Research On Rock Breaking Mechanism And Efficiency Of TBM Disc Cutter Based On Parallel Bond Model

With the rapid development of subway construction in Qingdao,a "rock-based city",tunnel boring machines(TBM)have been widely used in subway construction.As a common geological structure of rock formations,the characteristic parameters of joints have a non-negligible influence on TBM rock breaking.The thesis mainly starts from the theoretical research on the force and efficiency of the TBM hob in the process of rock breaking,and based on discrete element theory and practical engineering,the mechanism of the hob rock breaking and the change law of force and efficiency are deeply studied.The design and construction of TBM have certain guiding significance.The main research work of the paper is as follows:(1)The commonly used hob force prediction formula is expounded,and the results of the Rostami hob load prediction model are more accurate through analysis and verification;the ring specific energy prediction formula of TBM is proposed and verified.This formula has high practicability and is TBM The calculation of rock breaking efficiency and the design of cutter arrangement provide a theoretical basis.(2)Based on the PFC2 D discrete element software,the rock uniaxial compression,Brazilian splitting,and conventional triaxial compression models were established,and the influence of the meso-parameters of many parallel bonding models on the macro-mechanical parameters of the rock was analyzed and obtained.Observe the efficiency of parameter calibration.(3)Based on the PFC2 D software,the single and double hob rock breaking numerical models were constructed to study the rock breaking mechanism of the hob.The results show that the dense core of the hob breaking rock is mainly damaged by shear and tension combined damage,normal and lateral cracks and cracks.The penetrating crack of the double hob is mainly caused by tension failure and supplemented by shear failure.The uneven development speed of cracks leads to the phenomenon of rock breaking by leaping forward.(4)Based on the discrete element model of single hob rock breaking,the influence of joint position and angle on hob rock breaking is studied.The results show that joints can consume part of the rock breaking energy through deformation and dislocation,and have a hindering effect on the conduction of stress and deformation;In the state of single hob breaking rock,the larger distance between the flat joint and the face face can reduce the barrier effect of the joint,so that the dissipation effect of the joint on energy is reduced,resulting in the increase of the normal force of the hob and the improvement of the rock breaking efficiency.increases,the normal force of the hob gradually decreases,and the rock-breaking efficiency first increases and then decreases.When the joint inclination angle is 45,the rock-breaking efficiency is the highest.(5)Based on the discrete element model of rock breaking with double hob,the influence of the position of flat joint and inclined joint on the rock breaking of hob is studied.The results show that when the flat joint is close to the face,the rock breaking mode changes to the joint-double crack rock breaking mode.The rock-breaking efficiency is greatly improved;the increase in the distance between the oblique joint and the face causes the normal force of the hob to gradually increase,and the rock-breaking mode gradually changes from joint-double-crack rock-breaking mode to joint-single-crack mode and then to unjointed rock The rock-breaking mode is adopted,and the rock-breaking efficiency reaches the best state at the critical position of the latter two modes.(6)The formula of the rock-breaking efficiency improvement ratio of the crushed zone is proposed.Based on the actual engineering of Qingdao Metro,the influence law of the angle between the crushed zone and the tunnel axis on the rock-breaking efficiency of the TBM is explored.The results show that: the thrust of the TBM in the process of crossing the crushed zone The penetration and torque increase;when the angle between the direction of the crushing zone and the tunnel axis is about 52,t the effectiveness of the TBM rose efficiency is minimized.