COMPACTION OF AN EARTHY SAND BY RUBBER TRACKED AND TIRED VEHICLES

Normal stresses exerted by two agricultural vehicles (a rubber tracked Caterpillar Challenger 65 and a Steiger Tiger 550 4WD tractor fitted with low pressure dual wheels) were measured with electronic earth pre ssure cells at four depths (150, 300, 400 and 500 mm) in a sandy soil located in the West Australian wheatbelt. Cone penetration resistance and dry bulk density were also measured at these depths before and aft er traffic treatments. Uniaxial soil compression testing was done on s oil cores sampled at the 300 mm depth where the peak normal stresses w ere measured during vehicle passage. The Cat 65 exerted less normal st ress on the soil than the Steiger 550 at 400 and 500 mm depth. However , the soil had a higher penetration resistance after the passage of th e Cat 65 relative to the Steiger 550. Profiles of cone penetration res istance were more discriminating in distinguishing soil physical chang es among the trafficked and untrafficked treatments than dry bulk dens ity and most of the parameters derived from compression tests.