PERMFILE121407 - Laserfiche WebLink

Home Browse Search

x. Mr. Jim Mattern July 6, 2006 Page 4 Table 3. Assumed Soil Properties Representative for Deal Gulch Impoundmeut Sample Yomg's Poisson's Frictlon Cohesion Tensile Modulus Rstio Angle (ps0 (psl) Compacted Partially 250 0.20 29.7 72 0 Saturated Dam Material Compacted Saturated Dam 250 0.20 29.7 72 0 Material Subgrade Foundation 250 0.20 27 0 0 Partially Saturated Material Subgrade Foundation 250 0.20 27 0 0 Saturated Material Two geometries were analyzed for assessing overall stability of the dam An 8-ft-high dam with 5-ft water in the impoundment was considered as the base case. A second analysis was performed assuming a 12-ft dam height with a water impoundmem height of 9 ft. The geometry analyzed for these two sections is shown in Figure 4. The upstream embanlanent has a design slope of 2H:1 V and the downstream embankmem has a design slope of 3H:1 V. The upstream and downstream boundazies of the model were located 80 ft from the centerline of the embankment, and it was assumed that this was sufficient that no lateral displacement would occur at the boundary. The effect of the impounded water was applied to the model as a water pressure on the base of the pond and along the upstream dam face to simulate the 5-ft and 9-ft water depth, respectively. Water seepage was not directly computed. Rather, a phreatic surface extending from the upstream impoundment elevation sloping downstream to 1 ft above the downstream toe was applied as a water pressure condition. This is a conservative estimate of the steady-state water level within the embanlmtem tmteriaL The factor of safety was estimated by comparing the soil strength at equilibrium to the strength at the limit of equilibrium. Initial stresses were applied, and the model was run umil stresses and displacements cease to change, thus, the equilibrium condition. The simulation of equilibrium used the mechanical properties from Table 3. The limit of equilibrium was simulated by gradually reducing the cohesion and friction until the embankment did not come to an equilibrium condition. That condition is known as the failed state. Failure state of the model was cross-checked using several criteria (e.g., maximum out-of-balance force ratio, maximum velocity ratio, and maximum velocity). The criteria producing the lowest factor of safety have been reported. EXPECTED SLOPE STABILITY The model resuhs indicate that the designed embankment is stabile by coming to an equilibrium condition. Figure 5 illustrates that there aze no tension regions within the embankment for 8-ft-high dam The figure also shows the water table and disaetization of the model. No tension regions aze expected in the 12-ft embanlmtem section either. Figure 6 Agapito Associates, Inc.