Fracture Failure Mechanism Of Compacted Clay Under Compression-shear Loading Conditions

Soil-core rockfill dams have been widely used in complex terrain conditions due to their good deformation coordination capabilities,but the problem of cracks has not been solved so far.Numerous studies have shown that the clay core walls of rockfill dams are often in a state of compressive and shear stress.The compression-shear fracture mechanism of compacted clay is of great significance to solve the problem of core wall cracks.In view of this,this article uses a combination of indoor experimental testing and theoretical analysis,the crack inclination,dimensionless crack length and the influe nce of the sample size and other factors on the compression-shear fracture behavior of compacted clays.Secondly,based on the compression-shear-tension fracture criterion,the compression-shear-tension fracture mechanism of compacted clays is revealed.The main work and research results of the thesis are as follows:(1)The influence of crack inclination,dimensionless crack length,sample size and crack opening degree on the fracture behavior of non-closed cracks was found out from the failure mode and the strength and deformation characteristics of the specimen by means of laboratory tests.The results showed that:different crack dip angles all have airfoil tension cracks,and the initiation stress and peak stress of the sample show a trend of first decreasing and then increasing with the increase of the crack dip angle;The dimensionless crack length has a great influence on the failure mode of the specimen.;The failure modes of samples of different sizes are basically similar;The initiation stress,the initiation stress ratio,the peak stress and the deformation modulus of the sample all show a gradually decreasing trend with the increase of the opening degree.(2)The effects of crack inclination,dimensionless crack length and sample size on the fracture behavior of closed cracks have been investigated.The results show that the initiation stress,initiation stress ratio,peak stress and deformation modulus of the sample all vary with the crack inclination angle,the increase shows a trend of first decreasing and then increasing;When the dimensionless crack length is small(2a/W=0.2),only the airfoil tension cracks develop in the sample,in other cases,airfoil tension cracks and secondary shear cracks develop;The initiation stress,the initiation stress ratio and the peak stress of the specimen all show a gradual decrease with the increase of the dimensionless crack length;The sample’s crack initiation stress,crack initiation stress ratio,peak stress and deformation modulus all show a gradually decreasing trend with the increase of the sample size.(3)It is pointed out that the traditional theory cannot explain the tension fracture mechanism of compacted clay.According to the closed crack compression-shear-tens io n fracture criterion considering the T-stress,the influence of the lateral pressure coeffic ie ntλ,the friction coefficientμand other factors on the circumferential stress is found out.It reveals the mechanism of closed fracture compression-shear-tension cracking,and proves that the critical size r_c of the crack tip has an obvious size effect.(4)According to the non-closed fracture compressive shear-tension initia t io n criterion considering the relative passivation coefficient and T-stress,the influence of the relative passivation coefficientηand the relative critical sizeαon the circumferent ia l stress is investigated.The mechanism of compression-shear-tension fracture of non-closed cracks is revealed.