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In nature, expansive soil is generally in a state of swelling during rainfall, and its soil–water characteristic curve (SWCC) exhibits a three-dimensional space shape under the action of an increasing void ratio. In this study, expansive soil from Hefei, China, was used. SWCC and hygroscopic tests were performed. A three-dimensional hygroscopic swelling mathematical model of the dry density–void ratio–saturation degree was constructed based on the volume change behavior of expansive soils resulting from the hygroscopic test. In addition, depending on the variation in suction with the saturation degree of expansive soil under different values of dry densities, an SWCC mathematical model considering the swelling effect was constructed. The three-dimensional surface model of the hygroscopic swelling of the expansive soil was steeper in the lower saturation degree area. As the saturation degree increased, the three-dimensional surface gradually became flat. The SWCC model of the expansive soil under the action of swelling in a three-dimensional space is an S-shaped surface. The model exhibited dynamic changes in the suction and saturation degrees as the dry density of the soil decreased continuously. The model comprehensively revealed the hydraulic and swelling properties of expansive soil. [ABSTRACT FROM AUTHOR]

Expansive soils are extremely susceptible to swelling and shrinkage associated with seasonal changes in their moisture content. This can cause serious damage to structures constructed on expansive soils. Stabilization using additives is widely used to mitigate the concerns of expansive soils by controlling the changes in volume, thereby increasing the strength and durability of the soils. Multistabilizers, including a low percentage of conventional additives with nonconventional additives, can reduce the costs of stabilization. The performance of the stabilized soil can be enhanced by admixture optimization to ascertain that the agent's ratios are quite adequate to meet the optimal levels of modification. Unfortunately, despite the development of advanced techniques for investigating the stabilization of expansive soil, limited studies are devoted to the optimization of admixture to soils. Hence, in this research, an approach based on rough set theory, a mathematical data mining approach, is presented for multiagent optimization for efficient treatment of expansive soils. The multiadditives used in this study are almond shell ash (ASA), volcanic rock dust (VRD), and portland cement (PC). The differential free swell test, the California bearing ratio test, and the unconfined compressive strength test were applied for assessing the characteristics of the stabilized soil specimens. The obtained results and the confirmatory tests demonstrated that a combination of 20% ASA and 20% VRD with 8% PC provides the optimum results in the properties of expansive soil. The microstructural analysis denoted an enhanced modification of the soil engineering properties. The outcomes of this research confirm that the rough set optimization procedure is highly suitable for application in multiagent optimization for the efficient treatment of expansive soils. [ABSTRACT FROM AUTHOR]

Cement composite soil is a more stabilized method in expansive soil foundation projects, but it is essential to find an ecofriendly modification material to reduce the content of cement and its pollution for the environment. A series of unconsolidated–undrained (UU) triaxial tests were conducted to investigate the modification effect of graphene oxide (GO) on cement-stabilized expansive soil (CS), and the contents of GO were 0.05%, 0.1%, 0.15%, and 0.2%, respectively. The test results show that (1) the deviatoric stress–strain curves of CS gradually change from a weakly softening type to a strongly softening one after adding GO. (2) The compressive strength, shear strength, and toughness of GO-modified cement-stabilized expansive soil are better than CS, and the optimal GO content is 0.05%. (3) Microscopic tests show that GO can promote the hydration reaction of cement and reduce the internal pores of CS. Consequently, the mechanical properties and microstructure of CS can be significantly improved after adding GO, and it is feasible to replace a part of the cement with GO in expansive soil foundation projects. [ABSTRACT FROM AUTHOR]

This paper focuses on the effectiveness in the improvement of clay soils of using geopolymers of fly ash (FA), metakaolin (MK), or blast furnace slag, activated by an alkaline solution of sodium hydroxide (NaOH), sodium silicate (Na2SiO3), or a mixture of both. The unconfined compressive strength (UCS) of samples cured for 1, 7, and 28 days was determined, and X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were performed to record the mechanical, chemical, and mineralogical behaviors of the stabilized soils. The results showed an increase from 149.72 kPa (untreated clay) to 460.06 kPa for the clay soil treated with NaOH after 1 day of hardening. The highest UCS was obtained using a MK-based geopolymer (MKG) at 28 days. Oedometric testing showed a reduction in the swelling potential of the clay soil and a decrease in the swelling pressure from 600 to 300 kPa. It was found that all the tested treatments significantly improved the geotechnical properties of the clay soil. However, the MKG treatment was most effective in terms of increased resistance, while the FA-based geopolymer (FAG) provided better results in terms of reducing swelling. [ABSTRACT FROM AUTHOR]

This paper presents as a discussion of "Performance Evaluation of a Highway Slope on Expansive Soil in Mississippi" by Mohammad Sadik Khan, Masoud Nobahar, Mike Stroud, Sean Ferguson, and John Ivoke. https://doi.org/10.1061/(ASCE)GM.1943-5622.0002240. Repairs to the failed section of the slope were undertaken a few months following the initial slope construction and were carried out by removing the failed soil and replacing it with a backfill that was less plastic, and therefore, not as swell-prone as the original soil. This approach versus the traditional approach when determining the factor of safety of slopes that used the limit-equilibrium method was considered more appropriate to account for the physical changes within the soil matrix that would occur during its wetting and drying cycles. [Extracted from the article]