Abstract
One huge challenge TBM construction face is to improve the breaking ability of cutters for hard rocks, making the studies on new rock breaking approaches for cutters very important. Although a lot of previous tests have proved that it is feasible to reduce the cutter force by free-face-assisted rock breaking (FM), the mechanisms behind such feasibility and the estimation methods for key parameters involved, including the maximum free face distance, crushing angle, and cutting force, remain to be studied further, limiting its applications in cutterhead design and engineering construction practice. Based on the analysis of the phenomena and laws of FM tests, this paper proposes the tensile-shear failure mechanism of FM and a piecewise linear failure criterion, which could explain the reason for the reduction of cutting force. Subsequently, a series of estimation models for the parameters above are proposed, and a series of FM tests were performed. By comparing the data obtained from the tests and calculations of the estimation model and CSM model, the estimation model in this paper is verified for its feasibility and limitations, which offered some insights on these aspects in follow-up research.
Highlights
Disc cutters in TBM are highly efficient to break rocks, so they are currently the most widely applied mechanical construction equipment to build rock tunnels in the world
The tension-shear failure mechanism of FM is proposed and discussed, and several estimation models for key parameters involved in FM, including the rock crushing angle, the maximum free space distance, and cutting forces, are established and analyzed for their calculation accuracy. e main conclusions are as follows: (1) e tension-shear failure mechanism can be used to explain FM failure
In FM, the rock will crack under smaller tensile or shear strength compared to cutting methods (CM), which is the main reason that the force required for rock breaking reduces in FM
Summary
Disc cutters in TBM are highly efficient to break rocks, so they are currently the most widely applied mechanical construction equipment to build rock tunnels in the world. In the first two methods, the cutting force is significantly reduced, and rock breaking efficiency increases without extra force applied on the cutter. As for the last method, the penetration depth and rock breaking efficiency are improved as well, the force the cutter endures grows, making cutter failure more prone to occur. Advances in Civil Engineering assisted rock cutting (FM) on a linear cutting machine (LCM) and found that FM could effectively reduce disc cutting force and achieve large volume rock fragmentation with a higher rock breaking efficiency than conventional rock cutting methods (CM). In FM, the free surface is created by either a cutterhead with two or more stages [11] or a large depth slit carved by large flow water jets after its slow and repetitive cuts on the rocks (Figures 1(a) and 1(b)). We propose a tension-shear failure mechanism and establish several estimation models for key parameters of FM, which could provide further insights for engineering applications
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