Effects of gravel content and particle size on abrasivity of sandy gravel mixtures

During soft ground tunnel construction, the presence of sandy gravel stratum often causes serious wear and tear of cutting tools. In this paper, an experimental study to assess abrasivity of sand-gravel materials with different gravel content (GC) and gravel size (GS) was carried out with a horizontally oriented mechanical mixing device. The abrasive characteristics of testing materials were quantitatively assessed through the measurement of weight loss on the testing steel cube, with a focus on the influence of GC and GS of the mixtures. Experimental testing results indicate that GC and GS have significant impact on soil abrasion and tool wear, through affecting the packing density of the sand-gravel mixtures, breakage resistance of particles, and the soil-tool wear mechanisms. The torque required to drive the propeller in the sand-gravel mixtures during the abrasivity test was measured and provided more insights into the abrasivity of mixtures and the associated soil-tool wear mechanisms. In addition, potential relationships between coefficient of uniformity (Cu) and coefficient of curvature (Cc) of the sand-gravel mixtures and the tool wear were sought.