QUANTIFYING FREEZE/THAW-INDUCED VARIABILITY OF SOIL STRENGTH

Abstract

ABSTRACT This study, conducted over the winters of 1987/88 and 1988/89, examined the feasibility of determining strength and other related soil physical properties as they change over winter. Soil strength was measured with two Torvane shear devices, a pocket penetrometer, and a modified Swedish fall-cone device. Soil water content was determined gravimetrically. Frost depth was determined with a CRREL-Gandahl type frost gage and also by probing the soil with a knife. Strength was measured best, under the conditions encountered, with a metal Torvane device. Strength ranged from 1.2 kPa during soil thawing to 14 kPa under dry soil conditions. Under sunny and windy conditions, thaw-weakened soil regained most of its strength within a few hours after thaw. Strength was found to be inversely related to the water content of the top 10 mm of the soil profile. The soil water content of this layer during or immediately after rain or snow melt on unfrozen soil did not exceed 25% by weight; whereas, soil water content was as much as 58% while the soil was frozen and 44% while the soil was thawing.