There are currently two main criteria to identify the triggering time of soil liquefaction, namely when the excess pore water pressure reaches vertical effective overburden stress or the double-amplitude axial strain reaches 5 %. However, several researchers have pointed out that the excess pore water pressure may not reach confining pressure at some certain conditions, and the cycle numbers reaching liquefaction obtained by adopting two criteria for calcareous sand specimens are inconsistent, which may lead to overestimation or underestimation of the liquefaction resistance of calcareous sand. Therefore, this study introduces a parameter with physical meaning, secant shear modulus to evaluate the liquefaction potential of soil. To do that, a series of undrained shear tests were conducted on three types of sand. Firstly, the experimental results demonstrated that the difference in cycle numbers to liquefaction obtained by the two criteria increases with the increase of relative density. In addition, the study found that the degradation law of secant shear modulus with the number of cycles is not affected by loading conditions, initial state of soil, and soil type. On this basis, based on the relationship between secant shear modulus gradient and pore pressure ratio, it is highlighted that the liquefaction process can be quantitatively divided into three stages and the moment of liquefaction triggering can be correctly identified. Finally, the proposed liquefaction criterion is compared with widely used traditional criteria and latest apparent viscosity-based criterion, and the results showed that the liquefaction resistance obtained by the proposed criterion was more conservative, which benefits for reducing the occurrence of large strain development.

Calcareous sands provide the foundational support for various marine infrastructures. In the harsh marine environment, earthquake or wave loads apply multidirectional cyclic shear stresses to the foundation soil. To explore the undrained multidirectional cyclic response of sand, a series of simple shear tests were performed on reconstituted sand specimens considering the effect of phase difference (theta). By comparing the results with those of siliceous sand under similar conditions, the behavior of calcareous sand under multidirectional cyclic loading became clear. The results demonstrated that calcareous sand shows a lower degree of cyclic instability compared to siliceous sand, corresponding to the weaker strain-softening observed in calcareous sand during monotonic shear tests. The trend in normalized pore water pressure evolution in siliceous sand exceeds that in calcareous sand. Furthermore, under multidirectional cyclic shear conditions, the liquefaction resistance decreases by 30 % in extreme cases, irrespective of sand type. The liquefaction resistance of calcareous sand surpasses that of siliceous sand. However, as the cyclic stress ratio decreases, the reverse trend is observed, regardless of the impact of theta. Subsequently, the possible causes of the above experimental phenomena are explored from the perspectives of shear modulus and energy dissipation.

Soft clay soils inherently exhibit low mechanical strength, imposing significant challenges for various engineering applications. The present research explores various techniques and stabilizers to enhance soft clay's suitability for construction purposes. This study evaluates the mechanism of stabilizing kaolin using recycled macro-synthetic fibers (RMSF) for the first time. Samples were prepared with 5 % LKD, with 25 % replaced by VA, and varying RMSF amounts of 0, 0.5 %, 1 %, and 1.5 % in lengths ranging from 4 to 6 mm. The specimens were cured for 7, 28, and 56 days and exposed to 0, 1, 4, and 10 freeze-thaw (F-T) cycles. Laboratory investigations were conducted through standard compaction, Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS), Scanning Electron Microscope (SEM), California Bearing Ratio (CBR), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) tests on the samples at various stages of stabilizer addition, both before and after F-T cycles. The optimal mixture was 5 % LKD, with 25 % VA replacement and 1 % RMSF, which led to a considerable 11-fold enhancement in ITS and a 14-fold improvement in UCS compared to the untreated sample. Additionally, the secant modulus (E50) and energy absorption capacity (Eu) of the sample with the optimal combination content increased in comparison to the stabilized sample without RMSF. The CBR of the optimal sample reached 81 %, allowing for an 87 % reduction in pavement thickness compared to the untreated sample. According to the findings of this research, the combination of LKD, VA, and RMSF increased the compressive and tensile strength properties, bearing capacity, and durability of kaolin, making it an appropriate option for use in various practical civil projects like road construction.

Employing soil improvement techniques to mitigate and prevent the detrimental effects of liquefaction on foundations often leads to a significant increase in construction costs in engineering projects. Developing simple, cost-effective, and eco-friendly liquefaction mitigation methods has always been one of the main concerns of geotechnical engineers. Researchers introduced the induced partial saturation (IPS) method to increase the liquefaction resistance of the saturated foundations, which is based on decreasing the saturation degree of the saturated sand. In this study, hollow cylinder torsional shear tests were conducted on loose saturated and desaturated calcareous sand to assess the liquefaction behavior of desaturated sand. Soil compressibility is the primary parameter affecting the liquefaction behavior of desaturated sand. As saturation degree, back pressure, and effective confining pressure significantly influence soil compressibility, their effects on the liquefaction resistance of desaturated sand were investigated. The pore pressure development during cyclic loading reveal that, unlike saturated samples, desaturated samples do not exhibit an excess pore pressure ratio reaching one, even when the double amplitude shear strain surpasses 7.5 %. Finally, the test results demonstrated a notable correlation between liquefaction resistance ratio, maximum volumetric strain, and the maximum generated excess pore pressure ratio, and a pore pressure model was proposed.

As a new type of granular backfill material, calcareous sand is widely used in the construction of marine transportation infrastructure. And they are subjected to complex irregular long-term dynamic loading such as that from waves, traffic and even earthquakes. In this paper, 22 groups of undrained cyclic shear tests were performed with calcareous sand under various cyclic stress ratios and cyclic stress paths. The influence mechanism of stress path on the cyclic shear behavior of calcareous sand was investigated. The results show that the ultimate residual pore pressure at critical state was not affected by cyclic stress ratios and paths. But the cyclic shear behaviors of calcareous sand including failure pore water pressure and long-term deformation were changed significantly. Axial load plays a dominant role in each stress path. A stress path parameter omega was proposed to characterize the vertical shaking impact of cyclic stress paths with different initial orientation of the sigma 1 axis to vertical alpha sigma 0. And a power function of omega was used to describe the involvement level of soil skeleton in anti-liquefaction. This parameter performs well in representing cyclic stress paths with different orientation to the vertical. A series of formulas were proposed to predict the failure residual pore pressure and the long-term cumulative deformation behavior of calcareous sand. More accurate shakedown discriminant boundaries suitable for almost unbroken calcareous sand were proposed.

This study investigated the dynamic properties of red mud (RM)-reinforced volcanic ash (VA) by dynamic triaxial tests. The effects of stress state (dynamic stress sigma d, confining stress sigma 3), dynamic frequency (f) and load waveform (F) on the accumulative plastic strain (epsilon p) have been investigated. The findings indicate a significant influence of the stress state on epsilon p. When sigma d reaches 120 kPa, the specimens exhibit insufficient strength, leading to shear failure. As sigma 3 increases, the dynamic stresses that lead to specimen destabilization also exhibit an upward trend. The effect of f on epsilon p is limited. The epsilon p does not exhibit a clear or consistent developing pattern with increasing f. As for the F, the epsilon p exhibited by the specimens subjected to sinusoidal wave loads is less than that observed under trapezoidal wave loads. Shakedown theory classifies deformation responses into plastic shakedown, plastic creep and incremental collapse. The epsilon p curve patterns of RM-reinforced VA exhibit plastic shakedown and incremental collapse without significant plastic creep characteristics under cyclic loading. A predictive model for epsilon p under cyclic loading is established, which has good predictability. This study presents a novel application of VA and RM, offering substantial research insights into waste recycling.

Pumice soil grains are characterized by their vesicular nature, which leads to lightweight, crushable grains with an extremely rough and angular surface texture. These characteristics give pumiceous soils particular engineering properties that are distinct from more commonly encountered hard-grained materials, making them problematic for engineers interested in assessing the risk and potential consequences of liquefaction. Natural pumice-rich soils are found with varying amounts of pumice; however, it remains unclear how the quantity of pumice present in a soil mixture alters the behaviour. This paper investigates the effect of pumice content on cyclic resistance using blends of a hard-grained sand and a pumice sand through a series of triaxial tests. Overall, the cyclic resistance was found to reduce with increasing pumice content. Furthermore, the cyclic resistances appeared to fall into three bands: (a) little apparent reduction in cyclic resistance for pumice contents up to 40%, (b) a reduction in cyclic resistance of approximately 20% at pumice contents of 80% and higher, and (c) a transitional zone. However, despite the lower cyclic resistance, the patterns of pore pressure generation and strain development did not appear to be affected by the amount of pumice in the soil mixture. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).

Crushable porous soils, such as volcanic pumice, are distributed worldwide and cause a variety of engineering problems, such as slope hazards. The mechanical properties of these soils are complicated by their high compressibility due to voids in the particles themselves and changes in the soil gradation due to particle crushing. They are usually classified as problematic soils and discussed separately from ordinary granular soils, and their behaviour is not systematically understood. In this study, isotropic and triaxial compression tests were conducted on artificial pumice in order to determine the relationship between the mechanical properties and the particle crushing of crushable porous granular materials. The results showed that the mechanical behaviour of artificial pumice, representative of such materials, can be explained using a particle crushing index, which is related to the degree of efficient packing. Furthermore, a new critical state surface equation was proposed. It is applicable to crushable porous granular materials and shows the potential for expressing the critical state or isotropic consolidation state of such materials as a single surface in a three-dimensional space consisting of three axes: the stress - void ratio - crushing index. The validity of this new equation was confirmed by applying it to natural pumice from previous research. (c) 2025 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/).

Due to the widespread prevalence of respiratory diseases such as COVID-19 and H1N1, the use of disposable masks has increased significantly. Consequently, the environmental issues arising from their accumulation have become increasingly severe. This study, therefore, aims to investigate the potential of using masks as soil reinforcement materials. This study conducted triaxial and seepage tests on mask-calcareous sand mixtures with varying ratios to examine the effects of mask content on the strength, modulus, particle fragmentation, and permeability coefficient of calcareous sand, as well as the influence of different mask sizes on shear strength and shear dilation. The results demonstrate that with an increase in mask content, the peak stress ratio of the mask-calcareous sand mixture increases by 4% per level, and the internal friction angle rises by approximately 1.6% per level. Conversely, water permeability and shear swelling are reduced, and particle loss decreases by over 70%. The reinforcing effect of the mask is attributed to the high friction between the mask and the calcareous sand at the contact interface, which restricts the movement of soil particles during deformation, thereby enhancing the overall strength of the mixture. Among the three mask sizes, the smallest mask-calcareous sand mixture exhibited the greatest improvement in shear strength, and the shear shrinkage effect was more pronounced. This indicates that particle size also significantly influences the mechanical properties of the mixtures. The reinforcing effect of the mask on the soil results from the high friction at the interface between the mask and the calcareous sand. When the soil deforms, the mask enhances the overall strength of the mixture by restricting the movement of soil particles. Considering the impact of masks on the performance of calcareous sand, it can be concluded that the optimal mass content of masks is 0.3%. This study offers a new perspective on the reuse of discarded masks in civil engineering applications.

The distinct particle breakage characteristics of calcareous sand can induce extra settlement in calcareous sand foundations, posing a significant challenge to the safety of island and reef engineering. To explore the particle breakage, settlement characteristics and internal stress variations of calcareous sand foundations, the laboratory loading tests for calcareous sand foundations with different particle gradations were conducted. Particle Image Velocimetry (PIV) technology and tactile pressure sensor systems were also utilized. The study reveals that the tested calcareous sand foundations have differential settlements subjected to external loading, which has a strong relationship with the particle breakage. It is found that the nonuniform internal stresses between the sand particles can induce different degrees of the particle breakage, which in turn changes internal stresses and redistribution of particle positions in calcareous sands, and further causes the uneven settlement of the foundation. The degree of uneven settlement in calcareous sand foundations increases with an increase of external load and decreases with an increase of the coefficient of uniformity Cu for calcareous sands. During creep, the vertical and lateral stresses on the inter-particle contacts within the calcareous sand foundation exhibit an overall trend of decrease in weak forces and increase in strong forces. This continuous increase in strong forces results in a growth of creep deformation in calcareous sand foundation, while the degree of differential settlement in the foundation decreases with the progression of creep.