Testing and Constitutive Modeling of Lime-Stabilized Collapsible Loess. I: Experimental Investigations

Aeolian loess deposits are among problematic collapsible soils whose substantial settlements due to the increase in moisture content, stress level, or a combination of both, frequently cause serious structural failures, financial losses, and casualties worldwide. One way to increase the strength and bearing capacity of collapsible soils is to chemically stabilize them with lime. The behavior of lime-stabilized collapsible soils has been investigated mainly by conducting conventional laboratory tests without any measurement or control of unsaturated state variables, such as matric suction. In this research, the hydromechanical behavior of a reconstituted lime-stabilized loessial soil is investigated by conducting unsaturated suction-controlled odometer tests. For this purpose, variable vertical loads have been imposed on the unsaturated lime-stabilized loessial soil specimens (with different amounts of lime content) under constant matric suctions. During all unsaturated odometer tests, unsaturated state variables (e.g., matric suction, degree of saturation, volume change of the tested specimens) have been simultaneously controlled and measured. To capture the hydraulic characteristics of the soil, along with odometer tests, soil-water retention curves (SWRCs) of specimens have been obtained for both wetting and drying paths by conducting filter paper tests. Furthermore, to investigate the effects of adding lime to the evolution of soil pore structures, scanning electron microscope (SEM) micrographs have been captured from the structure of the soil specimens. Results of laboratory tests showed that adding a small amount of lime to collapsible loessial soils not only reduces the collapse-induced volume changes to a large extent, but also can increase the yield strength of the soil. Moreover, it was revealed that further increase of lime content in loessial soil specimens beyond a specific value has no significant influence on the hydromechanical characteristics of the treated soil. In a companion paper, the results from unsaturated odometer tests on treated and untreated loessial soil reported in this paper have been analyzed in an unsaturated effective stress context, and an empirical model for explaining the load-collapse behavior of the soil is presented. Also by implementing the disturbed state concept (DSC), a coupled semiempirical hydromechanical model is developed to predict the disturbance level and calculate the soil strains under applying vertical stress in the K-o condition.