Research On Dynamic Failure Of Frozen Soil Under The Rolling Cutter Of New Vertical Shaft Tunnelling

At present,most of the shaft construction in the deep alluvium adopts the freezing method construction technology.However,with the increasing thickness of the frozen soil layer,the frozen soil is a special four-phase mixed dense structure of solid,liquid,gas and ice crystals,and the failure mechanical properties of frozen soil are extremely complex due to the influence of temperature,moisture content and other factors.Face of the problems of conventional mechanical excavation of shaft tunnelling and umbrella drilling blasting,such as large potential safety hazards,low efficiency and discontinuous process,which seriously affect the rapid and safe construction of shaft.To change the excavation mode of shaft and improve the excavation efficiency of shaft frozen soil,a new vertical shaft tunnelling is employed.The tunnelling has good adaptability in shaft frozen soil excavation.It uses cutter to continuously roll down and walk to excavate frozen soil.Among them,the rotation speed of drum and penetration depth are important factors affecting the efficiency of cutter to excavate frozen soil.Based on the improvement of the excavation efficiency of shaft frozen soil,this paper establishes the theory of rolling cutter breaking frozen soil,analyzes the stress distribution of frozen soil under the action of rolling cutter,and analyzes the mechanism,stress theory and efficiency of cutter breaking frozen soil;With the aid of WAW-600 material testing machine and split Hopkinson compression bar(SHPB),the static and dynamic physical and mechanical properties of frozen soil are analyzed,and the parameters of frozen soil constitutive model are optimized;The finite element software is used to simulate the frozen soil damage process under the rolling state of the cutter.It is obtained that the optimal rotation speed of the drum is 30 r/min,the optimal penetration depth of the cutter is 40 mm,the degree of frozen soil damage is large,the specific energy consumption is the lowest and the efficiency is the highest;The orthogonal test is used to study the influence law of multi factor interaction on the overall frozen soil breaking efficiency,the influence degree of single factor and the best factor combination of comprehensive evaluation are obtained,and the dynamic failure mechanism of frozen soil under the action of rolling cutter is revealed;The ground similarity test of the new vertical shaft tunnelling is carried out,and the influence of the cutter on the failure efficiency of frozen soil under the action of different drum rotation speed and intrusion depth in the numerical simulation is compared and analyzed.It is obtained that the optimal drum rotation speed is 30 r/min and the optimal cutter intrusion depth is 40 mm.The concrete failure characteristics are obvious and the efficiency is the highest,Verify the feasibility of numerical simulation.The main work and research results of this paper are as follows:(1)Establish the theory of rolling cutter breaking frozen soil,analyze the stress distribution of frozen soil under the action of rolling cutter,and analyze the mechanism,stress theory and efficiency of cutter breaking frozen soil,and obtained the normal stress distribution and diffusion law in frozen soil.The stress distribution is basically symmetrical.In the contact area between frozen soil and cutter,the stress value is great,and the farther away from the action point of cutter,The stress decays exponentially.When the frozen soil is damaged,it is mainly affected by the rolling force and normal force of the cutter.The greater the force of the cutter,the more serious the frozen soil is damaged.According to the calculation formula of specific energy consumption of cutter breaking frozen soil,the lower the specific energy consumption,the higher the efficiency.(2)The uniaxial unconfined compression test and Brazilian splitting test are carried out on frozen soil specimens by WAW-600 material testing machine,and the compressive and tensile strength of frozen soil specimens are obtained.Through the impact test of frozen soil specimens with separated Hopkinson compression bar under different strain rates,it is found that there are two special properties of frozen soil specimens: strain rate effect and strain convergence phenomenon,and the strength of frozen soil constitutive model is obtained.Among them,the compression and tensile strength of frozen soil specimens are low,and the greater the impact force,the more prone to failure.(3)Combined with the original parameters of Holmquist Johnson cook compression damage model(HJC),the parameters of frozen soil constitutive model are optimized.Using the coupling of pre processor Hyper Mesh software,finite element solver LS-DYNA software and Solid Works three-dimensional software,the frozen soil breaking process of cutter under the single factor drum rotation speed of 20,25,30 and35 r/min and intrusion depth of 20,30,40 and 50 mm is simulated,and the influence law of cutter on the overall frozen soil breaking efficiency under the interaction of multiple factors is studied by orthogonal test,and the significance of single factor and the best factor combination of comprehensive evaluation are obtained.It is found that the optimal rotation speed of the drum is 30 r/min and the optimal intrusion depth is 40 mm in the process of breaking the frozen soil by the cutter.It increases the internal stress change of the frozen soil,weakens the bearing capacity of the internal structure of the frozen soil,and increases the generation and expansion range of frozen soil cracks.The damage characteristics of the frozen soil are obvious.The specific energy consumption of breaking the frozen soil by the cutter is the lowest and the efficiency is the highest.(4)Carry out ground similarity test of new vertical shaft tunnelling,and the concrete breaking process of the lower cutter is set with the drum rotation speed of 20,25,30 and 35 r/min and the intrusion depth of 20,30,40 and 50 mm.Compared with the damage process of the cutter invading the frozen soil under the corresponding conditions in the numerical simulation,it is obtained that the optimal rotation speed of the drum is 30 r/min and the optimal invasion depth is 40 mm.The damage range and depression degree of the concrete are increased,and the concrete breaking efficiency is the highest,which verifies the accuracy of the numerical simulation.This paper contains 47 figures,13 tables and 92 references.