Luxin Dai

Huanghuai area is rich in coal resources, but due to the increasingly complex geological environment faced by coal mining, the complexity of structural stress is one of the main problems. In order to find out the distribution law of deep in situ stress in the Huanghuai area, the in situ stress measurement data of 81 effective measuring points in 24 mines with depths ranging from −100 m to −1200 m are analyzed in the present study base on the in situ stress measurement data. Furthermore, numerical simulation and field observation are used to analyze the deformation and failure characteristics of the surrounding rock. The research results show that the deep mining area of Huanghuai exhibited a high stress level, and the vertical and horizontal principal stress increases with increasing depth. The ratio of the lateral pressure coefficient ranges from 0.90 to 2.70, and the in situ stress field presented a trend of transition to the quasihydrostatic pressure field type as the depth extended, in which 80.23% of the measuring points are distributed between 1.20 and 2.10, belonging to the typical tectonic stress field type in which tectonic stress is absolutely dominant. The observation results of the surrounding rock and numerical simulation reveal that when the layout axis of the roadway is approximately perpendicular to the direction of the maximum horizontal principal stress, a high stress concentration area is present on the roof and floor of the roadway, the deformation increases sharply, and the support pressure of the roof and floor increases.

Due to the lack of historical subsidence data on goaf sites alongside expressways, it is difficult to comprehensively evaluate the stability of goaf sites and accurately identify potential risk points. An investigation to study the stability of goaf sites in the Huaibei section of the Xu Huaifu Expressway is conducted through SBAS-InSAR technology and field investigation. Initially, the stability of the goaf site around the route is anticipated through field investigation. Afterwards, based on the extraction of Sentinel-1 satellite images, subsidence data of the goaf sites from 2017 to 2021 were extracted. Finally, the stability of risk points is analysed. Results demonstrate that although mining in the area stopped more than five years ago, the goaf site has continued to slowly sink. According to four years of goaf site subsidence data extracted by SBAS-InSAR technology, two subsidence risk areas, namely, Y1-05 and Y1-09, were discovered, and the subsidence areas displayed an obvious inverted “convex” shape. Of these two areas, Y1-05 is a potential risk point that was not found during the field investigation. The subsidence basin in the Y1-05 area has developed gradually, and the residual subsidence is expected to be close to 475 millimetres within the next 15 years. Although it can be considered a stable area, the subsidence value is quite large and may pose risks to route safety. Therefore, a flexible reinforced mesh can be adopted for the route. The subsidence basin of Y1-09 is the largest, but the expected residual subsidence is only 50 millimetres and will have insignificant influence on the route. Engineering practice shows that SBAS-InSAR technology can effectively analyse the surface deformation of goaf sites and has important practical significance in optimising the selection of special geological routes in expressways.