Mechanism Study Of Crack Initiation And Propagation In A Rock Mass With Complicated Cracks Under Compression

With the rapid development of China's economy and infrastructure,the mechanical properties of rock mass are inevitably involved in rock mass engineering.However,joints and fissures in the rock mass have different scales and shapes,so it is necessary to investigate the crack propagation of different shapes.In this dissertation,this paper study the initiation angle of wing crack with collinear cracks considering Tstress firstly.Then in order to investigate the effect of cracks with different shapes and scales on the failure process of fractured rock mass,the strain softening model in FLAC3 D code is adopted to describe the mechanical behavior of the rock.We consider the shape of crack as arc cracks,kink cracks and unequal-length cracks and study the influence on the mechanical properties of rock mass.The main contents are as follows.(1)Based on the Kachanov method and previous studies,the new MTS criterion is set up to simultaneously consider T-stress,rock properties,crack geometrical parameters,strength parameters,deformation parameters and interaction with collinear cracks.Therefore,it can perfectly reflect the initiation mechanism of collinear cracks of rock.The results indicate that the initiation angle of wing crack obtained from the proposed method agrees well with that obtained from the tests,and it can reflect the influence of interaction with collinear cracks on the initiation angle of wing crack.It is also found through the sensitivity analysis for the parameters that when the crack spacing is small,the influence of crack interaction on the crack initiation angle of wing cracks is very obvious.(2)When the crack is arc crack,the calculation results show that the peak strength of the sample decreases as the arch height increases.And the chord length also affects the peak strength.The crack inclination has an effect on the expansion path of arc cracks.The peak strength of the sample increases when the inclination becomes larger.With the increase in the crack interval,the interaction among the cracks gradually decreases and the peak strength of the samples gradually increases.The crack number has much effect on the sample's peak strength.(3)When the crack is kink crack,the calculation results show that the uniaxial compressive peak strength has effects with the crack length and bending length.When the two parts of the crack are perpendicular to each other,the peak strength of the sample has the highest peak intensity.With the increase in the crack interval,the interaction among the cracks gradually decreases and the peak strength of the samples gradually increases.The crack number has much effect on the sample's failure mode,and the peak strength of the samples gradually decreases with the increase in crack number.(4)When the cracks are unequal-length cracks,the calculation results are as follows.The peak strength of the sample decreases as the secondary crack length increases.The change of dip angle will influence the expansion path of cracks.When the dip angle is 30°,the peak strength of the sample has the lowest value,and then it increases with the increase of dip angle.When the parallel and vertical spacing of cracks increase,rock bridge will not occur between cracks,indicating that the interaction between cracks getting smaller.The crack number has much effect on the sample's peak strength.