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HomeMy WebLinkAboutAttach 1 Appendix FAugust 30, 1999 Job No. 1394.113 BGC BERLOGAR GEOTECHNICAL CONSULTANTS Ms Jennifer Lin c/o Mr. Ted Fairfield 5510 Sunol Boulevard Pleasanton, California 94566 Subject: Geotechnical Report Dublin Ranch - Pao-Yeh Lin Property Tassajara Road Dublin, California Dear Mr. Fairfield: Berlogar Geotechnical Consultants (BGC) is pleased to submit this geotechnical investigation report for the Pao-Yeh Lin Property at Dublin Ranch in Dublin, California. The enclosed report presents the results of our investigation regarding the site soils, bedrock and groundwater conditions, and our recommendations for site preparation and grading, stability of cut ami fill slopes, landslide mitigation, subdrainage, foundation considerations, exterior flatwork, retaining walls, underground utility installation and preliminary pavement sections. In regard to the issue of design gradients for fill slopes, this report presents various recommendations for slope gradients that vary with the height of the fill slope. While we expect that most fill slopes will be designed and constructed in accordance with the recommendations presented herein, we recognize that local design constraints may require fill slope gradients steeper than presented herein. These conditions are likely to occur in the interior of subdivisions, where lot pad elevations exceed a 10 foot elevation difference and where a slope- gradient of 2 horizontal to 1 vertical (2H: IV) is preferred for efficient lot layout. Steeper fill slope gradients will require site specific design in coordination with MacKay & Somps and will likely incorporate design features such as use of select fill material and/or geogrid reinforcement with improved strength parameters. Such fill slopes will be substantially more costly to construct. To reduce the erosion potential, benches with "V"-ditches are generally recommended for newly constructed slopes higher than 30 feet. The bench and "V"-ditch requirements may be waived provided the slope is built at an inclination of 4H: 1V or flatter and additional erosion protection is installed on the portion of the cut slope that is more than 30 feet in elevation below the highest point on the cut slope. SOIL ENGINEERS · ENGINEERING GEOLOGISTS · 5587 SUNOL BOULEVARD · PLEASANTON, CA 94566 · (925) 484-0220 · FAX: (925) 846-9645 August 30, 1999 Job No. 1394.113 Page 2 We appreciate the opportunity of providing our geotechnical services to you on this project and trust this report provides the information you require at this time. If you have any questions, please contact us. ERPectfully submitted, LOGAr'R GEOTEC~NSULTANTS /Principal Enginedr gar IPSL/FB:pP Copies: Addressee (1) MacKay & Somps (7) Attention: Mr. Jim Templeton wp51/reporff7600.1tr BERLOGAR GEOTECHNICAL CONSULTANTS TABLE OF CONTENTS INTRODUCTION ............................................ 1 PURPOSE ............................................. t PROPOSED DEVELOPMENT ................................ 2 FINDINGS ................................................. 2 SITE DESCRIPTION ...................................... :2 REGIONAL GEOLOGY AND SEISMICITY ....................... 3 SOILS AND BEDROCK CONDITIONS .......................... 4 Residual Soils ...................................... 4 Colluvial Deposits .................................... 4 Alluvium ......................................... 4 Landslides ......................................... 4 Bedrock .......................................... 5 Artificial Fill ...................................... 5 Ground Water ..................................... 5 CONCLUSIONS AND RECOMMENDATIONS ......................... 6 GENERAL ......................................... 6 EXPANSION POTENTIAL ................................ 6 SETTLEMENT ...................................... 7 LANDSLIDES ......................................... 9 SITE PREPARATION AND GRADING ...................... 9 SHRINKAGE/SWELL FACTOR ............................ 11 CUT SLOPES ........................................ 12 FItJ_, SLOPES ....................................... 13 SUBDRA1NAGE ........................................ 13 FOUNDATION CONSIDERATIONS ........................... 14- Residential Structures ................................. 14 Commercial and Office Structures ......................... 15 EXTERIOR FLATWORK .................................. 15 UTILITY TRENCHES .................................... 15 RETAINING WALLS ..................................... 16 PRELIMINARY PAVEMENT SECTIONS ........................ 17 CORROSION CONSIDERATIONS ............................ 18 SEISMIC HAZARDS ..................................... 19 Faulting ......................................... 19 Ground Shaking .................................... 19 Liquefaction ...................................... 19 Lurching ......................................... 19 Ground Subsidence .................................. 20 Earthquake-Induced Landsliding .......................... 20 LIMITATIONS ............................................. 20 BERLOGAR GEOTECHNICAL CONSULTANTS GEOTECHNICAL REPORT DUBLIN RANCH - PAO-YEH LIN PROPERTY TASSAJARA ROAD DUBLIN, CALIFORNIA FOR MS JENNIFER LIN ~TRODUCTION PURPOSE This report presents the results of a design-level geotechnical investigation for the Pao-Yeh Lin property located on the north side of Interstate 580, east of Tassajara Road in Dublin, California. This geoteclmical investigation was undertaken to gather information on the subsurface conditions at the site and to develop geotechnical conclusions and reconu'nendations for site development. Berlogar Geotechnical Consultants (BGC) previously performed a preliminary geologic and geotechnical of the property the property and presented the results in a report dated November 13, 1998. This investigation included the following scope: Review of pertinent geologic maps, available published and unpublished reports, and previous BGC reports for the site and surrounding areas; 2. Excavation of 96 backhoe test pits ranging from about 7 to 19 feet deep; Drilling of 16 borings ranging from about 12 to 70 feet deep. Sixteen additional borings were drilled in conjunction with a concurrent investigation for Assessment District roadways and utility corridors; that data was used in this evaluation); Laboratory tests performed on selected samples of soil and bedrock materials obtained from test pits and borings; 5. Engineering geology interpretation; 6. Geotechnical engineering analysis; and 7. Preparation of this report. BERLOGAR GEOTECHNICA/CONSULTANTS August 30, 1999 Job No. 1394.113 Page 2 Our findings regarding site, soil, geologic and ground water conditions are presented herein, together with our conclusions pertaining to expansion potential, settlements, cut and fill slope stability, landslide hazards, soils corrosivity and seismic hazards. This report presents recommendations for site development including: site preparation and grading, cut and fill slopes, landslide mitigation, subdrainage, foundation considerations, exterior flatwork, utility trenches, retaining walls and preliminary asphalt pavement design. The location of the Pao-Yeh Lin property in relationship to surrounding cultural features and landmarks is shown on the Vicinity Map, Plate 1. Regional geologic features are depicted on the Area Geologic Map, Plate 2. Site topography, predominant geologic features, and locations of our test pits and borings are included on the Geologic Map, Plate 3. Boring and test pit logs are included in Appendix A. Laboratory test results are presented in Appendix B except for moisture content and dry density test results which are included on the borings logs. The results of slope stability analysis are included in Appendix C. Logs of borings pertinent to the Pao-Yeh Lin property that were drilled as a part of a concurrent investigation for the Assessment District are included in Appendix D. The results of the soils corrosivity analysis are presented in Appendix E. PROPOSED DEVELOPMENT We understand that the site will be developed for a mixture of residential, commercial and office uses. A Preliminary Grading Layout by MacKay and Somps, dated October 30, 1998, indicates that grading in the northern half of the site will involve cuts and fill up to about 50 feet. Graded slopes higher than 10 feet are generally anticipated to have slope gradients of 3 horizontal to 1 vertical (3H:iV) or flatter, although some localized 2H:iV slopes are anticipated. Slopes less than 10 feet in height are planned to be no steeper than 2H: iV. Fills about 5 to 12 feet thick are planned in the relatively fiat southern half of the site. FINDINGS SITE DESCRIPTION The Pao-Yeh Lin property is a rectangular shaped parcel located on north side of Interstate 580 about 900 feet east of Tassajara Road , as shown on the attached Vicinity Map. The site is bounded by undeveloped open ranchland to the east and west. Land to the north is referred to as Phase 1 of Dublin Ranch and was sheet graded for development during the summer of 1998. The site is currently used for grazing. The site is topographically characterized by low rounded hills in the northern portion of the site and relatively flat ground in the southern half of the site as shown on Plate 3. The northern hills are incised with a stream course that drains to the south. Natural slopes are as steep as about BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 3 3 horizontal to 1 vertical (3H:iV) but generally are less than about 5H:IV. Elevations on site range from about 340 feet adjacent to Interstate 580, to about 500 feet near the northeast corner of the site. Vegetation is limited to grasses and weeds. An old ranch complex was previously located near the mouth of the drainage course in the north-central portion of the site. A stock pond is also located in the drainage course at the confluence of two swales. REGIONAL GEOLOGY AND SEISMICITY The site is situated in the central part of the Coast Ranges geomorphic province, which is characterized by a series of parallel, northwesterly-trending, folded and faulted mountain chains. In this part of the province, the gentle topography is underlain by nonmarine and marine sedimentary rocks deposited during the later Tertiary and/or the Quaternary period of geologic time, from about 7 million years before present to about 11 thousand years before present. The flat-lying areas appear to be covered by alluvial sediments deposited during the late Pleistocene and Holocene epoch of geologic time, about 40 thousand years before present to the present. The region has been folded and faulted as a result of tectonic forces generated during major uplift of the area beginning during the Pleistocene epoch. The site is not within a currently-designated State of California "Special Studies Zone" (1982) for the active faults. Two concealed, inferred faults shown on geologic maps covering the site were evaluated in our November 13, 1998 report. The Mocho Fault is mapped north of the proposed Gleason Drive (CDWR, 1966) and an unnamed fault is mapped along the base of the foothills north of Interstate 580 (Dibblee, 1980, Graymer, 1996). No evidence of the Mocho fault or a fault located along the base of the foothills north of Interstate 580 was found. Major active faults in the region that may influence the earthquake susceptibility of the site include the San Andreas, Hayward, Calaveras and Greenville faults located 30 miles, 11 miles, 4 miles, and 7 miles from the site, respectively (Bortugno, 1991). According to Peterson, et. al. (1996), maximum moment magnitude (Mw) estimated for the above faults is as follows: San Andreas (Peninsula Segment): 7.1; Hayward (Total Length): 7.1; Calaveras (north of Calaveras Reservoir): 6.8; Greenville: 6.9. Recent studies by Unruh and Sawyer (1997) postulate that the Mount Diablo Uplift is underlain at depth by a "blind" thrust fault system that may be capable of producing earthquakes of Mw 6.25 to 6.75. The distance from the site to the postulated blind thrust can not be accurately measured but could be in the range of 2 to 4 miles. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 4 SOILS AND BEDROCK CONDITIONS RESIDUAL SOILS Residual natural soils, derived by in-place weathering of the underlying parent bedrock, were encountered in test pits excavated on ridgelines and spur ridges on the northern portion of the site. The residual soils encountered consisted of dark gray and dark gray-brown silty clays (CL-CIt). The typical thickness of residual soil revealed by the test pits varied from about 2 to 4 feet. Laboratory test results indicate that the residual soils have moderate to high plasticity, and are considered highly expansive. COLLUVIAL DEPOSITS Colluvial deposits, generated by the downslope creeping of residual soils and/or their transportation by erosion, were revealed in test pits and borings in swales and valleys. Areas underlain by colluvium deposits are noted on the Geologic Map using the symbol "Qc". Where encountered in test pits and borings, the colluvial deposits were found to consist of dark gray to gray-brown silty clays (CL-CH) to depths ranging from 3 to 6 feet, overlying typically very stiff, dark brown silty and sandy clays (CL) to depths up to about 12 feet. A maximum of 20 feet of colluvium was encountered in Boring Bl-19. Laboratory test results indicate that the colluvial soils also have moderate to high plasticity, and are considered highly expansive. ALLUVIUM Alluvial deposits, material transported and deposited predominately by streams or flowing water, were revealed in test pits and borings in the southern portion of the site. Areas underlain by alluvium are noted on the Geologic Map using the symbol "Qal". Where encountered in test' pits and borings, the alluvial deposits were found to consist of dark gray-brown silty clay (CL-CH) to depths ranging from 3 to 6 feet, overlying a wide range of soil types. Below 3 to 6 feet, the alluvium encountered ranged from silty clay to silty sand with minor gravelly deposits. Laboratory test results indicate that the clayey alluvial soils have moderate to very high plasticity, and are considered highly expansive. LANDSLIDES Landslide mapping by Nilsen (1973) shows no landslides on the site. Mapping by Majmundar (1991) shows one possible landslide area in the northwestern part of the site. Eight test pits were excavated in the area questioned by Majmundar and no evidence of landsliding was encountered. Five suspected landslide areas were identified in our preliminary investigation. Based on examination of aerial photographs, site reconnaissance and subsurface exploration, two of these landslides are believed to exist. These two landslides are located in the northeastern portion of BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394:113 Page 5 the site as shown on the attached Geologic Map. The landslides have been classified as surficial, dormant landslides. No recently active or deep seated landslides were found on the site. Test pit exploration indicates that the surficial landslides range up to about 8 feet thick and contain slide debris consisting of silty clay and/or silty clay with some rock fragments and highly weathered bedrock. BEDROCK Bedrock on site is mapped as the Tassajara Formation by Dibblee (1980); a non-marine sedimentary rock. Portions of the site underlain at relatively shallow depths by bedrock are noted on the Geologic Map using the symbol "QTt". Bedrock encountered on site was found to consist of interbedded sandstone and siltstone, with minor interbedded claystone. In general, the bedrock was found to be poorly indurated, triable and thickly bedded. Bedding contacts observed were often gradational. Primary sedimentary features such as channel forms and cross bedding were numerous. Claystone, siltstone and silty to clayey sandstone beds were observed to be slightly cemented. Beds of well-sorted sandstone and conglomerate contained only trace amounts of silt and clay and were observed to be uncemented. These uncemented beds tended to cave where encountered in test pits and borings. Bedding attitudes strike typically northwest and dip predominantly to the southwest at inclinations of about 20 to 70 degrees. ARTIFICIAL FILL Two areas underlain by existing fill were observed on the site. An embankment for a stock pond is located in the valley in the northern portion of the site. Fill was also placed in the former ranch compound area located in the central portion of the site, GROUND WATER No free ground water was encountered in test pits during this phase of exploration. Seepage and phreatophytes (water seeking plants) were observed in the valley upstream of the stock pond located in the northern part of the site. Free ground water was encountered in borings at the following depths B1-4 23 feet, B1-5 23 feet, B1-6 24 feet, Bl-19 13 feet, B2-3 27 feet, B2-5 25 feet, B2-9 14 feet, B2-11 9 feet and B2-12 18 feet. The boring data indicates that ground water levels along the northern side of Highway 580 were about 23 to 25 feet below the ground surface at the time of our exploration. Ground water conditions should be expected to vary depending on variations in rainfall, irrigation, time of year, and perched ground water conditions. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 6 CONCLUSIONS AND RECOMMENDATIONS GENERAL From a geotechnical standpoint, the site is suitable for the proposed development provided the conclusions and recommendations contained in this report are incorporated into the project design and construction. The primary geotechnical issue affecting the proposed development is the predominance of expansive soils and mudstone bedrock materials at the site, which are susceptible to significant volume changes (swell and shrinkage) when subjected to variable moisture contents. Other geotechnical concerns addressed in this report include: stability of proposed cut and fill slopes, landslide hazards affecting the proposed development, foundation considerations, retaining wall design, preliminary pavement design, soils corrosivity and ground water. EXPANSION POTENTIAL As indicated by the results of the Atterberg Limits and single point consolidation/swell tests contained in Appendix B, the expansion potential of soil and bedrock materials at the site is highly variable, typically ranging from low to highly expansive. The degree of expansion of the on-site materials is a function of the following main factors: the type of soil and bedrock materials, and clay composition; the in-place moisture contents of the materials; the in-place density of the materials; and the overburden pressures or surcharge loads acting on the materials. The two main expansive material types at the site include: Expansive near-surface soil deposits consisting of residual soils, colluvium, landslide' debris and clayey alluvial soils; and 2. Mudstone bedrock units composed of interbedded siltstone and claystone. The on-site residual soils, colluvium, landslide debris and clayey alluvial soils are considered highly expansive when subject to changes in moisture content. The siltstone and claystone exhibit variable expansion characteristics ranging from medium to high, generally varying in expansion potential among individual beds of siltstone and claystone. Using the results of the single-point consolidation testing on remolded soil and bedrock materials, our estimate of the maximum swell of the fill placed and compacted following the requirements discussed in the "Site Preparation and Grading" section are estimated as follows: 1. At the flat land portion of the site - up to 3 inches 2. At the hilly portion of the site BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 7 Fill ThickneSs (Feet) ] Estin~ated MaXimUm. Fill Swell(inches) 5 [.5 10 1.5 15 2.5 20 3.0 25 3.8 30 4.5 35 5.3 40 5.9 45 6.4 50 6.8 The above-estimated preliminary swells provide a general picture of the swell potential in the fill areas. The actual swell in the fill areas depends strongly on the composition (type and amount) of fill, and in-place moisture content and density. To obtain a more reliable estimate of the fill swell, we recommend that a post-grading swell study be performed in the major fill areas. The post-grading swell study would involve drilling three to four borings at the major fill areas and obtaining undisturbed fill samples for Atterberg Limits and single point consolidation/swell tests. The borings would be extended to the bottom of the fill. The results of the post-grading swell study will aid in providing design-level foundation recommendations for the structures to be constructed in the fill areas. Based on the results of the multi-stage swell tests performed on undisturbed bedrock samples, up to about 2 to 3 inches of moisture-related swell is estimated in the cut areas. In general, the magnitude of swell will be related to the depth of cut and the relative expansiveness of the exposed bedrock. We also recommend that a post-grading swell study be performed in the major cut areas. The post,grading swell study would consist of drilling of three to four 30-foot borings in each major cut area and obtaining undisturbed bedrock samples for Atterberg Limits and single point swell tests. The results of the swell tests would be used to provide design-level foundation recommendations for structures to be located in the cut areas. SETTLEMENT The results of single-point consolidation testing on remolded soils and bedrock of the site are summarized in Appendix B. Based on these results, we estimate that on-site materials used as fill will undergo settlements during placement and for a duration following mass grading. The BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. i394.113 Page 8 total settlement of the fill placed and compacted following the requirements discussed in the "Site Preparation and Grading" section are estimated as follows: Fill ThiCknesS (Feet) Total Fill Settlement qndhes) i 5 0.5 10 1.5 15 2.5 20 3.5 25 4.5 3O 5.5 35 6.5 40 7.5 45 8.5 50 10.0 In-place colluvial deposits in deep fill areas are stiff to hard, and exhibit Iow to nominal compressibility characteristics. As such, provided the upper 2 to 3 feet of softened soils along swale bottoms are removed from these areas, we anticipate that the remaining stiff colluvium may generally be left in-place in fill areas. The colluvial deposits left in-place are anticipated to undergo limited settlements during fill placement and for a duration following mass grading. We estimate that potential settlements of the in-place colluvial material in the deeper fill areas could be on the order of 2- to 3-inches. Based on our experience, we anticipate that about 75 percent of the estimated total settlement of the fill and in-place colluvium should occur during mass grading. Post-grading long-term settlement is estimated to be up to 4-inches. The total and differential settlement at the site should be considered in the design of gravity underground utilities (such as storm drains and sanitary sewer lines) and surface drainage. The gravity underground utilities and surface drainage installed immediately after mass grading should be designed to accommodate the post-grading settlement. We recommend that 11/2 to 2 times the estimated post-grading long-term settlement be incorporated in the design of the storm drains and sanitary sewer lines. This recommendation is intended to result in the provision of additional gradient in gravity utilities and pavement surface; it is not intended to result in the use of special piping or special pipe joints. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 9 We recommend that the grading contractor install 3 settlement plates and 20 surface settlement markers in the deep fill areas to monitor the settlement characteristics of the deep fill. The settlement plates should be installed at about 5 feet below the finished rough grade and the surface settlement markers should be placed immediately after the completion of mass grading. We recommend that a surveyor be retained to survey the settlement plate and marker locations and elevations. Elevations of the settlement plates and markers should be measured every months during the first six months after their installation. The frequency future readings should be evaluated after the first 6 months readings have been evaluated. The data collected from the settlement plates and markers is expected to be useful for predicting post-grading long-term settlement of fills in developing foundation recommendations. LANDSLIDES Landslide A and B are located in an area of proposed cut that is expected to remove most of the landslide debris. Portions of these landslides not removed by the planned cuts should be removed and replaced with engineered fill. SITE pREPARATION AND GRADING All grading operations should be done in accordance with the following recommendations. These grading recommendations are intended for site sheet grading. We understand that pad grading will be performed prior to the house construction. The pad grading may change the thicknesses of fill or bedrock materials capping significantly and, as a result, may alter the settlement and/or swell characteristics of the sheet graded site discussed above. 1. Areas to be graded should be cleared and stripped of all vegetation. Stripping can be stockpiled and reused as topsoil. 2. The fills noted at the former ranch compound and the two mapped landslides should be removed in their entirety. 3. Backfill in test pits from this investigation should be removed and replaced with compacted fill except where the backfill will be removed by the planned cut. If the stock pond is to be removed, then the embankment fill and soft sediments in the pond bottom should also be removed in their entirety. 4. In the swale areas to receive fill, the upper 2 to 3 feet of the colluvium along the center line (about 20 feet wide) of the swale should be removed. 5. For cut/fill transitions, the residual soils and colluvium should be removed to a depth of not less than 5 feet but not more than 10 feet (below the proposed sheet grade) within 80 feet of the cut/fill transition. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 10 Zones of soft or saturated soils may be encountered during excavation and compaction; therefore, deeper excavation may be required to expose firm soil. This should be determined in the field by the soil engineer. The exposed surface in fill areas should be scarified to a minimum depth of 12 inches. The scarified materials should be properly moisture-conditioned and re-compacted as follows: Within the 20 feet of finished sheet grade At greater than 20 below finished sheet grade 84 to 88 percent relative compaction at not less than 5 percent above optimum moisture content. 88 to 92 percent relative compaction at not less than 5 percent above optimum moisture content 10. 11. 12. Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same soil, as determined by the ASTM D1557-91 compaction test method. Optimum moisture is the water content (percentage by dry weight) corresponding to the maximum dry density. In general, the on-site earth materials are considered acceptable for engineered fill, provided surface vegetation and all deleterious materials are removed Residual soils, colluvium and landslide debris may be used in engineered fills on site. The use of these materials as engineered fill within 10 feet of finished sheet grade should be limited to areas which are so designated on the grading plans. Areas designated to receive these materials will be determined by this office during preparation of the grading plans. Bedrock materials only (lighter color earth materials) should be used in the backfill of keyways from the base of the keyways to 15 feet above the base of the keyways. All fill and backfill materials should be subject to evaluation by the soil engineer prior to use. Fill should be placed in thin lifts (normally 8 to 12 inches thick), uniformly moisture conditioned and compacted (as one lift) to degrees indicated below. To avoid over-compaction of on-site expansive materials care should be taken during grading to minimize placement of thin lifts of expansive materials (less than about 8 inches). Modification to actual acceptable lift thickness should be based on demonstrated compaction performance during grading, which will depend on actual compaction equipment and methods used. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 11 l[Within the 20 feet of finished sheet grade At greater than 20 feet below finished sheet grade 84 to 88 percent relative compaction at not less than 5 percent above optimum moisture content. 88 to 92 percent relative compaction at not less than 5 percent above optimum moisture content 13. Keyway fill should be compacted to at least 90 percent at a moisture content of not less than 3 percent above optimum moisture content. 14. Where bedrock units are exposed in cut grades, these areas should be evaluated by the project geotechnical engineer for local variations of expansion among individual beds. Geologic mapping and laboratory testing should be performed in these areas. As deemed appropriate, additional recommendations for over-excavation and remedial grading would be developed in these areas during grading following evaluation. 15. Fill slopes should be overfilled and cut-back to expose a firm and compacted surface. 16. Observations and soil density tests should be carried on during grading to assist the contractor in obtaining the required degree of compaction and the proper moisture content Where compaction is less than required, additional compactive effort should be made with adjustment of the moisture content as necessary until the specified compaction is obtained. 17. The soil engineer should be notified at least 48 hours prior to any grading operation. The procedures and methods of grading may then be discussed between the owner, contractor and the soil engineer. This can facilitate the performance of grading operations and minimize possible construction delays. SHRINKAGE/SWELL FACTOR Based on the compaction test results for this investigation as well as those for mass grading of Dublin Ranch - Phase 1, on-site earth materials densities as encountered in the borings, and the compaction requirements outlined in the "Site Preparation and Grading" Section, we recommend that a Swell Factor of 5 to 10 percent be considered in the dirt quantity calculation. We understand that the remaining portion (Area A, Assessment District, Pao-Yeh Lin property and Areas B through E) of Dublin Ranch is to be graded in different phases. With the phased mass grading schedule, we strongly suggest that the cut and fill quantities of the early phases be tracked by the project civil engineer. This data can be used to refine and/or modify the preliminary swell factor presented above. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 12 CUT SLOPES We recommend that cut slopes be constructed at slope gradients no steeper than 3H: 1V, except for cut slopes less than about 10 feet in height which should be no steeper than 2H:IV. We recommend that all cut slope exposures be carefully examined by an engineering geologist for evidence of potential instability. Where cut slopes over 30 feet high are planned, intermediate benches spaced no greater than 25 feet vertically should be provided. Benches should be at least 8 feet wide and have a concrete lined V-ditch along the bench to intercept runoff. Subdrainage should be installed at the toe of major cut slopes as determined during our review of the grading plans. Following grading, cut slopes should be planted with deep-rooted, fast-growing vegetation prior to first winter to resist erosion. The stability of cut slopes is partially dependent on: 1) the orientation and location of the cut slope with respect to the structure of the bedrock; 2) the strength properties of materials comprising the cut slope; and 3) unknown adverse conditions (such as ground water, etc.), which could adversely affect the stability of the slope. We anticipate that cut slopes may expose the following adverse conditions in some areas of the site: 1) colluvium material exposed in cut slopes; and/or 2) bedrock materials showing adversely bedded rock structure in the slopes. 1. Colluvium Exposed in Cut Slopes - In general, areas where natural slope gradients are steeper than about 5H:iV colluvial deposits are considered susceptible to downslope creep and potential slope instability; ther.-~fore, where cut slopes are steeper than 5H: IV, colluvium exposures in cut slopes will warrant remedial treatment. This condition is likely to be encountered on the cut slope north of the proposed maintenance area. If conditions requiring remedial measures are encountered, o~ie of the following treatments would be appropriate to mitigate the conditions, as follows: Completely remove portion of colluvial deposits located adjacent to and upslope of the planned cut slope, to expose competent bedrock materials; or · Remove the colluvial deposits exposed in the cut slope area, and replace with engineered fill composed of bedrock materials, and install appropriate subdrainage and benching. 2. Cut Slopes in Bedrock Materials - The stability of cut slopes in bedrock materials is largely dependent on the planned cut location and the orientation of the cut slope with respect to the bedrock structure or other planes of geologic weakness. Bedrock structure on the site was found to be poorly developed with varied attitudes, but many bedding attitudes dipping to the south at inclinations of about 20 to 25 degrees were encountered. Bedding planes dipping at 20 degrees or steeper should not adversely impact cut slope stability; however, if areas of slightly flatter dips are exposed, adverse cut slope stability conditions could be a problem. We recommend that all cut slopes be carefully mapped during grading. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 13 Beds and lenses of uncemented sandstone were encountered during our exploration and will likely be exposed on cut slopes. These uncemented sandstone units are prone to erosion problems where exposed on cut slopes. In general, we recommend that cut slope areas exposing uncemented sandstone be overexcavated a minimum of 15 feet horizontally from the face of slope and the slope reconstructed with subdrainage and engineered fill. Specific remedial alternatives should be evaluated as cut slope conditions are exposed during grading. Where adverse bedrock structure or other zones of geologic weakness are encountered in cut slopes during grading, we anticipate that remedial measures such as flattening the slope, or construction of a slope buttress will be needed. Specific remedial alternatives shOuld be evaluated as cut slope conditions are exposed during grading. FILL SLOPES The stability of planned fill slopes depends on proper keyways and benching, subdrainage, fill compaction'and slope gradients. We understand that the proposed fill slopes will have maximum heights on the order of 30 feet. In general, fill slopes exceeding vertical heights of about 10 feet should be constructed at slope gradients no steeper than 3H:IV. Fill slopes less than about 10 feet in vertical height may be constructed at slope gradients up to 2H:iV, provided that these are constructed of predominantly bedrock materials. Fill slopes should generally be constructed in accordance with the recommendations shown on Plate 4. Keyways are recommended for all fill slopes to be placed on natural ground having a gradient of 7H: 1V or steeper. Generally, keyway width should be at least 15 feet, or one-half of the fill slope height, whichever is greater. Horizontal benches should be excavated into firm material or bedrock to key fill into native materials during slope construction. Fill slope' exceeding 30 feet in height should have intermediate benches spaced no greater than 30 feet vertically. Benches should be at least 8 feet wide with a concrete lined V-ditch to intercept runoff. Fill slopes should be planted with deep-rooted, fast growing vegetation prior to the first winter to reduce erosion. SUBDRAINAGE Seepage is expected to occur at the bottom of slopes, gullies, and at major cut slopes. recommend that subdrainage be provided in the following areas. At all springs and seepage areas; Along swales and gullies that receive fill; On the uphill side of all keyways; BERLOGAR GEOTECHNICAL CONSULTANTS We August 30, 1999 Job No. 1394.113 Page 14 4. At geologic contacts known to transmit seepage; In other areas of the site where seepage is observed during and after grading as determined by the soils engineer. Subdrains should consist of PVC perforated pipe conforming to ASTM Designation D 2751, Type SDR 23.5 for fill depths over 30 feet and Type SDR 35 for fill depths less than 30 feet and perforations should be placed down. Subdrains should be at least 6 inches in diameter. All subdrains should be surrounded by and be underlain by at least 6 inches of Class 2 "Permeable Material," as defined in Section 68-1.025 of the California Standard Specification (July, 1995). Subdrain trenches should be at least 18 inches wide and at least 4 feet deep. Final trench configurations should be approved by the soils engineer in the field. Subdrain trenches should be capped with engineered fill or topsoil, depending upon the subdrain location. Subdrains should be positioned along the upslope side of all keyway excavations. Subdrain details are presented on Plate 5. Subdrain systems should be discharged into storm drain structures where possible. Some areas of seepage may develop after grading and house construction are completed. Additional subdrains will likely be needed in these areas should seepage develop. FOUNDATION CONSIDERATIONS RESIDENTIAL STRUCTURES Because of the relatively significant long-term settlement and swell, it is judged that foundations for residential structures should consist of structurally reinforced mat systems designed to resist potential differential movement of the on-site expansive soils. The design criteria for mat' foundations should be developed based on the results of the post-grading swell studies of the fill and cut areas. For preliminary planning purposes, the following criteria may be used for estimating mat foundation systems: Structural mat foundations designed to accommodate an estimated 3 inches of differential movement over the length of the house (estimated to be about 60 feet), without experiencing: A. Structural distress to the mat; and B. Excessive deflections in the house framing and wall finishes. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 15 Structural mat foundations should be designed by a structural engineer for an allowable uniform soil pressure of 1000 psf. The resistance to lateral loading should be calculated using a base friction factor 0.3 acting between the slab subgrade. It is anticipated that additional measures would be required such as: 1) capping building areas with low expansive materials, or 2) pre-soaking surface expansive soils to at least seven percent above optimum moisture content extending at least 18 inches below the bottom of the mat subgrades, prior to mat construction. It may be necessary to revise the design criteria presented above if the collected settlement data and the results of the post-grading swell studies show that the fill settles or swells significantly different from our estimated settlements and swells. COMMERCIAL AND OFFICE STRUCTURES These structures will likely be supported on either shallow spread footings or deep foundations (either driven piles or cast-in-place driller piers). Such foundation systems will likely require a non-expansive imported fill cap several feet thick over the expansive on-site materials. EXTERIOR FLATWORK It is our opinion that, from a geotechnical engineering standpoint, exterior concrete flatwork can be supported directly on prepared subgrade. Flatwork placed upon on-site expansive ~naterials will be subject to movement due to soil expansion. From a cost-benefit standpoint, exterior concrete flatwork subgrades exposing expansive soils should be moisture conditioned to at least 5 percent above optimum moisture content to a depth of at least 12 inches to induce some soil expansion prior to placement of concrete; thus reducing the amount of post-construction soil expansion. Also, the exterior concrete work subgrades should not be subject to heavy' construction traffic because it may be overcompacted by these vehicles. UTILITY TRENCHES All excavations should conform to applicable State and Federal industrial safety requirements. Where trench excavations are more than 5 feet deep, they should be slopes and/or shored. Trench walls should be sloped no steeper than 11/2H: 1V in dry granular soils, and no steeper than iH:IV in dry, cohesive soils. Flatter trench slopes may be required if seepage is encountered during construction or if exposed soil conditions differ from those encountered by the test borings. If full-sloped trench walls cannot be excavated due to site constraints, shoring should be provided to ensure trench stability and safety. We will provide soil parameters for shoring design on request. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 16 Materials quality, placement procedures and compaction operations for utility line bedding and shading materials should meet the City of Dublin and/or other applicable agency requirements. Utility trench backfill above the shading materials may consist of native soils, processed to remove rubble, rock fragments over 8 inches in largest dimension, rubbish, vegetation and other undesirable substances. On-site expansive backfill materials should be placed in level lifts about 8 to 12 inches in loose thickness, brought to at least five percent over optimum moisture content and mechanically compacted to between 84 and 88 percent relative compaction at depths below 30 inches of finished grade and not less than 90 percent in the upper 30 inches. Low expansive backfill materials should be placed in lifts not exceeding 8 inches in loose thickness, brought to near optimum moisture content and compacted to not less than 90 percent relative compaction. No jetting is permissible on this project. Depending on time of year, rainfall and local irrigation practice, ground water could be intercepted during trench excavation in which case dewatering is likely to be required. RETAINING WALLS The retaining walls can be supported on footing foundation founded on engineered fill or firm native soils or bedrock. We recommend that the following geotechnical criteria be incorporated in the retaining wall design: Active equivalent fluid pressure Level backfill 3H: 1V backfill 2H: 1V backfill 45 pcf 55 pcf 65 pcf Allowable bearing capacity 2000 psf Passive equivalent fluid pressure 350 pcf Friction coefficient 0.35 Minimum footing depth 18 inches below the lowest adjacent grade 18 inches Minimum footing width The above recommended lateral pressures are based on drained condition and do not include any surcharges. Therefore, the designer should include the appropriate surcharge loads to the retaining wall design. To prevent hydrostatic pressure build-up, the retaining walls should be provided with permanent backdrains. The backdrain should consist of a blanket of Class 2 permeable material (conforming to Section 68.1025 of the State of California Standard Specifications, dated July, 1995) and a 4-inch diameter perforated PVC pipe (SDR 35). The permeable material blanket should be at least 12 inches thick and should be placed from the base of the retaining wall to BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 17 about 1 foot below the finished grade of the top of the retaining wall. The perforated pipe should be placed near the bottom of the wall to carry collected water to a suitable gravity discharge. PRELIMINARY PAVEMENT SECTIONS The following recommendations for preliminary asphalt concrete pavement sections are intended as a conceptual guide for planning only. Pavement analyses are based upon an assumed resistance (R)-value of 5, which we expect to be representative of final pavement subgrade materials, the Caltrans "Design Method for Flexible Pavement," and traffic indices ("T.I."'s) which are indications of load frequency and intensity. We have assumed that the assigned "T.I.s' include provisions for heavy truck traffic related to construction activities. We recommend the following preliminary pavement sections. Traffic Index (T.I.) 4 % Thickness Asphalt Concrete Type B 3* gq< inches) Aggregate Base Class 2 7 9 10 5% 3 12 6 3 14 6% 31/l 15 7 4 16 4% 71/l 81/l 4% 5 18 19 2O Note: * = Minimum asphalt concrete thickness required by the City of Dublin. Prior to subgrade preparation, all utility trench backfill should be properly placed and compacted. Subgrade soils should be rolled to at least 95 percent relative compaction to provide a smooth, ~ surface. Subgrade soils should be maintained in a moist and compacted condition until covered with the complete pavement section. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 18 Class 2 aggregate base should conform to the requirements in Section 26, Caltrans "Standard Specifications", (July, 1995). The aggregate base should be placed in thin lifts in a manner to prevent segregation, uniformly moisture conditioned, and compacted to at least 95 percent relative compaction to provide a smooth, unyielding surface. (Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same soil, as determined by the ASTM D1557-91 compaction test method). Since this is a relatively large grading project and the on-site material properties vary from sandstone to clayey materials, we recommend that samples be obtained from the rough roadway subgrades after mass grading. Resistance R-Value test should be performed on these samples. Final pavement section recommendations should be made on the basis of these test results. '17o prevent the subgrade soils and aggregate base from saturating by irrigation water or infiltrated rain water, roadway underdrains should be installed at the bottom of the aggregate and below the curb and gutter as shown on Plate 6. Where drop inlets or other surface drainage structures are to be installed, slots or weep holes should be provided to allow free drainage of the contiguous base course materials. CORROSION CONSIDERATIONS The soils corrosivity analysis results (including those from Area A, Assessment District and Areas B through E) presented in Appendix E shown that the residual soils, colluvium, slide debris and bedrock have conductivities ranging from 190 to 360 urnho-cm and the alluvial soils (located on the flat land portion of the site) have conductivities of 700 to 1,000 umh0-cm. Based on the conductivity, the residual soils, colluvium, slide debris and bedrock are classified as "moderately corrosive" while the alluvial soils are classified as "corrosive" to severely' corrosive" to buried metallic pipes and structures. Chloride concentration of 360 to 900 mg/kg were measured in several alluvial soil samples obtained along Interstate 580 and are found to be sufficient to attack steel embedded in concrete or cement mortar coating. In general, relatively low concentrations of sulfate ion (ranging from less than 30 to 50 mg/kg) were detected in all the on-site earth materials and are determined to be insufficient to damage reinforced concrete structures and cement mortar coating. Appropriate corrosion control measures or protection should be considered for the buried metallic pipes and structures, and steel embedded in concrete or cement mortar coating. Commonly used control measures include: 1. Low water/cement ratio concrete; 2. Fly ash additive in concrete; 3. Epoxy coated rebars; 4. Increased concrete cover or cement mortar coating on the rebar; BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 19 Use of non-metal piping; ,Apply protective coatiug to underground metallic pipes; and/or Cathodic protection. SEISMIC HAZARDS FAULTING The site is located outside designated State of California "Special Studies Zones" (1982) for active faulting and no evidence of active or potentially active faulting was found on the site. The potential for fault rupture at the site appears to be low. GROUND SHAKING The site is located in a region of high seismicity given the proximity of the Calaveras fault and other active fault systems in the bay area. As for all sites in the Bay Area, the project can be expected to experience at least one moderate to severe earthquake during the lifespan of the project. Ground shaking is a hazard that can not be eliminated but can be partially mitigated through proper attention to seismic structural design and observance of good construction practices. Analyses by the Association of Bay Area Governments (ABAG, 1988) indicates that the site may be subject to "violent" ground shaking from a major earthquake on the Calaveras fault. Probabilistic seismic hazard analysis by CDMG (Petersen, 1996) indicates that the ground acceleration at the site with a 10 percent chance of exceedance in 50 years is 0.7g. LIQUEFACTION Liquefaction is the temporary transformation of a saturated, cohesionless soil into a viscous liquid during strong ground shaking from a major earthquake. There is no evidence of historic ground failure due to liquefaction on the site, nor did we encountered any earth materials which might be susceptible to liquefaction. Therefore, the risk of liquefaction is believed to be low. LURCHING Lurching is the sudden swaying, spreading or rolling of the ground during a strong earthquake. Lurching usually is accompanied by the development of fissures on slopes overlain by weak soils. Grading in conformance with the recommendations presented in this report should reduce the risk of lurching to low. BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 20 GROUND SUBSIDENCE Ground subsidence can occur as a result of "shakedown" when dry, cohesionless soils are subjected to earthquake vibrations of high amplitude. In general, significant deposits of loose sandy soils do not exist at the site; therefore, seismic induced ground subsidence is not considered a geologic hazard on the property'. EARTHQUAKEqNDUCED LANDSLIDING Strong ground shaking during a major earthquake is likely to cause sympathetic reactivation of landslides in many parts of the bay area. The stability of all slopes is lower during earthquake disturbances than at other times. Grading in accordance with the recommendations in this report should reduce the risk of seismically induced landslides to low. L1NIITATIONS The conclusions and recommendations of this report are based upon the information provided to us regarding the proposed improvements, subsurface encountered at the test pit and boring locations, our geologic reconnaissance, the results of the laboratory testing program and professional judgment. This study has been conducted in accordance with current professional geotechnical engineering and engineering geologic standards; no other warranty is expressed or implied. The locations of the test pits and borings were determined by pacing from established cultural features and other points of reference indicated on the drawing supplied by MacKay & Somps, Inc., and should be considered approximate only. The elevations of the borings and other elevations discussed in the text of this report were determined by interpolation between nearest adjacent ground surface contours shown on topographic maps supplied by MacKay & Somps, Inc., and should also be considered approximate only. Site conditions described in the test are those existing at the time of our last field exploration and reconnaissance during January of 1999, and are not necessarily representative of such conditions at other locations and times. If it is found during construction that subsurface conditions differ from those described on the test pit and boring logs then the conclusions and recommendations in this report shall be considered invalid, unless the changes are reviewed and the conclusions and recommendations modified or approved in writing. Our firm should be accorded the opportunity to review the final plans and specifications to determine if the recommendations of this report have been implemented in those documents. The review would be acknowledged in writing. Field observation and testing services are essential and integral parts of this geotechnical investigation. Our firm should be retained to monitor the BERLOGAR GEOTECHNICAL CONSULTANTS August 30, 1999 Job No. 1394.113 Page 21 earthwork and other relevant construction operations; the recommendations of this report are contingent upon this stipulation. Respectfully submitted, BERLOGAR GEOTECHNICAL CONSULTANt/t ,/ ~ iZ~ ~rincipal Engineer~ Principal Geologist [[,~ ~ CEG 1239 ~7~~5//~¢) ~E 2326, Exp. 12/31/99 ~ RPS/PSL/FB:pv Attachments: References Plate 1 - Vicinity Map Plate 2 - Area Geologic Map Plate 3 - Geologic Map Plate 4 - Fill Slope Detail Plate 5 - Typical Subdrain Details Plate 6 - Below Curb and Gutter Subdrain Detail Appendix A - Boring and Test Pit Logs Appendix B - Laboratory Test Results' Appendix C - Slope Stability Analyses Appendix D - Assessment District Boring Logs Appendix E - Soils Corrosivity Analysis Results Copies: Mr. Ted Fairfield (1) MacKay & SOmps, Inc. (7) Attention: Mr. Jim Templeton wp51/report/7600 BERLOGAR GEOTECHNICAL CONSULTANTS REFERENCES Publications: Berlogar Ge(~technical Consultants. May 23, 1988, Preliminary Geotechnical Report, Dublin Ranch, Tassajara Road, Dublin California, unpublished report. .... February 24, 1988, Report, Mocho Fault Investigation, Dublin Ranch, Pappas and Fallon Business park Properties, Dublin California, unpublished report. .... June 19, 1995, Geoteclmical Investigation, Dublin Ranch - Phase 1, Dublin, California, unpublished report. .... June 12, 1997, Supplemental Geotechnical Investigation, Fallon Road Extension, Dublin Ranch, Dublin, California, unpublished report. .... November 13, 1998, Preliminary Geologic and Geotechnical Investigation, November 13, 1998, Pao-Yeh/Lin Property, Tassajara Road, Dublin, California, unpublished report. Borcherdt, R.D, Editor, 1974, "Studies for Seismic Zonation of the San Francisco Bay Region", U.S. Geological Survey Professional Paper 941-A. Borcherdt, R.D., Gibbs, J.F., and Lajoie, F.R., 1975, "Maps Showing Maximum Earthquake Intensity Predicted in the Southern San Francisco Bay Region, California, for Large Earthquakes on the San Andreas and Hayward Faults", U.S. Geological Survey Miscellaneous Field Studies Map MF-709. Crane, R.C., 1988, Geologic Map of the Livermore Quadrangle, Alameda and Contra Costa Counties, California, unpublished map. Dibblee, T.W., 1980, "Preliminary Geologic Map of the Dublin Quadrangle, Alameda and Contra Costa Counties, California", U.S. Geological Survey Open-File Report 80-537. ..., 1980, "Preliminary Geologic Map of the Livermore Quadrangle, Alameda and Contra Costa Counties, California", U.S. Geological Survey Open-File Report 80-533B. Graymer, R.W., Jones, D.L., Brabb, E.E, 1996, Preliminary Geologic Map Emphasizing Bedrock Formations in Alameda County, California: Digital Database, U.S Geological Survey Open file Report 96-252. Helley, E.J., Lajoie, K.R., and Burke, D.B., 1972, "Geologic Map of late Cenozoic Deposits, Alameda County, California", U.S. Geological Survey Miscellaneous Field Studies Map MF-429. BERLOGAR GEOTECHNICAL CONSULTANTS REFERENCES Publications' (continued) Helley, E.J., and Graymer, R.W, 1997, Quaternary' Geology of Alameda County and Surrounding Areas, California: Derived from the Digital Database, USGS Open-File 97 -97. Jennings, C.W., 1975, "Fault Map of California, with Locations of Volcanoes, Thermal Springs, and Thermal Wells', California DMsion of Mines and Geology Geologic Data Map Series Map No. 1. Majmundar, H.H., 1991, "Landslide Hazard in the Livermore Valley and Vicinity, Alameda County and Contra Costa Counties, California", CDMG Open File Report 91-2. Nilsen, T.H., 1973, "Preliminary Photointerpretation Map of Landslide and Other Surficial Deposits of the Livermore and Part of the Hayward 15-Minute Quadrangles, Alameda and Contra Costa Counties, California", U.S. Geological Survey Miscellaneous Field Studies Map MF-493~ Peterson, M~, et al, 1996, California Fault Parameters, San Francisco Bay Area Faults, www. consrv, ca. gov/dmg/shexp, html. State of California, California Division of Mines and Geology, 1.982, "Special Studies Zones, Livermore 7.5 Minute Quadrangle." .... California Division of Mines and Geology, 1982, "Special Studies Zones, Dublin 7.5 Minute Quadrangle. Unruh, J.R., and Sawyer, T.L., 1997, "Assessment of Blind Seismogneic Sources, Livermore Valley, Eastern San Francisco Bay Region, Final Technical Report, unpublished. U.S. Geological Survey, 1980, "Dublin 7.5-Minute Topographic Quadrangle"~ 80, "Livermore 7.5-Minute Topographic Quadrangle". Aerial Photographs' Pacific Aerial Surveys, date of photography: September 21, 1973; scale: 1:20,000; Flight Line 1, Panels 97-99. BERLOGAR GEOTECHNICAL CONSULTANTS SCAL'E: 1"= 2000' VICINITY MAP DUBLIN RANCH - PAO YEH LIN PROPERTY TASSAJARA ROAD DUBLIN, CALIFORNIA FOR MS. JENNIFER LIN BASE: PORTION OF U.8,G.8. 7.5 MINUTE TOPOGRAPHIC QUADRANGLE,DUBLIN & UVERMORE, CALIFORNIA, PHOTOREVISED 1980, AT A SCALE OF 1:24,000. BERLOGAR GEOTECHNICAL CONSULTANTS PLATE 1 Z o SCALE: 1"= 2000' EXPLANATION GEOLOGIC CONTACT Qa ALLUVIUM 851 STRIKE AND DIP OF BEDDING QTt TASSAJARA FORMATION AREA GEOLOGIC MAP DUBLIN RANCH - PAO YEH LIN PROPERTY TASSAJARA ROAD DUBLIN, CALIFORNIA FOR MS. JENNIFER LIN BASE: PORTIONS OF PRELIMINARY GEOLOGIC MAPS OF THE DUBLIN AND UVERMORE QUADRANGLES, CALIFORNIA, BY T.W. DIBBLEE, DATED 1980, AT A SCALE OF 1 ;24,000, BERLOGAR GEOTECHNICAL CONSULTANTS P~TE2