SR 06:060 - Laserfiche WebLink

Ms. Kerry Sinnott 3909 Vineyard Avenue 10 November 2005 Page 3 TreadwelI&RoIIo FIELD INVESTIGATION Prior.to performing our field investigation, we obtained an exploratory boring permit from the Zone 7 Water Agency. Furthermore, we notified Underground Service Alert to check that locations of exploratory pomts were clear of existing utilities, To evaluate the subsurface conditions for the creek slope we supplemented the existing geoteclmical borings and Cone Penetration Tests (CPTs) by performing one additional CPT near the crest of the slope, Locations ofthe Borings and CPTs are presented on Figure 1. The CPT extended to a depth of 50 feet below ground surface. The CPT was performed on 7 September 2005 by Gregg In Situ, Inc. of Martinez; using truck- mounted equipment, under the'direction of our engineer. The CPT log, which shows tip resistance and friction ratio with depth, as well as intelpreted undrained shear strength, is presented on Figure 3. Soil descriptions, as determined from the CPT, were defined in . accordance with. the chart presented on Figure 4. The CPT Was performed by hydraulically pushing a 1.4-inch-diameter (10 square centimeters), cone-tipped probe into the ground. The cone on the end of the probe is equipped to measure tip resistance, and the sleeve behirid the cone tip measUres frictional resistance, Electrical strain gauges within the cone measure soil parameters continuously for the entire depth advanced. Penetration data are transferred to a computer and processed to provide engineering information, such as the type of soil encountered and its approximate strength characteristics. The CPT was backfilled with cement grout after completion. SUBSURFACE CONDITIONS Borings and CPTs from our subsurface investigation encountered alluvial deposits consisting primarily of silts and clays with varying amounts of sand and gravel, interbedded with sand lenses. A geologic map of the Livermore Quadrangle indicates the site is underlain by two geologic units (Dibble, 1980). The southern portion of the site is underlain by older Pleistocene gravels (Qg). This material consists of stiff to hard silts and dense to very dense sand and gravel throughout the depths explored. The northern portion of the site is underlain by younger alluvium (Qa). This deposit consists of stiff silt with low plasticity. Near the crest of the creek slope this deposit is about 14 feet deep. Laboratory tests indicate the silt will collapse under load when it is saturated. The younger alluvium is underlain by stiff to hard silt and clay with varying amounts ofsand and gravel associated with the Pleistocene gravels. Groundwater was not encountered in the borings or CPTs performed at the site, The groundwater beneath the site likely corresponds to the water level ofthe creek, measured