Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining: a case study

Abstract

At present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

Analytical Damage Model for Predicting Coal Failure Stresses by Utilizing Acoustic Emission

“…During testing, AE signals were recorded simultaneously with the cracking process [54]. During loading, Liu et al and Zhu et al have made the effort to investigate the AE signal frequency features with both saturated and dry coals, and the outcomes revealed that the AE signals with a high frequency were pointedly reduced by water content [55][56][57][58][59][60].…”

Numerical Simulation Study on Stability Control Technology of Large-Area Wall Caving Area (LAWCA) in Large-Inclined Face

“…Numerical simulation overcomes the limitation of laboratory size and can well analyze the stability of rock mass under complex geological conditions [10][11][12]. Compared with experiments, numerical simulation can quantitatively control the properties and quantities of particles or elements, and numerical simulation is widely used to analyze large-scale engineering problems [13,14]. However, it is still tricky to correctly reproduce the spatial mechanical response of the stope in the numerical simulation of finite element and finite difference methods [15,16].…”

The Infrared Radiation Characteristics of Sandstone Fracture Seepage under Coupled Stress-Hydro Effect

“…It has been found, that when the rock breaks, it usually releases electromagnetic energy [26][27][28][29][30][31], elastic energy [32][33][34][35][36][37][38][39][40][41], thermal energy [42][43][44], acoustic energy [45][46][47][48][49][50][51], and other kinds of energy [52]. Hence, generating a variety of disaster warning methods related to rock mass, such as infrared radiation method [53,54], electromagnetic radiation method [55,56], acoustic emission method [57,58], potential method [51,59] and microseismic method [60,61]. Among these, as a non-contact method, the infrared radiation method has the advantages of high accuracy [62], strong reliability [63], simple operation [64], and visualization [65], etc., which provides a convenient and accurate early warning method for rock fracture seepage monitoring under coupled stress-hydro effect.…”