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• `..� off' a GEOTECHNICAL REPORT Lower Sacramento Road/UPRR Underpass ? and Bear Creek Bridge Replacement BCI Job No. 879.5 Stockton, California May 7, 2010 During the late Mesozoic and through most of Tertiary time (approximately 100 million to 20 million years before present), deposition of thousands of feet of marine sediments occurred- within ccurredwithin the Great Valley. Continental deposits (generally alluvium) of late Tertiary and Quaternary age (approximately 20 million years ago to the present) overlie these marine deposits. Both the continental deposits and the underlying marine sediments form a wedge of sediments that generally thickens from east to west. 2.2 Local Geology The California Geologic Survey(CGS)' maps surface materials within the project limits as upper and lower members of the Pleistocene Modesto Formation. Both upper and lower members of this formation consist of unconsolidated gravel, sand, silt, and clay. The upper member is mapped east of the UPRR tracks; the lower member is mapped west of the UPRR tracks. 3 SUBSURFACE CONDITIONS For the preliminary phase, BCI retained V&W Drilling to drill and sample one exploratory boring (132-06)near the UPRR tracks on September 8, 2006 to a depth of 81.5 feet. For the design phase, BCI retained V&W Drilling and Precision Drilling to drill eleven additional borings (B1-08 through B11-08)between March 19, 2008 to May 5, 2008 to depths of 3 feet to 10 1.5 feet to further characterize the subsurface conditions and obtain additional samples for laboratory testing. The drillers used 6-inch and 8-inch diameter hollow stem auger and mud rotary drilling methods to advance the borings. BCI obtained relatively undisturbed soil samples at various intervals using either a Standard Penetration Test(SPT) Sampler or 3-inch O.D. Modified California Sampler(equipped with 2.5- inch O.D. brass liners). These samplers were driven into the ground by the force of a 140-pound auto-trip hammer falling approximately 30 inches. We sealed the sample liners with plastic caps and placed disturbed samples from the SPT sampler in sealed plastic bags. We also obtained bulk soil samples from the auger cuttings. BCI installed a piezometer casing in Boring B7-08 (located near the UPRR tracks). We installed the screened interval in the lowermost 20 feet of the boring between 36.5 feet and 56.5 feet below ground surface (between elev.-18.5 and elev.-38.5). 3.1 Soil Conditions In general, soils consist of stiff-very stiff to hard sandy silt, clay with sand, and sandy clay interlayered with layers of medium dense to very dense (locally loose) clayey/silty sand, sand, and sand with gravel and sand to the maximum depth explored (101.5 feet, elev.-82.9). Refer to the LOTB drawings in Appendix A for soil descriptions, exploration details and sampling methods. Appendix B contains the LOTB drawings for the Lower Sacramento Road Underpass and Bear Creek Bridge. ' "Geologic Map of the Sacramento Quadrangle,California";Regional Geologic Map Series;Map No. IA; California Division of Mines and Geology;D.L.Wagner,C.W.Jennings,T.L.Bedrossian,and E.J.Bortugno; 1991 4