Laserfiche WebLink
Memo <br />To: Hubbard Shaft Project File <br />Frorm Collin L. Stewart, PE <br />Data 614/2008 <br />Re: Engineering Analysis, Stability of Hubbard Shaft Mud Pit Out Slope <br />The mud pit constructed at the Hubbard Creek Shaft site has been constructed as shown on Figure 1. <br />Additional rock has been added to the out slope to bring the overall out slope to approximately <br />1.8H : 1 V as shown on attached Figure 1. My inspections during construction and my numerical <br />modeling analysis indicated that this structure should be stable throughout the projected life of the mud <br />pit (less than 6 months). Should it be necessary, bentonite can be used in the mud pit as lining <br />material. <br />I was present throughout the construction of the mud pit and believe it meets the requirements of <br />4.05.9(7) and 4.05.9(8). As constructed, the out slope has a safety factor of greater 1.5 for the normal <br />pool elevation with steady state seepage saturation conditions. <br />Attached in support of this conclusion are the following: <br />1. Figure 1. Typical Profile, Hubbard Shaft Mud Pit. <br />2. Engineering materials property report prepared by Yeh and Associates dated May 29, 2008. <br />3. The Hubbard Shaft Mud Pit Outslope Stability Analysis program run output which shows no <br />development of failure surfaces; i.e., Critical SRF: unknown (all iterations converged). SRF is <br />the strength reduction factor which is equivalent to the Factor of Safety. The numerical <br />analysis was performed using the RocScience program, Phase.2, finite element analysis for <br />excavations and slopes. <br />Collin L. Stewart <br />Colorado Professional Engineer 16488