Effect Study Of Expansive Soil Slope Reinforced With Geogrid

Large scale pull-out tests are adopted first to study the frictional charateristics of geogrid and expansive soil, and a simplified interface model of geogrid and compacted expansive soil is suggested and the related parameters are given. Based on the tri-axial test results, FLAC^3D is applied to numerically analysize stress and deformation of the expansive soil slope with slope rate of 1:1 and height of 20m. The effect of geogrid distribution, moisture absorption and weathering on slope reinforcement and stability is discussed, some important results and conclusions are as follows:(1) The interface frictional force can reach peak value when the displacement of geogrid relative to soil arrives at l²cm, and no clear softening occurred after peak friction. The curves of average friction force and relative displacement at interface represent elastic perfectly plastic behaviors.(2) The water content of expansive soil has great influence on the interface quasi-cohesion which sharply reduces as the increase of water content, but not on quasi-friction coefficient. The dry density significantly impacts on the interface quasi-friction coefficient, but not on quasi-cohesion. The interface quasi-friction coefficient increases as the increases of dry density.(3) Geogrid should penetrate the weathered layer, otherwise the reinforcement effect is not remarkable. When geogrid exceeds the depth of weathered layer, to increase the length of geogrid can raise the restriction of stress and displacement. The safety factor of slope is raised 52%, and critical slip surface moves toward deep zone of slope.(4) When geogrid reaches the boundary of weathered layer, the stress state of reinforced zone is remarkably affected by vertical intervals of geogrids. The shear stress of reinforced zone reduces with the decrease of geogrid vertical intervals. And the horizon deformation of slope reduces. Compared with untreated slope, the safety coefficient of slopes with geogrid vertical interval of 0.4m and 1.2m raises respectively 35.6% and 28%. But when the geogrid is long enough, actually longer than 6m, the change of vertical intervals has little impact on the stability of slope.(5) Moisture absorption of expansive soil can cause great horizontal distortion. When the moisture absorption scope is fixed and the moisture absorption area is deeper, the slope horizontal distortion is greater. In the process of moisture absorption swelling, the shear stress of slope has increase to a certain extent, especially in the infiltration influence zone. The location where shear stress increases converges to the toe of slope, and above the slope toe, the shear stress equivalent line distributes approximately parallel to the slope surface.(6) When moisture absorption occurs at the surface of slope, the horizontal restrain effect of geogrid to expansive soil amplifies with increase of reinforcing length. The frictional resistance stress on the interface between geogrid and expansive soil decreases as the geogrid length increases, and the horizontal restrain is enhanced. The frictional resistance stress on interface is in reverse proportion with the geogrid length. The yielding position on interface in reinforcement zone locates at the moisture absorption area where water content tends to the saturated state.