Research On The Mechanical Properties Of Fracture Network Specimens Based On 3D Printing

In the construction process of large-scale rock mass engineering,the complex medium of fractured rock mass is often involved.For a long time,the research on fractured rock mass has been the focus and hot spot in the field of rock mechanics.The random distribution of geological structural planes in the rock mass is one of the main reasons for the failure of engineering rock mass.Under this background,this paper has carried out an experimental study on the rock mass with complex fracture network.Rock-like specimens with complex fracture networks were prepared by using 3D printing technology.Based on the characteristics of water-soluble printing materials being softened by water,a solid model of open crack network was fabricated and filled with soft fillings.On this basis,the uniaxial compression test of rock specimens with fracture network was carried out.The deformation evolution process during the loading process was quantitatively analyzed by using digital image correlation method.Two mathematical statistical indexes,standard deviation and differentiation rate,were introduced to quantitatively analyze the change of strain field.In addition,different filling materials were used for filling,and the effect of filling materials was further studied.At the same time,RFPA^2D numerical simulation software was used to simulate the fracture process of fracture network specimen under uniaxial compression.The main work and research results of this paper are as follows:（1）Through 3D printing technology,rock samples like fracture network can be reconstructed with high precision,and the model specimens prepared have stable mechanical properties and minimal coefficient of variation,good repeatability,and can effectively simulate the real complex rock structure,which has an important reference value for the study of fractured rock mass.（2）According to the characteristics of stress-strain curves during uniaxial compression tests,the failure characteristics of specimens can be divided into four stages:initial compaction,elastic deformation,crack propagation and strain softening.The post-peak curve is characterized by plastic strain softening.（3）The DIC technology was used to realize full-field non-contact and real-time monitoring,and the global strain field of crack network specimen under axial load was quantitatively described.The test results showed that the deformation and fracture process of specimen showed gradual evolution,and the mechanism of crack initiation and propagation was reflected from the perspective of strain field.（4）By calculating the standard deviation curves of the horizontal strain field(ε_xx),vertical strain field(ε_yy)and shear strain field(γ_xy),it is found that the standard deviation of the strain field mainly experiences the stage of slow growth,steady growth and accelerated growth.The differentiation rate curve of the horizontal strain field(ε_xx)was calculated by the finite difference derivation of the standard deviation.It was found that the peak value of the differentiation rate curve of the horizontal strain field corresponds to the occurrence of macroscopic cracks and can predict the crack initiation of the specimen to a certain extent.（5）The difference of the crack filling will affect the physical and mechanical properties of the specimen.Especially in the early stage of deformation development,the existence of the filling will cause significant changes in the surrounding strain field,and the degree of change is also different due to the difference of the filling itself.（6）RFPA^2D numerical simulation software can effectively simulate the loading process of real rock,and the distribution of stress field and the process of crack propagation can be observed intuitively by outputting relevant simulation results.