Study On Characteristics Of Concrete-cored Sand-gravel Pile Vertical Bearing

Concrete-cored sand-gravel pile, which is composed of sand external pile and concrete cored pile, is a new type of composite pile suitable for soft soil foundation. This kind of pile has plenty of advantages including less concrete usage, strong lateral rigidity, less post-construction settlement, convenient for construction, economical cost and stable and reliable body quality, and its future development is quite promising. However, since its theory research is far behind the engineering practice, through the theoretical derivation and finite element simulation method, this paper is to make a further study in the vertical load-bearing characteristics on the basis of existing research results. The main work is as follows.First of all, the paper theoretically analyzes the load transfer bearing mechanism of the concrete-coredd sand-gravel pile, and puts forward to set up the analysis model of its inner cored and external cored micro mechanics through the shear displacement method. According to Hooke’s Law and its equilibrium condition, basic equations of internal force and deformation of concrete-cored sand-gravel pile are listed, and then are solved by adopting appropriate shear displacement curve. Engineering examples in literature are employed to prove the validity of the derived equation, based on which the relationship between pile top displacement and cored pile area ratio, pile axial force and the depth is further analyzed.Secondly, a 3D model of concrete cored-gravel pile-soil is set up through the finite element analysis tool of MIDAS/GTS. By adding the 100 KN, 200 KN and 400 KN load on cored pile of different length, the paper analyzes the relationship between different cored pile ratio and the displacement of the pile top, reaching a conclusion that the area ratio of 0.4 is more economic and reasonable The effects that cored diameter, length of concrete cored, soil elastic modulus and sand pile elastic modulus have on concrete cored sand pile settlement are researched.Thirdly, the paper carries out a numerical simulation analysis of vertical bearing characteristics of concrete-coredd sand-gravel pile composite foundation, discussing the influences that load, pile length, thickness and elastic of cushion have on concrete-coredd sand-gravel pile, pile soil P-S curve, the inner cored, external cored and soil load share ratio between piles.