An experimental study on cutting tool hardness optimization for shield TBMs during dense fine silty sand ground tunneling

Abstract

The estimation of soil abrasivity and cutting tool wear during soft ground tunneling is complicated and arduous work due to the lack of a generally accepted testing system. To date, geotechnical baseline reports (GBRs) and geotechnical data reports (GDRs) still cannot provide reliable soil abrasion indices for tool life prediction. This is considered a deficiency in the geotechnical investigation of shield-driven tunnel projects. In this study, the Multifunctional Shield Test System (MSTS) developed by the Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province at Wuhan University is presented. The MSTS was motivated by the need for a test platform with the ability to simulate undisturbed soil conditions and actual tool working environments to explore the mechanism of cutting tool wear, bentonite slurry penetration, and filter cake formation in various geomaterials with grain sizes including clay, silt, sand, and gravel (< 15 mm). Experimental studies on the effect of alloy hardness on cutting tool wear are conducted. The soil samples used in the tests are dense fine silty sand from the Sutong GIL Yangtze River Crossing Cable Tunnel. When the wear extent is plotted against the alloy hardness, an inverted S-shaped band bounded by the highest and lowest alloy hardnesses is formed. The sensitive hardness interval is HRC = [47, 52]. If the alloy hardness is higher than 52 HRC, the wear extent is relatively small. Since alloy hardness is negatively correlated with bending strength, using a cutting tool material with a hardness slightly higher than the upper limit of the sensitive hardness interval is optimal. Thus, an alloy with a hardness interval of HRC = [52, 63] is recommended for the dense fine silty sand ground at the Sutong GIL Yangtze River Crossing Cable Tunnel. Keywords Cutting tool wear • Alloy hardness • Soil abrasivity • Testing system • Soft ground tunneling Terms HardnessThe ability of a material to resist hard objects pressed into its surface locally Relative hardnessThe ratio of the hardness of one material to that of another Sensitive hardness interval The hardness interval in which the wear extent decreases significantly as the hardness increases Sensitive relative hardness intervalThe relative hardness interval in which the wear extent decreases significantly as the hardness increases * Xiao-Ping Zhang

Evaluating the wear of cutting tools using a tunnel boring machine laboratory simulator

“…The LCPC test was used by Thuro and Kasling (2009) to study and classify soil and rock wear [8]. Zhang et al (2021) investigated the alloy hardness effect on cutting tool wear and found that wear extent increases as alloy hardness decreases [9]. Jakobsen and Lohne (2013) examined abrasivity properties at different moisture contents in a soil sample and found that weight loss of steel tools increases with an increase in water content from 0 to 8%, and decreases with an increase in water content from 8 to 25% [10].…”