Experimental Study of Hysteresis in Clayey Soils under Compression

Abstract

The energy dissipation for one cycle of clay soil deformation over the area of ​​a hysteresis loop under conditions of one-dimensional deformation has been experimentally studied. Several series of trials were carried out under different conditions of soil density and moisture and different loading modes. It was established by the experiments that after several cycles of loading and unloading of the samples, the transient process of the closed loop formation ends and certain dependences of stress on deformations are established in the sections of the ascending and descending branches of the hysteresis loop. To determine these dependencies, rheological relations obtained directly from the hysteresis loop by approximating the arcs of its contour have been used. By integrating the approximating rheological dependences along the branches of the loop, the dissipated energy per deformation cycle has been obtained as a function of cyclic deformation amplitude, measured by the area of the hysteresis loop. Experiments on obtaining a hysteresis loop were carried out on a compression device with a cyclic sample. Samples with different states of density and moisture content were produced by consolidating a paste having yield point moisture under different pressures. Several series of experiments have been carried out. In the first series, soil absorption coefficients were derived for different states of density-moisture at different loading rates. In the second series, three types of clayish soil (clay, loam, sandy loam) were studied. Dissipation coefficients have been found out for the indicated soils. In the third series, three types of clay soil were tested under different conditions of density and moisture. The dissipation coefficients have been obtained. In the fourth series, the dependences of the absorption coefficient on the amplitude value of the cyclic stress for three types of clay soil were disclosed. It was found that a change in the loading rate within the range from 0.05 MPa to 0.2 MPa does not lead to the significant change in the absorption coefficient, the increase in the number of clay fractions in the sample leads to an increase in the absorption coefficient, a change in the amplitude of cyclic loading (in the indicated range of change) does not affect the absorption coefficient.