Laserfiche WebLink
Geotechnical Evaluation of Mine-Induced Seismicity on Monument Dam <br />Dorsey 8 Whitney, LLP <br />Section 7 -Preventive Measures <br />7.1 Description of Preventive Measures <br />Several remedies are available for improving the static factor of safety and associated <br />capacity of the earth structures to withstand a horizontal seismic load. A proven approach is <br />to construct a stabilizing fill or buttress on the downstream slope of the structure, which <br />provides a gravity load at the toe of the structure to counteract other forces that are tending to <br />reduce stability. Another common approach is to remove sources of water that are associated <br />with reducing stability of a structure by installing drains. The benefit of constructing a <br />stabilizing fill or buttress can be evaluated with a high degree of certainty before <br />construction. However, the benefit of installing drains depends on the effectiveness of the <br />constructed drains and is therefore difficult to predict before the drains are installed and <br />operating. An approach that uses a stabilizing fill and buttress will be evaluated for <br />Monument Dam. Installation of drains will also be considered during implementation of the <br />improvements, however any improvements in stability provided by draitts will be in addition <br />to that provided by the stabilizing fill and buttress, <br />• A plan view of the preventive measures is shown in Figure 7.1. The preventive measures <br />include a stabilizing berm on the downstream slope of the dam and a buttress fill against the <br />toe of the landfill. The buttress fill abuts the stabilizing berm and contributes to additional <br />stabilization of the dam. <br />Across-section through the earthfill dam, stability fill, and buttress fill (Section B indicated <br />on Figure 7.1) is shown on Figure 7.2. The stability berm incorporates a combination <br />chimney and blanket drain to collect and control seepage through the dam. Seepage <br />collected by the chimney blanket drain would be discharged by a system of pipes at a <br />location downstream of the buttress fill. The granular materials used in construction of the <br />chimney blanket drain would be designed to be filter-compatible with adjacent soil. The <br />chimney blanket drain and collection pipes would be sized appropriately based on the <br />expected flow rates. Measures would be taken to extend the outlet conduit downstream <br />through the stability berm and buttress fill. This could be accomplished by either extending <br />the existing pipe or by slip-lining the existing pipe with a new smaller-diameter pipe. <br />Erosion protection would be provided at the downstream discharge area of the pipe. <br />A cross-section through the landslide and buttress fill (Section A indicated on Figure 7.1) is <br />shown on Figure 7.3. The buttress would be constructed to fill most of the existing discharge <br />channel downstream of the dam and would be configured, as shown on Figure 7.1, to <br />stabilize the landslide in two directions: in a generally northwest direction towards the <br />GEI~! 24 0603500603-16Mm~ummtDmeGw4cMiulFVd <br />March 2006 <br />