SBPM试验不同长径比颗粒流细观模拟

PFC3DMESO-SCALE SIMULATION OF SELF-BORING PRESSURE-METER TEST WITH PROBES OF DIFFERENT LENGTH-TO-DIAMETER RATIOS

自钻式旁压试验(Self-boring pressure-meter)具有对原位土体扰动小,测试深度大,能够得到不同深度处土体的应力-变形曲线,在测定地基土性参数和地基承载力上具有广阔的应用前景。然而受分析手段和研究水平限制,目前对SBPM试验不同长径比(length-to-diameter ratio)测定器加载过程中周围土体的细观变形响应研究较少,而土体参数的确定与其变形机制是密切相关的,基于此,应用PFC3D(Particle Flow Code in Three Dimensions)颗粒流程序对不同长径比L/D(6、10、15、20)下自钻式旁压试验进行了数值模拟,对测定器孔应变一定时,周围土体的位移场和应力场分布变化进行了分析研究。试验结果表明:根据长径比的大小,位移场和径向应力场分布可分为两种形式:当长径比L/D=6时,位移场和应力场分布呈"弧形壁灯笼状",测定器周围土体变形在其高度上不符合平面应变轴对称条件,且L/D=6时的土体应力小于后3值(L/D=10、15、20时);当L/D=10、15、20时,则呈"直壁灯笼状",此时在测定器高度上应力分布比前者均匀,其变形基本符合平面应变轴对称条件。径向应力在测定器附近两侧形成近似成对称分布的数个应力集中区。当测定器径向应变一定时,随着L/D的增大孔壁处土体径向应力逐渐呈负指数减小并趋于稳定。

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 are-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.