Microscopic Mechanism Affecting Shear Strength in Lignin-Treated Loess Samples

Abstract

In China, engineers have worked to create additional usable land for building construction by flattening the ridges of hills and filling in the adjacent valleys. China’s Loess Plateau comprises a type of soil (loess) with a large pore structure that can collapse and become unstable when exposed to groundwater. Conventional valley fill materials include remolded loess or remolded loess treated with cement, lime, gypsum, or other stabilizing additives. These stabilizers are often detrimental to the surrounding environment. Moreover, loess treated with conventional stabilizers exhibits excessive brittleness, which is not suitable for building foundations. Adequate stability of the building foundations in the filled valleys is required to ensure public safety. In this study, we tested 50 remolded loess samples treated with a lignin polymer compound to determine its potential as a valley fill material. Triaxial tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to study the mechanical characteristics of each sample, determine the effects of the lignin treatment on the loess, and identify the microscopic mechanism affecting shear stress in the lignin-treated loess. The corresponding development of excess pore pressure and volumetric responses under monotonic triaxial testing were also considered. Based on this study’s results, the optimum lignin content in the treated loess samples was 4%; lignin contents exceeding 4% decreased axial stress and increased dilation after saturation. The shear strength and strain-hardening phenomenon of the lignin-treated loess samples increased as the lignin content increased, while the excess pore water pressure decreased. Microscopically, the addition of lignin increased cohesion in the loess samples, while slightly contributing to the internal friction angle. The use of lignin as a stabilizing additive for valley fill material shows potential for controlling building foundation deformation by increasing soil strength and minimizing environmental impacts by maintaining the soil pH and limiting pollutant production.

Review on Applications of Lignin in Pavement Engineering: A Recent Survey

“…Similarly, a study (Singh and Sahoo, 2021) on clay soils subjected to cyclic loading and came to a similar conclusion that the addition of lignosulfonate to clay soils increased the service life of the soil matrix. In particular, the addition of lignin polymer compounds to loess soils in northwestern China (Liu et al, 2019) not only increased soil strength but most importantly, reduced the environmental impact. Alkali lignin (Zheng et al, 2019) was used as a soil stabilizer and the study showed that heat-curing can increase the strength of the soil by more than 40%, which may be caused by the water content in the soil.…”

Evaluation and Analysis of the Effect of Lignin Amelioration on Loess Collapsibility

“…At present, the researches of lignin soil improvement mainly focuses on improving the strength of sand, silt and clay, but there are few reports on the improvement of the poor engineering properties of collapsible loess. It was determined by dynamic triaxial test and seismic subsidence test that lignin could significantly improve the liquefaction resistance and shear deformation resistance of saturated loess [45,46]. Based on soil-water character curve test and wet disintegration test, the water holding capacity and water stability of modified loess with different lignin contents were studied.…”

Strength Tests and Numerical Simulations of Loess Modified by Desulfurization Ash and Fly Ash

“…The chemical methods are the methods using solidified materials to react with the loess, thereby improving the strength, plasticity and permeability of the loess. At present, there are many kinds of solidified materials, including cement, lime, nano clay, lignin [4,[10][11][12], etc.…”