Cemented sand-gravel (CSG) is an innovative material for dam construction with a wide range of applications. Nevertheless, a comprehensive understanding of the dynamic properties of CSG is lacking. A series of cyclic triaxial dynamic shear tests were carried out on CSG materials to investigate their complex dynamic mechanical properties, leading to the establishment of a dynamic constitutive model considering damage. The findings indicate that both the application of confining pressure and the addition of cementitious material have a noticeable influence on the morphology of the hysteresis curve. Further research scrutiny reveals that augmenting confining pressure and gel content leads to an increase in the dynamic shear modulus and a decrease in damping ratio. Furthermore, a constitutive dynamic damage constitutive model was constructed by linking a damage element to the generalized Kelvin model and defining the damage variable D based on energy interaction principles. The theoretical formulas for dynamic shear modulus and damping ratio were adjusted accordingly. In addition, the stiffness matrix of the dynamic damage constitutive model was derived, which demonstrated its strong fitting effects in dynamic triaxial shear tests on CSG. Finally, the dynamic response and damage distribution in the dam body under dynamic loading were analyzed using a selected CSG dam in China.

The application of disposable face mask fibers in the enhancement of the mechanical properties of cement-stabilized soils is rigorously examined in this study through performing several triaxial tests on fiber-reinforced sand-cement mixtures with varying contents of additives under different confining pressures. To this end, sand samples stabilized with different percentages of cement (4% and 8%) are reinforced with various contents of face mask fibers (0%, 0.25%, 0.5% and 0.75%). After seven days of curing, the fiber-reinforced stabilized specimens are subjected to a comprehensive series of consolidated drained (CD) triaxial tests with all-round pressures of 50, 100 and 200 kPa. The results generally show that the addition of mask fibers to sand-cement mixtures up to 0.25% increases their ultimate strengths; whereas further increase of fiber content is observed to have an adverse impact on the strength parameters of the composite. Therefore, 0.25% mask fiber inclusion is reported to be the optimum content, which constitutes maximum strength characteristics of the samples. The contribution of mask fiber addition to the variation of ultimate strength of stabilized mixtures is noticed to be more pronounced in the samples with higher cement contents under greater isotropic confining pressures. Moreover, with increasing the percentage of mask fibers, the failure strain of all stabilized samples increases, thus exhibiting more ductile behavior. Unlike for the samples containing relatively low cement contents (4% herein) where brittleness index is barely affected by the mask fiber content, this parameter significantly decreases with the fiber inclusion for the specimens stabilized with relatively high cement contents (8% herein). Secant modulus is also observed to experience a decreasing trend with the addition of mask fibers to the mixture; the trend which is more pronounced for samples containing higher cement contents. Finally, the internal friction angle and cohesion of cement-stabilized samples generally show increasing trends with the addition of mask fibers up to 0.25% and then reveal decrement. Overall, the combination of cementation and fiber reinforcement demonstrates a significant synergistic effect, resulting in notable improvements in the mechanical properties of fine sands.

This study presents the results of consolidated drained triaxial tests conducted to investigate the influence of various parameters on the volumetric change behavior of cemented sand reinforced with polyvinyl alcohol (PVA) fibers. The primary objective is to explore the interaction between fiber weight ratio, cement weight ratio, confining pressure, and relative density on the dilatation behavior of cemented sand reinforced with PVA fibers. PVA fibers were incorporated into dry sand-cement mixtures at weight ratios of 0.0%, 0.3%, and 0.6%. The specimens were prepared with cement content of 0%, 2%, and 4% by weight of dry sand and cured for 7 days. Two relative densities were used in specimen preparation, and triaxial compression tests were conducted under different confining pressures. The results reveal that decreasing relative density, increasing cement content, and adding fibers all contribute to a reduction in sample dilatation. Specifically, the peak dilation rate increases with higher relative density and cement content, while it decreases with higher fiber content and confining pressure. A notable aspect of this study is its investigation of how these parameters interact when combined, offering a deeper understanding of their collective effects on soil behavior.

In recent years, the rapid development of offshore exploration and coastal engineering has necessitated stringent requirements for foundation materials, particularly in complex geological environments. Cemented soils, widely used in large-scale offshore engineering projects, play a crucial role in ensuring the safety and stability of offshore structures. However, understanding the mechanical behavior of cemented sand, including its stress-strain relationship, strength characteristics, and long-term performance under different stress paths, remains a challenge. This study uses triaxial tests and discrete element method (DEM) simulations to investigate the mechanical properties of cemented sand, using offshore quartz sand as the aggregate and a gypsum plaster as the cementing agent. The results reveal that higher confining pressures and gypsum content significantly improve the peak and residual strength of cemented sand, while also increasing its brittleness. The particle-size increasing and natural curing results in increased strength, cohesion, and internal friction angle of cemented sand. The study also finds that the stress-strain relationship of cemented sand primarily shows a strain-softening behavior, but gradually transitions to strain-hardening behavior at higher gypsum contents. DEM simulation results show that the displacement of internal particles becomes more pronounced, with particle movement gradually shifting from the vertical to the lateral direction. The research provides a scientific foundation for offshore engineering design, ensuring the safe operation of structures under extreme marine conditions.

Cemented sandy gravel is often used to enhance the foundation soil of engineering projects. This paper presents results of triaxial tests on cemented sandy gravel specimens. We compared 8 cemented specimens and 4 uncemented specimens. The strength, dilatancy, and stiffness behavior of both cemented and uncemented specimens are compared. The strength of cemented specimens is significantly greater than that of uncemented specimens, and the cemented specimens demonstrate pronounced expansion characteristics. The peak friction angle of the cemented specimen shows a linear relationship with the confining pressure: psi = 68.1-18.2lg(sigma 3/pa). To quantify the structural strength of the cemented specimens, a structural damage parameter is introduced based on the differences in mechanical properties between the two materials. The structural damage parameter first increases and then decreases as shearing progresses, and a hump curve function is used to describe this behavior. In the frame of the generalized plasticity, a novel elastoplastic model is established, considering the structural parameter as a factor of the plastic modulus, loading vectors and plastic flow direction vectors. The calculated values fit well with the experimental results. The model can reflect the characteristics of cemented sandy gravel, in terms of stress softening, residual strength, and volumetric dilation. Finally, the model is used to evaluate the deformation of a sluice dam foundation after being enhanced with cemented sandy gravel. The results show that after treatment, both the settlement of the gate floor and the shear deformation of the waterstops can be reduced by more than 10%.

For noncrushable sand, this paper describes the experimental phenomenon of the opposite turning directions of stress-dilatancy curves between sands before and after cementation. Then, based on the thermomechanical framework and Legendre transformation, the stress-dilatancy model is obtained from the dissipation function. This stress-dilatancy model considers the coupled effect of bond breakage and rearrangement energy. This model also incorporates the mechanism that cementation-improved strength leads to the opposite turns of sands before and after cementation. Compared with the other four existing stress-dilatancy models, this paper's model can depict the opposite turning directions of stress-dilatancy curves between uncemented and cemented sands. This stress-dilatancy model is also verified through five types of cementation: colloidal-silica-cemented sand, (CaCl2+Na2SiO3) cemented sand, naturally bonded sand, microbially induced carbonate precipitation (MICP)-cemented sand, and portland cement-treated sand. The broader application of the model is that it can also be used for crushable sand with particle breakage, as well as artificially cemented sand after freeze-thaw damage.

Improvement of granular soils mechanical properties can be achieved by the addition of bonding agents. In this research, low amount of Portland cement was added to a sand and its beneficial shear strengthening effects were evaluated under a range of multiaxial stress paths. The influence of the orientation of the principal axes of stress and strain on the stress-strain response and failure of cemented sand has only been scarcely investigated. Therefore, this experimental investigation reports the results of a series of consolidated drained hollow cylinder torsional tests with constant principal stress path direction, alpha sigma, varying from 0 degrees to 90 degrees Results were compared with the shear behaviour of the uncemented sand tested under similar loading conditions. Results show that the addition of cement to the sand matrix increases the soil strength for all multiaxial stress path directions. The suitability of two multiaxial strength criteria for reproducing the shape of the failure envelope as a function of the orientation of principal stress axis alpha sigma has also been analysed.

The microbial-induced calcite precipitation (MICP) technique has been developed as a sustainable methodology for the improvement of the engineering characteristics of sandy soils. However, the efficiency of MICP-treated sand has not been well established in the literature considering cyclic loading under undrained conditions. Furthermore, the efficacy of different bacterial strains in enhancing the cyclic properties of MICP-treated sand has not been sufficiently documented. Moreover, the effect of wetting-drying (WD) cycles on the cyclic characteristics of MICP-treated sand is not readily available, which may contribute to the limited adoption of MICP treatment in field applications. In this study, strain-controlled consolidated undrained (CU) cyclic triaxial testing was conducted to evaluate the effects of MICP treatment on standard Ennore sand from India with two bacterial strains: Sporosarcina pasteurii and Bacillus subtilis. The treatment durations of 7 d and 14 d were considered, with an interval of 12 h between treatments. The cyclic characteristics, such as the shear modulus and damping ratio, of the MICP-treated sand with the different bacterial strains have been estimated and compared. Furthermore, the effect of WD cycles on the cyclic characteristics of MICP-treated sand has been evaluated considering 5-15 cycles and aging of samples up to three months. The findings of this study may be helpful in assessing the cyclic characteristics of MICP-treated sand, considering the influence of different bacterial strains, treatment duration, and WD cycles. (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/).

Microbially Induced Calcite Precipitation (MICP) is an eco-friendly method for improving sandy soils, relying on micro-organisms that require nitrogen and essential nutrients to induce carbonate mineral precipitation. Given the substantial annual generation of chicken manure (CM) and the associated challenges in its disposal resulting in environmental pollution, the nutrient-rich composted form of this waste material is proposed in this study as a supplementary additive (along with more costly industrial reagents, e.g., urea) to provide the necessary carbon and nitrogen for the MICP process. To this end, different CM contents (5 %, 10 %, and 15 %) along with various concentrations of cementation solution (1 M, 1.5 M, and 2 M) are employed in multiple improvement cycles to augment the efficiency of the MICP technique. Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), and Water Absorption (WA) tests are performed to assess the mechanical properties of the samples before and after exposure to freeze-thaw (F-T) cycles, while SEM, XRD, and FTIR analyses are carried out to delineate the formation of calcite within the porous structure of MICP-CM-treated sands. The findings suggest that an optimum percentage of CM (10 %) in the MICP process not only contributes to environmental conservation but also significantly enhances all the mechanical properties of bio-cemented sandy soils due to markedly improved bonding within their porous fabric. The results also show that although prolonged exposure to consecutive F-T cycles causes a reduction in strength and stiffness of enhanced MICP-treated soils, the mechanical properties of such geo-composites still remain within an acceptable range for optimal CM-enhanced biocemented mixtures, significantly superior to those of MICP-treated sands.

Microbial-induced carbonate precipitation (MICP) is a novel geotechnical reinforcement method that can be used for slope protection, erosion mitigation and seepage control without compromising the soil structure. Based on computed tomography (CT) 3D reconstruction, pore parameters such as the connected porosity, pore equivalent diameter and coordination number are extracted to quantitatively evaluate the effect of the calcium carbonate content on the microstructure of biocemented sand. Then, simulations are conducted to analyze the seepage characteristics of single-phase water flow in the pore space, and 3D visualization of porous seepage in biocemented sand is achieved. The results indicate that as the calcium carbonate content increases, there is a noticeable decrease in total porosity, which is accompanied by an increase in the number of isolated pores and a decrease in the number of connected pores. Concurrently, the average pore equivalent diameter increases, while the pore coordination number decreases. Seepage simulation shows that the permeability of biocemented sand has strong anisotropy, and the pore structure has a strong control effect on the seepage. With increasing calcium carbonate content, the biocemented sand streamlines gradually develop from a network to a branching shape until several main stems remain.