| The full face rock tunnel boring machine(Hereinafter referred to as TBM)has the advantages of safety and efficiency compared with the traditional drilling and blasting method.However,due to the bad load conditions and complex and changeable geological conditions,TBM has the technical bottleneck of unsatisfactory working life and low comprehensive cutting performance of disc hob.With the popularization and application of TBM to "three highs"(plateau rock confining pressure,high rock strength,high quartz content)and other special strata,the construction problems caused by the loss and failure of hob and low rock breaking efficiency become more and more serious,which need to be solved urgently.Laser technology has the advantages of high power density and non-contact energy transmission.In order to solve the above problems,based on the research results of verification,simulation and experiment of laser assisted TBM disc hob rock breaking,this paper proposes the mechanism and theoretical model of laser assisted TBM disc hob rock breaking and carries out numerical analysis after considering the dense core phenomenon at the edge,the boundary effect of laser hole row and the edge crack derivation effect.Then,the significant factors of hob blade width,blade angle,hole distance(i.e.the distance between laser hole and hole center line)and tool hole distance(i.e.the distance between axial surface of hob and laser hole row center line)were explored.On this basis,a dense core derived observation device and method are proposed,and the dense core derived observation experiment is carried out with rock type,edge width and hole spacing as variables.The main results are as follows.(1)With the increase of the maximum penetration depth of the first step rock breaking,the parameters of static pressure rock breaking result of hob increase greatly;With the increase of the blade width,the stress in the dense core area decreases slightly,and the maximum rock penetration load increases significantly.However,the radius of the elastic-plastic failure zone increases linearly,and the rock breaking effect increases significantly;With the increase of hole spacing and cutter hole spacing,the stress in the dense core area,the maximum rock penetration load and the radius of elastic-plastic failure zone decrease first and then increase.Therefore,there is an optimal combination of edge width,edge angle,hole distance and tool hole distance.(2)From the section plane of the rock trench,good internal morphology of the trench is observed,and the fracture morphology is composed of dense nuclear failure zone,fracture damage zone and crack failure zone.In addition,it is concluded from the test that the most significant factors affecting the rock breaking results of laser assisted hob are the blade width and laser hole spacing;In the experimental group with laser hole assisted rock breaking,there are a lot of rock fragments between the blade bottom and the laser hole row.This confirms the mechanism of laser assisted TBM hob rock breaking.(3)The whole process of rock fragmentation is observed,which is rock powder compaction core high pressure compaction core derived initial crack dense core unloading and crack propagation;It is found that the dense core is a white mass with a radius about half of the blade width.With the increase of edge width and rock strength,the larger the volume of dense core is,the slower the nodule velocity is,the deeper the penetration depth is,and the greater the vertical force is,and vice versa;With the intervention of laser-assisted rock breaking,the bonding speed of dense core is obviously accelerated,and the load required for rock invasion and the difficulty of rock invasion are reduced;However,with the increase of laser hole spacing,the rock invasion parameters first decrease and then increase,and there is an optimal hole spacing for auxiliary rock breaking.In conclusion,the optimal blade width is 3 mm and the optimal hole spacing is 4 mm. |
PDF Full Text Request