FREQUENCY OF FREEZE-THAW CYCLES, BULK-DENSITY AND SATURATION EFFECTS ON SOIL SURFACE SHEAR AND AGGREGATE STABILITY IN RESISTING WATER EROSION

Soil erodibility is the soil's inherent resistance to detachment and t ransportation by raindrops and runoff energy and is reflected in relat ive indices. Some of the factors from which these indices are calculat ed are surface shear strength and aggregate stability. These two soil properties were measured on remolded soil cores after subjecting them through a number of freeze-thaw cycles, a phenomenon which has been ob served to aggravate stream sediment events in late winter and early sp ring periods. The three Southern Ontario soil textures chosen for the experiments were a Conestogo silt loam, a Brookston clay, and a Fox lo amy sand. The surface shear strength and aggregate stability test was conducted to determine the influence of repeated freeze-thaw cycles on these properties and to incorporate the interactive effect of textura l class, bulk density, and saturation on these variables. The mean wei ght diameter (MWD) method was used as an index to quantify aggregate s tability. Surface shear strength was measured with a fall cone apparat us fitted with permanent magnetic suspension. Results of factorial ana lysis of variance indicate that the means of surface shear strength an d aggregate stability proved to be significantly different among soil textural classes and bulk density. Also, the mean surface shear streng th also indicated significant differences among the number of freeze-t haw cycles and saturation levels.