Physical simulation and theoretical evolution for ground fissures triggered by underground coal mining

Abstract

Underground coal mining activities are prone to cause movement and breakage in geological strata and also lead to mining subsidence and even ground fissures. Along the direction working panel advancing, ground fissures may occur in roof in front and/or behind working panel. However, the investigations of previous similarity tests in lab only emphasize on the region behind working panel. By improving strata material property in construction and mounting artificial pressure devices, two physical simulation tests were conducted and successfully investigated the simulated results. Then, the mechanical model of “cantilever beam and elastic foundation beam” was proposed to calculate the stress distribution and the crack initiation angle in overlying strata and it well explains the mechanisms of ground fissures generation and propagation. Results show that, the maximum internal force in roof always occurred in front of working panel. However, because the void space in gob due to excavation is large enough to cause the bend and rotation of roof strata, compare to the triaxially compressed region in front of working panel, the roof always broke off at some positions above gob since the stress concentration resulting from such bend and rotation of strata could easily reach the limit strength of strata rocks. Also, the length of cantilever beam changed dynamically as respect to the panel advancing and the breakage intervals. Thus, the breakage position where the internal force first reached the limit tensile strength is not fixed and there will be two different kinds of relative positions between the crack initiation point and the working panel. The crack initiation direction is always perpendicular to the internal force, and the crack propagation direction is affected by the initiation angle, overburden-separation degree and the position of the hydraulic shields. If there is no overburden-separation or less, the roofs will break off as a composite beam and the propagation direction will be roughly along the central line between the initial broken point and the support position. Otherwise, the roof strata will bend with the support shields moving forward, then the fracture angle will be close to the initiation angle and the fault surface will be stepped.

Determining the influencing factors of preferential flow in ground fissures for coal mine dump eco-engineering

“…Mine spoils are an important driver of environmental damage and land degradation, causing the disappearance of soil and vegetation; increases in erosion by wind and water; pollution of air, soil, and water; and general deterioration of the landscape ( Mukaro, Nyakudya & Jimu, 2017 ). Coal mining will result in different degrees of surface damage and deformation, causing ground fissures ( Yang et al, 2018 ; Zhang et al, 2015 ). Ground fissures have no obvious frame structure.…”

Research on Coal Pillar Malposition Distance Based on Coupling Control of Three-Field in Shallow Buried Closely Spaced Multi-Seam Mining, China

“…In a study referring to three-field evolution characteristics, Sun et al [31] analyzed the stress redistribution and fracture growth caused by mining, and two models were presented to study the vertical stress and fracture growth in the floor strata, respectively. Yang et al [32] proposed the mechanical model of "cantilever beam and elastic foundation beam" to calculate the stress distribution and fracture initiation angle of the overlying strata, studying the fracture propagation direction. Chen et al [33] studied the evolution characteristics of mining stress and fracture in superimposed mining.…”

Research on complex air leakage method to prevent coal spontaneous combustion in longwall goaf

“…During coal mining, the overlying strata will cave, fracture and subside with the expansion of the gob area [10], while the ground surface may collapse and crack [11]. The fracture and movement of strata produce many voids, including pores among the rubble, fractures in the strata, and fissures in the ground, which can act as air leakage passages that allow air penetration [12–13]. Furthermore, the oxygen present in the atmosphere and underground ventilation can enter the gob areas through these voids and interact with the residual coal in the goaf.…”