2007-08-10_PERMIT FILE - C1980007 ‎(3)‎

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 8/10/2007
• Doc Name: Design Report for Alteration of Monument Dam
• Section_Exhibit Name: Exhibit 76 Report April 2007
• Media Type: D
• Archive: No

Table 7 Summary of Unit Weights for Dam Stability Modeling
Unit Wei ht
Material Sat ~ motsc ~
Existing Materials
Embankment Material 132 110
Soft Sediment 119 90
Colluvium 130 108
Failure Surface Material 130 108
Weathered Bedrock* -
Pro osed Materials
Buttress 132 110
Downstream Drains a Blanket 130 120
U stream Cla Blanket 132 110
~- i nis maienai was assumes to ~e mtmitely strong In the model,
thus unit weights were not assigned.
8.2.2.2 Embankment Material
The shear strength of the embanlanent material was obtained from triaxial (TX) and direct shear (DS)
tests. Figure 7 shows the undrained shear strength envelope measured in the triaxial test with pore-
water pressure measurements. For comparison purposes, the envelope used in the previous analysis
is shown in Figure 7. The value used for stability modeling is ~~„ of 25.8 degrees with no cohesion.
This value is considered conservative because it yields lower strength than using cohesion and
friction (i.e. dashed line in Figure 3). Therefore, the embankment material was modeled with a ~~„ of
25.8 degrees for the USSA.
Figure 8 shows the drained shear strength envelope based on triaxial and direct shear tests. It can be
seen from Figure 8 that the drained failure envelope yields a drained friction angle of 32.2 degrees.
The results from both the triaxial and direct shear tests display fairly consistent results. Therefore,
the embankment material was modeled with a friction angle of 32.2 degrees for the ESSA.
8.2.2.3 Soft Sediment
The shear strength of the soft sediment was measured in the triaxial (TX) and direct shear (DS)
apparatus. The results of the triaxial tests yield an undrained failure envelope of ~~~ 29.4 degrees
with c=0.43 tsf. This value is considered high and non-representative of material with soft
consistency. A further review of the stress-strain relationship from the triaxial tests revealed that the
tested material exhibited dilative behavior and negative shear induced pore-water pressures were
developed during shear. Soft sediment material showing low blow counts from SPT in the range of 0
(weight of hammer) to 7 blows/ft, with typical values between 3 and 6 blows/ft, is expected to exhibit
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