Mine environmental restoration and management model

2) Dig deep pad shallow/local collapse pit backfill. The surface soil in the area to be repaired is mechanically peeled off, and the deformation area with small deformation is treated with deep digging and shallow pad. The existing collapse pit can be repaired with solid waste backfilling, and the pre-peeled topsoil is repeated after the design elevation is reached.

3) The water barrier layer of "deep digging area" is set. The water barrier layer is set with clay mud or impermeable film, and can be used as constructed wetland development area after the setting work is completed.

4) Development of constructed wetlands. According to the mine meteorological and hydrological conditions, a reasonable combination of wetland plants was selected based on the water accumulation caused by mine ground collapse and the technology of constructed wetland landscape development. In addition, with the mine water treatment technology, the coal mine wastewater purification and wetland landscape design can be combined to build constructed wetlands.

In terms of process flow, the topsoil in the area to be filled in the subsidence basin is firstly removed by mechanical stripping, solid waste such as gangue and fly ash is used to fill the filling area, and the pre-stripped topsoil is re-covered after the design elevation is reached. The uneven area in the affected area of the subsidence basin should be dug deep and shallow, and the water barrier layer should be set in the dug deep area to ensure that the water insulation of the dug deep area and the surrounding environment is intact. After the water barrier is set up, the dug area will be developed as constructed wetland or combined with the water subsidence area for unified development.

From the above description of the model, it can be seen that the topographic and geomorphic restoration of the ground subsidence area is a typical idea for the treatment of ground subsidence. On the basis of not affecting the original landform type, the use of coal gangue, fly ash and other repair

The terrain of the complex area can be repaired, and the restoration can be basically integrated with the original surrounding terrain. In general, because the collapse area is often large, the topographic slowdown is more economical than digging deep and shallow.

6.2 Baorixile mining area treatment project case

6.2.1 Mining area overview

Baolixile Mining area is located in the eastern part of the Chenqi coalfield, under the Chenbarhu Banner of Hulunbuir City. Since its development in the 1970s, it has been mined for nearly four decades. The mining area is wide-open and belongs to the high plain landform. The overall terrain is a gentle slope with a slope of 2° ~ 5° and a relative elevation difference of 120 m. The surface of the mining area is covered by the quaternary loose layer and there is no bedrock exposure. In the interior of the mine area, the strata are simple, mainly Cretaceous Jalainur Group, Cenozoic Quaternary Pleistocene series and Holocene series.

6.2.2 Distribution and cause analysis of ground collapse problems

The corresponding surface position of the main well fields in Baolixile mining area is mostly natural grassland. Due to the obvious surface collapse and deformation caused by mining for many years, a large area of surface collapse occurs along the coal mining face, most of which are subsidence basins with a large number of large subsidence pits inside the basins and strip-shaped fractures developing around the subsidence pits. The main reason for the formation of ground collapse in mining areas is the lack of awareness of mine environmental geological problems in the past. In the late 1990s, the number of small coal mines increased sharply, and large-scale and high-intensity mining caused serious mine ground collapse.

6.2.3 Mode selection and management project

Baolixile Mining area ground collapse control is the ground collapse control of the closed mine. Based on the analysis of the current situation of ground collapse problem in the mining area, considering the geological environment background of the mine, analyzing the terrain, geomorphologic characteristics of the area to be repaired, as well as the land use target and ecological restoration target in the later stage, the above model example 2 can be used for ground collapse control in Baolixile mining area. The improved model applied to the mining area is "dig deep and pad shallow/local collapse pit backfill + constructed wetland development". The mode is used as follows:

1) Dig deep and pad shallow: there are some water-logging areas in the sunken basin of Baolixile mining area. In the treatment project, dig deep and pad shallow in the water-logging area and its surrounding areas to further water storage, which has certain use value, such as drinking water points for livestock or fish ponds. The shallow bedding area is mainly the surface rupture area caused by the deformation of the subsidence basin. The soil in the deep digging area is used to cover the shallow bedding area, basically repair the topography of the shallow bedding area, and provide site preparation for the subsequent development of constructed wetlands.