砂砾石覆盖层的结构性本构模型与参数确定方法研究

China is facing great challenges of constructing high earth and rockfill dams and other hydraulic projects on thick gravel overburden layers. The existing technological and economical limitations, however, pose great difficulty in an in-depth understanding of the mechanical behavior of overburden soils, as was gained for dam materials. As a result, constitutive models proposed for reconstituted dam materials were generally used in evaluating the performance of dams and foundations, neglecting the obvious in-situ structure of overburden soils. In this study, compression, shearing and resonant column tests will be performed to investigate the mechanical behavior of artificially bonded overburden gravel soils. Particular attention will be focused on the difference of the mechanical behavior of structured soils and those of reconstituted samples as well as the influencing factors. Discrete element simulations will be carried out to study, on the microscopic level, the damage process of the internal structure along complex stress and strain paths. A structural index based on the small-strain shear modulus (or the shear wave velocity) will be suggested and the evolution function of this index will be constructed in the light of DEM simulations. A constitutive model considering the in-situ structure of overburden soils as well as its evolution during loading or straining will be proposed under the framework of hypoplasticity. The method of determining the model parameters using laboratory experiments and in-situ tests in a combined way will also be studied. It is expected to deepen the understanding of the mechanical behavior of overburden soils and enrich the constitutive modeling theory of structural soils by this study. It is also intended to provide a more reasonable and reliable constitutive model and corresponding parameter identification method for engineering practice.

我国具有在深厚砂砾石覆盖层上建设土石坝工程的重大需求，但目前对于砂砾石覆盖层力学特性的认识远不及土石坝筑坝材料。因此，在坝体和坝基工作性态分析时，大多套用重塑堆石料本构模型，忽略覆盖层砂砾石料原位结构对其力学特性的影响。本项目以具有初始胶结的覆盖层砂砾石为研究对象，通过压缩、剪切和共振柱试验研究不同应变水平时覆盖层砂砾石与其重塑样的力学特性差异及其影响因素；运用离散单元法（DEM）模拟复杂应力和应变路径下人工胶结覆盖层砂砾石料内部结构损伤过程；构建一个基于小应变剪切模量（或波速）的结构性指标及其演化方程；在亚塑性理论框架内，提出一个考虑覆盖层砂砾石料原位结构及其演化规律的本构模型；探索综合运用室内试验和现场试验确定结构性本构模型参数的方法。拟通过本项目研究，深化对砂砾石覆盖层力学特性的认识，丰富结构性土体的本构理论，为我国深厚覆盖层上工程建设提供更加符合实际的土体本构模型和参数确定方法。

深厚砂砾石覆盖层上建设土石坝工程是我国重大挑战，但长期以来对于砂砾石覆盖层力学特性的认识远不及土石坝筑坝材料。因此，在坝体和坝基工作性态分析时，大多套用重塑堆石料的本构模型，忽略覆盖层砂砾石料原位结构对其力学特性的影响。本项目以具有初始胶结的覆盖层砂砾石为研究对象，通过大型静动力三轴试验，研究了胶结结构对覆盖层砂砾石强度、剪胀（缩）、动模量以及阻尼比的影响规律；开展离散单元法（DEM）数值模拟，研究了颗粒间胶结结构的破坏损伤规律；在亚塑性理论框架内，提出一个考虑覆盖层砂砾石料原位结构及其演化规律的本构模型和参数确定方法。通过本项目研究，深化了对砂砾石覆盖层静动力学特性的认识，丰富了结构性土体的本构理论，为我国深厚覆盖层上工程建设提供了更加符合实际的土体本构模型和参数确定方法。