Experimental Study on Physical and Mechanical Properties of Beishan Granite after Cyclic Heating and Cooling with Water

Granite characterized by low permeability and high strength is commonly seen in underground construction. This paper is aiming at studying the influence of cyclic heating and water cooling on physicomechanical properties of Beishan granite, which is chosen as a potential host surrounding rock of a high level nuclear waste (HLW) repository. In this study, physical and mechanical properties of Beishan granite after repeated heating-cooling cycles are described. After five heating-cooling cycles with temperature up to 300 degrees C, the diameter and length of specimens increase by 0.090% and 0.052%, respectively. And the mass of specimen reduces by 0.32 g. In the following conventional triaxial compression (CTC) tests, the peak strength shows a slightly increase, but the dilatancy threshold decreases. And both peak strain and dilatancy threshold strain exhibit increase, which is responsible for the decrease of Young's modulus. During the test, acoustic emission (AE) is rarely monitored in the early loading and starts to generate systematically when the axial stress is beyond dilatancy threshold. On the other hand, in the hydraulic (HM) coupled experiments, both peak strength and dilatancy threshold show decrease. However, the ratio between dilatancy threshold and peak strength shows slightly increase. The same phenomenon can be observed for the peak strength and dilatancy threshold. The permeability shows rarely change compared with that of the specimen without experienced cyclic heating-cooling. AE is significantly monitored in the initial loading, which is seem more than that generated from dilatancy threshold to peak strength. The obtained results are useful for the construction of HLW repository.