Shear Strength And Nonlinear Constitutive Model Of Unsaturated Soil

The unsaturated remoulded clay is the subject investigated by this paper. SWCC and shear strength are researched by systematical tests and the test results are analyzed in depth. Unsaturated consolidation tests, conventional three-triaxial tests and unsaturated three-triaxial tests are conducted to research characteristics of the unsaturated soil. Based on the test results, a nonlinear constitutive model for unsaturated soil is developed. The main contents of the paper are summarized as follows:(1) SWCC gained by the unsaturated consolidation apparatus is used to study the influence of burden pressure on SWCC. With the test results, an equation describing the effect on SWCC from the burden pressure is established. According to the equation the influence of stress should be considered if using SWCC to calculate shear strength of unsaturated soils;(2) The unsaturated twin-cell system was introduced in detail. The volume change of the new system is calibrated; the old program of the twin-cell system is revised to redesign the new strain control-type part for shear test.(3) Conventional three-triaxial tests of saturated soil are conducted in different cell pressures to gain the shear strength parameters c' andφ'; based on the unsaturated three-triaxial tests with the same suction and the above shear strength parameters c' andφ', the parameterφ~b of unsaturated soils is calculated;(4) By comparing shear strengths calculated by unsaturated soil three-triaxial tests and SWCC, the shear strength calculated by the later is much small;(5) Based on the unsaturated soil three-triaxial test and three-parameter stress-strain model, this paper establishes a new nonlinear constitutive model for unsaturated soil.