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The Cone Penetration Test (CPT) is a widely used site investigation tool due to its accuracy and wealth of data at a relatively low cost. Virtually all CPT interpretations explicitly or implicitly depend on how the in-situ state parameter is correlated to the tip resistance. Accurate interpretation of the state parameter from CPT is the basis for evaluating strength and liquefaction susceptibility of granular soils. The handful of interpretation methods used in the industry range between empirical and semi-empirical. As is the case for all empirical methods, extrapolating these methods outside of the original database, especially to significantly different soils such as silt-rich tailings, brings about significant risk. This paper presents a new method of interpreting the state parameter from a fully validated model of the cone penetration in sand. The method has no empirical elements and produces soil-specific correlations between the tip resistance and the state parameter. It can be easily implemented in a spreadsheet and does not require complicated analyses. The method differentiates among soils through calibration of a critical state based constitutive model, Norsand, through triaxial compression tests. The potential errors induced by not measuring soil properties are quantified. [ABSTRACT FROM AUTHOR]

This paper reviews the load–settlement behaviour of 499 plate load tests of various diameters undertaken on granular soils and working platform materials to determine the angle of internal friction mobilised by the test. The observed settlement of individual plate load tests at relatively small settlement has been extrapolated to a theoretical failure of the plate at 10% and 15% of the plate's diameter (D). For each test an effective angle of internal shearing resistance was calculated based on the bearing resistance associated with the stress required to cause settlement of 0.10 or 0.15 times the plate diameter. The results are presented along with a discussion on the use of high-friction materials in working platforms and shallow foundations. Characteristic values for the effective angle of internal shearing resistance are provided for all working platform materials tested, as well as tests undertaken on platform materials comprising crushed brick and concrete. These values are compared to shear box test results on similar materials. Characteristic values of ϕ′ varying from 44° to 46.4° (0.1D) and 45.3° to 47.8° (0.15D) for crushed brick and concrete materials are calculated, which are slightly higher than those determined from tests on Type 1 material. [ABSTRACT FROM AUTHOR]

This study investigates, for the first time ever, the suffusion on gap‐graded granular soils under torsional shear conditions from a microscopic perspective. A numerical model of the hollow cylinder torsional shear test (HCTST) using the discrete element method (DEM) is first developed, where an algorithm for simulating the real inner and outer rubber membranes of the hollow cylinder apparatus (HCA) is introduced. After the validation, the computational fluid dynamics (CFD) approach is introduced for the coupling between the particle and fluid phases. Then, a series of the coupled CFD‐DEM suffusion simulations considering the rotation of the major principal stress axis (α) and intermediate principal stress ratio (b) are conducted. It is found that more fine particles are eroded in cases having smaller α and b, and the clogging phenomenon in the middle zones becomes more significant as both α and b increase. From the microscopic perspective, the specimens whose contact anisotropy principal direction is close to the fluid direction will lose more fines, and the anisotropy magnitude also plays an important role. In addition, the differences in structure and vertical connectivity of the pores in HCTST samples under various complex loading conditions cause fine particles to have different migration paths, further resulting in different fines mass loss. [ABSTRACT FROM AUTHOR]

Accurate three‐dimensional (3D) reconstruction of granular grains from x‐ray micro‐computed tomography (µCT) images is a long‐standing challenge, particularly for dense soil samples. This study develops a machine learning (ML) enhanced approach to automatically reconstruct granular grains from µCT images. The novel academic contributions of this paper include (a) a hierarchical strategy based on parameter‐independent polygonal approximation, area, and concavity analysis, for the first time, to identify and eliminate both intergranular and intragranular voids; (b) incorporation of a recursive segmentation scheme and ML‐based grain classifier to avoid over‐segmentation; (c) novel modifications on the determination of splitting paths to enhance segmentation accuracy; and (d) an effective approach of assigning initial level set functions for reconstructing granular grains automatically. The hybrid ML algorithm is applied to µCT images of dense Mojave Mars Simulant. The results indicate that the proposed method can accurately segment grain clumps with unclear boundaries. The new automatic reconstruction algorithm eliminates ineffective operations and achieves a three‐fold increase in computational speed than previous methods documented in the literature. Ninety‐one percent of grains with distinct boundaries can be reconstructed and the reconstruction ratio reaches 81% even for grains without distinct boundaries. The overall reconstruction ratio of grains increases by 20% compared with previous methods, achieving a step‐change improvement for one‐to‐one mapping of real soil samples. [ABSTRACT FROM AUTHOR]

Compaction is an essential compression process for sedimentary soils. Compared with in-depth studies on granular soil behaviors, numerical modeling of clay compaction is still in its infancy. This study presents an all-atomic modeling framework to investigate the compaction of anhydrous montmorillonite from initially fully exfoliated platelets. The total number of interparticle contacts increased, and the mesopores were dominant during the formation of card-house structures. As the local fabrics evolved into book-house structures, the contact evolutions became predominant, and partial mesopores transformed into micropores. The coordinated deformations during the formation of compacted aggregates dramatically increased interparticle contacts, and so the micropores became dominant. After rebound, the interparticle contacts decreased and partial micropores were restored. The total potential energy decreased during contact evolutions due to the significant reduction in interaction potential energy between clay particles, while hysteresis was observed during coordinated deformations and rebound due to the changes in internal potential energy within deformed clay particles. The internal potential energy was primarily determined by the electrostatic forces except under significant deformations, where the van der Waals forces became dominant. The interaction potential energy remained unchanged with specific contact types but decreased significantly due to electrostatic interaction when contacts evolved. As computational capacity develops, a greater number of larger hydrated clay particles can be used to improve simulations of compaction and other macroscopic behaviors via all-atomic molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

ABSTRACT The contact network of granular materials is often divided into strong and weak subnetworks, which play different roles in micromechanics. Within the strong contact network, there exists the largest connected component, that is, the largest cluster, which may connect system boundaries and could be the most important structure in force transmission of the whole system. This paper concerns the particular features of the largest cluster in the strong contact network of granular materials, by considering the combining effects of loading path and particle shape. A series of true triaxial tests with various intermediate principal stress ratios are conducted for granular assemblies of different shaped particles using the discrete element method (DEM). Both the macroscopic stress–strain responses and the microscopic topological changes of the contact network are investigated. It is found that both particle shape and loading path will influence the shear strength and the topological features of the strong network. The threshold ζ$\zeta $ (the ratio to the average force) is used to distinguish the strong and weak networks, and a critical threshold can be identified by comparing the network‐based metrics. The largest cluster within the strong network approaching the critical threshold can span the boundaries in each direction with minimum contacts, which occupies a small portion of particles and contacts but transmits a considerable portion of the applied stress. In addition, the similar contribution weight of the largest cluster to the deviatoric stress is identified for granular materials with different particle shapes. [ABSTRACT FROM AUTHOR]

The present paper aims to compare the behaviour of dense granular soils inside and outside the Shear Band (SB) during the Plane Strain Compression (PSC) test using the Discrete Element Method (DEM). The flexible membrane in the PSC test was modelled by adopting a discrete element–finite difference (DEM-FDM) hybrid approach. In contrast with previous 2D studies, the present study employed 3D simulations to consider the effects of out-of-plane characteristics such as the intermediate principal stress. According to the findings, the minimum and intermediate principal stresses outside the SB were twice as high as those inside at the residual state. It was also found that mechanical coordination numbers and redundancy indexes both inside and outside the SB decreased up to the onset of the residual phase, with a higher reduction rate inside the SB. As far as fabric anisotropy is concerned, the degree of anisotropy increased both in and out the SB until the peak state, with a somewhat higher rate inside the SB. A further finding was that the distribution of normal contact forces outside the SB remained symmetrical around the vertical axis after shear banding, however, it became asymmetrical inside the SB. [ABSTRACT FROM AUTHOR]

A wide range of applications of unsaturated hydraulic conductivity is well known in geotechnical, hydrological, and agricultural engineering fields. The standard prediction models for hydraulic conductivity function overlook the complexity of soil pore structure and employ a simplistic approach based on the bundle of capillary tubes. This study proposes an alternative approach employing pore network models calibrated to match soil water retention data to predict the hysteretic hydraulic conductivity function of granular soils. A novel approach to constructing a multidirectional pore network built on an irregular lattice with variable coordination numbers is presented for the realistic representation of soil voids. The geometric and topological parameters of the pore network model are optimized using the genetic algorithm, and adequate pore‐scale processes (piston‐like advance and corner flow during drainage and piston‐like advance, pore body filling, and snap‐off during imbibition) are modeled to get reasonable predictions of hysteretic hydraulic conductivity functions over the entire suction range of granular soils. Comparisons between the pore network model results, standard physically based models, and measured data for a variety of granular soils show that the proposed pore network has a superior performance over other models and compares favorably to the experimental data. [ABSTRACT FROM AUTHOR]

The role of particle shape on soil mechanical response has been studied extensively especially through numerical means. The underlying micromechanics of how particle shape may affect the soil mechanical responses at element scale remains unclear. Systematic micromechanical experiments that consider in situ tracking of the evolution of fabric during the shearing process is missing. Aided by a miniaturised triaxial apparatus and X-ray computed tomography (CT), this study presents a series of triaxial compression on four granular soils with different particle shapes yet the same mineralogy, grading, and initial density. Evolution of three-dimensional soil fabric quantifiers during shearing was captured based on 192 full-field CT images. The results revealed that the initial shearing reduced the packing density without changing the particle packing pattern, followed by particle sliding and particle rotation, which redistributed the force chains and formed a new packing pattern to resist shearing, causing strain localisation, and reductions in both the contact number and concentration of contacts direction. Fabric anisotropy increased before reaching the peak and attained the maximum value as the soil approached the critical state. Particle shape, especially when quantified by overall regularity or other combinations of descriptors, displayed more significant linear correlations with critical-state parameters than by local descriptor. [ABSTRACT FROM AUTHOR]

The granular soils of tailings, encompassing clay, gravel, sand, and silt, play a pivotal role in the behavior and stability of tailings dams. Different types of granular soils significantly influence the tailings material's strength, compressibility, and permeability. This study highlights the importance of understanding the relationship between soil types and contaminant properties when analyzing solute transport through numerical modeling. Consequently, various soil types were incorporated into the initial tailings dam model to simulate contaminant transport based on solute transport analysis. The findings underscored the essential role of granular soils in contaminant dispersion within tailings dams. Finer particles, such as clay and silt, demonstrated higher adsorption capacities, which slow contaminant movement. In contrast, coarser materials, like sand and gravel, enable faster transport, increasing the potential for rapid dispersion. [ABSTRACT FROM AUTHOR]

Artificial cementation of granular soils results in improved stabilization, increased stiffness, and greater mechanical strength. The porosity index and volumetric cement content η / C i v a is presented as a key measure to study the evolution of different soil stabilization types. However, this index had not been previously studied or adjusted for sands in Colombia. Therefore, this study evaluates the applicability of the η / C i v a index on unconfined compressive strength (q u ) and stiffness ( G o ), complemented by microstructural analysis, in four sandy soils from Luruaco (Atlántico), Lorica (Córdoba), Medellín (Antioquia), and Bogotá D.C. The soils were stabilized with Type III Portland cement in dosages of 3%, 5%, 7%, and 9%, and subjected to UCS, ultrasound, and SEM-EDS tests after a curing period of 7 days. It was found that increasing cement content results in higher q u values for the samples, and higher molding density also leads to higher q u values. Additionally, the grain size distribution influenced the adjustment of parameter "a". In the sands from Bogotá and Lorica, with high uniformity, the value of "a" was 1.00. In contrast, mineralogy and particle shape played a predominant role in the sands from Medellín and Luruaco, where the coefficient of uniformity is higher, suggesting a possible inverse relationship between particle angularity and the value of "a". [ABSTRACT FROM AUTHOR]

The fabric anisotropy in granular soils is a very important character in soil mechanics that may directly affect many geotechnical engineering properties. The principal objective of this study is to develop an efficient approach for assessing the degree of fabric anisotropy as a function of grading, particles shape and weighting specifications. By assuming cross-anisotropy, the anisotropic shear stiffness values of 1042 implemented tests on 200 various sandy and gravelly soil specimens from 43 different soil types were collected from the literature. Those were combined with their corresponding void ratios, stress conditions, grading parameters, particles shape and weighting attributes to generate a global database of anisotropic shear moduli in terms of testing conditions. The magnitudes of fabric anisotropy ratio were obtained using a well-known empirical equation, and they were plotted against the relevant soil grading and particles information to examine the dependency level of this ratio to the particularities. A series of multiple regression analyses were carried out to develop a global correlation for evaluating fabric anisotropy ratio in granular soils from grading, particles shape and weighting characteristic. The results showed that reliable quantities of fabric anisotropy ratio can be estimated using the surface appearance soil specifications. The findings may serve as an appropriate technique to yield good approximations for fabric and shear stiffness anisotropies using soil grading and particle properties. [ABSTRACT FROM AUTHOR]

The coefficient of earth pressure at rest (K0) is a crucial parameter in geotechnical design. In this study, coral sands with various initial relative densities were subjected to K0 consolidation tests and consolidated-drained triaxial compression tests to investigate the impact of the relative density, stress level, and particle breakage on K0. Based on the Mohr–Coulomb failure law and experimental data, a formula for estimating K0 related to the effective stress and effective friction angle was proposed. The results revealed that the K0 of coral sand decreased with an increase in effective stresses, while the impact of the initial relative density on K0 was more obvious. At the same effective stress, the smaller the initial relative density was, the larger the K0 can be. In the tested stress range, minimal particle breakage was observed during the K0 consolidation, whereas a greater degree of particle breakage occurred during triaxial shear. This particle breakage has the potential to undermine the stress-dilatancy and interparticle locking characteristics in coral sands, leading to a diminished effective friction angle and potentially affecting K0. The proposed formula for estimating K0 can be expressed as a function of the effective stresses and effective friction angle, and the effect of initial relative density on K0 can be reflected by the function parameters. This formula provides a reasonable estimate of the K0 value for coral sand within a certain range of relative densities and stress levels. Furthermore, it demonstrates favorable applicability to other types of granular soils, such as quartz sand and rockfills. [ABSTRACT FROM AUTHOR]

The pullout capacity of horizontal anchor plates plays a crucial role in ensuring the stability and performance of various structures subjected to uplift or lateral loading. This paper presents an investigation into the pullout capacity of horizontal anchor plates using the method of stress characteristics. The method offers a simplified analytical approach that allows for quick estimations and insights into the stress distribution and failure mechanism of anchor plates. The study focuses on circular anchor plates with varying embedment ratios, considering different soil friction angles. Through computational analyses and the generation of characteristic grids, the behavior and stress distribution of anchor plates are examined. The results are compared with several experimental data from the literature to validate the applicability of the method. The findings provide valuable insights into the influence of embedment ratios and soil friction angles on the pullout capacity of horizontal anchor plates. This research contributes to the understanding of anchor plate behavior and offers a practical tool for assessing their performance in geotechnical engineering applications. [ABSTRACT FROM AUTHOR]

Quantifying the process of particle breakage is essential whenever a macroscopic investigation into the phenomenon is addressed. Some authors relate an indicator of the evolution of particle breakage, usually the surface created, to a measure of the mechanical loading. Others refer to the evolution of the particle size distribution (PSD) to better understand the problem. In this study, a shape factor of the PSD curve is used as a breakage parameter. The slope of the linear trendline of the PSD in a log-log plot was found to be reasonably representative of the shape of the PSD, for engineering granular materials. It was shown that the new breakage parameter is adapted to both well graded and uniformly graded materials, but cannot be used to describe gap-graded soils. This parameter is first studied from a micromechanical point of view, before being compared to three widely used breakage parameters: Hardin, Marsal and Einav's breakage parameters. The transition between these three parameters and the proposed parameter is provided. The main objective of this study is to allow the operation and utilisation of experimental results, which are reported in the literature through one of the available breakage parameters, or through PSD plots. [ABSTRACT FROM AUTHOR]

Fabric anisotropy is a sought-after micro index to correlate macro mechanical responses of granular materials. In this work, the discrete-element method is utilised to simulate multi-directional bender element tests in granular soils to obtain the evolution of wave velocities during drained conventional triaxial (CT) and true triaxial (TT) tests; the contact normal-based fabric is simultaneously monitored for bridging the fabric anisotropy and wave velocity anisotropy. The results show that stress-normalised wave velocities and microscopic fabric, including contact normal distribution and coordination number, remain nearly constant until a stress ratio threshold is reached. After the threshold value is reached, stress-normalised wave velocities start to decrease, especially in the minor principal stress direction, accompanied by significant adjustment of coordination number and fabric anisotropy. The results also reveal that the normalised wave velocity depends on the contact normal densities in the wave propagation and particle oscillation directions. With the contact normal distribution represented by a density function, a good linear relationship between the microscopic fabric anisotropy and macroscopic wave velocity anisotropy is obtained for both CT and TT tests. [ABSTRACT FROM AUTHOR]

This document explores the impact of particle shape on the behavior of granular materials. The authors reference previous studies and present their own experimental results to evaluate the relationship between particle shape and critical state. They find that granular soils with rounded particles have lower and less steep critical state lines compared to soils with angular particles. The authors also discuss the effect of particle shape on instability triggering and highlight inconsistencies in simulation results. The study emphasizes the importance of considering particle shape in determining the mechanical behavior of granular materials. [Extracted from the article]

To enhance our understanding of soil behavior at critical states, considering that natural soil is composed of granular matter, a quasi-static inertia number taking soil compaction into account is proposed. In analyzing classical triaxial test data of soil, the scaling law of quasi-statically deforming grains at the critical state is explored; a simple linear relationship is found between the coefficient of friction and the proposed number. This scaling law describes quantitatively the influence of initial compaction, shear rate, confining pressure, and particle size on the frictional strength of granular soils when they reach the critical state. The number proposed is employed to describe the scaling of volumetric behavior of granular soils undergoing quasi-static deformation. The difference between the particle volume fraction at the critical state and that at the initial compacted state is also found to be linearly correlated with the quasi-static inertia number, for soil at the critical state. [ABSTRACT FROM AUTHOR]

The process of permeation damage of the filling medium in the fracture is critical to the stability of the fractured rock mass. This study focused on the seepage failure process of filling materials in fractures and faults. To investigate the effects of axial stress and clay content, a series of experimental tests were conducted on internally unstable granular soil specimens with different clay contents under different axial stresses. The variations of flow rate and hydraulic conductivity were recorded and analyzed during the tests, and the typical process of seepage failure was summarized. The flow rate, hydraulic conductivity, and their growth rates were found to be smaller under high axial stress compared to low axial stress, and the flow rate of samples with higher clay content was smaller than those with lower clay content. Initially, the hydraulic conductivity decreased slightly due to clay and fine particle rearrangement, and remained nearly constant when the hydraulic gradient was small. However, as the hydraulic gradient increased, the hydraulic conductivity began to increase in response to the loss of clay and fine particles. [ABSTRACT FROM AUTHOR]

A mechanism to explain pile shaft resistance during vibratory driving is discussed. One hypothesis is that horizontally oscillating stresses temporarily reduce shaft resistance. Vibration measurements were conducted in medium-dense to dense sand during vibratory driving. A large compaction probe was installed by a vibrator with variable frequency. The driving process and ground response were documented in detail. Geophones were installed on and below the ground surface. Horizontal ground vibrations were measured at three levels below the ground surface. The difference in vibration response of the ground during driving at a high frequency (27 Hz) and at the system resonance frequency (15 Hz) showed the effect of the vibrator operating frequency on penetration speed and emitted ground vibrations. Horizontal stress pulses are emitted along the probe shaft, which can temporarily reduce static horizontal stresses acting against it. This phenomenon can explain the temporary reduction of shaft resistance and efficiency of vibratory driving in granular soils. As a result of these pulses, the horizontal stresses are increased permanently. Using a monitoring and process control system, the system resonance frequency can be determined in the field – a critical parameter for vibratory driving resistance, emission of ground vibrations and vibratory compaction of granular soils. [ABSTRACT FROM AUTHOR]

Coral sand with microbial-induced calcite precipitation (MICP) is a promising material for practical engineering. This study attempts to improve the precipitation efficiency by using a modified bio-cement method based on MICP and sodium alginate (SA). It was found that adding an appropriate amount of SA in the bacterial solution could greatly improve the ability of immobilising bacteria, thus achieving an effective precipitation of calcium carbonate on the aggregate surfaces. As the SA content increased, the weight increment and unconfined compressive strength of each sample after MICP cementation initially increased and then decreased. Three main failure modes were observed, i.e., the particle unbroken failure, stepped failure, and steep drop failure. Owing to the macro pores of coral sand, the specific loss of calcium carbonate crystals produced by MICP had a significant effect on the cementation performance, while prolonging the single soaking time could favourably reduce the crystal loss. The calcium carbonate crystals occupied part of the pores between sand aggregates, but did not change the compression strength of a single aggregate significantly. [ABSTRACT FROM AUTHOR]

The 'shear-transformation zone' (STZ), which may be referred to as a weak domain in granular material, is the main source of plastic deformations in non-cohesive soils such as sand or gravel. To theoretically investigate the vibration-induced shear resistance reduction (ViSRR) of granular materials, in this paper an extended STZ model is proposed that considers the coupling effect between vibration and quasi-static loadings. The framework of the model consists of three components: (a) the motion of STZs including the transition, creation and destruction of STZs; (b) the relation between the motion of small-scale STZs and the observable, macroscopic plastic strain; and (c) the evolution law of a 'configurational temperature' that reflects the energy that drives the motion of STZs. The conventional STZ model developed for amorphous materials is enhanced to accommodate both volumetric and shear deformations in the spatial stress state. Specifically, in addition to considering plastic shear strains induced by the change in STZ orientation as the result of the transition, as in conventional STZ models, the extended STZ model correlates plastic volumetric strains with the change in STZ amount resulted from creation and destruction. [ABSTRACT FROM AUTHOR]

Particle morphology is multi-scale in nature. To investigate the effects of particle morphology at a specific length scale on the macro–micro mechanical behaviours of granular soils, morphological gene decay and mutation was incorporated into discrete-element method (DEM) simulations through spherical harmonic-based principal component analysis. All DEM samples were subjected to axial compression and constant confining stress. The macro-scale and grain-scale behaviours of the granular assembly were investigated. It was found that particle morphology shows significant effects on macro-scale behaviours including initial stiffness, peak stress ratio, volumetric contraction and dilation, and shear band formation, as well as grain-scale behaviours including coordination number, particle rotation and granular skeleton sustaining the major contact force chains. Among the different length scales, local roundness contributes the most to stress ratio, volumetric strain and particle coordination number, while general form contributes the most to shear strain, particle rotation and fabric structure. Another interesting finding was that the particle morphological effects are well reflected in the granular skeleton sustaining the major contact force chains, which is featured with a strong variation of the degree of particle shape irregularity among different kinds of gene-mutated samples. [ABSTRACT FROM AUTHOR]

Cavity formations by soil dissolution or underground collapses are at the origin of large surface subsidence that constitutes a risk of damage or failure for infrastructures. Soil reinforcement with geosynthetics positioned at shallow depth is an economical and functional solution to reduce the induced surface settlements. Previous research has mainly focused on the load transfer mechanism and the arching effect in cohesionless reinforced backfills when the cavity opens. Experimental and numerical studies dealing with cohesive soils are very rare, although this situation is commonly found in practice. To overcome this lack of knowledge, a numerical study based on Discrete Element Modelling is carried out to better understand the load transfer mechanisms that are mobilized in cohesive embankments prone to underground cavity opening. The results are compared with experimental data obtained on a small-scale laboratory model in terms of vertical and horizontal displacements of both soil and geosynthetics. The numerical results focus on the collapse mechanisms of the cohesive embankment, the load transfer mechanisms, the shape of the vertical load distribution acting on the geosynthetic layer, the strain and traction forces within the geosynthetic sheet. • A numerical DEM model is proposed to analyse the load transfer in geosynthetic reinforced cohesive soil at the failure • The experiments and the numerical results exhibit a backfill failure mechanism as a rigid trapezoidal-shaped block of soil • Displacements and strains of the membrane show a frictional and sliding mechanism of the anchorage areas near the cavity • The membrane shows a flatness in the central part of the cavity due to the presence of the collapsed rigid block onto it. All the mechanisms are different from those observed e case of a geosynthetic reinforced granular soil addressed in the literature [ABSTRACT FROM AUTHOR]

This paper presents the optimization work to obtain the most economical of counterfort retaining wall structure with shear key attached at its base using metaheuristic method. The metaheuristic algorithm is a global optimization method that can be used to find the optimum solution of complex problems. In this research, optimization is carried out using the Particle Swarm Optimization (PSO) and Symbiotic Organisms Search (SOS) methods. This research utilizes a retaining wall sitting on stiff clay layer subjected to ten (10) m of granular soil of backfill. The scope of the study is limited to the material cost, that consists of the cost of concrete and reinforcement bars, of the counterfort retaining wall with shear key. The results show that the SOS algorithm resulted a lower cost and relatively faster in obtaining optimum retaining wall design compared to that of the PSO algorithm. [ABSTRACT FROM AUTHOR]

In landfill cover, geosynthetic packages are often used to fulfil different and simultaneous functions: drainage, waterproofing, separation, reinforcement, and soil protection. In this regard, various types of geosynthetics are combined in succession to allow for water and biogas drainage and to waterproof, reinforce, and provide protection from erosion over the useful lifetime, ranging over many decades if we consider the long phases of disposal, closure, and quiescence of the landfill itself. The creation of the composite cover barrier requires the evaluation of various interfaces' frictional strength under low contact stresses, both in static and seismic cases. The main purpose of this study is to summarize the results of past laboratory tests carried out on different geosynthetic–geosynthetic and geosynthetic–soil–geosynthetic interfaces using experimental instrumentation developed at the geotechnical laboratory of the University of Padua, which allows for the characterization of the interface geosynthetic friction at low contact stresses. The main aspects highlighted are the kinematic mode of failure, the wearing of the contact surfaces, the presence or absence of interstitial fluid, and, finally, the density level of the granular soil in contact with the geosynthetics. [ABSTRACT FROM AUTHOR]

Deep horizontal vibrocompaction is an efficient method of compacting granular soils that has been used and optimized over decades. The state of research indicates that the best possible compaction results are achieved when the vibrator operates at the natural frequency of the vibrator-soil interaction system. However, this approach proved to be unsustainable in practical application. This paper presents a concept for determining the soil response by means of the soil contact force and its phase angle and proposes that an optimized compaction is possible at the natural frequency of the soil response. The considerations are explained using a single-degree-of-freedom (SDOF) model. The admissibility of the approach is demonstrated using measured data as an example. The soil contact force and the phase angle of the soil response are evaluated for selected compaction tests. The evaluation shows that reducing the excitation frequency allows compaction close to the natural frequency of the soil response, requiring less electrical energy, shorter compaction time, and less jetted water. Approaching the natural frequency of the soil response promises to be a valuable criterion for optimizing the deep vibrocompaction process. [ABSTRACT FROM AUTHOR]

The stress–strain behavior of granular soils is related largely to their grain-size distributions and density. If sand particles are crushed under load, some basic physical and mechanical properties of sands will be changed to a certain extent, and the traditionally defined critical state is not unique in this crushing process. To describe the complex effects of particle breakage, the volumetric and shearing responses of crushable sands to compression-shear loading are attributed to the rearranging and crushing state (RCS) of sand particles. The interrelation between rearrangement and breakage of sand particles was analyzed phenomenologically as the physical basis of this study. To characterize the RCS over a large stress range, a special curve named the RCS curve is defined in the e–ln p plane and quantified through a specific loading path. A new breakage model is proposed to correlate the crushing stress with the breakage index and to control the evolution of the RCS-curve. To account for the state-dependent dilatancy of sand particles, a new state parameter called the RCS parameter is introduced into the plastic potential function. An elastoplastic model for crushable sands was established based on the evolution of the RCS and verified by relevant triaxial test data of three representative crushable sands with an initial confining pressure ranging from 50 kPa to 68.9 MPa. The stress–strain behavior, excess pore-water pressure, and accumulated particle breakage of these crushable sands were simulated satisfactorily. In addition, procedures for calibrating the model parameters are suggested to make the established model more reliable. [ABSTRACT FROM AUTHOR]

The mechanical properties of granular soils are significantly influenced by stress paths and particle breakage. In this study, a four-modulus incremental nonlinear model that incorporates the effects of the stress path and particle breakage was established based on an analysis of triaxial compression test results conducted on calcareous sands subjected to varying stress paths. A mathematical expression for this model and the process of determining its parameters was proposed. Subsequently, the model was experimentally verified. Our findings revealed that the isotropic compression consolidation volumetric strain modulus exhibited a curvilinear relationship with the average effective principal stress, whereas it demonstrated a linear correlation with the relative breakage index. Furthermore, a four-parameter nonlinear model was constructed, integrating the dilatancy equation to consider stress path effects and establishing a functional relationship between the stress ratio and shear strain. By comparing the experimental results with the calculated results for calcareous sands and rockfill materials, the model effectively simulated the stress ratio-axial strain behavior of granular soils under different stress paths. However, it failed to fully capture the volumetric strain-axial strain characteristics of granular soils after reaching the peak stress ratio. Therefore, further research is necessary to develop a more comprehensive correction method for incremental nonlinear models. [ABSTRACT FROM AUTHOR]

A great deal of research has been conducted on the performance of granular columns under vertical loads. However, in some situations, the movement of the soil mass can lead to lateral deformations and, as a result, shear stresses in the soil and columns. The primary objective of the present study is to numerically investigate the shear performance of soft clay soil improved with a single Ordinary Granular Column (OGC) in the direct shear test using a hybrid Discrete Element-Finite Difference Method (DEMFDM). The numerical modeling method was first validated by simulating a direct shear test conducted previously on a soft clay-OGC composite in the laboratory. Afterward, an extensive parametric study was conducted to determine how various factors affect the shear strength of clay-OGC composites. According to the results, increasing the area replacement ratio from 15 to 35% can increase the peak shear strength of clay-OGC composites in the direct shear test by up to two times, depending on the level of applied normal stress. The micro-scale results also indicated that the surface roughness of soil particles in OGC has a greater effect on the shear strength of clay-OGC composites than their angularity. Furthermore, the results showed that the equivalent friction angle of clay-OGC composites should be calculated based on the residual friction angle of granular soil used in OGC. [ABSTRACT FROM AUTHOR]

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The aim of the current study is to provide evidence regarding the influence of particle size on the dynamic properties in granular materials. Experiments using a resonant column (RC) device were conducted on glass beads having similar coefficient of uniformity, but four different mean grain sizes to describe the tendencies in the magnitude of Gmax and Emax. It can be clearly seen that for similar particle gradation the influence of particle size is significant, in particular for larger mean grain sizes d50 exceeding 1·5 mm. The experimental data were fitted using existing empirical relationships with corresponding fitting parameters. The fitting parameters describing the void ratio and pressure dependence to estimate maximum stiffness were found to depend on grain size to a certain extent. This influence was diminished for the materials with a d50 < 1·5 mm. It was therefore possible to use a unique set of fitting parameters for these materials with a satisfying degree of accuracy. The results were compared with some previous studies to highlight the size dependency of Gmax and Emax for materials with mean size greater than 2 mm, but also the relatively small influence on materials with lower mean particle sizes (d50 < 2 mm) is acknowledged. The results are furthermore discussed through a micromechanical interpretation highlighting why larger grain sizes influence stiffness values. [ABSTRACT FROM AUTHOR]

This study investigates experimentally the water retention behavior of granular soils from saturation to oven-dry state. The soil–water retention curve (SWRC) tests were conducted on a well-graded sand with clay using tensiometer and chilled-mirror hygrometer techniques. The soil samples were statically compacted at various water contents to different initial densities. The results showed that individual linear segments in the log–log graph could characterize the desorption process of capillary and adsorption water. A novel water retention model in a simple mathematical form was developed by conceptualizing the total water content as the sum of the suction-dependent capillary and adsorption components. The model parameters possess an unambiguous physical meaning. They can be easily calibrated based on the graphical properties of the test data using simple linear regression, which is a significant advantage over conventional SWRC models. The model was validated using the water retention data of the tested soil in this study and the available data of granular soils in the literature. The reproduced curves agree well with the experimental results. This study also analyzed the influence of compaction water content, initial density, and clay content on the capillary and adsorption components of the water retention curve. Additionally, the proposed framework provides a quick approximation method for the adsorption capacity, which plays an essential role in assessing the effective stress and the simulation of liquid film flow in unsaturated granular soils. [ABSTRACT FROM AUTHOR]

The tunnel face stability is closely related to the migration behavior and clogging mechanism of the slurry particles in granular soils, which is not yet fully understood. In this study, the coupled computational fluid dynamics–discrete element method (CFD–DEM) is adopted to investigate the infiltration behavior of slurry at the particle scale. The full Johnson–Kendall–Roberts (JKR) contact model describing interparticle behavior that accounts for cohesion present even when particles are microseparated after collisions is adopted for clay‐clay or clay‐sand particles and the Hertz–Mindlin model is used for sand‐sand particles. Through simulations, the mechanism of the slurry particle's blockage is identified as physical, frictional and cohesive modes, and slurry particle migration usually undergoes the process of aggregation‐destruction‐migration‐reassembly. Meanwhile, the influences of pressure, cohesive force, and particle shape on infiltration are also analyzed. The results indicate that high pressure lengthens the infiltration path and increases the infiltration rate. The increase in cohesion enhances the effective clogging of the sand column by the slurry, and particles with smaller sphericity are more likely to clog in the sand column. These findings may enhance our understanding of the slurry infiltration mechanism and its practical application in TBM tunneling. [ABSTRACT FROM AUTHOR]

Particle breakage plays a pivotal role in shaping the deformation behavior of granular soils when subjected to compression. To comprehensively assess the influence of particle breakage on the evolution of particle size distribution and the compression characteristics of calcareous sand, this study conducted 63 sets of confined compression tests on calcareous sand, specifically under high-pressure conditions. The results indicated that the compression behavior of calcareous sand can be classified into three distinct stages within the logarithmic coordinate system of void ratio (e) and vertical pressure (σv): (1) σv < 2.18 MPa, (2) 2.18 MPa < σv < 4.35 MPa, and (3) σv > 4.35 MPa, with the first and third stages representing linear relationships. Furthermore, the concept of yield stress ascertained within the e–logσv coordinate system proves invaluable in assessing the effects of the initial void ratio (e0) and particle size (d) on particle breakage. Notably, when σv exceeds 2.18 MPa, the relative breakage index experiences a substantial increase. The characteristic particle sizes (d10, d30, d50, and d60) of calcareous sands exhibit a consistent decrease with an increase in the relative breakage index (Br); however, this relationship is independent of e0 but is closely related to the particle size (d) of calcareous sands. The one-dimensional compression characteristics of calcareous sand are effectively represented using a power function relationship, and a formula for calculating the compression modulus (Es) of calcareous sand is theoretically derived. The deformation (Δs) of calcareous sand can be calculated using the index parameters obtained through the Es–σv curve method. In addition, a method for computing the preconsolidation pressure (pc) of calcareous sand is introduced. This method uses the parameter (eb) as an indicator of particle breakage and has been experimentally validated. [ABSTRACT FROM AUTHOR]

Internal instability establishes when fine particles of bimodal soil migrate with seepage flow into voids created by coarse fabric, altering the original gradation. The tendency for soils to undergo internal instability centres on their compaction level and particle size distribution. This study employs the discrete element method to evaluate the potential for internal instability at the particle scale. Numerical simulations enable a thorough analysis of particle contacts in soils, encompassing both internally unstable and stable conditions. The study examines particle connectivity at different relative densities and uses particle connectivity and stress reduction factor to draw clear distinctions between soils that are internally unstable and those that are stable. Grain-scale data allows for a precise measurement of the stress reduction within the finer portion of the materials. The stress distribution is observed to be influenced by the particle-size distribution, percentage of finer fraction, and relative density. The predictions of the current numerical model align with the constriction-based criterion, enhancing practitioners' confidence in a timely preliminary evaluation of soil internal instability potential. [ABSTRACT FROM AUTHOR]

The leakage gas from a buried natural gas pipelines has the great potential to cause economic losses and environmental pollution owing to the complexity of the mountainous environment. In this study, computational fluid dynamics (CFD) method was applied to investigate the diffusion law and hazard range of buried natural gas pipeline leakage in mountainous environment. Based on cloud chart, concentration at the monitoring site and hazard range of lower explosion limit (LEL) and upper explosion limit (UEL), the influences of leakage hole direction and shape, soil property, burial depth, obstacle type on the diffusion law and hazard range are analyzed. Results show that the leakage gas is not radially diffused until it reaches the ground, and the velocity of gas diffusion to the ground and the hazard range decrease as the angle between the leaking direction and the buoyancy direction increases. Triangular and square leak holes have a faster diffusion rate and a wider hazard range than circular. The diffusion rate of leakage gas in soil rises as soil granularity and porosity increase. The time of leakage gas diffusion to the ground increases significantly with the increase of burial depth, and the hazard range reduces as burial depth increases. Boulder-type obstacles will alter the diffusion path of the leakage gas and accelerate the expansion of the hazard distance, while trench-type obstacles will cause the natural gas to accumulate in the trench and form a high concentration region slowing the expansion of the surface gas concentration. [ABSTRACT FROM AUTHOR]

In order to understand the dynamics of granular flow on an erodible base soil, in this paper, a series of material point method - based granular column collapse tests were conducted to investigate numerically the mobility and dynamic erosion process of granular flow subjected to the complex settings, i.e., the aspect ratio, granular mass, friction and dilatancy resistance, gravity and presence of water. A set of power scaling laws were proposed to describe the final deposit characteristics of granular flow by the relations of the normalized run - out distance and the normalized final height of granular flow against the aspect ratio, being greatly affected by the complex geological settings, e.g., granular mass, the friction and dilatancy resistance of granular soil, and presence of water in granular flow. An index of the coefficient of friction of granular soil was defined as a ratio of the target coefficient of friction over the initial coefficient of friction to quantify the scaling extent of friction change (i.e., friction strengthening or weakening). There is a characteristic aspect ratio of granular column corresponding to the maximum mobility of granular flow with the minimum index of the apparent coefficient of friction. The index of the repose coefficient of friction of granular flow decreased gradually with the increase in aspect ratio because higher potential energy of granular column at a larger aspect ratio causes a larger kinetic energy of granular soil to weaken the friction of granular soil as a kind of velocity - related friction weakening. An increase in granular mass reduces gradually the indexes of the apparent and repose coefficients of friction of granular soil to enhance the mobility of granular flow. The mobility of granular flow increases gradually with the decrease in friction angle or increase in dilatancy angle of granular soil. However, the increase of gravity accelerates granular flow but showing the same final deposit profile without any dependence on gravity. The mobility of granular flow increases gradually by lowering the indexes of the apparent and repose coefficients of friction of granular flow while changing the surroundings, in turn, the dry soil, submerged soil and saturated soil, implying a gradually increased excessive mobility of granular flow with the friction weakening of granular soil. Presence of water in granular flow may be a potential catalyzer to yield a long run - out granular flow, as revealed in comparison of water - absent and water - present granular flows. In addition, the dynamic erosion and entrainment of based soil induced by granular flow subjected to the complex geological settings, i.e., the aspect ratio, granular mass, gravity, friction and dilatancy resistance, and presence of water, were comprehensively investigated as well. [ABSTRACT FROM AUTHOR]

Quantifying the earth pressure acting on retaining structures is essential for a number of engineering applications, including the assessment of damaged structures. In response to the widespread corrosion found in many cantilever retaining walls in Switzerland, this study investigates the evolution of the earth pressure acting on a retaining wall rotating about its base: the dominant deformation mode for such structures. In a controlled setup, a scaled cantilever retaining wall is first backfilled and then subjected to rotation about its base. An extensive experimental program was conducted to evaluate the effects of different soil properties, packing densities, and initial soil stresses on the earth pressure during the life of a wall. Accurate measurements allow the stick-slip behavior typical of granular soils to be observed. An analysis of this behavior suggests that its impact on the practical safety assessment of retaining walls is negligible. Tests performed under 3D conditions show how local damage to a section of the wall results in a lower active earth pressure value on that section due to stress redistribution, which causes an increase in pressure on adjacent sections. It is also observed how the initial earth pressure acting on retaining walls after backfilling results from a perturbed stress state due to wall deflection and wall friction. Its distribution is bilinear for uncompacted soil and nonlinear for compacted soil. Loosely packed soil exerts higher pressures than densely packed soil. The unloading process shows the expected behavior of loose and dense soil: it is slower and monotonic in loose soil and faster in dense soil, where the initial unloading is followed by reloading due to softening in the backfill. The experimental results are available in a public repository and can serve as a resource for the development and validation of improved verification procedures. [ABSTRACT FROM AUTHOR]

To predict strain localization behaviors of granular soils, the modified Cam-Clay (MCC) model is incorporated into the second-order cone programming optimized micropolar continuum finite-element method (mpcFEM-SOCP). Based on a cylindrical cavity expansion problem, a biaxial compression problem, and a rigid strip footing problem, the numerical analyses reveal that the nonphysical strain localization behaviors including mesh-dependency of shear band, rumpling, or bifurcation can be alleviated or even removed if mpcFEM-SOCP is implemented appropriately. Furthermore, the internal characteristic length in mpcFEM-SOCP is a macroscopic physical parameter that characterizes the microscopic response of soil particles and is utilized to model the shear band width. A comparison between mpcFEM-SOCP and discrete element method (DEM) is performed, and the analysis results disclose that the internal characteristic length is closely related to the median particle size, and the evolution trend of the local void ratio in the specimen predicted by mpcFEM-SOCP agrees well with that by DEM. A larger shear dilatancy, however, is generally simulated by the latter. Finally, in the undrained analysis of the rigid footing problem, the evolution curves of excess pore-water pressure predicted by standard finite-element method and mpcFEM-SOCP may differ to some extent, as they enable the observations on the interesting evolution behaviors of excess pore-water pressure. [ABSTRACT FROM AUTHOR]

The North Island of New Zealand is a region of high volcanic activity, with significant eruptions over the past. Analogous to past events, future volcanic eruptions would produce a considerable volume of ash and granular soils, covering widespread areas and raising concerns for their disposal and storage. Such deposits, primarily airfall tephra, could be potentially used in geotechnical engineering applications such as foundations, roadway embankments and land reclamations. However, before their use as structural fills can be recommended, detailed laboratory investigations of their physical, chemical, compaction, and geotechnical engineering properties (strength, compressibility, collapsibility, liquefaction potential, etc.) must be conducted. Different tephra deposits can be products of different eruptions, so chemical composition analyses can be combined with the physical, compaction, and engineering properties to characterize such deposits. Accordingly, this paper provides useful insights from physical (grain size, specific gravity, and morphology), chemical (elemental and mineralogy using X-ray fluorescence and X-ray diffraction), and compaction tests (maximum dry density, optimum water content, and particle breakage) for eleven selected volcanic tephra samples sourced from the North Island of New Zealand in the Rotorua, Taupo, and Auckland regions. [ABSTRACT FROM AUTHOR]

This study presents a novel procedure and mathematical model employing four artificial intelligence AI algorithms to predict the cumulative degree of soil compaction CDSC during dynamic compaction DC. The four AI algorithms used in this study involve artificial neural network ANN, support vector regression SVR, gradient boosting machine GBM, and random forest RF. Input variables involve the average SPT N value Nini before dynamic compaction, cumulative applied energy normalized with a cross-sectional area of tamper Ea, and the number of the tamper drops Ndrops. Apart from cross-validation with a testing set, additional in situ test data gathered from a different section within the study site are used to assess the generalization capacity of the AI models. In addition, out-of-distribution analyses for the four AI algorithms are conducted in the context of parametric studies. The CDSC prediction performance for the four AI models leads to high prediction metrics of accuracy with the r2 greater than 0.9 for the testing scenario while the r2 of the other AI models is greater than 0.9 when out-of-sample data are considered except for the GBM. The ANN appears to be the best model as the parametric study takes into account out-of-distribution data and suggests a robust relationship between input variables and CDSC that is more coherent with engineering principles for DC. Finally, the ANN model is utilized to develop a new mathematical model for CDSC prediction. [ABSTRACT FROM AUTHOR]

Suction stress is one of the most significant factors affecting the serviceability and stability of soil structures. This study presents a framework for analyzing the stability of geosynthetic reinforced soil (GRS) walls and slopes under unsaturated conditions. An analytical formulation of suction stress-based effective stress was implemented into a limit equilibrium solution, namely, the top-down procedure. The developed framework enables the prediction of the tensile load distribution and connection load between the reinforcement and wall face considering the pullout resistance of reinforcements in GRS walls backfilled with granular and marginal soils under unsaturated conditions. The applicability of the framework was demonstrated by providing an illustrative example followed by three series of parametric studies to understand the effects of pore size distribution, air entry pressure, and infiltration rate on the performance of an unsaturated GRS wall. The results quantify the impact of suction, showing that as it increases, the maximum tensile loads and connection loads decrease while pullout resistance increases. Mostly affected by the suction effect are upper reinforcement layers, where combined effects of reduced tensile load and increased pullout resistance decrease connection load and reinforcement length requirements. The current study strongly discourages counting on the contribution of suction for the design of new GRS walls. The suction value cannot be accurately and reliably determined for the entire lifespan of the GRS wall, and it may decrease or diminish in an uncontrolled and random manner under infiltration. However, by quantifying the effect of suction, the proposed framework in this study provides a valuable tool for analysis purposes, enabling a rigorous interpretation of field-measured reinforcement loads during wall service as well as evaluation of the forensics of failed GRS walls. [ABSTRACT FROM AUTHOR]

In this paper, the numerical study of the ultimate bearing capacity (UBC) of two closely spaced strip footings on granular soil is investigated using the finite element method (FEM) and upper bound limit analysis (UBLA). Although the UBC of two adjacent footings has previously been studied in other experimental and numerical research, in all the previously reported studies, the footings were not allowed to rotate and move horizontally freely. Due to the deformation of the soil medium, two closely spaced footings are subjected to horizontal movements and tilting, even under central vertical loads. When the two adjacent footings are not permitted to rotate and move in the horizontal directions, the unwanted bending moment and horizontal force act on the footings. Indeed, the UBC of two closely spaced rough footings is evaluated under incorrect constraints in earlier research. In the present research, the UBC of two adjacent rough footings is evaluated with and without these incorrect constraints. The key finding of this study is that constraining the horizontal and rotational movement of the foundation artificially increases the UBC, which does not reflect field conditions. When foundations are permitted to rotate and move horizontally, there is no increase in UBC; however, there is an increased risk of differential settlement and structural instability. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study investigating the effect of particle shape of granular soils on the shear strength characteristics via direct shear tests. Thirty direct shear tests were conducted on spherical and crushed sand mixtures with different proportions (i.e. 0%, 25%, 50%, 75% and 100%). The overall regularity (OR) parameter of sand particles varies between 0.788 and 0.909, fairly reflecting the particle shape of sand mixture. A particular relation between OR and maximum shear strength was found, namely that maximum shear strength increases with a decrease in OR. Furthermore, a gradual increase was observed in the improvement factor (If) due to geotextile reinforcement with an increase in OR except for S25C75, representing 25% spherical and 75% crushed sand, at high and low normal stress levels (i.e. 29 kPa and 116 kPa). The interfacial friction angle (ϕ) of sand mixtures is improved by geotextile reinforcement. Additionally, geotextile reinforcement caused an apparent increase in ϕ with decreasing OR values. [ABSTRACT FROM AUTHOR]

The biological world serves as a vast reservoir of inspiration for human innovation, particularly in the realm of robotics designed to navigate intricate granular environments. Among these creatures adept at burrowing, the mole stands out due to its exceptional body structure and unparalleled efficiency, surpassing most engineering burrowing systems. Consequently, the mole serves as an ideal model for designing highly efficient burrowing robots. This study introduces a mole‐inspired robot burrowing with forelimbs, specifically designed for planetary soil exploration. By closely examining the distinctive body morphology of moles, a forelimb burrowing mechanism is devised through biomimetic mapping, and its kinematics is thoroughly analyzed. A robot prototype is developed and an experimental setup is constructed to evaluate its burrowing performance. A series of tests are conducted to assess the capabilities of the robot, including forelimb burrowing, robot crawling, and robot burrowing. The results demonstrate that the proposed mole‐inspired burrowing robot is capable of crawling and burrowing to a certain depth using its forelimbs. Although it exhibits some upward displacement, this issue can be mitigated by modifying the head configuration and adjusting the forelimb posture to effectively overcome the vertical stress and lift force exerted by granular soils due to intensity gradient. [ABSTRACT FROM AUTHOR]