Analysis of Influencing Factors of Roadway Stability and Adaptability Criterion for Gob-Side Pre-Backfill Driving

Abstract

To reduce the loss of coal pillars between two adjacent longwall working faces, gob-side pre-backfill driving (GPD) procedure is suggested. This paper introduces in detail the principles and characteristics of the GPD procedure. Based on the arc triangle block (ATB) formed by the fractures of the main roof, the Winkel Elastic Foundation Beam model of the relevant rock strata structure is established and analyzed. The influence of the different breaking positions of the ATB of the main roof, the different geological conditions of the surrounding rock, and the parameters of the backfill body on the stability of the backfill body are analyzed. Also, the adaptability of the GPD procedure under any geological conditions is analyzed. The results show that the sensitivity of the aforementioned factors on the stability of the backfill from high to low is as follows: the thickness of the immediate roof, the elastic modulus of the main roof, the elastic modulus of the immediate roof, the thickness of the main roof, the thickness of the coal seam, the elastic modulus of the coal seam, the width of the backfill body, the buried depth, and the elastic modulus of the backfill body. According to the geological conditions of the Changcun Mine, it can be determined that if the fracture location of ATB of the main roof from the backfill is less than 5 m, the GPD procedure cannot be adopted. For this situation, the required strength of the backfill is high; the backfill is difficult to maintain, and it is prone to fracture failure. The GPD procedure cannot be used for all geological conditions. Before the GPD procedure is implemented, a pre-judgment must be made not to cause unnecessary losses.

Nonlinear Modeling of Contact Stress Distribution in Thin Plate Substrates Subjected to Aspect Ratio

“…The values of A and B that have been determined are substituted into the contact stress distribution model (2) and integrated along the region to obtain Equation (8). F is calculated as follows:…”

“…Meanwhile, the parabolic model values are compared with the experimental values, and there is an error of 38.18%~39.54%. The large parabolic model error under concentrated loading, when the aspect ratio is relatively large, is mainly because the model requires stress equations and reaction forces at the four corner points when determining the model coefficients [8]. However, the free boundary conditions under this test condition resulted in inaccurate reaction forces at the four corner points, which caused an increase in parabolic error.…”

“…However, actual contact stresses are generally nonlinearly distributed and can be saddle-shaped, parabolic, or anti-parabolic, which is mainly determined by the substrate bed factor or soil type and the material properties of the sheet [6]. The three most common nonlinear contact stress distributions described in the generalized Winkel foundation model are saddle-shaped, parabolic, and anti-parabolic [7,8]. Scholars have conducted studies on the contact stresses of foundation footings under concentrated loads, and Wang et al [9] found that the measured field test values of foundation contact stress distribution present a convex parabolic form with small, middle, and large edges and the distribution of reaction forces does not vary much for different soils.…”