Evaluation of Cutting Tool Wear of Earth Pressure Balance Shield in Granular Soil Based on Laboratory Test

摘要

Cutting tool wear is a critical problem for tunneling in soft ground with the earth pressure balance shield. In this study, a cutting tool tester was developed in the China University of Geosciences in Beijing, and a series of tool wear tests were conducted to investigate the characteristics of tool wear in granular soils. The characteristics of cutting tool wear can be quantitatively assessed through the ratio (M-0 - M)/M-0 (i.e., tool wear rate, %; M-0 and M are the mass of the tested blocks before and after the wear test, respectively). The effects of five important factors, including mineralogy, moisture, soil conditioner, test time, and sand content, on tool wear were considered in various test conditions. According to the primary test results, it is observed that (1) high soil hardness produced significantly higher tool wear than low soil hardness in dry condition; (2) with increasing water content, the tool wear gradually increased to a maximum value and then decreased; (3) the foam conditioner mixed in sandy gravel reduced the tool wear dramatically regardless of the cutting tool material, e.g., cemented carbide and Q235 steel; (4) the tool wear increased with the test time in the dry sand mixture, and their relationship showed a good agreement with a power function; and (5) the tool wear decreased as the sand content increased in dry sand-gravel soil mixtures. The reasons for these phenomena were also explored.