Collapsible Loess in Iowa

Abstract

The collapsibility, or tendency towards rapid consolidation or settlement upon saturation by water, of many C‐horizon loess soils constitutes and important physical property pertinent to soil genesis, erosion, and engineering. The potential of a loess soil to collapse upon saturation by water may be established from undisturbed samples saturated while under load in a consolidation testing machine. A more convenient criterion, that the saturation moisture cntent must not exceed the liquid limit, was regressed against 0.005 mm clay content determined by the hydrometer method, and indicated that C‐horizon loess containing less than 20% 0.005 mm clay is very likely to be collapsible; with 30% clay there is a 50% probability of collapse, and with over 40% clay there is only a small likelihood of collapse. These percentages were compared to published clay content contours to estimate the areal extent of collapsible loess in Iowa. To convert to 0.002 mm clay content, hydrometer test 0.005 mm clay contents were regressed against pipette test 0.002 mm clay contents to give X002 = 0.8X005; thus the 0.002 mm clay contents corresponding to high, medium, and low probabilities of collapse are < 16%, 24%, and > 36% caly, respectively.

Bank‐collapse processes in a valley‐bottom gully, western Iowa

“…This conclusion is reinforced by the observation that the peak frequency of bank displacements occurred 2 months earlier than the mean peak water discharge through the gully (Thomas et al, 2004). The high collapsibility of loess -its tendency to consolidate substantially upon wetting (e.g., Handy, 1973;Lutenegger and Hallberg, 1988;Mitchell and Soga, 2005) -can also be ruled out as a bank-displacement mechanism. The loess alluvium that constitutes the gully walls was redeposited by water and is therefore less porous than primary loess.…”

Lateral In-Situ Stress Measurements to Diagnose Liquefaction

“…Loess containing less than 16 percent 2 μm clay is very likely to be collapsible, and one containing more than about 32 percent clay is not (Handy 1973).…”

A Novel Field Device for the Measurement of Soil Collapsibility

“…Since the late 1980's, considerable attempts have been made to offer mathematical and computer models. In these models, the attention was on modeling the behavior of collapsible soils and the distribution process of these soils' porosity (Handy 1973;Houston et al 1988). Since then, many studies have been carried out to estimate collapsibility, numeric modeling, failure model offering, etc.…”