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

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856 Seaview Drive PACIFIC ENGINEERING and ANALYSIS El Cerrito, CA 94530 (510) 528-2821 Fax 528-2135 pacificengineering@juno.com August 1, 2008 Dona Mann, C.E. Senior Engineer Alan Kropp & Associates 2140 Shattuck Ave., Berkeley, CA 94704 RE: DINGEE Project Dear Miss Mann, Following your request we have developed a horizontal component deterministic design response spectrum (5% damped) at the 84 th percentile and three spectrally matched time histories for embankment analyses at the Dingee Dam. The Dingee Reservoir is located in Piedmont, California (37.8295 o , -122.2176) 0.3 km west of the Hayward fault and over 20 km east of the San Andreas fault. To assess controlling earthquake sources, since the Dingee Dam is quite small with an average height of about 20 ft, the deaggregation of the recent USGS National Hazard Maps was examined at peak acceleration (e.g. about 30 Hz) as well as 1.0 Hz. This frequency range was taken to cover the frequency range of dominant response of the dam and clearly showed the Hayward fault as the controlling source. The deterministic MCE is considered to rupture the entire Hayward - Rogers Creek system with a magnitude of M 7.25 (Hanks and Bakun, 2002). Dingee Dam rests on a few feet of native soils overlying sandstone bedrock. For the planned analyses of the embankment, ground motions were computed for a soft rock outcrop site. Based on an analysis of values at rock sites which have recorded strong ground motions, a typical V S (30m) value for soft rock is about 600m/sec (Silva et al., 1999). While measured shear-wave velocities at the site were not available, nearby Estates Dam, about 0.25 km (800 ft) southeast from Dingee Dam, had suspension log profiles from two boreholes that penetrate into shallow bedrock (URS, 2006). Based on these suspension surveys, depth to 1 km/sec material is estimated to occur at about 5m (15 ft) at the Dingee Dam site. 1
The next Generation Attenuation relations (NGA, 2008) developed by Abrahamson and Silva, Boore and Atkinson, Campbell and Bozorgnia, and Chiou and Youngs were used to compute estimates of median plus 1-sigma ground motions. These four relations were selected as they have characterized site conditions in terms of V S (30m) in a consistent manner. Additionally, several of the relations have included depth to 1 km/sec (or 2.5 km/sec) material as independent variables to more accurately characterize strong ground motions at sites with shallow depths to bedrock materials, as occurs at Dingee Dam. The NGA relations (NGA, 2008) provide median as well as median plus 1 standard deviation estimates of 5% damped pseudo absolute response spectra over the period range of 0.01 sec to 10.00 sec. The estimates are for an average horizontal component termed GM roti which was developed to be independent of orientation of the horizontal component (NGA, 2008) and very closely reflects a geometrical average horizontal component. Figure 1 compares median plus 1 sigma estimates computed with the four selected relations for M 7.25 at a rupture distance of 0.3 km, a V S (30m) of 600 m/sec, and depth to 1 km/sec material of 5m. Also shown is the weighted average (log average) spectrum (Table 1), assuming equal weights. It should be noted the range in 84 th percentile estimate (epistemic variability) is not large and may be underestimated as a result of the close cooperation between the NGA developers. This consideration typically does not impact deterministic assessments of 84 th percentile motions as it is usually neglected in the averaging process. For probabilistic hazard analyses, the lack of adequate epistemic variability for source and site location conditions poorly reflected in the strong motion database can result in motions at a higher exceedence frequency than desired. In computing the average (log) median plus 1 sigma spectrum shown in Figure 1, the epistemic variability (differences between the four estimates of the 84 th percentiles) has been included. This process results in an average 84 th percentile motion that includes both aleatory (randomness defined by the standard deviation of each ground motion relation) and epistemic variability. To develop time histories, the spectral matching criteria prescribed in ASCE 43-05 (2005) was followed. Input (basis) time histories (Table 2) were selected which displayed strong forward directivity pulses, considered appropriate for 84 th percentile motions. The spectral matching used a frequency PACIFIC ENGINEERING and ANALYSIS 2
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Seismic Stability Evaluation Report
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1.0 Introduction 1.1 Background Thi
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2.0 Project Description 2.1 Site Se
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3.0 Geotechnical Exploration and La
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advanced using a hollow stem auger.
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3.3 Laboratory Testing Soil and roc
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5.0 Subsurface Conditions Based on
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Native Material The in-situ moistur
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For slope stability analyses, both
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We have tabulated the results for b
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Table 8 Seismic Slope Stability Ana
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8.0 Conclusions and Summary of Dam
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Mitigating Liquefaction Hazards in
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Reservoir Roof B A A’ XV-11 (Sta.
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DINGEE RESERVOIR DAM SEISMIC STABIL
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Elevation (Feet) 780 770 760 750 Re
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U-Line: PI =0.9*(LL-8) 60 50 40 30
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Total Density (PCF) 775.0 770.0 765
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0.200 0.300 0.400 0.500 0.600 0.700
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5000.0 4500.0 4000.0 3500.0 3000.0
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5000.0 4500.0 4000.0 3500.0 3000.0
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5000.0 4500.0 4000.0 3500.0 3000.0
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Material m (pcf) Dam Fill 126.8 Na
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Material m (pcf) sat (pcf) c (psf
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Material m (pcf) sat (pcf) C T (p
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1.5 Displacement (ft) 1.0 0.5 Kobe
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Appendix B Laboratory Test Results
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2 62 63 64 65 66 67 68 69 70 71 72
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TABLE B-1 SUMMARY OF LABORATORY TES
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TABLE B-3 SUMMARY OF CONSOLIDATED U
Page 75 and 76: TABLE B-4 UNCONFINED COMRESSION TES
Page 109: Appendix C Reference Drawings: LIST
Page 125: Appendix E Ground Motion Studies Pa
Page 130 and 131: Table 1 Target Response Spectrum: A
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Page 134 and 135: Figure Set 2 (cont.) PACIFIC ENGINE
Page 144: Figure Set 4 (cont.) PACIFIC ENGINE
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