Behavior Of Sand Research Articles

Study on the side friction resistance capacity of prefabricated pipe piles in coral reef strata

Coral reefs are widely distributed along the “Maritime Silk Road”, and their unique mechanical properties pose numerous challenges for marine engineering construction. The side friction resistance (SFR) capacity of traditional driven piles in coral reef strata remains unclear, and there is a lack of effective calculation methods. Furthermore, the complex marine environment imposes higher requirements on pile foundation construction and durability. In this study, a series of interfacial shear tests were carried out for coral sand and coral reef limestone (CRL) in the sea area near the Maldives islands and reefs, and the distribution law of the SFR of prefabricated pipe piles in coral sand was investigated by using a large-scale pile foundation model test apparatus. The interfacial shear behavior of the coral sand is similar to that of the crushed coral reef limestone, both of which experience ideal elastic-plastic changes, with an interfacial friction angle of approximately 35°. The ultimate SFR of the prefabricated pipe piles in coral sand increases gradually and then plateaus, and the distribution of the SFR along the depth direction can be simplified as a combination of triangular and rectangular patterns. Based on the distribution law of the pile SFR, this study establishes a modified formula for calculating SFR of the pile in coral sand, which is verified by comparing the calculated SFR capacity of driven piles of the China-Maldives Friendship Bridge with the results of the field test piles. This study provides an important theoretical basis and practical guidance for the design and construction of pile foundation engineering in coral reef sea areas such as Maldives.

A Constitutive Model for Anisotropic Sand Considering Fabric Evolution Under Proportional and Non‐Proportional Loadings

ABSTRACTA critical state plasticity model is proposed to describe the anisotropic sand behaviour under both proportional and non‐proportional loading conditions. An evolving fabric tensor is introduced into the model to reflect the influence of fabric anisotropy on the stress‐strain relation of sand. By employing a fabric‐dependent plastic flow direction, the non‐coaxial response can be simulated in a simple way. A non‐proportional loading mechanism is incorporated to consider the plastic deformation induced by the stress increment tangential to the yield surface. The influence of accumulative plastic strain on the dilatancy function and plastic modulus is properly considered, enabling the model to reasonably capture the evolutions of volumetric and deviatoric strains under both drained and undrained principal stress axes rotation. The model was validated based on the simulations of experimental results for monotonic loading and pure principal stress axes rotation tests covering a wide range of conditions.

The Influence of the Root Diameter of Cunninghamia lanceolata (Chinese Fir) on the Strength and Deformation Behavior of Sand

This study used triaxial tests to examine the impact of the root diameter of Cunninghamia lanceolata (Chinese fir) on the mechanical behavior of sand, including stress–strain development, strength, volumetric strain, and failure envelope. It also revealed the reinforcement mechanisms of roots with different diameters based on root–soil interactions. The results showed the following: (1) The addition of roots significantly enhanced sand strength and reduced volumetric deformation. The average peak strength increased by 31.8%, while the average peak volumetric strain decreased by 34.3%. (2) Roots provided additional cohesion and increased the friction angle of the sand, causing the failure envelope to shift upward and deflect. (3) Smaller-diameter roots improved the mechanical properties of sand more significantly, leading to higher peak strength, shear strength parameters, and smaller volumetric deformation. As the root diameter increased from 1 mm to 5 mm, the peak strength ratio decreased from 1.78 to 1.13, and the peak volumetric strain increased from 0.48 to 0.79. (4) Smaller-diameter roots, which form denser networks, allowing more roots to resist loads, and have a higher elastic modulus providing greater tensile stress, also possess higher tensile strength and critical sliding tensile stress, making them less likely to fail, thereby making the mechanical reinforcement of sand more significant.

Deciphering necking in granular materials: Micromechanical insights into sand behavior during cycles of triaxial compression and extension

Deciphering necking in granular materials: Micromechanical insights into sand behavior during cycles of triaxial compression and extension

Effects of Hydrated Lime and Zeolite on the Mechanical Behavior of Calcareous Sand Subjected to Wet–Dry Cycles

Effects of Hydrated Lime and Zeolite on the Mechanical Behavior of Calcareous Sand Subjected to Wet–Dry Cycles

Experimental Investigation of Internal Erosion of Gap-Graded Sands

Internal erosion often occurs in earthen water-retaining structures such as embankment dams, levees, or dikes, which are created by seepage flows through soil or other porous material where coarser and finer particles are mixed. This erosion process may be referred to as suffusion, resulting in the transportation of fine particles carried away from the soil structure by seepage. If internal erosion occurs, the strength of the soil will be changed, and gaps or cavities in the soil structure may be created, leading to the collapse of the soil, posing a risk of damage to earthen water-retaining structures. This research investigates internal erosion behaviour of gap-graded sands with various fine contents using a series of upward seepage tests. An in-house developed apparatus with a measurement of hydraulic gradient and permeability is used to investigate the initiation and progress of internal erosion.

Effect of multidirectional cyclic loading history on reliquefaction behaviors of sand: a microscale investigation

Effect of multidirectional cyclic loading history on reliquefaction behaviors of sand: a microscale investigation

Investigation of shear mechanical behaviors of geogrid-coral sand interfaces

Geogrid-reinforced coral sand (GRCS) effectively enhances the strength and stability of marine geo-structures in island and coastal areas. The complex interaction and underlying mechanism of the geogrid-coral sand interface potentially determine the mechanical properties of the GRCS. In this study, large-scale interfacial shear tests were carried out to investigate the mechanical behaviors of geogrid-coral sand interfaces under the coupled influence of grain size, geogrid properties, and stress level. Comparisons with siliceous sand indicate that the mechanical properties of the geogrid-coral sand interface are excellent but suffer from more complex influences originating from particle properties. The interfacial friction angle is more sensitive to grain size, whereas the pseudo cohesion is more sensitive to aperture properties. The shear interface shows a general evolution trend of “contraction-dilation-contraction”, with the maximum and final dilation becoming more prominent as the aperture size and stress level decrease. The increase in grain size, vertical stress and geogrid apertures induces a thicker interface with more particle crushing. Given the microscopic geogrid-coral sand interaction, the force characteristics of the aperture are further analyzed, and an equivalent additional stress calculation method is developed to quantitatively characterize the effects of grain size, geogrid properties, and stress level.

Behavior of FRP-Confined Sand and Cemented Sand under Axial Compression

Behavior of FRP-Confined Sand and Cemented Sand under Axial Compression

Limiting membrane behavior of compacted sand–bentonite mixture

Limiting membrane behavior of compacted sand–bentonite mixture

Laboratory evaluation of calcareous sand specimens with inclined sedimentary surfaces

Sedimentary processes often produce natural and blown calcareous sands that are deposited in inclined and layered formations. These calcareous sands frequently exist in a complex stress state with rotating principal stress axes that result in intricate mechanical properties. To investigate the mechanical behaviors of calcareous sands with inclined sedimentary surfaces, we developed a device to prepare hollow cylindrical specimens from artificially crushed calcareous sands. By combining this device with a hollow cylindrical torsional shear apparatus, undrained monotonic loading and pure principal stress rotation tests were conducted to investigate the static and dynamic properties of the inherently anisotropic calcareous sands. The results indicate that the shear dilatancy property is related to the principal stress direction; the shear dilatancy of calcareous sand decreases as the direction of the principal stress increases, and the peak stress ratio decreases with increasing principal stress direction and increases with increasing deposition direction. In the precyclic loading period, increases in the deposition direction led to increases in the stabilities of the specimens and decreases in excess pore pressure accumulation, which further affect the dynamic shear modulus and damping ratio of the calcareous sand. In the late stage of cyclic loading, the inherent anisotropies of the specimens are destroyed, so that the excess pressure and hysteresis loop characteristics start to converge.

Effect of High-Stress Levels on the Shear Behavior of Geosynthetic-Reinforced Marine Coral Sands

As an important construction material, the mechanical and deformation properties of marine coral sand determine the safety and stability of related island and coastal engineering construction. The porous and easily broken characteristics of coral sand often make it difficult to meet engineering construction needs. In particular, coral sand undergoes a large amount of particle breakage under high-stress conditions, which in turn negatively affects its mechanical and deformation properties. In this study, the macro- and micro-mechanical behavior of geosynthetic-reinforced coral sand under high confining pressure was investigated and compared with unreinforced cases using the three-dimensional discrete element method (DEM), which was verified by indoor triaxial tests. The results showed that the stress–strain responses of unreinforced and reinforced coral sand under high confining pressure showed completely different trends, i.e., the hardening tendency shown in the reinforced case. Geosynthetic reinforcement can significantly inhibit the stress–strain softening and bulging deformation of coral sand under high confining pressure, thus improving the shear mechanical performance of the reinforced sample. At the microscopic scale, high confining pressure and reinforcement affected the contact force distribution pattern and stress level between particles, determining the macroscopic mechanical and deformation performance. In addition, the breakage of particles under high confining pressure was mainly affected by shear strain and reinforcement. The particle fragment distribution, particle gradation, and relative breakage index exhibited different trends at different confining pressure levels. These breakage characteristics were closely related to the deformation and stress levels of unreinforced and reinforced samples.

Consolidation Behavior of Silty Sand Improved by Stone Column

Consolidation Behavior of Silty Sand Improved by Stone Column

Effect of Fines Content on the Compression Behavior of Calcareous Sand

Due to the hydraulic sorting effect in the hydraulic filling process, a fine-grained aggregate layer dominated by silty fine sand with uneven distribution is easily formed in reclamation projects, which triggers issues with the bearing capacity and nonuniform settlement of calcareous sand foundations. In this study, a series of one-dimensional compression tests were conducted to investigate the effect of different fines contents (fc) on the compression behavior of calcareous sand. The results show that at the same relative density (medium-density, Dr = 50%), the addition of fine particles leads to a reduction in the initial void ratio (for fc ≤ 40%). Furthermore, while the compressibility of the soil samples increases with the rising of fines content, it begins to decrease with further addition of fine particles beyond a threshold value of fines content (fc-th). Additionally, particle crushing contributes to the compressive deformation of calcareous sand, and the particle relative breakage of calcareous sand increases at the initial stage of adding fine particles. Moreover, a comparison of the compression test results between calcareous silty sand (fc = 10%) and clean sand reveals that the addition of fine particles accentuates the compressibility differences among calcareous sands with different relative densities. These findings provide valuable insights for addressing the challenges posed by fine-grained layers in calcareous sand foundations.

Behaviour of sand under the constant shear drained stress path: the role of fines

This paper presents a specifically designed experimental study aimed at exploring the role of fines in altering the behaviour of sand under a constant shear drained (CSD) stress path. The novelty of this study includes that the interplay of several key factors (fines shape, fines content, void ratio) was investigated systematically and the true constant shear stress condition was fulfilled by means of an advanced servo system, which allowed the entire loading response to be captured. One of the marked findings is that the presence of fines not only alters the onset of instability of loose sand but also affects the deformation development thereafter. Drained instability can be triggered more easily in loose sand mixed with silica fines compared with the sand on its own. At the same quantity of fines, instability can be triggered more easily for sand mixed with rounded fines. However, the effect of fines appears to be marginal for sand at a dense state. For all tested specimens, values of the axial strain rate at instability fall in a narrow range (0·008–0·016%/min), meaning that the axial strain rate can potentially be a useful guide for quantitatively determining the inception of instability under CSD conditions. The stress ratio q/p′ at onset of instability under the CSD conditions is also state dependent, as under the undrained conditions.

Investigating Calcareous and Silica Sand Behavior at Material Interfaces: A Comprehensive Study

Abstract This study centers on the crucial determination of the mobilized friction angle between soil and various materials, including steel and concrete, to enhance the modeling of soil-structure interaction. The primary objective of the current investigation was to assess the interfacial friction between calcareous and silica sands when interacting with concrete or steel surfaces. To achieve this, direct shear tests were conducted to examine the impacts of relative density (Dr), surface roughness (Rn), and shearing direction. The test results reveal that the shear strength of calcareous sand surpasses that of silica sand when considering a specific Rn. Furthermore, the interface friction of both sand types escalates with an increase in normal stress and Rn, with higher values observed in interactions with steel plates. Notably, the friction angle ratio (the interaction friction angle over the pure sand friction angle) demonstrates minimal dependence on the sand type. The most pronounced divergence in the friction angle ratio is evident at the maximum Rn value, which increases alongside Rn values for both calcareous and siliceous sands. With increasing Rn values, the maximum shear strength, contingent on normal stress and relative density, also rises. The influence of relative density on the interaction friction angle diminishes with escalating surface roughness.

Mechanical characterization of calcareous sand reinforced by EICP multivariate tests and synergistic biochar reinforcement

The foundation bearing capacity in island reef infrastructure construction is often inadequate due to the poor engineering properties of calcareous sand. Enzyme-induced carbonate precipitation (EICP) has emerged as an efficient and environmentally friendly method to improve these properties, significantly enhancing the mechanical behavior of calcareous sand. However, the effectiveness of EICP is constrained by environmental factors that affect free urease activity and the limited availability of nucleation sites. To further improve the mechanical properties of EICP-reinforced calcareous sand, this study explores the addition of biochar to the sand. The characteristics of the samples were evaluated using unconfined compressive strength tests, calcium carbonate content measurements, and scanning electron microscopy. The results indicate that incorporating biochar into EICP significantly increases calcium carbonate production, strengthens the reinforced sand, and reduces surface porosity. This improvement is attributed to biochar’s surface properties, which provide additional nucleation sites for calcium carbonate formation, enhancing calcium carbonate content and sand strength. However, controlling the biochar content at approximately 5% is crucial to avoid excessive porosity, which could weaken the material. These findings offer a theoretical foundation for applying EICP-biochar-reinforced calcareous sand in engineering projects.

The role of incremental stress ratio in mechanical behavior and particle breakage of calcareous sand

The role of incremental stress ratio in mechanical behavior and particle breakage of calcareous sand

Study on monotonic direct shear characteristics of geosynthetics–calcareous sand interface

The investigation of shear behavior at the geosynthetics–calcareous sand interface is crucial for the internal stability design of reinforced revetment structures. A series of large-scale monotonic direct shear tests was conducted to examine the interface shear characteristics of geotextile–calcareous sand (GT–CS), geogrid–calcareous sand (GG–CS), and unreinforced calcareous sand (URCS). The interface shear behavior was investigated by considering the effects of interface types, including URCS, GT–CS, and GG–CS interfaces, and normal stresses ranging from 25 to 100 kPa. The interface interaction mechanism for different interface types is disclosed. The results indicate that embedding geotextiles and geogrids into calcareous sand filler alters the interface dilatancy behaviour of calcareous sand, which is significantly affected by normal stress. The dilatancy curves of GT–CS and GG–CS interfaces predominantly exhibit contraction–dilation and contraction, whereas the dilatancy curves of the URCS interface primarily display contraction–dilation–contraction and contraction. The shear softening behavior of GT–CS and GG–CS interfaces is primarily influenced by interface interaction mechanisms at the hardening stage and post-peak softening stage. The use of geogrid/geotextile has a reinforcing effect on calcareous sand fillers, leading to an increase of 1.22–1.44 times in interface peak cohesion. This increase falls within the range observed for geosynthetics–siliceous sand and geosynthetics–soil.

Study on micromechanical behavior and energy evolution of granular material generated by latent diffusion model under rotation of principal stresses

In this study, advanced image processing technology is used to analyze the three-dimensional sand composite image, and the topography features of sand particles are successfully extracted and saved as high-quality image files. These image files were then trained using the latent diffusion model (LDM) to generate a large number of sand particles with real morphology, which were then applied to numerical studies. The effects of particle morphology on the macroscopic mechanical behavior and microscopic energy evolution of sand under complex stress paths were studied in detail, combined with the circular and elliptical particles widely used in current tests. The results show that with the increase of the irregularity of the sample shape, the cycle period and radius of the closed circle formed by the partial strain curve gradually decrease, and the center of the circle gradually shifts. In addition, the volume strain and liquefaction strength of sand samples increase with the increase of particle shape irregularity. It is particularly noteworthy that obvious vortex structures exist in the positions near the center where deformation is severe in the samples of circular and elliptical particles. However, such structures are difficult to be directly observed in sample with irregular particles. This phenomenon reveals the influence of particle morphology on the complexity of the mechanical behavior of sand, providing us with new insights into the understanding of the response mechanism of sand soil under complex stress conditions.