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HYDRO28780
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Last modified
8/24/2016 8:47:54 PM
Creation date
11/20/2007 9:50:36 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1979195
IBM Index Class Name
Hydrology
Doc Date
2/24/2004
Doc Name
Design Technical Memorandum
From
GEI Consultants, Inc.
To
Denver Water
Media Type
D
Archive
No
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HazeltinelRoad Runners Rest iilBrinkmann-Woodward Gravet Pits Lining Project- Design Technical Memorandum <br />Denver Water <br />August 2003 <br />4.7 Selected Design Factor of Safety <br />The results of the parametric seepage analyses was discussed in a meeting between GEI and <br />Denver Water on May 28, 2003. Based on a qualitative evaluation of risk and cost for the <br />various factors of safety, it appeared that a factor of safety of 1.5 would provide an appropriate <br />balance between economy and safety. The group concluded that to increase the factor of safety <br />beyond 1.5 against the SEO Design Standard would require a significant increase in <br />penetration depth for a resulting small increase in the factor of safety. This provides a FOS of <br />4.5 against the Performance Standard. <br />It is our opinion that a FOS of 1.5 would provide an appropriate balance between economy and <br />the construction of an effective liner. The risks of not meeting the SEO criteria could be <br />mitigated during reconstruction of the reservoir side slopes. It is anticipated that the reservoir <br />would be dewatered after construction to accommodate construction of 120'h Avenue. During <br />this period, the infiltration could be measured. <br />4.8 Soil-Bentonite Cutoff Wall Vertical Alignment <br />For the selected target FOS of 1.5 against the SEO Design Standard, the estimated depth of <br />soil-Bentonite cutoff wall penetration into bedrock, computed leakage rate, depth of alluvium <br />to top of bedrock, section length, and total computed section leakage rate for each section <br />analyzed are presented in Table 4.5. The total length of the soil-Bentonite cutoff wall is about <br />14,800 feet. The soil-Bentonite cutoff wall would need to extend between about 4 and 10 feet <br />into bedrock to achieve the selected seepage design FOS of about 1.5. The weighted average <br />penetration of the soil-Bentonite cutoff wall into bedrock would be about 5.7 feet. The actual <br />FOS in Table 4.5, on which the design is based, is 1.56 against the SEO seepage Design <br />Standard. <br />In Table 4.5, the fourth column shows the depth of the cutoff wall that was used in the analysis <br />while the fifth column shows the actual depth of wall used in design. For Sections 1 and 3, the <br />design cutoff depth was increased by 1 foot to ensure that the wall was keyed into the bedrock <br />layer below the one that was used in the analysis for the target seepage. <br />The design bottom of the soil-Bentonite cutoff wall along with summary borings from the <br />Geotechnical Data Technical Memorandum (GEI, 2000) and [he Addendum to Geotechnical <br />Data Technical Memorandum (GEI, 2003) is presented in plan and profile on Construction <br />Drawings 4 through 8 in Appendix C. <br />The soil-Bentonite cutoff wall would consist of a vertical excavation of a minimum 2.5-foot <br />width that is constructed using slurry wall construction techniques. The excavation would be <br />backfilled with a homogenous material consisting of the excavated soils, excavated bedrock, <br />GEI COnSUltaritS, Inc. 21 o: oaa o;-m-t u,~-n:~dn~e o~,~~~rm <br />
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