Shear Behavior of Compacted Silty Loess

Abstract

Loess, a uniform-sized, wind-blown, cohesive soil can be problematic in geotechnical engineering applications. Natural deposits have high strength and exhibit stable vertical slopes; however, dramatic collapse can occur when loess becomes saturated. In remolded, compacted applications, the behavior of loess is less well known. Regionally (central USA), embankments of compacted loess can exhibit deformation and slope failure after years of service. The initial phase of a larger effort to characterize the strength behavior of compacted loess is reported herein. This phase is limited to assessing the short-term, undrained shear strength of compacted loess. Undrained strengths of compacted loess were measured to be up to 500 to 650 kPa. Higher compactive effort, dry of optimum water content, maximizes the undrained strength. Modified Proctor energy increased undrained shear strength by up to 2.5 to 3.0 times higher than loess compacted at the same water contents using standard energy. Loess compacted at or greater than optimum moisture content, as determined in the standard Proctor test, had similar undrained strength (100 to 200 kPa) regardless of the compactive effort. In order to maximize short term strength of compacted loess, use the greatest compactive effort and compact the soil well dry of optimum moisture content.