About the author:

1. Key Laboratory of Urban Security and Disaster Engineering of China Ministry of Education, Beijing University of Technology, Beijing 100124, China;2. School of Civil and Environmental Engineering, Nanyang Technological University, 639798, Singapore; 3. Yellow River Engineering Consulting Co., Ltd., Zhengzhou, Henan 450003, China

Abstract:

Tunnel boring machine (TBM) has the problems of low advance rate and severe cutter wear when tunnelling in the high-strength rock mass. High-pressure water jet (HPWJ) can create kerfs on the tunnelling face to reduce the integrity of the rock mass and improve the rock breaking performance of TBM cutters. Therefore, investigating the rock cutting mechanism of HPWJ is one of the key issues of studying HPWJ-assisted TBM tunnelling. A computer numerical control HPWJ platform was used to carry out cutting tests on the sandstone, marble, and granite specimens. The water jet pressure increased from 150MPa to 300MPa. By observing the apparent damage on the specimens and measuring the depth and width of the kerfs, it was found that the kerfs on the sandstone surface were mainly straight, whereas continuous craters were found on the marble surface. Although the craters on the granite surface were larger, but the number significantly reduced. Based on the sieving tests of rock breaking debris and the observation of cracks around the kerf cross-sections with fluorescent dyes, the damage characteristics of the rocks were analyzed. The results indicated that the formation of the kerfs on the sandstone was mainly due to the erosion of the HPWJ, the cementation between the grains was broken. The effect of HPWJ impact was not obvious, no cracks were observed around the kerf cross-sections. Two other crystalline rocks with higher strength were influenced by the erosion and impact of the HPWJ, trans-granular failures in the marble caused the necked-funnel shaped kerfs, while more inter-granular failures caused by the water wedge effect created large craters on the granite.