Study On Working Behavior Of Gravel Pile Composite Foundation Under Load Of Large Tank

With the development of petroleum industry, oil tanks are used more than before. At the same time, many bad groundwork are met during the course of construction. So many of them must be treated with. How can we solve the problem with the lowest price? It is the problem that we must face with. As a kind of way of solving the problem of bad groundwork, composite foundation has two merits. The first one is that it can make piles and soil work together, and the second is that it cost low. The subject it studied is gravel pile composite foundation, the bearing characteristics and deformation performation was studied.At the beginning of the thesis, some conclusions on composite foundation under flexible base and gravel pile composite foundation are provided. There are also a short introduction on the foundation of tanks, such as kinds of foundation used under tanks, The deformation tracks of foundation and many ways of treating with bad groundwork.Put forward application of Multi-Objective Fuzzy Optimum Theory to evaluate and choose the foundation treatment scheme. Raise the principle, model and its application procedure and test and verify it with engineering case.Evaluate the effect of gravel pile treatment from bearing capacity and physical and mechanic index in pre-& post-processing through static load test of single pile, dynamic penetration test and the standard penetration test.And then the gravel pile composite foundation are simulated using a software Flac-3D. From the results of simulation, combined with an engineering example, we get to know some rules about the composite foundation. Here are some results :(1) The modulus of cushion under tank's base is about 80～200 MPa, It is larger than that of under other kind of base. The thickness of cushion is about 400～600mm. (2) There is a length for pile, the stress and displacement is stable gradually. So there is a length for bearing ability, and a length for displacement for foundation. The major role for gravel pile is to decrease settlement.(3) A suitable replacement ratio should be choosed when design the diameter of pile for giving full play to pile and soil's bearing ability. It is not advisable to increase the modulus of strengthen place to decrease the settlement by increase the replacement ratio all along. The best replacement ratio should be choosed according to geological condition of engineering and load of building when design it.(4) The strengthen effect is not remarkable by using gravel pile when the modulus of soil around pile more then 8 MPa.