Evaluation of the seismic stability of earth dams with consideration of the characteristics of their construction

Abstract

dinThe construction specification and regulations (SNIP) call for calculating the stability and seismic stability of earth dams with consideration of the factors determining the behavior of earth materials under static and seismic loads.In calculations of earth dams the stability of the slopes is evaluated by the method of fixed surfaces of sliding (in particular, along cylindrical surfaces) under the assumption that the sliding mass of soil behaves as a rigid undeformable body (model of a consolidated slope). At the same time, consideration of a possible unstabilized state is carried out on the basis of Terzaghi's principle of effective stresses by determining the excess pore pressure.It is indicated in the SNiP for earth dams that when calculating the pore pressure from consolidation of soils in cores of earth-rock dams with a height of more than 70 m it is necessary to take into account the stress state of the structure.Calculations of the stress state must be performed for earth-rock and rockfill dams of classes I and II with a height of more than 70 m. The use of relations of the linear and nonlinear theory of elasticity is allowed in the calculations.At present a number of organizations, the All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG), Leningrad Polytechnic Institute (LPI), All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt), etc., have developed computer programs for calculating the stability of dam slopes realizing the SNiP methods.In these methods the excess pore pressure is determined on the basis of the theory of consolidation due to seepage, but the total stresses are found, as a rule, without consideration of the real stress state in the sliding soil mass; furthermore, the degree of water saturation and change of saturationduring consolidation are often not taken into account when determining the pore pressure.We note that consideration of the air content in soils is extremely necessary, since even a small air content considerably reduces the pore pressure and accelerates the consolidation process, and, consequently, considerably affects the safety factors being determined.Calculations of structures on the basis of limitation of the absolute and relative displacements should provide their normal service and not allow a decrease of their service life. If we turn to the SNiP for earth dams, then it is recommended in it to determine the settlement of the crest for evaluating the amount of construction rise of the dam and amount of differential settlement of its various parts.In this case it is recommended to calculate settlements by the layer-by-layer summation method with the use of compression formulas. There are also known recommendations containing empirical formulas for calculating the possible amount of settlement.It is recommended to estimate the horizontal displacements of dams on the basis of analogues, and for preliminary estimates of horizontal displacements of dam crest it is recommended even to assume them to be equal to settlement of ...