The solidification of dredged marine sediments with high water content is important for maintenance dredging and reclamations. To reduce the carbon emission of solidification, low-carbon recycled wastes such as incinerated sewage sludge ash (ISSA) and ground granulated blastfurnace slag (GGBS) have been recently adopted as binding materials to replace conventional Portland cement. For soil slurry with ultra-high water content, using the consolidationsolidification combined method is an effective way to reduce the volume and improve the final mechanical properties. However, it is unclear how the consolidation interacts with solidification using the binding materials. In this study, a series of laboratory tests were conducted on dredged Hong Kong marine deposit slurry mixed with ISSA and GGBS with alkali activation by lime. The elemental consolidation tests controlled with different constant rates of strain and multistage loadings demonstrate that the rate of consolidation has significant effects on volume reduction and yielding stress development during consolidation-solidification treatment. Consolidationsolidification achieves higher volume reduction and yielding stress than pure solidification. As the rate of consolidation decreases, there is a smaller volume reduction at the same effective stress and less yielding stress enhancement at the same curing time. A scanning electron microscope with energy dispersive spectrometer was used to investigate hydration products and soil fabric after treatment. The slower rate of consolidation causes the looser structure and finer needleshaped products with the same curing period, which can explain the mechanical properties observed from the element tests.

Landslides commonly evolve from slow, progressive movements to sudden catastrophic failures, with saturation and displacement rates playing significant roles in this transition. In this paper, we investigate the influence of saturation, displacement rate, and normal stress on the residual shear strength and creep behaviour of shear-zone soils from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Results reveal a critical transition from rate-strengthening to rate-weakening behaviour with increasing displacement rates, significantly influenced by the degree of saturation. This transition governs the observed patterns of slow movement punctuated by periods of accelerated creep, highlighting the potential for exceeding critical displacement rates to trigger catastrophic failure. Furthermore, partially saturated soils exhibited higher residual strength and greater resistance to creep failure compared to nearly and fully saturated soils, underscoring the contribution of matric suction to shear strength.

Studying the rheological properties of deep-sea shallow sediments can provide basic mechanical characteristics for designing deep-sea mining vehicles driving on the soft seabed, providing anchoring stability of semi-submersible mining platforms, and assessing submarine landslide hazards. Shallow sediment column samples from the Western Pacific mining area were obtained, and their rheological properties were studied. A series of rheological tests was conducted under different conditions using an RST rheometer. In addition, conventional physical property, mineral composition, and microstructure analyses were conducted. The results showed that shallow sediments have a high liquid limit and plasticity, with flocculent and honeycomb-like flaky structures as the main microstructure types. The rheological properties exhibited typical non-Newtonian fluid characteristics with yield stress and shear-thinning phenomena during the shearing process. In contrast to previous studies on deep-sea soft soil sediments, a remarkable long-range shear-softening stage, called the thixotropic fluid stage, was discovered in the overall rheological curve. A four-stage model is proposed for the transition mechanism of deep-sea shallow sediments from the solid to liquid-solid, solid-liquid transition, thixotropic fluid, and stable fluid stages. The mechanism of the newly added thixotropic fluid stage was quantitatively analyzed using a modified Cross rheological model, and this stage was inferred from the perspective of mineralogy and microstructure. The results of this study can be useful for improving the operational safety and work efficiency of submarine operation equipment for deep-sea mining in the Western Pacific Ocean. (c) 2025 Japanese Geotechnical Society. Published 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/).

Stress-strain results from high-strain rate consolidated-undrained (CU) triaxial compression tests on partially saturated kaolin clay are presented. The work addresses the scarcity of high-strain rate data for cohesive soils and provides updated strain rate coefficients for kaolin clay. It covers strain rates from quasi-static (0.01%/s) to dynamic (800%/s) regimes. Kaolin clay specimens were prepared wet of optimum using static compaction at a constant water content of 32 +/- 1% and a degree of saturation of 96 +/- 2%. The specimens were then loaded into triaxial cells and consolidated under pressures ranging from 70 to 550 kPa for 24 h prior to testing. Tests were conducted using a modified hydraulic frame, and a methodology for correcting compression data to account for inertial effects observed during high-rate testing was adopted. The data revealed significant strengthening of clays with increased strain rates, especially at low confining pressures. Lightly confined clays (sigma 3 = 70 kPa) experienced a 165% strength increase, while highly confined clays (sigma 3 = 550 kPa) showed a 52% increase. Analysis using secant moduli revealed increased stiffening with loading rate. Posttest examination of specimens revealed a decrease of shear localization with increasing strain rate, indicating that a transition in failure mode contributes to the increased strengthening and stiffening of clays at high rates. The stress-strain data were used to calibrate the semilogarithmic and power law strain hardening models, yielding lambda and beta values that decreased linearly with increasing confining pressure. Equations relating lambda and beta to confining pressure were developed for practical applications, applicable to normally consolidated clays under confining pressures up to approximately 5 atmospheres.

Accurate characterization of soil dynamic response is paramount for geotechnical and protective engineering. However, the impact properties of unsaturated cohesive soil have not been well characterized due to lack of sufficient research. For this purpose, impact tests using the Split Hopkinson Pressure Bar (SHPB) were elaborately designed to investigate the dynamic stress-strain response of unsaturated clay with strain rates of 204 similar to 590 s(-1). As the strain rate increased up to 500 s(-1), a lock-up behavior was observed in the plastic flow stage, which can be explained as the breakage and rearrangement of soil gains under a high level of stress. Further, the strain rate dependency of the dynamic strength was quantitatively characterized by the Cowper Symonds (CS) model and the CS coefficients were determined to be the intercept of 55 and slope of 0.8 in the double logarithmic scale of Dynamic Increase Factor (DIF) and strain rate space. Furthermore, the SHPB test was reproduced using a modified Material Particle Method (MPM), which involves an improved dynamic constitutive model for unsaturated soil considering the strain rate effect. The simulated stress-strain curves basically agree with the experimental results, indicating the feasibility of MPM for investigating the dynamic properties of unsaturated soil under SHPB impact loading.

Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation. Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production. In this study, using the well-known notched semi-circular bend (NSCB) sample and the novel double-edge notched flattened Brazilian disc (DNFBD) sample combined with a split Hopkinson pressure bar (SHPB), various dynamic anisotropic fracture properties of Lushan shale, including failure characteristics, fracture toughness, energy dissipation and crack propagation velocity, are comprehensively compared and discussed under mode I and mode II fracture scenarios. First, using a newly modified fracture criterion considering the strength anisotropy of shale, the DNFBD specimen is predicted to be a robust method for true mode II fracture of anisotropic shale rocks. Our experimental results show that the dynamic mode II fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode I fracture. The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation, while the maximal ones occur in the Divider orientation. In addition, it is interesting to find that the mode II fracture toughness anisotropy index decreases more slowly than that in the mode I fracture scenario. These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published 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/).

The conventional similarity theory derived from dimensional analysis struggles with the well-known issue of non-scalability of material strain-rate effects between scaled models and prototypes. This limitation has significantly hindered the application of scaled model tests, particularly small-scale centrifugal model tests, in the study of structures against blast loading. To overcome this challenge, this study proposes a rate-dependent similarity theory for scaling the dynamic tensile responses and failure of large-scale underground concrete silos (46 m in height) subjected to large-yield soil explosions. The proposed theory includes a correction method derived from a verified dimensionless number, Dcs, which accurately reflects the overall bending-induced tensile response and failure mechanism of concrete silos. The correction strategy involves maintaining an equal Dcs between the scaled model and the prototype by adjusting the explosive weight and the concrete's static tensile strength in the scaled model to account for differences in strain-rate effects. To verify the theory, a series of geometrically similar silo models with scaling factors beta = 1, 1/2, 1/5, 1/10, 1/20, 1/50, and 1/100 were designed. High-fidelity numerical simulations were performed using a fully coupled numerical model encompassing the explosive-soil-silo system. The results demonstrate that, with the conventional dimensional analysisbased similarity theory, the tensile damage and failure of the scaled silo models differ significantly from those of the prototype. However, with the proposed rate-dependent similarity theory, the failure patterns of the silo models with beta = 1 similar to 1/100 are almost identical, indicating that the proposed theory can effectively address the troublesome issue of dissimilar material strain-rate effects between scaled models and prototypes. This similarity theory offers a solid theoretical foundation for designing scaled models that accurately reflect prototype behavior, thereby advancing the application of scaled model tests in the study of structures against blast loading.

This study investigates the geotechnical properties of soft Pak Phanang marine clay, prevalent in Nakhon Si Thammarat province, Thailand, where rapid economic development demands a comprehensive understanding for sustainable construction. Triaxial tests on undisturbed marine clay specimens with various stress histories and strain rates were conducted, focusing on over-consolidation ratios (OCRs) of 1, 2, 4, and 8. Shearing was performed at rates of 0.020%, 0.075%, 1.000%, and 8.500% per minute after K0 consolidation. The strain rates selected for this study represent specific values that have been chosen for a comprehensive exploration of Pak Phanang clay behavior under different loading conditions. The effects of stress histories on the marine clay behavior at various strain rates under K0 conditions were investigated. It is indicated that the greater strain rates under K0 conditions potentially lead to the larger undrained shear strengths and reduce pore water pressure for varied over-consolidation ratios. On the other hand, the greater over-consolidation ratios commonly result in lower shear strengths at all strain rates. Examination of pore pressure parameter at failure (Af\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${A}_{f}$$\end{document}) and secant Young's modulus reveals significant strain-rate-dependent behavior and OCR influence on the marine clay's response. Undrained shear strength increases with higher OCRs, emphasizing OCR's pivotal role. Rate effect analysis confirms undrained behavior, with a consistent 28% strength increase, regardless of OCR variations. Pore pressure responses exhibit a transition at OCR 4. Secant Young's modulus decreases with rising OCR, establishing a linear correlation with undrained shear strength.

Stiff clay exists widely in the world, but its significant time- and temperature-dependent mechanical features have not been fully modeled. In the context of fractional consistency viscoplasticity and bounding/subloading surface theory, this study proposes a novel nonisothermal fractional order two-surface viscoplastic model for stiff clays. First, by proposing a generalized plastic strain rate, the isotach viscosity is modified and extended to both over-consolidated and nonisothermal conditions that take into consideration the effects of temperature and OCR on thermal accelerated creep. Then, two strain rate and temperature-dependent yield surfaces are proposed with isotropic and progressive hardening rules to consider thermal collapse, strain rate effects, and smooth transition from elastic to viscoplastic behaviors. Next, the stress-fractional operator of the loading surface, according to the principle of fractional consistency viscoplasticity, is introduced to describe the nonassociativity of stiff clays. Finally, the predictive ability of the model is validated by simulating triaxial tests on Boom clay with various stress paths considering the temperature- and time-dependent features of stiff clays.

The soil behavior is rate-dependent as observed in the laboratory and field tests, and the undrained shear strength of clay is shown to increase with the strain rate in different shear modes. In practical situations, the foundations can be loaded at various time and rate scales, which will result in a wide range of magnitudes and inhomogeneous distribution of strain rates in the surrounding soil. This may cause difficulties in calculating the undrained bearing capacity of clay using the undrained shear strength from standard laboratory and field tests at a reference strain rate. In addition, the rate-dependent soil behavior will also affect the interpretation of in situ tests conducted at different loading rates (e.g., CPT, T-Bar, and pressuremeter tests) using procedures based on rate-independent soil models. This paper investigates the effect of loading rate on the undrained bearing capacity of clay using finite element analyses and a rate-dependent constitutive model, the MIT-SR, based on two classical problems in soil mechanics (i.e., the deeply-embedded rigid pile/pipe section, and the rigid strip footing). Computed results suggest that the undrained bearing capacity of clay is strongly affected by the loading rate of foundations, which is consistent with the model and field tests. It also highlights the difficulty to select appropriate undrained shear strength used for practical design, and the uncertainty to interpret field tests using bearing capacity factors derived from analytical solutions.