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ABSTRACT In order to assess the rock mass classification for rock slopes in cold regions, freeze-thaw cycling tests of granite were performed with the samples collected on site according to the particular climate conditions in cold regions, and related parameters were obtained. With the entropy weight method and the matter-element extension theory, an evaluation model of rock mass quality for rock slopes in cold regions was established on the basis of entropy weight and the extension theory with the eight mechanical parameters of rock physics. When this model was applied to evaluating the granite quality which had undergone 0, 10, 20, 40 and 60 freeze-thaw cycles, the evaluation result accorded with the real situation, which verified the accuracy of the evaluation model. The result shows that this model of evaluating the rock mass classification for rock slopes in cold regions could provide guidance to safe production.
1. INTRODUCTION The permafrost regions of China have an area of 2.15 million square kilometers in cold regions, ranking third in the world, most of which are located at the high latitudes of northeast China and high altitudes in the west area (Liu et al., 2005). Due to the particularity of the climate in the cold regions, the rock is often affected by the freeze-thaw cycles, which causes the cracks in the rock mass to expand, increase and penetrate, resulting in the damage of the mechanical properties of the rock mass and leading to slope instability. A scientific and accurate understanding of rock mass classification for rock slopes in cold regions is an important prerequisite for the stability evaluation. Therefore, it is great significance to conduct research on rock mass classification for rock slopes in cold regions.
At present, the studies on the rock classification for slope rock masses mainly focus on common slopes and underground hard rock engineering. For example, the extension theory was used to make a graded prediction of the rock mass classification for high slopes (Kang et al., 2007; Liang et al., 2010; Liu et al., 2013). Hu (Hu et al., 2012) selected five influencing factors based on the RSTOPSIS method, and took the first phase underground project of Guangzhou pumped storage power station as an example to evaluate the quality of the rock mass. Wu (Wu and Wang, 2014) proposed a method of rock mass classification for rock slope based on the rock mass quality index BQ, and verified its applicability. In the study of rock slopes in cold regions, Qiao (Qiao et al., 2015) analyzed the freeze-thaw damage mechanism of rock masses at different scales through field investigations and laboratory tests. Wen (Wen et al., 2015) performed a freeze-thaw cycle experiment on three typical types of hard rock (granite porphyry, limestone, and quartz sandstone) on the slope of the Yulong Copper Mine in Tibet. The changes of the physical and mechanical properties of the hard rock in the saturated state were studied, and the safety factor of the mine slope before and after freezing and thawing was calculated by the strength reduction method. Two machine learning methods of correlation vector regression and support vector regression were used to the RMR prediction of the main rock of the tunnel (Gholami et al., 2013). The results show that the empirical RMR value is greater than the model prediction value. Liu (Liu and Chen, 2007) combined the analytic hierarchy process and Delphi method to take the rock slope rock mass as a group decision problem, and applied fuzzy logic theory to the weighting factor calculation. Finally, the linear discriminant method was used to determine the stability of rock mass for the slope. Luo (Luo et al., 2015) combined with the hardness and freeze-thaw coefficient of rock on the basis of freeze-thaw cycle test, and the damage of rock under freeze-thaw cycle was quantified. Li (Li et al., 2018) took samples from slopes in cold regions, performed the freeze-thaw cycles and uniaxial compression tests on rock samples. The experimental results were used to analyze the stability of open-pit mine slopes, and the slope safety factors before and after freeze-thaw were obtained. These research results provide reference for the evaluation of rock mass classification in cold regions. But there are still few studies on the rock mass classification for rock slopes in cold regions. Therefore, a method for evaluating the rock mass classification for rock slope in cold regions is needed.
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