A Multi-Scale Study on the Property Degradation of High-Temperature Treated Beishan Granite

Abstract

Granite is the main host rock for the underground storage of nuclear waste in Beishan, China. Heat is continuously generated during the long-term disposal of nuclear waste; therefore, it is important to investigate the influence of high temperature on the physical and mechanical properties and the constitutive relation of Beishan granite. In this study, laboratory experiments on heat-treated (25 ∘C, 200 ∘C, 400 ∘C, 600 ∘C and 800 ∘C) Beishan granite samples were performed in combination with nuclear magnetic resonance (NMR) analysis and regular physical-mechanical tests. The results show that the elastic modulus tends to decline faster at the temperature ranges of 25–200 ∘C and 600–800 ∘C by approximately 26.767% and 66.996%, respectively. Compared with the results at 25 ∘C, the peak stress decreases by 72.664% at 800 ∘C. The peak strain increases gradually from 25 ∘C to 600 ∘C and abruptly from 600 ∘C to 800 ∘C. The peak strain at 800 ∘C is 2.303× greater than that at 25 ∘C. Based on the damage theory, the Weibull distribution, the rock damage threshold point, and the residual strength, this study corrected the Drucker–Prager (D–P) criterion to consider the damage stress and then to establish the constitutive model of thermally damaged Beishan granite. The parameters required for the model are conventional mechanical parameters that can be calculated from the uniaxial test results, thus making the model convenient to apply. Meanwhile, the mechanical behavior of thermally damaged Beishan granite under uniaxial compression was simulated using the Particle Flow Code (PFC) to explore the development of cracks from the microscopic scale. The research results can provide theoretical support for the calculation and numerical simulation related to the mechanics of high-temperature treated rocks.

Study on the Evolution of Physical Parameters and Dynamic Compression Mechanical Properties of Granite after Different Heating and Cooling Cycles

“…From Figure 14 a,b, it can be seen that the effect of the number of heating and cooling cycles on the strain rate of granite is more significant under the water cooling method, and the slopes of the fitted curves for water cooling are 0.6419, 0.8975 and 1.8579 for the heating temperatures of 200 °C, 400 °C and 600 °C, respectively; the slopes of the fitted curves for natural cooling are 0.2510, 0.5347 and 1.5678, corresponding to 2.56, 1.68 and 1.19 times of the slope of the water-cooled fitted curve than that of the natural-cooled fitted curve, respectively. The trend of strain rate variation is consistent with the results obtained by Zhang et al [ 12 ].…”

“…Xu et al [ 10 ] and Zhou et al [ 11 ] investigated the thermal microcrack extension of granite using optical microscopy, thin section observation and scanning electron microscopy (SEM). Zhang et al [ 12 ] and Hao et al [ 13 ] investigated the effect of temperature on the physical and mechanical properties, as well as the intrinsic structure relationship, of granite. Ding et al [ 14 ] studied the effect of temperature on the permeability of fractured granite.…”