土体结构性数值模拟及应用研究

Numerical simulation on soil structure and its application research

随着现代地基原位取土技术的发展以及对土体微观结构认识的提高,越来越多的研究认识到未扰动状态下的自然原状土与重塑土相比其力学特性存在显著差异。为研究土体结构性的影响,在剑桥模型基础上考虑超固结与结构性状态变量因素的影响,在上下负荷面剑桥模型理论框架下,通过三轴压缩试验对结构性土的受力响应特性进行了模拟试验研究,对受结构性因素影响下土体的屈服过程、可压缩性、在循环加载作用下超孔隙水压的发展以及相应状态变量演化规律进行了详细对比分析。试验研究结果表明:与重塑土相比,结构性土的加载响应存在明显的屈服软化过程,加载过程中伴随着结构性的破坏表现出更高的可压缩性且更容易导致动力液化的发生。在对土体结构性详细研究的基础上,通过数值模拟桩柱结构在自然地基环境下的地震响应,对结构性因素对结构动力响应的影响进行了研究分析。研究结果表明:由于更高的非线性以及可压缩性特征,自然原状土地基在地震作用下能够引起更高的超孔隙水压,加速土体力学强度的衰减进程,进而表现出更大位移响应以及震后塑性位移,直接影响结构的稳定与安全。研究结论加深了对自然土体结构性的认识,可为高结构性自然原状土地基条件下的结构受力分析与设计提供参考。

With the development of modern in-situ soil sampling technology and the progressive understanding of natural soil's microscopic structure,more and more studies have revealed that the undisturbed natural soil has distinct mechanical performance compared with remould soil.In order to investigate the mechanical properties of soil structure,based on the classic Cam-clay model and in consideration of structure and over-consolidation factors,we propose a new structured soil model under framework of super-subloading surface Cam-clay model.Under the theoretic framework,the influence of structure on soil's yielding process,compressibility,development of excess pore water pressure and the corresponding evolution law of state variables were investigated in detail through triaxial compression tests.The results show that compared with remould soil,the structured soil shows obvious yield softening process,higher compressibility and easier liquefied tendency along with the decay of soil structure in the loading process.Based on the comprehensive investigation on soil structure,seismic simulation of a pile structure constructed on natural soil foundation was carried out and the influence of soil structure was studied.From the simulation results,it can be derived that due to the stronger nonlinearity and high compressibility of structured soil,the excess pore water pressure is more rapid to buildup and decay process of soil strength is accelerated,thus resulting in decrease of structure stiffness and larger dynamic response and more plastic deformation.The conclusions deepened the understanding of structured soil and provide some reference to the analysis and design of geotechnical structures built in undisturbed highly structured soil foundation.