含端部裂隙大理岩单轴压缩破坏及能量耗散特性

Uniaxial compression failure and energy dissipation of marble specimens with flaws at the end surface

对含端部双裂隙ϕ50 mm×50 mm的圆柱体大理岩试样进行单轴压缩试验,并利用高速摄影仪实时记录试样破坏过程,研究了端部裂隙长度和倾角对大理岩力学特性及裂纹扩展规律的影响.研究表明,当裂隙长度达到门槛值前,试样的单轴抗压强度的弱化程度较低,弹性模量、峰值应变的变化较小.相对垂直裂隙,相同长度的倾斜裂隙对大理岩的影响更加显著.试验结果与理论分析均表明,裂纹一般不从端部垂直裂隙尖端起裂,试样的起裂裂纹大多发展为主裂纹,扩展过程中较少产生分支与分叉,试样表面会产生局部剥落,倾斜裂隙试样宏观上呈剪切或拉剪复合破坏,垂直裂隙试样呈劈裂拉伸破坏.试样能耗参数与单轴抗压强度的变化趋势一致,试样总应变能和其单轴抗压强度有较好的正相关关系.最后,比较了动、静载荷作用下含端部裂隙大理岩力学响应与裂纹扩展过程的差异.

It is a fact that a large number of defects such as cracks,voids,inclusions,weak planes,and joint sets are generated within the rock mass during the process of rock formation because of geological-tectonic evolution.The existence of these preexisting natural defects poses potential threats to the stability and safety of structures built on the rock mass.Therefore,it is highly significant to better understand the effects of the preexisting defects on the rock mechanical and fracture behaviors for the stability and safety assessment of rock structures.Uniaxial compression tests were carried out by using ϕ50 mm×50 mm cylindrical marble specimens with double parallel flaws at end surfaces.When tests were performed,a high speed camera was used to capture the failure processes of the marble specimens.The effects of the flaw length and inclination angle on the mechanical properties and crack propagation of marble specimens were investigated.Further,the experimental results indicate that the uniaxial compressive strength,elastic modulus,and peak strain of the specimen decrease slightly before the flaw length reaches the threshold value.Compared to flaws at vertical angle 90°,flaws at inclined angles(0°<α<90°)of the same length have larger effect on the mechanical properties of marble.It is found from both the experimental and theoretical analysis that cracks usually do not start from the tip of vertical end flaws and most of initiation cracks are developed into dominant cracks.In addition,there are few branches and bifurcations in the crack propagation process,and further,local spalling also occurs at the surface of the specimen.The specimens with inclined flaws exhibit shear failure or combined shear and tensile failure and the ones with vertical end flaws show axial splitting tensile failure.The variation trend of energy consumption parameters is consistent with that of uniaxial compressive strength.It is found that total strain energy of the specimen is positively correlated with its uniaxial compressive strength.Finally,the difference between mechanical and crack propagation processes of marble specimens with end flaws under dynamic and static loads were compared.