Damage And Fracture Phase Field Model Of Rock And Its Application In Tunnel Excavation Damage Zone

Damage and fracture are the most widespread damage modes of rock materials,which are prone to induce disaster and instability of engineering structures,and have become the key factors affecting the development of rock mechanics theory and the improvement of engineering construction.The development of fine structure inside the rocks leads to rock damage fracture as a complex nonlinear mechanical problem,and the excavation unloading behavior and non-uniform ground stress environment aggravate the complexity of engineering rock failure behavior and mechanical response of engineering structures.The damage fracture phase field method solves the crack discontinuity problem by crack regularization.As a non-local continuous medium mechanics theory,the damage fracture phase field method avoids complicated crack tracking algorithm and fracture criterion,and can simulate the whole process of crack emergence,expansion,bifurcation and fragmentation without pre-defined cracks,which provides innovative ideas for the analysis of damage zone in tunnel(cave)or underground excavation.Based on the damage fracture phase field theory and considering the plastic deformation and non-homogeneous characteristics of rocks,this paper constructs a non-local damage fracture phase field model for rocks and proposes a method for the analysis of damage zone in tunnel excavation on this basis.The main contents include.(1)The numerical calculation program of TL-FEMS,a solid damage fracture phase field model,is developed.Based on the finite element discrete format of the damage fracture phase field,the numerical calculation program of TL-FEMS is developed based on the user-defined unit subroutine(UEL),including the displacement field layer(UEL subroutine),the damage phase field layer(UEL subroutine)and the numerical result display layer(UMAT subroutine),using the Fortran language was used to prepare the software subroutine interface.Comparing the two-dimensional and three-dimensional single-sided notched flat plate tensile and shear fracture simulation results,the validity of the TL-FEMS numerical calculation program was verified,and the fracture of Brazilian discs containing prefabricated cross cracks with different dip angles was further explored.(2)The rock damage fracture phase field model and numerical calculation procedure were constructed,considering the difference of critical capacity release rate and nonhomogeneity characteristics of rocks,introducing the non-homogeneity of fracture parameters,modifying the linear fracture criterion of rocks,and combining the elastic strain energy sphere-bias decomposition and plastic strain energy function to construct the rock elastic-plastic coupled damage fracture phase field model.The damage fracture characteristics of rock containing prefabricated cracks under compressive loading are analyzed according to the modified TL-FEMS numerical calculation program in discrete finite element format,and the ability of the model to analyze rock crack extension is verified by comparison with the results of rock mechanics tests.(3)A dynamic damage fracture phase field model and a numerical calculation program were established,based on the elastic-plastic coupled damage fracture phase field model of rock,the energy equation,the control equation and the finite element discrete format of the phase field model were derived by introducing the inertia force term,and the TL-FEMS numerical calculation program of the dynamic damage fracture phase field model of rock was used to analyze the dynamic tensile fracture of prefabricated notched rectangular plate and the dynamic load thick-walled cylinder.The dynamic TL-FEMS numerical calculation procedure is validated by the dynamic damage fracture phase field model of rock.The fracture characteristics of rock crack damage under dynamic compression load are given,and the dynamic extension characteristics of single and double cracks with different inclination angles are analyzed.(4)Based on the rock damage fracture phase field model,a tunnel excavation damage zone analysis method is proposed,including the concept of excavation damage zone and the zoning criteria.Define the damage fracture phase field as a quantitative index to characterize the excavation damage zone,that is,the excavation damage zone and the surrounding rock damage phase field changes in line with the excavation boundary damage fracture phase field value close to 1,to the deeper part of the surrounding rock damage excavation unloading effect gradually weakened,the damage fracture phase field value from 1 to 0 gradually reduced;the inflection point of the damage phase field gradient change curve as the excavation damage zone criteria,divided into excavation damage zone,excavation disturbance zone and the original rock stress zone.Based on this method,we analyze the excavation damage zone of Mine-by tunnel at the URL test chamber of Atomic Energy of Canada Limited(AECL)-420 m level,and compare it with the results of field monitoring,microseismic monitoring and numerical simulation to verify the rationality of the excavation damage zone analysis method based on rock damage fracture phase field.(5)The proposed theoretical model and the developed calculation program were applied to the analysis of excavation damage zone in deep tunnel surround rock,analyzed the tunnel excavation damage characteristics of surrounding rock fractures and ground voids,discussed the influence law of surrounding rock fractures and ground voids on tunnel excavation damage zone,and quantitatively predicted the depth of tunnel excavation damage zone;the developed calculation program was applied to the analysis of excavation damage zone in shallow buried soft surround rock tunnel,analyzed The analysis of the excavation damage zone in Mawei Mountain tunnel under different burial depth and rock level conditions was carried out to provide reference suggestions for oversupporting Mawei Mountain tunnel.