Experimental study of the mechanisms of deformability and flow of soil under conditions of the two-dimensional boundary-value problem with respect to strains

Abstract

Recent laboratory investigations of soil samples under conditions of composite three-dimensional stress--strain in triaxial compression revealed considerable complexities in the behavior of soils under a load as a deformable material [1,2]. In laboratory experiments with a soil sample under various stages of deformation and subsequent flow the investigations are carried out for a prescribed trajectory of the development of stresses or strains applied to the boundary surfaces of the sample for a conditionally homogeneous stress state. Under operating conditions in a structure the soil is deformed by heterogeneous stress developing in different trajectories of the prelimiting state, which influences all stages of the soil operation under the boundary conditions of the prescribed boundary-value problem.This article presents the results of an experimental study of the main regularities in the development of heterogeneous stress obtained under condRions of the strain two-dimensional problem of loading the soil around an expanding cavity. The experiment was carried out in a special test flume measuring in plan 200 x 120 cm with a height of 175 cm (see Fig. 1). Expansion of the perfectly flexible cavity was attained by applying a pneumatic pressure inside an initially 12-cm-dtameter cylindrical cavity. The pneumatic pressure was increased in increments P ofl kg/cm z to a value of 5 kg/cm z. A uniform load q = 0.3 kg/cm z was applied to the soil surface before applying the indicated main load. The soil in the flume after applying the load q and each load increment P was brought to a conditionally stabilized state. For the experiments we used air-dried, urirounded sand of the following grain composition in %: 1,12%The average porosity of the soil in the initial state after placement n = 027, I d = 0.56 (I d is the density index). "The main feature of the flume experiments on a study of the state of stress and strain, which were carried out at the V. V. Kuibyshev Moscow Institute of Civil Engineering (MISD. consisted in taking measurements at various points in the soil of the stress and strain components over various areas, which yielded experimental data on the characteristics of change of the stress and strain tensors during loading of the soil under prescribed boundary conditions of the investigated boundary-value problem. The necessary information on the regularities of the development of stresses and strains, including the complete characteristic of the stress and strain tensors and the trajectories of their development during loading, is obtained thereby.The stresses in the soil were measured by membrane gauges. On processing the results we introduced corrections taking into account the distortion of the measured stress by the gauges. These corrections were obtained by a special investigation of the gauge operation at diffe~ent soil stresses. The gauges measured the stresses Ozz, Oxx,Oyy and also the stresses o v over an area inclined at an angle of 45"to the z and x axes (shown in Fig. 1), which made it possible to...