Similarity Model Test On The Skin Friction Along Pile In Thick Newly Filling Soil

With the implementation of the Grand Development Plan of Western China and the rapid development of the western, a number of buildings have to be built on deep filled soil in hilly areas. Due to the settlement caused by fill and low strength and high compressibility, pile foundation located in fill may undergo large negative friction, which will increase axial force on pile and large settlement may occur.In this paper, the similarity model test is used to study the skin friction along pile in thick filling soil. The work is as follows:(1) A model test equipment was developed, which can be used to simulate self-weight stress field of filling soil. The external wall of the model box is composed by steel rings separated with cushion blocks. When the blocks are removed, the weight of the rings will transfer to the filling sink and produces a simulation self-weight stress field.(2) The following conclusions are obtained from the model test:1) The neutral point is located at depth of about 0.7 times of the pile length for the pile placed on soft stratum.2) With the increase of load, the position of neutral point will move up, which means decrease of the range of negative skin friction, and the value of negative skin friction decreases.3) The stiffness of bearing stratum has great influences on the negative skin friction. The position of neutral point will gradually move down with the increase of elastic modulus of bearing stratum.4) Loading sequence has little effect on the negative skin friction.(3) Based on the test results, a simplified calculation model for limit negative skin friction of pile is established, in which the negative skin friction increases linearly from 0 to the maximum with depth, then decreases till transit to positive friction.