Experimental Investigation of Thermal Cracking and Permeability Evolution of Granite with Varying Initial Damage under High Temperature and Triaxial Compression

Xiangxi Meng,Weitao Liu,Tao Meng

doi:10.1155/2018/8759740

Abstract

Thermal cracking and permeability evolution of granite under high temperature and triaxial compression are the key to designing high-level waste disposal sites. In this paper, uniaxial compression tests of granite specimens with different axial compression are designed, and then a solid-head-designed coupling triaxial testing system is applied to study thermal cracking and permeability evolution of granite specimen with different damage at different inlet gas pressures (1, 2, 4, and 6 MPa) and temperatures (ranging from 100 to 650°C). The test results show that granite, nearly impermeable rocks, can show a striking increase of permeability by heating beyond the critical temperature. When the initial axial pressure is 60% or 70% of the uniaxial compressive strength, the growth of granite permeability exhibits three stages during 100∼650°C heating process. Permeability increases by two orders of magnitude, but it does not reach the maximum value (i.e., a network of interconnected cracks is not fully formed in the specimen). With increasing initial damage, permeability shows a sharp increase. Permeability increases by three orders of magnitude, it is in equilibrium state, and a network of interconnected cracks is fully formed in the specimen. Permeability of granite has a critical temperature at which permeability increases sharply. When the temperature is lower than the critical temperature, the magnitude of permeability is 10−18 m2 with a slight increase. When temperature is higher than the critical temperature, the magnitude of permeability is 10−15 m2 with a sharp increase. The critical temperature is related to the initial damage of specimen, and the critical temperature is smaller with the initial damage going larger. Therefore, studying thermal cracking and permeability evolution of granite with different initial damage under high temperature and triaxial compression is expected to provide necessary and valuable insight into the design and construction of high-level waste disposal structures.

Highlights

Construction of an underground disposal for high-level nuclear waste is a complex project currently being studied by the nuclear states. e development of a nuclear waste disposal repository generally requires basic research, site selection, underground laboratory studies, and disposal library design, which is a long-term project
When the initial damage of granite is di erent, the change rule of permeability is different. e evolution of permeability can be roughly divided into two patterns, that is, granite specimen with the low initial damage and granite specimen with the high initial damage
For granite specimen with the high initial damage, with increasing temperature, permeability increases rapidly at the critical temperature, producing a rapidly growing surface, which is similar to a vertical face

Summary

Introduction

Construction of an underground disposal for high-level nuclear waste is a complex project currently being studied by the nuclear states. e development of a nuclear waste disposal repository generally requires basic research, site selection, underground laboratory studies, and disposal library design, which is a long-term project. E development of a nuclear waste disposal repository generally requires basic research, site selection, underground laboratory studies, and disposal library design, which is a long-term project. It is of great importance to examine the evolution of thermal damage and granite permeability high temperature and high stress conditions to provide support for nuclear waste disposal sites. For high-level radioactive waste repositories, a comprehensive understanding of the evolution of permeability with increasing temperature is fundamental. The above studies on the thermal cracking and permeability of granite mainly focus on the influence of high temperature. Few studies on thermal cracking and permeability evolution of granite with different initial damage under triaxial compression exist. E results of this study are expected to provide a necessary and valuable reference for the design and construction of high-level waste disposal sites Ermal cracking and permeability of the granite are studied by the self-designed solid-head-coupled triaxial rock permeability testing system. e results of this study are expected to provide a necessary and valuable reference for the design and construction of high-level waste disposal sites

Experimental Work

Experimental Procedure and Results Analysis

MPa 6 MPa

Conclusions