| China has carried out a large number of mountain and water tunnel construction projects.The full-face rock tunnel boring machine(TBM)is a major high-end engineering equipment for excavating various types of rock tunnels.It is highly respected because of its significant advantages such as high efficiency,safety and environmental protection.However,the widely used plane cutterhead TBM has the bottleneck problem of ’ low rock breaking efficiency ’when excavating hard rock geology.In view of this,scholars at home and abroad have proposed cone-shaped,multi-stage,corrugated and other special-shaped structure cutterheads,and deeply discussed their rock-breaking tunneling mechanism.However,the research on the mucking mechanism and the design of the mucking structure are not deep enough and systematic,and continuous mucking is one of the core functions that directly affect the TBM tunneling speed.Therefore,this study adopts the method of combining large-scale particle discrete element numerical simulation with laboratory tests to systematically study the mucking mechanism of three special-shaped cutterheads with conical,two-stage spiral and corrugated structures,and the influence of corresponding structure and tunneling parameters on their mucking performance.The main research contents are as follows :Construction of high-precision large-scale numerical model for TBM cutterhead mucking process.The large-scale particle discrete element software EDEM is used to construct the numerical model of TBM cutterhead mucking process considering the whole stage of ’ mucking,falling,shoveling,slipping and guiding ’.The rigid wall is used to construct the structure models of cutterhead,tunnel face and tunnel face.The rigid particle cluster is used to construct the rock debris model considering the morphology and gradation and conforming to the engineering statistical law.The Hertz-Mindlin model is used to characterize the contact characteristics of rock debris itself and between rock debris and structure.The residual rock mass of the cutterhead is proposed,that is,the real-time residual rock mass at the lower part of the front face of the cutterhead and the real-time residual rock mass at the bottom of the cutterhead cavity are used as the evaluation index of the cutterhead mucking performance.Development of TBM cutterhead mucking process test system and verification of numerical model.It is very difficult to carry out the field test of TBM cutterhead mucking process.Therefore,a small TBM cutterhead mucking process test system(patent has been authorized)is developed,including an inclined screw conveyor feeder and a cutterhead host composed of a base,a transparent cover,a cutterhead body and a scraper bucket,a spindle,a drive motor and a chain drive,and a mucking slot.The small-sized block stone suitable for stable transportation and simulated mucking is selected to carry out the indoor mucking process test.The EDEM numerical model with the same structural size,cutterhead speed and rock mass flow rate as the indoor test is constructed.The test and simulation results are compared and analyzed from the aspects of mucking process and residual rock mass change law,and the numerical method is verified.It is found that in the middle stage(about 10 ~ 30s)of the residual mass change inside the cutterhead in the result curve of the test and simulation model analysis,the error of the average mass between the two is 9.6 %,which can verify the reliability of the numerical modeling method.Based on the verified numerical modeling method,the numerical model of the mucking process is constructed for the three special-shaped structure cutterheads of cone type,two-stage spiral type and corrugated type.Analysis and law research on mucking mechanism of TBM cutterhead with special-shaped structure.The mucking simulation of three kinds of special-shaped structure cutterheads of cone type,two-stage spiral type and corrugated type is carried out,and the mucking process is analyzed.Compared with the conventional plane cutterhead,the working face of the cone cutterhead is inclined to the periphery of the cutterhead surface,and the cone angle of the cutterhead surface directly affects the mucking performance.The key of the two-stage cutterhead is to transport the rock debris generated by the first-stage cutterhead to the second-stage cutterhead area smoothly,and then discharge it out of the tunnel.The rock debris flow route is long and there are many influencing factors.The section of the face of the corrugated cutter head and the face of the cutter head is S-shaped,so the falling track of the rock slag in the front space of the cutter head is also S-shaped.The rock slag will fall from the S-shaped gap and accumulate in the front of the cutter head,and then be shoveled into the cutter head.The rules of the special-shaped structure TBM cutterhead mucking can be summarized as follows : The front and rear spirals of the two-stage cutterhead are the key structures that affect its mucking performance.The function of the front spiral is to send the rock debris at the back mucking port to the rear spiral,and the function of the rear spiral is to further send the rock debris transported to the rear spiral position to the front of the two-stage cutterhead.The diameter ratio of the flat cone area of the conical cutterhead and the cone angle of the disc surface are important factors affecting its mucking performance.It is suggested that the diameter ratio of the flat cone area of the conical cutterhead is not less than1 and the cone angle of the disc surface is not more than 45°,which can ensure the smooth mucking of the conical cutterhead.The corrugated cutterhead can be discharged smoothly,and the peaks,troughs and transition zones in the local structural ripples have no significant effect on the mucking performance of the cutterhead. |
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