深部煤岩体卸荷损伤变形演化特征数值模拟及验证

为研究保护层开采过程中下伏煤岩体卸荷损伤变形演化特征,运用FLAC3D数值模拟方法及现场实验测量手段,以山西保德煤矿实际情况为研究背景,对保护层开采过程中下伏煤岩体应力、变形、塑性演化规律进行了研究及验证。研究表明:保护层开采过程中,被保护层应力呈增大—减小—增大的变化规律,下伏煤岩体应力在空间上呈现出明显的“O”形应力分布规律;受保护层采动影响,下伏煤层测点经过原岩应力、应力集中、采动卸压、应力恢复4个阶段;最大应力集中系数与最小卸荷比为固定值,且出现时间相同,工作面前方应力集中系数与工作面后方卸荷比均呈往复性变化,变化周期与工作面来压周期相关;本文实例中,最大应力集中系数约为1.32,此时测点受到的z向应力值达到最大;最小卸压比约为4.4%,此时测点受到的z向应力值达到最小,卸压效果最好;受应力变化影响,被保护层呈压缩—恢复—膨胀—回缩的基本变化规律,最终状态保持一定的膨胀变形,与应力分区相对应,根据不同变形特征可将下伏煤层分为原岩状态区、压缩变形区、卸压膨胀区、变形恢复区;本文实例中11号煤层最大膨胀变形量约为0.6%,此时测点裂隙最为发育,增透效果最好,有利于瓦斯卸压抽采;受应力变化影响,下伏煤岩体塑形区域范围在空间上呈先xyz三向增大—x轴方向单向增大y轴z轴2个方向稳定的变化规律;随着工作面的回采,被保护层煤体塑性区范围在x轴方向不断增加;通过实测保德煤矿81307工作面回采过程中下伏11号煤地应力、膨胀变形量,对深部煤岩体卸荷损伤变形演化特征数值模拟结果进行了验证,下伏11号煤地应力、膨胀变形量变化规律与数值模拟规律较为吻合。

Numerical simulation and verification of unloading damage evolution characteristics of coal and rock mass during deep mining

To study the evolution characteristics of unloading damage and deformation of underlying coal and rock during the protective layer mining period,FLAC3D numerical simulation was conducted based on the actual conditions of Baode Coal Mine in Shanxi Province,China.In-situ investigations were also adopted to verify the simulation results on stress,deformation and plastic property evolution laws.The results show that the stress of the protected layer increases firstly,then decreases and after which increases again during the mining process.The spatial distribution of stress on underlying coal and rock shows an obvious “O” shape.Influenced by the protective layer mining,the measurement points in underlying coal seam experienced four stages including original rock stress,stress concentration,mining pressure relief and stress recovery.The ratio of the maximum stress concentration factor and the minimum unloading stress is a constant value,and the occurrence of the two extreme values shares the same time.The stress concentration factor in front of the working face and the unloading ratio behind the working face all change reciprocally,and the change period is related to the cycle stress from the working face.In this paper,the maximum stress concentration factor is about 1.32,at which time the value of the z-direction stress at the measuring point is the largest.The minimum pressure relief ratio is about 4.4% and the z-direction stress value at the measuring point is the smallest at this time and the pressure relief effect is also the best.Under the effects of changing stress,the deformation of the protected layer presents the basic rule of compres-sion-recovery-expansion-retraction cycle.The final state maintains a certain expansion deformation,which corre-sponds to the stress zoning.According to the different deformation characteristics,the underlying coal seam can be divided into original rock state zone,compression deformation zone,pressure relief expansion zone and de-formation recovery zone.The example in this paper shows that the maximum expansion deformation of No.11 coal seam was 0.6%.The cracks at the monitoring points developed well and the permeability increased significantly,which was conducive to gas pressure relief and extraction.Under the influence of stress changes,the plastic area increased in triaxial directions first,then increased in x-axis direction but y-axis and z-axis direction kept stable.With the advance of working face,the plastic zone of coal body in protected seam increased continuously in the x-axis direction.By measuring the in-situ stress and expansion deformation of No.11 coal in the mining process of 81307 working face in Baode Coal Mine,the numerical simulation results of the evolution characteristics of unloading damage and deformation during deep mining were verified.The variation laws of in-situ stress and expansion deformation of No.11 coal agree well with those of numerical simulation.