神东矿区不同赋存深度沉积岩抗拉强度与断裂韧度研究

为研究神东矿区不同赋存深度沉积岩抗拉及断裂性能,利用声发射监测系统对神东矿区不同赋存深度沉积岩样品巴西劈裂加载过程中的声发射参数进行监测,探讨了岩样抗拉强度、I型断裂韧度及两者比值k随赋存深度的变化规律;分析了劈裂破坏过程中损伤演化、破坏特征及前兆信息。结果表明:抗拉强度和断裂韧度随赋存深度增加而增大,且二者均与赋存深度呈幂函数关系,埋深-300 m以浅岩样的抗拉强度和断裂韧度分别在0. 5 MPa和0. 15 MPa·m1/2以下,而-300 m以深岩样则分别在1. 0 MPa和0. 15 MPa·m1/2以上;岩样抗拉强度与断裂韧度的比值k也随赋存深度的增加而增大,且与赋存深度呈对数函数关系,即埋深-300 m以浅岩样k值为2～3,-400 m左右k值为3～6,-500 m以下k值相对离散。同时,神东矿区不同赋存深度岩样破坏为张-剪混合型,张拉破坏贯穿整个破坏过程,但剪切破坏发生时间不同,即-300 m以浅岩样剪切破坏发生在峰后阶段,而-300 m以深岩样剪切破坏发生在峰前阶段;不同赋存深度岩样在峰值强度前均会出现破坏前兆点,-300 m以浅岩样(除中粗砂岩外)基本在应力峰值的70%～90%,而-300 m以深多在应力峰值的92%以上;可以看出沉积岩失稳预警时间随赋存深度增加而减少,且随深度增加其失稳破坏更加迅速且剧烈。

Tensile strength and fracture toughness of sedimentary rocks at different buried depths in Shendong coal field

To investigate the tensile strength and fracture properties of sedimentary rock buried at different depths in Shendong coal field,the acoustic emission (AE) parameters of sedimentary rock specimens at dif-ferent depths in Shendong coal field were monitored by AE monitoring system during the Brazilian splitting experiment.The variation of tensile strength,model I fracture toughness and the ratio k(tensile strength with respect to fracture toughness) of rock specimens with respect to the buried depth was discussed.The damage evolution,failure features and precursory features of specimens were also analyzed.The results indicate that the tensile strength and the fracture toughness increase with the increase of the buried depth and have power function relationship to the buried depth.In general,the tensile strength and the fracture toughness of rocks buried depth above -300 m are lower than 0.5 MPa and 0.15 MPa·m1/2,while those buried depth deeper than -300 m are higher than 1.0 MPa and 0.15 MPa·m1/2,respectively.The ratio k also increases with the rise of the buried depth,and has a logarithmic function relationship with the depth.The k values of rocks with the buried depth over -300 m are 2-3.The k values are 3-6 for the rocks with the buried depth close to -400 m,while the k values are relatively discrete for the rocks with the buried depth deeper than -500 m.In addition,the failure modes were observed similarly existing in the tested specimens,tension-shear mixed failure is the dominant pattern.However,the shear failure occurs at different time for the specimens with the various buried depths.For example,the shear failure begins to appear in the post-peak stage for the rocks with the buried depth less than -300 m,while the shear failure appears in the pre-peak stage for the rocks with the buried depth larger than -300 m.The failure precursors of the tested rocks appear normally before the peak strength,except the difference of the triggered stress.The precursors of the specimens (except medium-coarse sandstone) with the depth less than -300 m appear at the stress reaching 70%-90% peak stress.For the specimens with the buried depth larger than -300 m,the precursors appear at the stress larger than 92% of the peak stress.This indicates that the warning time of the specimen failure decreases with the increase of the buried depths.