Unsaturated Soil Mechanics Research Papers (original) (raw)

2025, Journal of Geoscience and Environment Protection

The mechanics of unsaturated soils is a relatively recent and evolving field of study. This paper introduces an innovative machine learning-based approach for developing constitutive models to describe the soil-water retention curve, hydraulic conductivity, and shear strength of unsaturated soils. These models were built using comprehensive soil characterization data and triaxial test results, incorporating parameters such as gravel, sand, silt, and clay content, plasticity index, porosity, and permeability. Equations were implemented using algorithms developed in the Mathematica ® programming environment. The results demonstrate that the proposed models are both physically consistent and experimentally validated, exhibiting high precision and practical applicability. While this approach significantly optimizes the development of constitutive models, it does not replace the need for conventional testing, instead serving as a robust complementary tool. The proposed methodology offers an efficient and reliable solution for generalizing constitutive models across various unsaturated soil types, advancing knowledge and applications in the field.

2025, Engineering Geology

The formation of residual soil of Grade V and Grade VI due to tropical weathering process introduces small hydraulic heterogeneities in the soil mantle which greatly alter the suction distribution during rainfall infiltration, and hence the stability of the residual soil slopes. This paper presents field evidences of suction distributions in a heterogeneous residual soil slope. Several modeling approaches were attempted to simulate the observation by considering the presence of thin layer of Grade VI, the variation in the hydraulic conductivity of Grade V layer as well as the effect of evaporation. The soil hydraulic heterogeneity in Grade V layer was modeled by adopting continuum method, in which the residual soil was subdivided into three zones of average hydraulic conductivities. The analysis results show that the presence of thin layer of Grade VI residual soil and the relict discontinuities in Grade V soil must be considered in the analysis as these features introduced permeability disparity and thus a natural capillary barrier effect that limited the downward movement of infiltrated rainwater even during the exceptionally wet condition. The results also show that the inclusion of evaporation effect provided a better prediction to the suction distributions during wet condition than dry condition.

2025, Publication of: Balkema (AA)

Conventional coupled elastoplastic deformation-flow finite element methods are not suitable for stability problems, since numerical results often become unstable as stresses in the elements arrive at the critical state. An analytical method using the imaginary viscosity method, a standard viscoplasticity computation scheme, is developed to analyse soil behaviour from start to failure. The procedure is validated using the examples of the bearing capacity of a footing on clay and an embankment on soft soil.

2025, Transportation Geotechnics

Pavement base layers are constructed to specified quality standard to distribute traffic loads and drain excess
water from the pavement structure. The use of recycled concrete aggregates (RCAs) as base material has become
increasingly common due to their mechanical properties and sustainability benefits. However, poor drainage and
the presence of unhydrated cement in RCAs can lead to pavement saturation, adversely affecting their performance.
Therefore, it is essential to thoroughly evaluate the physical, mechanical, and hydraulic properties that
may impact the pavements’ performance. In this research, twelve RCA base materials, including three Open-
Graded Drainage Courses (OGDC), a blended mix, and five natural aggregates (GMs) were evaluated for index
properties, hydraulic properties, and stiffness (resilient modulus, MR). Using the FHWA Drainage Requirement in
Pavements (DRIP) software and the laboratory test results, the time required to drain 50 % of the saturated layer
was also evaluate. The GMs, with MR ranging from 114 to 513 MPa, had higher density but exhibited “poor” to
“very poor” drainage quality. In contrast, the coarse gradation of RCAs, with MR varying from 162 to 730 MPa,
led to higher stiffness and better drainage. However, coarse RCAs exhibited 4 to 6 times higher moisture absorption,
while the sand fraction had 3 to 5 times higher absorption, causing RCAs to retain moisture longer than
GMs. No material exhibited “excellent” drainage quality, not even the OGDCs. Furthermore, increasing the layer
thickness had minimal impact on improving drainage quality, highlighting the importance of considering
alternative pavement drainage solutions for effective pavement drainage.

2025, Civil Engineering Infrastructures Journal (CEIJ)

The soil is a heterogeneous and anisotropic medium. Hydraulic conductivity, an intrinsic property of natural alluvial deposits varies both deterministically and randomly in space and has different values in various directions. In the present study, the permeability of natural deposits and its influence on the seepage flow through a natural alluvial deposit is studied. The 2D Finite Difference code, FLAC 5.0, is used for modeling permeability as a random variable with lognormal distribution and correlated structure. Effect of spatially varying permeability on the seepage flow through deposit is investigated for both isotropic and anisotropic conditions. Results show that in isotropic condition, the mean discharge flow rate calculated from stochastic analyses is less than the equivalent deterministic value and this reduction depends on the coefficient of variation, COV of permeability and the correlation length. The directionality of permeability introduced as mechanical anisotropy was also studied along with the heterogeneity. It was found that increasing the anisotropy ratio of permeability leads to the formation of horizontal flow canals and increasing the seepage flow consequently at a constant vertical permeability. Variation of permeability coefficient was found to have almost no impact on mean discharge flow rate for anisotropic fields in comparison to the isotropic condition.

2025, HAL (Le Centre pour la Communication Scientifique Directe)

We present a three-dimensional discrete-element approach for numerical investigation of wet granular media. This approach relies on basic laws of contact and Coulomb friction enriched by a capillary force law between particles. We show that the latter can be expressed as a simple explicit function of the gap and volume of the liquid bridge connecting a pair of spherical particles. The length scales involved in this expression are analyzed by comparing with direct integration of the Laplace-Young equation. We illustrate and validate this approach by application to direct shear and simple compression loadings. The shear and compression strengths obtained from simulations reproduce well the experimental measurements under similar material and boundary conditions. Our findings show clearly that the number density of liquid bonds in the bulk is a decisive parameter for the overall cohesion of wet granular materials. A homogeneous distribution of the liquid within the bridge debonding distance, even at low volume contents, leads to highest cohesion. The latter is independent of the liquid content as far as the liquid remains in the pendular state and the number density of liquid bonds remains constant.

2025

This paper shows the different in the volumetric strains between the Oedometer tests with different soaking durations and the unsaturated triaxial tests. The disturbed samples were taken from Al-Najaf city in Iraq. All specimens have the same high gypsum content of 29 %. For Oedometer tests, the specimens are tested in the different soaking durations; the first is in natural moisture content then half hour, one week and two weeks. While in triaxial tests, a wetting induce has been conductive to estimate the volumetric strains under two stress levels (2.5 and 5 kg/𝑐𝑚 2 ) with presence of matric suction in four levels; initial matric suction (ψo), 0.6 ψo, 0.3 ψo and zero ψ. The results from unsaturated triaxial tests indicate that the volumetric strains are increased as matric suction decreased and the trend of stress-strain curve became steep. While from Oedometer tests, when the specimen is soaked in natural and for a half hour, the volumetric strains are not significantly changed and close to the high matric suction. When the soaking time is increased to a one week, there is relatively increase in volumetric strains. But after two weeks soaking in Oedometer cell, the volumetric strains are very clear in increasing and close to the volumetric strains from unsaturated tests in low matric suction.

2025

Many structures that have been constructed on gypsiferous soils have big problems, especially in drying-wetting sequence, contrast of construction on non-gypsum-soils due to the collapsibility of gypsum. These soils are formed by the evaporation of saline groundwater when the water table is near the ground surface. Gypsiferous soils are widespread in the Middle East especially in regions peripheral to the Red sea and Arabian Gulf. They cover large areas of Iraq which may be extended to 20% of the total Iraq's area. The present work condenses on the effect of soaking and leaching progresses on the soil stability in the saturated and unsaturated conditions.

2025, Malaysian Technical Universities Conference on Engineering and Technology 2015

Laterite soil is commonly considered as a good natural foundation and building material. This type of soil is found in abundance in most of the tropical countries including Malaysia. In any project, the properties of laterite soil are determined through borehole sampling which is the actual determination of the subsurface soil but on contrary it is very expensive and time consuming process and also requires too much effort. Therefore, in order to save cost, time and energy, electrical resistivity method is an alternative method which could provide quick and rapid assessment of the subsurface soil without causing any disturbance to the soil and thus much time and money could be saved. In this research paper, a conceptual model for the assessment of strength properties of compacted laterite soil has been proposed based on the correlations of soil properties mainly cohesion and angle of internal friction with electrical resistivity values. The results analyzed from the study hopefully will contribute for the possible assessment of the electrical resistivity method to be used for the determination of geotechnical properties of laterite soil in geotechnical calculations such as factor of safety (FOS) and bearing capacity.

2025, Malaysian Technical Universities Conference on Engineering and Technology 2015

Geo-electrical assessment is an appealing instrument for depicting subsurface properties without soil unsettling influence and also can be considered as an intermediary for the spatial and fleeting variability of numerous other soil physical properties (i.e. structure, water substance, or liquid synthesis, porosity, degree of saturation etc.) and strength parameters (i.e. cohesion and angle of friction). Since the system is non-dangerous and exceptionally delicate, it offers an extremely fascinating apparatus for depicting the subsurface properties without burrowing. In this paper a conceptual model is developed for the assessment of slope stability and FOS using electrical resistivity values of the insitu soil at controlled moisture content (30%). The obtained results will be interrelated with soil physical properties (moisture content, plasticity index, specific gravity, porosity, degree of saturation etc.), chemical properties (Cation exchange capacity (CEC), p H and mineralogy) and strength parametres of soil such as, cohesion and internal angle of friction. Assessment of geotechnical hazards will incorporate by applying 1D electrical resistivity survey on a laboratory scale using fabricated soil box. The established results will hopefully contribute in the calculations of bearing capacity, slope stability and factor of safety for soil.

2025

2025, AL-Rafdain Engineering Journal (AREJ)

Infiltration of water in unsaturated soils has long been an interest of study in geotechnical engineering. A wide range in permeability coefficient has been proven to be a major obstacle in analyzing seepage problems. Soil-water characteristic curve (SWCC) is a fundamental constitutive relation for the explanation of the engineering behaviour of unsaturated soil. The effect of anisotropy on SWCC and unsaturated coefficients of permeability and diffusion has been studied in this paper, by taking sets of duplicate disturbed and undisturbed specimens prepared in the vertical, 45º inclined and horizontal directions. The results showed that there is a noticeably anisotropic in the basic characteristics of SWCC and the unsaturated coefficients of permeability and diffusion specially at the low values of suction. The variations of the hydraulic conductivity and vapor diffusivity versus suction gradient were opposite. Furthermore there is a noticeable difference between the disturbed and undisturbed specimens in the SWCC and coefficients of diffusion and permeability.

2025, International Journal of Engineering Research

In this paper, we evaluate the performance of the most widely used semi-empirical models (van Genuchten (1980), Fayer and Simmons (1995) and Fredlund and Xing (1994)) and, an empirical model, the Modified Kovacs (MK) model for the determination of soil-water characteristic curve at the low water contents of two horizons of a soil from Burkina Faso. Combining terms from capillary state and adsorbed state of soil water gives a physical basis for the Modified Kovacs model. Our study confirms that the use of semi-empirical models requires somewhat large dataset covering the entire range of water content while the empirical model MK requires only basic geotechnical properties of soil and a few experimental points to adjust the parameters m and a c of the model. It appears that the MK model, by its simplicity and lower cost for the acquisition of experimental data, is the most appropriate.

2025, Highway Research Board Special Report

Introductory Remarks by the Chairman "I believe the day must come when the biologist will-without being a mathematician-not hesitate to use mathematical analysis when he requires it." This statement was made by Karl Pearson in the January 17, 1901, issue of "Nature." The day has come, indeed, not oniy for the biologist but also for his brother the soil scientist, as the author proves in his excellent contribution to this symposium. It may be appropriate to supplement Pearson's words by the following remarks which Dr. Johnson made in the fourteenth "Rambler, 11 May 5, 1750: "The mathematicians are well acquainted with the difference between pure science, which has to do only with ideas, and the application of its .Laws to the use of lif~, i!! '.Vhich they are constrained to submit to the imperfections of matter and the influence of accident. 11

2025

Transient moisture flow in an unsaturated soil in response to suction changes is controlled by the unsaturated moisture diffusion coefficient. The moisture diffusion coefficient can be determined by measuring suction profiles over time. The laboratory testing approach involves measurement of the total suction changes with time using thermocouple psychrometers in cylindrical soil specimens with predetermined boundary conditions. The determination of the diffusion coefficient by this method is simple and relatively rapid and can be carried out on a routine basis in a geotechnical engineering laboratory. It is well-known that soils exhibit hysteresis with drying and wetting cycles. A similar hysteresis has been observed between the drying and wetting diffusion parameters for a number of undisturbed soil samples obtained from field borings across Oklahoma. The wetting diffusion coefficients are generally greater than the drying diffusion coefficients by a factor of up to 2.

2025

As we know, landfills contain large amounts of various pollutants, and any instability or destruction on the landfill slope can lead to significant human and financial losses. In such conditions, pollution can easily spread in the environment and lead to an ecological disaster. Therefore, the sustainability analysis of the landfill slope is of great importance. Since, due to climatic conditions, the amount of rainfall and the level of groundwater, soils are generally in an unsaturated state, in this article, the sustainability of the landfill is investigated using the unsaturated theory by considering the concept of suction stress and coding in C# in the Geo-studio software environment. To properly model and design the landfill, the properties of the soil materials of the covering parts of the landfill surface and the impermeable barriers at the bottom were considered. The safety factor of the landfill slope in the dry state was obtained, then the changes in the safety factor at different volumetric moisture percentages for the unsaturated surface and bottom soils of the landfill were calculated, and the effect of reinforcing the clay layers of the cover and bottom of the landfill on the slope stability was also investigated. The results obtained indicate that the safety factor in the unsaturated state compared to the dry state increases significantly; also, in the area of unsaturated soils, with a decrease in the volumetric moisture percentage, the safety factor increases. The notable result is that in unsaturated soils, the safety factor does not necessarily increase with the occurrence of reinforcement.

2024

Rainfall-triggered landslide will continue to pose serious threats to slopes in Thailand with the current climate change situation. To understand the mechanisms of such slope failure and develop a proper mitigation approach, the properties of residual soils in unsaturated state need to be fully characterized. This paper reports on laboratory results of Soil-Water Characteristic Curve (SWCC) of some residual soils in Thailand together with their prediction based on grain size distribution (GSD) curve. Miniature tensiometers as well as relative humidity sensors were used in determining the SWCC on undisturbed samples. Arya and Paris (1982) approach has been used to develop SWCC based on GSD. Excellent correspondence between the experimental and predicted curves was obtained.

2024

Soils located above the groundwater table are generally unsaturated and possess negative pore-water pressures. A soil-water characteristic curve (SWCC) that relates the water content of a soil to matric suction is an important relationship for the unsaturated soil mechanics. The SWCC essentially shows the ability of an unsaturated soil to retain water under various matric suctions. The filter paper method is a soil suction measurement technique. Soil suction is one of the most important parameters describing the moisture condition of unsaturated soils. The measurement of soil suction is crucial for applying the theories of the engineering behavior of unsaturated soils. In this paper, three soil samples were collected from three sites within Baghdad city in Iraq. These soils have different properties and they were prepared at different degrees of saturation. For each sample, the total and matric suction were measured by the filter paper method at different degrees of saturation. The soil samples were mixed with different percentages of Nacl salt. It was concluded that the suction increases with the decrease of the degree of saturation. The relationships between the total and matric suction and the filter paper water content are approximately linear and indicate decrease of suction with the increase of the filter paper water content. All soil samples exhibit unique linear relationship between the total suction and filter paper water content and matric suction. When salt exists in the soil, there is a noticeable increase in both matric and total suction.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

This paper presents selected aspects of the model preparation and the experimental procedures used for testing the unsaturated soil behaviour in centrifuge environment. The study is based on the results of centrifuge tests carried out to investigate the influence of partial saturation on the behaviour of laterally loaded piles. The soil used in the experimentation is a high permeability silty clay soil, named B-grade kaolin. The models were statically compacted at two different densities with the same water content. In order to reduce the after compaction suction, the samples were subjected to an imbibition process at 1×g connecting the bottom of the model with the water reservoir. The influence of the compaction process and the imbibition stage on the subsequent inflight soil conditions are discussed and analysed. The centrifuge tests were realised at the centrifuge centre of the University Gustave Eiffel, in Nantes, France, in the framework of the GEOTRANSALP project.

2024

Improvements in early warning systems against rain-induced landslide such as prediction modelling using rainfall records, is urgently needed in vulnerable regions. The existing warning systems have been applied using stability chart development and real-time displacement meas-urement on slope surfaces. However, there are still some drawbacks such as: ignorance of rain-induced instability mechanism, mislead prediction due to the probabilistic prediction and short time for evacuation. In this research, a real-time predictive method was proposed to alleviate the drawbacks mentioned above. A case-study soil slope in Indonesia that failed in 2010 during rainfall was used to verify the proposed predictive method. Using the results from the field and laboratory characterizations, numerical analyses can be applied to develop a model of unsaturated residual soils slope with deep cracks and subject to rainwater infiltration. Real-time rainfall measurement in the slope and the prediction of fu...

2024

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2024

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2024, Journal of Ferdowsi Civil Engineering

In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior interaction is presented. The dam structure is flexible with infinite reservoir Exact consideration of the radiation boundary condition of the infinite reservoir and deformation of dam structure are included in the formulation which explicitly expresses the physical phenomena of fluid-structure system. The hydrodynamic pressure in the fluid domain of the structure-reservoir system is assumed to be governed by the pressure wave equation. The upstream face of the dam is considered vertical. The dam structure is modeled as a cantilever Euler-Bernoulli beam. The thickness of the dam is assumed to be variable. A new method for analysis of non-prismatic beams is presented. This new method is based on using new functions namely Basic Displacement Functions (BDFs).These functions are obtained by solving the governing equation of motion of a non-prismatic Euler-Bernoulli beam. Using this method dynamic shape functions are efficiently obtained for non-prismatic beams. Interactive behavior of the dam-reservoir system with different geometrical properties is demonstrated by numerical examples when the system is subjected to ramp acceleration and El Centro earthquake ground motions. The results are compared with those of literature and the competency of the method is shown in both economy and exactness.

2024, Journal of Ferdowsi Civil Engineering

The main role ofcore in earth dams is to reduce and control the seepage flow through the dam. In order to achieve this purpose, the core material is usually selected from pure or mixed clays.Due to very small coefficient of permeability, the clay cores can prevent water leakageeasily. However, pore water pressures developed inside the core during construction, can not be dissipated quickly. As a result, increasing the rate of embankment filling during the construction stage, may lead to large development of the pore pressure inside the core. In this study,based on a hardening elasto-plastic constitutive model, the total stresses and pore pressures inside the core of MASJED-E-SOLEYMAN rockfill dam, are calculated using the PLAXIS software during the construction and first reservoir filling stages.The analysis is in term of effective stress coupled with consolidation analysis. In order to verify the result of the numerical analysis, the measurment data from installed instruments intherockfill dam have been compared with the numerical results.This comparsion shows that the numerical analysis results are in a good agreement with the instrument results. Excess amount of pore pressures in the core of this dam is due to very small coefficient of permeability and high rate of embankment filling.

2024, Journal of Ferdowsi Civil Engineering

A significant increase in pore water pressure during construction of earth dams may lead to the hydraulic fracture of dam body in pounding. Thus having sufficient information about generation pattern of excess pore water pressure inside the core is essential. In the present study, using finite element method in coupled analysis of earth dams, excess pore water pressure and displacement values are estimated during the construction of Daroongar dam by developed Fortran code, and the results were compared with instrumentation data. Finally the actual amounts of horizontal and vertical permeability coefficients were determined for the materials by regression analysis.

2024, Journal of Ferdowsi Civil Engineering

Soil slope stability analysis, is one of the most important issues in the design of earth dams, roads, canals and levee. One of these methods is the limit equilibrium analysis with horizontal and vertical slices method.To evaluate the results of horizontal and vertical slice method in the calculation of stability safety factor, at first Two formulations of each method selected, then stability Safety factor has been achieved with the use of these methods for several slopes. The exact amount of stability safety factor by using of the analytical method has been obtained then the accuracy of the each method and comparison of their results with each other is studied.Considering studies at this research, concludes that at generally vertical slices method results exact and with a few confidence rand. Whereas horizontal slices method results have a relationship with selected formulation. In cases where the soil is layered horizontal or issues with horizontal forces, horizontal slices method provide greater ease of use. Finally, explained recommendations for using slice method.

2024, HAL (Le Centre pour la Communication Scientifique Directe)

This document reflects only the authors' views and not those of the European Community. This work may rely on data from sources external to the members of the FloodProBE project Consortium. Members of the Consortium do not accept liability for loss or damage suffered by any third party as a result of errors or inaccuracies in such data. The information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and neither the European Community nor any member of the FloodProBE Consortium is liable for any use that may be made of the information.

2024, Australian Geomechanics Journal

A series of interface direct shear box tests are performed between a compacted completely decomposed granite (CDG) soil and cement grout under different matric suctions and net normal stresses by using a modified direct shear apparatus. Axis-translation technique is applied to control the pore-water and pore-air pressure. The behaviour of shear stress-displacement curves of soil-cement grout interface tests is similar to those of soil-soil direct shear tests. Matric suction and net normal stress have significant influence on the hardening-softening behaviour of soil-cement grout interface. The interface-dilation is also greatly influenced by matric suction and net normal stress. The variation of interface shear strength with respect to net normal stress (failure envelope) for different matric suctions is observed as linear. The apparent angle of interface friction and adhesion intercept increase with matric suction. The compacted CDG soil-cement grout interface behaves as a rough interface. The apparent interface friction angles for different suctions are nearly equal to the apparent friction angles of CDG soil under the same suctions. However, the apparent adhesion values are higher than the apparent cohesion values of CDG soil in lower suction range, but are lower in higher suction range. The variation of interface shear strength with matric suction (suction envelope) is nonlinear and b δ value decreases with increase in matric suction.

2024

In the content of this study, non-linear consolidation behavior of unsaturated soils was investigated. In this respect a non linear differential equation for consolidation has been proposed. This proposed differential equation and its solutions enlighten both the diffusive characteristics and the time rate of settlement of soils. Besides, this study also enables to perform the matric suction calculation which is the one of the most important parameter of unsaturated soils. Two types of unsaturated consolidation test, constant water content test and controlled matric suction test were carried out, respectively. Theoretical and experimental results were compared and it was found that they are in close agreement with each other. It was also observed that the proposed method can be applied to the saturated soils.

2024, Research Square

In this paper the applying of inverse problem for calculation of diffusion coefficient distribution into porous cylindrical sample into one-dimensinal case is demonstrated. The main purpose of work is concentrated for adaptation of well know diffusion equation with boundary conditions to experimentally obtained humidity profiles into porous sample. Empirical equations for diffusion coefficients according to obtained humidity distribution are also reviewed. The proper physical interpretation of water vapor diffusion coefficient for coordinate and time dependencies is proposed. For this purpose the averaged quantities are introduced.

2024

Transport of water in concrete under real environment was analyzed by the hybrid model of capillary suction and nonsaturated diffusion. While concrete surface was subjected to liquid water, the water transport phenomenon was modeled by capillary suction process into concrete pores. The water loss or gain, while concrete surface was exposed to the air, was described by nonsaturated diffusion model considering capillary condensation and diffusion of vapor and liquid water in concrete pores. The analytical results were verified with the experimental results under real environment.

2024

The paper presents a mechanical model for non-isothermal behaviour of variably saturated soils. The model is based on an incrementally non-linear hypoplastic model for saturated clays and can therefore tackle the non-linear behaviour of overconsolidated soils. A hypoplastic model for non-isothermal behaviour of saturated soils was developed and combined with the existing hypoplastic model for unsaturated soils based on the effective stress principle. The number of model parameters is kept to a minimum, and they all have a clear physical interpretation, to facilitate the model usefulness for practical applications. The step-by-step procedure used for the parameter calibration is described. The model is fi nally evaluated using a comprehensive set of experimental data for the thermo-mechanical behaviour of a variably saturated compacted silt.

2024

RESPONSE OF UNSATURATED SILTY SAND OVER A WIDER RANGE OF SUCTION STATES USING A NOVEL DOUBLE-WALLED TRIAXIAL TESTING SYSTEM Ujwalkumar D. Patil, PhD The University of Texas at Arlington, 2014 Supervising Professor: Anand J. Puppala Co-Supervising Professor: Laureano R. Hoyos In recent decades, the state-of-the-art of our understanding of unsaturated soil performance has been considerably enhanced by the incorporation of novel and advanced features into the conventional testing devices such as direct shear device, ring shear device, triaxial device and true triaxial device. The novel suction-controlled triaxial system used in this research is fully automated and has enhanced features such as volume change device and double-walled cell to monitor the volume change accurately during all the stages of the unsaturated triaxial test. Despite their sophistication, such devices can help in testing mechanical behavior of unsaturated soils only up to the matric suction (s) value of 1500 kPa (...

2024, Géotechnique

Rammed earth is a manufactured material comprising sand, gravel and clay, which is compacted between forms to build walls. Primarily a historic method of construction, it is now receiving considerable interest worldwide owing to its zero reliance on materials such as cement, and its potential for recycling. Despite its longevity, the source of its shear strength is poorly understood. This paper presents initial laboratory test results that point to the main source of strength in rammed earth being suction, and indicating that recent advances in unsatu-rated soil mechanics may also be applied to this material.

2024

This communication presents an overview of the MUSE Research Training Network. The MUSE project is funded by the European Commission and involves six European universities and five industrial partners in a cooperative research and training programme over a period of four years in the area of unsaturated soil mechanics. The research activities include laboratory testing, constitutive modelling, numerical analysis and application to boundary value problems. The training activities include the participation of ...

2024, HAL (Le Centre pour la Communication Scientifique Directe)

We herein present a recent micromechanical approach combining analytical homogenization with Discrete Element Method (DEM) simulations for a better understanding of the mechanical behavior of granular soils in an intermediate state of water saturation. Analytical homogenization first leads to a so-called µUNSAT general expression for the macroscopic stress state, starting from micro-scale internal forces. The µUNSAT equations involve surface tension in addition to capillary pressure, and show a tensorial nature in accordance with preferential directions for the internal forces at the micro-scale. A DEM approach then enables one to access all stress quantities in the specific case of ideal wet granular materials. The results discuss the stress-strain-strength effective nature of the contact stresses stemming from contact forces, as well as the tensorial, anisotropic, character of fluid-induced capillary stresses.

2024

The design of foundations for sites having expansive soils is one of the greatest challenges facing geotechnical engineers today. Intolerable heave of foundations on expansive soils often affects critical safety aspects of structures. Therefore, it is imperative that design of foundations for expansive soils includes analyses of expected heave and consequences of foundation movement over the design life of the structure. Current technology generally considers the amount of predicted heave that will ultimately occur at a site. Design of foundations for extreme ultimate conditions is not always practical and economical in engineering practice. When large values of heave are predicted, the depth of potential heave may be very deep, and the time required for the wetting front to reach large depths of potential heave may exceed the design life of the structure. In that case, it is important to consider the rate of water migration in the vadose zone. Thus, design of foundations for buildings on expansive soils must consider the migration of the subsurface water that will occur during the design life of the structure, and the amount of heave that such wetting will produce. Current design procedures that are in common use are deficient in this respect. Aappropriate design of foundations on expansive soils must consider accurate prediction of soil/bedrock heave and the effect of that heave on foundation movement

2024, 1st European Conference on Unsaturated Soils

Volume change in expansive soils occurs due to changes in the soil water system that change the stress equilibrium of the soil. Consequently, when determining the Soil Water Retention Curve (SWRC) of an expansive soil, it is important to consider the volume change that occurs as the suction, and hence water content, changes during the test. Experiments using the Fredlund SWCC device and the filter paper method were conducted to take into account the effect of the volume changes on the soil water retention relationship of expansive soils. Claystone samples of the Denver and Pierre Shale Formations obtained near Denver, Colorado, USA were used in the study. A moist tamping system was used to obtain "identical" soil specimens. The observed experimental data were used to evaluate the previously published mathematical equations of SWRC. It is shown that the Fredlund and Xing equation is in the best agreement with the experimental data among the equations. In addition, a bilinear form was used to express the SWRC for the expansive soils. It is concluded that the bilinear form of the SWRC gives the best fit to the measured experimental data.

2024, 1st European Conference on Unsaturated Soils

An evaluation of swell prediction utilizing the filter paper test for measurement of soil suction was conducted in this investigation. Filter paper tests were conducted on four types of clay soils including claystone of the Denver and Pierre Shale Formations, from Colorado, USA, Black Cotton clay from Texas, USA and a sandy clay from Nunn, Colorado, USA. This paper presents the results of the filter paper calibration and measurement of suction values at low water contents for unsaturated soils and their use in predicting volume change. Total oven-dry suction values for the four soil types tested ranged from 6.32 pF to 6.51 pF. The calculation of the suction compression index, C(h), based on an oven-dry suction value of 6.25 pF rather than an oven-dry suction value of 6.4 pF results in an increase in C(h) of 19.4% for the Denver formation and 16.0% for the Pierre Shale tested.

2024

Construction of light structures in arid climates generally results in an increase in water content of the subsoil profile due primarily to irrigation and a reduction of evapo-transpiration. Water introduced by irrigation at the surface migrates downward and increases the water content at depth as it advances. Although the subsurface is wetted significantly, the soil above the wetting front may not become saturated. If the wetting front encounters an aquatard, a perched water condition may develop and the soils above the aquatardmay become saturated. Determination of a final water content profile for design of foundations on expansive soils is an important design parameter. In the absence of other data, it is conservative to assume that the entire profile is saturated. Alternately, modeling of water migration in the vadose zone can be performed to determine water content profiles for various site conditions. The results of this rigorous analysis can be used to determine a final water content profile for use in optimizing the design of foundations. However, this rigorous analysis is not always economical for small projects. Thus, a simplified procedure is presented that can be used to hand calculate final unsaturated water content profiles for design of foundations on expansive soils. The results of the water migration modeling and hand calculation methods are presented and the applicability of these methods is discussed. The resulting foundation design based on the final water content profiles determined from these two methods, as well as the assumption of full saturation, is presented and discussed.

2024

Soils that are stable when dry, but undergo a decrease in volume with an increase in water content are commonly termed, "collapsible soils". This paper presents the results of an investigation of the fundamental mechanism of collapse in unsaturated soils as it relates to stress state variables. A critical value of soil suction was determined at which collapse initiates. It was observed that the critical value of soil suction is that at which the soil begins to imbibe water as exhibited on the soil water characteristic curve (SWCC) curve for imbibition conditions.

2024, Geotechnical Engineering Journal of SEAGS&AGSSEA

Slope failures in embankments constructed in expansive soils are often induced by rainfall infiltration during wet seasons or after a heavy rainfall event. Field investigations regarding the effect of rainfall infiltration on slope instability for expansive soil embankments indicate that shrinkage cracks developed during the drying and wetting cycles play an important role in slope instability. The excessive amount of infiltration through the shrinkage cracks decreases the matric suction of the expansive soil, and hence, results in a reduction of the shear strength of the soil accompanied with soil expansion, or heave. Furthermore, the modulus of elasticity of the soil decreases as water content increases and the soil heaves. The influence of these factors on the slope stability of expansive soil embankments is reviewed and discussed in the paper. Numerical modeling using the finite element computer programs SEEP/W and SIGMA/W was conducted to evaluate the volume change of an expansive soil embankment slope due to changes in suction arising from infiltration. Longterm stability of the expansive soil embankment slope was conducted using the computer program SLOPE/W. The expansive soil slope was also analyzed with a proposed remediation scheme to evaluate the effect of the remediation on long-term stability. The results of the numerical modeling for the slope with remediation were compared to those obtained for the slope without remediation. Furthermore, heaving of the expansive soil is accompanied by a reduction in the shear strength of the soil. Therefore, analysis of heave using the oedometer method was discussed in the paper. The results of the heave prediction using the oedometer method were compared to those obtained from the numerical modeling method. Reasons for the differences in amounts of predicted heave using both methods are discussed in the paper.

2024, Proceeding of the 21st SEAGS and 4th AGSSEA Conference

The study focuses on the changes in seepage and stability of the dam with a clay core constructed with expansive soils. Laboratory testing was conducted to evaluate the swelling potential and hydraulic properties for the compacted expansive soils under various dry unit weights and initial water contents. Numerical modeling was conducted to evaluate the changes in seepage flow and slope stability due to the heaving of the expansive clay core for the dam. The findings suggest that to reduce seepage flow, the swelling soil should be compacted to a lower degree of compaction at a moisture content exceeding the optimum moisture content (OMC), which effectively reduces soil swelling and consequently minimizes seepage. Conversely, if stability is the primary concern, the swelling soil should be compacted to a relatively higher degree of compaction at a moisture content lower than the OMC, providing enhanced strength to the dam. In conclusion, the study demonstrates that for expansive soil used in dam cores, the same traditional compaction conditions utilized for seepage and stability in normal clayey soil can be applied. However, it is crucial to consider the specific characteristics of the swelling soil during the compaction process. By implementing suitable compaction techniques based on the desired outcome, seepage control, and dam stability can be effectively managed when utilizing swelling soil in dam construction. The findings offer valuable insights to engineers and practitioners involved in dam design and construction, aiding in informed decision-making and optimal compaction practices when incorporating swelling soils in dam cores.

2024

Loosely packed sandy soil, created via aeolian deposition and stabilised by interparticle bonding via gypsum crystals (dispersed within the soil fabric), are a significant geohazard in hot, arid environments such as the Middle East (for example, these deposits cover a large area of Iraq). Gypsum, being a moderately soluble salt, can have a substantial influence on the To My Mother; My Husband Hussain; My Kids Fatimah, Kawther and Ali v ACKNOWLEDGEMENT Foremost, I would like to express my sincere gratitude to my supervisors-Dr. Alexander Royal and Prof. Ian Jefferson for the continuous support of my PhD study and research, for their patience, motivation, enthusiasm, and immense knowledge. Their guidance helped me in all the time of research and writing of this thesis. My special thanks go to Mr Phil Atkins for his technical expertise in solving the electricalresistivity-acquisition system problems. I would also like to express my deep gratitude to Professor Nigel Cassidy for his help in the design the ER for the evaporation pipe. I would like to thank the reviewers: Prof. David Chapman and Prof. Gurmel Ghataora for their insightful comments and valued feedback during the annual progress reviews. I would like to express my deepest thanks to the technical staff at Civil Engineering laboratory for their assistance in the lab. Many thanks to Dr Anna Faroqy and Dr Giulio Curioni for their support, discussions and sharing literature. I would like to express my greatest gratitude to my family, specially my mother for her invaluable love, support and guidance throughout my research, my husband for his love, patience and support, and for my kids Fatimah, Kawther and Ali for their innocence and spontaneity. I would like to thank the Ministry of Higher Education and Scientific Research (MOHESR) of Iraq for financial support during my study. Lastly, my loyalty and thankfulness to every person regarded, encouraged and taught me since my childhood till the end of this thesis. Undoubtedly, there is a share for everyone of them in my career. vi

2024

Saeed Mojtabazadeh
سعید مجتبی زاده

2024

Apart from the supreme creator, my parents and my teachers are responsible for my life success and they are most respectfully acknowledged. My parents always wanted me to be an important and useful man. I always wanted to make them happy and I think I succeeded. The one who made my life comfortable and enjoyable is my wife Chitra and I thank her for looking after me. When speaking of teachers, I specially acknowledge my supervisor Dr. D.J Painter for his full support in both the research and writing, correcting my thesis with incredible patience and looking after my family welfare during this work. I also wish to acknowledge Prof. G.T Ward who kindly acceptedmy application to study in Lincoln University. All the staff in the Natural Resources Engineering Department are acknowledged with gratitude for their support for my work, specially my associate supervisor Dr. T.R.H. Davies for correcting my thesis and Dave Lees and Kelvin Nicoll for helping in instrumentation. This work would not be possible without the approval of the Governments of Sri Lanka and of New Zealand. I greatly acknowledge the authorities concerned and the people of New Zealand for financial support. I use this opportunity specially thank to my uncle Prince, Punchi and family, Robyn Painter, Michael, Ann and Jenifer for looking after us during our stay in New Zealand. I thank all of my friends who were available for making my life an enjoyable one during this study.

2024

The performance of lateritic soil treated with Bacillus coagulans (B. coagulans) in biocementation for use as a hydraulic barrier in municipal solid waste (MSW) containment application was evaluated.The natural lateritic soil was classified as A-4(2) using American Association of State Highway and Transportation Officials (AASHTO) classification system and SC using Unified Soil Classification System (USCS).Tests carried out include Atterberg limits, specific gravity, compaction test, cation exchange capacity (CEC), calcite content, volumetric shrinkage (VS), unconfined compression (UC), hydraulic conductivity,ultrasonic pulse velocity, micro analysis, batch equilibrium adsorption and column. Atterberg limits and specific gravity tests were done using four mix ratios which considered 25% of liquid limit of natural soil to be B. coagulans suspension (B) and 75 % of liquid limit of natural soil to be cementation reagent (C) making a total of 100 % liquid limit of natural soil, 25 % B-75 % C; 50 % B-50 % C and 75 % B-25 % C as well as 50 % B-50 % C of optimum moisture content (OMC). Soil samples for VS, UC, hydraulic conductivity and column tests were treated with B. coagulans at one-third (1/3) pore volume (Pore volume is the numerical difference between initial and final degree of saturation after full saturation of the soil specimens in water) in stepped suspension density of 0, 1.5 x 10 8 , 6.0 x 10 8 , 1.2 x 10 9 , 1.8 x 10 9 and 2.4 x 10 9 cells/ml, respectively. Soil samples were prepared at moulding water contents (MWCs) of-2, 0, +2 and +4% relative to OMC and compacted using the reduced British Standard light (RBSL), British Standard light (BSL), West African Standard (WAS) and British Standard heavy (BSH) energy, respectively. Cementation reagent was injected into the compacted soil by gravity until partial saturation was achieved. The plasticity of the soil improved for all the treatment mix ratios.The volumetric shrinkage strain (VSS) values of the lateritic soil did not vii significantly change with higher B. coagulans suspension density. The hydraulic conductivity values decreased from 1.27×10-6 , 1.59×10-7 ,3.94 ×10-8 and 5.42 × 10-9 m/s for the natural lateritic soil to minimum values of 3.69 × 10-9 , 1.89 × 10-9 , 2.81 × 10-9 and 6.71 × 10-10 m/s for specimens prepared at MWC-2 % relative to OMC and compacted with RBSL, BSL, WAS and BSH energy, respectively. The unconfined compressive strength (UCS) values of lateritic soil increased with higher B. coagulans suspension density. The overall acceptable zone (OAZ) for VSS, hydraulic conductivity and UCS for the natural soil (i.e 0 cells/ml) was obtained at MWC in the range 13.4-16.3% for BSH energy level only. For optimum B. coagulans suspension density of 2.4 x 10 9 cells/ml, the range of MWCs for the OAZs were 16.2%, 15.3, 12.5-14.5 %, and 11.8-13.8 % for RBSL, BSL WAS and BSH compaction, respectively.The predicted unsaturated hydraulic conductivity (UHC) marginally decreased with increased B. coagulans suspension density for van Genuchten (VG),Brooks-Corey (BC) and Fredlund-Xing (FX) models. Compatibility tests results showed reduction in long-term hydraulic conductivity values for all the treatment mix ratios with decrease in the sorption capacity of cations and anions as B. coagulans suspension density increased. Bacterial Foraging Optimization (BFO) and Particle Swarm Optimization (PSO) results showed that specimens prepared at MWCs in the range 11.8-15.3 % and treated with at least B.coagulans suspension density of 1.20×10-9 cells/ml when compacted with BSH energy recorded the least hydraulic comductivity values for both algorithms. Chemical compactibility studies, BFO and PSO show that at least B.coagulans suspension density of 1.20 ×10-9 cells/ml treated lateritic soil compacted with BSH energy at MWC in the range 11.8-15.3 % obtained from OAZ delineated using laboratory data can be used as liners and covers in MSW containment systems. viii TABLE OF CONTENTS