Initial Void Ratio Research Articles

Prediction of compressibility and shear strength behaviour of in-situ cohesive soil from reconstituted clay

ABSTRACT In the present study, simplified sample preparation and testing methodology are proposed for reconstituted clay that can predict the strength and deformation behavior of its in-situ state with minimal sample preparation disturbances. Reconstituted clay specimen was prepared in designed mould for each disturbed sample. Later, predetermined proportions of admixtures were mixed to vary the liquid limits. The test results showed that the change in compression index is directly proportional to the change in the liquid limit, moisture content, and the initial void ratio of the soil samples. However, the change in angle of internal friction was inversely proportional to the liquid limit, plasticity index, and clay fraction percentage. Scanning electron microscopy tests provided in-depth insight on the comparable pore and clay flake sizes. The proposed empirical relationships from the test results could reasonably estimate the compressibility and shear strength behavior of the in-situ clay soil from the basic index properties.

Investigation on the Influencing Factors of K0 of Granular Materials Using Discrete Element Modelling

Earth pressure coefficient at rest K0 is commonly estimated by empirical equations, which to date has had insufficient accuracy and universality. For better prediction, the investigation on the factors influencing K0 is required. A series of discrete element method (DEM) simulations of oedometer tests are conducted to verify the key factors influencing K0 of granular materials. The influences of initial fabric anisotropy, particle shape, initial void ratio, inter-particle friction angle is investigated. The evolution of microstructure is monitored during the tests to reveal the relationship between the microstructure evolution and K0 values. The results show that the effect of fabric anisotropy exists but is limited. Particle shape, initial void ratio, and inter-particle friction angle all significantly affect the K0 values alone. According to the DEM results, an attempt is made to propose a more reasonable empirical equation in which K0 is a function of relative density, critical state friction angle, and “shape factor”. This new empirical equation has higher accuracy and can consider the effect of particle shape, inspiring the determination of K0 values in practical engineering.

Modeling of flexible membrane boundary using discrete element method for drained/undrained triaxial test

A modeling method for the particle-based flexible membrane boundary for the drained/undrained triaxial test is proposed herein. First, the particle placement manner to construct a cylindrical membrane is described. Second, the vertical and radial stiffnesses/moduli of the entire membrane are derived and related to the interparticle contact stiffness, thereby enabling the calibration of the interparticle stiffness and correcting the confining pressure acting on the sample. Third, the application strategy of confining pressure is presented for the drained test, and a two-stage loading strategy is proposed to explore the excess pore pressure incrementally for the undrained tests. Using this membrane boundary, triaxial compression tests under the drained/undrained condition by discrete element method (DEM) were conducted on the samples with different initial void ratios and membrane stiffnesses. Simulations reproduced the behavioral transition by increasing the initial void ratio, the influence of membrane stiffness and the characteristics of shear banding, demonstrating the effectiveness of the proposed method. Differences from the referencing results with the rigid wall boundary were observed and attributed to the additional confining pressure from the membrane radial modulus, the persistence of the shear band allowed by the membrane flexibility, and the membrane penetration.

Use of CFD-DEM to evaluate the effect of intermediate stress ratio on the undrained behaviour of granular materials

This study investigates the effect of intermediate stress ratio (b) on the mechanical behaviour of granular soil in true triaxial tests. A CFD-DEM solver with the ability to model compressible fluid and moving mesh has been developed and calibrated based on existing experimental test results on Nevada sand. The effect of b on the undrained true triaxial test, which has been neglected in the literature, was investigated using a reasonable number of models. The effects of the initial confining stress and initial void ratio also have been studied. The developed model was used to calculate the hydrodynamic forces on the particles and evaluate the ratio of the particle–fluid interaction force to the resultant force on the particles. It has been demonstrated that, in numerical studies, the effect of these forces cannot be neglected.

Model for predicting evolution of microstructural void ratio in compacted clayey soils

The hydromechanical behavior of compacted clayey soils is significantly influenced by its microstructure. The microstructural void ratio is a key parameter that is strongly associated with the microstructural state. The objective of this study is to provide a practical and reliable estimation approach for predicting the evolution of the microstructural void ratio of compacted clay soils subjected to wetting and drying paths. In this paper, the microstructural evolution of 12 clayey soils was investigated quantitatively using the mercury intrusion porosimetry (MIP) results. Based on this study, a comprehensive criterion has been developed for identifying different pore populations of compacted clayey soils for interpreting the MIP results. The “as-compacted state line” was proposed to estimate the initial microstructural void ratio of clayey soils at the as-compacted state. An incremental linear constitutive model was proposed for correlating the microstructural void ratio to the “microstructural average skeleton stress” in compacted clayey soils following monotonic wetting and drying paths. The developed approach is validated by providing comparisons between the predicted and interpreted microstructural void ratios for all the examined soils. The proposed approach can be extended in constitutive modeling of the hydromechanical behavior of compacted clayey soils by incorporating explicitly the microstructural information.

Stabilization of muskeg soils using two additives: sand and urease active bioslurry

Muskeg soils are considered problematic. They are distinguished by their high initial void ratio and water content. Therefore, they exhibit high compressibility and low shear strength when they are subjected to external loads. Microbially induced calcite precipitation (MICP) is a promising soil stabilization technique because it is considered environmentally friendly. In this study, the MICP technique using the urease active bioslurry approach was coupled with sand collected from a local source to stabilize muskeg soils. The effect of changing the sand percentage on the compressibility properties of muskeg soil was studied. The results showed that the addition of 10% sand and injection of two-pore volumes of cementation solutions significantly improved the compressibility properties such that the initial void ratio decreased by 70%.

Forecasting the Compressibility Parameters of Gypseous Soil using Artificial Neural Networks

To ensure safe design of structures against settlement, it is necessary to determine the compressibility parameters of the underneath soil especially compression and rebound indices. In this paper, an approach to forecast the compressibility parameters of gypseous soils based on index parameters was developed using Artificial Neural Networks technique. Two equations were developed to estimate compression and rebound indices using back propagation algorithm to train multi-layer perceptron, in which good agreements were achieved. The input parameters used were: the depth, gypsum content, liquid limit, plastic limit, plasticity index, passing sieve No.200, dry unit weight, water content and initial void ratio. Two output parameters were determined including compression index and rebound index. A parametric study was also conducted to investigate the generalization and robustness of both models. The findings indicate that both models were reliable within the range of utilized data. It was found that gypsum content has the highest effect on the compressibility index followed by water content, plasticity index, dry unit weight and plastic limit, while other parameters have lower effect. The gypsum content has the highest effect again on the rebound index followed by passing sieve No.200, initial void ratio, plastic limit and plasticity index, while other parameters have lower effect.

Large-Strain Self-Weight Consolidation of Dredged Sludge

Prediction for self-weight consolidation of dredged sludge is important for its reuse in civil engineering applications. In this work, considering the special nonlinear relationships of e – k and e – σ′ for dredged sludge, Gibson’s large strain consolidation equation was modified to simulate the self-weight consolidation process of dredged sludge. Using the finite difference method (FDM), the influences of four main parameters, including initial height, initial void ratio, void ratio at the liquid limit, and specific gravity of soil particles, on the consolidation process of dredged slurry were analyzed. For the aforementioned four parameters, the self-weight consolidation of dredged slurry is most sensitive to the variation of void ratio at the liquid limit, whereas its response to the change of specific gravity of soil particles is relatively subtle. Consolidation behaviors under other commonly used constitutive models were also calculated for comparison. It was found that the total settlement obtained by the present relation is larger than the results obtained using typical nonlinear constitutive relations, and the speed of consolidation is higher.

Large Scale Direct Shear Box Tests on Gravels

The determination of shear strength characteristics of gravelly soils is difficult through the use of conventional small scale, triaxial or simple shear testing devices in the laboratory due to membrane compliance and boundary effects; or due to inconsistent penetration resistances measured as part of standard or cone penetration testing in the field. These limitations require the use of available empirical or semi-empirical relationships or the execution of large scale laboratory or field tests. In the literature there exists inconsistent, and large range of recommendations for shear strength parameters. Within the confines of this study, direct shear box test results performed on poorly- (GP) and well-graded (GW) gravel samples with initial void ratio ranging from 0.42 to 0.53 are presented, which are tested under effective normal stresses ranging from 77 to 205 kPa. The estimated peak secant-angles of shearing resistances vary in the range of 49 to 54 degrees. On the basis of volumetric change vs. shear strain responses, the peak angle of dilation and elastic Poisson’s ratio are estimated to vary in the range of 10-16 degrees and 0.28-0.39, respectively. These estimated values are compared with available literature.

Characterization of the High Swelling Green Clay in the Vicinity of Amman Area

Introduction: Jordan is awarded huge areas in the north and western part of the country in which brown and green clay is dominant. This research focuses on the problems and behaviour of the green clay only. The main problem of the green clay is its high swelling pressure which is the main cause of excessive settlement and wall cracks in buildings, especially during the wet season. Methods: This study aims to investigate the engineering properties and behaviour of the green clay deposits in the Amman area, which will serve as a guide for both geotechnical and structural engineers when preparing the foundation design. Results: Based on the consolidation test, the investigated green clay showed high swelling pressure of 3.11 kg/cm2, liquid limit (LL) of 73%, plasticity index (PI) of 40%, the shrinkage limit (SL) of 12%, and liquidity index (LI) of 0.125. The moisture content at saturation is 35.14%, while the natural moisture content is 28%, dry density is 1407 kg/m3, cohesion (C) is 0.20 kg/cm2 and unconfined compressive strength is 1.05 kg/cm2. The XRD results of the clay size fraction have confirmed the presence of the expansive clay mineral smectite as the essential clay mineral together with kaolinite. Results provide a general understanding of the behaviour and properties of the green clay, and the regression analysis showed good correlations between the liquid limit and initial moisture content with the compression index and also between the initial void ratios with the swelling index. Conclusion: Changes in the volume are due to the unsaturation level of clay when provided with initial water content.

On compression behavior and particle breakage of carbonate silty sands

Carbonate soils are high in compressibility and low in particle strength, and therefore need special treatment for many geotechnical applications. This paper presents comprehensive one-dimensional compression tests to investigate the compression behavior and particle breakage of carbonate soils with various initial particle size distributions (PSDs) and a wide range of initial void ratios at a high effective vertical stress of 32 MPa. A clear shape transition in terms of the void ratio against effective vertical stress was observed with varying silt fraction and void ratio. The deformation mechanism for the samples with less silt fraction and higher void ratio is mainly dominated by the particle-breakage-induced unlocking effect. Samples with more silt fraction and lower void ratio will experience less particle breakage and their deformation mechanism is mainly attributed to interparticle locking effect. A ‘transitional’ mode of behavior without a unique normal compression line was identified for the samples with silt fraction ranging from 1.6% to 33%. It was also found that carbonate soil samples with both ‘transitional’ and ‘non-transitional’ modes of compression behavior may both experience considerable amount of particle breakage and show different trends in the evolution of particle shape.

Strength and Compressibility of Ammonia-Soda Residue from the Solvay Sodium Plant

This work presents the discussion of the results for an experimental study conducted to characterise the mechanical behaviour of ammonia-soda residue (ASR). The calcareous sludge is an alkaline waste formed during the production of soda ash and deposited at the area of the former Solvay Sodium Plant factory in Krakow, Poland. Isotropically consolidation drained (CID) triaxial tests and constant rate of strain (CRS) consolidation tests include the full saturation with water, completion of the consolidation, and the loading/strain rate choice. For this purpose, ASR undisturbed samples were collected from the ground and submitted to laboratory experiments. These samples show a distinct difference in the initial bulk density, the initial level of compaction, initial void ratio, and the natural water content. The CD triaxial tests were conducted under three different levels of confining pressure; in turn, CRS tests were run with two appropriate input strain rates. According to the physical state of ASR and the depth of sampling, two different evolutions of the critical state in the stress–strain space were observed. In the light of the assessed stress–strain–strength behaviour, key design engineering parameters of ASR were calculated.

Effects of hydro-mechanical material parameters on the capillary barrier of reinforced embankments

This paper presents a numerical analysis of the water infiltration process in embankments reinforced with permeable geosynthetics. An emphasis is given to the study of the capillary barrier permanence at the soil-geotextile interface. For the analysis, an infiltration-deformation coupled model is used, and the numerical results are validated with experimental data. The proposed model properly describes the main characteristics of the capillary barrier phenomenon observed experimentally. A parametric analysis is performed to investigate the effects of the initial void ratio (e0), overconsolidation ratio (OCR), initial shear elastic modulus (G0), coefficient of compressibility (λ), anisotropy of the hydraulic conductivity (kr), initial suction (ψi), and water retention curve parameters (α and n′) on the performance of the capillary barrier during a rain infiltration process. Finally, a statistical analysis is carried out to evaluate the parameters that have influence on the development of pore water pressure (PW). The implemented infiltration-deformation coupled model shows the effect of the hydraulic parameters on the development of the capillary barrier -as commonly considered in conventional analysis- as well as the effect of the mechanical parameters of the soil and geotextile. The overall results highlighted the capability of the model, in combination with statistical analyses, to capture the complexity of the capillary barrier development in reinforced soil structures.

Study on the packing and shear characteristics ofgranular mixtures via the DEM

Granular mixtures are often encountered in civil engineering, but the micromechanical implications of their packing and shear characteristics are still unclear. In this study, the packing and shear characteristics of binary mixtures were studied using a three-dimensional discrete element method (DEM). The binary mixtures contained realistic gravel-shaped coarse particles and one of two tested fine particle shapes (namely, spherical or elongated particles). The densest isotropic samples were generated by using a frictionless condition. The initial void ratio and particle contacts of the packed samples were examined. This study shows that the particle shape of the fines affects the relationship between the initial void ratio and fines content (FC). The contact types in binary mixtures can be classified as coarse particle-coarse particle (CC contacts), coarse particle-fine particle (CF contacts) and fine particle-fine particle (FF contacts). A microscopic investigation of the particle contacts indicated that the coarse and fine particle shapes influenced the partial coordination numbers of the CC and CF contacts and the CF and FF contacts, respectively. All the samples were then subjected to numerical triaxial compression tests. The results show that the particle shape of the fines affected the magnitudes and evolutions of the peak (φp) and critical (φc) friction angles of the binary mixtures. Finally, an anisotropic analysis was performed to highlight the microscopic mechanisms that cause the shear strength to be dependent on the particle shape and FC.

State-Dependent Behavior of a Crushable Sand in Drained Triaxial Tests

Abstract This article presents a laboratory experimental study on the state-dependent behavior of a crushable sand that was crushed progressively in a number of the drained triaxial tests. The critical state line of sand showed a straight line in the e-logp′ plane, in the e-p′α=0.7 plane and in the q-p′ plane despite of involving the progressive particle breakage. It showed a family of the relations between stress ratio and dilatancy factor rather than a unique stress-dilatancy relation. While increasing the initial void ratio or the initial confining pressure, the peak-state friction and maximum dilatancy angles of sand showed a decrease, but the peak-state basic friction angle of sand increased. Linear representation was revealed for the relations of the maximum dilatancy angle - the peak-state stress ratio and the peak-state basic friction angle - the peak-state stress ratio. An increase in the peak-state state parameter resulted in a linear decrease of the peak-state friction and dilatancy angles of sand, but a linear increase of the peak-state basic friction angle of sand. It revealed a unique linear friction-dilatancy relation of sand incorporating the progressive particle breakage. The peak-state volumetric strain and deviator strain of sand increased while increasing the initial void ratio or the initial confining pressure or the peak-state state parameter, but decreased with increasing the peak-state stress ratio. The peak-state dilatancy factor d incorporating the progressive particle breakage decreased linearly with increasing the peak-state stress ratio, but linearly increased along the increase of the peak-state state parameter. Dilatancy of sand should be dependence of the pressure and density of sand as well as the progressive particle breakage.

Analysis of Geotechnical Characteristics of Coastal Clay Soil Found in Incheon and Gwangyang

Recently, there has been an increase in the number of projects involving the planning and construction of business complex facilities and land development in coastal regions. However, coastal regions are characterized by very soft clay soil. Consequently, such clay soil needs to be augmented for facilitating land procurement. Furthermore, to realize land improvement, the associated geotechnical characteristics need to be analyzed through laboratory tests by acquiring pristine samples of cohesive soil. According to the results obtained from previous studies, the characteristics of the cohesive soil found in Korea can vary depending on the region and depositional environment. The objective of this study is to examine the representative physical and mechanical characteristics of marine clay found in Namhae coast (Gwangyang) and Seohae coast (Incheon) by comparing and analyzing these characteristics. To this end, land examinations were conducted during planning and construction, and data were gathered from 445 sites in Incheon and 844 sites in Gwangyang for comparing the associated physical and mechanical characteristics. Subsequently, by conducting regression analysis, equations of correlation between liquid limit and natural water content, effective surface load and pre-consolidation load, compression index and liquid limit, and compression index and natural water content were deduced. The obtained results indicate that compared to the soil found in Incheon, the clay fraction, natural water content, liquid limit, plasticity index, liquidity index, initial void ratio, and compression index of the soil found in Gwangyang are higher.

Comparative FE-studies of interface behavior of granular Cosserat materials under constant pressure and constant volume conditions

This article shows the outcomes of a systematic series of finite element (FE) calculations relevant to the shear behavior of a particulate-continuum interface system under different normal boundary conditions. In this respect, shearing of a thin and long granular Cosserat layer in the vicinity of a rigid moving wall with varied surface roughness values is analyzed under constant normal pressure and constant volume conditions. The material behavior is defined with a special elasto-plastic Cosserat model, taking into account micro-rotation, micro-curvature, couple stress, and mean particle size. The interaction between the layer of boundary particles and the surface roughness of the adjoining bottom wall is modeled by the rotation resistance of particles along the wall surface. Herein, the coupled effects of normal confining constraints imposed on the layer and the surface roughness of the bottom wall, are considered on the response of granular material under shearing. The influences of pressure level and initial void ratio are explored as well. Numerical results demonstrate that the dilatancy constraint prescribed to the interface plane in the normal direction, and the wall roughness have visible influences on the interface shear resistance as well as the deformation field formed within the layer. After large shearing, the width of the localized zone along the wall does not necessarily depend on the normal confining constraint and the applied pressure level. However, the localized zone characteristics and the interface shear response are mainly affected by the initial void ratio of the material. In addition to FE analyses, DEM-based simulations are also performed to investigate the micro-mechanical response of granular medium adjacent to a wall under shearing. FE predictions are qualitatively compared with DEM results, and reasonable agreement is observed.

Simple Graphical Prediction of Relative Permeability of Unsaturated Soils under Deformations

At present, there are only a few existing models that can be used to predict the relative permeability of unsaturated soil under deformations, and the calculation process is relatively complex. In order to fit the measured value of the relative permeability coefficient of unsaturated soil before deformation, this work employs the simplified unified model of the relative permeability coefficient of unsaturated soil, and it obtains the index λ before deformation of the soil. In addition, the value of index λ remains unchanged before and after deformation. Based on the actual measured value of the soil–water characteristic curve before deformation, the air-entry value prediction model is used to predict the air-entry value of soil with different initial void ratios. The relative permeability coefficient of unsaturated soil is then conveniently predicted using the graphical method in combination with the simplified unified model. The method is validated by using the test data of silt loam, sandy loam, and unconsoildated sand. The results show that the predicted results are consistent with the measured values. The prediction method in this paper is simple and overcomes the limitations associated with the determination of the index λ. It expands the application range of the unsaturated relative permeability coefficient model while improving the accuracy of predictions.

Analysis of Mechanical response of Granular Buried Ditch under high-fill foundation

High-fill foundations can solve the problem of land shortage in mountainous cities. In high ground stress and water immersion environment, stress concentration will lead to gravel particle breakage in drainage blind ditch, and the drainage blind ditch exists a risk of drainage failure, which will bring great harm to high-fill foundation. In this paper, model tests and PFC simulation were carried out to analyze the mechanical response of gravel particles in drainage blind ditch under high ground stress and water immersion. Firstly, large-scale triaxial shear tests were carried out to explore the effects of confining pressures, dry-wet conditions and initial void ratios on breakage and mechanical characteristics of gravel particles. The stress-strain curve of gravel particles was studied and the influence of variation of gravel graduation and particle crush rate on peak strength and dilatancy were analyzed. Then, the single particle breakage model under high pressure was established and the influence of immersion was considered in numerical simulation. The crushing test of gravel particles was carried out and the impact of particle breakage on mechanical characteristics was studied. The results show that the stress-strain curve of gravel particles has a behavior of strain hardening. Particle breakage has a significant impact on the strength and dilatancy of gravel particle. The gravel particle breakage rate is approximately linear with confining pressure and initial void ratio. Immersion of the gravel particle increased the volumetric strain, weakened the dilatancy and increased the gravel particle breakage rate.

Experimental investigation of the permanent deformation and void ratio attenuation of porous asphalt mixtures with hydraulic effects

To investigate the quantitative influence of the material gradation characteristics, saturation degree and loading frequency on the permanent deformation of porous asphalt (PA) mixtures under temperature, loading, and hydraulic coupling conditions, a hydraulic coupling repeated loading test is conducted for five types of PA mixtures with different nominal maximum aggregate sizes, void ratios, saturation degrees and load frequency inputs. The test results indicate that the PA-20 mixture has better anti-deformation performance than the PA-13 and PA-16 mixtures. A larger void ratio corresponds to weaker anti-permanent deformation performance. When the initial void ratio is 24%, the flow number prominently decreases to approximately less than 11% of the initial void ratio of 16%. The results of the loading test with water storage show that the saturation state has a more significant impact on the permanent deformation of PA-13 mixtures than PA-16 and PA-20. When the frequency increases, the cumulative microstrain of the mixture greatly decreases, and the influence degree of frequency on the deformation becomes increasingly obvious when the void ratio increases due to the effect of hydraulic coupling. To easily evaluate the void ratio attenuation of PA, a uniform expression is proposed to characterize the three-stage strain growth, which shows that the permanent deformation curve exhibits nonlinear growth in the second stage of deformation. Then, the minimum permanent deformation growth rate is presented to quantitatively evaluate the deformation resistance performance. Overall, a higher saturation degree of the lower loading frequency corresponds to a smaller PDGRmin. A formula is presented to analyse the effect of permanent deformation on the change in void ratio: the loading frequency, saturation degree and initial void ratio significantly affect the attenuation of the AV ratio. Specifically, the coupling of frequency and water storage slows the decrease in air void ratio.