Effects of relative hardness and moisture on tool wear in soil excavation operations

This paper presents an experimental study of tool wear using a laboratory tester which simulates the operating conditions of cutting tools in soil excavation operations. The testing is performed in a test chamber that allows high contact stress between soil and cutting tools. The test conditions mimic the condition of pressurized face shield machines used in soft ground tunneling, where the impact of wear is costly and crucial. Various tool to soil hardness ratios were obtained by changing both the tool material and the percentage of soil's constituent minerals, i.e. quartzetic and limestone grains. In dry soil conditions, when the tool wear is plotted against the relative hardness, an inverted S band bounded by curves of highest and lowest tool hardness is formed. As hardness of cutting tools in actual soil excavation applications, including soft ground tunneling, lies in a narrow range, the expected S band becomes thinner which better helps in the design and selection of the cutting tools and materials used for inner components of these machines which come to contact with soil during the operation. The results of testing on this tester also show that as the moisture content of the soil increases to 10%, the tool wear drastically increases. The trend is reversed as the moisture content further increases and reaches full stauration of soil where the tool wear is smaller than that experinced in the dry soil.