PFC3D MESO-SCALE SIMULATION OF SELF-BORING PRESSURE-METER TEST WITH PROBES OF DIFFERENT LENGTH-TO-DIAMETER RATIOS

The self-boring pressure-meter(SBMP) has little to no disturbance to the surrounding soil and has a long measurement depth. It can determine the stress and strain curve of soil at depth and has an extensive application prospect in the determination of soil parameters and foundation bearing capacity. However, because of the limitations of the analytical tools and research level, the deformation response of surrounding soil during loading process in SBMP test with probes of different length-to-diameter ratio (L/D) has seldom been studied up to present. At the same time, the determination of the soil parameter is closely related to its deformation mechanism. Based on this, the self-boring pressure-meter(SBPM)test with different length-to-diameter ratio(L/D=6, 10, 15, 20) is simulated by PFC3D(Particle Flow Code in Three Dimensions) program in this study. The development and distribution of the displacement and stress field of the soil surrounding the probe are studied. The results of numerical experiments show that the distribution of the displacement and radial-stress field can be divided into two forms according to the size of the L/D. When L/D equals 6,the distribution shape of the displacement and stress field shows an arc-shaped lanterns appearance; the deformation of the surrounding soil along the height of the probe dose not satisfy with the plane strain and axial symmetry conditions. And the soil stress of L/D=6 is smaller than the later three. However, when L/D has a value of 10, 15 and 20,the distribution shape shows a straight wall lanterns appearance; the deformation of the surrounding soil along the height of the probe basically satisfies with the plane strain and axial symmetry conditions. The stress distribution along the height of the probe is relatively uniform than that of the L/D=6, and the soil stress decreases with the increase of the L/D. Several radial stress cores which are approximately symmetrical distribution have formed near both sides of the probe. In addition, the radial-stress at the borehole wall descends in a negative exponential form with the increase of the L/D when the radial strain of the probe is constant.