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

Native Material
The in-situ moisture contents of the native materials varied from 15.3% to 28.9%, with an
average of 19.3% and standard deviation of 3.1%. In-place dry unit weights of the native
materials ranged from 97.3 to 117.5 pcf, with an average of 109.9 pcf and standard deviation of
5.0 pcf. The average void ratio and degree of saturation are 0.5 and 95.3 %, respectively.
Sandstone Bedrock / Franciscan Assemblage
The in-situ moisture contents of the Sandstone Bedrock / Franciscan Assemblage varied from
15.2% to 34.6%, with an average of 27.4% and a standard deviation of 5.9%. In-place dry unit
weights of the Formation ranged from 83.8 to 120.0 pcf, with an average of 97.1 pcf and a
standard deviation of 10.2 pcf. The average void ratio and degree of saturation are 0.8 and 99%,
respectively. Table 3 below summarizes these averaged properties.
Table 3: Average of the Index Test Results
MC %
Total
Density
(PCF)
Dry Density
(PCF)
Void Ratio
Saturation
(%)
Specific
Gravity
Dam Fill 18.7 126.8 106.8 0.55 90.5 2.65
Native Materials 21.2 127.3 105.0 0.60 94.7 2.70
Sandstone
Bedrock
18.0 132.2 112.0 0.49 98.6 2.67
Based upon review of the laboratory testing results, the native materials are expected to exhibit
shear strength properties lower than the dam fill materials. Plates 8 through 11 show the
variation of moisture content and total unit weight of the materials encountered in the borings
XV-1 through XV-15.
6.3 Liquefaction Potential/Loss of Shear Strength
Plate 7 and Plate B-2 in Appendix B show the results of the Atterberg limits tests. Data points
shown on this plate indicate that the materials fall under the CL (lean clay) and CH (fat clay)
classification. Table B-2 in Appendix B includes results of the Atterberg limits tests and the insitu
moisture content of the samples tested. The plasticity chart also shows three zones: A, B,
and C. According to Seed (2003), soils in these zones are defined as follows:
Zone A:
Zone B:
Zone C:
Considered potentially susceptible to classic cyclically induced liquefaction.
In some cases, can be susceptible to liquefaction (especially if their in-situ water
content is greater than about 85 % of their liquid limit).
Generally not susceptible to cyclically induced liquefaction.
Table B-2 in Appendix B includes results of the Atterberg limits tests and the in-situ moisture
content of the sample tested. Boring number, sample number, and elevation of the sample have
also been provided. As the table indicates, of all the samples tested, none are susceptible to
liquefaction.
Seismic Stability Evaluation Report
Dingee Reservoir Dam
13
August 2008