At present either the earth pressure at rest or the active pressure is taken as the main pressure on retaining structures as a function of their mobility. In this case the pressure at rest is determined under the assumption of no displacement of the retaining wall relative to the soil for values of the lateral earth pressure coefficient found under conditions of compression of the soil. For a smooth vertical wall with a horizontal surface of the backfill this coefficient has the expression:where 9 is the Polsson ratio.As a rule, the lateral earth pressure coefficient is assigned constant, not dependent on the acting compressing load. At the same time it is known that in a number of cases the distribution of pressures over the height of fixed walls predicted by calculation does not correspond to the results of on-site observations. Thus, for a small (up to 10 m) height ofwalls or in the upper zones of high walls the measured pressures exceed those calculated, and the distribution of pressures over the height is nonlinear and does not correspond to the Coulomb relation [i].In the case when the active pressure (occurring upon deflection of the wall away fromthe soil) is taken as the main pressure on retaining structures, the lateral earth pressure coefficient ~a for a smooth wall with a horizontal surface of the backfill according to the Coulomb solution is expressed in terms of the angle of internal friction of the soil by the relation ~.=t~ (~-~m/2) (2)The lateral earth pressure coefficient is often determined in calculations of fixedwalls by the Coulomb relation (2), substantially underestimating it. Many scientists have investigated the lateral pressure of noncohesive soils under compression conditions: K. Terzaghi, G. P. Tschebotarioff, N. M. Gersevanov, G. I. Pokrovskii, M. V. Malyshev, and others. The investigations of lateral earth pressure under conditions of compression and plane strain under static and cyclic loads described below were carried out with three varieties of noncohesive soils: with fine homogeneous sand for three initial density states characterized by the relative density JD = 0.8, 0.55, 0.23, where JD = (emax--e)/(emax --emin); density of the soil particles p = 26.6 kN/mS; ema x = 0.89; emi n = 0.56; coefficient of uniformity K u = 1.7; with uniform sand of medium size characterized by p = 26.6 kN/mS; ema x = 0.83; emi n = 0.47; K u = 2.8, with JD = 0.55 and moisture contents corresponding to an air-dry state and w = 0.04; with gravel with particle size 5-10 mm with JD = 0.30 and 0.80 (p = 26.5 kN/m 3, ema x = 0.77, emi n = 0.55).The experiments were performed on an experimental stand developed at the research institute of the All-Union Planning, Surveying, and Scientific-Research Institute (Gidroproekt) on the basis of an instrument with independent control of the principal stresses designed by the Moscow Institute of Civil Engineering (MISI) [2]. The stand permits testing soil samples in a form close to cubic with an edge length of about l0 cm under a combination of static and cyclic load...

Following are the results of the l i m i t equilibrium condition studies as applied to clay and sand soils, conducted by the authors at MISI Foundations and Soil Mechanics D e p a r t m e n t Laboratory for Structural Properties of Soils as a continuation of laboratory investigations published before [1,2].

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