Experiment And Numerical Simulation Of Propagation Mechanism Of 3D Crack In Rocks

The natural rock mass which contains lots of defects such as joints and cracks is a heterogeneous material,and its internal structure is very complex.The mechanical properties of rock masses are largely determined by defects such as different scales fissures inside it.Therefore,studying the crack propagation mechanism inside rock masses is very important for the study of mechanical behavior of fissured rock mass.Due to the influence of non-uniformity,the law of three-dimensional fracture expansion in rocks is complex and difficult to be analyzed by analytical method.Meanwhile,it's difficult to make and observe the internal fissure in the laboratory test,and the loading control or measurement is extremely difficult.Therefore,the study on the expansion mechanism of the three-dimensional internal fissure in rock is extremely limited.It is more difficult to study the influence of the direction and magnitude of the principal stress on the fracture propagation mechanism of rock mass under complex true triaxial loading and unloading.Based on previous studies on rock failure mechanism and crack propagation,this paper studied the propagation rule of rock mass internal crack under uniaxial compression through physical experiment,numerical simulation and 3D printing technology,and analyzed the fracture propagation mechanism of samples containing internal 3D crack under true triaxial loading and unloading.Some results were reached in this thesis:(1)Resin samples,gypsum samples and coated sand samples were prepared based on three 3D printing technologies,and the fabrication technology,failure mode and mechanical properties of the samples were studied under uniaxial compression.The results showed that the resin sample had good brittleness at low temperature and showed brittle failure,which was caused by the joint action of tensile shear.The gypsum sample had a large plastic deformation and the failure mode of the coated sand sample is similar to that of the real rock sample.(2)An experimental study on the expansion of three-dimensional internal double fractures in rock mass was carried out.The results show that: under the action of uniaxial compression,the failure mode of the sample is mostly split failure,and the failure surface is almost parallel to the loading direction.The failure degree of the sample corresponds to the peak strength,when the peak strength of the sample is high,the failure degree is relatively serious.And with the increase of the fissure angle in space,the peak strength of the sample shows an “anti-n” type change: the minimum value is obtained when the included Angle of the crack is 30°,and the maximum value is obtained when the included angle of the crack is 60°.The stress-strain curves of the intact samples are in good agreement with each other through numerical simulation.(3)The influences of the fissure inclination,the size and direction of the medium principal stress on the crack propagation under true triaxial loading were studied,and the two dimensional and three dimensional crack propagation were compared.The results show that the peak strength decreases gradually with the increase of fracture inclination angle,and the ability of the specimen to resist failure and deformation becomes worse and worse.The medium principal stress can improve the strength of the sample to some extent,but the peak strength of the sample will be reduced and the destruction of the sample will be accelerated when the medium principal stress is too large.The relationship between the direction of the middle principal stress and the fracture plane directly affects the fracture expansion.There is obvious directionality in the three dimensional internal fissure,and its expansion mode is more complex than the other two.(4)The influence of unloading path and the magnitude of medium principal stress on crack propagation and mechanical properties of samples were simulated.The results show that the failure modes of the samples are different when unloading different principal stresses.The greater the medium principal stress is,the lower the damage degree of rock is,and the more likely it is to produce violent damage.