含弱夹层组合岩石变形破坏演化特征实验研究

Experimental study on deformation and failure evolution characteristics of combination rock with weak interlayers

针对含弱夹层组合岩石试件,利用CCD相机作为观测手段,采用数字散斑相关方法,得到变形场分析结果,研究含弱夹层组合岩石变形破坏演化特征,并对层间作用效应进行理论分析。结果表明:(1)中间弱强度岩石最先出现水平拉应变局部化带,随着荷载增加,局部化带向岩层接触面发展,并通过层间作用对上下层岩石施加拉应力,使上下层岩石最先出现竖向拉裂缝,大大降低了弱夹层组合岩石的抗压强度;(2)中间弱强度岩石受上下层岩石影响发生张拉破坏,导致试件最终破坏。上下层岩石出现裂隙后,在该裂隙左侧区域内,上下层岩石对中间弱强度岩石的约束作用减弱甚至产生张拉作用,致使该部分岩石抗压强度突降,发生突然破坏;(3)理论计算表明,距层间接触面一定范围内,上下2层岩石抗压强度降低,中间层岩石抗压强度上升,其变化幅度与岩石力学参数有关。就本次实验对应的理论计算而言,上下2层的花岗岩抗压强度降低为花岗岩单轴抗压强度的0.32倍,为32.514 MPa,小于中间弱强度岩石的抗压强度,成为弱夹层组合岩石抗压强度的控制因素;(4)通过实验得到弱夹层组合岩石抗压强度为33.91 MPa,与结论(3)中的理论计算结果相吻合。且实验过程中,上下层花岗岩首先出现裂隙,表明其抗压强度小于中间弱强度岩石,也与结论(3)中的理论分析一致。研究成果对煤柱型冲击地压的发生机理与防治有一定的指导借鉴作用。

The deformation and failure evolution characteristics of combination rock with weak interlayers are studied by using a CCD camera as observation method,and the deformation field under uniaxial compression is analyzed by the digital speckle method.Then the effect of the interlayer interaction is theoretically analyzed.The results indicate that the horizontal tensile strain localization zone first appears in the middle weak interbedded rock,and that,as the load increases,the localized zone develops towards the rock contact surfaces.Under the interlayer action,the upper and lower layers of rocks produce localized zones and appear vertical tensile cracks first,greatly reducing the compressive strength of the weak interlayer composite rock.The middle weak-strength rock is affected by the upper and lower layers of rock and undergoes tensile failure,resulting in the final failure of the specimen.After cracks appear in the upper and lower rocks,in the area to the left of the cracks,the restraining effect of the upper and lower rocks on the weak-strength rocks in the middle is weakened,causing the compressive strength of this part of the rock to drop suddenly and even failure.The theoretical calculation shows that,in a certain range from the interlayer contact surface,the compressive strengths of the upper and lower layers of rocks decrease while the compressive strength of the middle weak layer increases.The variation range of the compressive strength is related to rock mechanics parameters.The theoretical calculation also reveals that the compressive strength of the upper and lower layers of granite is reduced to 32.514 MPa,about 0.32 times of the initial strength and smaller than the compressive strength of the intermediate weak-strength rock,and hence,is the controlling factor of the compressive strength of the weakly interbedded rock.The compressive strength of the rock with weak interlayers obtained through model experiment is 33.91 MPa,which is consistent with the theoretical calculation result.It is observed that,during the experiment,the upper and lower layers of granite first appear cracks,indicating that their compressive strength is lower than that of the middle weak-strength rock,which is also consistent with the theoretical analysis.The results can be used as a reference for the occurrence mechanism and prevention of coal pillar rock burst.