The existence of rock weathering products has an important effect on the infiltration of water in the soil. Understanding the mechanism of water infiltration in a mixed soil and weathered rock debris medium is highly important for soil science and hydrology. The purpose of this study is to explore the effects of mudstone hydrolysis on water infiltration in the soil under different mixing ratios (0-70 %) of weathered mudstone contents. Soil column experiments and numerical modelling were used to study the processes of hydrolysis of weathered mudstone and water infiltration in the mixed medium. The results revealed that water immersion can cause the dense mudstone surface to fall off, thus forming pores, and that the amount of these pores first increase but then decrease over time. The disintegration of post-hydrolysis mudstone debris occurs mainly among particles ranging from 2-2000 mu m, predominantly transforming sand particles into finer fractions. Increasing the mudstone content in the soil from 0 % to 50 % enhances the infiltration rate and cumulative infiltration volume. However, when the mudstone content exceeds 50 %, these parameters decrease. The mudstone weathering products promote water infiltration in the soil within a certain range of mudstone contents, but as the ratio of weathered products increases, excessive amounts of mudstone hinder the movement of water in the soil. The identified transformation phenomenon suggests that the infiltration capacity of mixed soil will not scale linearly with mudstone content. The findings enable some mitigation strategies of geologic hazards based on the hydrological stability in heterogeneous environments.

Red-bed mudstone from civil excavation is often treated as waste due to its poor water stability and tendency to disintegrate. This study proposes a sustainable approach for its utilization in controlled low-strength material (CLSM) by blending it with cement and water. Laboratory tests evaluated the fresh properties (i.e., flowability, bleeding rate, setting time, and subsidence rate) and hardened properties (i.e., compressive strength, drying shrinkage, and wet-dry durability) of the CLSM. The analysis focused on two main parameters: cement-to-soil ratio (C/S) and water-to-solid ratio (W/S). The results show that increasing W/S significantly improves flowability, while increasing C/S also contributes positively. Flowability decreased exponentially over time, with an approximately 30% loss recorded after 3 h. Bleeding and subsidence rates rose sharply with higher W/S but were only marginally affected by C/S. To meet performance requirements, W/S should be kept below 52%. In addition, the setting times remained within 24 h for all mixtures tested. Compressive strength showed a negative correlation with W/S and a positive correlation with C/S. When C/S ranged from 8% to 16% and W/S from 44% to 56%, the compressive strengths ranged from 0.3 MPa to 1.22 MPa, meeting typical backfilling needs. Drying shrinkage was correlated positively with water loss, and it decreased with greater C/S. Notably, cement's addition significantly enhanced water stability. At a C/S of 12%, the specimens remained intact after 13 wet-dry cycles, retaining over 80% of their initial strength. Based on these findings, predictive models for strength and flowability were developed, and a mix design procedure was proposed. This resulted in two optimized proportions suitable for confined backfilling. This study provides a scientific basis for the resource-oriented reuse of red-bed mudstone in civil engineering projects.

Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir (TGR) region in China. The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer, which may cause slope instability during rainfall. In order to understand the strength behavior of Jurassic silty mudstone shear zone, the so-called Shizibao landslide located in Guojiaba Town, Zigui County, Three Gorges Reservoir (TGR) in China is selected as a case study. The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress. Therefore, a series of drained ring shear tests were carried out by varying the water contents (7%, 12%, 17%, and 20%, respectively) and normal stresses (200, 300, 400, and 500 kPa, respectively). The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress. The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit, above which the cohesion decreased. In contrast, the residual cohesion showed the opposite trend, indicating the cohesion recovery above a certain limit of water content. However, both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content. Furthermore, the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content, while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree. The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone. Finally, the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope; however, continuous rainfall is the main factor triggering sliding.

The time-dependent deformation behavior of silty mudstone brings pronounced difficulties for the construction and maintenance of slope engineering, which has attracted much attention. This study examines the creep characteristics of silty mudstone through multistaged loading tests and studies the creep-induced microstructural evolution using Scanning Electron Microscopy (SEM). To mitigate the variability caused by natural defects in the rock, similar material specimens were prepared to substitute silty mudstone for experiments. The results demonstrate that creep strain escalates stepwise with stress level, with the magnitude of each increment being contingent upon the applied confining pressure (sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}). The strain rate undergoes three phases including attenuation, stabilization, and acceleration. Cumulative strain correlates positively with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}, while the initial creep rate declines before slightly increasing. Creep failure predominantly manifests in a shear pattern, with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} controlling the development of fractures in terms of their length, number, and angle. SEM analysis reveals that increased sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} facilitates the expansion of transgranular cracks, displaying a coupled ductile-brittle fracture mode. Furthermore, sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} variably affects the micropore morphology (pore size, area, roughness, and regularity), with the differences in pore structures under various sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} being distinguished by the fractal dimension. Also, the fractal dimension is positively correlated with porosity, which can be quantitatively characterized using a nonlinear logarithmic function. The interaction between particles and cement, coupled with the development of cracks and pores, is identified as the primary mechanism of structural failure during the creep process.

Understanding the reactivation causes of ancient landslides is imperative for the prevention of landslides. However, the reasons for the reactivation of thick loess-mudstone ancient landslides and evolutionary mechanisms are unclear. This paper investigates the Gaojiawan thick loess-mudstone ancient landslide as an example using field investigation, InSAR time series analysis, and laboratory testing methods to analyze the reactivation deformation characteristics and reactivation causes of the thick loess mudstone ancient landslides, which were and verified by numerical simulation. The results show that fault fracture zones and groundwater primarily control the reactivation of Gaojiawan's thick loess-mudstone ancient landslide. Due to the fragmentation of rock mass and the development of structural planes in the fault fracture zones, as well as the excavation and unloading zone formed by the surrounding rock of the tunnel, it is beneficial to the enrichment of groundwater. It intensifies the interaction of groundwater-rock-fault fracture zones, especially for the red mudstone with more clay mineral content. The strength degradation is significant after encountering water, resulting in an imbalance in the stress state in deep strata and the reactivation of the landslide.

Predisintegrated carbonaceous mudstone (PCM) that exhibits low strength and continuous disintegration is prone to wetting deformation after repeated seasonal rainfall. A reasonable assessment of wetting deformation is required to facilitate the settlement control of the PCM embankment when exposed to repeated rainfall. Herein, to reveal the wetting deformation mechanism of the PCM subjected to drying-wetting cycles, the effects of drying-wetting cycles on the wetting deformation characteristics of the PCM are investigated using the double-line method. Microscopic pore characteristics of the PCM under different drying-wetting cycles were analyzed through scanning electron microscope (SEM) micrographs. Comparative analysis of the wetting deformation data between the tests and the constitutive model considering the damage of drying-wetting cycles was carried out. The results showed that the deviator stress-strain relationship curves of the PCM exhibit the strain hardening without obvious peak and no strain softening phenomena. The critical wetting strain of the PCM was positively correlated with the number of drying-wetting cycles, while the critical deviator stress decreased with an increase in the number of drying-wetting cycles. As the number of cycles increased, the gelling material between the particles dissolved, the volume of pores inside the PCM increased, and the number of pores inside the PCM decreased. The porosity of PCM had a significant quadratic function with the number of drying-wetting cycles. A wetting deformation damage model was developed to calculate the wetting deformation of the PCM by considering the effects of drying-wetting cycles, which can be useful for evaluating rainfall-induced settlements of relevant engineering structures made from PCM.

Mudstone is a common rock in underground engineering, and mudstone with fractures, have the certain self-closing capability. In this paper, we employed experiments and numerical analyses to investigate the mechanism of such a characteristic, and also examined the permeability pattern of mudstone overburdens. The experiments were performed with the MTS815.02 testing system, involving material properties under different water contents and their crack-closing behaviors. The principal task of numerical analysis is to determine the permeability of fractured mudstone layers, working with the COMSOL platform. The experimental results show that the Young's Modulus of water-saturated mudstone is just 2.2% of that of natural mudstone, and the saturated also exhibit a remarkably obvious creep behavior. As the surrounding pressures increase, the permeability coefficient of fractured mudstone decrease exponentially, even dropping by two orders of magnitude corresponding to over 2.0MPa pressures. Based on these experiment outcomes, we can easily infer that rapid or complete fracture-closing is the main reason of permeability drop, and furthermore, both softening and creep are the major factors of self-closure of mudstone fractures, and especially, the softening behavior plays an absolutely fundamental role. The numerical analyses show that either a higher in-situ stress or lower fracture density can obviously become one of the advantageous conditions for fractured mudstone layers to restore towards impermeability. These results are also verified by the engineering observation in Yili No. 4 mine of China. There obviously existed the recovery of water-blocking capacity of overlying strata after a period of time. We hereby recommend this investigation as refences for underground mining or engineering construction involving mudstone.

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.

In the waterway construction projects of the upper reaches of the Yangtze River, crushed mudstone particles are widely used to backfill the foundations of rock-socketed concrete-filled steel tube (RSCFST) piles, a structure widely adopted in port constructions. In these projects, the steel-mudstone interfaces experience complex loading conditions, and the surface profile tends to vary within certain ranges during construction and operation. The changes in boundary conditions and material profile significantly impact the bearing performance of these piles when subjected to cyclic loads, such as ship impacts, water level fluctuations, and wave-induced loads. Therefore, it is necessary to investigate the shear characteristics of the RSCFST pile-soil interface under cyclic vertical loading, particularly in relation to varying deformation levels in the steel casing's outer profile. In this study, a series of cyclic direct shear tests are carried out to investigate the influential mechanisms of roughness on the cyclic behavior of RSCFST pile-soil interfaces. The impacts of roughness on shear stress, shear stiffness, damping ratio, normal stress, and particle breakage ratio are discussed separately and can be summarized as follows: (1) During the initial phase of cyclic shearing, increased roughness correlates with higher interfacial shear strength and anisotropy, but also exacerbates interfacial particle breakage. Consequently, the sample undergoes more significant shear contraction, leading to reduced interfacial shear strength and anisotropy in the later stages. (2) The damping ratio of the rough interface exhibits an initial increase followed by a decrease, while the smooth interface demonstrates the exact opposite trend. The variation in damping ratio characteristics corresponds to the transition from soil-structure to soil-soil interfacial shearing. (3) Shear contraction is more pronounced in rough interface samples compared to the smooth interface, indicating that particle breakage has a greater impact on soil shear contraction compared to densification.

Small strain properties of subgrade fill material are essentially required for the accurate estimation of deformation behavior of railway subgrade. Many attentions have received on small strain properties of soils under the isotropic stress state or low shear stress level. The high level of shear stress and stress ratio induce reduction in small strain stiffness and thus present the potential challenge to the deformation stability of the subgrade. However, there is not much attempt to investigate the small strain properties under high stress ratio. This paper explores the effects of stress path and stress state on small strain stiffness Gmax and Poisson's ratio v of heavily compacted fully weathered red mudstone (FWRM) under a broad range of stress ratio, via a series of stress-controlled triaxial and bender element tests. Three stress paths, named as constant stress ratio (SSP), constant confined pressure (VSP), constant axial stress (HSP) with stress ratio up to 33.0 were considered. Low level of shear stress slightly promotes Gmax, while a significant reduction of Gmax is triggered as the stress ratio exceeds a critical value. A unified correlation between the critical stress ratio and confined pressure is developed. The evolution of Poisson's ratio is also described by a unified three-dimensional feature surface, which influence of stress path is identified by the location and shape of the surface.