【作者】 李金柱；

【导师】 谢新宇； 朱向荣；

【作者基本信息】 浙江大学 ， 岩土工程， 2011， 博士

【摘要】 固结理论是土力学研究的基本课题之一,自Terzaghi一维固结理论提出以来,各国学者在其基础上进行了不断的深入和完善。在沿海和沿江沿河地带广泛分布着深厚软土层,人们通过这些地区长期的软土工程实践发现,软黏土地基的固结变形较大,Terzaghi固结理论中的小应变假设不再成立,而需要采用大应变假定。同时,随着现代工程地基工后沉降要求的越来越严格,对合理、准确地预测地基沉降发展过程提出了更高的要求,软黏土的流变特性也随之受到人们的重视。基于此,本文通过理论研究、室内试验、数值模拟和工程实例,对软黏土地基的大应变流变固结问题进行了深入地探讨。本文主要工作有：(1)基于连续介质力学原理,同时考虑了几何非线性和材料非线性,建立了U.L.描述的大应变固结问题的平衡方程和连续性方程,并进一步得到了大应变固结有限元法控制方程。(2)对宁波软土进行了一系列的一维固结流变试验,并利用自行改装的应力控制式三轴剪力仪,进行了不同围压条件下的三轴固结排水流变试验,对一维固结流变试验结果和三轴固结排水流变试验结果进行了对比研究,系统分析了宁波软土的流变特性。(3)将西原模型推广到三维,采用修正剑桥模型屈服准则来描述土体的塑性屈服,推导了土体的本构关系,建立了能够全面反映宁波软土流变特性的三维流变模型,并对三轴排水流变试验成果进行了曲线拟合,验证了本文模型的合理性,得到了不同围压及偏压条件下的模型参数。(4)在大型通用有限元软件ABAQUS的基础上,开发了本文所建立的流变模型的用户材料子程序UMAT。通过单轴压缩数值模拟与解析理论的对比,验证了本文UMAT的正确性,并对模型参数进行了敏感性分析。基于本文模型,研究了同时考虑流变效应、自重荷载、渗流非线性等复杂条件下的软黏土地基大应变固结过程中的超静孔压消散过程和地基沉降发展规律,与小应变固结计算结果进行了对比分析。(5)利用本文建立的流变模型和拟合的模型参数,通过三维数值模拟计算了某软土地基堆载预压试验过程中地基长期沉降发展过程和超静孔压消散过程,并与实际观测数据进行了对比,验证了本文提出的流变模型应用于宁波软土的适用性,同时验证了深厚软土地基固结过程中考虑大应变效应的必要性。本文研究同时考虑了固结过程中的大应变效应和流变效应,所得结果对软黏土地基处理具有重要的参考意义,丰富了软黏土地基的固结理论,为进一步研究软黏土地基复杂非线性固结问题奠定了基础。更多还原

【Abstract】 Consolidation theory is one of the basic subjects of soil mechanics, since one dimensional consolidation theory was proposed by Terzaghi in 1920s, there were many researchers had made further researches and continuously improvement on the basis of Terzaghi’s theory. There is widely distributed of deep soft soil along the coastal areas and rivers all over the world, people found that the consolidation displacement usually was very large, then the hypothsises of Terzaghi’s theory were not suitable any more, and the hypothesis of large strain was needed. In the same way, with the increasing strict requirement of foundation post-construction settment, the requirement of reasonably and accurately prediction of foundation settment process was higher and higher, the rheological property of soft soil was paid more and more attention. Based on this, the thesis studied the large strain consolidation of soft soil considering rheological effect through theory analysis, laboratory experiment and engineering example. The main work of this thesis is as follows:(1) On the basis of continuum mechanics principle, the balance equation and the continuity equation of large strain consolidation were derived by updated Lagrange description considering the geometric nonlinearity and material nonlinearity simultaneously, further more:the FEA control equation of large strain consolidation was obtained.(2) A series of one dimensional consolidation rheological tests were taken on Ningbo soft soil, and triaxial consolidated drained rheological tests were taken through self-refitted stress-controlled triaxial apparatus. The results of one dimensional consolidation rheological tests and triaxial rheological tests were compared, based on which the rheological property of Ningbo soft soil was analyzed systematically.(3) The Nishihara model was extended to three dimensions, and the plastic yield of soil was described by modified Cambridge model combined with over-stress theory. The constitutive relationship of soil was derived, and a three dimensional rheological model which can describe the rheological property of soil comprehensively was set up. The model was fitted by triaxial rheological tests, and the model parameters of different confining pressure and deviatoric pressure were obtained.(4) On the basis of general FEA software ABAQUS, the user material subroutine (UMAT) of the rheological model proposed by this thesis was coded. The correctness of the UMAT was verified by a uniaxial compression numerical simulation. Based on the model of this thesis, large strain consolidation of soft soil was studied considering rheological effect, self load and permeability nonlinearity simultaneously, and the rules of the dissipation of the excess pore pressure and the displacement of soil was analyzed. The results of large strain were compared with that of small strain, and the sensitivity of the model parameters was analyzed.(5) Using the proposed rheological model and the fitted model parameters, three dimensional numerical simulation was performed on a surcharge preloading test of soft soil. The measured data of the displacement of soil and the dissipation of excess pore pressure was compared with the computed results, through which the property of the proposed model and the UMAT was verified.Considering the large strain effect and rheological effect simultaneously, the results of this thesis have important reference significance in the foundation treatment of soft soil. The results also will be an enrichment of the consolidation theory of soft soil and an establishment of the foundation of further study of complex nonlinearity consolidation problem.更多还原