on the basis of our observations and laboratory test results, and are attached as Figure Nos. IIIa-e. The exploratory trench logs and related information depict subsurface conditions only at the specific locations shown on the plot plan and on the particular date designated on the logs. Subsurface conditions at other locations may differ from conditions occurring at the locations. Also, the passage of time may result in changes in subsurface conditions due to environmental changes. V. LABORATORY TESTING & SOIL INFORMATION Laboratory tests were performed on retrieved soil samples in order to evaluate their physical and mechanical properties. The test results are presented on Figure Nos. Illa-e and IVa-c. The following tests were conducted on representative soil samples: 1. 2. 3. 4. 5. 6. 7. 8. Moisture Content (ASTM 02216-19) Density Measurements (ASTM D2937-17e2) Standard Test Method for Bulk Specific Gravity and Density of Compacted Bituminous Mixtures using Coated Samples ( ASTM D1188-07) Laboratory Compaction Characteristics (ASTM 01557-12el} Determination of Percentage of Particles Smaller than # 200 Sieve (ASTM D1140-17) Resistivity and pH Analysis (Department of Transportation California Test 643) Water Soluble Sulfate (Department of Transportation California Test 417) Water Soluble Chloride (Department of Transportation California Test 422) Moisture content and density measurements were performed by ASTM methods D2216-19 and D2937-17e2 respectively, in conjunction with D1188-07 to establish the in-situ moisture and density of samples retrieved from the exploratory trenches. ;:A ... ... ... ... ... -.. ... -... -- - • - - - ... ... ... - ... .. ... - - -------- -------------- ---- - - -- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 7 respectively, indicating that chloride is not a major factor in corrosion to ferrous metals. The primary cause of deterioration of concrete in foundations and other below ground structures is the corrosive attack by soluble sulfates present in the soil and groundwater. The results of water-soluble sulfate testing performed on a representative sample of the near surface soils in the general area of the proposed structures, yielded soluble sulfate contents of less than 30 ppm or 0.003 percent, indicating that the proposed cement-concrete structures that are in contact with the underlying soils are anticipated to be affected with a negligible sulfate exposure. As such, there is no restriction on selection of cement type. The table below summarizes the laboratory results for chemical testing of the sampled soils: Sample Location/ pH Soluble Sulfate Soluble Chloride Soil Resistivity Denth, (I'll (PPM) (PPM) (Ohm-cm) HP-2 12.0-4.0 7.2 <30 30 5,800 HP-41 3.0-5.0 6.9 <30 IO 8,800 The laboratory testing results are presented in figures IVa-c It should be noted that Geotechnical Exploration Inc., does not practice corrosion engineering and our assessment here should be construed as an aid to the owner or owner's representative. A corrosion specialist should be consulted for any specific design requirement. f1SI ------- -.. - -.. - --- - - ----- - - •- ---- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 9 Peninsular Ranges with primarily Cenozoic sedimentary rocks to the west and east of this central mountain range (Demere, 1997). In the Coastal Plain region, where the subject property is located, the "basement" consists of Mesozoic crystalline rocks. Basement rocks are also exposed as high relief areas (e.g., Black Mountain northeast of the subject property and Cowles Mountain near the San Carlos area of San Diego). Younger Cretaceous and Tertiary sediments lap up against these older features. These sediments form a "layer cake" sequence of marine and non-marine sedimentary rock units, with some formations up to 140 million years old. Faulting related to the La Naci6n and Rose canyon Fault zones has broken up this sequence into a number of distinct fault blocks in the southwestern part of the county. Northwestern portions of the county are relatively undeformed by faulting (Demere, 1997). The Peninsular Range form the granitic spine of San Diego County. These rocks are primarily plutonic, forming at depth beneath the earth's crust 140 to 90 million years ago as the result of the subduction of an oceanic crustal plate beneath the North American continent. These rocks formed the much larger Southern California batholith. Metamorphism associated with the intrusion of these great granitic masses affected the much older sediments that existed near the surface over that period of time. These metasedimentary rocks remain as roof pendants of marble, schist, slate, quartzite and gneiss throughout the Peninsular Ranges. Locally, Miocene-age volcanic rocks and flows have also accumulated within these mountains (e.g., Jacumba Valley). Regional tectonic forces and erosion over time have uplifted and unroofed these granitic rocks to expose them at the surface (Demere, 1997). The Salton Trough is the northerly extension of the Gulf of California. This zone is undergoing active deformation related to faulting along the Elsinore and San Jacinto ill Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 10 Fault Zones, which are part of the major regional tectonic feature in the southwestern portion of California, the San Andreas Fault Zone. Translational movement along these fault zones has resulted in crustal rifting and subsidence. The Salton Trough, also referred to as the Colorado Desert, has been filled with sediments to depth of approximately S miles since the movement began in the early Miocene, 24 million years ago. The source of these sediments has been the local mountains as well as the ancestral and modern Colorado River (Demere, 1997). As indicated previously, the San Diego area is part of a seismically active region of California. It is on the eastern boundary of the Southern California Continental Borderland, part of the Peninsular Ranges Geomorphic Province. This region is part of a broad tectonic boundary between the North American and Pacific Plates. The actual plate boundary is characterized by a complex system of active, major, right- lateral strike-slip faults, trending northwest/southeast. This fault system extends eastward to the San Andreas Fault (approximately 70 miles from San Diego) and westward to the San Clemente Fault (approximately SO miles off-shore from San Diego) (Berger and Schug, 1991). In California, major earthquakes can generally be correlated with movement on active faults. As defined by the California Division of Mines and Geology, now the California Geological Survey, an "active" fault is one that has had ground surface displacement within Holocene time, about the last 11,000 years (Hart and Bryant, 1997). Additionally, faults along which major historical earthquakes have occurred (about the last 210 years in California) are also considered to be active (Association of Engineering Geologist, 1973). The California Division of Mines and Geology defines a "potentially active" fault as one that has had ground surface displacement during Quaternary time, that is, between 11,000 and 1.6 million years (Hart and Bryant, 1997). .. .. .. .. .. .. .. .. .. .. ... - .. .. .. .. ... -- ----- - --------.. .. - - ----- ----- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 11 During recent history, prior to April 2010, the San Diego County area has been relatively quiet seismically. No fault ruptures or major earthquakes had been experienced ln historic time within the greater San Diego area. Since earthquakes have been recorded by instruments (since the 1930s), the San Diego area has experienced scattered seismic events with Richter magnitudes generally less than M4.0. During June 1985, a series of small earthquakes occurred beneath San Diego Bay, three of which were recorded at M4.0 to M4.2. In addition, the Oceanside earthquake of July 13, 1986, located approximately 26 miles offshore of the City of Oceanside, had a magnitude of MS.3 (Hauksson and Jones, 1988). On June 15, 2004, a MS.3 earthquake occurred approximately 45 miles southwest of downtown San Diego (26 miles west of Rosarito, Mexico). Although this earthquake was widely felt, no significant damage was reported. Another widely felt earthquake on a distant southern California fault was a MS.4 event that took place on July 29, 2008, west-southwest of the Chino Hills area of Riverside County. Several earthquakes ranging from MS.Oto M6.0 occurred in northern Baja California, centered in the Gulf of California on August 3, 2009. These were felt in San Diego but no injuries or damage was reported. A MS.8 earthquake followed by a M4.9 aftershock occurred on December 30, 2009, centered about 20 miles south of the Mexican border city of Mexicali. These were also felt in San Diego, swaying high-rise bulldings, but again no significant damage or injuries were reported. On April 4, 2010, a large earthquake occurred in Baja California, Mexico. It was widely felt throughout the southwest including Phoenix, Arizona and San Diego in California. This M7.2 event, the Sierra El Mayor earthquake, occurred in northern Baja California, approximately 40 miles south of the Mexico-USA border at shallow Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 12 depth along the principal plate boundary between the North American and Pacific plates. According to the U. S. Geological Survey this is an area with a high level of historical seismicity, and it has recently also been seismically active, although this is the largest event to strike in this area since 1892. The April 4, 2010, earthquake appears to have been larger than the M6.9 earthquake in 1940 or any of the early 20th century events (e.g., 1915 and 1934) in this region of northern Baja California. The event caused widespread damage to structures, closure of businesses, government offices and schools, power outages, displacement of people from their homes and injuries in the nearby major metropolitan areas of Mexicali in Mexico and Calexico in Southern California. This event's a~ershock zone extends significantly to the northwest, overlapping with the portion of the fault system that is thought to have ruptured in 1892. Some structures in the San Diego area experienced minor damage and there were some injuries. Ground motions for the April 4, 2010, main event, recorded at stations in San Diego and reported by the California Strong Motion Instrumentation Program (CSMIP), ranged up to 0.058g. On July 7, 2010, a MS.4 earthquake occurred in Southern California at 4:53 pm (Pacific Time) about 30 miles south of Palm Springs, 25 miles southwest of Indio, and 13 miles north-northwest of Borrego Springs. The earthquake occurred near the Coyote Creek segment of the San Jacinto Fault. The earthquake exhibited right lateral slip to the northwest, consistent with the direction of movement on the San Jacinto Fault. The earthquake was felt throughout Southern California, with strong shaking near the epicenter. It was followed by more than 60 aftershocks of Ml.3 and greater during the first hour. ... ... -- - - -- -... -.. .. .. .. .. .. --------.. ---.. -- --.. -.. --- --- --- ---- Garfield Street Condominium Project Carlsbad, California A. Local and Reaionat Faults Job No. 20-12942 Page 15 Reference to the Geologic Map and Legend, Figure No. V (Kennedy and Tan, 2007), indicates that no faults are shown to cross the site. Furthermore, our site reconnaissance presented no indications of faulting crossing the site. In our professional opinion, neither an active fault nor a potentially active fault underlies the site. A brief description of the nearby active faults including distances from the mapped fault to the subject site at the closest point (based on the USGS Earthquake Hazards- Interactive Fault Map), is presented below: Newport-Inglewood-Rose Canyon Fault Zone System: The Oceanside section of the Newport-Inglewood-Rose Canyon Fault Zone is mapped approximately 4.3 miles west-southwest of the site. The offshore portion of the Newport-Inglewood Fault Zone is described as a right-lateral; local reverse slip associated with fault steps (SCEDC, 2020); the reported length is 46.2 miles extending in a northwest-southeast direction. Surface trace is discontinuous in the Los Angeles Basin, but the fault zone can easily be noted there by the existence of a chain of low hills extending from Culver City to Signal Hill. South of Signal Hill, it roughly parallels the coastline until just south of Newport Bay, where it heads offshore, and becomes the Newport- Inglewood-Rose Canyon Fault Zone. A significant earthquake (M6.4) occurred along this fault on March 10, 1933. Since then, no additional significant events have occurred. The fault is believed to have a slip rate of approximately 0.6-mm/yr with an unknown recurrence interval. This fault is believed capable of producing an earthquake of M6.0 to M7.4 (Grant Ludwig and Shearer, 2004). ill Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 16 Rose Canvon Fault Zone: The Rose Canyon Fault Zone is the southern section of the Newport-Inglewood-Rose Canyon Fault Zone system mapped in the San Diego County area as trending north-northwest to south-southeast from Oceanside to La Jolla and generally north-south into San Diego Bay, through Coronado and offshore downtown San Diego, from where it appears to head southward. The Rose Canyon Fault Zone system is considered to be a complex zone of onshore and offshore, en echelon right lateral, strike slip, oblique reverse, and oblique normal faults. This fault is considered to be capable of generating an M7.2 earthquake and is considered microseismically active, although no significant recent earthquakes since 1769 are known to have occurred on the fault. Investigative work on faults that are part of the Rose Canyon Fault Zone at the Police Administration and Technical Center in downtown San Diego, at the SDG&E facility in Rose Canyon, and within San Diego Bay and elsewhere within downtown San Diego, has encountered offsets in Holocene (geologically recent) sediments. These findings confirm Holocene displacement on the Rose Canyon Fault, which was designated an "active" fault in November 1991 (Hart and Bryant, 1997). Rockwell (2010) has suggested that the Rose CFZ underwent a cluster of activity including 5 major earthquakes in the early Holocene, with a long period of inactivity following, suggesting major earthquakes on the RCFZ behaves in a cluster-mode, where earthquake recurrence is clustered ln time rather than in a consistent recurrence interval. With the most recent earthquake (MRE) nearly 500 years ago, it is suggested that a period of earthquake activity on the RCFZ may have begun. Rockwell (2010) and a compilation of the latest research implies a long-term slip rate of approximately l to 2 mm/year. IA ... .. .. ... .. ... .. ... .. .. --.. ... ... - - .. .. ... .. ... .. ... .. .. .. ... .. .. .. Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 18 4-mile-wide, northwest-southeast-trending zone of discontinuous and en echelon faults extending through portions of Orange, Riverside, San Diego, and Imperial Counties. Individual faults within the Elsinore Fault Zone range from less than 1 mile to 16 miles in length. The trend, length and geomorphic expression of the Elsinore Fault Zone identify it as being a part of the highly active San Andreas Fault system. Like the other faults in the San Andreas system, the Elsinore Fault is a transverse fault showing predominantly right-lateral movement. According to Hart et al. (1979), this movement averages less than 1 centimeter per year. Along most of its length, the Elsinore Fault Zone is marked by a bold topographic expression consisting of linearly aligned ridges, swales and hallows. Faulted Holocene alluvial deposits (believed to be less than 11,000 years old) found along several segments of the fault zone suggest that at least part of the zone is currently active. Although the Elsinore Fault Zone belongs to the San Andreas set of active, northwest- trending, right-slip faults in the southern California area (Crowell, 1962), it has not been the site of a major earthquake in historic time, other than a M6.0 earthquake near the town of Elsinore in 1910 (Richter, 1958; Toppozada and Parke, 1982). However, based on length and evidence of late-Pleistocene or Holocene displacement, Greensfelder (1974) has estimated that the Elsinore Fault Zone is reasonably capable of generating an earthquake with a magnitude as large as M7.5. Study and logging of exposures in trenches placed in Glen Ivy Marsh across the Glen Ivy North Fault (a strand of the Elsinore Fault Zone between Corona and Lake Elsinore), suggest a maximum earthquake recurrence interval of 300 years, and when combined with previous estimates of the long-term horizontal slip rate of 0.8 to 7.0 mm/year, suggest typical earthquake magnitudes of M6.0 to M7.0 (Rockwell et al., 1985). The Working Group on California Earthquake Probabilities (2008) has estimated that there .. .. -.. -.. .. -.. ----- .. -.. .. .. -... -.. .. .. .. .. .. .. Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 20 on the San Bernardino, San Jacinto Valley and Anza segments, respectively, capable of generating peak horizontal ground accelerations of 0.48g to 0.53g in the County of Riverside. A MS.4 earthquake occurred on the San Jacinto Fault on July 7, 2010. The United States Geological Survey has issued the following statements with respect to the recent seismic activity on southern California faults: The San Jacinto fault, along with the Elsinore, San Andreas, and other faults, is part of the plate boundary that accommodates about 2 inches/year of motion as the Pacific plate moves northwest relative to the North American plate. The largest recent earthquake on the San Jacinto fault, near this location, the M6.S 1968 Borrego Mountain earthquake April 8, 1968, occurred about 25 miles southeast of the July 7, 2010, MS.4 earthquake. This MS.4 earthquake follows the 4th of April 2010, Easter Sunday, M7.2 earthquake, located about 125 miles to the south, well south of the US Mexico international border. A M4.9 earthquake occurred in the same area on June 12th at 8:08 pm (Pacific Time), Thus, this section of the San Jacinto fault remains active. Seismologists are watching two major earthquake faults in southern California. The San Jacinto fault, the most active earthquake fault in southern California, extends for more than 100 miles from the international border into San Bernardino and Riverside, a major metropolitan area often called the Inland Empire. The Elsinore fault is more than 110 miles long, and extends into the Orange County and Los Angeles area as the Whittier fault. The Elsinore fault is capable of a major earthquake that would significantly affect the large metropolitan areas of southern California. The Elsinore fault has not hosted a major earthquake in more than 100 years. The occurrence of these earthquakes along the San Jacinto fault and continued aftershocks demonstrates that the earthquake activity in the region remains at an elevated level. The San Jacinto fault is known as the most active earthquake fault in southern California. Caltech and USGS seismologist continue to monitor the ongoing earthquake activity using the Caltech/USGS Southern California Seismic Network and a GPS network of more than 100 stations. .. .. .. .. .. .. .. .. .. .. .. .. .. • .. - - - .. .. -.. .. .. .. .. - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 22 site. The site is underlain by relatively stable and dense Old Paralic Deposits, Unit 6- 7 formational materials at a depth of 1.0 to 3.0 feet. In our opinion, there is not a slope stability issue with the site. Liquefaction: The liquefaction of saturated sands during earthquakes can be a major cause of damage to buildings. Liquefaction is the process by which soils are transformed into a viscous fluid that will flow as a liquid when unconfined. It occurs primarily in loose, cohesionless saturated silt, sand, and fine-grained gravel deposits of Holocene to late Pleistocene age and in areas where the groundwater is shallower than about SO feet (DMG Special Publication 117) when they are sufficiently shaken by an earthquake. On this site, the risk of liquefaction of formational materials due to seismic shaking is considered to be very low due to the dense to very dense nature of the underlying formational materials and the lack of shallow static groundwater. The site does not have a potential for soil strength loss to occur due to a seismic event. Tsunamis and Seiches: A tsunami is a series of long waves generated in the ocean by a sudden displacement of a large volume of water. Underwater earthquakes, landslides, volcanic eruptions, meteor impacts, or onshore slope failures can cause this displacement. Tsunami waves can travel at speeds averaging 450 to 600 miles per hour. As a tsunami nears the coastline, its speed diminishes, its wave length decreases, and its height increases greatly. After a major earthquake or other tsunami-inducing activity occurs, a tsunami could reach the shore within a few minutes. One coastal community may experience no damaging waves while another may experience very destructive waves. Some low-lying areas could experience severe inland inundation of water and deposition of debris more than 3,000 feet inland. UI ... .. .. ... .. .. .. .. .. .. - - ---- - -- .. .. .. .. .. .. ------- ------- ... -.. --- --.. ------- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 23 The site is located approximately 0.17-mile from the exposed coastline and at an elevation of approximately 59 to 67 feet above MSL. Review of the Tsunami Inundation Map for Emergency Planning, Encinitas Quadrangle, the site is located outside the inundation area. There is no risk of tsunami inundation at the site. A seiche is a run-up of water within a lake or embayment triggered by fault-or landslide-induced ground displacement. The site is located near a coastal lagoon, that is not considered capable of producing a seiche and inundating the subject site. Flood Hazard: Review of the FEMA flood maps number 06073C0764H, effective on 12/20/2019, the project site is located within the Special Flood Hazard Area (SFHA) X. Zone Xis described as minimal flood hazard. The civil engineer should verify this statement with the City of Carlsbad and County of San Diego (FEMA, 2019). Geologic Hazards Summary: It is our opinion, based upon a review of the available maps, our research and our site investigation, that the site is underlain at shallow depth by stable Old Paralic Deposits formational materials and is suited for the proposed residential structures. retaining walls and associated improvements provided the recommendations herein are implemented. Furthermore, based on the available information at this stage, it appears the proposed site development will not destabilize or result in settlement of adjacent property or improvements if the recommendations presented in this report are implemented. :a Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 24 No significant geologic hazards are known to exist on the site that would prohibit the construction of the proposed residential structures, retaining walls and associated improvements. Ground shaking from earthquakes on active southern California faults and active faults in northwestern Mexico is the greatest geologic hazard at the property. Design of building structures in accordance with the current building codes would reduce the potential for injury or loss of human life. Buildings constructed in accordance with current building codes may suffer significant damage but should not undergo total collapse. In our explicit professional opinion, no active or potentially active faults underlie the project site. IX. GROUNDWATER Free groundwater was not encountered in our exploratory excavations to the maximum depths explored. A more detailed description of the subsurface materials encountered in our exploratory excavations Figure Nos. Illa-e. It should also be recognized that minor groundwater seepage problems might occur after development of a site even where none were present before development. These are usually minor phenomena and are often the result of an alteration in drainage patterns and/or an increase in irrigation water. Based on the permeability characteristics of the soil and the anticipated usage and development, it is our opinion that any seepage problems, which may occur, will be minor in extent. It is further our opinion that these problems can be most effectively corrected on an individual basis if and when they occur. ill .. .. ---.. .. - - • - - - - - - - - -.. .. .. .. .. --------- --- - --- - - - - ----- -.. - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 25 We do not anticipate significant groundwater problems to develop in the future, if the property is developed as proposed and proper drainage is implemented and maintained. It should be kept ln mind that any required construction operations will change surface drainage patterns and/or reduce permeabilities due to the densification of compacted soils. Such changes of surface and subsurface hydrologic conditions, plus irrigation of landscaping or significant increases in rainfall, may result in the appearance of surface or near-surface water at locations where none existed previously. The damage from such water is expected to be localized and cosmetic in nature, if good positive drainage is implemented, as recommended in this report, during and at the completion of construction. On properties such as the subject site where dense, low permeability soils exist at shallow depths, even normal landscape irrigation practices on the property or neighboring properties, or periods of extended rainfall, can result in shallow "perched" water conditions. The perching (shallow depth) accumulation of water on a low permeability sulface can result in areas of persistent wetting and drowning of lawns, plants and trees. Resolution of such conditions, should they occur, may require site-specific design and construction of subdrain and shallow "wick" drain dewatering systems. Subsurface drainage with a properly designed and constructed subdrain system will be required along with continuous back drainage behind any proposed lower-level basement walls, property line retaining walls, or any perimeter stem walls for raised- wood floors where the outside grades are higher than the crawl space grades. Furthermore, crawl spaces, if used, should be provided with the proper cross- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 26 ventilation to help reduce the potential for moisture-related problems. Additional recommendations may be required at the time of construction. It must be understood that unless discovered during site exploration or encountered during site construction operations, it is extremely difficult to predict if or where perched or true groundwater conditions may appear in the future. When site fill or formational soils are fine-grained and of low permeability, water problems may not become apparent for extended periods of time. Water conditions, where suspected or encountered during construction, should be evaluated and remedied by the project civil and geotechnical consultants. The project developer and property owner, however, must realize that post-construction appearances of groundwater may have to be dealt with on a site-specific basis. Proper functional surface drainage should be implemented and maintained at the property. X. CONCLUSIONS & RECOMMENDATIONS The following recommendations are based upon the practical field investigations conducted by our firm, and resulting laboratory tests, in conjunction with our knowledge and experience with similar soils in the Carlsbad area. The opinions, conclusions, and recommendations presented in this report are contingent upon Geotechnlcal Exp/oration, Inc. being retained to review the final plans and specifications as they are developed and to observe the site earthwork and installation of foundations. Accordingly, we recommend that the following paragraph be included on the grading and foundation plans for the project. lli ... ... .. ... .. .. .. .. .. .. .. ... - - 4 .. - .. .. -.. ... .. - ... .. .. .. .. .. .. ---------.. - ------ --------- - ----- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 27 If the geotechnical consultant of record is changed for the project, the work shall be stopped until the replacement has agreed in writing to accept responsibility within their area of technical competence for approval upon completion of the work. It shall be the responsibility of the permittee to notify the governing agency in writing of such change prior to the recommencement of grading and/or foundation installation work and comply with the governing agency's requirements for a change to the Geotechnical Consultant of Record for the project. We recommend that the planned residential structures, garages and retaining walls be supported by conventional, individual-spread and/or continuous footing foundations founded on medium dense to dense formational soils and minimum 90 percent compacted structural fill soils. Individual structures may bear on dense formational or fill soils depending on their locations, final grading elevations and exposure of formational materials. Existing fill soils across the entire site will be disturbed during the demolition of the existing structures, and are not suitable in their current condition to support new structures or associated improvements. A full removal and recompaction of existing fill and residual soils across the site will be required to support the proposed structures and associated improvements. Fill soils across the site will be required to be compacted to at least 90 percent relative compaction. Existing fill soil and formational materials are suitable for use as recompacted fill soils. Any buried trash and roots encountered during site demolition and fill soil recompaction should be removed and exported off site. It is our opinion that the site is suitable for the planned residential project provided the recommendations herein are incorporated during design and construction. 111 Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 28 A. 1. 2. Preparation ot Soils for Site Deve/ooment General: Grading should conform to the guidelines presented in the 2019 California Building Code (CBC, 2019), as well as the requirements of the City of Carlsbad. During earthwork construction, removals and reprocessing of fill materials, as well as general grading procedures of the contractor should be observed and the fill placed selectively tested by representatives of the geotechnical engineer, Geotechnical Exploration Inc. If any unusual or unexpected conditions are exposed in the field, they should be reviewed by the geotechnical engineer and if warranted, modified and/or additional remedial recommendations will be offered. Specific guidelines and comments pertinent to the planned development are provided herein. The recommendations presented herein have been completed using the information provided to us regarding site development. If information concerning the proposed development is revised, or any changes in the design and location of the proposed property modified or approved in writing by this office. Clearing and Stripping: Complete demolition of the existing residential structure and associated improvements should be undertaken. This is to include the complete removal of all subsurface footings, utility lines and miscellaneous debris. After clearing the entire ground surface of the site should be stripped of existing vegetation within the areas of proposed new construction. This includes any roots from existing trees and shrubbery. Holes resulting from the removal of root systems or other buried obstructions that ill - ----.. .. ... .. - ◄ - - ... .. ... .. ... .. .. ... .. .. .. .. .. .. Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 30 4. 5. improvements, or fill slopes, where feasible, or to the depth of excavation or fill at that location, whichever is greater. Cut-Fill Transition: Based on the review of the preliminary survey plans it appears that the new residential structure may be planned to be constructed on a cut-fill transition line. New structures should not bear on a cut-fill transition line. If a cut-fill transition line exists within the proposed building envelope, we recommend that the cut portion of the building pad, be undercut to a minimum of 24 inches below the bottom of the proposed footing depth. The bottom of the over excavation should be observed and approved by a representative of Geotechnical Exploration Inc., to verify that all loose and unsuitable soils have been completely removed prior to reprocessing. After approval, the bottom of the excavation should be scarified to a minimum depth of 8 inches below removal grade elevations, brought to near-optimum moisture conditions and recompacted to at least 90 percent relative compaction (based on ASTM Test Method D1557). Backfill and compaction of the remaining structural fill should be performed based on the recommendations presented in the following sections. No structures should be supported on a building pad with structural fill soil thickness differential of greater than 5 feet. Subqrade Preparation: After the site has been cleared, stripped, and the required excavations made, the exposed subgrade soils in areas to receive new fill and/or slab-on-grade building improvements should be scarified to a depth of 6 inches, moisture conditioned, and compacted to the requirements for structural fill. While not anticipated, in the event that planned cuts expose any medium to highly expansive formational materials in the building areas, they 111 .. .. .. .. -.. -.. .. -- - - - .. -.. .. -.. - .. -.. - ------------.. --- -.. --------------- - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 31 6. 7. should be scarified and moisture conditioned to at least 3 percent over optimum moisture for low expansive soils and 5 percent for medium and highly expansive soils (if encountered). Material for Fill: Existing on-site low-expansion potential (Expansion Index of 50 or less per ASTM D4829-19) soils with an organic content of less than 3 percent by volume are, in general, suitable for use as fill. Imported fill material, where required, should have a low-expansion potential. In addition, both imported and existing on-site materials for use as fill should not contain rocks or lumps more than 6 inches in greatest dimension if the fill soils are compacted with heavy compaction equipment (or 3 inches in greatest dimension if compacted with lightweight equipment). All materials for use as fill should be approved by our representative prior to importing to the site. If encountered at the site, medium to highly expansive soils should not be used as structural fill at a depth of less than 5 feet from footing bearing surface elevation or behind retaining walls. Backfill material to be placed behind retaining walls should be low expansive (E.I. less than 50), with rocks no larger than 3 inches in diameter. Structural Fill Compaction: All structural fill, and areas to receive any associated improvements, should be compacted to a minimum degree of compaction of 90 percent based upon ASTM D1557-12el. Fill material should be spread and compacted in uniform horizontal lifts not exceeding 8 inches in uncompacted thickness. Before compaction begins, the fill should be brought to a water content that will permit proper compaction by either: ( 1) aerating and drying the fill if it is too wet, or (2) watering the fill if it is too dry. Each lift should be thoroughly mixed before compaction to ensure a uniform distribution of moisture. For low expansive soils, the moisture content should 111 Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 34 d) Verify use of proper materials, densities and thicknesses during placement and compaction of compacted fill prior to placement of compacted fill, inspect subgrade and verify that site has been prepared properly Section 1705.6 "Soils" statement and Table 1705.6 indicate that it is mandatory that a representative of this firm (responsible engineering firm), perform observations and fill compaction testing during excavation operations to verify that the remedial operations are consistent with the recommendations presented in this report. All grading excavations resulting from the removal of soils should be observed and evaluated by a representative of our firm before they are backfilled. Quality control grading observation and field density testing for the purpose of documenting that adequate compaction has been achieved and acceptable soils have been utilized to properly support a project applies not only to fill soils supporting primary structures; unless supported by deep foundations or caissons, but all site improvements such as stairways, patios, pools and pool decking, sidewalks, driveways and retaining walls etc. Observation and testing of utility line trench backfill also reduces the potential for localized settlement of all of the above including all improvements outside of the footprint of primary structures. Often after primary building pad grading, it is not uncommon for the geotechnical engineer of record to not be notified of grading performed outside the footprint of the project primary structures. As a result, settlement damage of site improvements such as patios, pool and pool decks, exterior landscape walls and walks, and structure access stairways can occur. It is therefore strongly recommended that the project general contractor, grading contractor, .. .. .. .. ◄ ◄ - - - -... -... .. .. .. .. .. .. .. --- --- --- ----- --------- --- - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 35 and others tasked with completing a project with workmanship that reduces the potential for damage to the project from soil settlement, or expansive soil uplift, to be advised and acknowledge the importance of adequate and comprehensive observation and testing of soils intended to support the project they are working on. The project geotechnical engineers of record must be contacted and requested to provide these services. Failure to comply with this recommendation can result in several costly and time-consuming requirements from the governing municipality or county engineering and planning departments. For example, the geotechnical and/or civil engineer of record may be required to: • • • Clarify if observation and testing services were performed for all grading shown on the Grading Plans. If not, indicate the areas NOT observed or tested on the As-Graded Geological Map. A construction change must be processed to indicate the revised grading recommendations by the geotechnical engineer of work on the plans. The geotechnical engineer must submit on addendum letter addressing the change to the grading plan specifications for the earthwork presented on the grading plans. • The geotechnical consultant must evaluate the existing unobserved/undocumented fill as an uncontrolled embankment and provide a statement indicating the uncontrolled embankment will not endanger the public health, safety and welfare. In order to make this statement the geotechnical engineer would have to clearly define the DI Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 36 potential problems such as damage to project improvements that could result from construction on undocumented fill soils. • The geotechnical consultant must indicate if the unobserved fill placed during earthwork within the limits of work is suitable for the intended use. To render such an opinion the geotechnical consultant would have to place a sufficient number of test excavations and conduct enough testing to warrant such an opinion. • If the geotechnical consultant cannot render an opinion that the unobserved fill is suitable for the purpose intended, "They must indicate if additional fill remedial grading is recommended." • • • The limits of the "Unobserved fill/uncontrolled embankment must be shown on revised grading plans along with the "Uncontrolled Embankment Maintenance Agreement Approval Number." The owner must execute an "Uncontrolled Embankment Agreement: for the portion of the undocumented fill to remain. This must be coordinated with the LDR Drainage and Grading reviewer. The title and date of the requested addendum letter or geotechnical investigation report must be added under note no. 1 of the "Grading and Geotechnical Specification" Certification as construction change "A". • These changes must be made on a redline copy, and submitted as a "Construction Change A" for review and approval by the geology section and Drainage and Grades Section. iii .. .. .. .. .. .. .. .. .. .. .. .. - - - - --- -.. .. .. .. .. .. .. .. • - - - - - -.. - --.. - - ---- - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 37 8. • All approved changes will then be transferred to the mylars for approval and signatures by the Deputy City Engineer. The Geotechnical Engineer of Record, in this case Geotechnical Exploration, Inc., cannot be held responsible for the costs and time delays associated with the lack of contact and requests for testing services by the client, general contractor, grading contractor or any of the project design team responsible for requesting the required geotechnical services. Requests for services are to be made through our office telephone number (858) 549-7222 and the telephone number of the G.E.I. personnel assigned to the project . seismic Desian Criteria 10. Seism;c Data Bases: The estimation of the peak ground acceleration and the repeatable high ground acceleration (RHGA) likely to occur at the site is based on the known significant local and regional faults within 100 miles of the site. 11. Seismic Design Criteria: The proposed structure should be designed in accordance with the 2019 CBC, which incorporates by reference the ASCE 7- 16 for seismic design. We have determined the mapped spectral acceleration values for the site based on a latitude of 33.1550 degrees and a longitude of -117 .3357 degrees, utilizing a program titled "Seismic Design Map Tool" and provided by the USGS through SEAOC, which provides a solution for ASCE 7- 16 utilizing digitized files for the Spectral Acceleration maps. See Appendix B. iii Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 38 12. Structure and Foundation Design: The design of the new structures and foundations should be based on Seismic Design Category D, Risk Category II for a Site Class Stiff Soils D. 13. Spectral Acceleration and Design Values: The structural seismic design, when applicable, should be based on the following values, which are based on the site location, soil characteristics, and seismic maps by USGS, as required by the 2019 CBC. The summarized seismic soil parameters are presented in table I below, have been calculated with the SEAOC Seismic Design Map Tool. The complete values are included in Appendix B. The Site Class Stiff Soil D values for this property are: TABLE I Mapped Soectrat Acceleration Values and Ossian Parameters Ss s, SMs Sos So, Fa Fv PGA PGAM SDC 1.098 0.396 1.318 0594 0.878 0.396 1.2 1.5 0.486 0.583 D C. Foundation Recommendations 14. Footings: We recommend that the proposed structures be supported on conventional, individual-spread and/or continuous footing foundations bearing on undisturbed formational materials or on properly compacted fill soils over formational soils. No footings should be underlain by undocumented fill soils. AU building footings should be built on formational soils or properly compacted fill prepared as recommended above in Recommendation Nos. 3, 4 and 5. The footings should be founded at least 18 inches below the lowest adjacent finished grade when founded into properly compacted fill or formational soils. Ul ... --.. ... .. ... -.. ... ---- • -.. .. .. ... .. ... ... ... .. ... .. ... .. .. .. .. .. .. .. -----.. --- - --- ---.. .. ----- ----- ---- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 39 Footings located adjacent to utility trenches should have their bearing surfaces situated below an imaginary 1.0: 1.0 plane projected upward from the bottom edge of the adjacent utility trench. Otherwise, the utility trenches should be excavated farther from the footing locations. Footings located adjacent to the tops of slopes should be extended sufficiently deep so as to provide at least 8 feet of horizontal cover between the slope face and outside edge of the footing at the footing bearing level. 15. Bearing Values: At the recommended depths, footings on formational or properly compacted fill soils may be designed for allowable bearing pressures of 2,500 psf for combined dead and live loads and 3,325 psf for all loads, including wind or seismic. The footings should, however, have a minimum width of 15 inches. An increase in soil allowable static bearing can be used as follows: 800 psf for each additional foot over 1.5 feet in depth and 400 psf for each additional foot in width to a total not exceeding 4,000 psf. The static soil bearing value may be increased one-third for seismic and wind load analysis. As previously indicated, all of the foundations for the building should be built on dense formational soils or properly compacted fill soils. 16. Footing Reinforcement: All continuous footings should contain top and bottom reinforcement to provide structural continuity and to permit spanning of local irregularities. We recommend that a minimum of two No. 5 top and two No. 5 bottom reinforcing bars be provided 1n the footings. All footings should be reinforced as specified by the structural engineer. A minimum clearance of 3 inches should be maintained between steel reinforcement and the bottom or sides of the footing. Isolated square footings should contain, as a minimum, a grid of three No. 4 steel bars on 12-inch centers, both ways. In order for us :, Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 40 to offer an opinion as to whether the footings are founded on soils of sufficient load bearing capacity, it is essential that our representative inspect the footing excavations prior to the placement of reinforcing steel or forms. NOTE: The project Civil/Structural Engineer should review all reinforcing schedules. The reinforcing minimums recommended herein are not to be construed as structural designs, but merely as minimum reinforcement to reduce the potential for cracking and separations. 17. Lateral Loads: Lateral load resistance for the structure supported on footing foundations may be developed in friction between the foundation bottoms and the supporting subgrade. An allowable friction coefficient of 0.35 is considered applicable. An additional allowable passive resistance equal to an equivalent fluid weight of 275 pounds per cubic foot (pcf) acting against the foundations may be used in design provided the footings are poured neat against the dense formational or properly compacted fill materials. These lateral resistance value assume a level surface in front of the footing for a minimum distance of three times the embedment depth of the footing and any shear keys, but not less than 8 feet from a slope face, measured from effective top of foundation. Retaining walls supporting surcharge loads or affected by upper foundations should consider the effect of those upper loads. 18. Settlement: Settlements under structural design loads are expected to be within tolerable limits for the proposed structures. For footings designed in accordance with the recommendations presented in the preceding paragraphs, we anticipate that the total and differential static settlement for the proposed improvements will be on the order of 1-inch and approximately, post- construction differential settlement angular rotation should be less than 1/240. Bi - .. .. .. .. .. .. .. .. .. .. .. -- .. --.. .. .. .. .. .. .. -.. .. .. .. .. - - - --- ---.. - ----- •· - ------- Garfield Street Condominium Project Carlsbad, California D. Concrete Slab on-Gracie Criteria Job No. 20-12942 Page 41 Slabs on-grade may only be used on new, properly compacted fill or when bearing on dense formational soils. 19. Minimum Floor Slab Thickness and Reinforcement: Based on our experience, we have found that, for various reasons, floor slabs occasionally crack. Therefore, we recommend that all slabs on-grade contain at least a minimum amount of reinforcing steel to reduce the separation of cracks, should they occur. Slab subgrade soil should be verified by a Geotechnica/ Exploration, Inc. representative to have the proper moisture content within 48 hours prior to placement of the vapor barrier and pouring of concrete. New interior floor slabs should be a minimum of 4-inches actual thickness and be reinforced with No. 4 bars on 18-inch centers, both ways, placed at mid- height in the slab. Soil moisture content should be kept above the optimum prior to waterproofing placement under the new concrete slab. Shrinkage joints shall be specified by the structural engineer. We note that shrinkage cracking can result in reflective cracking in brittle flooring surfaces such as stone and tiles. It is imperative that if movement intolerant flooring materials are to be utilized, the flooring contractor and/or architect should provide specifications for the use of high-quality isolation membrane products installed between slab and floor materials. 20. Slab Moisture Emission: Although it is not the responsibility of geotechnical engineering firms to provide moisture protection recommendations, as a service to our clients we provide the following discussion and suggested IP Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 42 minimum protection criteria. Actual recommendations should be provided by the project architect and waterproofing consultants or product manufacturer. It is recommended to contact the vapor barrier manufacturer to schedule a pre-construction meeting and to coordinate a review, in-person or digital, of the vapor barrier installation. Soil moisture vapor can result in damage to moisture-sensitive floors, some floor sealers, or sensitive equipment in direct contact with the floor, in addition to mold and staining on slabs, walls and carpets. The common practice in Southern California is to place vapor retarders made of PVC, or of polyethylene. PVC retarders are made in thickness ranging from 10-to 60-mil. Polyethylene retarders, called visqueen, range from 5-to 10-mil in thickness. These products are no longer considered adequate for moisture protection and can actually deteriorate over time. Specialty vapor retarding and barrier products possess higher tensile strength and are more specifically designed for and intended to retard moisture transmission into and through concrete slabs. The use of such products is highly recommended for reduction of floor slab moisture emission. The following American Society for Testing and Materials (ASTM) and American Concrete Institute (ACI) sections address the issue of moisture transmission into and through concrete slabs: ASTM E1745-17 Standard Specification for Plastic Water Vapor Retarders Used in Contact Concrete Slabs; ASTM E1643- 18a Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs; AC! 302.2R-06 Guide for Concrete Slabs that Receive .. ... .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. -.. .. .. .. .. .. .. .. .. .. .. .. .. .. - - - - ---- - • - • Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 43 Moisture-Sensitive Flooring Materials; and ACI 302.lR-15 Guide to Concrete Floor and Slab Construction. 20.1 Based on the above, we recommend that the vapor barrier consist of a minimum 15-mil extruded polyolefin plastic (no recycled content or woven materials permitted). Permeance as tested before and after mandatory conditioning (ASTM E1745 Section 7.1 and subparagraphs 7.1.1-7.1.5) should be less than 0.01 perms (grains/square foot/hour/per inch of Mercury) and comply with the ASTM E1745-17 Class A requirements. Installation of vapor barriers should be in accordance with ASTM E1643-18a. The basis of design is 15-mil Stego Wrap vapor barrier placed per the manufacturer's guidelines. Reef Industries Vapor Guard membrane has also been shown to achieve a permeance of less than 0.01 perms. We recommend that the slab be poured directly on the vapor barrier, which is placed directly on the prepared properly compacted smooth subgrade soil surface. 20.2 Common to all acceptable products, vapor retarder/barrier joints must be lapped at least 6 inches. Seam joints and permanent utility penetrations should be sealed with the manufacturer's recommended tape or mastic. Edges of the vapor retarder should be extended to terminate at a location in accordance with ASTM E1643-18a or to an alternate location that is acceptable to the project's structural engineer. All terminated edges of the vapor retarder should be sealed to the building foundation (grade beam, wall, or slab) using the manufacturer's recommended accessory for sealing the vapor retarder to pre-existing or freshly placed concrete. Additionally, in actual practice, stakes are often driven through the retarder material, equipment is dragged or ;, --- - . ' -- -- --- ---.. ---... - - ----- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 45 E. designed and constructed for the existing soil conditions. The improvements should not be built on loose soils or fills placed without our observation and testing . For exterior slabs with the minimum shrinkage reinforcement, control joints should be placed at spaces no farther than 15 feet apart or the width of the slab, whichever is less, and also at re-entrant corners. Control joints in exterior slabs should be sealed with elastomeric joint sealant. The sealant should be inspected every 6 months and be properly maintained Retaining Wall Design Criteria 22. Design Parameters -Unrestrained: The active earth pressure to be utilized in the design of any cantilever site retaining walls, utilizing on-site low-expansive (EI less than 50] or imported very low-to low-expansive soils [EI less than 50] as backfill should be based on an Equivalent Fluid Weight of 38 pcf (for level backfill only). For 2.0:1.0 sloping backfill, the cantilever site retaining walls should be designed with an equivalent fluid pressure of 52 pcf. Unrestrained retaining walls should be backfilled with properly compacted very low to low expansive soils. Unrestrained building retaining walls should be designed for 38 pcf for level low expansive soil backfill, and use a conversion load factor of 0.31 for vertical surcharge loads to be converted to uniform lateral surcharge loads. Temporary cantilever shoring walls may use 45 pcf active pressure, and a conversion factor of 0.36 to convert vertical uniform surcharge to horizontal uniform pressure. For passive resistance, use the value of 685 pd times the diameter of the soldier pile, times the depth of embedment below the grade excavation in front of the piles. al Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 46 23. Design Parameters -Restrained: Temporary or permanent site restrained shoring walls or restrained building retaining walls supporting low expansive level backfill may utilize a triangular pressure increasing at a rate of 56 pcf for wall design (78 pcf for sloping 2.0: 1.0 backfill). The soil pressure produced by any footings, improvements, or any other surcharge placed within a horizontal distance equal to the height of the retaining portion of the wall should be included in the wall design pressure. A conversion factor of 0.47 pcf may be used to convert vertical uniform surcharge loads to lateral uniform pressure behind a restrained retaining wall with level backfill and 0.64 when supporting a 2 to 1 sloping backfill. The recommended lateral soil pressures are based on the assumption that no loose soils or unstable soil wedges will be retained by the retaining wall. Backfill soils should consist of low-expansive soils with EI less than 50, and should be placed from the heel of the foundation to the ground surface within the wedge formed by a plane at 30° from vertical, and passing by the heel of the foundation and the back face of the retaining wall. 24. Retaining Wall Seismic Design Pressures: For seismic design of unrestrained walls over 6 feet in exposed height, we recommend that the seismic pressure increment be taken as a fluid pressure distribution utilizing an equivalent fluid weight of 16 pcf. This seismic increment is waived for restrained basement walls. If the walls are designed as unrestrained walls, then the seismic load should be added to the static soil pressure. 25. Basement/Retaining Wall Drainage: The preceding design pressures assume that the walls are backfilled with properly compacted low expansion potential materials (Expansion Index less than SO) and that there is sufficient drainage behind the walls to prevent the build-up of hydrostatic pressures from surface water infiltration. We recommend that drainage be provided by a composite D ... .. ... .. .. .. .. .. .. .. .. ... .. ... -... -... ... ... ... .. ... ... ... .. .. ... .. ... .. .. • .. - • -- --------- - - - - •· Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 47 drainage material such as J-Drain 200/220 and J-Drain SWD, or equivalent . No perforated pipes or gravel are utilized with the J-Drain system. The drain material should terminate 12 inches below the exterior finish surface where the surface is covered by slabs or 18 inches below the finish surface in landscape areas (see Figure No. VI for Schematic Retaining Wall Subdrain Recommendations). Waterproofing should extend from the bottom to the top of the wall. Backfill placed behind retaining walls should be compacted to a minimum degree of compaction of 90 percent using light compaction equipment. If heavy equipment is used, the walls should be appropriately temporarily braced. Crushed rock gravel may only be used as backfill in areas where access is too narrow to place compacted soils. Behind shoring walls sand slurry backfill may be used behind lagging. Geotechnical Exploration, Inc. will assume no liability for damage to structures or improvements that is attributable to poor drainage. The architectural plans should clearly indicate that subdrains for any lower-level walls be placed at an elevation at least 1 foot below the bottom of the lower- level slabs. F. Slopes 26. Temporary Slopes: Based on our subsurface investigation work, laboratory test results, and engineering analysis, temporary cut slopes up to 12 feet in height in the formational materials should be stable from mass instability at an inclination 0.75 :1.0 (horizontal to vertical). Temporary cut slopes up to 12 feet in height in loose fill soils should be stable against mass instability at ~ Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 48 an inclination of 1.5:1.0. In properly compacted fill soils, temporary slopes should be stable at a slope ratio of 1.0 to 1.0. Some localized sloughing or raveling of the soils exposed on the slopes may occur. Since the stability of temporary construction slopes will depend largely on the contractor's activities and safety precautions (storage and equipment loadings near the tops of cut slopes, surface drainage provisions, etc.), it should be the contractor's responsibility to establish and maintain all temporary construction slopes at a safe inclination appropriate to the methods of operation. No soil stockpiles or surcharge may be placed within a horizontal distance of 10 feet or the depth of the excavation, whichever is larger, from the excavation top. If these recommendations are not feasible due to space constraints, temporary shoring may be required for safety and to protect adjacent property improvements. Similarly, footings near temporary cuts should be underpinned or protected with shoring. 27. Slope Observations: A representative of Geotechnical Exploration, Inc. must observe any steep temporary slopes during construction. In the event that soils and formational material comprising a slope are not as anticipated, any required slope design changes would be presented at that time. IJ ... .. .. .. .. .. .. .. -.. .. .. - --- .. .. -.. -.. .. .. -- Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page SO H. Standard Specifications for Public Works Construction, 2018 Edition; or 6 inches of No.57 crushed rock gravel per ASTM D448 gradation. The upper 6 inches of the pavement subgrade soil as well as the aggregate base layer should be compacted to a minimum degree of compaction of 95 percent. Preparation of the subgrade and placement of the base materials should be performed under the observation of our representative. Site Drainage Considerations 31. Erosion Control: Appropriate erosion control measures should be taken at all times during and after construction to prevent surface runoff waters from entering footing excavations or ponding on finished building pad areas. 32. Surface Drainage: Adequate measures should be taken to properly finish- grade the lot after the structures and other improvements are in place. Drainage waters from this site and adjacent properties should be directed away from the footings, floor slabs, and slopes, onto the natural drainage direction for this area or into properly designed and approved drainage facilities provided by the project civil engineer. Roof gutters and downspouts should be installed on the residence, with the runoff directed away from the foundations via dosed drainage lines. Proper subsurface and surface drainage will help minimize the potential for waters to seek the level of the bearing soils under the footings and floor slabs. Failure to observe this recommendation could result in undermining and possible differential settlement of the structure or other improvements on the site or cause other moisture-related problems. Currently, the CBC requires a minimum 1-percent surface gradient for proper drainage of building pads ill .. .. .. .. .. .. .. -.. .. - - --- --.. .. .. -.. .. .. -.. .. .. -- - ------- - -.. -.. -.. - ------- - - Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 51 unless waived by the building official. Concrete pavement may have a minimum gradient of 0.5-percent. 33. Planter Drainage: Planter areas, flower beds and planter boxes should be sloped to drain away from the footings and floor slabs at a gradient of at least 5 percent within 5 feet from the perimeter walls. Any planter areas adjacent to the residence or surrounded by concrete improvements should be provided with sufficient area drains to help with rapid runoff disposal. No water should be allowed to pond adjacent to the residence or other improvements or anywhere on the site. 34. Drainage Quality Control: It must be understood that it is not within the scope of our services to provide quality control oversight for surface or subsurface drainage construction or retaining wall sealing and base of wall drain construction. It is the responsibility of the contractor to verify proper wall sealing, geofabric installation, protection board (if needed), drain depth below interior floor or yard surface, pipe percent slope to the outlet, etc. I. General Recommendations 35. Pro,iect Start Up Notification: In order to reduce work delays during site development, this firm should be contacted 48 hours prior to any need for observation of footing excavations or field density testing of compacted fill soils. If possible, placement of formwork and steel reinforcement in footing excavations should not occur prior to observing the excavations; in the event that our observations reveal the need for deepening or re-designing foundation structures at any locations, any formwork or steel reinforcement in the affected footing excavation areas would have to be removed prior to correction of the ill Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 52 observed problem (i.e., deepening the footing excavation, recompacting soil in the bottom of the excavation, etc.). 36. Cal-OSHA: Where not superseded by specific recommendations presented in this report, trenches, excavations, and temporary slopes at the subject site should be constructed in accordance with Title 8, Construction Safety Orders, issued by Cal-OSHA. 37. Construction Best Management Practices (BMPs): Construction BMPs must be implemented in accordance with the requirements of the controlling jurisdiction. Sufficient BMPs must be installed to prevent silt, mud or other construction debris from being tracked into the adjacent street(s) or storm water conveyance systems due to construction vehicles or any other construction activity. The contractor is responsible for cleaning any such debris that may be in the street at the end of each work day or after a storm event that causes breach in the installed construction BMPs. All stockpiles of uncompacted soil and/or building materials that are intended to be left unprotected for a period greater than 7 days are to be provided with erosion and sediment controls. Such soil must be protected each day when the probability of rain is 40% or greater. A concrete washout should be provided on all projects that propose the construction of any concrete improvements that are to be poured in place. All erosion/sediment control devices should be maintained in working order at all times. All slopes that are created or disturbed by construction activity must be protected against erosion and sediment transport at all times. The storage of all construction materials and equipment must be protected against any potential release of pollutants into the environment. 81 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Garfield Street Condominium Project Carlsbad, California Job No. 20-12942 Page 54 As stated previously, it is not within the scope of our services to provide quality control oversight for surface or subsurface drainage construction or retaining wall sealing and base of wall drain construction. It is the responsibility of the contractor to verify proper wall sealing, geofabric installation, protection board installation (if needed), drain depth below interior floor or yard surfaces; pipe percent slope to the outlet, etc. This report should be considered valid for a period of two (2) years, and is subject to review by our firm following that time. If significant modifications are made to the building plans, especially with respect to the height and location of any proposed structures, this report must be presented to us for immediate review and possible revision. It is the responsibility of the owner and/or developer to ensure that the recommendations summarized in this report are carried out in the field operations and that our recommendations for design of this project are incorporated in the project plans. We should be retained to review the project plans once they are available, to verify that our recommendations are adequately incorporated in the plans. Additional or modified recommendations may be issued if warranted after plan review. This firm does not practice or consult in the field of safety engineering. We do not direct the contractor's operations, and we cannot be responsible for the safety of personnel other than our own on the site; the safety of others is the responsibility of the contractor. The contractor should notify the owner if any of the recommended actions presented herein are considered to be unsafe. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. - - --- --- - •· - - •· -------- - REFERENCES JOB NO. 20-12942 November 2020 2007 Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2), U.S Geological Survey Open-file Report 2007-1437 and California Geological Survey Special Report 203. Association of Engineering Geologists, 1973, Geology and Earthquake Hazards, Planners Guide to the Seismic Safety Element, Association of Engineering Geologists, Southern California Section. Berger, V, and Schug, D.L., 1991, Probabilistic Evaluation of Seismic Hazard in the San Diego-Tijuana Metropolitan Region, Environmental Perils, San Diego Region, Geological Society of America by the San Diego Association of Geologists, October 20, 1991, p. 89~99. Crowell, J.C., 1962, Displacement Along the San Andreas, Fault, California, Geological Society of America, Special Papers, no. 71. Demere, T,A. 1997, Geology of San Diego County, California, San Diego Natural History Museum, http://archive.sdnhm.org/research/paleontology/sdgeol.html, accessed July 30, 2020. Grant Ludwig, L.B. and Shearer, P.M., 2004, Activity of the Offshore Newport-Inglewood Rose canyon Fault Zone, Coastal Southern California, from Relocated Microseismicity. Bulletin of the Seismological Society of America, 94(2), 747-752. Greene, H.G., Bailey, K.A., Clarke, S.H., Ziony, J.I. and Kennedy, M.P., 1979, Implications of fault patterns of the inner califomia continental borderland between San Pedro and San Diego, in Abbott, P.L., and Elliot, W.J., eds., Earthquakes and other perils, San Diego region: San Diego Association of Geologists, Geological Society of America field trip, November, 1979, p, 21-28. Greensfelder, R.W., 1974, Maximum Credible Rock Accelerations from Earthquakes in california, california Division of Mines and Geology. Hart E.W. and Bryant, W.A., 1997, Fault-Rupture Hazard Zones in California, California Division of Mines and Geology, Special Publication 42. Hart, E.W., Smith, D.P. and Saul, R.B., 1979, Summary Report: Fault Evaluation Program, 1978 Area (Peninsular Ranges-Salton Trough Region), California Division of Mines and Geology, Open-file Report 79-10 SF, 10. Hauksson, E. and Jones, L.M., 1988, The July 1986 Oceanside (ML=S.3) Earthquake Sequence in the Continental Borderland, Southern California Bulletin of the Seismological Society of America, v. 78, p. 1885-1906. Hileman, J.A., Allen, C.R. and Nordquist, J.M., 1973, Seismicity of the Southern California Region, January 1, 1932 to December 31, 1972; Seismological Laboratory, cal-Tech, Pasadena, California. Kennedy, M.P, and Tan, S.S., 2007, Geologic Map of the Oceanside 30'x60' Quadrangle, California, California Geological Survey, Department of Conservation. Richter, C.F., 1958, Elementary Seismology, W.H. Freeman and Company, San Francisco, California. REFERENCES/Page 2 Rockwell, T.K., 2010, The Rose Canyon Fault Zone in San Diego, Proceedings of the Fifth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. Paper No. 7.06C. Rockwell, T.K., Dawson, T.E., Young Ben-Horin, J. and Seitz, G., 2014, A 21-Event, 4,000-Year History of Surface Ruptures in the Anza Seismic Gap, San Jacinto Fault, and Implications for Long-term Earthquake Production on a Major Plate Boundary Fault. Pure and Applied Geophysics, v. 172, 1143- 1165 (2015). Rockwell, T.K., Millman, D.E., McElwain, R.S. and Lamar, O.L., 1985, Study of Seismic Activity by Trenching Along the Glen Ivy North Fault, Elsinore Fault Zone, Southern California: Lamar-Merifield Technical Report 85-1, U.S.G.S. Contract 14-08-0001-21376, 19 p. Ross, Z.E., Hauksson E. and Ben-Zion Y., 2017, Abundant Off-fault Seismlcity and Orthogonal Structures in the San Jacinto Fault Zone, Science Advances, 2017; 3(3): e1601946. Published 2017 Mar 15. Toppozada, T.R. and Parke, D.L., 1982, Areas Damaged by California Earthquakes, 1900-1949, California Division of Mines and Geology, Open-file Report. 82-17. U.S. Dept. of Agriculture, 1953, Aerial Photographs AXN-14M-19 and 20. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. - .. .. .. .. .. •· LABORATORY REPORT Telephone (619) 425-1993 Fax 425-7917 Established 1928 CLARKSON LABORATORY AND SUPPLY INC. 350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarksonlab.com A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S Date: December 9, 2020 ,,,,,, , ''" , Purchase Order Nwnber : :GAR!'!ELD- Sales Order Number: 50003 Account Nwnber: GEOE.RS To: *-------------------------------------------------* Geotechnical Exploration Inc. 7420 Trade Street San Diego, Ca 92121 Attention: Hector Estrella Laboratory Number: S08034-1 Sample Designation: Customers Phone: 858-549-7222 Fax: 858-549-1604 ~ *-------------------------------------------------* One soil, .. •lll\lJllEt. ,;ec.e.i)'!l'''-Qnllf~0/20 at 12: 30pm, -from Garfiel<!:' marli:ed<U <HP~21!-2•4. •· - - - - • Analysis By California Test 643, 1999, Department of Transportation Division of Construction, Method for Estimating the Service Life of Steel Culverts. pH 7.2 Water Added (ml) 10 5 5 5 5 5 5 41 years to perforation for a 53 years to perforation for a 73 years to perforation for a 94 years to perforation for a 114 years to perforation for a Resistivity (ohm-cm) 16 gauge metal culvert. 14 gauge metal culvert. 12 gauge metal culvert. 10 gauge metal culvert. 12000 9500 7700 7000 5800 6000 6200 8 gauge metal culvert. Water Soluble Sui.fate, Calif. Test 417 Water Soluble oli~i:Sa& Calif. Test 422 <0. 003% 0.003% ~ RMB/dbb Figure !Vb LABORATORY REPORT Telephone (619) 425-1993 Fax 425-7917 Established 1928 C L A R K S O N L A B O R A T O R Y A N D S U P P L Y I N C. 350 Trousdale Dr. Chula Vista, ca. 91910 www.clarksonlab.com A N A L Y T I C A L A N D C O N S U L T I N G C H E M I S T S Date; December 9, 2020 ,,., ,,,,,.,, ,, Purchase Order Nwnber : 'QDl!:t&LD Sales Order Number: 50003 Account Number: GEOE.RS To: *-------------------------------------------------* Geotechnical Exploration Inc. 7420 Trade Street San Diego, Ca 92121 Attention: Hector Estrella Laboratory Number: S08034-2 Customers Phone: 858-549-7222 Fax: 858-549-1604 Sample Designation: *-------------------------------------------------* ~:~m•~~l~[~~Ji-~WC:.:i~fu~~/20 at 12: 30pm, Analysis By California Test 643, 1999, Department of Transportation Division of Construction, Method for Estimating the Service Life of Steel Culverts. pH 6.9 Water Added (ml) 10 5 5 5 5 5 5 36 years to perforation for a 47 years to perforation for a 65 years to perforation for a 83 years to perforation for a 101 years to perforation for a 16 gauge 14 gauge 12 gauge 10 gauge 8 gauge Water Soluble '.guf.ffe.', Calif. Test 417 Water Soluble Cfil~~~: Calif. Test 422 ~ RMB/dbb metal metal metal metal metal Resistivity (ohm-cm) 27000 17000 13000 culvert. culvert. culvert. culvert. culvert. 9800 8800 9100 9600 <0.003% 0.001% Figure !Ve .. .. .. .. .. .. .. .. .. .. .. .. .. ----- .. -.. .. .. - APPENDIX A UNIFIED SOIL CLASSIFICATION CHART SOIL DESCRIPTION Coarse-grained (More than half of material Is larger than a No. 200 sieve) GRAVELS, CLEAN GRAVELS (More than half of coarse fraction is larger than No. 4 sieve size, but smaller than 3") GRAVELS WITH FINES (Appreclable amount) SANDS, CLEAN SANDS {More than half of coarse fraction Is smaller than a No. 4 sieve) SANDS WITH FINES (Appreciable amount) GW GP GC SW SP SM SC Welt-graded gravels, gravel and sand mixtures, little or no fines. Poorly graded gravels, gravel and sand mixtures, little or no fines. Clay gravels, poorly graded gravel-sand-silt mixtures Well-graded sand, gravelly sands, little or no fines Poorly graded sands, gravelly sands, little or no fines. Silty sands, poorly graded sand and silty mixtures. Clayey sands, poorly graded sand and clay mixtures. Flne•gralned (More than half of material Is smaller than a No. 200 sieve) SILTS AND CLAYS Liouid Limit Less than .5Q ML Inorganic silts and very fine sands, rock flour, sandy silt and clayey-silt sand mixtures with a slight plasticity CL Inorganic clays of low to medium plasticity, gravelly clays, silty clays, clean clays. CL Organic silts and organic silty clays of low plasticity. Liquid Limit Greater than 50 MH Inorganic silts, mlcaceous or dlatomaceous fine sandy or sllty soils, elastlc silts. CH Inorganic clays of high plasticity, fat clays. OH Organic clays of medium to high plasticity. HIGHLY ORGANIC SOILS PT Peat and other highly organic soils --- ------ ' • • • • • • •