Experimental study on in-situ properties of residual soil by self-boring pressuremeter

Residual soil is a regional and special soil, and accurate evaluation of its mechanical properties and bearing capacity is a necessary condition for the treatment and foundation for any types of engineering projects. The residual soil in the studied area within the range 20 min depth is tested by using the self-boring pressuremeter. The strength and stiffness parameters of the soil are evaluated through theoretical analysis. The variations of mechanical properties with respect to depth and horizontal direction are also analyzed. The decay law of stiffness characteristics and its applicability under different strain levels are evaluated. The results show that the values of the stiffness and strength of the soil are much different in the site, and the residual soil has obvious weathering crust. Initially the shearing and deformation parameters decrease up to a certain depth and then increase gradually with the increasing depth. Within the test site, the mechanical parameters of soil at shallow depths are quite different and converge after reaching a certain depth. G_s and G_t show non-linear relationship with γ_c. In a small strain range, G_s and G_t decay rapidly when the strain is 2% to 3% and tend to be stable. The non-linear analysis method is more reasonable for determining the shear modulus. It is believed that in the engineering design of such site, shear modulus should be chosen based on the strain level of self-drilling lateral pressure test results, and the linear secant shear modulus G_ur is somewhat risky. Moreover in the small strain, shear modulus of the soil is more sensitive to difference of the soil, and in order to ensure the representative parameters, the test density of soil at shallow depth should be increased.