This study investigates the strain-rate-dependent mechanical properties of unsaturated red clay under varying temperatures and matric suction conditions through triaxial shear tests on red clay fill materials from the Sichuan-Tibet Railway region. The tests were conducted with multiple shear strain rates, complemented by advanced microstructural analysis techniques such as mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM), to examine the evolution of pore structure. The results indicate that high matric suction significantly reduces the rate-dependency of strength in red clay fill materials, whereas temperature has a relatively smaller effect. As matric suction increases, the strain-rate parameter decreases across different temperatures, with a diminishing rate effect observed at higher suction levels. Compared to temperature, strain rate has a more pronounced influence on failure time. An increase in strain rate leads to a significant reduction in failure time. At low strain rates, failure time exhibits substantial variability, while at high strain rates, the effects of temperature and matric suction on failure time become less significant. Under high-temperature conditions, the strength of red clay is enhanced, and failure time is delayed. These findings provide critical theoretical support for controlling settlement deformation and predicting failure times of subgrade fill materials under complex climatic conditions, offering valuable insights for engineering applications.

A numerical model that accounts for fully coupled long-term large strain consolidation and heat transfer provides a more realistic analysis for various applications, including geothermal energy storage and extraction, buried power cables, waste disposal, groundwater tracers, and landfills. Despite its importance, existing models rarely simulate fully coupled large-strain long-term consolidation and heat transfer effectively. To address this research gap, this study presents a numerical model, called Consolidation and Heat Transfer (i.e., CHT), designed for one-dimensional (1D) coupled large-strain consolidation and heat transfer in layered soils, with the added capability to account for thermal creep. The model employs a piecewise-linear approach for the coupled long-term finite strain consolidation and heat transfer processes. The consolidation algorithm extends the functionality of the CS-EVP code by incorporating thermally induced strains. The heat transfer algorithm accounts for conduction, thermomechanical dispersion, and advection, assuming local thermal equilibrium between fluid and solid phases. Heat transfer is consistent with the spatial and temporal variation of void ratio and seepage velocity in the long-term consolidating layer. This paper details the development of the CHT model, presents verification checks against existing numerical solutions, and demonstrates its performance through several simulations. These simulations illustrate the effects of seepage velocity, thermal boundary conditions, and layered soil configurations on the coupled heat transfer and consolidation behavior of saturated compressible soils.

Grouting below the tunnel invert is commonly used to remediate the settlement. Case histories demonstrate that the tunnel settlement still develops after the grouting is completed, especially in structured clay. The principal mechanism behind this is the grouting-induced soil disturbance, including the generation of excess-pore-water pressure (EPWP), degradation in soil structure, and changes in compressibility. To date, the mechanism behind the grouting-induced soil disturbance and responses of the ground heave is not yet fully understood. Toward this end, laboratory tests on grouting in mud with different sand content are carried out. Earth pressure, pore water pressure, shear stiffness, undrained shear strength, and ground heave are measured and analyzed. The results indicate that grouting causes increases in the lateral earth pressure and significant EPWP in the surrounding soil. Changes in undrained shear strength and shear stiffness are closely related to the comprehensive effects of increases in stress level and shear disturbance. The increased stress level leads to the growth in stiffness and strength, while shear disturbance causes degradation. The soils right nearby the grouting zone are subjected to significant shear disturbance and also increases in stress level. As a result, the soil stiffness and strength exhibit negligible change. In comparison, the soils above and below the grouting zone mainly experience an increase in stiffness and strength, because shear disturbance is comparatively smaller than the influence of the increases in stress level. Furthermore, the development of the vertical displacement of the ground surface demonstrates two stages of initial uplift during grouting and then settlement after the grouting is completed. In addition, stronger soil structure corresponds to larger settlement after the grouting is completed.

Marine soft clays are known for their poor engineering properties, which, when subjected to prolonged static and dynamic loading, can lead to excessive settlement of offshore pile foundations and subsequent structural instability, resulting in frequent engineering failures. This study examines the bearing and deformation behavior of jacked piles in these clay deposits under both static and cyclic loading conditions using a custom-designed model testing apparatus. Emphasizing the time-dependent load-carrying capacity and accumulated cyclic settlement of piles, the research uses artificially structured clay to more accurately simulate stratum conditions than traditional severely disturbed natural clays. Model pile testing was carried out to analyze the effects of soil structure and cyclic loading patterns on the long-term response of jacked piles. Key factors investigated include initial soil structure, pile jacking-induced destruction, soil reconsolidation post-installation, disturbed clay's thixotropic effects, and cyclic loading's impact during service. Results show that increasing the cement content within the clays from 0 % to 4 % nearly doubled pile penetration resistance, led to a more significant accumulation of excess pore water pressure (EPWP), and accelerated its dissipation rate. Additionally, the ultimate load-carrying capacity of jacked piles also doubled. Higher cement content slowed pile head settlement rates and reduced stable cumulative settlement values, requiring more cycles to reach instability. Under high-amplitude, low-frequency cyclic loads, hysteresis loops of the model piles became more pronounced and rapid. This study enhances understanding of the long-term cyclic behavior of jacked piles in soft soils, providing valuable insights for designing offshore piles.

Sandy red clay, abundant in clay minerals, exhibits a marked sensitivity to variations in water content. Several of its properties are highly prone to deterioration due to wet-dry cycling, potentially leading to slope instability. To investigate the multi-scale deterioration patterns and the underlying chain mechanism of sandy red clay subjected to wet-dry cycles, this study conducted systematic tests on remolded sandy red clay specimens through 0 to 5 wet-dry cycles, with the number of cycles (N) as the variable. The study's results indicated the following, under wet-dry cycling: (1) Regarding the expansion and shrinking properties, the absolute expansion rate (delta a) progressively increased, whereas the absolute shrinkage rate (eta a) gradually decreased. Concurrently, the relative expansion rate (delta r) and relative shrinkage rate (eta r) gradually declined. (2) At the microscale, wet-dry cycles induced significant changes in the microstructure, characterized by increased particle rounding, disrupted stacked aggregates, altered inter-particle contacts, enlarged and interconnected pores, increased number of pores, and a reduction in clay mineral content. (3) At the mesoscale, cracks initiated and propagated. The evolution of cracks undergoes stages of initiation stage, propagation stage, and stable stage, and with the crack rate increasing to 2.0% after five cycles. (4) At the macroscale, the shear strength exhibited a continuous decline. After five cycles, cohesion decreased by as much as 49.6%, whereas the internal friction angle only decreased by 4.3%. This indicates that the loss of cohesion was the primary factor contributing to the strength deterioration. (5) A 19.4% decrease in the slope factor of safety (Fv) occurred after five cycles. This reduction was primarily attributed to the decrease in material cohesion and the upward shift in the potential sliding surface. Under the influence of wet-dry cycles, slope failures typically transitioned from overall or deep sliding to localized or shallow sliding.

Loess in Northwest China is widely deposited atop the Hipparion Red Clay. Unlike red clay stratigraphy, loess is mostly seasonally frozen, with physical properties that change easily at low temperatures, increasing the risk of natural disasters like slope instability and landslides. To study the low-temperature properties of loess and red clay strata, loess-red clay composite samples with varying water contents were subjected to freezing at different low temperatures. Their resistivity and P-wave velocity were measured postfreezing. The results indicate that as water content increases, soil resistivity decreases due to enhanced electrical conduction, with a slower rate of decline. When the temperature decreases, resistivity rises gradually in the unfrozen stage (25 degrees C to - 5 degrees C) and increases rapidly in the frozen stage (-10 degrees C to - 20 degrees C) as water transitions to solid ice. At low water contents, soil resistivity is more sensitive to temperature changes due to reduced liquid conductive pathways. P-wave velocity decreases almost linearly with increasing water content in unfrozen soils, but this trend reverses in frozen soils. With decreasing temperature, P-wave velocity shows minimal change in unfrozen soils but increases significantly after freezing, with greater sensitivity to temperature changes at higher water contents. This experiment provides valuable data support for engineering construction, soil frost heave risk assessment, and geophysical investigations in permafrost regions.

In the Niigata-ken Chuetsu-oki Earthquake of 2007, ground liquefaction was outstanding at the foot of a sand dune and in old river channels. Although no distinct disaster was found in the clayey ground after the earthquake, the long-term settlement of the ground was observed after the earthquake in the Shinbashi district of Kashiwazaki City. At one observation site, the cumulated ground subsidence of the layers from the ground surface to a depth of 23 m had reached 71 mm 14 years after the earthquake. In order to study the mechanism of the deformation during the earthquake and the long-term settlement after the earthquake, ground investigations, such as a boring survey at the observation site and indoor element tests on sampled soil, were conducted in this study. The results showed that the sampled soil was very soft, strongly compressible, and relatively highly structured. Subsequently, the transformation stress-cyclic mobility (TS-CM) constitutive model, developed by Zhang et al. (2007), was used to simulate the results of the indoor element tests, and the soil parameters were determined based on the results of these tests. The TS-CM model contains the concepts of subloading, described by Hashiguchi (1977), and superloading, described by Asaoka et al. (2002). Therefore, the subsidence behavior of the ground was simulated by a soil-water coupling elasto-plastic finite element (FE) analysis using the TS-CM constitutive model and the determined parameters. The FE simulation results agreed well with the actual site subsidence observation data. Based on the simulation results, the post- earthquake behavior of the soft clay and its mechanism were discussed, and the successive subsidence was predicted forward. According to the simulation results, the relatively highly structured susceptible clay at this site was found to have greater potential in terms of longterm consolidation than relatively less structured susceptible clay due to the large excess pore water pressure generation during the ground motion and the consolidation process after the earthquake. This conclusion was verified by consolidation tests on two types of clay. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Variations in excavation construction periods for fissured soil transportation engineering lead to differing unloading rates, which affect the soil's mechanical properties. This study utilizes a triaxial testing system to conduct monotonic and cyclic loading undrained shear tests on undisturbed fissured samples as well as remolded samples subjected to three distinct unloading rates. The K0 consolidated samples are regarded as soil mass that undergoes no unloading during testing. The findings indicated that the initial unloading rate influences the reloading shear mechanical properties of undisturbed and remolded specimens. The effects of unloading rates differ between undisturbed and remolded soil, a discrepancy attributed to inherent fissures. Specifically, undisturbed soil exhibits significant damage at low unloading rates due to fissures, while remolded soil experiences strength augmentation due to compaction with decreased unloading rates. Similarly, unloading will cause a loss of strength. Structural disparities result in the monotonic loading strength of undisturbed specimens being higher than that of remolded ones. In contrast, remolded specimens demonstrate greater dynamic strength under cyclic loading, likely because fissures deform, diminishing overall dynamic strength. Subsequent microscopic analysis, utilizing SEM images, along with a discussion of macroscopic inherent fissures, elucidated the impact of unloading rate on soil damage mechanisms, advancing the understanding of fissured soil behavior post- unloading. The study of mechanical properties of fissured soil following varying unloading rates is crucial for comprehending its damage mechanism and determining post-unloading soil strength parameters, providing valuable insights for practical applications in soil engineering.

There are a large number of microorganisms such as bacteria and fungi in the soil, which affect the physical and mechanical properties of the rock and soil. Microbial solidification technology is the use of microbial metabolism to induce mineral precipitation, thereby changing the soil structure and improving the physical and mechanical properties of the soil. This article uses microbial activated magnesium oxide solidification technology to treat red clay samples, and explores the effects of magnesium oxide content, bacterial solution concentration, and initial moisture content on the shear strength and disintegration of red clay. The experimental results are explained reasonably through scanning electron microscopy experiments and ImageJ quantitative analysis software. The experimental results show that the shear strength of red clay is positively correlated with the content of magnesium oxide and bacterial solution concentration, but negatively correlated with the initial moisture content; The hydrated magnesium carbonate generated in the experiment is the key reason for the improvement of shear strength. Hydrated magnesium carbonate can play a role in bonding red clay particles and filling the pores of red clay; Significant reduction in disintegration of microbial magnesium oxide solidified red clay.

In geotechnical engineering, the small-strain shear modulus and its attenuation characteristics are pivotal for analyzing and evaluating soil vibration responses to various engineering construction projects. This study conducts the resonant column test on undisturbed fissured clay samples, exploring the impacts of fissure inclination and confining pressure on the shear modulus in small-strain range. Results indicated that the shear modulus and its attenuation behavior in undisturbed fissured clay are substantially affected by both the fissure inclination angle and the confining pressure. With constant confining pressure, the shear modulus increases as the fissure inclination angle grows, reaching its maximum value at a fissure angle of 90 degrees. In addition, as the confining pressure rises, there is a notable increase in the shear modulus and a corresponding reduction in the decay rate. Through the threshold strain, the elastic deformation of the specimen increases as the fissure inclination angle increases, and the confining pressure increases the ability of the fissured soil to deform at small strains elastically. Based on the acquired data, this research analyzes the relationship between the fitting parameters A and N and the fissure angle in the context of the Harding-Drnevich formula. Consequently, a mathematical model based on the fissure inclination angle and the effective confining stress was established to predict the maximum dynamic shear modulus (Gmax) and decay attributes of undisturbed fissured clay. Additionally, the study offers a comparative analysis of the maximum shear modulus and its attenuation features in clay with varied degrees of fissure development. The stiffness anisotropy is related to the orientation of particles and the normalized decay rate of the fissured clay has a certain relationship with the fissure density.