To understand the tensile fracturing mechanism of rock, the fracture toughness of rock should be defined. We performed 3-point bending tests for 4 types of rocks. Then, the LS-Dyna code was adopted to simulate the 3-point bending tests and the tensile fracturing procedures of rock. The sample rock was modeled using the HJC (Holmquist-Johnson-Cook) rock material model, and the key parameters were selected by sensitivity analysis and then optimized to precisely describe the mechanism. Finally, the suggested material model and the simulation results were validated with the 3-point bending experiment results. The proposed 3 key parameters (e.g. PL, kl, and evol) can successfully describe the tensile fracturing process of rock model.

1 Introduction

The application of rock blasting method in urban area is gradually regulated because the noises and vibration induce inconvenience to civilians. To minimize the disadvantages of the blasting method, some methods producing less vibration (e.g. smooth blasting, drilling-splitting, water jetting method, etc.) has been used in urban site. However, these methods are suffering from the low working efficiency and poor excavation rate when encountering the hard rock.

The study is developing a new cutting-splitting method which is for rapid excavation rate for hard rocks. The procedure is that cutting rock at a certain depth by a rock saw, and then splitting the rock into two blocks by inserting a chisel into the crevice. The key mechanism of the method is tensile fracture propagation on the basement of rock blocks. To understand the fracture mechanism of rock, the fracture toughness (mode I) of each rock should be determined. 3-point bending tests were performed for four strength rock classes (i.e., low, moderate, medium and hard strength). From the results, fracture toughness (mode I) values of the samples were obtained.

Then, the LS-Dyna code was used to simulate the tensile fracturing procedures during 3-point bending tests. HJC (Holmquist-Johnson-Cook) material model (Holmquist et al., 1993) was adopted. The model has many input parameters which are very hard to be defined with limited numbers of laboratory experiments. We performed sensitivity analysis to filter out the important parameters before the main simulations. After selecting key parameters, a series of 3 point bending simulations were carried out. The simulation data were compared to the experimental results by the optimization method. After the procedure, we suggested the optimum values for the four classes of rocks. This can help solving tensile fracturing process in rock splitting method to the future study.

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