Page - 10 - in Book of Full Papers - Symposium Hydro Engineering

In soil compaction, the target values of dry density and water content were specified to be equal to the maximum dry density and the optimum water content by Standard Proctor while controlling the degree of saturation to become the optimum degree of saturation (i.e., Sr= (Sr)opt) irrespective of variations in the soil type and compaction energy in actual compaction. When Sr= (Sr)opt, the highest dry density (so, the highest shear strength and stiffness) and sufficiently low hydraulic conductivity of saturated soil is obtained under any given field condition. 2. STABILITY AND DEFORMATION ANALYSIS The collapse was successfully simulated by simplified practical analysis incorporating the time histories of undrained stress-strain relation and peak strength of saturated soil that degrade by cyclic undrained loading during an earthquake (Figs. 2a & b). The residual slip evaluated by the Newmark method and the residual deformation outside the slip layer by pseudo-static FEM, both incorporating the time history of response acceleration, were summed up. No slip with very small residual deformation of the new dam by the seismic load by which the old dams collapsed was confirmed by analysis by this method. The effect of compaction on the dam stability is tremendous. Fig. 2c shows the average drained and undrained shear strengths mobilized along the critical slip circles in the top zone of the old and new main dams (as shown in Fig. 2a). With the new dam, the average degree of compaction (Standard Proctor) Dc is equal to 101 %, thus the undrained shear strength at the end of seismic loading is higher than the drained strength while substantially higher than the value at Dc= 87 % of the old dam. a) b) c) Fig. 2 a) & b) Residual deformation for two critical slip circles by numerical analysis of the old dam; & b) average shear strengths mobilized in the upper zone. s Settlement at crest=1.63m (s/H=9.2%) 10 m for residual deformation Settlement at left end of crest = 4.4m (s/H=25%) s 10 m for residual deformation 85 90 95 100 105 0 50 100 150 200 250 Drained strength at the peak acceleration Initial drained strength Undrained strength at the end of earthquake Degree of compaction (Standard Proctor), D c = d /( d ) max (x 100 %) Initial undrained strength  f =  ' {tanφ } eq +{c} eq New main dam Old main dam Notes: 1. These average shear strengths are those along the critical slip circle in the top zone of respective dams. 2. During an earthquake, undrained shear strength decreases from the initial value to lower values due to degradation by cyclic undrained loading, while the drained shear strength decreases from the initial value due to a decrease in the normal stress along the slip circle by seismic inertia. 10