Surface Subsidence Prediction Method for Coal Mines with Ultrathick and Hard Stratum

Abstract

Overburden conditions consisting of ultrathick and hard stratum (UTHS) are widespread in China and other countries, but existing surface subsidence prediction methods ignore the strong impact of UTHS on surface subsidence. They are thus not applicable for surface subsidence prediction for coal mining with the presence of UTHS. We conducted actual measurements of surface and UTHS subsidence in the Tingnan Coal Mine. The results showed that under the UTHS mining condition, the required gob dimension is much larger than the empirical value when the surface reaches sufficient mining and that the actual measured maximum value of surface subsidence is much smaller than the empirical value. The UTHS subsidence is approximately equal to the surface subsidence. The movement of UTHS has a strong impact on surface subsidence and has a controlling function for it. It was proposed that surface subsidence could be approximately predicted by calculating the UTHS subsidence. The UTHS movement characteristics were studied using Winkler’s theory of beams on an elastic foundation, the subsidence prediction equation of the main sections in the strike and dip directions was obtained under different mining dimensions, and the subsidence prediction equation of any arbitrary cross section parallel to the two main sections was established. Then, the surface subsidence prediction method for coal mining with the presence of UTHS was developed, and the influences of UTHS thickness, strength, and layer position on the surface subsidence were discussed. The Tingnan Coal Mine was taken as an example, and the subsidence curves of the strike and dip main sections were calculated using different mining dimensions. Subsequently, the surface subsidence after the mining of working faces 204, 205, 206, and 207, respectively, was predicted, and the prediction method was verified by comparing the results with the measured surface subsidence results of working faces 204, 205, and 206.

Method to Calculate Working Surface Abutment Pressure Based on Key Strata Theory

“…ere is an ultrathick (222.14 m), hard sandstone KS, which is a moderately water-rich aquifer with an average uniaxial compressive strength of 42.2 MPa. On the basis of the integrated stratigraphic column in the Tingnan coal mine [30], the location of the overburden KS is shown in Figure 2. e recovery periods of working faces 204, 205, and 206 were Nov. 2011-Nov. 2012, Jun.…”

“…In Chinese coal mines, the most commonly used mining method is longwall mining in which the stoping space created by the stoping of one or more working faces is rectangular in shape and the mining area contains two main sections [30,31]: the along-dip main section I and the along-strike main section II, as shown in Figure 1. As the working face is advanced along main section II, often for thousands of meters, this section is deemed to be under full subsidence [30,31]. A mechanical model for calculating Advances in Civil Engineering abutment pressure that considers the overburden KS was established along main section I, as shown in Figure 5.…”

“…A mechanical model for calculating Advances in Civil Engineering abutment pressure that considers the overburden KS was established along main section I, as shown in Figure 5. After a coal seam is mined, a breaking movement and a flexural subsidence are expected in the overburden strata of the mining site, which is composed of the caving zone, fissure zone, and curve subsidence zone [11,12,17,21,30]. e KS, which is in the curve subsidence zone, is subject to a curve subsidence rather than a breaking movement [11,12,17,30].…”

“…After a coal seam is mined, a breaking movement and a flexural subsidence are expected in the overburden strata of the mining site, which is composed of the caving zone, fissure zone, and curve subsidence zone [11,12,17,21,30]. e KS, which is in the curve subsidence zone, is subject to a curve subsidence rather than a breaking movement [11,12,17,30]. e height of the fissure zone can be estimated by applying Xu et al's prediction method [17] based on the KS position.…”

“…is study uses KS theory [7,11] and Winkler's theory of elastic foundation beams [12,15,16,20,30] to establish a method to calculate abutment pressure that considers the influence of the overburden KS. e abutment pressure distribution of working surface 207 after mining was then calculated using our method, based on mining conditions present in the Tingnan coal mine.…”