The accurate prediction of surface subsidence is a significant foundation for the damage assessment of coal seam mining and ecological environment reclamation in loess donga. However, conventional models are very problematic, and the reliability of prediction is usually low. Therefore, we propose a method for predicting surface subsidence of coal seam mining in loess donga that is based on the probability integration model, combined with the movement principle of rock and soil layers in the respective study area, and considering the influence of slope stability and additional mining slip on mining subsidence. The feasibility of our new method was verified by a case study in the N1114 working face of the Ningtiaota coal mine (China) that is situated in an area with abundant loess dongas. The results show that slope slippage is the source of error in the prediction of subsidence in loess donga. The prediction idea of “dividing the surface of loess donga into horizontal strata area and slope sub-area, and predicting the subsidence value of the two areas, respectively” is put forward. A method for predicting the subsidence value of two regions is established. First, based on the theory of probability integral and rock formation movement, the probability integral parameters of the horizontal stratum area are determined, and the subsidence basins in the area are superimposed and calculated. Secondly, according to the slope stability and slip principle, the additional displacement of subsidence in the slope area with mining instability coefficient G_cs > 0.87 is calculated. Finally, combined with the subsidence prediction results of the strata area and the slope sub-area, and the position of the slope, the accurate prediction of the surface subsidence in loess donga is realized. Our results show that the agreement between the curves predicted from our calculations and from the measured data are between 88.7–97.8%. The calculated error of the additional displacement of slope mining slip is between 1.0–9.8%. The excellent correlation between the modelled and measured data documents that our method provides, demonstrated a new efficient and valuable tool for the precise prediction of damages induced by mining of underground coal seams in loess donga.

This paper aims to evaluate the severities and causes of ground surface building and cropland damages after coal mining in a better way, and to clarify the correlation between the damage assessment indexes that influence mining. Against the backdrop of multi-seam mining in certain coal mines in China, the estimated results of each displacement and deformation were analyzed using GIS technology. The damage range determined for each deformation index is divided according to the displacement and deformation combined with the virtue of damage judgment threshold. The damage ranges on the ground surface based on the comprehensive value of each displacement and deformation index were obtained through superimposing those ranges delineated by each displacement and deformation index, and the law on influence from displacement indexes upon various levels of damage was analyzed in a quantitative manner accordingly. The results showed that coal mining destroyed 14 buildings and a cropland area of 11.96 hm²; among them, building damage was only associated with displacement indexes E (horizontal deformation) and T (inclined deformation). Seven buildings were solely destroyed by T alone; five buildings were solely damaged by E; two buildings were damaged jointly by E and T; and, moreover, with the aggravation in building damage level, the proportion of building damage due to E decreased while the proportion of building damage under the same level due to T increased. Regarding cropland destruction, the damage due to T accounted for 33.48% while the damage jointly caused by W (Subsidence), E and T accounted for 30.45%. Moreover, the proportion of damaged cropland area due to inclined deformation T was positively correlated with cropland damage level. These findings can provide a reference for rational judgment regarding civilian building and cropland destruction on the ground surface after coal mining.

In order to investigate the compression damage characteristics of the “interface section coal pillar–backfill body (ICPF)” composite structure formed after coal pillar excavation and gangue material backfill in the key technologies of coal pillar excavation and gangue material backfill replacement in the interface section of thick coal seams, an ICPF single-axis compression damage experiment under different internal dimensions of backfill was conducted using the PFC^2D numerical model, with the interface section coal pillar of a working face at a certain mine in northern Shaanxi Province as the research background. In addition, the stress–strain state, peak strength characteristics, damage mode, energy evolution, and damage characteristics of the ICPF composite were analyzed, and models for the evolution of the ICPF elastic modulus and compressive strength were established. The results showed that the stress–strain state of the ICPF changed from brittle to ductile as backfill strength decreased. The distribution of the elastic modulus is primarily influenced by backfill strength, and as the excavation–backfill width increases, the curve exhibits a distinct S-shaped distribution. The compressive strength decreases by up to 63.4% with an increase in excavation–backfill width and by up to 65.1% with a decrease in backfill strength. The sensitivity of compressive strength to backfill strength is greater than that to excavation–backfill width. Based on the established ICPF elastic modulus and compressive strength evolution model, the two mechanical properties were compared using model fitting, and the model fitting results were satisfactory. The ICPF exhibits three types of damage characteristics as the excavation and backfill width increases: oblique shear and tensile damage, edge coal stripping and X-shaped conjugate damage of the backfill body, and large-area plastic damage of the backfill body. By establishing a theoretical damage variable based on linear dissipation energy, damage factors can be quickly obtained from stress–strain curves. The damage curves all exhibit exponential growth, and their growth rates show certain dispersion as the excavation and backfill width increases and backfill strength decreases. Based on the brittleness index analysis of the ICPF composite, as the backfill strength decreases and excavation and backfill width increases, the brittleness index of the composite increases, and the tendency for impact increases. At an excavation and backfill width of 80 mm, rib damage tends to happen.