On Stresses and Deformations of Soils in Triaxial Compression Tests

Abstract

During the triaxial compression test, the frictional force applied to the end surfaces causes the test specimen to take on a barrel shape with the central portion expanded. Noting this deformation characteristic, the author conceived of treating the assumed lateral stress in equattion 7, figure 3 as one of the boundary conditions in place of the frictional force applied to the end surfaces and thus derived the equation for the various components of stress (equation 15) and displacement (equation 16). In view of the nonlinear stress-strain relationship of soils, the author then suggested a method of calculating the Δφ_s constant (equation 21), the secant modulus ΔE (equation 22), and Poisson's ratio Δν(equation 20) by expressing equation 16 by the incremental procedure and substituting the measured values for the stress difference, axial displacement, and lateral displacement in the resulting equation (equation 17). When the Δφ_s constant, the secant modulus, and Poisson's ratid are known, the various stress increments can be calculated from equation 23.
Using methods such as those described above, the author investigated the deformation behavior of test specimens in triaxial compression and stress distribution (Fig. 6-9) and calculated the secant modulus and Poisson's ratio as constants of the mechanical properties of soils (Fig. 10-11).