In this paper, a simple and efficient fractal-based approach is presented for capturing the effects of initial void ratio on the soil-water characteristic curve (SWCC) in a deformable unsaturated soil. In terms of testing results, the SWCCs (expressed by gravimetric water content) of the unsaturated soils at different initial void ratios were found to be mainly controlled by the air-entry value (Ψ_a), while the fractal dimension (D) could be assumed to be constant. As a result, in contrast to the complexity of existing models, a simple and efficient model with only two parameters (i.e., D and Ψ_a) was established for predicting the SWCC considering the effects of initial void ratio. The procedure for determining the model parameters with clear physical meaning were then elaborated. The applicability and accuracy of the proposed model were well demonstrated by comparing its predictions with four sets of independent experimental data from the tests conducted in current work, as well as the literature on a wide range of soils, including Wuhan Clay, Hefei and Guangxi expansive soil, Saskatchewan silt, and loess. Good agreements were obtained between the experimental data and the model predictions in all of the cases considered.

Biopolymer stabilization of soils has emerged as a viable solution for enhancing the engineering properties of soils in recent years. Xanthan gum and guar gum are two commonly used biopolymers. When combined, these materials have the ability to create stronger gels or gel strengths comparable to those achieved by using xanthan or guar gum individually, but at lower total concentrations. However, the extent of this synergistic viscosity-enhancing effect on soil improvement remains unclear. This study analyzes the effects of xanthan gum and guar gum on the physical and mechanical properties of clay under both individual and combined conditions using Atterberg limits tests, compaction tests, and triaxial consolidation undrained tests. At a 2% biopolymer content, the liquid limit of clay treated with a combination of XG and GG compounds increases by up to 8.0%, while the plastic limit increases by up to 3.9% compared to clay treated with a single colloid. With an increase in the mixing ratio, the optimal water content initially rises and then declines, peaking at 27.3%. The maximum dry density follows a pattern of initially decreasing and then increasing, with the lowest value recorded at 1.616 g·cm⁻³. Moreover, the shear strength of specimens treated with the XG and GG combination generally surpasses that of specimens treated with XG or GG alone. Furthermore, the combined treatment results in increased plasticity, highlighting its potential to enhance safety and stability in engineering applications.

Accurate determination of soil-water characteristic curve (SWCC) is of immense importance for understanding the mechanical behavior of unsaturated soils. Due to the difficulty and long duration of experimental procedures, it is of great significance to estimate the SWCC by indirect methods. To address this issue, in this article an effective fractal method is proposed for predicting the SWCC based on mercury intrusion porosimeter (MIP) data. Only two characteristic parameters, namely the fractal dimension and air-entry value, are needed in the presented approach. Detailed procedures for determining the parameters are clearly elaborated. Due to the influence of sample size difference on the equivalent connected pore size, a sample scale effect coefficient is proposed to predict air-entry values. The concept of “critical pore size” is introduced to obtain the optimal fractal dimension, which can accurately reflect the fractal behaviour of SWCC samples. By comparisons between predicted and experimental SWCCs, the validation of the proposed method is verified. The comparisons reveal the good agreement between the proposed approach and laboratory experiments.