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SOIL PHYSICS

A Laboratory Rig and a Scale- and Energy-Controlled Procedure for Tender Soil Fragmentation Test

^a Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural Univ., Nanjing 210095, China
^b College of Engineering, Nanjing Agricultural Univ., Nanjing, 21003, China

^* Corresponding author (qsding{at}njau.edu.cn).

A laboratory rig was developed for a scale- and energy-controlled tender soil fragmentation test, which required multiple impacts and step-by-step decomposition of the soil structure on a macroscale. Soil sample size classes were scaled down by a factor of two, giving ranges of 128, 64, 32, 16, 8, 4, 2, 1, and 0.5 mm, respectively. These size classes were also used as control scales for respective fragmentation stages. Fragmentation tests were conducted to illustrate the possible influences from shape effects, falling weights, displacements, and fragmentation stages, and to investigate the relations among specific fragmentation energy, number of strokes per fragmentation stage, and fragmentation fractal dimension. Specific fragmentation energy was influenced by both the size and the shape of the soil samples. The cylindrical- and ball-shaped soil samples behaved similarly. Thus ball samples were used for a benchmarking test on soil structural stabilities. Subsequent fragmentation on 60- and 80-g ball samples with changed displacements from 5 to 45 cm yielded a decreased number of strokes from around 150 to 10. Whereas, their respective fragmentation fractal dimensions varied insignificantly, ranging from 1.52 to 1.64 for samples of 60-g mass and 1.55 to 1.72 for 80 g, values much smaller than previously reported. Fragmentation fractal dimension appeared to be a nominal index for remolded soils under laboratory impacting actions. There was a slight increase in specific fragmentation energy as the number of impacts increased. But this increase was aggravated for a single or only few impacts. Thus 20 to 40 strokes was the appropriate stroke number to finish one fragmentation stage. A five-stage fragmentation on a sample in the 32- to 64-mm size range yielded fragmentation fractal dimensions of 1.29, 1.52, 1.45 and 1.61, for the first four stages, respectively, whereas their specific fragmentation energies increased linearly.