【作者】 何开胜；

【导师】 沈珠江；

【作者基本信息】 南京水利科学研究院 ， 岩土工程， 2001， 博士

【摘要】 本文调查了天然粘土中存在的结构性，应用大变形有限元法模拟了土颗粒骨架在内部分子吸力和电荷斥力以及外部荷载作用下的变形和蠕变机理，在此基础上建立了考虑天然粘土变形过程中结构性不断受损的弹粘塑损伤模型，并进行了室内和现场试验，论证了模型的有效性。 天然沉积粘土都具有一定的结构性（组构和胶结）和结构强度。大多数天然粘土的沉积压缩曲线位于重塑土固有压缩曲线的上方，其位置取决于沉积条件和沉积后的作用。天然粘土的沉积压缩曲线、重塑土的压缩曲线可以用孔隙指数来归一化，它清晰地显示出结构性土和重塑土的内在差别。重塑土反映了土体与自然状态无关的“固有特性”，它提供了一个评估原位自然沉积粘土特性的参考构架。从固结仪压缩曲线更可反映土体受荷后结构性的渐进破坏过程。 考虑小变形分析法在吹填土、软土地基和大位移问题上的局限性，从非线性连续介质力学出发，采用Jaumann应力率和Boit平面固结理论，推导了大变形本构方程。编制了大变形有限元分析程序，比较了大变形Lagrange法（TL和UL法）与小变形法的差异。结果表明：当应变小于7％时两者差异很小，只有在应变大于10％时才显示出愈来愈大的差异，这时用小变形法分析会大大高估地基的沉降值；大、小变形法的孔降水压力在应变较小时同步，在应变较大时并不同步，特别是TL法，故大小变形计算法的最终沉降比较应针对完全排水情况才有意义。大变形控制方程是高度非线性方程，经过线性化后，必须使用很小的时间步长，才能取得合理的计算精度和沉降结果。 为了解决大变形条件下多个物体间任意接触、滑移和旋转的模拟问题，提出了点面接触单元。将其与更新的Lagrange大变形有限元法相结合，可以很好的模拟微观土颗粒接触面的胶结、滑动、脱开，新接触的形成和老接触的转向。然后，用大变形有限元这个工具，研究了土颗粒骨架在双电层的物理化学力和外加荷载作用下的变形过程，揭示了结构性土体发生变形、破坏和蠕变的微观内在机理，为建立结构性土的本构模型提供微观基础。 针对过去用重塑土试验建立的本构模型，没能考虑天然土体中存在的结构性，没有描述结构性土从天然原状到加荷破坏的这一过程，建立了一个描述结构性土的弹粘塑损伤模型和参数确定方法。通过对室内试验的数值模拟表明，提出的弹粘塑损伤本构模型能模拟结构性粘土的拟超固结现象，加荷过程中的变形和孔压，排水蠕变和不排水蠕变，计算结果与试验值符合较好，初步验证了模型的有效性。 对长江下游河漫滩深厚软土地基进行了堆土预压试验。预压前在地基中埋设了沉降标、深层沉降管、测斜管、孔隙水压力计等土工观测仪器，堆土预压过程中对地基的变形和孔隙水压力进行全面观测，以及预压后长达3年的流变观测，为模型的工程验证提供了实测资料。堆土预压试验还表明，对26m厚淤泥质粘土用30m深的塑料排水板是可行的。 编制了结构性粘土的弹粘塑损伤模型有限元程序，对深厚软土地基堆土预压工程进行了数值模拟验证。通过现场钻孔取土和室内外试验，确定了淤泥质粘土层的弹粘塑性损伤模型参数；计算结果与观测结果的一致性表明，建立的弹粘塑损伤模型能很好反映结构性粘上的加荷变形、固结变形和蠕变变形，可用于结构性粘土的工程设计、计算和流变预测。 本项研究由国家自然科学基金资助（批准号：19772019）更多还原

【Abstract】 Microdeformation Mechanism of Structural Clays and Elasto-viscoplastic Damage Model ABSTRACT On the basis of the investigation of the structure of natural sedimentation clays and the simulation of the deformation and rheology of soil particle skeleton under the internal molecule attractive force and electric charge repulsion and the exterior load, a elasto-viscOplastic damage model is constructed in which the soil structure is considered to be gradually damaged in the course of loading, and the effectiveness of the model is verified by the results of laboratory tests and field tests. The clays from natural sedimentation have always the structure (fabric and bond) and structure strength. Most sedimentation compression lines of natural clays are located above the intrinsic compression lines of reconstituted clays; theirs locations are dependent on the sedimentation condition and the action after sedimentation. The sedimentation compression lines, intrinsic compression lines can be normalized by a void index, then the difference of the structural clays and reconstituted clays are showed. The reconstituted clays represent the soil intrinsic properties independent of the natural state, and provide a reference frame being used to evaluating the properties of in-situ sedimentation clays. From the oedometer compression curves, the gradual damage course of soil structure is indicated apparently during loading. The large strain constitute equations are derived according to nonlinear continuum mechanics, the rate of Jaumann stress and the theory of Boit consolidation on account of the limitation of small strain theory in hydraulic fill, soft ground and large displacement projects. A large strain FEM program is compiled to compare the difference of large strain method and small strain method. The results show that the deformation and pore water pressure are almost the same to the total and updated Lagrange method and small strain method when the strain is less then 7%. The different is evidently increased when the strain is more than 10% and the final settlements of large strain method are smaller than that of small strain method. The pore pressures are not the same to large and small strain method, so the comparison of final settlement should be based on total stress method(complete drainage). Moreover, in order to achieve reasonable calculating precision and settlement values, the time step should be very small due to the linearization of the high non-linear equation of large strain. The point-surface contact element is put forward to solve the large strain simulation of contact, slide and rotation among multi-objects. Combining with updated Lagrange method, it can well simulate the cementation, slide, unhitch, the formation of new contact and turnaround of present contact. Then, the deformation of soil particle skeleton under the physical chemistry of electrical double ]ayer and exterior load are simulated, indicating the micro-mechanism of deformation, failure and creep for structural soil. Because conventional constitute models are constructed according to reconstituted clays, not considering the structure in natural clays and structure damage course during loading, a elasto-viscoplastic damage model and the parameter determining method are put forward. The calculating results of laboratory tests demonstrate that the model can simulate the yield pressure of structure soil, the更多还原