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TTM 28409 - Geotechnical Investigation
1 1 1 1 1 i JUTNL4ND D1NKAL FUUNDATIoN ENGINEERS AND MATERIALS LAnS le_ GEOTECHNICAL INVE TIGATICIN TENTATIVE TRACT NO 28409 • LA QIJINTA, CALIFOR-NIA� j'.'EI id FEB 4 3 1997 n CITY OF LAQIJINTA PLANNING DEPARTMENT 242 NORTH 8TH STREET EL CENTRO, CALIFORNIA 92243 • {619) 352-1242 79-607 COUNTRY CLUB DRIVE, SUITE 5 • BERMUDA DUNES, CALIFORNIA 92201 • (819) 360-0665 2211 EAST RALO VEIRDE STREET -YUMA, ARIZONA85385 • (52C) 344-8844 S484 CHESAPEAKE DRIVE, SUITE 301 • SAN CIEGO, CALIFORNIA 92123 • (B19} 487-4900 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 GEOTECHNICAL INVESTIGATION TENTATIVE TRACT NO 28409 LA QUINTA, CALIFORNIA * Prepared for: AN Construction P.D. Box 366 La Quints, California 92253 * Prepared by: Southland Geotechnical, Inc. 79-607 Country Club Drive, Suite 5 Bermuda Dunes, California 92201 Report No. P97002 January, 1997 1 4JT-II.AND = FOUNDATION ENGINEERS AND MATERIALS LABS January 30, 1997 A/M Construction P.D. Box 366 La ❑Uinta, California 92253 Attn: Mr. Rick Morris Geotechnical investigation Tentative Tract 28409 La Quinta, California Report No. P97002 Dear Rick: We are pleased to present this geotechnical report for the proposed 19-lot subdivision in La Quinta, California. Our geotechnical investigation was conducted in response to your request for our services, The enclosed report describes the investigation conducted and presents our recommendations for geotechnical aspects of design and construction of the project. The findings of this study indicate that the subsurface soils at the site consists of alluvial gravelly sands and should be reworked to provde suitable building pads, This is especially important in an old alluvial wash beneath Lots 3,4,18 and 19. The site is suitable for the proposed development, provided the recommendations contained in this report are implemented in the design and construction of this project. ' We appreciate the opportunity to provide our professional services. If you have any questions or comments regarding our findings, please call our office at 360-0665. 1 ' h ! Shelton L. Stringer, PE, GE ' Senior Geotechnical Engineer Copies submitted: (5) 1 Respectfully Submitted, SOUTHLAND GEOTECHNICAL INC. 242 NORTH 8TH STREET • EL CENTRO, CALIFORNIA 92243 - (619) 352-1242 79-607 COUNTRY CLUB DRIVE, SUITE 5 • BERMUDA DUNES, CALIFORNIA 92201 • (619) 369-0665 2211 EAST PALO VERDE STREET - YUMA, ARIZONA85365 • (520) 344-5844 9484 CHESAPEAKE DRIVE, SUITE 801 • SAN DIEGO, CALIFORNIA92123 • (819) 467.4900 1 TiBLE OF CONTENTS • Section 1 INTRODUCTION Page1 1.1 Project Description 1 1 ,2 Purpose and Scope of Work 1 1.3 Authorization 2 Section 2 METHODS OF INVESTIGATION 3 2.1 Field Exploration 3 2.2 Laboratory Testing 4 2.3 Review of Historical Aerophotographs 4 Section 3 DISCUSSION .. 6 3.1 Site Conditions 3.2 Geologic Setting 5 3.3 Seismicity and Faulting 6 3.4 Site Acceleration and UBC Seismic Coefficients 12 3.5 Subsurface Soils .. 16 Section 4 RECOMMENDATIONS 17 4.1 Site Preparation I� 17 E 4.2 Foundations 20 4,3 Slabs on Grade ... 21 4,4 Concrete Mixes and Soil Corrosivity 22 4.5 Excavations 23 4.6 Lateral Earth Pressures 23 4.7 Seismic Design Criteria 24 4,8 Pavements 25 Section 5 LIMITATIONS AND ADDITIONAL SERVICES 26 5.1 Limitations 26 5.2 Additional Services 27 REFERENCES E?HiBITS Plate Vicinity Map 1 Site and Exploration Plan .. 2 Subsurface Logs . 3-7 Key to Logs , .. .. 8 Laboratory Test Results 9_12 1 AIM Construction Report P97002 Section 1 INTRODUCTION 1.1 Project Description This report presents the findings of our geotechnical investigation for the proposed 19- lot subdivision (Tentative Tract Map Nc. 28409) in La Quints, California, The project site is located between Avenida Montezuma and the Bear Creek Channel in the La Quints Cove. (See Vicinity Map, Plate 1). The proposed development will consist of 19 single family residence on a 7 acre site with interior streets, retention basin, and infrastructure improvements. The residential structures are anticipated to consist of single -story, wood -frame and stucco construction. Expected footing loads at exterior bearing walls are 1 to 2 kips per lineal foot. Expected column Toads range from 10 to 25 kips. Site development will include site grading, building pad preparation, underground utility installation, street construction, and concrete driveway and sidewalk placement. 1.2 Purpose and Scope of Work The purpose of this geotechnical study was to investigate the upper 10 feet of subsurface soils at the site for physical/engineering properties and to provide professional opinions regarding geotechnical design parameters at this site for the proposed construction, The scope of our services included the following: I. field exploration and in -situ testing of the site soils at selected locations ► laboratory testing for physical characteristics and strength parameters on selected samples ► review of published geologic and seismologic literature in the project vicinity and historical aerophotegraphs p analysis and evaluation of the data collected ► preparation of this report presenting our comments, opinions, and recommendations for the geotechnical aspects of the project. Southland Geotechnicai page 1 AIM Construction Report P97002 This reports addresses the following geotechnical issues: ▪ Subsurface soil and groundwater conditions I. Site geology, regional faulting and seismicity, and site acceleration p• Hydroconsolidation and its mitigation Recommendations considering the above issues are presented for the following: • Site grading and earthwork ip Building Pad and foundation subgrade preparation ► Allowable soil bearing pressures and expected settlements • Concrete slabs -on -grade ▪ Excavation conditions and buried utility installations ■ Mitigation of the potential effects of salt concentrations in native soils to concrete mixes and steel reinforcement w Seismic design parameters ► Pavement structural sections Evaluation of the site for the presence of potential environmental hazards was not included in the scope of our work. 1.3 Authorization Authorization to proceed with our work was provided by written agreement with C. Brain Murphy of CBM Construction on January 8, 1997 in accordance with our written proposal dated December 30, 1996. Southland Geatechnical Page 2 ATM Construction Report P97002 Section 2 METHODS OF INVESTIGATION 2.1 Field Exploration We conducted a subsurface exploration on January 15, 1997 by using a backhoe service to excavate five test pits to an approximate depth of 10 to 1 1 feet below the existing ground surface. The test pits locations are shown on the Site and Exploration Plan on Plate 2. Bulk samples and tube samples driven into undisturbed soil were obtained at selected depths in the test pits. A nuclear densometer (ASTNI D2922) was used to evaluate in -situ densities and natural moisture content at selected depths in the upper five feet of the backhoe pits, The test pits were located by paced measurements and should be considered approximate. A staff geologist maintained logs of the test pits during exploration. The logs were edited in final form after a review of retrieved samples and the field and laboratory data. The test pit logs are presented on Plates 3 through 7 in the Exhibits section of this report. Soils encountered have been classified according to the Unified Soil Classification System. A key to the Togs is presented on Plate 8. The stratification lines shown on the subsurface Togs represent the approximate boundaries between the various strata. However, the transition from one stratum to another may be gradational. Southland Geotechnical Page 3 A/M Construction Report P97002 2.2 Laboratory Testing Laboratory tests were conducted on selected soil samples to aid in classification and evaluating pertinent engineering properties. The tests were conducted in general accordance with the procedures of the American Society for Testing and Materials (ASTM) or other standardized methods as referenced below. Our laboratory testing program consisted of the following tests: ► Particle Size Analyses (ASTiVS D422) ► Moisture Density Relationship (ASTM D1557) IP Collapse Potential (AST(ASTNI D5333) 1. Selected Chemical Analyses {pH, Electrical Conductivity, Soluble Sulfates and Chlorides} The laboratory test results are presented on the subsurface Togs and on Plates 8 through 12 in the Exhibits section of the report. 2.3 Review of Historical Aerophotographs As part of our investigation, we reviewed available historical aerophotographs on file at the Coachella Valley Water District (CVWD) offices. Photographs of the project site reviewed by us included the years 1939, 1955, 1972, 1982, 1985 and 1987. The primary purpose of this review as to delineate the likely alignment of a drainage wash that no longer exists. Within this wash, we encountered a loose sandy silt deposit that presents a moderately severe site risk for hydroconsolidation, Southland Geotechnical Page 4 AN Construction Report P97002 Section 3 DISCUSSION 3.1 Site Conditions The seven acre irregular -shaped project site is currently open desert and has sparse desert vegetation covering the site. The topography is generally gently sloping southeasterly. Elevation ranges from EL 62 to 78 above mean sea level. The site is highest along the northwest boundary. The site is bounded by the Bear Creek Flood Control Channel to the northwest. This channel is about 10 to 20 feet deep with a soil -cement lining along the slope face and bottom. The site is bounded by Avenida Montezuma to the south and bounded by residences on the east. The Bear Creek Channel was constructed in 1986. Prior to its construction, a drainage wash traversed across the project site. The drainage wash also existed parallel to the north side of Avenida Montezuma. According to historical aerophotographs tamarisk trees/shrubs existed along the wash until removed in 1986. Minor filling (1 to 2 feet) may have occurred during grading for the Bear Creek Channel. The project site lies in the La Quinta Cove area of the Coachella Valley region of the California low desert. Annual rainfall in this arid region is less than 4 inches per year with four months of summertime temperature ranging from 100 to 120'F. Winter temperatures are rnild, seldom reaching freezing. 3.2 Geologic Setting The project site is at the northern portion of the Salton Trough physiographic province. The Salton Trough is a geologic structural depression resulting from large scale regional faulting. The trough is bounded on the northeast by the San Andreas Fault and the southwest by faults of the San Jacinto Fault Zone. The Salton Trough represents the northward extension of the Gulf of California and has experienced continual in -filling with both marine and non -marine sediments since the Miocene Epoch. Southland Geotechnical Page 5 AIM Construction Report P97002 Figure 1 shows the location of the site in relation to regional faults and physiographic features. The surrounding regional geology includes the Peninsular Ranges (Santa Rosa and San Jacinto Mountains) to the south and west, the Salton Basin to the southeast, and the Transverse Ranges (Little San Bernardino and Orocopia Mountains) to the north and east. In general, the Coachella Valley is underlain by hundreds of feet to several thousand feet of Quaternary fluvial, Iacustrine, and aeolian soil deposits. The eastern part of the Coachella Valley lies below sea level and has been submerged in the geologic past by the ancient Lake Cahuilla. Calcareous tufa deposits may be observed along the ancient shoreline as high as El 45 to 50 MSL along the Santa Rosa Mountains from La Quinta southward. Lacustrine (lake) deposits comprise the subsurface soils over much of the eastern Coachella Valley with alluvial outwesh along the flanks of the valley. 3.3 Seismicity and Faulting Historical Seismicity: Five significant historical events (5,9 M or greater) have affected the Coachella Valley this century. They are as follows: ► Desert 1-lot 5pr/ngs Event - On December 4, 1946 a magnitude 6.a NIL i6,0Mwi earthquake occurred east of Desert Hot Springs. (Proctor 1968). ► Palm Springs Event - A magnitude 5.9 ML (6.2Mv,) earthquake occurred on July 8, 1986 in the Painted Hills causing minor surface creep of the Banning segment of the San Andreas Fault. {USES 1987). ▪ Desert Hot Springs Event - On April 22, 1992 a magnitude 6.1 ML (6.1 M,) earthquake occurred in the mountains 9 miles east of Desert Hot Springs. (OSMS 1992). • Landers Event - Early or June 28, 1992, the Coachella Valley was subjected to the largest seismic event to strike Southern California in 40 years. The Landers earthquake had a main shock 7.5Ms (7.3 Mvv) magnitude. Surface rupture occurred just south of the town of Yucca Valley and extended some 43 miles towards Barstow along portions of Camp Rock -Emerson, Johnson Valley, and Homestead Valley Fault systems. Surface horizontal offsets attained a maximum of 21 feet. (OSMS 1992). ▪ Big Bear Event - Some three hours later, on June 28, 1992, a magnitude 6.6 Ms (6,4M,,) earthquake occurred 1 U nii southeast of Big Bear Lake. The earthquake occurred on a previously unknown fault trending northeast from the San Andreas fault in the San Bernardino Mountains. (OSMS 1992). Southland Geotechnical Page 6 AIM Construction 1. Reference: Geologic Map of California, Salton Sea Shot (Jennings, 1967) Stale: 1 isi,— 5mI Figure 1. Regional Geologic Map Report P97002 ra•t Project Site Southland Geotechnical Page 7 AN Construction Report Pe7002 Faulting and Seismic Sources Our research of regional faulting indicates that 16 known faults or seismic zones lie within 36 miles of the project site as shown on Table 1. The Maximum Magnitude Earthquake (Mmax) listed was taken from published geologic information available for each fault (CDMG, 1996). The Mmax corresponds to the maximum earthquake believed to he tectonically possible. For most faults considered, the Mmax also corresponds to the Design Basis Earthquake (DBE) having an estimated probability of occurrence of at least 10% in 50 years (equivalent to an average return period of about 475 years). This is the probability of occurrence to develop the Uniform Building Code (UBC) seismic coefficients (ICBO, 1994, 1997). Seismic Risk: While accurate earthquake predictions are not possible, significant geologic information and statistical analysis have been compiled, analyzed, and published intensely by various agencies over the past 25 years. In 1996, the California Division of Mines and Geology (CDMG) and the United States Geological Survey (USGS) have jointly completed the latest generation of probabilistic seismic hazard maps for incorporation into the 1997 UBC. We have used this maps as part of our evaluation of the seismic risk at the site. In 1995, the Working Group of California Earthquake Probabilities (WGCEF) released its Phase II report (WGCEP, 1995). In that report they assigned a 22% conditional probability of occurrence for the 30-year period from 1994 to 2024 that a magnitude 7.4 event or greater would occur along the Coachella Valley segment of the San Andreas Fault. Conditional probabilities are estimates of the chance of occurrence that a future earthquake wilt occur based on the time since the last rupture.. In other words, the conditional probability suggests how "ripe" or overdue the fault is for the next major earthquake. Type A faults listed are those faults for which there is sufficient geologic information to conjecture both a characteristic earthquake that ruptures the fault and conditional probabilities. (WGCEP, 1995). Type B faults may have characteristic earthquakes, yet information an these faults are too limited to speculate such an event. The CDMG and the new 1997 UBC uses different criteria to classify the type of fault. Southland Geotechnical Page 8 AIM Construction Report P97002 The prirnary seismic risk to the project site is the San Andreas Fault. The' San Andreas Fault zone is considered to have characteristic earthquakes that ruptures each fault segment. The characteristic earthquake is estimated to be magnitude 7.4 for the Coachella Valley Segment that comprises the southern 115 km of the fault zone. This segment has the longest elapsed time of any portion of the San Andreas Fault, last experiencing an event about 1690 AD based on USGS dating of trench surveys near Indio (WGCEP 1995). The segment has also ruptured on about 1020, 1300, and 1450 AD, with an average recurrence interval of about 220 years. The San Andreas Fault may rupture in multiple segments producing a higher magnitude earthquake. Recent paleoseismic studies along the San Bernardino Mountain Segment to the north indicates that both it and the Coachella Valley segment may have both ruptured together in 1450 and 1690 AD (1NCCEP, 1995). The long term slip rate is estimated to average about 25 mm/year, some surface creep has been occurring. Seismic Ha?arse s.: ► Groundshaking. The primary seismic hazard at the project site is strong groundshaking from earthquakes along the San Andreas and San Jacinto Faults as discussed further in Section 3.4. ► Surface Rupture. The project site does not Iie within a State of California, Afquist- Pr/ofo Earthquake Fault Zone. Fault rupture is not anticipated to occur at the project site because of the well -delineated fault lines through this region as shown on United States Geological Survey (USGS) and California Division of Mines and Geology (CDMG) maps. However, because the site is located in an area of high tectonic activity, we cannot preclude the potential for surface rupture on undiscovered or new faults that may underlie the site. ► Liquefaction. Liquefaction is not considered a potential hazard at the site since the groundwater is believed to be deeper than 60 feet (the maximum depth that liquefaction is known to occur). ► Other Secondary Hazards. In that the site is nearly level, the hazard of landsliding is non-existent. Potential rockfalls from the Santa Rosa Mountains would be stopped by the Bear Creek Channel. The site is far inland and does not Iie near any large bodies of water. So the threat of tsunami, sieches, or other seismically induced flooding is non-existent. Southland Geotechnical Page 9 A'M Construction Report P97002 31s0 34,25 62 *(62) 33-5 M.00 4-7.90-116.75-116.50 excright1867by6hetanLStringer,GE MAP OF REGIONAL FAULTS AND SEISMICITY i,„ 73 ti Ng) Mk BC - RIVERSIDE CO. Rahn Desert A`� 1r 4c Project Siteuinra -116.25 Desesrt -11600 Legends to Feints: Lu BC: Blue Cut BM : Borrego Mountain BSA: Brawley Seismic Zane CC : Coyote Creek ON: Calico -Newberry EL: Elmore Ranch ELS: ElsIncre EM-G: Emerson -Copper Mtrn. EP: Eureka Peak H: Helendale IHB Hot Springs -puck Ridge JV Johnson Malley IAA;: Imperial h1; Morongo ML: Mesquite Lake NE ; North Frarital Zone DINS; Old Werner Springs P-B: Ping -Bullion PM Pinto Mtn SA San Areas SG$ : Seri Gnrgonici-B nning SH: Sup ambition Hills SJ: San Jacinto 55 4( -115.75 Was Faults and Seismic Zones from Jennings (1994). Earthquakes modified from Ellawarth (1990) catalog. Figure 1. Map of Regional Faults and Seismicity -115.50 Southland Geatechnical Page 10 AIM Construction Report P97002 i i i Table 1 FAULT PARAMETERS & ESTJMATES OF DETERMINISTIC PEAK GROUND ACCELERATION (PGA) Distance Maximum Avg Avg Largest Fault Name or fault (mil. & Magnitude Slip Return Historical Site Seismic Zone 11,3) Type Direction Mmax Rate 12} Period Events PGA 12} (3) from Site IM, 1 {4} irnmtyr) tyrs113) (> 5.5M) {5) Wei Type A Faults: San Andreas Fault Segments: Coachella Valley (Southern) A A 9 NE 7.4 25 220 6.5ML (1948) 0.29 San Gorgonio -Banning A A 9 NE 7.4 25 220 5.9ML (1986) 0.35 San Bernardino Mountain A A 25 NNW 7.3 24 433 -- 0.13 Whole S. Calif. Rupture 12I A - 9 E 7.9 556(21 7.8Mw (1857) 0.37 San Jacinto Fault Segments,. San Jacinto Valley. A A 34 W 6.9 12 83 6.4M5 (1899) 0.09 Anza (Casa Lorna -Clark) A A 17 SSW 7.2 12 250 6.8Mw (1918) 0.17 Coyote Creek A A 19 SW 6.8 4 175 6.411v1w (1954) 0.13 Borrego Mountain A A 34 SSE 6,6 4 175 6.5Mw (1968) 0.07 Buck Ridge -Hot Spgs. - C 14 SSW 6,5 2 -•• 6.OML (1937) 0.14 Whole Zone Rupture {2i A - 17 SW 7.5 93512} 0,20 Tone B Faults,: Traverse Ranges & Mojave Eureka Peak C B 20 N 6.4 0.6 5000 6,1 1L (1992) 0.10 Burnt Mountain C B 19 N 6,4 0.6 5000 7.3M, (1992) 0,10 Pinto Mountain R B 31 NNW 7.0 2.5 499 -- 0.10 Landers Segments (7) C B 34 N 7.3 0.6 5000 7.3M , (1992) 0.10 Pisgah -Bullion -Mesquite Lk. C B 36 NE 7.1 0,6 5000 -- 0.09 S Emerson -Copper Mtn C B 35 NNE 6.9 0.6 5000 -- 0.03 Morongo C C 29 NNW 6.5 0,5 -- 5.5ML (1947) 0.08 Blue Cut C C 17 NNE 6.6 1.8 -- -- 0.14 Notes: 1. Jennings (1994) 2. WGCEP (1995), where; A - Type A (Characteristic), B - Type B, C- Type C 3. CDMG 11996), where Type A faults, Mmax > 7 and slip rate >5 rnmlyr, Type C faults, Mrnax <6.E and slip rate < 2 mmfyr. 4. CDMG 11996) based on Wells & Coppersmith (1994) 5. Ellsworth Catalog in USGS PP 1515 (1990), M, = moment magnitude, Mr = local (Richter) magnitude 6. The estimates of the PGA are based on site attenuation relationships of Bowe, Joyner & Fumal (1994) - mean value, larger of the two components using moment magnitudes as given for Site Class B. Mean + 1a values are 1.59 times higher, 7. Includes S. Johnson Valley, Camp Rook, and N. Emerson Faults Southland Geotechnical Page 11 AIM Construction Report P97002 3.4 Site Acceleration and UBC Seismic Coefficients Site Acceleration: To assess the potential intensity of ground motion, we have estimated the horizontal peak ground acceleration {PGA). Deterministic estimates of site acceleration are presented on Table 1. Ground motions are dependent primarily on the earthquake magnitude and distance to the seismogenic (rupture) zone. Accelerations also are dependent upon attenuation by rock and soil deposits, direction of rupture, type of fault, and other factors. For these reasons, ground motions may vary considerably in the same general area. The variability can be statistically quantified by a standard deviation about the mean. The mean plus one standard deviation (mean + 1 G) acceleration corresponds to an 84% confidence level of not being exceeded. The standard of practice is to use either mean and mean+10 site attenuation relationships when estimating ground acceleration. The PGA is en inconsistent scaling factor to compare to the UBC Z factor (EPA) and is generally a poor indicator of potential structural darnage during an earthquake {SEADC, 1990}. This is because the duration and frequency of strong ground motion, local subsurface conditions, soil -structure interaction, and structural details are all important factors influencing structural performance. The PGA represents the peak instrumental value predicted to occur at recording instruments located away from structures (free -field) during future earthquakes. To account for factors such as the PGA value occurring only once during each particular seismic event and the averaging effects of foundation and soil -structure interaction, an effective peak acceleration (EPA/ is usually used in structural design. Estimate of PGA and EPA from 1996 CDMG/USGS Probabilistic Seismic Hazard Maps - -- Risk Equivalent Return Period (years) PGA (g) (1 } Approximate EPA {g) (2) 10% exceedance in 50 years 475 0.42 0,40 Notes: 1.} Based an soft rock site, Site Gass Se, (BJF Site Class A1B). 2.) Spectral acceleration (SA) at period of 0,3 seconds divided by 2.5 factor for 5% damping. Southland Geotechnical Page 12 i NM Construction Report P37002 i i 1 UBC SeisrnicCcefficients The UBC seismic coefficients are roughly based on a probabilistic estimate of the EPA value for a 10% probability of exceedance in 50 years. The UBC seismic force provisions should be regarded as a minimum design in that the UBC equation for base shear allows for inelastic yielding of structures. The UBC design criteria allow for some damage and possible loss of use of structure after an earthquake. The PGA and EPA estimates given above are provided for information en the seismic risk inherent in the UBC design. The following table lists the reverent seismic and site coefficients used in both the current 1994 and the impending 1997 UBC for earthquake forces given in Chapter 16. The new seismic provisions were recently adopted by ICBO for incorporation in the 1997 UBC scheduled for press release in May, 1997 and effective enforcement in January, 1998. The new 1997 seismic provisions are more stringent for areas less than 10 km (6.2 miles) from major seismic sources. UBC Seismic Coefficients for Chapter 16 Seismic Provisions UBC Code Edition Soil Profile Type Seismic Source Type Distance to Critical Source Near Source Factors Seismic Coefficients Na Nv Ca Cv 1994 S2 S factor =1.5 - - --- --- Z = 0.4 Z =0.4 Ref . Table 16-J --- --- --- 16-1 16-1 1997 Sr, (dense soil) A 15 km 1.0 1,0 0.44Na = 0.44 0.64Nv — 0.64 Ref. Table 16-J 16-U --- 16-S 16-T 1 6-Q 16-R Southland Geotechnical Page 13 A}M Construction Report P97002 Seismic Zoning: The Seismic Safety Element of the 'l954 Riverside County General Plan (see Figure 3) establishes seismic hazard zones. These zones are used in determining suitability of land use based on the seismic hazard. The project site and proposed development can be categorized from the Seismic Safety Element as follows. Land Use: Normal -low risk, residential County Groundshaking Zone: III Soil & Groundwater Condition: B - alluvium of thin to immediate thickness GWT> 50 ft Liquefaction Potential: non-existent Land Use Suitability: provisionally suitable _ _ Southland Gsot echnical Page 14 NM Construction Report P97002 RVRX.ROInb E ASE1E ) woe ,* Itu CelaFtli0 br THE IVER110E CCVNTf rLAIffi GEHWTI1EMT, .ANUARY 1903. LREV1SED AVAIL 1S8e) AHD L.RQUEfADT14H HAZA iR AWA_ . T Oa -NWT OF AREA of P0IENTIAL . _ -1— LIOUEFAG iEa t M JMDSZAK!NG ZONES I� iE BOUNDARY OF GRCiU► DVIAKIi9 IOI1E BASED ON OISTArICE 74 CALSFTI E FAULT. -aUSA.HD P EA3 V ACTIVE ROMANO AREA 11045SPARY, FAI L1Q 1E5.,. ilLOUIST - PRIOL,G $p!wL STUDIES ZONE. , Iola rl�'ERLLL Figure 3. Excerpt from Riverside County Seismic-Geofogfc Map ar SAL flW Southland Geotechriical Page 15 A!M Construction Report P97002 3.5 Subsurface Soils The field exploration conducted on January 15, 1997 indicates that the surficial and subsurface soils consist generally of medium denser Gravelly Silty Sand (SM) or (SP- SM) with some cobble and boulder size stones. The soil is part of the Carsitas soil unit as mapped by the USDA Soil Conservation Service and is of alluvial (water -lain) origin. At Test Pit T-1, a deposit of loose, dry Sandy Silt (MU} was encountered at a depth of 3.5 feet. This soil is probably a outwash deposit. The USGS topographic map (see Plate 1) indicates a drainage wash traversed across the site at this area prior to the construction of the Bear Creek Channel. Stratigraphic relationships of the various soil types are depicted on the test pit logs presented in the Exhibits section of this report (Plates 3 through 7). In arid climatic regions, granular soils have a potential to collapse upon wetting. This collapse (hydroconsolidation) phenomena is the result of the lubrication of soluble cements (carbonates) in the soil matrix causing the soil to densify from its loose configuration during deposition. Standard geotechnical engineering practice in this area is to test for collapse potential that may result in immediate settlement of the soil upon wetting. Collapse potential tests (see Plates 10 and 11) indicate 1 and 7% collapse upon inundation and is considered a slight to moderately severe site risk. The moderately severe risk is associated with potential hydraconsolidation of a loose, sandy silt outwash deposit encountered at Test Pit T-1. Therefore, development of building foundations should include provisions for mitigating the hydroconsolidatiori caused by soil saturation from landscape irrigation or broken utility lines. This is commonly accomplished by overexcavation and recompaction of a zone beneath building pads. Groundwater was not encountered in the test pits during the time of exploration. Groundwater is believed to exist at a depth of over 90 ft based on nearby historical CVWD water well measurements. Southland Geotachnicai Page 16 AIM Construction Report P97002 Section 4 RECOMMENDATIONS 4.1 Site Preparation Clearing and Grubbing: All debris or vegetation such as grass, desert shrubs, or weeds that may exist on the site at the time of construction should be removed from the construction area. Any root balls should be completely excavated. Organic strippings should be hauled from the site and not be incorporated into any engineered fills. Any trash, construction debris, concrete slabs, old pavement, landfill, and buried obstructions should be located by the grading contractor and removed before site grading. Any excavations resulting from site clearing should be dish -shaped to the lowest depth of disturbance and backfilled with engineered fill as described bellow. Building Pad Preparation (Lots 1 _2, 5_17): All building pads should be provided with a zone of moisture conditioned and compacted zone of soil that is at least three feet below finish pad grade and five feet laterarly from exterior dimensions of the structure. This zone should be compacted to the criteria for fill be soils given below. The existing ground beneath building areas to receive fill should be thoroughly moisture conditioned to achieve moisture penetration to at least three feet depth and at least 90% relative compaction CASTM D1557}.to at least two foot depth. Because of the granular native of the site soils, compaction may be achieved by thorough watering and wheel rolling from the surface. Compaction and moisture conditioning should be verified by testing. If the above requirements cannot be met by watering and surface compaction, overexcavation and recompaction may be required, Building Pad Preparation {Lots 3-4. 18-19)_ In addition to the preparation requirements given above, additional investigation is required during site grading to determine the lateral extent of the Nose, sandy silt deposit that has a moderatley severe collapse potential, Beginning at about the location of Test Pit T-1, the building pads should be overexcavated to about four feet depth, to expose the sandy silt deposit. The bottom of the subexcavation should be scarified, moisture conditioned and recompacted to at least 90% relative compaction CASTM D1557). The subexcavation should be Southland Geotechnical Page 17 AIM Construction Report P97002 backfilled with engineered fill as given below. This overexcavation need -only extend for the building pads where this sandy silt deposit is encountered. While these four lots are the only lots believed to be impacted at this time, the wash deposit might extend into other lots, requiring the same site preparation. Failure to follow these recommendations may place the residential structures at risk for differential settlements of about one inch. We strongly advise that Southland Geotechnical, Inc. be retained to monitor this overexcavation and recompaction.. Street Subctrade: Subgrade for streets or concrete slabs, the ground surface should be scarified to 12 inches, moisture conditioned, and recompacted to a minimum of 90% relative compaction (ASTM ❑1557). Fill Solis: The nature granular soil is suitable for use as engineered fill and utility trench backfill. The native soil should be placed in maximum 8-inch tifts (loose) and compacted to a minimum of 90% of ASTM D1557 maximum dry density at optirnurn moisture ± 2%. All imported fill soils (if required) should be non -expansive, granular soils meeting the USCS classifications of SM, SP- M, or SW-SM with a maximum rock size of 3 inches and 5 to 20% passing the No. 200 sieve. The geotechnical engineer should approve imported fall soils before hauling to the site. The imported fill should be placed in lifts no greater than 8 inches in loose thickness and compacted to a minimum of 90% of ASTM D1557 maximum dry density at optimum moisture ± 2 percent. Moisture Control and Drainage: The moisture condition of the building pad should be maintained during trenching and utility installation until concrete is placed or be rewetted before initiating delayed construction. Positive drainage should be maintained away from all structures (five feet minimum) to prevent ponding and subsequent saturation of the foundation soils. Gutters and downspouts may be considered as a means to convey water away from foundations. If landscaping water is allowed next to the building, drip irrigation systems or lined planter boxes should be used. Drainage should be maintained for paved areas. Water should not pond on or near paved areas. Southland Geotechnical Page 18 A!M Construction Report P97002 Observation and Density Testing: All site preparation and fill placement should be observed and tested for density by a qualified geotechnical engineering firm. This is emphasized during the over -excavation and scarification process to detect any undesirable materials or conditions that may be encountered in the construction area. The geotechnical firm that provides observation and testing during construction shall assume the responsibility of "geotechnical engineer of record". Auxiliary StrUctUres Foundation Prepara ion: Auxiliary structures such as free standing or retaining walls should have the existing soils beneath the structure foundation prepared in the manner recommended for the building pad except the preparation needed only to extend 12 inches beyond the footing. Southland Geotechnical Page 19 IA/M Construction _ _ Report P97002 I4.2 Foundations IShallow spread footings and continuous wall footings are suitable to support the residential structures provided they are founded on a zone of properly prepared and Icompacted soil. This zone should extend at least 18 inches below the footing and extend at least 18 inches laterally from the edge of the footings. The foundation Ishould be designed using allowable net soil bearing pressures of 2000 psf for dead and live Toads. This bearing pressure may be increased by 400 psf for each foot of Iembedment below the 12 inches minimum embedment. The allowable soil pressure may be increased by one-third for short term Toads induced by winds or seismic 1 events. IAll exterior foundations should be embedded a minimum of 12 inches below the lowest adjacent final grade. Interior footings should be embedded at least 12 inches into Iprepared subgrade. Continuous wail footings should have a minimum width of 12 inches. Spread footings should have a minimum width of 30 inches. Minimum Ireinforcement for continuous wall footings should be two, No. 5 or No. 6 steel reinforcing bars, one placed near the top of the footing and one near the bottom. This i reinforcing is not intended to supersede any structural requirements provided by the structural engineer. IResistance to horizontal loads will be developed by passive earth pressure an the sides I of footings and frictional resistance developed along the bases of footings and concrete slabs. Passive resistance to lateral earth pressure may be calculated using I an equivalent fluid pressure footings of 300 pcf to resist lateral loadings. The top one foot of embedment should not be considered in computing passive resistance unless Ithe adjacent area is confined by a slab or pavement. An allowable friction coefficient of 0.35 may also be used at the base of the footings to resist lateral loading. 1 Non -seismically induced settlements are estimated to not exceed 3/4 inch with Idifferential settlements of about two-thirds of total settlement for the loading assumptions stated above when the subgrade preparation guidelines are followed. I Southland Geotechnical Page 20 A/iMI Construction Report P97002 1 4.3 Slabs -On -Grade Concrete slabs and flatwork should be a minimum of 4 inches thick. Concrete floor slabs may either be monolithically placed with the foundations or dowelled after footing placement. The concrete slabs may be placed on the granular fill pad that has been compacted to 90% of ASTM D1557 maximum density and moistened to approximately optimum moisture just before the concrete placement. A 6-mil visqueen vapor barrier and 2-inch sand cover should be placed over the subgrade as a capillary break to prevent moisture migration into the slab section. Concrete slab and flatwork reinforcement should consist of a minimum of chaired rebar slab reinforcement (No. 3 bars at 18-inch centers, both horizontal directions) placed et slab mid -height to resist cracking. Slab and steel reinforcement recommendations are minimums only and should be verified by the structural engineer/architect knowing the actual project loadings. The project architect or geotechnical engineer should continually observe all reinforcing steel in slabs during placement of concrete to check for proper location within the slab. Control joints should be provided in all concrete slabs -on -grade at a maximum spacing of 32 x slab thickness (10 feet maximum on -center, each way) as recommended by American Concrete Institute {ACI) guidelines. All joints should form approximately square patterns to reduce randomly oriented contraction cracks. Contraction joints in the slabs should be tooled at the time of the pour or sawcut (1/4 of slab depth) within 8 hrs of concrete placement. Construction (cold) joints should either be thickened butt -joints with one-half inch dowels at 24-inches on center or a thickened keyed -joint to resist vertical deflection at the joint. All construction joints in exterior flatwork should be sealed to prevent moisture or foreign material intrusion. Precautions should be taken to prevent curling of slabs in this arid desert region. All independent flatwork (sidewalks, driveways, patios) should be underlain by 12 inches of moisture conditioned and compacted soils. All flatwork should be jointed in square patterns and at irregularities in shape at a maximum spacing of 10 feet. Southland Geotechnical Page 21 AJM Construction Report P97002 4.4 Concrete Mixes and Soil Corrosivity Selected chemical analyses for corrosivity were conducted on samples at the project site (Plate 1 2). The native soils were found have Iow sulfate ion concentration (0.05%). Sulfate ions can attack the cementittous material in concrete, causing weakening of the cement matrix and eventual deterioration by raveling. The Uniform Building Code requires that increased quantities of Type II Portland Cement be used at a Iow water/cement rati❑ when concrete is subjected to moderate sulfate concentration. A minimum of 53 sacks per cubic yard of concrete of Type II Portland Cement with a maximum water/cement ratio of 0.55 (by weight) should be used for concrete placed in contact with native soils on this project. The native soils have moderate chloride ion concentrations (0.02%). Chloride ions can cause corrosion of reinforcing steel. Resistivity determinations on the soils indicate severe potential for metal Toss due to electrochemical corrosion processes. Mitigation of the corrosion of steel can be achieved by using steel pipes coated with epoxy corrosion inhibitors, asphaltic coatings, cathodic protection or by encapsulating the portion of the pipe lying above groundwater with densely consolidated concrete_ A minimum concrete cover of three (3) inches should be provided around steel reinforcing or embedded components exposed to native soil or landscape water (to 16 inches above grade). Additionally, the concrete should be thoroughly vibrated during placement. Southland Gectechnical Page 22 NM Construction Report P97002 4.5 Excavations Shallow, temporary excavations in the native soils be no steeper than 1.5:1 (horizontal:vertical). Sandy soil slopes should be kept moist, but not saturated, to reduce the potential of raveling or sloughing. Any excavations over 5 feet in depth will require shoring or slope inclinations in conformance to CAL/OSHA standards. Surcharge Toads of stockpiled soils or construction materials should be set back from the top of the slope a minimum distance equal to the height of the slope. All permanent scopes should not be steeper than 3:1 to reduce wind and rain erosion. 4.6 Seismic Design Criteria This site is subject to strong ground shaking due to potential fault movements along the San Andreas and San Jacinto Faults. Engineered design and earthquake -resistant construction are the common solutions to increase safety and development of seismic areas. The minimum seismic design factors should comply with the latest edition of the Uniform Building Code for Seismic Zone 4 using the seismic coefficients given in Section 3.4 of this report. The UBC seismic coefficients are based on scientific knowledge, engineering judgment, and compromise_ Factors that play an important role in dynamic structural performance ere: (1) effective peak acceleration (EPA) , (2) duration and predominant frequency of strong ground motion, (3) the period of the structure, (4) soil -structure interaction, (5) total resistance capacity of the system, (6) redundancies, (7) inelastic load -deformation behavior, and (8) the modification of damping and effective period as structures behave inelastically. Factors 5 to 8 are accounted by the structural ductility or quality factor (Rw) used in deriving a reduced value for design base shear. The intent of the UBC lateral force requirements is to provide a structural design that will resist collapse to provide reasonable life safety from a major earthquake but may experience some structural and non-structural damage. A fundamental tenet of seismic design is that inelastic yielding is allowed to accommodate the seismic demand on the structure, in other words, damage is allowed, The UBC lateral force Southland Geatechriical Page 23 A/M Construction Report P97002 requirements should be considered as a minimum design criteria. The owner and the designer should evaluate the level of risk and performance that is accceptable. Performance based criteria could be set in the design. The design engineer has the responsibility to interpret and adapt the principals of seismic behavior and design to each structure using experience and sound judgement. The design engineer should exercise special care so that all components of the design are all fully met with attention to providing a continuous Iaad path. An adequate quality assurance and control program is urged during project construction to verify if the design is met and good construction practices followed. This is especially important for sites lying close to the major seismic sources. 4.7 Pavements Pavements should be designed according to CALTRANS or other acceptable methods. Since no traffic loadings were provided by the project engineer or owner, we have assumed traffic loadings for comparative evaluation. The owner or design engineer should decide the appropriate traffic conditions for the pavements. Maintenance of proper drainage is necessary to prolong the service life of the pavements. Based on the current State of California CALTRANS methods and assumed traffic Toads, the following table provides our recommendations for asphaltic concrete pavement sections. Southland Geatechnical Page 24 AIM Construction Fort P97002 1 i i i i Table 2 RECOMMENDED PAVEMENTS SECTIONS R-Value Subgrade Soils - 50 (minimum Design Method - CALTRANS 1990 Traffic Index (assumed) Pavement Type Flexible Pavements Rigid Pavements Asphaltic Concrete Thickness - (in.) Aggregate Base Thickness (in.) Portland Cement Concrete (in.) Aggregate Base Thickness (in.) 4.0 5.0 Interior Streets Entrance Drive 2.5 3,0 4.0 4.0 4.0 5.0 4.0 4.0 Notes: 1) Asphaltic concrete should be Ca!trans, Type B, 112 in. maximum -medium grading, compacted to a minimum of 95% of the 75-blow Marshall density ' (ASTIVI D1559). 2) Aggregate base should be Caltrans Class 2 (3/4 in. maximum}, compacted to a minimum of 95% of ASTM D1557 maximum dry density. 3) All pavements should be placed on 8 inches of moisture conditioned, native soils compacted to a minimum of 90% of ASTM D1557 maximum dry density. 4) Portland cement concrete should have a minimum of 3250 psi compressive strength @ 28 days. SouthL nd Geotechnicai Page 25 A/M Construction Report P970-02 Section 5 LIMITATIONS AND ADDITIONAL SERVICES 5.1 Limitations The recommendations and conclusions within this report are based on current information regarding the proposed 19-lot subdivision, Tentative Tract No. 28409 in La Quinta, California. The conclusions and recommendations of this report are invalid if: • The structural Toads change from those stated or the structures are relocated. ▪ The Additional Services section of this report is not followed. This report is used for adjacent or other property. ► Changes of grade or groundwater occur between the issuance of this report and construction other than those anticipated in this report. • Any other change is implemented, which materially alters the project from that proposed at the time this report was prepared. Thy ennnlipsinn ar!el rPnommeinriatinns in this report are haRRri nn c&lprtprl pninta Yf field exploration, laboratory testing, and our understanding of the proposed project. Our analysis of data and the recommendations presented herein are based on the assumption that soil conditions do not vary significantly from those found at specific exploratory locations. However, it is possible that variations in soil conditions could exist between and beyond the exploration paints or that groundwater elevations may change. These conditions may require additional studies, consultation, and possible design revisions. This report was prepared according to the generally accepted, geotechnical engineering standards of practice that existed in Riverside County at the time the report was prepared. No warranty, expressed or implied, is made in connection with our services. Because of potential changes in the Geotechnica! Engineering Standards of Practice, this report should be considered invalid after two years from the report date without a review of the validity of the findings and recommendations by our firm. Southland Geotechnical Page 26 AIM Construction Report P97002 The client has responsibility to see that all parties to the project including, designer, contractor, subcontractor and future owners are made aware of this entire report. The use of information contained in this report for bidding purposes should be done at the contractors option and risk. 5.2 Additional Services The recommendations made in this report are based on the assumption that an adequate program of tests and observations will be conducted during construction to verify the field applicability of subsurface conditions and compliance of the recommendations that are the basis of this report. Because of our experience and familiarity with the project, we recommend that Southland Geotechnical be retained as the gectechnical consultant to provide the tests and observations. The geotechnical engineering firm providing tests and observations should assume the responsibility of geotechnicaf engineer of record. These tests and observations should include, but not necessarily be limited to the following: ■ According to UBC Sections 1701 and 3317, full-time observation and testing by the geotechnical consultant of record during site clearing, grading, excavation, placement of fills, building pad and subgrade preparation, and backfilling of utility trenches; ▪ Observation of foundation excavations and reinforcing steel before concrete placement; ► Consultation as may be required during construction. In addition, we should review the project plans and specifications to check for compatibility with our recommendations and conclusions. Additional information concerning the scope and cost of these services can be obtained from our office. -o0o- Southland Geotechnicai Page 27 REFERENCES Blake, Thomas F. (1989-1996), FR1SKSP - A Computer Program for the Probabilistic Estimation of Seisrnic Hazard usury Faults as Earthquake Sources. Bolt, B. A., 1974, Duration of Strong Motion: Proceedings 5th World Conference on Earthquake Engineering, Rome, Italy, June 1974. Boore, D. M., Joyner, W. B., and Fumal, T. E., 1994, Estimation of response spectra and peak accelerations from western North American earthquakes: U.S. Geological Survey Open File Reports 94-127 and 93-509. California Division of Mines and Geology {CDMG}, 1996 California Fault Parameters, available at httpflwww.consrv.ca.govldmglshezplfItindex.html. Ellsworth, W. L., 1990, "Earthquake History, 1769-1989" in: The San Andreas Fault System, California: U.S. Geological Survey Professional Paper 1515, 283 p. International Conference of Building Officials (ICBO), 1994, Uniform Building Code, 1994 Edition. UUBO, 1997 in press, Uniform Building Code, 1997 Edition. Jennings, C. W., 1994, Fault activity map of California and Adjacent Areas: California Division of Mines and Geology, DMG Geologic Map No. 6. Mualchin, L. and Jones, A. L., 1992, Peak acceleration from maximum credible earthquakes in California (Rock and Stiff Soil Sites): California Division of Mines and Geology, DIM Open File Report 92-01. Naeimr F. and Anderson, J. C., 1993, Classification and evaluation of earthquake records for design: Earthquake Engineering Research Institute, NEHRP Report. OSMS, (Office of Strong Motion Studies) (1992), Quick Report on CSMIP, Strong Motion Records from the April 22, 1992 Desert Hot Springs, California Earthquake, California Division of Mines and Geology. OSMS, (Office of Strong Motion Studies) (1992), CSMIP Strong Motions Records from the Landers. California Earthquake of June 28, 1992, California Division of Mines and Geology. OSMS, (Office of Strong Motion Studies) (1992), CSMIP Strong Motions Records from the Big Bear, California Earthquake of June 28, 1992, California Division of Mines and Geology. Southland Geatechnical Page 28 REFERENCES Proctor, Richard J. (1968), Geology of the Desert Hot Springs - Upper Coachella Valley Area, California Division of Mines and Geology, DMG Special Report 94. Riverside County (1984), Seismic Safety Element of the Riverside County General Plan, Amended. Stringer, 5. L., 1997, EQFAULT.WK4, A computer program for the estimation of deterministic site acceleration. Structural Engineers Association of California (SEAOC), 1990, Recommended lateral force requirements and commentary, U.S. Geological Survey, 1987, Strong -Motion Data from the July 8r 186 North Palm Springs Earthquake and Aftershocks, Open -File Report 87-1 55. U.S. Geologic& Survey, 1996, National Seismic Hazard Maps, available at http/igloiage.or.usgs.gov Wallace, R. E., 1990, The San Andreas Fault System, California: U.S. Geological Survey Professional Paper 1515, 283 p. Working Group on California Earthquake Probabilities (WGCEP), 1988, Probabilities of large earthquakes occurring in California on the San Andreas Fault: U.S. Geological Survey Open -File Report 88-398. Working Group on California Earthquake Probabilities (WGCEP), 1992, Future seismic hazards in southern California, Phase I Report: California Division of Mines and Geology. Working Group on California Earthquake Probabilities (WGCEP), 1995, Seismic hazards in southern California, Probable Earthquakes, 1994-2014, Phase I1 Report: Southern California Earthquake Center. Southland Geotechnical Page 29 EXHIBITS Reference: USGS Topographic Map, La 4Llirtta 7.5 ruin Quadrangle Vicinity Map T Approximate Test Pit Location (typi I I i i i I i i i 1 i CLIENT: A & M Contru don METHOD OP EXCAVATION: Backhoe PROJECT: Tenabve Tract Map # 28499 DATE OBSERVED1115f97 LOCATION:See Site & ExIoration Plan LOGGED BY: K. Harmon $,Li I I g LOG OF TEST PIT T-1 MEET 1 4F 1 a DESCRIPTION OF MATERIAL o p SURFACE ELEV, +!- s o -4 � W r . LL a i2 L' e, Q k � a 2 a d 1 ■■ i.� 11111 1 . ail in2 _ ii I GRAVELLY SILTY SAND (Slyly Gray - brown, dense, 1.4* 114.7 87hi �� moist, with cobbles and trace boulders I GRAVELLY SAND SP): Gra , dense. d , wtth cobbles ME 11111. IL.SANDY SILT ML}: L�pht brown, medium dens$, hump 3.6k 97.16�..i 4.3 84.9 ■IIII■■ 6 1� SILTY SAND {SM): Lig>�t brawn, mediarn dense to dense, - humid, fine to me iurn grained, wf some grave and aabbl- �■�■ 7 e� ! 1 si■� . — 8 .. 9 Ihih 1 i ;! - 10 t1? - � - - — - - .11 - -- Battam of Exaevation i 12 M■■ �-� No Gr undw ter Encountered 13 ' Iuciear Densometer Readings -14 -■■■■�■ -15 le .__ — - ■�� ■.. 1718 19 _'_--- �NM■ 21 ,..li n ■■■ ■■=■■ Project No: mipA' Plate P97002 1 i I I i ■ 1 i CLIENT: A & M Contruction PROJECT: Tenathre Tract Map## 28409 LOCATION:See Site & ExIoration Plan 2 METHOD OF EXCAVATION Baukhoe DATE OBSERVED:1115/97 LOGGED BY: K. Harmon LOG OF TEST PIT T-2 SHEET 1 OF 1 DESCRIPTION OF MATERIAL SURFACE ELEV. +/- GRAVELLY SAND (Si -SM): Gray - brawn, medium dense, humid to moist, with silt, cobbles end boulders (-3') 1.5' 1 a 84 *Dense 1.9` 111.31 85 2,6 108.g 1 SILTY SAND (S1u1): Light brown, very dense, dry to humid, fine to coarse grained, some gravel Trace cobbles and small boulders 2.5* 117_5' 89 botton3 or Excavation c 11 it 13-i 14 15 17 No Groundwater Encountered • Nuclear Densometer Readings 16- 19- 20 21� Project No: P97002 *P)1-11-AIND NNICAL r Plate 4 I i i i i i i i i CLIENT: A & M Contructk,n METHOD OF EXCAVATION: Backhoe PROJECT: Tenettve Tract Map # 28409 DATE OBSERVED:1/15/97 LOCATION:Sae Site & ExIoration Plan LOGGED BY: K. Harmon - e 1 0 E LOG OF TEST PIT T-3 SHEET 1 OF 1 DESCRIPTION OF MATERIAL SURFACE ELEV. +1_ . E s 1 8 t g c i. a Q ac S} ti 0 P, g 2 -., ,� : -Moist ;- -1-fti� - 2 - • - _ `',. GRAVELLY SILTY SAND (M): Gray - brown, dense, 1.0* 122.6' 93 1' e dry to humid, fine to coarse grained,with cobbles . i and some Ibautders 4 -y 4 ' F . IL I� SAND (SW-SM): Brown, dense, humid, trace gravel, 1.7* 114.1' 87 :,; . well graded +:41� - — - ti• 6,Sr ti47_ r,�,� -Trace cobbles i lei•}_. �r •'r='rMil •-J• .'fti.rtr ti.1,.ti • 9 _1 "}2 L J`Ri rT { -Gravel and cobbles y �r 10-' - - - 1- Bottom of Excavation it 10 ft. _ 12 No Groundwater Encountered 13 * Nuclear Densometer Readings 14 .15- 16 17 19 20 i 21 Project No: Plate P97002 r o T wvic u 4 CLIENT: A & M Ocntruction METHOD OF EXCAVATION: Backhoe PROJECT: Tena1ive Tract Map # 28409 DATE OBSERVED' 1115/97 LOCATION:Sea Site & Exloralion Plan LOGGED BY: K. Harmon 51 u m E W 0. LOG OF TEST PIT T- SHEET 1 OF 1 DESCRIPTION OF MATERIAL. SL1 FACE ELEV. �1- w E RI . � � ¢ w 0 1.3 it 12 R a ;c f~ F m • ' SILTY SAND {SM): Brown, medium dense, moist, with . . gravel and cobbles L SAND (SW): Gray - brown, dense, humid, with t� gravel, cobbles and trace boulders 2 - ' GRAVELLY -SILTY SAND (BM): Gray - brown, dense, 1.4' 118.9' 90 • humid, wsth cobbles and boulders -- -i: •• I - _Grades less silty end gravelly 2.0* 120.8' 92 $ r '� -Trace gravel 2.5` 117.2� 89 _ • ' — SAND ( VT- IF): Brown, dense, humid, with gravel and some cobbles ' .a, -- io- Bottom orExcavation @ 10 ft, 11 NO (iroundwater Encountered -12- ' Nuckeer Densarneter Readings -- is - 114, (15 I, •15 ,17- -1s - 19 _ i , T -21� - - •22 , Project No:P1ate #DQ )y-TILLr_28.4,—L= 6 i i i i i t 1 i i CLIENT: A & M Contruction METHOD OF EXCAVATION: Backhoe PROJECT; Tenati►re Tract Map # 28409 DATE OBSERVED:1115/97 LOCATION:See Site & Exlaration Plan LOGGED BY: K. Harmon g ,1SURFACE g LOG OF TEST PIT T-5 SHEET 1 OF 1r DESCRIPTION OF MATERIAL ELEV,+1- SCi 5 _ U. g i a + 15 st•y: SAND (,SP-Shy): Gray, medium dense, moist, fine to . coarse grained, micassous, with gravel and cobbles SILTY SAND (SIv1): Brown, dense, drytc humid, fine 1.3* 109,8' 84 - '_ ' to coarse waffled, with gavel, cobble and boulders (--2') , F I# - 2.0' 109,1' 83 1 • j 5 _ • - -.--- - 1 � 11 Bottom of Excavatlan @ 10 it. - 12 No Groundwater Encountered 1 Nuclear Densometer Readings 14 - - 15 16 -, 17 18 I 1 119 20 21-. 22 Project No: Plate - P97002 � l = 7 DEFINITION OF TERMS PRIMARY DIVISIONS Gravels Mere man hull Of Wavle Coarse grained sails I fr rclion is larger than More than half of IV�d Steve material is larger 1'an Mo 20O sieve Sends More than half of swat, fraction is mailer than No. d rams Clean Gravels (leas then ryi!i, Rrwal Gravel wit}I fines Chasm sands (less than 5%fires) Sands whh fines SYMBOLS SECONDARY DIVISIONS "•,o-rq. GW Wall gravel -send malureG, little or no fines early graded gravels, or gavel -Send mbdiires, little or no pings GM Silty gravels, gravel -sand -silt nibdurna. non -plastic fines GC J Clayey graves, 9raplay Mi1CIU1111S. plastic fines SW I Wel graded sands, gravely wands, little or no fines IF Peony graded sands or gravelly sands, tittle cr na fines SM Silty sands. rand -aft misrhrss. non -plastic fines SC Clayey sands, send -clay matures, pldbtio fines Fine grai+ed soils Mara than half of material is smaller than No. 200 sieve Sate and clays Liquid rrrsitis Ids$ than 50% Silts and clays l�qud unit is more than 550% Highly organic was illNIL Urorgarte sits. clayey saki %bin slight plestfolty CL OL MH CH Iriorgenic days of bwta medium t . gravely, sandy. or lien clays Organic s is and organic days of law plasticity Inorganic sits, micaceous or dlotlomacea►rs silty snits elastic sifts Inapanly clays of high pl85tcity. Fat clays OH 1 Orrenfc clays of medium to high Ply, rxge<rdc sills PT Prot and oderhighly organic &adz GRAN S1Z.S She and Clays Sand Gravel 1 Floe Medium 1 Coarse Fi Cobbles Boulders 200 40 10 4 US Standard Series Sirive Sends, Grovels, etc-ll &tw aft . Very Loose Medium Dens Dense Vary Cerise CN 41 rJ 0-3Q 30-50 Over 50 314' 3' 12' Clear Srere Openings rays & Plastic Silts Stranglh'• Very Soft &aft HMI Stiff Very Seri Hard 0-0.25 0-2 0.25-0.5 2-4 U. —1.(.1 413 I -16 2.0-4.0 15-32 Over 4.0 Over 32 • Number of Mews of 1401o. hammer Falllri 30 krches to drive a 2 inch 0.6. { 1 3!B in. LD.} split spoors (ABTM D1508). ▪ Unconfined campressrre strength In Ions/ , r. a6 defarmired by Iabvratary lestklig ar oppioxlinotad by the Standard Penatratian Test(ASTM cmae), Paelwl Penetrometer, Torvane. or visual observation. Type o1 Samples' 3 Rang Semple N Standard Penetration Teat I Shelby Tube • sulk (Bag) Sample Drilling Notes; 1. Sampling and Blow Counts Rrsg Sampler - Number of Wove par foot of a 140Ib. hemmer Falling 30 inches. Standard Penetration Test - Number of blows per foot Shelby Tie Three (31 inch nominal diameter babehydraullcaly pushed_ 2. P_ P. = Padget PenaOuneter (tons1e.f }, 3. NFL - Na recovery. 4. GWI = Ground Water Table} observed Cg, Specified time I4LANID -" MCP Project No: P97002 Key to Logs Plate 8 i 0 0 0 0 UNIFIED CLASSIFICATION SYSTEM Films — Sin & L�r E 2 a 2 6061'3v Graver Flan Graral Coarse Sand 0 L U.S. Standard Sieve Nurnb.rs O• M 47 O 0 O O 01 05 N. L6 Lii h/} 11-1013M A9 d3111A 1N3343d .* u -.F. .NUS !C4L= Project No: P97002 a cic W 6 W J z W N Q 0 Grain Size Distribution Symbol Location Sample ID USCS Classification Well graded Gravefly Sand (SW—SM) 0 Plate 145 . 140 h m 135 130 125 120 115 110 105 0 5 10 Project No: P97003 Client: Project: Project Nc. Date: SUMMARY Description: Well Sample Location: Test Method: Maximum ! ry Density (pa): Optimum Moisture Content (%): AIM Construction TT 26409 P97003 01 /21'97 OF TEST RESULTS Graded Gravelly Sand w1 silt T-1 c 1 to 4 feet ASTM D15570 & D4718 15 20 Moisture Content (%) 131.5 6.2 Curves of 100% saturation for speck gravity equal to: 2.75 2.70 2.85 25 Moisture Density Relationship 30 Plate 9 I 1 1 1 1 I I 1 Percent Change in Height -6 -14 COLLAPSE POTENTIAL TEST (ASTM D5333) cr ?Mgt )% (Slight) Gravelly Silty Sand (SFM) 7-2©aft 1 0.1 1 1Q 100 Pressure (ksf) fTi-IL AND = Project No: P37002 Results of Test: Initial Final Dry Density, pcf: 106.5 '111.6 Water Conterrt, %: 2.6 18.2 Void Ratio, e: 13.525 0.482 Saturation, %: 13 100 Collapse Potential Test Results _� Plate 10 Percert Change in Height -5 .s -14 COLLAPSE POTENTIAL TEST (ASTM I75333j _ 1, Po 03.8 % (Mock retell( Seer Sandy Silt {ML) T-1 r7h 4f 0.1 Pressure (ksf) 1TNLAND -= Project No: P97002 10 10t} Results of Test: inl#iai Final Dry Density, pcf: 84.9 95.1 Water Content, %: 4.3 27,9 Void Ratio, e: 0.948 0.73E Saturation, %: 12 1 DO Collapse Potential Test Results Plate 11 SOUTHLAND GEOTECHNICAL CLIENT: AIM Construction PROJECT: Tentative Tract No. 28409 JOB NO: P97002 DATE: 0/123197 CHEMICAL ANALYSES Boring: T-3 Sample Depth, ft: 3 pH: 8.2 Electrioal Conductivity (mohmslcm): Resistivity (ohm -cm): 2000 Chloride (CI), ppm: 200 Sulfate (SO4), ppm: 469 Note: Tests performed by Agricultural Testing Service, Inc, of Brewley, CA under subcontract to our firm, General Guidelines for Soil Corrosivity Material Chemical Amount in Affected _Agent Soil (iporn or ohn-cm) Concrete Soluble 0 -1000 Sulfates 1000 - 2000 2000 - 5000 > 5000 Normal Grade Steel Normal Grade Steel Soluble Chlorides 0-200 200 - 700 700-1500 > 1500 Resistivity 1-1000 '2000-2000 2000-10,000 10,000+ Project No: P97002 Degree of Corro ivity Low Moderate Severe Very Severe Low Moderate Severe Very Severe Very Severe Severe Moderate Low Selected Chemical Analyses Results Plate 12