Dingee Reservoir Final Seismic Report - East Bay Municipal Utility ...

advanced using a hollow stem auger. Borings XV-12 and XV-14 were advanced using rotary
wash drilling to reduce sample disturbance and stabilize the boreholes. The borings were drilled
to a maximum depth of 50 feet below the existing ground surface through the dam fill and into
the foundation materials.
The subsurface materials were logged in the field by a District Materials Testing Technician,
under the review and direction of the project manager. Samples for visual classification and
laboratory index testing were obtained using a California (CAL) split-barrel sampler (3-inch
outside diameter and 2.44-inch inside diameter). The CAL sampler was used in accordance with
the American Society for Testing and Materials (ASTM) Method D 1586. The CAL sampler
was driven 18 inches into the subsurface materials with a 140-pound automatic hammer falling
30 inches. The penetration resistance (blow counts), measured in number of hammer blows to
advance the sampler the final 12 inches (or a fraction thereof) of the 18-inch drive, were added
and shown on the boring logs at the appropriate sample depth.
Relatively undisturbed samples were obtained by using 36-inch long, thin-walled Pitcher tubes
coated with resin (3-inch outside diameter with 0.065-inch wall thickness). The Pitcher tubes
were used in accordance with the ASTM Method D 1587. The Pitcher tubes were advanced by
steadily applying both hydraulic pressure and by rotary drilling appropriate to the resistance of
the soil and rock.
After careful withdrawal from the ground, the samples were visually inspected. Selected
samples for index testing obtained with the CAL sampler were capped, taped, labeled, and
transported in a padded box. The Pitcher tube samples were carefully placed upright, sealed with
plastic caps, taped, and cleaned of disturbed soil at the ends of each tube.
Field data and laboratory test results were used to classify the subsurface materials and to
prepare boring logs that are presented in Appendix A. The boring logs include a visual
classification of the soils based on the Unified Soil Classification System; an estimate of the
relative density of cohesionless soils or consistency of fine-grained soils based on the blow
counts; color, plasticity and moisture content. The laboratory test results for density, moisture
content, Atterberg limits, fines content, clay content, specific gravity and triaxial compression,
are included on the boring logs at the appropriate sample depth. The complete summary of the
laboratory test results is included in Appendix B.
At the completion of each borehole, the hole was backfilled with five-sack cement grout using a
tremie pipe. The field technician observed the grouting process. Drill cuttings and fluids
generated during drilling were temporarily stored on site in 55-gallon drums which were later
delivered to Republic Services Inc. in Livermore, California for disposal according to applicable
local, state, and federal regulations.
3.2.3 Dam Surveillance Instrumentation
Existing Piezometers
The existing piezometers at the project dam site are the open well type, and are monitored
monthly. No new piezometers were installed at the site during this investigation. The most
Seismic Stability Evaluation Report
Dingee Reservoir Dam
7
August 2008