Mechanical and Acoustic Emission Responses of Rock Fragmentation under Disc Cutter Penetration

Qi Liu,Penghai Deng,Yucong Pan

doi:10.1155/2021/8829046

Abstract

To better understand the rock fragmentation mechanism and optimize cutter design and selection for rock excavation by TBM, a set of three-dimensional indentation tests was conducted with different rock and cutter types. Acoustic emission (AE) monitoring technique was employed to capture the information of the rock damage evolution real-timely. It is found that the penetration by using the constant cross section (CCS) cutter tends to induce inconspicuous rock chips formation before the sudden occurrence of the macrocrack, but that by using the V-type cutter tends to induce gradual rock fragmentation accompanied by the multiple local rock chips formation and the sawtooth force-penetration curve. Meanwhile, rock fragmentation models for CCS and V-type cutters were compared, and the spatio-temporal evolution of AE events was quantitatively analyzed to reflect the rock damage zone development process. Results indicate that the V-type cutter has greater penetration ability and the CCS cutter can cause larger unit damage zone radius. Microscopic observation by using the scanning electron microscope (SEM) reveals that the fracture mechanism for the crushed zone of rock is mainly shear type and that for the major crack is tensile type. It does not matter with rock types or cutter types.

Highlights

Tunnel boring machine (TBM) is an engineering machine for tunnel excavation that is highly automated and widely used
Yin et al [16] explored the influence of confining stress on the crack initiation, distribution and rock fragmentation through indentation tests using granite and marble specimens, and the acoustic emission (AE) system was applied for real-time monitoring, but the damage evolution and cracking process of rock were not fully analyzed due to the limitation of the location accuracy and analysis method
After the lateral stress was exerted slowly, the P-wave speed of rock was measured with the AST function of the Acoustic emission (AE) system. en, several iterations of pencil-lead break tests were conducted on the upper surface of the specimen as the method suggested by ASTM [37], to ensure the good sensor-rock coupling and calibrate the AE location accuracy

Summary

Introduction

Tunnel boring machine (TBM) is an engineering machine for tunnel excavation that is highly automated and widely used. Yin et al [16] explored the influence of confining stress on the crack initiation, distribution and rock fragmentation through indentation tests using granite and marble specimens, and the acoustic emission (AE) system was applied for real-time monitoring, but the damage evolution and cracking process of rock were not fully analyzed due to the limitation of the location accuracy and analysis method. The development of the crushed zone which is highly fractured and inelastically deformed due to the high compressive stress beneath the disc cutter is an essential process of rock fragmentation It is comprised of rock powders or extremely small rock particles and acts as the important force transmission medium for crack initiation and propagation. Effective rock chips formation is only 5–10% [11, 16, 32]. erefore, when rock chips are formed effectively, the smaller crushed zone means higher cutting efficiency, less rock dust generation, and lower specific energy of cutting [4, 31, 33, 34]. e rock damage zone size can be regarded as a significant index to evaluate the cutting efficiency of different disc cutters

Experiment

Experimental Result and Analysis

Damage Zone Analysis Based on AE Events Distribution

Findings

C Figure 11