【作者】 贾建华；

【导师】 王士杰；

【作者基本信息】 河北农业大学 ， 岩土工程， 2009， 硕士

【摘要】 近年来,随着我国石油化工工业的快速发展,大型储罐的使用逐渐增多。新建储罐工程越来越多的遇到不良地基,对地基处理的要求也越来越广泛。如何在保证工程质量的情况下节省工程投资成为摆在众多岩土工作者面前的一个问题。复合地基因其能利用桩体和土体共同承载、造价低廉,在工程界得到广泛应用。本文以碎石桩复合地基为研究对象,对其承载特性及变形特性进行了较为深入的探讨。论文首先回顾了目前柔性基础下复合地基和碎石桩复合地基已有的研究成果。对储罐常用的基础、储罐下地基的变形规律和控制标准以及常用的地基处理方式做了简单的阐述。提出应用多目标模糊数学优选理论来评价和选择地基处理方案,给出了该方法的原理、模型及应用步骤,并结合工程实例进行验证。通过实际工程进行的碎石桩单桩复合地基静载试验,桩体重型动力触探,标准贯入试验等,从处理前后地基的承载力、土层的物理力学性质指标等方面对碎石桩的处理效果进行了综合评价。利用Flac-3D软件对大型储罐下的碎石桩复合地基进行了模拟。分析了桩体、土体、垫层的参数变化对复合地基的影响,并结合工程实例,进一步分析了柔性基础下碎石桩复合地基的工作性状。论文所得主要结论如下:(1)在储罐这样的柔性基础下,垫层模量在80～200MPa比较合适,大于一般复合地基所选用的垫层模量;厚度宜在400～600mm。(2)当桩长增长到一定程度,复合地基的应力场和位移场的分布逐渐稳定,所以不仅对承载力存在临界桩长问题,对于复合地基的变形来说在一定条件下也存在临界桩长。碎石桩复合地基中桩的作用主要是减小沉降。(3)为了充分发挥桩、土的承载能力,在设计碎石桩桩径时,应选取一个合适的置换率。一味的增加置换率来加大加固层的刚度以达到减小沉降的方法是不可取的,设计中应根据工程地质条件和建筑的上部荷载大小选取最优置换率。(4)当桩周土的变形模量大于8MPa后,采用碎石桩加固效果不明显。更多还原

【Abstract】 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.更多还原