Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository.
Coalbed methane is a kind of clean energy source and also a kind of hazardous gas threatening the safety of coal mine production. Permeability is a key parameter to evaluate gas migration capability. However, the permeability is influenced by moisture content. Here, a series of seepage experiments were conducted to analyze the development tendency of flux and permeability to reveal the impact mechanism. Experimental results show that permeability tends to be a sharp drop with increasing moisture, but it had a slight fluctuation with relative gas pressure increasing under the constant mean effective stress. Considering the effect of moisture and gas sorption, a new gas–solid coupling model was developed based on experimental results and theoretical analysis and was implemented into FEM software for simulation. The numerical results of the new gas–solid coupling model were in good accordance with the experimental results and have a priority to cube law in precision. This study reveals that, on the one hand, the moisture can influence the adsorption-induced strain and, on the other hand, it can lead to a significant decrease in porosity due to pore volume occupation. 相似文献