| When the full-face rock Tunnel Boring Machine(hereinafter referred to as TBM)is used for underground space engineering such as mountain-crossing tunnels,the discshaped cutter(hereinafter referred to as cutter)located on the cutter head directly contacts the rock breaking surface of the tunnel face;Due to the complex and changeable geological conditions,and the poor cutting conditions of the cutter,it was easy to cause frequent failure of the cutter,resulting in a substantial increase in the cost of engineering construction time and tool wear.This paper is based on a deep understanding of the traditional rock breaking mechanism by cutter and the laser thermal cracking effect,especially for the "three highs"(high rock hardness,high confining pressure,high quartz content)and other special extreme formations,the difficult for the cutter to penetrate the hard rock,and the radial wear of the cutter ring is severely invalid,and other bottlenecks.It is proposed to propose a new concept of laser-assisted TBM cutter rock breaking.At the same time,taking the reduced-scale cutter pressure head as the research object,combining theoretical analysis,finite element simulation and physical testing methods,to systematically study the cutting load characteristics and macro-micro rock failure mechanism of the laser-assisted TBM cutter rock breaking process and the multi-factor influence law,the main research work of this paper is listed as follows:(1)Based on the principle of thermodynamic and using the method of killing or activating elements,a FE model of laser rock fragmentation was established,and the interaction mechanism between laser and granite specimens under different powers was studied.The changing law of the obtained laser hole depth/aperture with laser power is approximately consistent with the experimental results,which verifys the correctness of the FE model of laser rock breaking.(2)In the LS-DYNA environment,the HJC constitutive model of the granite sample was established.Comparing the similarities and differences between the stressstrain characteristics and the macroscopic damage morphology of the granite during the SHPB simulation and the experiment,which verifys the effectiveness of the HJC constitutive model of granite samples in simulating transient nonlinear large deformation problems;the FE model of cutter penetration rock was further established.By carrying out the numerical and physical tests of cutter penetrating rock,the correctness of the FE model in predicting cutting load and rock damage morphology was verified.(3)The “two-step method” used to simulate the laser-assisted cutter rock breaking process is proposed.The first step,is to use the laser rock fragmentation FE model to predict the morphology of laser holes;and the second step,ist to reconstruct the rock HJC FE model with the same pore morphology from the FE model of cutter penetrating rock.(4)Based on the aforementioned "two-step method",a preliminary study on laserassisted rock breaking simulation by a reduced-scale cutter has been carried out.The results show that the laser hole can effectively reduce the vertical load of the cutter rock breaking and promote the expansion of the lateral cracks to the laser hole,which greatly increases the amount of rock breaking,thereby significantly reducing the specific energy consumption of the cutter.(5)A two factors(hole-hole distance and cutter-hole distance)and five levels laserassisted cutter penetrates the rock test was carried out.The research results show that the granite is mainly crushed by extrusion/shearing when the cutter-hole distance is too small;With the increase of the cutter-hole distance,the effect of tensile on rock breaking mechanism gradually increases;when the cutter-hole distance exceeds the critical value,the laser hole has almost no influence of cutter penetrates the rock;within a certain range,the larger the hole-hole distance,the higher the fragmentation of granite;the existence of laser holes enlarges the area of cutter penetrates the rock,increases the total mass of rock debris and the fragmentation of rock,and reduces the vertical load,invasion difficulty coefficient and specific energy consumption,comprehensively improve the rock breaking performance of the cutter.This paper has verified the feasibility of laser-assisted TBM rock breaking,and proposed a "two-step method" of laser-assisted TBM cutter rock breaking simulation modeling method that meets engineering accuracy requirements.And the optimal cutting parameters of laser-assisted cutter breaking rock were obtained.The research results of this paper have certain reference value for the future discussion of laserassisted TBM cutter rock breaking technology. |
