In order to study the tensile-shear behavior of rock discontinuities

the self-developed tension-shear device was used to carry out the direct shear test of the natural limestone bedding planes under normal tensile stresses

and the shear stress-displacement curves

the bedding plane fracture morphologies and strength characteristics were analyzed. The fracture surfaces have no friction crushing zone and local split under a tensile-shear stress. The shear strength decreases nonlinearly with the increase of normal tensile stress. Further

PFC simulation was used to study the influence of saw-tooth bedding plane undulation characteristics on its tensile-shear rupture and strength characteristics. As the normal tensile stress increases

the shear cracks decrease and the tensile cracks increase. When the undulation angle is small

cracks are generated along the saw-tooth bedding planes; when the undulation angle is large

cracks are generated along the saw-tooth bedding planes and saw-tooth. The saw-tooth bedding plane failure can be divided into three modes: tensile and shear ruptures along the saw-tooth planes

tensile and tensile-shear ruptures along the saw-tooth planes

and mixed saw-tooth plane and saw-tooth ruptures. And the damage evolution of each failure mode was analyzed. The shear strength of the saw-tooth bedding planes decreases first and then increases with the increase of the undulation angle

and the minimum is at 30º. It decreases almost linearly with the increase of the normal tensile stress

which can be described by the Mohr-Coulomb criterion. The friction angle and cohesive force decrease with the increase of the undulation angle. The variation of shear strength

friction angle and cohesion force with undulation angle is mainly controlled by the failure mode. With increasing levels of adhesive strength of bedding plane

the saw-tooth plane rupture is gradually converted into a mixed saw-tooth plane and saw-tooth ruptures. When the adhesive strength reaches a certain level

tensile-shear strength no longer increases

mainly controlled by the strength of the saw-tooth rock.