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

Based on our above evaluations of the Dam fill and native materials, we do not anticipate that the
onsite materials will undergo liquefaction or significant strength loss during seismic loading.
6.4 Shear Strength
To estimate the shear strength of fill, native, and sandstone bedrock materials, three types of
testing were conducted:
1. Isotropically consolidated undrained (ICU) triaxial compression test with pore pressure
measurement.
2. Unconsolidated consolidated (UU) triaxial compression test.
3. Direct Shear Test (DS).
In general, the results of the ICU tests provided the most appropriate results and were most
suitable for use in the analysis. UU and DS tests were also considered; however, due to the
larger scatter in the results, these were not used. Direct shear test results were conducted mostly
on the fill materials. Results from the ICU tests were used in developing shear strength
parameters for the fill, native materials, and sandstone bedrock.
6.4.1 Effective Shear Strength Failure Envelope
The static shear strengths of the dam fill and foundation materials were estimated using
Isotropically Consolidated Undrained (ICU) Triaxial Compression tests with pore water pressure
measurements. Plates 12, 13, and 14 show the effective strength failure envelope for the dam
fill, native material, and sandstone bedrock, respectively. The effective material strength
parameters used in the analysis are shown in Table 4A.
Material
Table 4A: Effective Shear Strength Parameters
Moist
Unit
Weight m
(pcf)
Cohesion
Intercept c’
(psf)
Friction
Angle’
(degree)
Ref. Plate
No.
Dam Fill 126.8 172 29.0 12
Native Materials 127.3 616 13.0 13
Sandstone Bedrock 132.2 1223 19.9 14
6.4.2 Total Shear Strength Failure Envelope
For the seismic (pseudo-dynamic) analysis, undrained shear strength was used. For this study,
we used the static total strength parameters from the ICU tests. Plates 15, 16, and 17 show the
total strength failure envelope for the dam fills materials, native materials, and weathered
bedrock, respectively. The total material strength parameters used in the analysis are shown in
Table 4B. Results of the ICU triaxial tests are summarized in Table B-3 in Appendix B.
Seismic Stability Evaluation Report
Dingee Reservoir Dam
14
August 2008