Numerical Studies On The Fracture Characteristics Of Defective Rock Under The Indentation Of TBM Cutter

TBM（Tunnel Boring Machine）play a pivotal role in tunnelling.Cracks and holes are common in natural rock and have a significant impact on the mechanical properties of the rock.These defects will not only reduce the efficiency of TBM disc cutter on rock fragmentation,increase TBM boring costs,and even cause tunnel engineering collapse accidents.As a key component of TBM on rock fragmentation,the cutter is in direct contact with the rock.It is of great theoretical significance and engineering value to study the effect of the cutter on breaking up defective rock and to further reveal the mechanism of rock fragmentation and crack propagation mechanism.In this thesis,the finite element method is combined with a bilinear constitutive model based on CZM（Cohesive zone model）to simulate brittle fracture and crack propagation of rocks.The model is divided into three stages: initial damage criterion,damage evolution stage,and stages of fracture and friction calculation after complete damage.The feasibility and accuracy of the adopted cohesion-based bilinear instantonal model is verified by combining the model with numerical simulations of rock triaxial compression and other experiments and comparing the experimental results with the literature.A finite element model of TBM cutter on rock fragmentation was established,and the influence of inclination angle,depth position,geometric dimension and position of the intrusion of the cutter.The results show that the greater the hole inclination and depth,the greater the contact force of the cutter and the more difficult it is to press the cutter into the rock.Hole defect at smaller depth location prevent crack expansion and the rock model has the smallest total crack area.The larger the geometry the lower the cutter contact force and the total area of cracks and fracture patterns do not differ significantly between models with different geometries.The effect of the hole on the extension of cracks in the rock is also reduced when the cutterbing position is reduced.The effects of crack defect location（both depth and offset location）,length and confining pressure in the rock were investigated.The effect of depth location on cutter press-in was particularly significant,with increasing cutter contact force with increasing depth,smaller depth crack defects inhibiting crack initiation and propagation,and the smaller the total area of cracking in the rock.There is a limit to the effect of offset location on crack extension.Rock containing longer lengths of crack defects have less cutter contact force but produce a similar total crack area,the cutter is more likely to break the rock and the residual strength within the rock is less.Most of the cracks produced in rocks with no confining pressure under cutterbing exhibit tensile fracture.Higher confining pressure will cause more cracks caused by shear damage,and will hinder the further germination and expansion of cracks,making it more difficult for the cutter to break up the rock.