To study the degree of strength parameter deterioration (DSPD) of Lushi swelling rock in the high slope area under wetting-drying cycles, 114 samples are remodeled. Wetting-drying cycle and triaxial tests are conducted to comprehensively analyze the influence of dry density, wetting-drying cycle path, and number of wetting-drying cycles on the strength deterioration characteristics of Lushi swelling rock. Using the fitting analysis and function superposition methods, the DSPD model of Lushi swelling rock under wetting-drying cycles is established, which considers the previous four influencing factors. The influence of the DSPD of Lushi swelling rock on the stability of high slopes under rainfall seepage and circulation conditions is studied. Lushi swelling rock exhibits significant strength deterioration characteristics under wetting-drying cycles. The overall DSPD for cohesion is higher than that of the internal friction angle. Under rainstorm conditions, strength deterioration leads to a shallower depth of the critical slip surface of the slope and a smaller safety factor. After eight rounds of rainfall seepage and circulation, the safety factor gradually decreases by approximately 14%-28%. This study provides and verifies the DSPD model of Lushi swelling rock under wetting-drying cycles, and the results could provide a basis for disaster prediction and the optimization design of swelling rock slopes.

Granite residual soils (GRS) are often encountered in geotechnical projects in the Guangdong-Hong Kong-Macao Greater Bay Area (briefly written as the Greater Bay Area, or abbreviated as GBA). The rea experiences frequent rainfall, leading to wetting-drying cycles that progressively diminish the shear strength of GRS. This weakening effect is not only significant but also accumulates, exhibiting a direct positive correlation with the number of cycles. Current studies on the soil strength attenuation due to wetting-drying cycles are typically limited to no more than 10 cycles, which is rather insufficient to uncover the long-term water-weakening behaviors and their accumulative impacts on GRS. To address this gap, typical GRS samples were first taken from the GBA and then prepared by making them go through a certain number of wetting-drying cycles (maximum of up to 100). Next, a total of 552 small- and large-scale direct shear tests were conducted to investigate the mechanisms of water-weakening effects on soil internal friction angle, cohesion, and shear strength. The degree of saturation and number of cycles were also examined to see their effects on the cumulation of water weakening. Based on results from the small-scale direct shear tests, a model was developed for assessing the weakening impact of water on soil strength. The accuracy of the model prediction was statistically evaluated. Last, the effectiveness and efficiency of the proposed model were demonstrated by validating against the results from the large-scale direct shear tests.

Improper anti-drainage treatment of weakly expansive soil subgrades can lead to significant post-construction deformation and uneven settlement, which severely affect the operational safety and service life of engineering projects. To comprehensively analyze the evolution of soil volume and strength under different hydraulic coupling paths during wetting-drying (W-D) cycles, a loaded W-D cycle testing device was developed. Soil volume was measured during the W-D cycles, and the shear strength and soil-water characteristic curves were analyzed after different cycles. The results indicate that during the W-D cycles, changes in soil volume and strength exhibited distinct stages with similar evolution characteristics. Under the investigated loading conditions, the soil demonstrated significant collapsibility during the wetting process, which gradually diminished as the number of cycles increased. Eventually, the W-D cycles caused the soil to reach an equilibrium state, where its swelling and shrinkage behavior became nearly elastic. At equilibrium state, there is a corresponding void ratio for any moisture content, which is the elastic void ratio (e0el). The e0el is irrespective of the number of cycles and initial dry density. Conversely, higher load and larger amplitude in W-D cycles tend to decrease the e0el. Furthermore, by correlating the unsaturated soil matric suction, secant modulus, and stress path, the volume evolution mechanism of the soil was analyzed based on the soil effective stress theory and pore evolution. The results of this study can serve as a crucial reference point for revealing the deformation mechanism of weakly expansive soil subgrades and selecting appropriate road settlement control methods.

The application of novel materials that enhance soil engineering properties while maintaining vegetation growth represents an innovative strategy for ecological protection engineering of expansive soil slopes. Laboratory tests, including wetting and drying cycle tests, direct shear tests, unconfined swelling ratio tests, and vegetation growth tests, were conducted to analyze the effects of xanthan gum on both engineering and vegetation-related properties of expansive soil. The feasibility of xanthan gum for soil improvement was systematically evaluated. The interaction mechanism between xanthan gum and expansive soil was elucidated through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Results demonstrated that xanthan gum effectively inhibited crack development and strength loss. With increasing xanthan gum content, the crack area ratio decreased logarithmically by up to 58.62%, while cohesion increased by 82.96%. The unconfined swelling ratio exhibited a linear reduction, with a maximum decrease of 43.58%. Notably, xanthan gum accelerated seed germination rate but did not significantly affect long-term vegetation growth. Mechanistically, xanthan gum improved soil properties via two pathways: (1) forming bridging structures between soil particles to enhance cohesion and tensile strength; (2) filling soil voids and generating a polymer film to inhibit water-clay mineral interactions, thereby reducing hydration membrane thickness. These findings offer both theoretical insights and practical guidelines for applying xanthan gum in ecological protection engineering of expansive soil slopes.

This study addresses the utility of polyelectrolytes, i.e., cationic poly(diallyldimethylammonium chloride) (PDADMAC) and anionic polystyrene sulfonate (PSS), as additives to improve properties of the polymer-stabilized soil. This paper specifically focuses on the resistance of polymer-stabilized soils to degradation and/or damage during and following multiple wetting-drying cycles (zero, one, two, three, five, and seven cycles). Each cycle consisted of 24 h of moisture conditioning using capillary rise followed by 24 h of drying. Then, these specimens were evaluated for their unconfined compressive strength (UCS). The microstructure and composition of the soils were investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray fluorescence analysis (XRF). Based on the results, the soils used in this study for polymer treatment were primarily composed of carbonates and silicates with a small amount of clay minerals. The polyelectrolyte stabilizers (PDADMAC and PSS) and polyelectrolyte complexes (PECs) were added to the soils at dosages ranging from 0.2% to 1.6% by weight of dry polymer to dry soil. Treated soils demonstrated increased UCS compared with untreated counterparts. The untreated soils exhibited rapid degradation of UCS and mechanical collapse within three to four wetting-drying cycles. On the other hand, the polymer-treated soils exhibited a strength reduction of between 10% and 50% following the first cycle and then maintained the UCS of about 3-6 MPa after completion of all wetting-drying cycles. Furthermore, the stabilized soil demonstrated significant improvement in toughness compared with their untreated and cement-treated counterparts. The ability of the polymer-stabilized soils to stand up to wetting-drying cycles is a key finding and contribution of this study.

The variation in soil moisture can lead to unfavourable deformation of highway embankments, threatening their long-term stability under seasonal groundwater level fluctuations and frequent changes in evaporation and precipitation. This paper conducted unsaturated soil triaxial tests to examine soil water retention and volumetric deformation behavior during wetting-drying cycles. The results show that soil water retention decreases with increasing wetting-drying cycles, particularly in the low suction range from 0 to 100 kPa, where gravimetric moisture content (GMC) declines sharply. With more wetting-drying cycles, the soil's capacity for volumetric deformation diminishes. The soil has a loose soil structure and is more prone to plastic deformation. Furthermore, three soil water retention models, the Gallipoli, Tarantino, and Hu models were employed to analyse soil's hydromechanical behaviours and evaluate the effect of wetting-drying cycles. It was found that Tarantino's model used only three fitting parameters, which were more concise and maintained a good fitting effect. This study clarifies soil-water retention and volumetric deformation behavior during wetting-drying cycles, which is essential for effective water control in subgrade construction and operation.

Electroosmotic drainage has been proposed as a method for reducing moisture content and simultaneously increasing shear strength, thereby enhancing the stability of soft clays. Understanding electroosmotic consolidated soil behavior under wet-dry cycles is vital for assessing long-term stability and performance in a changing environment. In this investigation, electroosmosis-treated soft clay specimens were prepared and subjected to different wetting-drying cycles. The experimental results emphasized that in the case of soft clay which has been treated under identical electroosmosis conditions and subsequently subjected to varying numbers of wetting-drying cycles, it was determined that with an increment in the number of wetting-drying cycles, the crack ratio exhibits an increasing trend. However, the extent of the crack ratio exerts a minimal and almost negligible effect on the average moisture content of the soil mass. Specifically, five wetting-drying cycles can induce a pronounced reduction in the coefficient of variation (COV) of the soil moisture content distribution. Moreover, it was observed that a relatively smaller crack ratio is associated with a relatively greater average shear strength. Simultaneously, the corresponding COV will be larger. Conversely, a larger crack ratio gives rise to a smaller average shear strength, and the corresponding COV will be smaller.

Red mudstone is highly sensitive to water content variations. Lime treatment is recommended when using red mudstone as subgrade fill material. The mechanical properties of lime-treated red mudstone fill material (LRMF) degrade due to wetting-drying (WD) cycles caused by seasonal environmental effects. A series of WD cycle tests, unconfined compression tests, and bender element tests were conducted to investigate the degradation of strength and small strain stiffness of LRMF. Combining with the successive water-dripping scanning electron microscope (SEM) tests, the microstructure disturbance of LRMF after WD cycles was examined. Swelling of specimens on both the wet and dry sides was observed during low-amplitude WD cycles. For high-amplitude WD cycles, swelling on the wet side was also observed. On the dry side, initial volume shrinkage was recorded, followed by swelling in successive cycles, even though the water content was significantly lower than the initial state. Swelling results in the degradation of strength and small strain stiffness. Volumetric shrinkage increased strength, but small strain stiffness was still reduced due to crack propagation. A unified model is proposed to identify the degradation of strength and volumetric strain, while the small strain stiffness for dry specimens under large-amplitude WD cycles is significantly below the degradation line. The degradation rate of small strain stiffness is significantly higher than that of strength. After water exposure, the LRMF generally retains its initial microstructure. However, loosened aggregates, slaking, and crack propagation are clearly seen in water-exposed specimens. Degradation of the mechanical properties of LRMF can be attributed to damage to the soil fabric.

Lignosulfonate (LS), an environmentally friendly and non-toxic material, has attracted attention as a non-traditional soil stabilizer. However, LS could be easily washed out from soil due to its high water-solubility, which leads to the consequent loss of strength. Therefore, an additional admixture is needed to overcome this limitation. In this study, polyethyleneimine (PEI) was mixed with LS to stabilize silica sand. The consequent improvements in the water-resistant and strength characteristics of LS-treated soil were investigated through the unconfined compressive strength (UCS) test, triaxial test, and cyclic wetting- drying tests. The results demonstrated that the UCS had an increasing trend with a rise in LS content. Moreover, the UCS was influenced by the drying out of the water from the specimen related to the LS concentration and the curing time: a higher concentration and a longer curing duration improve the UCS. According to the triaxial test, the deviatoric stress also increased with the LS content. In addition, both the soil's cohesion and secant elastic modulus were improved in a more ductile manner than typical cemented soil. In the cyclic wetting-drying test, no disintegration of the specimen was observed. Although the UCS of the treated soil in wet condition revealed a notable decrease, after re-dry for seven days in a controlled room, its strength recovered to about 86% of that in its initial dry condition.

In this paper, the EC-5 water sensor and the MPS-6 water potential sensor were used to measure water content and suction, respectively, to investigate the evolution of soil-water retention properties of compacted loess samples prepared at different dry densities and subjected to different numbers of wetting-drying cycles. The water retention data were integrated with a detailed microstructural investigation, including morphological analysis (by scanning electron microscopy) and pore size distribution determination (by nuclear magnetic resonance). The microstructural information obtained shed light on the double porosity nature of compacted loess, allowing the identification of the effects of compaction dry density and wetting-drying cycles at both intra- and inter-aggregate levels. The information obtained at the microstructural scale was used to provide a solid physical basis for the development of a simplified version of the water retention model presented in Della Vecchia et al. (Int J Numer Anal Meth Geomech 39: 702-723, 2015). The model, adapted for engineering application to compacted loess, requires only five parameters to capture the water retention properties of samples characterized by different compaction dry densities and subjected to different numbers of wetting-drying cycles. The comparison between numerical simulations and experimental results, both original and from the literature, shows that only one set of parameters is needed to reproduce the effects of dry density variation, while the variation of only one parameter allows the reproduction of the effects of wetting and drying cycles. With respect to the approaches presented in the literature, where ad hoc calibrations are often used to fit density and wetting-drying cycle effects, the model presented here shows a good compromise between simplicity and predictive capabilities, making it suitable for practical engineering applications.