Initial Void Ratio Research Articles

Influences of ink-bottle effect evolution on water retention hysteresis of unsaturated soils: An experimental investigation

The ink-bottle effect, resulting from the non-uniformity of pore structure, plays a significant role in the hydraulic behaviour of soils. In this paper, a series of laboratory tests including standard mercury intrusion porosimetry (MIP), intrusion-extrusion cyclic MIP (IEC-MIP), and scanning electron microscopy (SEM) were conducted on two soils (a Nanyang expansive clay and a Kaolin mixture) to examine the evolution pattern of ink-bottle effect in soils with different initial void ratios. To evaluate the impact of such evolution on the soil-water retention behaviour, the axis translation and vapour equilibrium techniques were utilised to measure the water retention curve of the tested soils (SWRC). A key part of the analysis involved a separation between pore bodies (or ink-bottle pores) and pore throats to facilitate a more thorough examination of the pore structure. The test results indicated that the reduction in soil volume during compression is mainly attributed to the reduction in pore body size, whereas the pore throat size remains relatively constant. Therefore, the ink-bottle effect would weaken with a decreasing initial void ratio, which will reduce the hysteresis potential of soils, manifesting as a contraction of the SWRC hysteresis loop. Additionally, under a fixed void ratio but with decreasing pore size, the ink-bottle effect will also weaken, which will reduce the distance between the drying and wetting curves with increasing matric suction. Finally, the mechanisms regarding how the evolution of ink-bottle effect during soil deformation influences water retention hysteresis were addressed.

Simplified solution for large-strain consolidation considering the time-dependent well resistance

In this study, a simplified solution of the large-strain consolidation theory, which considers the time-dependent well resistance, has been presented. This solution is suitable for consolidation issues involving the influence of either the smear zone or the soil column. To confirm the proposed solution's accuracy, it was compared to fully nonlinear consolidation results calculated using the finite element method. Parametric analysis was conducted to examine the impact of the time-dependent well resistance in combination with the soil thickness, the ratio of the compression index to the radial and vertical permeability indices, and the initial void ratio at the soil surface. Finally, the proposed solution’s applicability was confirmed through a comparison of calculated results based on two case studies with both field measurements and numerical simulations.

DEM study on the micromechanical behaviour of sand-clay mixtures

A DEM model incorporating realistic sand shape was developed to simulate sand-clay mixture (SCM) behaviour based on CT images acquired during uniaxial compression of a SCM containing quartz sand (SCM_R) and a SCM containing glass beads (SCM_S) with in-situ X-ray micro-tomography scanning. The influences of shape, size and content of sand grains on the uniaxial behaviour of SCM were studied. SCM_R revealed a higher peak strength and elastic modulus than SCM_S with the same sand content, sand size and initial void ratio. Increasing sand content led to significantly reduced peak strength for both SCM, and remarkably increased and unnoticeably changed elastic modulus for SCM_R and SCM_S, respectively. Meanwhile, increasing sand size resulted in dramatically decreased yet insignificantly varied peak strength and elastic modulus for SCM_R and SCM_S, respectively. The different phenomenon between SCM_R and SCM_S were attributed to the significantly different sand-clay bond intensities and interface interlocking effects between them.

Multivariate probabilistic assessment of a regional database in Copenhagen

Extensive research has been carried out to establish empirical equations between two geotechnical properties and in spite of the increase in correlation studies, a construction of a multivariate distribution function of more than two parameters is still rare. The objective of this study is to investigate the possibility of constructing two multivariate distribution functions, each consisting of 5 geotechnical parameters based on a) triaxial and soil classification tests and b) oedometer and soil classification tests in stiff over-consolidated clay till from Copenhagen. For this purpose, laboratory measurements from twenty-six sites in Copenhagen are utilized and two multivariate databases are constructed. The correlations among the ratio of deviatoric and mean effective stresses (q/p´), over-consolidation ratio (OCR), secant modulus at reference stress 100 kPa (E50ref), initial void ratio (eo) and liquid limit (LL) are investigated in multivariate model A, while multivariate model B demonstrates the correlations among oedometer modulus at 100 kPa reference stress (Eoed(ur)ref), over-consolidation ratio (OCR), permeability change index (Ck), initial void ratio (eo) and liquid limit (LL). The Nataf transformation model is used for the construction of the multivariate distributions, which are then used to simulate the correlations between geotechnical properties by generating artificial samples. Finally, the artificial samples are compared with the original database for an initial validation of the model. The constructed multivariate models obtained as a result of this study can act as prior for Bayesian updating in multivariate distribution functions when additional geotechnical tests are carried out.

Investigating the influence of sample size on measurement of collapse of gypseous soil

This study aims to analyze the behavior of soils containing gypsum, specifically focusing on the impact of gypsum content and different soil parameters. Several physical tests and assessments were conducted on synthetic gypseous soil, which consists of silty clay and different proportions of gypsum (20%, 40%, and 60%). The research emphasizes the notable influence of gypsum concentration on soil collapsibility, whereby higher levels of gypsum are associated with a heightened propensity for collapse. The soil behavior is significantly influenced by various factors, including but not limited to the initial void ratio, total unit weight, and degree of saturation. Quantitative predictive models have been constructed to describe these interactions, offering significant tools for engineers and researchers engaged in the study of gypseous soils. Furthermore, this study provides insights into the intricate patterns of human settlement throughout history, focusing on the significance of gypsum bonding and unit weight in reducing soil settlement. The results demonstrate that the single oedometer test exhibits greater collapse potential values at 200 kPa compared to the double oedometer test, showing an increase of 27% and 44%, respectively. The observed discrepancy can be ascribed to softening and gypsum dissolving, which commence before reaching a pressure of 200 kPa in the double oedometer test. Moreover, the research presents a modified collapse test with a more dependable methodology for identifying collapsible gypseous soil in contrast to conventional techniques. The proposed methodology entails employing larger sample sizes and achieving complete particle saturation by upward water flow, mitigating the drawbacks observed in traditional methodologies, namely inadequate sample sizes and incomplete particle saturation. In general, this study greatly enhances our comprehension of the mechanics of gypseous soil and offers useful methodologies for evaluating and addressing soil collapsibility in geotechnical and building endeavors.

Liquefaction behaviour of aluminium and plastic rod assemblies using bi-axial apparatus with application of image analysis

It has recently been shown that the overall deformation characteristics of granular materials during liquefaction seems to be governed by local void ratio characteristics. The aim of this study is to investigate the relationship between mechanical properties and local void ratio changes during liquefaction in two materials of different weights (aluminium-type and plastic-type rod assemblies). A series of constant-volume cyclic bi-axial loading tests was conducted together with the image analysis obtaining local void behaviour. The experimental results demonstrate that the first liquefaction resistance of the plastic sample is higher than the aluminium one, corresponding to its smaller initial void ratio and less contractive behaviour observed in the early stage of drained monotonic compression. However, after experiencing the first liquefaction and subsequent re-consolidation histories, a liquefiable assembly of aluminium and plastic rods both became either denser (densification) or more homogenous (homogenization) in terms of local void ratio, suggesting an increase in liquefaction resistance in the next liquefaction stage. This work also includes a preliminary analogous study using a semi-3D discrete element method (DEM) with one single layer of spherical particles to simulate the similar liquefaction behaviour observed in the laboratory tests.

Analytical analysis of cylindrical cavity expansion considering particle breakage effect of sand and its application for cone penetration tests

AbstractThe particle breakage effect in sand exerts a significant influence on the design of underground space structure. However, the existing theories seldom consider the breakage effect and often lack accurate descriptions of void ratio changes, leading to substantial errors in the numerical calculations compared to the actual scenario. This study employs the simple critical state sand model (SIMSAND) to account for the particle breakage effect and transforms the drained cylindrical cavity expansion problem into a set of first‐order ordinary differential equations described by the Lagrangian method. The analytical solution of the cylindrical cavity expansion problem is calculated using Matlab programming codes. Firstly, Fontainebleau sand is investigated to analyse the influence of initial stress, void ratio and specific volume around the cavity. The combined effects of initial stress and particle breakage on the soil around the cavities result in dilatancy characteristics and a reduction in void ratio. The stress path analysis reveals that the soil around the cavities only reaches a critical state under high initial stresses. Secondly, a plane strain numerical model is established for twice expansion to verify the calculation outcomes from the cylindrical cavity expansion theory. Finally, an axisymmetric cone penetration test (CPT) model is developed to analyse the theoretical and numerical solutions for expansion stress and sleeve friction. The research results indicate that the CPT in sand need to consider the particle breakage effect, especially under high stress conditions. Without considering particle breakage, the sleeve friction is overestimated. These research findings can offer guidance for geotechnical engineering applications, such as CPT, pressuremeter tests and predictions of bearing capacity for pile foundations in sand.

A general model for the small-strain stiffness of saturated residual soils: back analysis of a database and case study

A review analysis of a database of 237 small strain stiffness measurements performed on 35 different residual soils is presented. The reinterpretation of the tests was conducted with respect to the loading conditions and physicochemical parameters published in the literature. Besides, the database was completed with the results of a case study from a dam construction project in the French West Indies. On the basis of a detailed and carefully justified analysis, parameters influencing the response of saturated residual soils to small strains are identified, is proposed. The correlations between the identification characteristics of the residual soils (initial void ratio, Atterberg limits, clay fraction) and the model parameters are investigated. The article proposes a general model for the evaluation of the small-strain stiffness of saturated residual soils using, in addition to the mean effective stress (p’) and the maximum mean effective stress (p’max ) the initial void ratio (e0 ) and, for intact soils, the clay fraction (CF) or, for remoulded soils, the plasticity index (PI).

Changing law of permeability coefficient during compression for reconstituted sandy clays

Sandy clay is defined as a sand–clay mixture with the mechanical behavior dominated by fine clay but affected by coarse sand. Twenty sets of one-dimensional incremental load consolidation and falling head permeability coefficient tests were performed on sandy clays. The samples of sandy clays were prepared by mixing two hosted clays with different sand fractions from 0% to 60%. The interrelation between the change of permeability coefficient with void ratio and the compression curves is established. The results indicate that the effect of sand fractions on permeability coefficient can be attributed to the variation of void ratio at liquid limit induced by sand fractions. The initial void ratio affects permeability coefficient by changing the void ratio under the same effective vertical stress. These two findings highlight that the permeability coefficient-void ratio relationship of sandy clays is a function of void ratio at liquid limit and void ratio. An empirical method of estimating permeability coefficient is also proposed using two physical indices of void ratio and void ratio at liquid limit for sandy clays having void ratio at liquid limits ranging from 0.63 to 1.73 and initial void ratios varying from 0.72 to 2.67.

A generalized water retention model in a wide suction range considering the initial void ratio and its verification

A generalized water retention curve (WRC) model in a wide suction range considering the initial void ratio is presented in this paper. Both capillary and adsorbed water in soil pores are considered. Based on the experimental results that the adsorbed water content wa is not dependent on the initial void ratio, a new degree of saturation equation of adsorbed water is established. Meanwhile, a new degree of saturation equation of capillary water at various initial void ratios is proposed with a void ratio-related expression of the air entry value. Compared to Lu’s model, only one parameter b is introduced in the established model, which can be easily calibrated using WRCs under two initial void ratios. The measured WRC results of 5 soils are used to verify the proposed model in comparison with the other 3 widely used WRC models. The soil used in the model validation covers a wide range of soil types from sandy soil to clay soil, including clayey silty sand, sandy clay till, clayey silt, expansive soil and lateritic soil. The proposed model is well verified for its ability to describe soil water retention characteristics in a wide suction range at various initial void ratios.

A new analytical method for estimating hydraulic parameters of a nonlinear consolidated aquitard with variable drawdown in adjacent aquifers

Estimation of hydraulic parameters and groundwater depletion of aquitards is necessary to evaluate the groundwater resources and land subsidence. In this study, an analytical solution for water release from a nonlinear consolidated aquitard was derived by approximating the drawdown history as a continuous piecewise linear drawdown function (PLD) with several stages, while the water level in adjacent aquifers varies arbitrarily over time. According to dimensionless and parameter sensitivity analyses, groundwater depletion of an aquitard increases with an increase in compression index, aquitard thickness, and water drawdown rate in adjacent aquifers, decreases with an increase in initial void ratio and effective stress, and is not affected by the consolidation coefficient. In addition, we proposed a type-curve fitting method to calculate the hydraulic parameters of the aquitard under the condition of PLD in adjacent aquifers. The proposed method was applied to estimate the hydraulic parameters of aquitards at two field sites in the Yangtze River Delta in China, i.e., Changzhou and Shanghai. Results show that the compression index of the aquitards in Changzhou and Shanghai are 0.074 and 0.24, respectively, while the consolidation coefficients are 7.62 × 10-7 m2/s and 2.16 × 10-6 m2/s, respectively. The hydraulic conductivity and specific storage estimated by the proposed method are in good agreement with previous studies and the results of the geological method of Konikow and Neuzil (2007). The proposed analytical method for estimating hydraulic parameters and groundwater depletion of aquitards will contribute to the sustainable management of groundwater resources in multi-layer aquifer systems.

Effects of biochar on the compressibility of soil with high water content

This study investigates the potential utilization of biochar in reclamation fills to improve the compressibility of soil with high water content. Biochar, a recycled carbon-rich biomass commonly used for contaminated soil remediation and carbon sequestration, is examined for its impact on the compression behavior of treated soils. The influence of biochar content, initial water content (w0), and biochar saturation on the compression behavior of biochar-treated soils with high water content is analyzed. The results revealed that the addition of both raw biochar and biochar saturated with water significantly enhances the remolded yield stress (σ′yr) and reduced the void ratio (eyr) at σ′yr. Raw biochar exhibits higher σ′yr and lower eyr values compared to water-saturated biochar, mainly due to its greater water absorbing potential of raw biochar. The variations of σ′yr and eyr induced by biochar can be attributed to the decrease in initial void ratio (e0) and the increase in void ratio at liquid limit (eL), which can be effectively normalized using empirical equation developed for reconstituted soil without biochar. Furthermore, the compression parameters (e*100 and C*c) show a decreasing trend with increasing biochar content and decreasing initial water content. Soil with saturated biochar displays higher e*100 and C*c values in comparison with soil with raw biochar. The changes in e*100 and C*c corresponded well to empirical equations developed for reconstituted soil without biochar, indicating that the compressibility changes induced by biochar depended on variations in physical properties (e0 and eL), following similar patterns observed in reconstituted soils without biochar. Therefore, the compression curve of biochar-treated soil in the postyield regime can be effectively normalized by using void index into the ICL or EICL, suggesting its practical applicability for predicting the compressibility of reclamation soil with biochar. These findings demonstrate that biochar-treated soil with high water content exhibits favorable geotechnical properties, making it suitable for use as soil reclamation fills or in landfill applications.

Microscopic study of the impact of particle morphology on the compressibility of calcareous sands

As a kind of unique marine sediment, Calcareous sand exhibits high compressibility because its irregular particle morphology leads to the formation of large interparticle voids. In this study, using calcareous sand samples from the South China Sea, we employed X-ray CT scanning technology to reveal the microstructural evolution of calcareous sand during compression. This allowed us to establish correlations between particle morphology, relative density, vertical stress, and microstructural parameters. The research findings are as follows: (1) Samples with a higher proportion of cube shape particles have larger initial void ratios, and experience a more significant decrease in void ratio under stress. Dense samples exhibit greater deformation resistance and lower particle breakage rates, resulting in a slower reduction in void ratio under stress. (2) The number of pores in the samples follows a V-shaped trend with an increase in the proportion of cube shape particles, reaching its minimum when the proportions of cube shape and platy shape particles are balanced. The number of pores increases with an increase in vertical stress and relative density. (3) The equivalent pore diameter and pore volume of the samples exhibit an inverted V-shaped trend with an increase in cube shape particle content, reaching their maximum when the proportions of cube shape and platy shape particles are balanced. (4) The more cube shape particles in the sample, the more irregular the pore shapes become. Under vertical stress, the influence of particle morphology on pore shape gradually diminishes until it disappears. (5) The particle coordination number in the samples predominantly falls within the range of 3.79–5.68. The coordination number increases with increasing relative density and vertical stress, with vertical stress exerting a significantly greater influence on the coordination number than relative density. Under vertical stress, samples with more cube shape particles exhibit smaller coordination numbers and higher particle breakage rates.

Elastic-viscoplastic model for coarse-grained soil considering particle breakage

This paper presents a novel elastic-viscoplastic constitutive model for reproducing the time-dependent behaviour of coarse-grained soil considering particle breakage, by integrating the Unified Hardening (UH) model, the elastic-viscoplastic (EVP) model and the overstress theory. The relationship between the degree of particle breakage and the loading rate is established, and the state variables associated with the critical state of coarse-grained soil are derived to jointly consider both time and particle breakage. A new three-dimensional elastic-viscoplastic constitutive model is then constructed through combining the one-dimensional viscoplastic hardening parameter with a secondary consolidation coefficient considering particle breakage. The proposed model requires 19 parameters and it can well describe the influence of time-dependency and particle breakage to the shear, dilatancy, and compression behaviours of coarse-grained soil with various confining pressures or initial void ratios. Comparisons between the model predictions and experimental data are employed to validate the capability of the proposed model to replicate the time-dependent behaviour of coarse-grained soil.

Uniqueness of the Normal Consolidation Line for Gold Tailings

Abstract Depending on the stress state, mine tailings are generally accepted to be susceptible to static liquefaction. A common method to assess the in situ stress state of tailings in relation to static liquefaction susceptibility involves the use of the state parameter. Because most tailings materials are normally consolidated (NC), this type of assessment requires knowledge about the normal consolidation line (NCL). It has been shown experimentally that the uniqueness of the NCL is vastly different for fine-grained and coarse-grained soils, with clays usually exhibiting a unique NCL and clean sands exhibiting an infinite number of parallel NCLs. Gold tailings, a sandy silt, fall between clays and clean sands, and there are limited experimental data regarding their compression behavior over a range of initial void ratios. This lack of data results in inconsistent interpretation of the uniqueness of the NCL for gold tailings in the industry. This can influence the results of designs and safety evaluations of tailings dams. In this study, a number of oedometer tests were conducted on gold tailings sourced from an active tailings dam in South Africa. Several specimens were prepared at various initial densities and were consolidated in small increments to a high effective stress. The oedometer tests were supplemented with triaxial compression tests, from which a unique critical state line was identified. Across the oedometer and triaxial tests, it was found that the behavior of the NC and overconsolidated samples was consistent with that typically observed for fine-grained soils. Therefore, for practical purposes, it appears that the gold tailings tested can be viewed in a framework with a unique NCL. No significant influence of particle crushing was noted.

Numerical modelling of shield tunnel face failure through a critical state sand plasticity model with nonlocal regularization

During shield tunneling in sand strata, variations in the state of sand can lead to localized instability and strength loss, which brings about numerical difficulties. This paper numerically investigates how nucleation and propagation of plastic deformation zones, including those leading to localized banding, possibly promote failure of shield tunnel faces excavated in sand. To this end, a material state-dependent model is used to capture the mechanical responses of sand. Nonlocal enhancement is introduced, through the volumetric strain increment that drives the change of void ratio and related material hardening/softening behavior, to regularize ill-posed boundary value problems caused by the activation of strain localization. Simulations of tunnel face failure indicate that lower initial void ratios result in more concentrated plastic deformation in the vicinity region near the face and a strain-softening trend in global deformation responses. Conversely, initial looser states drive the deformation zone to propagate spatially to the ground surface, and the resultant global deformation responses exhibit strain-hardening. The second-order work is used to explain the link between material instability around the tunnel faces and initial density. It was found that material instability usually occupies a fraction of plastic deformation regions, and shrinks as sand initial density increases.

Investigation on the triaxial creep characteristic of coarse granular materials with different initial void ratios

The creep deformation of coarse granular materials is closely related to the state of creep stress and the degree of compaction. A serious of triaxial creep tests using the single-line method were carried out to investigate the influence of initial void ratio and triaxial stress state on the creep deformation and creep strain direction of coarse granular materials. The test results primarily indicate that the creep strain increases with an increase in initial void ratio under identical stress conditions, and the volumetric creep strain decreases with an increase in stress ratio under high confining pressure conditions. Furthermore, the variation in the initial void ratio has little influence on the direction of creep strain under the same creep stress state. The effect of generalized stress on the final creep strain and creep dilation ratio were further discussed. It was observed that the final deviatoric creep strain exhibits a stronger correlation with the deviatoric stress q compared to the mean normal stress p. Additionally, the creep dilatancy decreases with an increase in stress magnitude under identical stress ratio conditions. Based on the test results, a computation model for the final deviatoric creep strain with the consideration of initial void ratio and creep stress was proposed by modifying a basic power function with deviatoric stress q as the variable. After that, a modified stress-dilatancy equation for coarse granular materials was used to predict the direction of strain during creep process. Finally, the final volumetric creep strain was indirectly calculated by integrated the computation model for the final deviatoric creep strain and the creep stress-dilatancy equation. The reasonable of the proposed model was verified through a comparison of computation results and test results.

Study on the Unified Mechanical Properties of Ili Undisturbed Loess under the Influence of Soluble Salt

Through three stress path tests of unsaturated Ili undisturbed loess, the effect of soluble salt content on the deformation of net mean stress, suction, and deviated stress were investigated. The mechanical properties of the normalized compression curve, soil water characteristic curve and critical state line were revealed. The test results indicate that: in the isotropic compression test, the normal compression curves controlling different suctions can be characterized by using the initial void ratio and the yield net mean stress, and can be described as a two-parameter exponential function. In the triaxial shrinkage test, the soil water characteristic curves controlling vary net mean stresses are dimensionless by using saturated moisture and air entry value, and the normalization formula can be characterized by a single parameter exponential function. In the consolidation shear test, the corresponding effective net mean stress is calculated by suction and saturation. The critical state lines under the unsaturated condition controlling vary suctions can be described as the critical state line under the saturated condition on the plane of effective net mean stress and deviator stress. When the effective net mean stress is constant, the critical state lines under the unsaturated condition can be characterized by the degree of gas saturation and the ratio of unsaturated void ratio to saturated void ratio. The research will offer reference pointing at the regulation and utilization of water and salt in the loess region of Central Asia, so as to better guarantee the sustainable development of saline-alkali land project construction.

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Enhancing reliability of consolidation design parameters for residual settlement estimation: a sensitivity analysis approach for existing container yard in Belawan, Medan

Data variation in geotechnical engineering poses challenges in setting up reliable design parameters used for design or analysis. This study aims to accommodate the uncertainty of consolidation design parameters, including the compression index (Cc), initial void ratio (e0), and coefficient of consolidation (Cv), to estimate the residual settlement. A case study of Belawan New Container Terminal (BNCT), which consists of two container yards situated in a reclamation area, has been presented in this paper. A robust method employing parameter sensitivity analysis and loading scenario has been carried out. Sensitivity analysis has been performed by considering ranges for each compressibility parameter consisting of low, best, and high estimates. This approach leads to nine analysis scenarios and doubles after including the service load scenario. The results are then compared with available settlement plate and topographic/bathymetric data (pre, during and post-construction). The scenarios that best fit the monitoring data are selected as the basis for estimating the residual settlement over a design lifetime of 50 years. The residual settlement is expected between 1 m and 1.27 m without service load condition, and 1.92 m to 2.46 m. with a service load of 60 kPa (equivalent to six stacks of 20-foot containers).