Granular Soils Research Articles

Safety Factor and Settlement Analysis of Borepile Foundation in Warmadewa Gianyar Hospital Building

Building structure planning must be distinct from foundation structure planning. The foundation plays an important role in transferring building loads to the ground. The Warmadewa Gianyar Hospital building consists of 5 floors with a building area of 8323. 471 m2 on a granular soil location where there are three layers of soil types, namely sandy silt soil, silty sand, and sand mixed with rock grains. The Borepile foundation is installed at a depth of 12 m with an N SPT value of 60. This building carries dead loads, live loads, rain loads, wind loads, and earthquake loads. This building will use a bore pile foundation by modeling bore pile piles in GEO5 software to obtain safety factor values and installed reinforcement. Based on the analysis results, the pile diameter used is 450 mm and has a length of 12 m. The analysis obtained the carrying capacity with a safety factor of 2.1> 2 and a maximum settlement of 4.77 mm.

Study on the depth of cantilever sheet pile wall based on the type of soil where sheet pile embedded

The northern part of Semarang is known as a region having a thick depth of soft clay. In the construction of sheet pile wall for Terboyo Retention Pond dike Semarang must take into account stability aspect and financial aspect. The characteristic of granular soil is different from that of cohesive soil, and the stability aspect relies on the type of soil. This study aims to investigate the influence of the type of soils where sheet pile embedded to the theoretical depth of cantilever sheet pile wall. This research used the soil data from Terboyo Retention Pond of Semarang. Modelling of wall was differentiated based on the type of soil where sheet pile embedded whereas the type of soil above the dredge line was the same. Two type of soils where sheet pile embedded, clay and sand were modelled. The variation of soil parameters of both soils was also modelled. Safety factor for clay soil was taken 1.5. The result shows that different soil in which wall embedded give significant difference of length of sheet pile. Based on N-SPT, with the same N-SPT value theoretical depth of cantilever sheet pile wall in sand soil is deeper than that of in clay soil.

Predicting the precipitated calcium carbonate and unconfined compressive strength of bio-mediated sands through robust hybrid optimization algorithms

Biological soil stabilization through Microbial-Induced Calcite Precipitation (MICP) demonstrates the potential to be an eco-friendly and sustainable approach to enhance the strength properties of cohesionless granular soils. In this study, based on a comprehensive set of experimental data compiled from literature, the amounts of Precipitated Calcium Carbonate (PCC) and Unconfined Compressive Strength (UCS) of MICP-treated sands are estimated through hybridizing Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) models with metaheuristic algorithms. During the data extraction procedure, a total of 70 and 115 datasets are used to predict the PCC and UCS, respectively. Accordingly, five key features of urea concentration (Mu), calcium chloride (Mcc), optical density of bacterial suspension (OD600), pH and total volume of injection per volume of sample (Vt), are first selected as the inputs of the hybrid models to estimate the amount of calcium carbonate precipitation within the porous structure of MICP-treated granular medium. The experimental data on the PCC along with the basic characteristics of the host sand including mean grain size (D50), uniformity coefficient (Cu) and void ratio (e), are then adopted as the inputs of the numerical models in the second phase whilst the UCS of bio-mediated sands is set as the output. The performance and accuracy of implemented models are rigorously assessed through analyzing various statistical indices and performance criteria. According to the numerical analysis, the ANN-PSO and ANFIS-PSO hybrid models show the best performance in predicting PCC and UCS of bio-mediated sands, respectively. Using the well-established Gene Expression Programming (GEP) algorithm, practical correlations are developed to predict the PCC and UCS values of MICP-mediated soils based on the characteristics of biological binding agents as well as the host material. The Machine Learning (ML)-based models presented in this study provide engineers with a fruitful framework for the rough and preliminary estimation of the amount of calcite precipitation as well as the UCS of bio-mediated sands in the field prior to stabilization and performing complementary tests.

Effective thermal conductivity of granular soils: a review of influencing factors and prediction models towards an investigation framework through multiscale characters

The effective thermal conductivity of soil is important to geo-engineering applications, and it is controlled by factors across different length scales. Through a comprehensive review of these factors, we found that while other more traditional factors have been well studied, there is still a lack of characterisation of soil microscale and mesoscale structures and their influence on effective thermal conductivity. In addition, after reviewing the models available in the literature for soil effective thermal conductivity prediction, it was found that compared with empirical and theoretical models, machine learning models can account for the influence of multi-scale factors; however, research into them is scarce. To overcome the limitations of previous research, we proposed a framework that can investigate the factors influencing soil effective thermal conductivity at multiple scales. It includes the impact of soil structural factors at micro to mesoscale, and this impact is integrated with the influence from other factors for accurate thermal conductivity prediction.

Dynamic response of piles embedded in granular soil to lateral impacts

Soil-embedded vehicle barriers, such as W-beam guardrail systems, play a pivotal role in transportation safety, mitigating the risks associated with vehicular collisions with roadside hazards. The efficacy of these barriers greatly depends on the pile-soil system's kinetic energy dissipation capability during vehicular impacts. However, a comprehensive understanding of how soil strength, embedment depth, and impact velocity collectively govern the dynamic behavior of the pile-soil system remains a gap in current research. This study explores the dynamics of lateral impacts on piles embedded in various granular soils. The process of dynamic lateral impact and interaction between the pile and the soil was modeled using the Updated Lagrangian Finite Element Method (UL-FEM). A damage-based element erosion algorithm was incorporated into the model to accommodate severe mesh distortions and element entanglements of the soil material brought by the pile impact. Validation against well-documented large-scale physical impact tests ascertained the model's fidelity. Our findings elucidate the significant differences in resistive forces between piles in strong versus weak granular soils – notably, the former exhibited resistive forces roughly double their weaker counterparts under equivalent embedment depths and varied impact velocities. Intriguingly, a stiff pile in weak soil necessitates nearly double the embedment depth to match the energy dissipation of its strong-soil counterpart. Furthermore, the study discerned consistent depth of rotation point ranges for piles embedded in distinct soil strengths, regardless of embedment depth and impact velocity.

Mole‐Inspired Robot Burrowing with Forelimbs for Planetary Soil Exploration

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.

Numerical study on the shear strength of granular materials under the low confining pressure

The relationship between stress and strength in granular soil differs under low confining pressure as compared to high confining pressure, which is of great importance for the geotechnical engineering. Numerical simulations using discrete element method (DEM) are conducted to model consolidated-drained triaxial compression tests, with the confining pressure σc ranging from 1 to1000 kPa. From the analysis of the shear strength of granular soils under various confining pressures and void ratios, it is found that the peak stress ratio ηp under a low σc is significantly lower than that under the high σc, particularly for samples with the same initial void ratio. As the confining pressure increases, ηp for samples with the same initial void ratio increases up to 29 % under the low σc while stabilizing under the high σc. Conversely, ηp for samples with the same void ratio after the consolidation can increase up to 13.5 % under the low σc while declining under the high σc. In addition, the critical confining pressure distinguishing the low and high confining pressures is about 200 kPa for dense samples with initial void ratio of 0.605 used in the study, and it increases as the sample void ratio increases. From the microscopic analysis, the variation of ηp under the low σc can be attributed to the enhanced anisotropy of normal contact force and contact normal under the low confining pressure. Finally, a modified Mohr-Coulomb failure criterion is proposed, which can determine the strength of granular soils under the low confining pressure with different void ratios.

A comprehensive numerical investigation of multi-scale particle shape effects on small-strain stiffness of sands

The effects of multi-scale particle shape characteristics on the small-strain stiffness of granular soils remain controversial. This study revisits this topic using well-calibrated three-dimensional discrete-element simulations incorporating a particle roughness–embedded contact model and particles of realistic shape. Based on the numerical simulation results, the multi-scale particle shape effects on the small-strain stiffness of sands and the magnitude of Hardin's equation parameters are systematically investigated, and the underlying micro-mechanisms are also thoroughly explored. Results indicate that the small-strain stiffness increases with the increase of particles’ overall irregularity due to the increased mechanical coordination number, but decreases with the increase of particle surface roughness because of the decreased contact normal stiffness. In addition, the constant term parameter and void ratio term parameter of Hardin's equation increases and decreases linearly, respectively, with the particles’ overall regularity, but reduces and grows with the particle surface roughness, respectively. Furthermore, the stress exponent is almost unchanged with the particles’ overall regularity, but increases with the particle surface roughness, which determines the relative proportions of contacts under asperity-dominated, transitional and Hertzian stages. The study helps to advance the cross-scale understanding of multi-scale particle shape information in relation to small-strain stiffness of sands.

Shear Strength and Consolidation Behaviour of Kaolin Clay Reinforced with a Granular Column Backfilled with Crushed Waste Glass

Granular columns are commonly used for ground improvement. However, minimal research is presently available on the effect of backfill particle size on the geotechnical performance of granular column-reinforced soil. Geo-environmentally, using crushed waste glass (CWG) as a sustainable replacement for depleting traditional construction sands could offer a cleaner feedstock to backfill granular columns while helping recycle growing stockpiles of waste glass, potentially supporting the circular economy transition and decarbonisation of the construction industry. Given these multi-pronged motivations, this study investigated the shear strength and consolidation behaviour of kaolin reinforced with a CWG granular column. Three different particle size ranges (PSR) of CWG were discretely used to install a granular column in the kaolin bed, including fine (0.50–1.0 mm), medium (1.0–1.7 mm) and coarse (1.7–3.35 mm) particles with median particle sizes of 0.78 mm, 1.42 mm and 2.30 mm, respectively. The geocomposite containing a medium CWG column showed the highest increase in friction angle, increasing from 14.0° for kaolin only specimens to 20.7° for the geocomposites. Similarly, the consolidation behaviour of reinforced kaolin (geocomposites) was typically superior to that of kaolin only specimens. Notably, installing a coarse, medium or fine CWG column decreased the average compression index (Cc) of the geocomposites by almost 17%, 35% or 50%, respectively, compared to that of the kaolin only specimens. Given the promising results of this initial study, some suggestions are provided for future studies on assessing the application of CWG as an alternative backfill and sustainable geomaterial in granular column construction.Video abstractThis internationally-partnered Video highlights the findings of the research study, indicating that crushed waste glass (CWG) could potentially serve as a sustainable geomaterial and be used as a replacement for traditional construction sand to backfill granular columns in clayey soils for ground improvement, helping reduce the unsustainable exploitation of sand resources and increasing waste glass recycling, potentially supporting the paradigm shift to a circular economy and contributing to decarbonisation of the construction industry.EwdaqE4KyyTKvkX4_pnUt6Supplementary material 1 (MP4 3737519 kb)

Physical, Chemical and Compaction Characteristics of Slightly Weathered Tephras of New Zealand

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.

Determination of the size of representative volume element for gap-graded granular materials

Gap-graded granular soils have a wider grain size distribution and more heterogeneous fabric structure than normal soils. It is critical to choose the sample size of element tests in a faithful and repeatable manner. The Discrete Element Method (DEM) is utilized to determine the size of representative volume element (RVE) of gap-graded mixtures with varying particle size distributions. Over seven hundred triaxial tests are performed to investigate the effect of particle size ratio and coarse fraction on the typical RVE size. Microscopic parameters are analyzed to validate the reproducibility of the determined RVE sizes. The optimal RVE size is negatively proportional to particle size ratio and positively correlated with the coarse fraction. Empirical equations are further established to correlate the RVE sizes with particle size ratios for different coarse fractions. The findings may provide a useful reference for experimental and numerical studies in choosing the RVE size for gap-graded soils.

Micromechanical analysis of pipeline-soil interaction in unsaturated granular soil undergoing lateral ground movement

The micro- to macro-scale pipeline-soil interaction mechanism in unsaturated granular soil remains unclear. This study investigates the unsaturated suction effect on the pipeline-soil interaction undergoing lateral ground movement using coupled discrete element method and finite element method (DEM-FEM) simulations. The Johnson-Kendall-Roberts (JKR) adhesive model was used to simulate the interparticle suction while the pipe segment was simulated with finite element meshes. The findings reveal that discontinuity and large deformation occurrences in unsaturated sandy soil in model tests can be successfully modelled by the DEM-FEM method. Besides, the interparticle suction effects on contact forces, particle collision behaviours, and special soil pressure distributions near the pipeline-soil interfaces were discovered and successfully explained. Additionally, progressive soil deformation and failure behaviours in dry and unsaturated soils were compared while the partial similarity between the suction effect and buried depth effect on pipeline-soil interaction was discussed. Finally, several conclusive pipeline-soil interaction failure patterns in different interparticle-suction conditions were identified after analysing a series of particle-scale behaviours including particle trajectories, particle contacts, and particle rotation distributions. The study indicated that neglecting the unsaturated effect can result in severely underestimating the intensity of pipeline-soil interaction and misjudging the soil failure patterns.

A graph-based approach for modeling the soil–water retention curve of granular soils across the entire suction range

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.

X-ray CT quantification of in-situ fabric evolution and shearing behaviour of granular soils of different particle shapes

The role of particle shape on soil mechanical response has been studied extensively especially through numerical means. The underlying micro-mechanics of how particle shape may affect the soil mechanical responses at element scale remains unclear. Systematic micro-mechanical 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, 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 di-rection. 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 cor-relations with critical-state parameters than by local descriptor.

A fracture-based discrete model for simulating creep in quartz sands

Creep of granular soils is frequently accompanied by grain breakage. Stress corrosion driven grain breakage offers a micromechanically based explanation for granular creep. This study incorporates that concept into a new model based on the discrete element method (DEM) to simulate creep in sands. The model aims for conceptual simplicity, computational efficiency and ease of calibration. To this end a new form of normalized Charles power law is incorporated into a DEM model for rough-crushable sands based on the particle splitting technique. The model is implemented using a controlled on-off computational strategy. The model is validated by simulating creep in quartz sands in oedometric and triaxial conditions. Model predictions are shown to compare favourably with experimental results in terms of creep strain, creep strain rates and particle breakage. The model proposed would facilitate the calibration of phenomenological continuum models, but may be also useful to directly investigate structural scale phenomena, such as pile ageing.

Modelling rapid non-destructive test using light weight deflectometer on granular soils across different degrees of saturation

This study introduces an advanced finite element model for the light weight deflectometer (LWD), which integrates contact mechanics with fully coupled models. By simulating LWD tests on granular soils at various saturation levels, the model accurately reflects the dependence of the LWD modulus on dry density, water content, and effective stress. This model addresses and overcomes the limitations of previous finite element models for this specific problem. Simultaneously, this research presents the first experimentally validated fully coupled contact impact model. Furthermore, the research provides a comparative assessment of elastoplastic and nonlinear elastic models and contrasts an enriched node-to-segment method (developed in this study) with the more precise mortar technique for contact mechanics. These comparisons reveal unique advantages and challenges for each method. Moreover, the study underscores the importance of careful application of the LWD modulus, emphasising the need for sophisticated tools to interpret soil behaviour accurately.

Investigations of bioinspired soil penetration strategies via a numerical model: Does radial expansion improve soil intruder performances?

This paper investigates the performances shown during underground exploration by a plant root-inspired soil intruder. Plant roots are efficient soil explorers, moving by growing at their apical extremities and morphing their bodies in response to mechanical constraints. A three-dimensional (3D) discrete element model (DEM) was developed to mimic selected features of plant roots and verify their usefulness in soil penetration operations. Specifically, the model is used to simulate the penetration of an intruder that grows at the tip into both cohesionless granular and cemented soils. In the former case, dense and loose granular media are considered. The model is adopted to compare penetration performances with purely axial growth and a combination of radial and axial growths. Radial growth is hypothesized to be adopted in roots to facilitate soil penetration. Results from our model suggest that implementing a radial growth preliminary to an axial growth is more advantageous in cohesionless dense granular soil, reducing the soil resistance experienced by the intruder for deeper penetration after radial enlargement. When the penetration occurs in cemented soil, the radial expansion results advantageous over a lower penetration depth, and its beneficial effect drops with increasing inter-particle contact adhesion values. The proposed 3D DEM numerical model provides a methodology for evaluating the intruder penetration efficiency and supports the design of artificial robotic systems for the autonomous exploration of soil by allowing the selection of the most performant penetration strategies for their artificial implementation.

Effect of initial fabric anisotropy on cyclic liquefaction behavior of granular soils using discrete element method

Effect of initial fabric anisotropy on cyclic liquefaction behavior of granular soils using discrete element method

Numerical simulation of the critical hydraulic gradient of granular soils at seepage failure by discrete element method and computational fluid dynamics

Seepage failure is a common problem in engineering, and the calculation and analysis of critical hydraulic gradient are of great significance for the safety and protection of engineering. Based on the principle of discrete element method and computational fluid dynamics, the fluid–solid coupled models were established to study the critical hydraulic gradient and particle loss rate of granular soils at seepage failure. The evolution of seepage failure was divided into four stages: seepage development stage, local damage stage, volume expansion stage and overall damage stage. The validity of numerical simulation was demonstrated by comparing the critical hydraulic gradient obtained by numerical simulation and by Terzaghi’s formula. According to the fabric damage and flow velocity variation of the models at seepage failure, the influences of model size and particle size on the critical hydraulic gradient and particle loss rate were analyzed. The results indicate that critical hydraulic gradient and particle loss rate were not sensitive to changes in model size. A wide particle size distribution range resulted in large critical hydraulic gradient and small particle loss rate at seepage failure. The discrete element numerical simulation can not only be used to determine the critical hydraulic gradient of geotechnical and hydraulic engineering, but also offer a visual portrayal of the evolution of seepage failure, serving as an important complement to comprehend the intricate microscopic mechanisms underlying soil seepage failure.

Deep transfer learning-aided constitutive modelling of granular soils considering out-of-range particle morphology

Based on a large discrete element method (DEM) simulation database, a novel data-driven constitutive model of granular soils was established using the long short-term memory (LSTM) neural network. The excellent training and testing results reflect the superiority of LSTM in the constitutive modelling of granular soils under loading. Based on the previous study, twelve new samples with out-of-range particle morphology were generated to test the model extrapolation ability. It is found that the LSTM-based model has poor extrapolation ability with notable predictive differences when out-of-range input parameters are utilised. In light of this deficiency, deep transfer learning (DTL) is adopted to transfer the pre-trained model to the new out-of-range database quickly. The excellent training and testing results show that the DTL-LSTM can accurately predict cases with out-of-range particle morphology. DTL-LSTM is further compared with a newly trained LSTM model using the extended database, and an overall good agreement is obtained except for some slight differences of volumetric strain at small axial strains. Given the drastically reduced computational costs and the excellent predictive performance, DTL-LSTM is deemed to be suitable and competent in the constitutive modelling of granular soils with out-of-range data.