Study On Dynamic Damage Constitutive Model Of Rock And Low Damage Blasting Method

Drilling and blasting construction in the surrounding rock with structural plane is easy to cause excessive damage and over/under-excavation of the surrounding rock.Existing studies on the fracture characteristics and fracture mechanisms of laminations and joints coupled with multiple characteristic parameters are scarce,and there is a lack of research on the evolution of blasting damage,fracture mechanisms and damage control in surrounding rocks containing discrete fracture zones and random fractures.Therefore,with the support of the Huangguashan tunnel,this paper studies the rock static failure forms and impact fracture characteristics.Based on Holmquist-Johnson-cook（HJC）model,a dynamic damage constitutive model of rock considering initial damage is proposed.Then the Blasting simulation test of surrounding rock with structural plane is carried out,and the blasting fracture evolution law of surrounding rock with structural plane is studied.On this basis,a low damage blasting method based on asymmetric uncoupled pre-charge is proposed,and the blasting damage control effect of asymmetric uncoupled charge structure in surrounding rocks is further explored.Finally,the proposed asymmetric uncoupled low damage blasting technique is applied to the Huangguashan tunnel project,and the concrete consumption is reduced from more than 300%before optimization to less than 150%after optimization.The detailed research contents and results are as follows:（1）Static dynamic tests on pre-damaged sandstone were carried out to obtain the basic mechanical parameters,static and dynamic damage modes,static and dynamic stress-strain curve characteristics,impact crushing characteristics and transient crack expansion patterns of pre-damaged sandstone.Based on the mathematical morphological method of topological theory,the block fractal dimensional characteristics,fractal size variation law and fractal energy evolution characteristics of different pre-damaged rocks were revealed.The results showed that the block fractal dimension of sandstone was positively correlated with the degree of pre-damage,the fractal size of fractured rock was negatively correlated with the degree of pre-damage,and the fractal energy was non-linearly increasing with the degree of pre-damage.（2）An improved HJC dynamic damage constitutive model was developed to take into account the existing damage characteristics of the original rock and the effect of static and dynamic strain rate.Based on the extended strain equivalence principle and damage mechanics theory,a new damage equation is derived by comprehensively considering the initial damage D₀,dynamic tensile damage D_td,and dynamic compression damage D_cd on the basis of the original HJC model.By introducing the threshold pressure P_dr,static/dynamic pressure hardening indexes B₁ and B₂,static/dynamic pressure hardening coefficients m₁ and m₂,a new yield surface equation is derived.Combined with the derived damage equation and yield surface equation,an improved HJC model is established.（3）The reliability of the improved HJC dynamic damage constitutive model is verified by numerical simulation and experimental methods.The stress-strain curves,physical and mechanical parameters and failure modes of uniaxial compression,triaxial compression,Brazilian splitting,drop weight impact test and field blasting test were obtained by LSDYNA embedded in the improved model,and compared with the physical tests.The results show that the numerical simulation results are basically consistent with the physical test results,thus verifying the reliability of the improved HJC dynamic damage constitutive model.（4）Based on the dynamic contact algorithm,Monte Carlo algorithm and element deletion method,the blasting model of surrounding rock with bedding,joints,fracture zones and random cracks is established,and the blasting fracture mechanism of surrounding rock with structural planes is obtained.The propagation law of blasting cracks in the fracture zone and the fracture morphology in the crushing zone of Jointed Surrounding Rock and bedding surrounding rock with different angles,spacing,quantity,combination and thickness are simulated,and the evolution law of blasting fractal dimension is analyzed according to the fracture form of surrounding rock.The blasting fracture characteristics of the surrounding rock in the fracture zone with different fracture range,degree and spacing are simulated.The blasting fracture characteristics of random fractured surrounding rock with different fracture density,fracture group number and fracture length are simulated,（5）A whole process Blasting simulation method of tunnel based on ten million level grid division and multi-step restart is proposed.The blasting model segmentation method based on global segmentation and local partition,and the hybrid grid and multi gradient density transition method are used to realize the ten million level grid division of the tunnel large-scale model.The multi-step restart method and the sequential controlled initiation method are introduced.Combining the above two methods,the whole process Blasting simulation of the tunnel is realized.（6）A low damage blasting method based on asymmetric uncoupled charging is proposed,and an asymmetric uncoupled refined pre-charged casing device is developed.The asymmetric uncoupled blasting of homogeneous surrounding rocks with different hole diameters and explosive offset distances,as well as the asymmetric uncoupled blasting of surrounding rocks with structural faces,were realised by numerical simulation.The asymmetric uncoupled charge showed better blast damage control in both homogeneous and non-homogeneous surrounding rocks compared to conventional charge blasting.