| Tapered concrete screw pile whose mechanism of load delivering differs remarkable from the conventional straight pile’s because of the screw on it, is a new kind of method to deal with the foundation. Tapered concrete screw pile has tremendous potentiation in dealing with the weak foundation, and the problem of settlement is a class of extremely important ones in engineering practice. Using model test and numerical simulation, the paper according to the theory analyzed the characteristics of the settlement of the tapered concrete screw pile, and established the calculation method of the settlement of the single pile and group piles. The main work is as follows:1) 3D numerical simulation is carried out, and the results reveal the distribution laws of subsidiary stress in the tapered concrete screw pile composite foundation. Subsidiary stress decreases along the depth and horizontal direction. When it is close to the piles, subsidiary stress in the soil is greater and the subsidiary stress changes bigger along the depth and horizontal direction. When it is far from the piles, subsidiary stress in the soil is smaller and nearly no changes along the depth and horizontal direction. Based on the settlement results of numerical simulation and the theoretical analysis of the composition of settlement deformation, this paper establishes the analytical model of the single pile and the pile group and provides a basis for theoretical analysis computation.2) Laboratory model test are carried out to comparatively analyze difference characteristics of settlement among the concrete screw piles with variable cross-section, straight screw piles and general straight piles. The results show that when under the smaller loads, the settlement of the concrete screw piles with variable cross-section is close to that of straight screw piles. But as the loads increase, the concrete screw piles with variable cross-section and the straight screw piles are more and more outstanding than general straight piles in decreasing the settlement. When the load on pile top is 1.25kN, the settlement of the general straight pile is 8.011mm. The ratio of the settlement of tapered concrete screw pile to that of straight pile is 53%, and the ratio of the settlement of straight screw piles to that of straight pile is 44%.3) 3D numerical simulation and laboratory model tests are carried out to analyze the stress characteristics when load on the top of the tapered concrete screw pile, determine the ratio of shaft friction and base resistance, and established the calculation model of the settlement of the single pile and group piles; And on this basis, using Geddes solution, established the calculation method of the settlement of the tapered concrete screw pile and the group piles. Compared the settlement results of theoretical calculation and numerical simulation of tapered concrete screw pile composite foundation, the error is within 25%.4) Comparatively analyze the characteristics of the load-settlement curve of tapered concrete screw pile and conventional straight pile, compared with the conventional straight pile, the special structure of the tapered concrete screw pile improved the side friction, which strengthened the interlocking between the pile and the soil in the vicinity whose resistance was fully developed. Thus, the load-settlement curve is relatively flat.5) Through 3D numerical simulation, on aspects of the size of the pile and the screw, the characteristics of the reinforcement layer and the cushion in the work area, analyze the influence and regulation of various factors on settlement of the pile, and suggest some design parameters which is more suitable for practical engineering, provide a reference for the optimization design for the tapered concrete screw pile used in composite foundation.The research results of the settlement of tapered concrete screw pile composite foundation, can provide guidance and reference for relevant engineering design. |
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