Soft Roof Failure Mechanism and Supporting Method for Gob-Side Entry Retaining

Abstract

To study the soft roof failure mechanism and the supporting method for a gateway in a gently inclined coal seam with a dip angle of 16 ˝kept for gob-side entry retaining, and through the methodology of field investigation and numerical and analytical modeling, this paper analyzed the stress evolution law of roof strata at the working face end and determined that the sharp horizontal stress unloading phenomenon along the coal wall side did not appear after the working face advanced. Conversely, the horizontal stress along the gob side instantly decreased and the tensile stress produced, and the vertical stress in the central part of the roof had a higher reduction magnitude as well. An in-depth study indicates that the soft roof of the working face end subsided and seriously separated due to the effect of the front abutment pressure and the roof hanging length above the gob line, as well as certain other factors, including the rapid unloading of the lateral stress, tension and shear on the lower roof rock layer and dynamic disturbance. Those influencing factors also led to rapid crack propagation on a large scale and serious fracturing in the soft roof of the working face end. However, in the gob stress stabilized zone, the soft roof in the gob-side entry retaining has a shearing failure along the filling wall inside affected by the overburden pressure, rock bulking pressure, and roof gravity. To maintain the roof integrity, decrease the roof deformation, and enable the control of the working face end soft roof and the stabilization of the gob-side entry retaining roof, this study suggests that the preferred bolt installation angle for the soft roof situation is 70 ˝based on the rock bolt extrusion strengthening theory.

Influence Mechanism of Main Roof Height on Surrounding Rock Stability of Gob-Side Entry Driving

“…Su et al [17] studied two main difficulties in maintaining surrounding rock stability in actual geological conditions, and the technology of "roofing control and wall strengthening" was proposed. Yang et al [18] studied soft roof failure mechanism and the supporting method for gob-side entry retaining in a gently inclined coal seam; bolt parameters were optimized and analyzed. In the preceding studies mentioned, mechanical models are not established according to different geological conditions, and Fast Lagrangian Analysis of Continua (FLAC) [14,15] and Universal Distinct Element Code (UDEC) [16][17][18] are used to quantitatively analyze the stress and strain distribution characteristics of surrounding rock.…”

“…Yang et al [18] studied soft roof failure mechanism and the supporting method for gob-side entry retaining in a gently inclined coal seam; bolt parameters were optimized and analyzed. In the preceding studies mentioned, mechanical models are not established according to different geological conditions, and Fast Lagrangian Analysis of Continua (FLAC) [14,15] and Universal Distinct Element Code (UDEC) [16][17][18] are used to quantitatively analyze the stress and strain distribution characteristics of surrounding rock. However, FLAC is conducive to analyzing stress distribution characteristics, while UDEC is conducive to analyzing the characteristics of the region and the broken position of main roof.…”

Key Parameters of Gob-Side Entry Retaining in A Gassy and Thin Coal Seam with Hard Roof

“…Gob-side entry retaining (GER), where a roadway of previous panel is retained without coal pillars by constructing a roadside backfill body (RBB) lagging behind the working face along the gob-side, was proposed to solve these problems, as shown in Figure 1. GER is an effective approach for sustainable and efficient exploitation of coal resources [4,5]. Through the analysis of the ground pressure and physical simulation, Lu [6] believed that the "given deformation" of roof subsidence in GER is proportional to mining height.…”

Development of a New Gob-Side Entry-Retaining Approach and Its Application

“…Generally, an artificial wall is required on the gob side to isolate the gob of previous panels and make sure that the cross section of the retained entry can still satisfy the service requirement panels and make sure that the cross section of the retained entry can still satisfy the service requirement after deformation [9,10]. Since the 1950s, gob-side entry retaining has been widely used in the UK, Germany, Poland, Russia, and China [11,12]. Reducing the entry-retaining cost and improving the entry-retaining speed have long been crucial issues that need to be further and continuously addressed by engineers and researchers.…”