Laboratory experimental study on mechanical properties and failure modes of soft and hard interbedded rock mass

Soft and hard interbedded rock mass is a bad geology body often encountered in engineering project,and its special structure leads to some frequent safety accidents. In order to study the mechanical properties and failure mechanism of soft and hard interbedded rock masses,using indoor rock mechanics test methods,the soft and hard interbedded rock masses with different rock layer dip angles and different layer thickness ratios were investigated. The study shows that ①soft and hard interbedded rock mass begins to break from the hard layer and then gradually expands to the soft layer. Under uniaxial conditions,as the thickness of the soft layer increases,the ability of the soft layer to inhibit crack propagation tends to increase,but it will cause the peak strength decrease. Under the triaxial condition,with the increase of soft layer thickness,the ability of soft layer to inhibit crack propagation first increases and then decreases,the peak intensity is inverted "V",the cohesive force is significantly decreased,and the internal friction angle is kept stable. ② Under uniaxial conditions,the 0° and 30° samples have a stress drop phenomenon,the difference is the stress-strain curve at 30° has a rising period after the stress drop,and the ductile failure characteristics are more obvious. Under the triaxial condition,the 0° rock mass has obvious post-peak softening characteristics,while the 30° rock mass does not have same obvious characteristics. Most are hardened flow damage. As the thickness of the soft layer increases,the degree of strain softening increases first and then decreases. ③Confining pressure has different effects on the expansion and deformation of soft and hard layers,which is easy to cause a shear failure of soft and hard interbedded rock mass. With the increase of confining pressure,the decreasing rate of partial stress-strain curves becomes slower and the degree of strain softening is gradually weakened and the ductility is increased. The peak strength,peak strain and elastic modulus of the soft and hard interbedded rock mass are increased. ④When the rock layer has an inclination angle,the sensitivity of the joint of the weak interbedded rock mass is enhanced,and the test sample is more likely to have a through crack. The dip angle of the rock within a certain range will weaken the mechanical properties of the soft and hard interbedded rock mass,resulting in the decrease of the elastic modulus,peak strength and internal friction angle of the soft and hard interbedded rock mass.