Investigation On The Specific Energy Due To Indentation And Numerical Simulation Of Indentation Induced Stress Fields In A Jointed Rock

Determination of the optimum cutter spacing is critical to the design of cutterhead of tunnel boring machines (TBMs). Since the optimum cutter spacing is closelyrelated to the cutter-induced fragmentation, especially the lateral cracking, bysimulating the cutters as indenters, the stress distribution due to two elastoplasticallyindented cutters, the lateral cracking and the specific cutting energy, and the stressdistribution in a jointed rock mass under a single indenter have been studied in thepresent work.Firstly, by resorting to ABAQUS, the stress distribution in an ideal elastoplasticrock indented by two cutters has been calculated. It has been demonstrated that theinteraction between the two indenters is very weak and stress field in the range ofeach indenter can be approximated by that due to a single indenter. Consequently, thelateral cracking has then been studied through finite element method andsemi-analytical method. The relationship between the energy release rate and thelateral crack size has been analyzed from which the specific energy in relation to thecrack size or the cutter spacing has been obtained. A minimum specific energy hasalso been obtained to yield the optimum cutter spacing. It has been revealed that theoptimum spacing is governed mainly by the stiffness, hardness and the cutter profile.Typical values for rock stiffness and hardness give the optimum cutter spacingconsistent with what were observed in linear cutting test.Secondly, with in mind that the practical rock mass contains many discontinuitieslike joints, by introducing a linear constitutive law for the joints, they have beensimulated via COHESIVE model in ABAQUS. And the stress distribution in a jointedrock mass has been investigated subsequently by using ABAQUS. Thesemi-analytical solution for the horizontally oriented joint has also been obtained. Inthe case of the horizontally oriented joint, the simulated results agree well with thesemi-analytical results, which verifies the validity of the finite element model. It hasalso been demonstrated that within certain range of the embedded depth for the joint,a region of tensile stress or relatively large shear stress may develop, which issignificantly different from that in the ideal rock mass. The orientation of the jointdepth may also influence the stress distribution remarkably. All the results indicate that failure pattern may be very different as compared to that in ideal rock mass.