深井薄基岩沿空高位覆岩改性下应力及地表沉降特征

Characteristics of stress and surface subsidence under modification of high-level overburden rock along goaf of thin bedrock in deep well

  • 摘要: 巷道与高位巷联合卸压爆破卸压方式能够有效降低矿山压力和冲击灾害风险,但此类卸压方式下覆岩应力演化、地表沉降特征及其与冲击动载之间的关联尚不明确。以巨野煤田新巨龙煤矿8302工作面为研究对象,针对深井薄基岩地层结构特点,分别构建了仅巷道卸压、巷道与高位巷联合卸压力学模型,推导了工作面超前支承压力估算表达式,分析了不同卸压方式下地表沉降特征,数值模拟及工程验证了巷道与高位巷联合卸压减冲效果,探讨了应力分布及地表沉降与冲击动载的联动效应,得到以下主要结论:① 联合卸压通过爆破预裂对高位坚硬岩层进行改性,显著降低其破断步距,使基岩传递应力峰值下降7.8 MPa,支承压力超前影响范围减少约40 m。② 数值模拟及工程实践表明,与仅巷道卸压相比,联合爆破卸压破坏了高位厚硬岩层完整性,减小了周期来压步距,周期来压动载、超前支护受力及钻屑量均呈现降低趋势,降低了覆岩运动能量集中释放强度,验证了所建立模型的科学性。③ 相比仅巷道卸压方式,联合卸压时超前影响距由565 m增大至694 m,超前影响角由57.7°减小至52.1°,联合卸压降低了高位关键层破断步距,使硬薄基岩向软弱基岩地层结构转化。④ 联合卸压方式下地表沉降各测点速率变化趋于平缓,地表沉降速率峰值由50.28 mm/d(巷道卸压)降至22 mm/d(联合卸压),沉降速率峰值降低56%,表明地表沉降由突变型转化为渐变型,弱化了基岩及表土层能量积聚,降低了高位覆岩突变垮落诱冲风险,凸显了巷道与高位巷联合卸压防冲的有效性。⑤ 大能量微震事件发生前地表沉降速率呈增大趋势,地表沉降速率增大先于大能量事件发生的比例为56.17%,地表沉降速率和动载冲击存在明显的联动效应,而工作面超前应力增大又超前于地表沉降速率增大,分别将超前支承压力、地表沉降速率显著增大作为冲击预警的中期判据、临近判据,判别方法可为冲击预警提供新思路。

     

    Abstract: Combined pressure-relief blasting in the mining roadway and a high-level roadway can effectively reduce strata pressure and rockburst risk. However, the stress evolution of the overburden, surface subsidence characteristics, and their correlations with rockburst-induced dynamic loads under this pressure-relief mode remain unclear. Taking No. 8302 working face of Xinjulong Coal Mine in the Juye Coalfield as the engineering background, mechanical models for roadway-only pressure relief and combined pressure relief in the mining roadway and high-level roadway were established respectively according to the structural characteristics of deep mine with thin bedrock. An expression for estimating the front abutment pressure of the working face was derived, and the surface subsidence characteristics under different pressure-relief modes were analyzed. The rockburst mitigation effect of combined pressure relief was investigated through numerical simulation and field verification, and the coupled responses among stress distribution, surface subsidence and rockburst-induced dynamic loads were further examined. The main conclusions are as follows. ① Combined pressure relief modifies the high-level hard strata through blasting-induced pre-splitting and significantly reduces their breaking interval. Consequently, the peak stress transmitted through the bedrock decreases by 7.8 MPa, and the advance influence range of the abutment pressure is shortened by approximately 40 m. ② Numerical simulations and engineering practice show that, compared with roadway-only pressure relief, combined pressure-relief blasting destroys the integrity of the high-level thick and hard strata and reduces the periodic weighting interval. The dynamic load during periodic weighting, loads on the advance supports, and drilling cuttings volume all exhibit decreasing trends. The intensity of concentrated energy release caused by overburden movement is thereby reduced, verifying the validity of the proposed mechanical models. ③ Compared with roadway-only pressure relief, combined pressure relief increases the advance influence distance from 565 m to 694 m, while decreasing the advance influence angle from 57.7° to 52.1°. By reducing the breaking interval of the high-level key stratum, combined pressure relief transforms the overburden structure from the hard thin-bedrock structure into the weak-bedrock structure. ④ Under combined pressure relief, the variations in surface subsidence rate at different monitoring points become more gradual. The peak surface subsidence rate decreases from 50.28 mm/d under roadway-only pressure relief to 22 mm/d under combined pressure relief, representing a reduction of 56%. This indicates that surface subsidence changes from the abrupt mode to the gradual mode, thereby weakening energy accumulation in the bedrock and topsoil layer and reducing the risk of rockbursts induced by the sudden collapse of the high-level overburden. These results demonstrate the effectiveness of combined pressure relief in the mining roadway and high-level roadway for rockburst prevention. ⑤ The surface subsidence rate tends to increase before large energy microseismic events. The proportion of surface subsidence rate increasing before the occurrence of large energy events is 56.17%, indicating a pronounced coupled response between the surface subsidence rate and dynamic impact loading. Moreover, the increase in front stress at the working face precedes the increase in surface subsidence rate. Therefore, significant increases in the advanced abutment pressure and surface subsidence rate are proposed as medium-term and imminent warning criteria for rockbursts, respectively. This identification method provides a new approach for rockburst early warning.

     

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