Sdudy On Consititutive Model For Brittle Rocks And Excavation Damage Zone Prdiction Of Deep Tunnels

With the deepening of infrastructure construction and resource exploitation,and the urgent requirement of nuclear waste disposal,the excavation damage zone(EDZs)of deep underground engineering has become a hot issue for domestic and foreign scholars.In this paper,theoretical analysis,numerical simulation and validation through field monitoring information are used to study the brittle failure characteristics during the excavation of deep tunnels and the numerical simulation method in predicting EDZs.The dissertation first summarizes the evolution of mechanical properties of brittle rocks during failure process,and then analyzes the rock mass constitutive models suitable for describing the brittle mechanical behavior on the basis of theory and existing research results.Elastic-brittle-plastic(EBP)model,cohesion-brittleness-friction strength(CBF)model and fracture initial-splitting boundary(DISL)model are provided for numerical modeling.The numerical simulation method is determined by observing the simulation results of Canadian Mine-by test tunnel from the finite element software Phase2.Compared with the field observation,the angle of damage zone calculated by EBP model is larger than the observed one,and both the depth and angle resulted from CBF model are smaller than the field values.While the range of the damage zone calculated by the DISL model are comparable to the in-situ record,which demonstrates the superiority of DISL model.Considering the high degree of irregularity of the actual excavation profile,a smooth circle and a series of semicircle are built to respectively simulate the “designed” and “built” profile of excavation surface.The result shows that the irregular model based on DISL model obtains the damage zone with a good agreement with field observations,which reveals the irrationality of ignoring the boundary condition to predict damage zone.The side walls are also damaged,so the gradual excavation method is applied to simulate the process of excavation.The results show that selecting the DISL constitutive model and gradual excavation method,with the actual excavation boundary captures the shape of EDZs accurately.The aforementioned numerical simulation method is used to simulate a smooth circular tunnel.It was demonstrated that the DISL model follows stress path in surrounding rock well.The outer boundary of the highly damaged zone,HDZ,is related to volumetric strain and a reduction in minor stress confinement.Both an inner and outer excavation damage zone(EDZi and EDZo)could be differentiated using the reversal point in the volumetric strain(contraction to extension).This indicates the transition between a confined micro-damaged state(EDZo)and a potentially dilated EDZi.The EDZo–EIZ transition was taken as the start of yielding.This method of partitioning provides a new way to accurately delineate the dimensions of the excavation damage zones.The further development and application to engineering practices of this result will generate an important guiding significance for the long-term stability prediction of these projects.