Initial Soil Density Research Articles

Study on the effect of ground stratification on heat transfer of vertical ground heat exchangers in lateritic clay areas

The potential effect of ground stratification on the efficiency of ground heat exchangers (GHEs) in lateritic clay regions remains unclear. Model experiments were conducted to investigate the effects of soil dry density, water content, and ground stratification on the heat exchange between GHEs and the surrounding lateritic clay. A 3D numerical model accounting for ground stratification was proposed and validated using experimental data. The model further examined the influence of soil moisture on the dynamic heat exchange process. The findings of the model experiments indicate that the heat from buried pipes increase soil temperature by 12.8 % when the initial water content of lateritic clay (with dry density of 1.1 g/cm3) rises from 5 % to 28 %. Raising the dry density from 1.1 to 1.3 g/cm3 at 28 % water content results in a 7.5 % temperature increase. The initial soil moisture and density have negligible effects on the temperature gradient within 18 cm of the geothermal pipes. The temperature increased faster in the sand layer than in the lateritic clay layer owing to the difference in thermal properties. The impact of heat produced by GHEs on the temperature field in homogeneous soil layers differs considerably from that in stratified soil layers. The 3D numerical model provided a good fit for the measured soil temperature in the stratified soil layer, including the soil temperature variation at the layered interface. The simulation results showed that for dry and saturated strata, the temperature of the lateritic clay around the GHEs increased with increasing initial stratum moisture. For unsaturated lateritic clay strata, because of the possible impacts of moisture and heat coupling migration, the temperature of the stratum around the GHEs first increased and subsequently decreased as the initial stratum moisture was enhanced.

Estimating Shear Strength of Marine Soft Clay Sediment: Experimental Research and Hybrid Ensemble Artificial Intelligence Modeling

In the design of offshore engineering foundations, a critical consideration involves determining the peak shear strength of marine soft clay sediment. To enhance the accuracy of estimating this value, a database containing 729 direct shear tests on marine soft clay sediment was established. Employing a machine learning approach, the Particle Swarm Optimization algorithm (PSO) was integrated with the Adaptive Boosting Algorithm (ADA) and Back Propagation Artificial Neural Network (BPANN). This novel methodology represents the initial effort to employ such a model for predicting the peak shear strength of the soil. To validate the proposed approach, four conventional machine learning algorithms were also developed as references, including PSO-optimized BPANN, Support Vector Machine (SVM), BPANN, and ADA-BPANN. The study results show that the PSO-BPANN model, which has undergone optimization via Particle Swarm Optimization (PSO), has prediction accuracy and efficiency in determining the peak shear performance of marine soft clay sediments that surpass that offered by traditional machine learning models. Additionally, a sensitivity analysis conducted with this innovative model highlights the notable impact of factors such as normal stress, initial soil density, the number of drying–wetting cycles, and average soil particle size on the peak shear strength of this type of sediment, while the impact of initial soil moisture content and temperature is comparatively minor. Finally, an analytical formula derived from the novel algorithm allows for precise estimation of the peak shear strength of marine soft clay sediment, catering to individuals lacking a background in machine learning.

Correlation of Initial Soil Density and Maximum Soil Density Under Drying-Wetting Cycles and Their Soil Erodibility

Correlation of Initial Soil Density and Maximum Soil Density Under Drying-Wetting Cycles and Their Soil Erodibility

Evaluating influences of deposition direction and state-dependence on large deformation processes of granular column collapse

This paper examines the impacts of deposition direction and density of granular soils on their large deformation behavior encapsulated by column collapse processes. We combine a critical state-based, anisotropic constitutive model for sand and material point method (MPM). The constitutive model includes state- and fabric-dependent dilatancy and hardening, thus accounting for the effects of density and deposition direction on the mechanical behavior of soils. The MPM model is first validated against experimental results. We then investigate the fundamental connections between local constitutive properties of soils (e.g., friction and dilation) and global column collapse response. Based on these correlations, this work further studies how material density and deposition direction influence collapse behavior, including run-out distance, residual height, and slope angle of the static region. Results indicate that run-out distance is relatively insensitive to initial soil density but can be significantly altered by the deposition direction of soils. Peak run-out distance is observed as the deposition direction is aligned with sliding band formed within the granular column. Moreover, a higher density or a smaller inclination of deposit direction leads to a greater residual height and a steeper slope of the static region. The mechanisms of above effects from soil properties perspectives are discussed.

Volume Contraction in Shallow Sediments: Discrete Element Simulation

Displacements induced by mineral dissolution and subsurface volume contraction affect overlying soils. In this study, we examine the consequences of mass loss or volume contraction at shallow depths using a discrete element method. The goal of the study is to identify particle-scale and global effects as a function of the relative depth of a dissolving inclusion, initial soil density, and granular interlocking. There are successive arch formation and collapse events, and a porosity front propagates upwards as grains slide down to refill the space. Grains around and within the refilled cavity are loosely packed and have small contact forces that are sufficient to avert the buckling of granular arches that form around the dissolving zone. Denser packings and interlocking combine to exacerbate rotational frustration and lead to more pronounced force chains along granular arches, looser fill, and reduced surface settlement. In fact, surface settlement vanishes, and the sediment hides the localized dissolution when deep inclusions z/D ≥ 5 dissolve within dense sediments. While scaling relations limit the extrapolation of these numerical results to tunneling and mining applications, macroscale trends observed in the field resemble results gathered in this study.

Field tests of the experimental installation for soil processing

The subject of the study is the parameters of the soil crumbling, depending on the rotation frequency of the rotor of the soil treatment installation under different initial parameters of moisture and density of the soil structure. Field tests of an experimental soil tillage installation with a loosen-separating device have been carried out. In order to determine the value of the soil crumbling, depending on the rotor rotation frequency of the grinding and separating device of the soil tillage installation, different mathematical models of soil crusting were obtained at different initial humidity and soil density parameters. The object of the study is the influence of the investigated factors on the soil crumbling. The effective grinding of soil with a soil cultivating installation with a wide range of initial parameters of the density of the structure and the moisture content of the surface layer of soil was revealed, increasing the rotor speed increased with adverse parameters of density and soil moisture. In variants with increased parameters of the density of the structure (1,3–1,4 g/cm3) after the passage of guns managed to get a sowing layer with a satisfactory content of agronomic useful lumps. The target group of information consumers in the article - designers, specialists who are engaged in the development of soil working working bodies.

Imaging local soil kinematics during the first days of maize root growth in sand

Maize seedlings are grown in Hostun sand with two different gradings and two different densities. The root-soil system is imaged daily for the first 8 days of plant growth with X-ray computed tomography. Segmentation, skeletonisation and digital image correlation techniques are used to analyse the evolution of the root system architecture, the displacement fields and the local strain fields due to plant growth in the soil. It is found that root thickness and root length density do not depend on the initial soil configuration. However, the depth of the root tip is strongly influenced by the initial soil density, and the number of laterals is impacted by grain size, which controls pore size, capillary rise and thus root access to water. Consequently, shorter root axes are observed in denser sand and fewer second order roots are observed in coarser sands. In all soil configurations tested, root growth induces shear strain in the soil around the root system, and locally, in the vicinity of the first order roots axis. Root-induced shear is accompanied by dilative volumetric strain close to the root body. Further away, the soil experiences dilation in denser sand and compaction in looser sand. These results suggest that the increase of porosity close to the roots can be caused by a mix of shear strain and steric exclusion.

Shallow strip foundations subjected to earthquake-induced soil liquefaction: Validation, modelling uncertainties, and boundary effects

Despite recent advancements in predicting the response of shallow strip foundations during earthquake-induced liquefaction, significant modelling–related uncertainties remain, which are the focus of this paper. The problem is analysed through coupled hydromechanical analyses, employing an advanced constitutive model. The model is calibrated based only on the initial void ratio, and then validated against 6 centrifuge model tests, conducted at the University of Cambridge. Through a strict validation procedure, based on pore pressures, settlement and rotation time histories, as well as deformation mechanisms, the strengths and weaknesses of the numerical model are identified. It is shown that final settlement and rotation can be predicted with adequate accuracy, but more work is needed to achieve accurate predictions of settlement rate, maximum rotation, and pore pressures in the vicinity of the foundation. The numerical model is then used to investigate key modelling uncertainties. After revealing the sensitivity to initial soil density and to parasitic vertical acceleration, the effects of the centrifuge model container and of the distance of lateral model boundaries (L) are parametrically investigated. Boundary effects are minimized with a laminar container, where a normalized boundary distance L/DL≥1 is shown to be adequate for all liquefiable layer depths (DL) examined. The use of a rigid container is proven problematic, as it always imposes an unrealistic wave propagation pattern. The use of Duxseal inclusions offers a major advantage, allowing accurate reproduction of foundation settlement even with L/DL≥1, a key conclusion for the design of centrifuge tests.

Vibro-fluidization of sand under coupled static loading and high-frequency cyclic loading

An increase in the operation speed of high-speed trains often leads to an increase in the loading frequency on subgrade soil. Hence, the long-term dynamic behavior of the subgrade and the service performance of high-speed tracks are affected. To determine the stress–strain characteristics of granular soil under high-frequency loading, a triaxial test setup was modified to investigate the effects of loading acceleration and duration, water content, vibration frequency, cell pressure, and initial soil density. The experimental results indicate that there are reductions in axial stress and volumetric strain during high-frequency loading. The reduction in axial stress is as high as 40%, and that of volumetric strain, which is permanent, could approach 0.1%. The stress reduction, strain compression, and excess pore pressure are found to vary linearly with vibration acceleration when a/g > 0.02, where a is vertical vibration acceleration and g is gravitational acceleration. The reduction in strength and strains are found to depend on the loading acceleration and effective cell pressure, but independent of the loading duration, water content, frequency, and initial density. A threshold acceleration a = 0.02g is observed, below which the changes in the shear strength and volumetric strain induced by vibration are negligible. At high vibration acceleration, the strain amplitude could increase, eventually leading to a collapse of the specimen.

Soil behaviour under load in case of finite thickness

Abstract This study intends to examine the soil behaviour in the case of finite thickness, represented by the hard layer under a soft layer of soil. A further aim is to define load-bearing capacity parameters (n and k). The experimental work is carried out under laboratory conditions by using hydraulic bevameter to apply the load. A circular plate with a diameter of 100 mm is used to push down the load over the targeted area with a penetration rate of about 9 cm/min for sinkage plates. The study was conducted in a soil bin (length of 200 cm, width of 100 cm and variable thickness) using a sandy loam soil. First, the study has been done with loose soil with a thickness of 11 cm, which maintained with 10% moisture content and initial density of 1.190 g/cm3. After that, a two thickness of 6 and 18 cm with 8% moisture content and initial soil density of 1.375 g/cm3 were tested to explain the effect of thickness. In each test, the bevameter plate was loaded at multiple locations, the result showed the soil was near uniform. The result suggests that it is not easy to obtain one equation for the load bearing capacity because the layer near to the surface behaves like soil with infinite thickness and the deeper layer like soil with finite thickness.

Numerical modelling of granular column collapse using coupled Eulerian–Lagrangian technique with critical state soil model

PurposeCurrent modellings of granular collapse are lack of considering the effect of soil density. This paper aims to present a numerical method to analyse the collapse of granular column based on the critical-state soil mechanics.Design/methodology/approachIn the proposed method, a simple critical-state based constitutive model is first adopted and implemented into a finite element code using the coupled Eulerian–Lagrangian technique for large deformation analysis. Simulations of column collapse with various aspect ratios are then conducted for a given initial soil density. The effect of aspect ratio on the final size of deposit morphology, dynamical collapse profiles and the stable region is discussed comparing to experimental results. Moreover, complementary simulations with various initial soil densities on each aspect ratio are conducted.FindingsSimulations show that a lower value of initial density leads to a lower final deposit height and a longer run-out distance. The simulated evolutions of kinetic energy and collapsing profile with time by the proposed numerical approach also show clearly a soil density-dependent collapse process.Practical implicationsTo the end, this study can improve the understanding of column collapse in different aspect ratios and soil densities, and provide a computational tool for the analysis of real scale granular flow.Originality/valueThe originality of this paper is proposed in a numerical approach to model granular column collapse considering the influences of aspect ratio and initial void ratio. The proposed approach is based on the finite element platform with coupled Eulerian–Lagrangian technique for large deformation analysis and implementing the critical-state based model accounting for the effect of soil density.

Pore-scale model for estimating the bimodal soil–water characteristic curve and hydraulic conductivity of compacted soils with different initial densities

This paper proposed a pore-scale model to simulate the effect of initial soil density on the bimodal soil water characteristic curve (SWCC) of compacted soils. The pore-scale model is developed based on the bimodal pore-size distribution. Soils with bimodal pore-size distribution is assumed to have dual porosity, namely the macropore structure and the micropore structure, and hypothesized that the micropore structure is hard to be compressed under mechanical loading. The water stored in the macropore structure is divided into two parts, the bulk water and the meniscus water, respectively. The deformation of soil (bulk water flow) is obtained by horizontal shifting and vertical scaling of the pore-size distribution (PSD) function. A toroidal model is used to describe the influence of initial density on the meniscus water. The pore structure of compacted coal gangue was qualitatively imaged as an evidence of the pore structure changes, and the SWCC of the compacted coal gangue was quantitatively analyzed. Finally, a numerical method is advised for simulating bimodal permeability function by using the proposed model with Mualem function. Laboratory test results in published literature are employed to validate the proposed model and permeability function, and the model predictions showed good agreement with the experimental data in the literature.

Hydromechanical modeling of granular soils considering internal erosion

This paper attempts to formulate a coupled practical model in the framework of continuum mechanics to evaluate the phenomenon of internal erosion and its consequences on the mechanical behavior of soils. For this purpose, a four-constituent numerical approach has been developed to describe the internal erosion process. The detachment and transport of the fine particles have been described by a mass exchange formulation between the solid and fluid phases. The stress–strain relationship of the soil is represented by a nonlinear incremental model. Based on experimental data, this constitutive model has been enhanced by the introduction of a fines content–dependent critical state, which allows accounting for the influence of fines on soil deformation and strength. The applicability of the practical approach to capture the main features of the internal erosion process and its impact on the mechanical behavior of the eroded soil have been validated by comparing numerical and experimental results of internal erosion tests on Hong Kong completely decomposed granite (HK-CDG) mixtures, which demonstrated that the practical model was able to reproduce, with reasonable success, the experimental data. Furthermore, the influence of the stress state, the initial soil density, and the initial fraction of fines have been analyzed through numerical simulations using the proposed model.

Erosion Potential of Compacted Surface Soils for Multilayered Cover System

Abstract Industrialization and urbanization have led to a rapid increase in hazardous and reactive wastes that need to be disposed safely. Multilayered cover systems (MLCS) are used for such waste disposal to impede contaminant interaction with the subsurface and atmosphere. Based on multiple forensic studies, soil erosion has been identified as a primary stressor of landfill covers that results in cover failure and exposure to contamination. The pinhole test is one of the most commonly adopted index tests to evaluate the erosion rate of soil. The main objective of this technical note is to measure the erosion potential of a soil at nine different compaction states and three runoffs, which correspond to three forms—rainfall-heavy, excessive, and cloudburst—that can result in significant erosion. A total of 729 pinhole tests on 9 different loamy soils were conducted in the current study, and the individual effects of initial moisture content, soil density, and runoff flow rate are discussed. It is observed that compaction of the surface layer for MLCS can be done at wet optimum moisture content with the highest possible soil density to minimize risk of erosion for all loamy soil. Furthermore, fine fractions of soils (percentage finer than 75 μm) was identified as a parameter that can be used to predict the maximum erosion rate of a soil using a simple linear relation.

Soil liquefaction as an identification test

Time-consuming and complicated investigations of soil liquefaction in cyclic triaxial tests are the most common way of laboratory analysis of this phenomenon. Moreover, the necessary equipment for the performance of cyclic triaxial tests is very expensive. Much simpler method for laboratory testing of the soil liquefaction has been developed at the Institute of Geotechnical Engineering at the TU Dresden. This method takes into account the pore water pressure build-up during cyclic shearing within a short time period. During the test, the soil sample is subjected to horizontal cyclic loading and the generated pore water pressure is measured. In the first series of these experiments, a dependence of the pore water pressure buildup on the initial density of soil could be observed, as expected. When comparing different soils, it is shown that the tendency to liquefaction depends also on the granulometric properties (e.g. grain size distribution) of the soil. The aim of the further development is to establish a simple identification test for laboratory testing of the soil liquefaction.

Impact of wetting-drying cycles and cracks on the permeability of compacted clayey soil

Several geotechnical structures constructed with fine soils submitted to wetting and drying (W-D) cycles face a variety of disorders. This is the case of some roads and slopes in the North of Tunisia where the upper soil layers are silty and clayey. Due to desiccation cracks, preferential pathways for rainfall infiltration and contaminant transport are created. In fact, the permeability varies significantly considering the evolution of desiccation cracks during W-D cycles. In the current research work, we developed an equipment of 150 × 150 × 50 mm, to measure the clay permeability during W-D cycles taking into consideration the influence of initial soil density. In addition, the role of the micro-structural evolution during the W-D cycles was investigated. The permeability was predicted using a proposed fractal model, based on the evaluation of the morphological parameters of cracks and the saturated permeability before crack development. The predicted and measured values of saturated hydraulic conductivity were found in good agreement. With cracking, the permeability can be increased to a limit value and the impact of the initial density becomes insignificant after seven W-D cycles.

Novel SPH SIMSAND–Based Approach for Modeling of Granular Collapse

Granular collapse is a common issue in natural hazards. This paper proposes a novel numerical approach on modeling granular column collapse. A newly developed critical state-based constitutive model, SIMSAND, was adopted to combine with the smoothed particle hydrodynamics (SPH) method for realistically reproducing large deformation during collapse. A rectangular channel and two-dimensional column tests were first simulated for the validation. The effects of aspect ratio and initial soil density were further investigated by additional simulations. It was demonstrated that the novel SPH-SIMSAND approach is helpful in improving the understanding of granular collapse and should be an effective computational tool for the analysis of real-scale granular flow.

Soil plug behaviour of open-ended pipe piles during installation

This study experimentally investigates the effects of the pile diameter and initial soil density on the change of the soil plug state during pile driving through model pile tests. Model piles with ...

Study of the volumetric water content based on density, suction and initial water content

Abstract The practical application of determination of the soil water retention curves (SWRC) is in seepage modelling in unsaturated soil. The models based on the physics behind the seepage mechanism has been developed for predicting the SWRC. However, those models rarely consider the combined effects of initial volumetric water content and soil density. One of the best routes to study these effects is to formulate the SWRC models/functional relations with volumetric water content as an output and the soil density, initial volumetric water content and soil suction as input parameters. In light of this, the present work introduces the advanced soft computing methods such as genetic programming (GP), artificial neural network and support vector regression (SVR) to formulate the volumetric water content models based on the suction, density and initial volumetric water content. The performance of the three models is compared based on the standard measures and goodness-of-fit tests. The findings from the statistical validation reveals that the GP model performs the best in generalizing the volumetric water content values based on the suction, density and initial water content. Further, the 2-D and 3-D plots, evaluating the main and the interaction effects of the three inputs on the volumetric water content are generated based on the parametric procedure of the best model. The study reveals that the volumetric water content values behave non-linearly with respect to soil suction because it first decreases till a certain point of soil suction and then increases suddenly.

Effect of surface roughness on the shaft resistance of non-displacement piles embedded in sand

This paper presents the results of axial load tests performed on instrumented model piles pre-installed in a large-scale, half-circular chamber with a viewing window in its flat-side wall. Uniform silica sand samples were prepared with different densities using dry pluviation. The effects of pile surface roughness and soil density on the response of the soil during loading of the model piles were studied by analysing sequences of digital images using the digital image correlation technique. Test results show that the extent of the zone next to the pile that is affected by loading of the pile increases as the pile surface roughness and soil density increase. The development of a shear band next to the pile shaft was also studied by carefully analysing images taken with a digital microscope during loading of the model piles. The average thickness of the shear band is in the 3·2D50–4·2D50range for rough model piles, whereas no shear band was observed for smooth model piles. Understanding of shear band formation along the pile–soil interface provides insights into the calculation of the shaft resistance of the pile as a function of initial soil density and stress as well as pile surface roughness.