Due to Paleo-clay's unique properties and widespread distribution throughout China, it is essential in geotechnical engineering. Rainfall frequently causes the deformation of Paleo-clay slopes, making slope instability prediction crucial for disaster prevention. This study explored Paleo-clay's strength degradation and slope stability under soaking and wet-dry cycles. Using Mohr-Coulomb failure envelopes from experiments, curve fitting was used to find the patterns of Paleo-clay strength degradation. Finite element simulations and the strength discounting method were used to analyze the stability and deformation of Paleo-clay slopes. The results indicate that wet-dry cycles impact them more than soaking. Paleo-clay's cohesion decreases exponentially as the number of wet-dry cycles and soaking times rise, but the internal friction angle changes very little. After 10 wet-dry cycles and 24 days of soaking, iron-bearing clay's cohesion decreased to 17% and 44% and reticular clay's to 32% and 48%. Based on the study area characteristics, three slope types were constructed. Their stability exhibited exponential decay. Under soaking, stability remained above 1.4; under wet-dry cycles, type I and II stability fell below 1.0, leading to deformation and failure. All types showed traction landslides with sliding zones transitioning from deep to shallow. Practical engineering should focus on the shallow failures of Paleo-clay slopes.

The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake; however, rare work has been devoted to this subject due to lack of attention. In this study, experimental investigations on shear strength weakening of discontinuities with different joint wall material (DDJM) under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province, China as research objects. A total of 99 pairs of similar material samples of DDJM (81 pairs) and discontinuities with identical joint wall material (DIJM) (18 pairs) were fabricated by inserting plates, engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field, into mold boxes. Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress, joint surface morphology, shear displacement amplitude and shear rate. The results indicate that the shear stress vs. shear displacement curves under each shear cycle and the peak shear strength vs. cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone, while closer to those of DIJMs with mudstone. The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6% to 55.9% for samples with varied surface morphology under different testing conditions. The normal stress, joint surface morphology, shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading, with the degree of influence being greater for larger normal stress, rougher surface morphology, larger shear displacement amplitude and faster shear rate. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting 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/).

River silt deposited by water in coastal areas is unsuitable for engineering construction. Thus, the in situ stabilization treatment of river silt as the bearing layer has been an important research area in geotechnical engineering. The strength degradation behavior and mechanism of stabilized river silt reinforced with cement and alginate fibers (AFCS) in different engineering environments are crucial for engineering applications. Therefore, freeze-thaw (F-T) cycle tests, wetting-drying (W-D) cycle tests, water immersion tests and seawater erosion tests were conducted to explore the strength attenuation of stabilized river silt reinforced with the same cement content (9% by wet weight) and different fiber contents (0%, 0.3%, 0.6% and 0.9% by weight of wet soil) and fiber lengths (3 mm, 6 mm and 9 mm). The reinforcement and damage mechanism of AFCS was analyzed by scanning electron microscopy (SEM) imaging. The results indicate that the strength of AFCS was improved from 84% to 180% at 15 F-T cycle tests, and the strength of AFCS was improved by 26% and 40% at 30 W-D cycles, which showed better stability and excellent characteristics owing to the hygroscopic characteristics of alginate fiber arousing the release of calcium and magnesium ions within the alginate. Also, the strength attenuation of AFCS was reduced with the increase in the length and content of alginate fibers. Further, the strength of specimens in the freshwater environment was higher than that in the seawater environment at the same fiber content, and the softening coefficient of AFCS in the freshwater environment was above 0.85, indicating that the AFCS had good water stability. The optimal fiber content was found to be 0.6% based on the unconfined compressive strength (UCS) reduction in specimens cured in seawater and a freshwater environment. And the strength of AFCS was improved by about 10% compared with that of cement-stabilized soil (CS) in a seawater environment. A stable spatial network structure inside the soil was formed, in which the reinforcing effect of fibers was affected by mechanical connection, friction and interfacial bonding. However, noticeable cracks developed in the immersed and F-T specimens. These microscopic characteristics contributed to decreased mechanical properties for AFCS. The results of this research provide a reference for the engineering application of AFCS.

To study the influence of climate and the environment on the stability of loess slopes in Yan'an, China, the macromechanical deterioration and changes in its internal structure were explored by simulating its behavior during drying, wetting, freezing and thawing under natural conditions. A triaxial apparatus was used to conduct multiple shear tests to obtain stress-strain relationships and shear strength parameters of the soil under different cycle modes, and the results were applied to analyze the macromechanical changes of the loess samples with increasing numbers of cycles. The results of the stress-strain curves and the trends of the shear strength parameters showed that when a sample experienced coupled dry-wet and freeze-thaw cycles, its shear strength was considerably lower than that under a single type of cycle. Additionally, dry-wet cycles had a stronger negative effect than freeze-thaw cycles on soil strength. Microscopic tests showed that the contact mode of particles tended to be unstable due to the effects of dry-wet and freeze-thaw cycles, resulting in the reduction of soil cementation. The results of this multiscale research provide a reference for future work on geological disaster prevention and engineering control in areas where loess is present.

Granite residual soil (GRS) exhibits favorable engineering properties in its natural state. However, a hot and rainy climate, combined with vibrations generated during mechanical construction, can cause a notable decrease in its strength. In this study, the evolution of stress-strain curves and strength parameters (cohesion c and internal friction angle phi), unconfined compression strength (UCS) under drying and wetting(DW) cycles and vibration were investigated by means of direct shear test and UCS test. Furthermore, modified formulas for calculating shear strength and UCS under DW cycles and vibration were proposed, and their accuracy was verified. The results are as follows: The stress-strain curve of shear strength exhibits strain-hardening characteristics, and the shear compressibility of the sample increases with the number of DW cycles and vibration time. However, the stress-strain curve of UCS shows strain-softening properties, and the peak strength shifts forward with the number of DW cycles and vibrations. With the increase in the number of DW cycles and the vibration time, c shows a non-linear degradation, with a maximum degradation of 58.6%. phi fluctuates and increases due to the densification effect of DW cycles, but the influence of vibration on phi decreases with the increase in the number of DW cycles. UCS rapidly decreases and gradually stabilizes after DW cycles and vibration, with a maximum degradation of 81.1%. This study can serve as a reference for the stability analysis of GRS pits subjected to long-term influences of hot and rainy climates and mechanical vibration, providing valuable insights for future research.

The strength deterioration of soil-rock mixtures (SRM) subjected to freeze-thaw (F-T) cycles leads to instability and failure of upper engineering structures in cold regions. However, the mutual feedback response mechanism pertaining to the changes of pore and strength in SRM under F-T cycles are rarely addressed. Nuclear magnetic resonance and triaxial tests were carried out to study the pore structure characteristics and strength response patterns of samples. A correlation model of SRM porosity and strength deterioration was first proposed under F-T cycles, and the model rationality was verified by test data. The results demonstrated that the pore connectivity and porosity increased throughout the F-T process, with the T2 spectral distribution curves exhibiting three peaks. Among these peaks, the main peaks underwent slight changes, while the secondary and micro peaks presented significant changes. Before 3 F-T cycles, the pore distribution evolved to small pores uniformly, followed with the large pores increasing and the micropores disappearing. With increasing of F-T times, the strength and cohesion of SRM experienced a drastic decline, while the internal friction angle demonstrated a slight decrease accompanied by fluctuations. Based on the analysis of test results, a correlation model regarding the porosity and strength deterioration was proposed through the relationship between the micro-structure evolution and the macro-mechanical response during F-T cycles. Furthermore, intrinsic mechanism of SRM strength deterioration under F-T cycles was revealed by considering the pore structure characteristics. The results can provide theoretical insights for the analysis of F-T disaster mechanism and prevention of SRM in cold regions.