Construction and restoration technology of terrain remodeling layer in the restoration of ecological geological layer in open-pit mining areas

Mining can easily result in a series of change in the geomorphic form, such as irregular mining pits, high and steep slopes, slag hills, primitive soil failure and accumulated water in mining pits in the plateau and alpine mining area, which is in disharmony with the surrounding environment. Such changes of geomorphic form will not only adversely affect the surface ecological environment, but also bring different degrees of influence and damage to the shallow groundwater seepage field and the permafrost. In particular, the geological hazards and disasters such as landslides and collapses may even be resulted in. In response to these problems, the author put forward the idea and method of remodeling the mine landform after mining by constructing the terrain remodeling layer from the geological perspective. The key restoration technique of terrain remodeling layer was applied to the ecological environment governance and restoration in plateau and alpine open-pit mining area of Muli in Qinghai, with remarkable results achieved. Firstly, the terrain remodeling layer is identified, which is the complex shaped surface that plays a decisive role in controlling the stability and safety of terrain undulation, mining pits, and slag hill slopes. Definitely, the terrain remodeling layer is a complex, irregular and dynamically changing remodeling layer, which is a case of eco-geological restoration. Herein, the construction idea and method of terrain remolding layer was proposed as follows. (1) The mining pit, its slope and the slag hill after mining are systematically investigated, monitored and evaluated through the air-space-ground integrated geological exploration and monitoring. (2) The target geological body to be restored is classified based on the different restoration and governance objects. Here, the rock slopes were classified into 4 categories and 13 types by the changes in the lithology of the slope and the relationship between the inclination of the rock layers and the slope direction. (3) The morphology and occurrence of terrain remodeling layers for different restored geological bodies are determined through the theoretical calculations and field survey. (4) The comprehensive management of the mining pits and slag hills, as well as the restoration of mining terrain and landforms, can be achieved by soil covering and greening according to the field conditions. In this paper, the construction and restoration technology of terrain remolding layer was systematically discussed based on Muli mining area in Qingdao. For the restoration of the mining pit bottom, a reasonable bottom pattern should be designed with consideration to the depth of the damaged mining pit and the current condition of the terrain, so as to prevent the occurrence of geological disasters such as the secondary landslide or collapse. For slope treatment and restoration, it was determined through theoretical calculation and field observation that the reasonable slope angle should be less than 26° for the slope stability in Muli mining area. For slope treatment, the methods, including slope cleaning and building of step slope, should be adopted according to different types of rock slope, so as to ensure the stability of mining pit slope and later vegetation greening. For the treatment of special slag hill slope, it is necessary to form a shell of slag hill like an egg shell by building a hard terrain remodeling layer, to stabilize the terrain and landform, prevent soil erosion and conserving water sources. Comparison of the treatment results with the remote sensing image data before and after the mining area treatment shows that: the terrain of the mining area was disordered, the slope angle was large and unstable, and the vegetation was degraded before treatment. However, the slope angle of the mining area is basically below 26° and the vegetation grows well after the topographic and geomorphic remodeling, indicating a remarkable result of treatment. Generally, the construction method and restoration technology of terrain remolding layer proposed in this paper provide a new idea and method for the ecological management of plateau and alpine mining areas and the restoration of mine topography.