Research Of Interface Shearing Properties Between Concrete And Soil And Self-balanced Method

Self-balanced method is a kind of static load test under a special device, because the location of equilibrium point is difficult to determine in practical engineering tests, which led to a part of the pile reaches the ultimate bearing capacity, but the other part has not been reached, finally it is difficult to get the results of scientific tests. So this article based on the basic principle of Self-balanced method and it’s main problem、the load transfer mechanism of top-loaded pile and down-loaded pile and their difference, according to the direct shear test, researched the shearing properties of the interface that between completely decomposed granite soil and concrete, and that provided the basis for the result of self-balanced method. The main conclusions:(1) For down-loaded pile, the distribution of skin friction along the depth is outer convex, the axial force of pile and axial deformations are diminishing with depth; for top-loaded pile, the distribution of skin friction along the depth is inward, the axial force of pile and axial deformations are diminishing with the distance from the bottom of the pile.(2) The result of direct shear test showed:the shear strength of smooth surface is 75.8%～94.7% compared to rough surface, the shear strength of 21days has improved 6.4%～15.6% compared to 14days, the shear strength of slurry surface is 90% compared to without slurry. The curve of τ-S under different contact surfaces could provide a basis for the part of pile which did not reach the limit state, so we can get the ultimate skin friction, then the ultimate bearing capacity can be got through back calculation.(3) The result of Self-balanced method showed:the axial force of pile to load box as the boundary curve, the axial force in the load test box is the maximum, both of the axial force is reduced when upward and downward. For strongly weathered granite, the unit of friction increases with load, it is much larger than an initial value based on the type of soil of gravel. The ratio between negative friction and positive friction also increases with load, in the test load range is 0.7～0.9. The load-displacement curve of lower-pile changes slowly, and the placement is also very small, the ultimate bearing capacity can not be got exactly.