Structures constructed on collapsible soil are prone to failure under flooding. Agro-waste like rice husk ash (RHA) and its geopolymer (LGR), consisting of lime (L), RHA, water glass (Na2SiO3), and caustic soda (NaOH), present a potential solution to address this issue. RHA and LGR were mixed up to 16% to improve the collapsible soil. Samples were remolded at optimal water content and maximum dry density for strength and collapsible potential tests. Unconfined compressive strength, deformation modulus, and soaked California bearing ratio exhibit exponential improvement with the inclusion of LGR. Additionally, for comparison of microstructural characteristics, analyses involving energy-dispersive X-ray spectroscopy (EDAX) and scanning electron microscope (SEM) were conducted on both virgin and treated specimens. LGR resulted in the emergence of new peaks of sodium silicates and calcium silicates, as indicated by EDAX. The formation of H-C-A-S gel and H-N-A-S gel observed in SEM suggests the development of bonds among soil particles attributed to geopolymerization. SEM reveals the transformation of the inherent collapsible soil from a dispersed and silt-dominated structure to a reticulated structure devoid of micro-pores following the incorporation of LGR. A numerical model was constructed to forecast the performance of both virgin and stabilized collapsible soils under pre- and post-flooding conditions. The outcomes indicate an enhancement in the soil's bearing capacity upon stabilization with 12% LGR. The implementation of 12% LGR significantly resulted in a lower embodied energy-tostrength ratio, emissions-to-strength ratio, and relatively lower cost-to-strength ratio compared to the soil treated with 16% cement kiln dust (CKD). (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

This research investigated the effect of nano-Al2O3 on the shear and hydraulic properties of collapsible soils. Direct shear, permeability, and consolidation tests were performed on samples stabilized with nano-Al2O3 at different curing times. The results showed that the addition of nano-Al2O3 to collapsible soil led to an increase in shear strength. The cohesion and internal friction angle of stabilized collapsible soil with optimum nano-Al2O3 content (0.6%) increased by 3.25 times and 18%, respectively. Ultrasonic pulse velocity (UPV) measurements demonstrate a significant reduction in void ratio with the addition of nano-Al2O3 and confirm its effectiveness in predicting soil mechanical properties. The R-2 coefficients for estimating cohesion and internal friction angle based on UPV are 0.90 and 0.87, respectively. Moreover, the strong correlation coefficient (0.905) between UPV and the collapse index indicates its significant role in determining soil collapsibility. These results highlight the potential of UPV as a reliable and non-destructive evaluation tool in geotechnical applications. Consolidation test results showed that adding 0.6% nano-Al2O3 to collapsible soil decreased the collapse index by 81%. Nano-Al2O3 with fine-filling properties reduced the permeability coefficient by 87% compared to unstabilized collapsible soil. In general, the results of this research show that using nano-Al2O3 as a stabilizer can significantly improve the characteristics of collapsible soils.

Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Dealing with collapsible soils consistently presents a crucial challenge for geological and geotechnical engineers. Loess soil is among the most widely recognized types of collapsible soils, covering approximately 10 % of the Earth's land surface. Loessic soil is a sedimentary deposit primarily composed of silt-size grains, loosely bound together by calcium carbonate. In Iran, approximately 17 % of Golestan province is covered by silty, clayey, and sandy loesses, primarily composed of loessic soil. Additionally, several energy transmission lines in this province traverse these loess-covered areas. Based on the reports from Golestan Gas Company experts, the scouring of gas pipeline channels in various regions, such as Dashli-Alum in Maraveh-Tappeh city, causes significant risks in the traffic roads and is one of the most critical issues facing this company. This research assessed the dispersion and collapse potentials of loess soil using a range of field exploration and laboratory testing methods. These methods included atomic absorption spectroscopy, the double hydrometer, scanning electron microscope photography, wavelength-dispersive X-ray fluorescence spectrometry, and consolidation tests. The results indicate that soil collapsibility was acquired as one of the components of the scouring phenomenon occurrences. To achieve an optimal solution, the effectiveness of the chemical stabilization method involving cement, bentonite, micro- silica, and synthesized nano-titanium additives was evaluated through an oedometer, Atterberg limits, uniaxial compression, and direct shear tests. Additives dry mixing of cement and nano-titanium were obtained as the optimal stabilization solutions against scouring compared to other additives. However, considering the environmental impacts of cement production and use, nano-titanium presents a more environmentally sustainable option due to CO2 absorption and reduced damage potential to vegetation.

This study establishes a foundational framework addressing challenges, implications, and potential remedies related to collapsible soils. Serving as a cornerstone for global exploration, it emphasizes the importance of understanding geological, structural, and mechanical characteristics for early identification and proactive mitigation. The study underscores the significance of preventing structural damages in regions prone to collapsible soils, discussing their diverse types and origins, structural composition, and mechanical behavior. A detailed exploration highlights their prevalence in semi-arid and arid regions, emphasizing distinct geological features associated with their occurrence.

Aeolian and kaolin deposits contribute greatly to infrastructural damage during the rainy seasons because of massive collapse settlements. The prediction of wetting-induced collapse potential and compressibility behavior under partly saturated states is essential for the development of infrastructure on these deposits. In this study, a general constitutive model was developed from the suction-controlled compression and wetting-induced collapse tests. The effect of particle orientation resulting from various initial compaction conditions, drying paths, and wetting paths on the yielding behavior of soil was investigated. A new collapsible soil model (CoSM) was presented by considering the wetting-induced changes to the clay fabric associations in the collapsible soils. The proposed CoSM requires eight parameters for evaluating the mechanical behavior. These model parameters can be readily estimated from simple compression tests, which is the major advantage of the model. The derived equations were capable of predicting three crucial mechanical characteristics, namely, loading-collapse yield, compression, and collapse behavior from the basic compression data. The model shows an excellent agreement with the measured data for two kaolin soils from the present work and several collapsible soils from the literature. The generalized model is capable of predicting mechanical behavior of collapsible soils with various initial compaction states and loading stress histories.

Collapsible soils are located in various parts of the world. These soils are characterized by their low values of dry unit weight and natural water content. Collapse and large induced settlements at the saturation state damage the structures built on them. Therefore, measuring the collapse potential of these soils is essential for safe engineering works. This study aims to investigate the collapse index and collapse potential of clayey soil stabilized with calcium carbide residue (CCR). For this purpose, seven different contents of CCR, five curing periods, three different water contents, and two relative compactions were used. The results of tests showed that the CCR contents, relative compaction, and water content during sample preparation were the most key factors in collapsibility measurements. It was observed that CCR contents greatly reduced collapse index and collapse potential of soil and changed the degree of collapse from moderately severe to slight and non-collapsible one. Furthermore, increasing the relative compaction reduces the pore space between the soil particles, leading the denser structure. The denser the soil, the lower the initial void ratios, hence, there is less collapse upon wetting. Finally, the stabilized samples prepared with 2% less than optimum water content have a higher degree of collapse than those with optimum water content and 2% more than optimum water content. The results of this study corroborate the effectiveness of CCR as a by-product material to improve collapsible soils.

The objective of this research is to examine the use of precipitated calcium carbonate (PCC), obtained during the production of sugar from sugar beets, and to stabilize subgrades beneath highway pavements or to stabilize foundations built on loess (windblown silt). The research also aims to permanently capture the carbon from PCC in soil. The experimental process involved the collection of representative loess samples, the addition of variable percentages of PCC, and conducting laboratory experiments on compacted PCC soil mixes to evaluate the effect of PCC on subgrades beneath pavement and foundations beneath buildings. Samples of PCC were obtained from the Amalgamated Sugar Corporation, located 187 km away from Pocatello. In addition, soil was collected from local sources in which saturation collapse and damage have occurred in the past. Unconfined compressive strength tests, which index subgrade bearing failures, were performed on both untreated and PCC-treated soils to evaluate the effect of PCC in stabilizing pavement subgrades and foundations as well as sequestering carbon. The experimental test results revealed a significant average increase of 10% to 28% in the strength of loess samples stabilized with 5% PCC compared to the native soil. The chemical composition and microstructure of PCC were further analyzed through energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) tests. EDX analysis unveiled a carbon content of 9% by weight in PCC, which could contribute to the carbon footprint when it breaks down. Additionally, SEM images displayed an unsymmetrical and sub-rounded microstructure of PCC particles. Based on these findings, the study suggests that utilizing PCC could improve the resistance of loess to saturation collapse and potentially reduce carbon emissions associated with cement or lime production while offering an opportunity to use PCC in soil application.

The major problematic soils in semi-arid regions include expansive soils and collapsible soils. These two types of soils cause problems and are hazardous for buildings when moisture is introduced following a dry or semi-dry season. In order to assess the risk and damage likely to occur, a protocol of investigation needs to be considered by geotechnical engineers to quantify and assess the possible heave or collapse that may occur. The characterization and prediction of unsaturated soil behavior in semi-arid areas can now be enabled following the advancement of unsaturated soil mechanics. Heave is associated with the wetting of expansive soils, while excessive settlement or the sudden loss of support may occur when water is introduced to collapsible soils. This work calls for more than one parameter for the assessment of problematic soils to avoid misleading predictions based on a single test. This study presents an investigation of two sets of soil samples obtained from semi-arid areas in Saudi Arabia known for their collapsible or expansive nature. Tests under controlled suction and variable effective stress were conducted. The air entry values, inflection points, and residual points were established and compared for the two problematic soils. A series of oedometer tests was conducted for typical soils, and settlement and collapse were measured and assessed. The swell potential for the tested clays varied from 4% to 22%. It is possible to integrate the data from the soil-water characteristic curve (SWCC) and compressibility tests with any project specification and applied stresses to produce reliable recommendations for the construction and protection of structures in hazardous soils.

A fully-automated unsaturated triaxial device is developed at the Advanced Soil Mechanic Laboratory of the Sharif University of Technology (SUT) to investigate the hydromechanical behavior of unsaturated soils under any complicated path. The main improvements of the developed device are (1) the ability to continuously measure accurately different stress/ strain variables during long duration of unsaturated tests. This is of great importance in capturing the sudden deformations of the specimen, under wetting (2) providing a user-friendly controller software enabling the definition of any desired stress/strain variable and stress/strain paths under either stress-controlled or strain-controlled conditions. Finally, to evaluate the performance of the developed apparatus, two wetting tests were carried out to study the effect of initial shear stress on the hydromechanical behavior of unsaturated reconstituted specimens of Gorgan loess. In these wetting tests, the specimens were wetted under isotropic and anisotropic stress states by stepwise reduction of suction to approach to the saturated condition. The obtained results showed the excellent performance of the developed device to accurately follow the defined stress path along with the continuous measurement of stress/strain variables. The tested collapsible soil specimen that was wetted under the effect of initial shear stress exhibited a larger volume decrease accompanied by a larger degree of saturation compared to those of the specimen wetted under the isotropic stress state with the same initial mean net stress.