Reclamation Suitability Evaluation of Damaged Mined Land Based on the Limit Condition Method－Example of Pingdingshan Tianan Ten Coal Mine

Reclamation suitability evaluation is the basis for determining the reuse direction of damaged land. Limit condition method is the most widely used method in land reclamation suitability evaluation at present. In this paper, the limit condition method is used to evaluate the suitability of land reclamation of damaged land in Pingdingshan Tianan ten coal mine. The evaluation index of damaged area is determined as six main factors: field slope/land flatness, ponding, depth of collapse, soil texture, thickness of soil layer, irrigation and drainage conditions, and finally determine the reclamation direction of the land to be reclaimed in combination with the overall local land use planning and the overall wishes of local residents.


INTRODUCTION
With the increasingly prominent conflict between human and land in China, cherishing and rational use of land has been elevated to a national strategic level. More than 95% of primary energy, 80% of industrial raw materials and 70% of agricultural production materials in China come from mineral resources [1] . Large-scale mining of mineral resources inevitably results in the occupation and destruction of large amounts of land, which seriously restricts the sustainable development of mining areas. Land reclamation work can effectively reduce the impact on ecological environment in the process of resource extraction. Therefore, restoring land productivity, increasing effective arable land area, and reclamation of damaged land is an important initiative to realize the sustainable development of ecological environment in mining areas.
Land reclamation suitability evaluation is a prospective and predictive evaluation that determines the reasonable direction of land use to be reclaimed based on the investigation of the overall land quality and the statistics and prediction of the damaged land, and provides the basis and foundation for realizing the effective reclamation of land in mining areas [2][3] . Land reclamation suitability evaluation in mining areas lays the foundation for the planning and design of reclamation programs, the determination of reclamation directions, and the implementation of reclamation techniques, and provides a scientific basis for the rational use of land resources and the optimal allocation of land structure, and it is an important way to achieve sustainable development and ecological civilization in mining areas [4 ]. In this paper, based on the analysis of the site survey and proposed damage prediction of Pingdingshan Tianan ten coal mine, the evaluation units are divided and the most suitable land reclamation direction for each evaluation unit is obtained using the limit condition method, which provides a scientific basis for the reasonable reclamation of land resources in the mine area.

GENERAL SITUATION OF STUDY AREA
The mine area spans two counties, Weidong District, Pingdingshan City and Xiangcheng County, Xuchang City, and is located in the transition area between the hills and the plains, with the overall topography being high in the north and low in the south, and the topography being moderately undulating. Surface water bodies are not developed in the mine area, which has a warm temperate continental semi-humid monsoon climate.
The total area of the mine site is 2061.58hm 2 , and the total area of reclamation responsibility is 1943.84hm 2 , including 453.16hm 2 of arable land; 163.73m 2 of garden (2) Division of evaluation unit The division of evaluation units should reflect the relatively homogeneous or similar nature within the unit, and comparability between units, which can objectively reflect the differences of land in a certain period and space [5] . Based on the principles of "similar land properties in the same evaluation unit" and "differences between evaluation units" [6] . The land reclamation suitability evaluation unit was divided into ten mine reclamation responsibility areas based on the type of land use, degree of damage, and the time sequence of damage of Pingdingshan Tianan ten coal mine.
The evaluation unit of land suitability was divided into 23 evaluation units within the reclamation responsibility area, based on the damage unit, and then divided into evaluation units according to the degree of damage and damage land type within the damage unit, and the basic information of each evaluation unit is shown in Table 1.
Among the damaged land types, the affected towns and villages and industrial and mining land will be repaired and reinforced in time (rebuilt after individual compensation for serious damage), while transportation land and land for water and water conservancy facilities will continue to be used through maintenance and reclaimed as the original land type, and no quantitative analysis will be done. (3)Evaluation method The limit condition method was used to evaluate the suitability of the land reclamation. The limiting method is based on the "barrel principle" of systems engineering, which means that the final quality of a classification unit depends on the quality of the least conditioned factor [7] .
According to the principle of the law of least factor, the suitability of the land and its grade are determined by the factor with the lowest suitability grade of a single factor among the selected evaluation factors [8] .
The calculation formula of the Limit Method is as follows: In the formula: Yi-final score of the ith evaluation unit Yij-score of the ith evaluation unit's jth eligible factor

Selection of evaluation factors and ranking indicators
The selection of the most important factors affecting land suitability for a particular land use or land use pattern as items to be evaluated is called evaluation factors [9] .Combining with the actual situation of Pingdingshan Tianan ten coal mine, the suitability evaluation indexes were determined as follows: field slope/land flatness, Ponding, depth of collapse, soil texture, thickness of soil layer, irrigation and drainage conditions.
The main limiting factors were selected for suitability evaluation grade criteria, and other limiting factors were used as reference factors to develop the grade criteria for the main limiting factors for land reclamation suitability evaluation in the project area, as shown in Table 2.  Table 3.   Table 4.
"Reclamation Suitability Evaluation of Damaged Mined Land Based on the Limit Condition Method-Example of Pingdingshan Tianan Ten Coal Mine"