【作者】 刘畅；

【导师】 郑刚；

【作者基本信息】 天津大学 ， 岩土工程， 2008， 博士

【摘要】 目前天津滨海新区正在和将要进行大力开发和建设,针对软土基坑开挖中的关键性问题,结合目前基坑工程研究现状,本文主要进行以下几方面的工作:总结了基坑开挖中土体应力路径,采用薄壁取土器取得天津滨海新区淤泥质软粘土土样,按照不同的卸荷应力比进行K 0固结应力路径试验,分析了基坑开挖不同卸荷应力路径下土体的变形特性,归纳了土体初始卸荷模量的计算公式,并给出了不同卸荷应力路径的初始卸荷模量值。结合天津滨海新区某基坑工程,对基坑开挖影响范围内软土层进行了常规三轴试验和考虑应力路径的K 0固结卸荷试验,对比分析了不同固结压力和应力路径条件下土体的抗剪强度指标的不同,探讨了应力路径对天津滨海新区软粘土强度特性的影响。根据三轴试验结果,选用硬化土体模型进行有限元分析,分析了各模量参数取值对有限元计算结果的影响;结合天津开发区某深基坑工程,进行了硬化土体模型模量参数测定,试图找到硬化土体模量参数与压缩模量的关系;对土样进行了直剪固结快剪试验、常规三轴固结不排水剪和K 0固结卸荷不排水剪试验,应用不同强度指标及模量参数试验结果对工程进行有限元模拟,对比分析了不同强度指标对工程有限元计算结果的影响,并与工程实测结果进行了对比。探讨反压土与支护结构相互作用的机理,采用有限元计算分析了反压土宽度、坡度、高度等截面特性对支护结构位移和内力的影响规律,找到了最优截面参数与基坑开挖深度等的关系,以此为依据给出了反压土与支护结构相互作用的弹性抗力法简化计算方法,以弹簧来模拟反压土的作用,并给出了弹簧刚度的确定方法。并运用本文提出的简化计算方法对一个离心模型试验和两个典型工程实例进行了模拟,并与有限元和实测结果进行了对比分析。在对支护结构土压力计算理论与方法研究现状进行充分了解的基础上,建立考虑支护结构变形对土压力影响的线性和非线性土压力的计算公式,并编制了有限元软件,首次对比分析了线性、非线性(三角函数法、双曲线法)主动区土压力模型对支护结构内力、变形和土压力分布的影响差异,探讨了参数取值的影响。在对基坑支护平面分析的基础上,编制了一套引入线性及非线性土压力的空间计算软件,并编制了强大的前后处理程序,运用该软件对存在深、浅不同挖深的基坑及某工程实例进行了计算和分析。得到了可供工程借鉴的结论。更多还原

【Abstract】 Nowadays, the new coastal region of Tianjin is developing greatly. On basis of the present research and the key problems in foundation pit in soft soil, the main work of this thesis is as follows:Based on summarizing the stress paths under unloading state during excavation, the soft clay samples in the new coastal region of tianjin are obtained by using thin wall sampler and a series of K0 consolidation stress path tests have been carried out according to different unloading stress ration to study the unloading deformation properties of foundation pit in different unloading stress paths. The soil calculation formula of the initial unloading modulus is induced and the values of the initial unloading modulus under different unloading stress path are given. In combination with one foundation pit project in the new coastal region of Tianjin, the general tri-axial tests and K0 consolidation stress path tests have been done in the soft soil layer of the foundation pit. The comparative analysis of the difference of the shear strength parameters in various consolidation pressures and stress paths is made and the influence of the stress path to the soft soil strength properties in the new coastal region of Tianjin is preliminaryly studied.According to the results of tri-axial tests, the finite element analysis is made by using hardening-soil model, and the influence of the values of model parameters in finite element calculation is analyzed. In combination with a deep foundation pit project in Tianjin Economic Technique Development Area, the modulus of hardening-soil model are determined and the relationship between the modulus of hardening model and the compression modulus is attempted to be found. The project is simulated by finite element method with different strengths according to direct shear consolidation fast test and regular tri-axial consolidation undrained test and K0 consolidation unloading undrained test. The influence of different strength parameters to the result of finite element calculation is analyzed and the calculation result is comprised to the result of the project monitoring.In order to find the interactional mechanism of soil and the foundation pit retaining structure ,the influence rules of the width and the slope and the height etc of the berm earth to the displacement and internal force of the retaining structure is analyzed with finite element method. The relationship between the optimal section parameters and the height of the foundation pit is found and the simplified elastic reaction method which reflects the interaction of the berm earth and the retaining structure is given. The effect of the berm earth is simulated by spring and the method of confirming the spring is given. A centrifugal model test and two typical projects are simulated by using the simplified calculation method in this thesis. The simplified calculation result is contrasted to the finite element calculation result and the monitoring result.Based on realizing the status of the earth pressure calculation theory and method, the linear and non-linear earth pressure calculation formulas considering the influence of the retaining structure displacement are found and the finite element program is made. For the first time, the influence of the linear and non-linear(trigonometric function method and hyperbola method) active region earth pressure models to the retaining structure inter force and displacement is analyzed and the effect of the parameter values is explored. Based on the analysis of foundation pit retaining plane problem, a space calculation software with linear and non-linear earth pressure and with preprocessing and postprocessing is made. By using the software , a foundation pit with different excavated depthes and a real project are calculated and analyzed, and some useful conclusions are gained.更多还原