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seepage problems. It can formulate saturated and unsaturated flow, steady-state and transient <br />conditions, and a variety of boundary conditions. <br />SEEP/W generates an output file containing the heads at the nodes of the finite element mesh. <br />Integration of GEO-SLOPE products allows the use of a SEEP/W head file in the slope stability <br />' program to compute effective stresses. In this manner the impact of seepage on stability can be <br />evaluated. <br />8.1.3.1 Mesh, Boundary Conditions, and Type of Analysis <br />The mesh for the analysis consisted of triangular, unstructured finite elements. The mesh was made <br />fine enough to capture the effects of any areas of high hydraulic gradient and to ensure that the <br />boundary conditions were applied effectively to the interior of the model. <br />Boundary conditions applied in the seepage model include: <br />• Total heads applied along the reservoir bottom on the upstream face to the reservoir pool <br />elevation. The total heads were fixed at Elevation 7330.2 for the steady-state analysis and <br />lowered versus time for the transient analysis. <br />Potential seepage face review nodes placed along the downstream face from the crest to the <br />downstream boundary of the model. During model cycling, these nodes check for any total <br />heads or total flux values above zero and, if found, resets them to zero. This makes it possible <br />for a realistic phreatic surface to develop. <br />• Default no-flow boundary conditions on the bottom of the model. Also, the same boundary <br />conditions were applied on the upstream and downstream edges of the model. At Cross- <br />Section C, it was deemed appropriate to use infinite elements on the downstream edge in <br />order to more accurately match measured piezometer readings. These elements treat a <br />boundary as if it extends infinitely. <br />The steady-state analysis included the following assumptions: <br />There is always a constant head of water in the reservoir at Elevation 7330.2- requiring a <br />constant source of water pooling continually. <br />• There is no infiltration on the ground surface (other than from the water in the reservoir) or <br />leakage from the 12" cast iron pipe. <br />The transient (rapid drawdown) analysis included the following assumptions: <br />• The water level in the reservoir was drawn down from nearly full (Elevation 7,329.2) to <br />empty (Elevation 7,280.7) based on actual water level readings taken between July 18 and <br />September 28, 2006. Table 4 shows the total head versus time used as boundary conditions <br />for the upstream face in the transient analysis. <br />P:\Mpls\06 CO\26\0626067\WorkFiles\DesignReport\FINAL\DesignReportFINAL.doc 21 <br />