| Full-face rock tunnel boring machine(TBM)is a high-end major engineering equipment that integrates tunnel excavation,rock ballast transportation,and tunnel support.It is widely used in the construction of large long rock tunnels in highway,railway,and water conservancy projects.However,when TBM encounters high hard rock,it can cause problems such as low rock breaking efficiency and slow excavation speed,seriously affecting the construction progress.Therefore,exploring new efficient and rapid rock breaking tunneling methods is of great significance for improving the rock breaking efficiency of cutters and TBM tunneling efficiency,and is also one of the hot research issues in the current industry.The basic principle of free-face assisted rock breaking is to change the traditional "rolling" mechanism to "splitting" by removing the lateral constraints of surrounding rock or changing the penetration direction of the cutter.Currently,the existing research on auxiliary rock breaking in free-face mainly focuses on the rock breaking process of a single or two cutters under free-face conditions,while the research on the tunneling characteristics of cutterhead cutters in free-face mode is insufficient.Therefore,this paper uses a combination of full-scale indoor tunneling experiments and large-scale numerical simulation to systematically study the dynamic evolution mechanism of the free-face group and the impact mechanism of its form and structural parameters on TBM tunneling performance in the context of assisted rock breaking scenarios with two-stage TBM cutterheads,corrugated TBM cutterheads,and high-pressure hydraulic coupling TBM cutterheads.The main research contents are as follows:Construction of numerical models for excavation process of surrounding rock with different TBM cutterhead cutter groups.The interaction properties between the cutter and rock are analyzed,and rock breaking mechanism of cutter under free-face is revealed;The FEASPH coupling method based on ABAQUS is introduced.Aiming at the mechanical failure characteristics of rock sample materials,the Mohr-Coulomb elastoplastic constitutive model combined with Rankine criterion is adopted;The material parameters were obtained by uniaxial compression and Brazilian splitting mechanical tests on the sample,and the parameters of its numerical model were calibrated.The conversion conditions for converting the FEA element mesh to SPH particles were set;Establish a three-dimensional model of rock breaking for a group of cutters in two-stage cutterhead mode,pre-grooved cutterhead mode,and corrugated surface cutterhead mode.Set boundary conditions for the rotary cutting process of the cutter group,and set parameters such as the rotation,revolution,and propulsion speed of the cutterhead cutter during rotary cutting of the sample.Complete a large-scale numerical model of rock breaking for a group of cutters in "rolling while penetrating" tunneling.Full-scale indoor test of two-stage TBM cutterhead excavation process in surrounding rock.Relying on full-scale TBM cutterhead dynamic tunneling and rock breaking test rig,concrete samples were prepared instead of rock samples.Under the same cutterhead rotation speed,experimental research was conducted on tunneling process of TBM cutterhead group under free-face with different cutterhead penetrations.Force monitoring sensors were used to take normal rock breaking force of each cutter and the thrust and torque of cutterhead in real time.After excavation was completed,rock debris from each ring was collected and grading and screening tests were conducted for each ring of rock debris.To explore the impact mechanism of cutterhead penetration on collaborative rock breaking of cutter groups under specimen freeface,thereby revealing the collaborative rock breaking effect of multiple cutters near free-face side and the dynamic evolution mechanism of free-face group;Compare tunneling test of cutter group under free-face of two-stage cutterhead with tunneling test of flat-face cutterhead cutter group of the research group,analyze the impact of free-face on rock breaking efficiency of cutter group using physical indicators such as normal force of cutter and the amount of rock breakage,and confirm improvement effect of free-face on cutterhead tunneling efficiency.Numerical simulation of rock breaking by cutter group tunneling under different cutterhead modes.Carry out numerical calculation of the collaborative rock breaking model of cutter group under free-face in two-stage cutterhead mode,and compare the simulation results of numerical model with the excavation test to verify the feasibility of established numerical model;Based on the validated numerical model of rock breaking process of cutter group tunneling,numerical simulation of rotary cutting of cutter group under the coupling effect of different tunneling parameters is conducted,and the influence of different cutter spacing and cutterhead penetration on rock breaking performance of free-face side cutter group is studied.The best parameter combination is selected based on indicators such as rock breaking load.Carry out numerical simulation of cutterhead excavation in pre-grooved mode,explore the rock breaking performance of cutters in pre-grooved mode,focus on studying the impact of pregrooved depth on rock breaking performance of cutters,and use indicators such as rock breaking load of cutters to evaluate their rock breaking performance;For rock breaking in the excavation of corrugated surface cutterhead cutters,introduce the rock breaking methods under the free face,adjust the layout positions of cutters in the wave crest,wave valley,and transition zone,conduct numerical simulation of the collaborative rock breaking model of cutters in corrugated surface mode,analyze the factors that affect the excavation performance of corrugated surface cutterhead cutters,and study the influence law of distance between wave crest and wave valley on rock breaking efficiency,Further reveal the improvement effect of free face on the efficiency of rock breaking during excavation. |
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