Analysis of failure mode and deformation evolution characteristics of slopes under the influence of highwall mining

The slope has the typical deformation failure and instability characteristics under the interaction of natural and human factors which has been given a lot of attention in geotechnical and mining engineering. During highwall mining, in particular, deformation evolution characteristics and failure mode are more complex under dual influence of open pit mine and underground mine. Physical modelling is an important means to study the characteristics and behavior of deformation and evolution of various types of rock and soil mass, and it is also an important supplement to the field study of large-scale rock and soil mass. It is widely used in mines and geotechnical engineering. The determination of the material used for physical modeling is the foundation and key links of research. Therefore, the article firstly selected river sand/aggregate, lime and gypsum/cemented material as the experimental materials through the relevant literature review and based on the principle of economic and convenience, and adopted two proportioning schemes to make standard specimens. The uniaxial compression test was carried out to compare and analyze the strength of the original rock, and it was determined that the scheme 2 could be used as the research scaling number of the physical modelling; Secondly, on the basis of determining the material proportion, the physical and structural model of highwall mining is established, and the analysis shows that the evolution characteristics of slope deformation and failure in the process of highwall mining can be divided into superficial transformation stage, structural transformation stage and aging deformation stage, the deformed and damaged rock mass can be divided into “vertical three zones”, namely caved zone, fractured zone and continuous bending zone. According to the length of the panel, the coal seam can be divided into three stages: initial stage, middle stage and final stage. The lower coal seam can be divided into two stages: the initial stage and the final stage. The evolution of the slope rock mass due to the extraction of the upper coal seam to the stopping line is characterized by the formation of subsidence faded areas along the center of the goaf to both sides, and finally a symmetrical distribution of semi-“pyramid” shape is formed. The rock mass that is deformed and damaged due to the extraction of the lower seam to the mining stop line is in a semi-curve-like shape; Finally, based on the analysis of physical modelling and field monitoring, it is concluded that when the upper coal seam of the highwall coal seam is mined to about 120 m, the slope shows a slight instability. When the lower coal seam is mined to about 120 m, the goaf between the upper and lower coal seams is connected, and the instability is intensified until the mining reaches the stopping line. In the upper part of the slope, 1400 step forms a local collapse instability zone pointing to the open-pit, while the rest of the step are anti-dip instability pointing to the goaf.