天然沉积土结构渐进损伤机理与定量演变规律研究

It has been well documented that natural soils are generally subjected to the effects of soil structure. The soil structure becomes unstable and is easily damaged under external loads, consequently resulting in engineering disasters. Hence, how to evaluate quantitatively the progressive destructuration for natural soils under external loads is an important issue in engineering practice. This study is focused on the complementary works of the sensitivity framework proposed by Chandler (2000), which is the most advantageous theory in assessing quantitatively the effects of soil structure on mechanical behavior of natural soils. The Liu-Carter model is incorporated with intrinsic compression theory, extended intrinsic compression line and intrinsic strength line for developing the change law in progressive destructuration during compression. The research results obtained in this study will not only improve the Chandler sensitivity theory, but also provide a simple way of applying the sensitivity theory in engineering practice. The main contributions of this study are expected as follows: 1) establishing a simple method of determining the normalized compression line and the normalied strength line of various reconstituted soils at different initial water contents, overcoming the difficulty in the Chandler sensitivity framework of determining the compression reference and the strength reference with special equapments; 2) proposing the model of describing the rate of progressive destructuration, breaking through the limit of the Chandler sensitivity framework unable to evaluate the progress destructuration of natural soils during compression; 3) making clear the essential relationship between the yielding and the undrained shear strength during the progressive destructuration, breaking through the assumption of stress sentivity equal to strength sentivity in the Chandler sensitivity framework, consequently enabling it to meet the requirements of application in engineering practice.

天然沉积土在外部环境作用下极易发生土结构损伤而导致工程灾变， Chandler灵敏度体系是目前得到广泛采纳的定量评价土结构性的一个理论框架。针对Chandler灵敏度体系只能定量评价土结构性的强弱程度而不能评价土结构渐进损伤的关键科学问题，本研究耦合Liu-Carter模型、固有压缩理论和固有强度线，构建土结构性和渐进损伤发展过程的定量评价方法，为完善Chandler灵敏度理论体系及其应用于实际工程奠定基础。预期的主要贡献如下：1）提出天然沉积土结构渐进损伤基准的确定方法，突破Chandler灵敏度体系中评价基准线依赖专用试验设备且精度要求高的困境；2）提出在外加荷载作用下天然沉积土结构损伤速率的定量演变规律，弥补Chandler灵敏度体系没有考虑土结构渐进损伤的缺陷；3）揭示天然沉积土屈服渐进损伤与强度渐进损伤的内在联系，解决Chandler灵敏度体系适用条件经常与实际工况不吻合的难题。

天然沉积结构性土地基在外部环境作用下经常发生土结构损伤而导致地基工后沉降大、基坑塌陷、大面积滑坡等重大工程灾变问题。本项目针对现有灵敏度体系只能分析土结构性的强弱程度而不能评价土结构渐进损伤的关键科学问题，以天然沉积结构性土为研究对象，采用试验、理论分析与数值模拟相结合的方法，展开了系统研究，获得了以下主要创新成果：（1）结合项目课题组提出的重塑屈服概念和初始状态对压缩性状的影响规律，建立了能够覆盖实际工程中遇到的大多数天然沉积土的压缩屈服渐进损伤评价基准，提出了相关关键参数的确定方法与定量表达式，弥补了现有土结构性评价体系忽视重塑土初始状态影响的重大缺陷；（2）基于课题组提出的天然沉积土压缩性状三个阶段控制机理，构建了描述土结构压缩渐进屈服损伤的演化模型，弥补现有土结构性灵敏度体系没有考虑土结构渐进损伤的缺陷；（3）构建了能够考虑应力路径和初始状态影响的固结不排水抗剪强度与孔隙指数关系随强度应力比的定量演变规律，揭示了天然沉积土压缩屈服渐进损伤与强度渐进损伤的内在联系，解决了现有土结构性灵敏度体系经常与实际工况不吻合的难题。本研究的成果不仅攻克了现有土结构性评价体系的重大缺陷，也为灵敏度理论应用于实际工程提供一条简单实用的路径，能够有效应用于天然沉积土地基处理、边坡工程、基坑开挖、地下工程的技术创新与实践。