Expansive soil due to wet expansion and dry contraction of engineering properties, resulting in the stability of the riffle slope, has been one of the key issues in the expansion of soil area earthworks; this paper, through the three representative riffle slope site field visits and indoor tests, respectively, from the dry bulk weight, unconfined compressive strength, three-way expansion force and expansion with the change rule of the depth of the law to be explored. The three-way expansion force test shows that the extension and proximity direction of the horizontal expansion force are the same. The vertical direction is greater than the horizontal direction, and its ratio is about 0.5. Further analysis of the relationship between the characteristics of the parameters with the depth can be seen: the surface soil indicators are more varied, between 0.5 and 1.0 m, the soil layer dry density is small, the expansion of the soil wet expansion and drying shrinkage is significant, and the unconfined compressive strength is close to or has reached the lowest value; expansion force and expansion volume test indicators along the depth of the graben slope, the expansion force and expansion volume test indicators are more varied. Expansion force and expansion amount test indexes change along the depth of the riffle slope but remain unchanged after 2.0 m. Therefore, the damage of the expansion soil riffle slope mainly occurs in the soil layer near the depth of 1.0 m, which is manifested explicitly as a failure to adapt to the change of stress in the soil and the inability to adjust to the atmospheric natural camping force.

This study investigates the vulnerability of expansive soil slopes to destabilization and damage, particularly under intense rainfall, due to their heightened sensitivity to moisture. Focusing on a project in Yunnan Province, numerical simulation software is employed to address slope stability challenges. Meanwhile, the soil mechanical parameters of this study were acquired through experimentation. The analysis considers six conditions: unsupported, conventional anchor and stabilizing pile reinforcement, and NPR (Negative Poisson's ratio) anchor and stabilizing pile reinforcement, evaluated under both normal and rainstorm conditions. The research outcomes reveal noteworthy insights: (1) The efficacy of NPR anchors in mitigating deformation in expansive soil landslides is investigated, broadening their application potential, particularly in restricting maximum slope displacement compared to conventional anchors. (2) No significant difference in safety factors for slope stability is observed between NPR and conventional anchors. Under rainstorm conditions, safety factors are 1.39 and 1.32 for NPR and conventional anchor and stabilizing pile support, respectively, while under normal conditions, they are 1.42 and 1.39. (3) The NPR anchor, in contrast to the conventional anchor, ensures a more uniform force distribution across the stabilizing pile. (4) While combined support structures contribute to slope stabilization, NPR anchors surpass conventional anchors in limiting slope displacement.

To explore an effective method for deformation monitoring and behavior prediction of expansive soil slope, field tests are conducted for a flexible slope protection scheme with soilbags that has been implemented in an expansive highway soil slope. A new monitoring system, i.e., the universal Beidou deformation monitoring system, is developed to overcome the limitations of traditional Global Navigation Satellite System (GNSS) software and hardware, simplify the hardware structure and realize the power sharing mode; furthermore, this system can create and upload a large amount of monitored data to a cloud platform to enable real-time calculation. Compared with traditional GNSS, the volume of equipment required is reduced by approximately 75%, and the cost is reduced by approximately 80%. Secondly, a multilevel safety early-warning evaluation system is constructed by integrating the monitoring results of the universal Beidou deformation monitoring system, bag damage states, rainfall conditions, and slope fissure development; additionally, a deformation early-warning mechanism of flexible support of soilbags was established. Finally, the deformation and collapse of flexible supports of soilbags can be successfully predicted in the field. This research on flexible support of soilbags provides new ideas and methods of deformation monitoring, safety evaluation, and early warning for expansive soil slopes.

Slope stability analysis is a classical mechanical problem in geotechnical engineering and engineering geology. It is of great significance to study the stability evolution of expansive soil slopes for engineering construction in expansive soil areas. Most of the existing studies evaluate the slope stability by analyzing the limit equilibrium state of the slope, and the analysis method for the stability evolution considering the damage softening of the shear zone is lacking. In this study, the large deformation shear mechanical behavior of expansive soil was investigated by ring shear test. The damage softening characteristic of expansive soil in the shear zone was analyzed, and a shear damage model reflecting the damage softening behavior of expansive soil was derived based on the damage theory. Finally, by skillfully combining the vector sum method and the shear damage model, an analysis method for the stability evolution of the expansive soil slope considering the shear zone damage softening was proposed. The results show that the shear zone subjected to large displacement shear deformation exhibits an obvious damage softening phenomenon. The damage variable equation based on the logistic function can be well used to describe the shear damage characteristics of expansive soil, and the proposed shear damage model is in good agreement with the ring shear test results. The vector sum method considering the damage softening behavior of the shear zone can be well applied to analyze the stability evolution characteristics of the expansive soil slope. The stability factor of the expansive soil slope decreases with the increase of shear displacement, showing an obvious progressive failure behavior. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.

An expansive soil in 4970 special railway line in Dangyang City, China, has encountered a series of landslides due to the expansion characteristics of expansive soil over the past 50 years. Thereafter, a sheet- pile retaining structure was adopted to fortify the expansive soil slope after a comprehensive discussion. In order to evaluate the efficacy of engineering measure of sheet- pile retaining structure, the field test was carried out to investigate the lateral pressure and pile bending moment subjected to construction and service conditions, and the local daily rainfall was also recorded. It took more than 500 days to carry out the field investigation, and the general change laws of lateral pressure and pile bending moment versus local daily rainfall were obtained. The results show that the effect of rainfall on the moisture content of backfill behind the wall decreases with depth. The performance of sheet- pile retaining structure is sensitive to the intensity of rainfall. The arching effect is reduced significantly by employing a series of sheet behind piles. The lateral pressure behind the sheet exhibits a single- peak distribution. The turning point of the horizontal swelling pressure distribution is correlated with the self- weight pressure distribution of soil and the variation of soil moisture content. The measured pile bending moment is approximately 44% of the ultimate pile capacity, which indicates that the sheet- pile retaining structure is in a stable service condition with enough safety reserve.

This study examines the evolution of instability in induced expansive soil slopes under varying rainfall intensities. The destabilization evolution of expansive soil slopes and their stability under three different rainfall intensities were revealed through indoor modelling and numerical simulation. The findings indicate that slopes are not destabilized by short duration and low rainfall intensity alone. Slope failure under strong rainfall intensity follows a three-stage evolutionary process. As rainfall intensity increases, the slope's water content, soil pressure, and pore water pressure increase. However, the stress at each monitoring point of the slope affected by rainfall follows a different pattern. Under low rainfall intensity, the water content of the slope surface is higher than that of the slope foot. Under strong rainfall conditions, the water content of the slope foot is higher than that of the slope surface. Therefore, it is important to implement seepage prevention measures on the slope surface and drainage measures on the slope foot to ensure slope stability. Rainfall affects the soil pressure at each monitoring point of the slope, causing unloading on the slope surface and fluctuation at the foot of the slope. This phenomenon becomes more pronounced with increasing rainfall intensity. Numerical simulation confirms that the overall horizontal displacement distance of the slope increases with rainfall intensity, but the horizontal displacement range becomes shallower. The slope's maximum horizontal displacement occurs at its foot, with values of 0.29 m and 0.34 m under moderate and heavy rainfall, respectively, representing a growth rate of 17 %. Settlement of the slope under different rainfall intensities was greatest at the top of the slope area. The lateral stresses generated by the settlement resulted in soil uplift at the leading edge of the slope.

This study was conducted to explore the use of non-expansive soil as protective cover for expansive soil slopes. Laboratory model experiments were carried out on expansive soil systems with varying thickness of non-expansive soil cover. The models were subjected to three wet-dry cycles. Variation in soil moisture content was monitored using moisture probes. Surface and internal cracking of soil was observed using cameras. Variation of infiltration rate of the cover with wet-dry cycles was measured in-situ. Results of the study show correlation between cover thickness and evaporation rate and crack formation in the expansive soil. Crack size, quantity, depth, and interconnectivity in the expansive soil increased with decreasing cover thickness. Even the thinnest cover significantly reduced the the number and depth of cracks. The infiltration rate of the cover remained unchanged after three cycles wet-dry cycles. The final water content, after the third drying, in the expansive soil increased with increasing cover thickness.

Rainfall infiltration softens the filling material of deep cracks in expansive soil, significantly reducing its mechanical strength and causing slope instability and failure. Investigating this influence is crucial for preventing slope disasters. This study established a model with a weak interlayer to conduct rainfall infiltration tests on an expansive soil slope. Analyzing the moisture absorption and deformation model test results, the study delved into the temporal and spatial variations of the slope's seepage field. It also clarified the evolution characteristics and action modes of the strain field under seepage influence. Results indicate that runoff leads to pooling at the slope foot, causing significant softening and swelling. The seepage and deformation fields exhibit a start-rapid growth-slow growth-tend to stability pattern on the time curve. Soil affected by rainfall infiltration is concentrated at depths of 10-20 cm. The start-up stage of deep soil displacement change is primarily due to water infiltration delay, intensifying with depth. The weak interlayer weakens and is destroyed after moisture absorption, resulting in the upper slope losing support force, leading to continued collapse and slope failure. The research provides a systematic understanding of the mechanism and failure mode of slope disasters, verifying and analyzing permeability, swelling, shrinking, and seepage characteristics of expansive soil.

There is a complex multifactorial coupling effect among the damages of various protection structures on slopes. Existing research focused on the health assessment of individual structures is often insufficient in representing the overall health status of the protection engineering system. Considering the characteristics of expansive soil slope protection engineering, this study proposes a health diagnosis method using combined weights and binary K-means clustering algorithm. The method quantifies the damage data of protection structures based on subjective and objective weights, and clusters the data by combining the binary K-means method and target vector layer to obtain the diagnosis results. Furthermore, an XGBoost-based surrogate diagnosis model is constructed to omit the repetitive modelling process in practical applications to achieve dynamic diagnosis. The proposed method is validated to an expansive soil slope in Gaochun district, Nanjing. The results show that the proposed method can accurately evaluate protection engineering with different degrees of damage; the surrogate model follows the same weight assignment process as the diagnostic method to establish reliable prediction. Based on the proposed method, damage coupling effects between individual protection structures are captured, and targeted maintenance and repair can be implemented. The proposed method can be further extended to other slope engineering.