Search Results (37)

Coral sand is characterized by unique particle morphology and pore structure, which result in pronounced dilatancy and a high internal friction angle during shear. The dilatancy angle is a critical parameter for finite element analyses of sand foundation bearing capacity; the inappropriate selection of this parameter can lead to significant computational errors. In this research, a series of consolidated drained triaxial tests were conducted on coral sand samples from the South China Sea to investigate the dilatancy behavior and its effect on shear strength parameters. A dilatancy equation for coral sand was proposed, incorporating the dilatancy index, relative density, and mean effective stress. The results indicate the following: (1) Within the confining pressure range of 25–400 kPa, the stress–strain curves exhibit varying degrees of strain softening. When the effective confining pressure reaches 400 kPa, the dilatant behavior is nearly suppressed, resulting in a transition from dilatancy to contraction; (2) The peak internal friction angle decreases significantly with increasing effective confining pressure. However, the sensitivity to confining pressure varies for samples with different relative densities (Dr = 30–90%), with denser samples showing a more rapid reduction in peak friction angle; (3) At a confining pressure of 25 kPa, the maximum dilatancy angle of coral sand samples reaches 44.2°, significantly exceeding the typical range observed in terrestrial quartz sands. This difference may be attributed to the irregular and angular characteristics of the coral sand particles; (4) Based on Bolton’s dilatancy theory, a dilatancy equation applicable to coral sand was developed, demonstrating a strong linear relationship among the dilatancy index (I_R), relative density (Dr), and peak mean effective stress (p′_f). These findings provide valuable guidance for the selection of strength parameters for engineering applications involving coral sand. Full article

Hybrid composite pile foundations face critical challenges in terms of optimizing load transfer mechanisms across variable soil densities, particularly in regions like Kano, Nigeria, characterized by loose to dense sandy deposits and fluctuating groundwater levels. This study addresses the need for sustainable, high-performance foundation systems that are adaptable to diverse geotechnical conditions. The research evaluates the mechanical behavior of steel–concrete and timber–concrete hybrid piles, quantifying skin friction dynamics, combining eight (8) classical ultimate bearing capacity (UBC) methods (Vesic, Hansen, Coyle and Castello, etc.) with numerical simulations, and assessing load distribution across sand relative densities (10%, 35%, 50%, 75%, 95%). Laboratory investigations included the geotechnical characterization of Wudil River well-graded sand (SW), direct shear tests, and interface shear tests on composite materials. Relative densities were calibrated using electro-pneumatic compaction. Increasing Dr from 10% to 95% reduced void ratios (0.886–0.476) and permeability (0.01–0.0001 cm/s) while elevating dry unit weight (14.1–18.0 kN/m³). Skin friction angles rose from 12.8° (steel–concrete) to 37.4° (timber–concrete) at Dr = 95%, with timber interfaces outperforming steel by 7.4° at Dr = 10%. UBC for steel–concrete piles spanned from 353.1 kN (Vesic, Dr = 10%) to 14,379 kN (Vesic, Dr = 95%), while timber–concrete systems achieved 9537.5 kN (Hansen, Dr = 95%). PLAXIS simulations aligned closely with Vesic’s predictions (14,202 vs. 14,379 kN). The study underscores the significance of soil density, material interfaces, and method selection in foundation design. Full article

Sandy soils are prone to engineering issues due to their high permeability and low cohesion in the natural environment. Therefore, eco-friendly reinforcement techniques are required for projects such as subgrade filling and soft soil foundation reinforcement to enhance their performance. This study proposes a synergistic reinforcement method that combines Enzyme-Induced Calcium Carbonate Precipitation with Glutinous rice slurry (G-EICP). The macroscopic mechanical properties and pore structure evolution of reinforced sand were systematically investigated through triaxial permeability tests, unconfined compressive strength (UCS) tests, and microstructural characterization based on Scanning Electron Microscope (SEM) and Micro- Computed Tomography (CT) tests. The results indicate that when the glutinous rice slurry volume ratio (V_G) reaches 10%, the UCS of G-EICP-reinforced soil peaks at 449.2 kPa. The permeability coefficient decreases significantly with increasing relative density (D_r), V_G, confining pressure (σ₃), and seepage pressure (p). Microstructural analysis reveals that glutinous rice slurry may promote calcium carbonate crystal growth, potentially by providing nucleation sites, establishing a dual mechanism of skeleton enhancement and pore-throat clogging. The increased incorporation of glutinous rice slurry reduces the number of connected pores, lowers the coordination number, and elevates tortuosity, thereby inducing marked enhancements in both the strength and permeability of the treated soil compared to plain soil. Full article

At least 32 case histories have shown that liquefaction can occur in gravelly soils (both natural deposits and manmade reclamations) during severe earthquakes, causing large ground deformations and severe damage to civil infrastructures. Gravelly soils, however, pose major challenges in geotechnical earthquake engineering in terms of assessing their deformation characteristics and potential for liquefaction. In this study, aimed at providing valuable insights into this important topic, a series of isotropically consolidated undrained cyclic triaxial tests were carried out on selected sand–gravel mixtures (SGMs) with varying degrees of gravel content (G_c) and relative density (D_r). The pore water pressure generation and liquefaction resistance were examined and then further scrutinized using an energy-based method (EBM) for liquefaction assessment. It is shown that the rate of pore water pressure development is influenced by the cyclic resistance ratio (CSR), G_c and D_r of SGMs. However, a unique correlation exists between the pore water pressure ratio and cumulative normalized dissipated energy during liquefaction. Furthermore, the cumulative normalized energy is a promising parameter to describe the cyclic resistance ratio (CRR) of gravelly soils at various post-liquefaction axial strain levels, considering the combined effects of G_c and D_r on the liquefaction resistance. Full article

The population surge has led to a corresponding increase in the demand for high-rise buildings, bridges, and other heavy structures. In addition to gravity loads, these structures must withstand lateral loads from earthquakes, wind, ships, vehicles, etc. A piled raft foundation (PRF) has emerged as the most favored system for high-rise buildings due to its ability to resist lateral loads. An experimental study was conducted on three different piled raft model configurations with three different relative densities (D_r) to determine the effect of D_r on the lateral response of a PRF. A model raft was constructed using a 25 mm thick aluminum plate with dimensions of 304.8 mm × 304.8 mm, and galvanized iron (GI) pipes, each 457.2 mm in length, were used to represent the piles. The lateral and vertical load cells were connected to measure the applied loads. It was found that an increase in D_r increased the soil stiffness and led to a decrease in the lateral displacement for all three PRF models. Additionally, the contribution of the piles in resisting the lateral load decreased, whereas the contribution of the raft portion in resisting the lateral load increased. With an increase in D_r from 30% to 90%, the percentage contribution of the raft increased from 42% to 66% for 2PRF, 38% to 61% for 4PRF, and 46% to 70% for 6PRF. Full article

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 (f_c) on the compression behavior of calcareous sand. The results show that at the same relative density (medium-density, D_r = 50%), the addition of fine particles leads to a reduction in the initial void ratio (for f_c ≤ 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 (f_c-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 (f_c = 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. Full article

We first briefly review the adventure of scale invariance in physics, from Galileo Galilei, Weyl, Einstein, and Feynman to the revival by Dirac (1973) and Canuto et al. (1977). In the way that the geometry of space–time can be described by the coefficients $g_{\mu \nu }$, a gauging condition given by a scale factor $\lambda \left(x^{\mu }\right)$ is needed to express the scaling. In general relativity (GR), $\lambda =1$. The “Large Number Hypothesis” was taken by Dirac and by Canuto et al. to fix $\lambda$. The condition that the macroscopic empty space is scale-invariant was further preferred (Maeder 2017a), the resulting gauge is also supported by an action principle. Cosmological equations and a modified Newton equation were then derived. In short, except in extremely low density regions, the scale-invariant effects are largely dominated by Newtonian effects. However, their cumulative effects may still play a significant role in cosmic evolution. The theory contains no “adjustment parameter”. In this work, we gather concrete observational evidence that scale-invariant effects are present and measurable in astronomical objects spanning a vast range of masses (0.5 ${\mathrm{M}}_{\odot }<$ M $<{10}^{14}$${\mathrm{M}}_{\odot }$) and an equally impressive range of spatial scales (0.01 pc < r < 1 Gpc). Scale invariance accounts for the observed excess in velocity in galaxy clusters with respect to the visible mass, the relatively flat/small slope of rotation curves in local galaxies, the observed steep rotation curves of high-redshift galaxies, and the excess of velocity in wide binary stars with separations above 3000 kau found in Gaia DR3. Last but not least, we investigate the effect of scale invariance on gravitational lensing. We show that scale invariance does not affect the geodesics of light rays as they pass in the vicinity of a massive galaxy. However, scale-invariant effects do change the inferred mass-to-light ratio of lens galaxies as compared to GR. As a result, the discrepancies seen in GR between the total lensing mass of galaxies and their stellar mass from photometry may be accounted for. This holds true both for lenses at high redshift like JWST-ER1 and at low redshift like in the SLACS sample. Of note is that none of the above observational tests require dark matter or any adjustable parameter to tweak the theory at any given mass or spatial scale. Full article

As the critical dynamic parameters for soil, an extensive examination of the dynamic elastic modulus E_d and damping ratio λ in coarse-grained soil is of significant theoretical and practical importance. Currently, there is a scarcity of experimental equipment and methods for measuring the dynamic elastic modulus and damping ratio of coarse-grained soils. Moreover, studies examining the influence of relative density on these parameters in coarse-grained soils are largely absent. To investigate the behavior of the dynamic elastic modulus and damping ratio in coarse-grained soil under varying relative densities, a number of dynamic triaxial tests were conducted on a specific coarse-grained soil using the DYNTTS type dynamic triaxial test apparatus. The findings reveal that, under various gradations, the E_d of coarse-grained soils exhibits a decreasing trend with increasing dynamic strain, a trend that intensifies with higher relative densities. Additionally, as relative density increases, the degradation rate of the dynamic shear modulus ratio G_d/G_dmax to dynamic shear strain γ_d curve escalates. The maximum dynamic shear modulus G_dmax rises with increasing relative density D_r, displaying a linear relationship between G_dmax and D_r. Furthermore, both the increasing rate of λ to γ_d curve and the maximum damping ratio λ_max progressively diminish with the escalation of relative density D_r. Notably, the maximum damping ratio has a power function relationship with the relative density. Full article

Cancers can manifest large variations in tumor phenotypes due to genetic and microenvironmental factors, which has motivated the development of quantitative radiomics-based image analysis with the aim to robustly classify tumor phenotypes in vivo. Positron emission tomography (PET) imaging can be particularly helpful in elucidating the metabolic profiles of tumors. However, the relatively low resolution, high noise, and limited PET data availability make it difficult to study the relationship between the microenvironment properties and metabolic tumor phenotype as seen on the images. Most of previously proposed digital PET phantoms of tumors are static, have an over-simplified morphology, and lack the link to cellular biology that ultimately governs the tumor evolution. In this work, we propose a novel method to investigate the relationship between microscopic tumor parameters and PET image characteristics based on the computational simulation of tumor growth. We use a hybrid, multiscale, stochastic mathematical model of cellular metabolism and proliferation to generate simulated cross-sections of tumors in vascularized normal tissue on a microscopic level. The generated longitudinal tumor growth sequences are converted to PET images with realistic resolution and noise. By changing the biological parameters of the model, such as the blood vessel density and conditions for necrosis, distinct tumor phenotypes can be obtained. The simulated cellular maps were compared to real histology slides of SiHa and WiDr xenografts imaged with Hoechst 33342 and pimonidazole. As an example application of the proposed method, we simulated six tumor phenotypes that contain various amounts of hypoxic and necrotic regions induced by a lack of oxygen and glucose, including phenotypes that are distinct on the microscopic level but visually similar in PET images. We computed 22 standardized Haralick texture features for each phenotype, and identified the features that could best discriminate the phenotypes with varying image noise levels. We demonstrated that “cluster shade” and “difference entropy” are the most effective and noise-resilient features for microscopic phenotype discrimination. Longitudinal analysis of the simulated tumor growth showed that radiomics analysis can be beneficial even in small lesions with a diameter of 3.5–4 resolution units, corresponding to 8.7–10.0 mm in modern PET scanners. Certain radiomics features were shown to change non-monotonically with tumor growth, which has implications for feature selection for tracking disease progression and therapy response. Full article

The structural stability of pipe pile foundations under seismic loading stands as a critical concern, demanding an accurate assessment of the maximum settlement. Traditionally, this task has been addressed through complex numerical modeling, accounting for the complicated interaction between soil and pile structures. Although significant progress has been made in machine learning, there remains a critical demand for data-driven models that can predict these parameters without depending on numerical simulations. This study aims to bridge the disparity between conventional analytical approaches and modern data-driven methodologies, with the objective of improving the precision and efficiency of settlement predictions. The results carry substantial implications for the marine engineering field, providing valuable perspectives to optimize the design and performance of pipe pile foundations in marine environments. This approach notably reduces the dependence on numerical simulations, enhancing the efficiency and accuracy of the prediction process. Thus, this study integrates Random Forest (RF) models to estimate the maximum pile settlement under seismic loading conditions, significantly supporting the reliability of the previously proposed methodology. The models presented in this research are established using seven key input variables, including the corrected SPT test blow count (N₁)₆₀, pile length (L), soil Young’s modulus (E), soil relative density (Dr), friction angle (ϕ), soil unit weight (γ), and peak ground acceleration (PGA). The findings of this study confirm the high precision and generalizability of the developed data-driven RF approach for seismic settlement prediction compared to traditional simulation methods, establishing it as an efficient and viable alternative. Full article

The aim of this study is to investigate the bearing capacity-settlement behavior of strip footing settling on sand soil randomly reinforced with glass fiber, basalt fiber, macromesh fiber, and four different hybrid fiber additives in which these fibers are used together. Model tests were carried out in the laboratory on the strip footing and placed on the unreinforced and reinforced sand with different fibers. In the study, model tests were carried out on seven types of randomly reinforced soils by using glass, basalt, macrame, and mixtures of these fibers as reinforcement. In the model tests, two different fiber contents, 1% and 2%, and two different fiber lengths, 24 mm and 48 mm, were used. Tests were carried out with Dr = 30% and 50% relative density, and reinforcement depths 1B, 2B, and 3B were selected. In addition, the photographs taken during the test were analyzed with the particle image velocimetry (PIV) method and the displacements on the soil were examined. As a result of the reinforced and unreinforced model tests, the highest ultimate bearing capacity was measured as 680 kPa from the tests with Dr = 50% relative density, 48 mm length, 2% contents, and 3B depth macromesh fiber reinforced. In hybrid fibers, the highest ultimate bearing capacity was measured as 495 kPa, with Dr = 50% relative density, 48 mm length, 2% contents, and 2D depth micromesh and basalt fiber-reinforced tests. In the reinforced tests, it was concluded that the most effective fiber on bearing capacity is macromesh fiber. It can be seen that in the PIV analysis, as the fiber additive increased, the settlements made by the foundation decreased under the same pressure. It has also been observed that adding reinforcement to the soil transfers the stresses occurring in the soil to a wider area. Full article

Estimating a pile shaft’s frictional capacity is challenging and has been a controversial subject among researchers. In this study, the shaft friction resistance of non-displacement (pre-installed) model piles under axial load was investigated. Four different model piles were used, including steel, timber, and two composite piles (FRP and PVC filled with concrete). The angle of interface friction (δ) between test sand, and pile materials was determined using an interface shear test (IST) at four relative densities. Axial pile load experiments were implemented in a soil tank and piles were embedded into loose to very dense sand. Model pile load tests were performed in such a way that there was no end (point) bearing capacity (only friction was generated), and lateral friction resistance between the pile material and the soil along the pile shaft formed the complete bearing capacity of the model pile. According to experimental results, it was observed that, with increasing sand relative density and surface roughness of the pile material, the shaft friction resistance of the model pile increases. A back-calculation analysis was also performed to find the values of lateral earth pressure coefficient (K) using Burland’s (1973) equation with the help of measured shaft friction capacity of the model pile load test. By performing multivariate regression analysis, an equation was obtained between the back-calculated lateral earth pressure coefficient (K) and other parameters. The obtained equation was used to calculate the K values given in other studies in the literature. It was determined that the obtained equation was in good agreement with the data in other studies. This equation can be beneficial in practice and can be advantageous for further study in the future. Full article

The literature confirms that fine recycled concrete aggregate (fRCA) can be used as a replacement for natural soil in new concrete, offering many advantages. Despite these advantages, there are also critical barriers to the development of fRCA in new mixes. Among these, the first challenge is the variability of fRCA properties, in both physical, chemical, and mechanical terms. Many individual studies have been carried out on different RCA or fRCA properties, but little investigative work has been performed to analyze their dynamic properties. Therefore, the influence of the non-cohesive fine fraction content of RCA on the dynamic properties of this waste material, when used as a specific anthropogenic soil, has been studied in laboratory conditions, employing a standard resonant column apparatus, as well as piezoelectric elements. In the present research, special emphasis has been placed on the dynamic shear modulus, dynamic damping ratio, small-strain shear modulus, and small-strain damping ratio, as well as shear modulus degradation G(γ)/G_max, the damping ratio increase D(γ)/D_min, and the threshold shear strain amplitudes γ_tl and γ_tv. Artificially prepared fRCAs with varying fine fraction contents (0% ≤ FF ≤ 30%, within increments of 5%) have been tested at different pressures (p′ = 90, 180, and 270 kPa) and relative densities of D_r > 65%. This study also examined the effect of two tamping-based sample preparation methods, i.e., dry and wet tamping. The results presented herein indicate that the analyzed anthropogenic material, although derived from concrete and produced by human activities, behaves very similarly to natural aggregate when subjected to dynamic loading. The introduction of a fine fraction content to fRCA leads to changes in the dynamic properties of the tested mixture. Concrete material with lower stiffness but, at the same time, with stronger damping properties can be obtained. A fine fraction content of at least 30% is sufficient to cause a significant loss of stiffness and, at the same time, a significant increase in the damping properties of the mixture. This study can serve as a reference for designing fRCA mixtures in engineering applications. Full article

The coefficient of earth pressure at rest K₀ is a state soil variable correlated with relative density D_r. As previously conducted K₀ tests could not guarantee zero lateral deformation in the sand specimens, significant errors occurred in the test results. In this paper, a centrifugal model test method is used to study the K₀ of sand with varying densities. The sand specimens with varying relative densities are prepared by sand pluviation, and a 50 g-ton centrifugal force is applied. Subsequently, the relationship of K₀ and D_r with different densities is analyzed. The test results show that for the same type of sand, the value of K₀ gradually increased with D_r. Based on the meso-evolution characteristics of sand particle recombination, various relationships between K₀, the displacement deflection angle, and the friction offset angle between particles are analyzed. Furthermore, the relationship between particle volume fraction and K₀ is derived, the assumption of increasing the coefficient K₀ with the increase in D_r is verified, and the effect of D_r of sand on the force transfer behavior of the internal particle fabric is briefly discussed. The research results could significantly improve the current earth pressure theories. Full article

Tailings dam accidents emphasize the importance of an adequate understanding of the strength parameters of tailings to improve the efficiency and effectiveness of the design, construction, and operation of such structures. Usually, the tailings strength is addressed in a deterministic manner. However, a statistical approach would better represent their behavior due to its inherent heterogeneity. The literature about tailings strength distribution is relatively rare or superficial, which impairs the probabilistic analyses which are essential for risk management. Therefore, this article focuses on the probability density function (PDF) of the effective friction angle (ϕ′) of iron ore tailings from the reservoir of Germano dam, Mariana, Brazil, based on data from publicly available CPTu tests. The influence of the relative density (D_r), and the presence of plastic layers amidst the sand tailings on the strength of the sand are also discussed herein. Several correlations were employed to estimate ϕ’ and D_r. According to the results, the presence of plastic layers influences the estimated properties, and the relative density has a log-normal distribution. The effective friction angle, on the other hand, presents a normal distribution. Full article