孔隙水对花岗岩卸荷损伤演化的影响机理及理论模型研究

Due to its good integrity, low porosity and low permeability, the Beishan granite is considered as the most potential geological barriers for Chinese high-level radioactive waste repository. In Beishan area where the future repository will be excavated, the estimated in-situ pore water pressure is more than 4MPa. The excavation of disposal gallery concerns not only the redistribution of the initial in-situ stresses, but also the unloading of initial pore water pressure. The previous experimental investigation shows that pore water plays an important role in damage evolution and mechanical behaviour of granite. The proposed project aims at the effect of pore water on the granite damage evolution during unloading. The laboratory program is composed of a series of conventional triaxial tests, lateral extension tests and true triaxial tests. Moreover, the damage (micro-cracks) evolution during the laboratory tests is followed by using acoustic emission and CT techniques. Based on the experimental observations, a stress-dependent anisotropy damage tensor is firstly formulated. Afterward, using the poromechanics theory of Coussy, a poroplastic damage model will be proposed for granite with different water contents. The analysis and interpretation of obtained result in the present project will provide both the theoretical and numerical tools for the conception and construction of underground disposal galleries in Chinese repository for high-level radioactive wastes.

北山花岗岩因其完整性、低孔隙率、低渗透性被认为是我国核废料地下实验室和存储库的首选围岩。在北山地下工程建设范围内，其原位水压力可超过4MPa且花岗岩基本为水饱和状态。因此地下洞室开挖过程不仅是初始地应力的卸荷过程，同时也是初始孔隙水压力的卸荷过程。大量试验研究表明，孔隙水的存在对岩石的力学强度及损伤演化有重要影响。本项目以含水北山花岗岩卸荷过程中损伤演化规律为研究核心，通过一系列的宏细观试验研究，系统揭示并深入认识北山花岗岩卸荷过程中的损伤机理及其演化规律，特别是孔隙水对损伤演化规律的影响；提出能够合理描述含水北山花岗岩卸荷过程中细观物理演化机制和宏观力学行为的本构模型；建立能够较准确地模拟地下实验室及存储库开挖过程中初始地应力及水压力同时卸荷的数值分析方法。本项目的研究成果可为我国拟建地下实验室及核废料处置库设计、安全施工及长期稳定性分析提供基本的科学依据与重要的理论和技术支持。

北山花岗岩因其完整性、低孔隙率、低渗透性被认为是我国核废料地下实验室和存储库的首选围岩。按照项目的原计划主要开展了如下研究工作：分别进行了干燥和饱和条件下的北山花岗岩进行了常规三轴和真三轴的加卸荷实验和对应条件下的CT扫描试验，对北山花岗岩多场耦合状态下的应力与变形机理进行了研究；基于室内实验和细观分析，定义了损伤变量，建立了含水北山花岗岩细观-宏观损伤模型；针对地下洞室的开挖过程进行了数值模拟研究，验证了模型的合理性并获得了北山花岗岩地下洞室开挖过程的变形规律。本项目的研究成果可为我国拟建地下实验室及核废料处置库设计、安全施工及长期稳定性分析提供基本的科学依据与重要的理论和技术支持。