Study on the Structural Instability Characteristics of Interlayer Rock Strata During Mining Under Interval Goaf in Shallow Coal Seams

In order to study the instability characteristics of interlayer rock strata (IRS) in shallow buried close-distance coal seams under insufficient mining areas, based on the background of interval mining under goaf in Nanliang Coal Mine, this paper studies the instability characteristics of interlayer strata in interval mining under goaf by means of similar simulation, numerical simulation, and field measurement. The results indicated that the first weighting interval of the main roof during mining in the lower coal seam was 49 m, while small and large periodic weightings with intervals of 10–14 m and 15–19 m were identified. During periodic weighting, the support resistance ranged from 6813 to 10,935 kN, with a dynamic load factor of 1.07–1.74, and the peak abutment pressure in front of the working face was 5.85–9.85 MPa. The mining under the interval coal pillar (ICP) was the ‘stress increase zone’, and the mining under the temporary coal pillars (TCPs) and the interval goaf was the ‘stress release zone’. During the working face mining out of the ICP, the support resistance reached 10,934 kN, the dynamic load factor reached 1.74, and the abutment pressure (AP) reached 9.85 MPa, which was 60% higher than the AP mining under the “stress release zone”. Analysis suggests that the cutting instability of the IRS was the root cause of the increased AP in the working face of the lower coal seam. A numerical simulation was performed to verify the instability characteristics of the IRS in the interval goaf. The relationship between support strength and roof subsidence during the period of the working face leaving the coal pillar was established. A dynamic pressure prevention method involving pre-splitting and pressure relief of the ICP was proposed and yields superior field application performance. The findings of the study provide a reference for rock strata control during mining under the subcritical mining area in shallow and closely spaced coal seams.