【作者】 胡士兵；

【导师】 朱向荣；

【作者基本信息】 浙江大学 ， 岩土工程， 2007， 博士

【摘要】 随着经济社会的发展，城市化进程不断加快，城市用地也越来越紧张，在密集城区进行建设成为不得已的选择。如何在建设过程减少对环境的影响成为一个值得研究的重大课题。在密集城区沉桩影响环境是其中的一个重要问题，有效地预估沉桩挤土效应以减少对邻近建筑物和地下公用设施等的影响和破坏具有重要的理论和实际意义。圆孔扩张理论、有限元法数值模拟是研究沉桩挤土问题最常用的两种方法，本文在前人工作的基础上，合理假设，考虑各种因素的影响，采用解析理论与数值模拟的方法对沉桩挤土效应进行研究。首先，根据土塑性力学的基本原理和常规三轴试验结果，假设土体应力应变关系为均质各向同性的三折线或四折线线性软化模型，认为土体软化过程是土体屈服强度随应变线性降低，引入剪胀角考虑土体的剪胀性，采用Mohr-Coulomb屈服准则、双剪统一强度屈服准则，考虑土体大小应变，推导得到了球孔扩张问题解析解，分析了塑性区变形、软化参数、大小应变对孔扩张解答结果的影响。其次，为模拟在半无限空间中的沉桩挤土问题，假定沉桩过程是若干个球孔在不同位置的扩张效应的累加，以本文所得的球孔扩张解析解为基础，借助源-源和源-汇手段，推导得到了沉桩挤土效应的解析解。第三，根据现有有限元方法在模拟沉桩挤土过程之不足，采用符合实际沉桩过程的位移贯入法，考虑初始应力场的影响，采用Mohr-Coulomb模型，数值模拟研究沉桩挤土效应，分析了土性等参数(黏聚力、摩擦角、弹性模量、泊松比、剪胀角、桩土界面摩擦系数)对沉桩挤土位移的影响，讨论了考虑初始应力场与否对挤土效应的差别，分析了桩体下沉过程中土体内各点挤土效应的变化规律，讨论了桩长不同时对挤土性状的影响。最后，采用有限元模拟分析了饱和土体中沉桩引起的超静孔隙水压力的分布和固结规律，讨论了静孔压消散、有效应力增长、地表初始隆起量降低的发展过程，研究了土性等参数(黏聚力、摩擦角、弹性模量、泊松比、桩土界面摩擦系数、渗透系数)对固结过程的影响。更多还原

【Abstract】 With the rapid development of economic, urbanization developed quickly, available earth in city become rare, so it became inevitable that buildings are constructed in dense city zone, which make it become an important subject that how to reduce the bad effect produced during construction, the bad effect caused by driving pile is severe, how to predict and reduce the effect on surrounding region would have theoretical and practical value. Cavities expansion and finite element method are used widely in studying pile driving effects, on the base of past researches, such two methods were improved by introducing more appropriate hypothesis and considering more completely the factors involved in pile driving.Firstly, by using the principle of the elasto-plastic theory and the outcomes of routine triaxial test, the soil was assumed to be a homgeneous, isotropic matrial obeying tri-linear and tetra-linear softering model that considered the yield strength was dropped lineary with strain the dilation was considered, the Mohr-Coulomb and twin -shear united strength theory yield criterion were adopted individualy, big strain theory and small strain theory were also considered, on all these supposes, analytic solution of spherical cavities expansion was got. the influence of wether or not to consider elastic deformation in plastic zone and test and softening parameters and big and small strain were analyzed.Secondly, on the suppose that the effect of pile driving was the accumulation of effects of a lot of sole spherical cavity expansion, on the base of the analytical solution got, by making use of a source-source and a source-sink imaging technique, a anlytical solution predicting the effect of pile driving was obtained.Thirdly, according to some shortcomings in simulation of pile driving by finite element method, on the idea of displacement penetration, finite element method was used to analyze the compacting effects of pile driving with the consideration of influence of initial stress and with the use of Mohr-Coulomb model. The influence of some factors were analyzed, the difference of whether or not to consider the initial stress was discussed, the variation of discipline of compacting effect with the the sink of pile was analyzed, the discipline of compacting effect of different length of pile was also analyzed.Finally, the discipline of distribution and consolidation of excess hydraulic pressure was simulated when piles were drived in saturated soft soil, the unified process of the dissipationof excess hydraulic pressure and the increase of effective stress and the decrease of heave of soil surface was discussed, the influence on discipline of consolidation of some factors of soil are analyzed.更多还原