Advances in Measurement and Modeling of Soil Behavior

In the early days of Soil Mechanics and Foundation Engineering, two important assumptions were made as a part of the limiting equilibrium stability analysis of undrained failure of soft clay and silt deposits. It was assumed that undrained shear strength is independent of the laboratory or in situ testing methods used to determine it, and that the shear strength mobilized in a full-scale undrained failure in the field is equal to the undrained shear strength measured by a laboratory or in situ test. However, during the latter part of Geotechnical Engineering, it was realized that these two assumptions, in general, are not correct because undrained shear strength is influenced by mode of shear, shearing time to failure, progressive failure, and soil disturbance. As these controlling factors are rarely the same for any two testing methods or for any test and a full-scale field failure situation, undrained shear strengths determined by various tests are expected to be different; and the laboratory and in situ test measurements must be corrected before they are used for stability analysis of full-scale field undrained failures. Using undrained shear strength data back-calculated from failures of embankments, footings, and excavations, and data from in situ and laboratory tests, the relationship of s_uo(mob) is reviewed to s_uo(FV), s_uo(UC), s_uo(TC), s_uo(TE), s_uo(DSS), and also to N_k from push cone penetration test.

Soil responses are dependent on the stress path. This property is not typically considered in traditional constitutive relations for soils. This paper summarizes an original approach to modeling these soil responses, which resorts to the most basic form of any constitutive relation — the tangent modulus. It is shown that tangent moduli need to be correctly interpreted to account for characteristics of frictional materials, which results in an anisotropic tangent matrix with different coupling moduli. Moreover, experimentally derived relations can be established for each modulus to take incremental non-linearity into account, which essentially overcomes the limitation of traditional variable moduli models in simulating plastic behavior. These ideas have led to a new type of model that is able to accurately simulate soil responses in the stress probe tests.

Rapid growth in the urban areas such as Houston and Galveston in Texas is leading to construction of civil infrastructure facilities, including bridges and highways on soft clays. In this study, soft clays are characterized based on their mineralogy, physical and mechanical properties. The X-ray diffraction (XRD) and scanning electron microscope (SEM) studies were performed to investigate the mineral composition and microstructure of the clays respectively. Both CL and CH soft clays are present in the Houston area. Based on over 100 data sets, statistical mean, standard deviation, variance and coefficient of variance and distribution of properties and property correlations for the CL and CH soft clays have been developed. The natural moisture content of 97% of the soft clay was lower than the liquid limit. The undrained shear strength of the soft soils was related to the natural moisture content of the soils. The CL soil showed greater variation in the undrained shear strength compared to the CH clay. XRD and TGA analyses with the plasticity index chart confirmed the presence of illite in the soft CL clay.

A simple and direct procedure for estimating the preconsolidation stress (σ^'p) from constant rate of strain consolidation (CRS) excess pore pressure data is described. For soft clays, excess pore pressure (u_b) measured at the base of a CRS test specimen normalized by total vertical stress (σ_v) almost always reaches a distinct minimum value during the test. The vertical effective stress (σ^' v) at the minimum value of u_b/σ_v corresponds well with σ^'p as determined from commonly used interpretation methods such as Casagrande construction and the strain energy method. The method of σ^'p = σ^' v at the minimum u_b/σ_v is straight forward and objective; whereas most existing σ^' p interpretation methods use log scales, require graphical construction procedures and often subjective interpretation of the construction. Examples are given in the paper for a variety of soft clays from test sites located worldwide.

More and more construction projects are encountering soft clays and hence there is a need to better quantifying the properties of soft clays. In this study, physical, index and strength properties of marine (different parts of the world) and deltaic soft clays (Houston, Texas) were determined using the soft soil database developed from the published data in the literature. Data was analyzed using statistical methods (mean, standard deviation, variance and probability density function). Based on the coefficient of variation (COV), the deltaic deposit from one location showed greater variation in the index properties than the marine deposits collectively. Although the undrained shear strengths for both deposits were beta distribution the COV for the undrained shear strength for the marine and deltaic soft clays were 38% and 26% respectively. The linear relationship between undrained shear strength (S_u) and preconsolidation (σ_p) was verified for the marine clays. A new relationship between undrained shear strength (S_u) and in-situ vertical stress (σ_v) has been developed for the soft clays. Also constitutive models used for predicting the soft soil behavior have been summarized.

Bioengineering aspects of native vegetation are currently being evolved to improve soil stiffness, slope stabilisation, and erosion control. Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressures, and increasing the shear strength by induced matric suction. This paper looks at the way that vegetation influences soil matric suction, shrinkage, and ground settlement. A theoretical model previously developed by the authors for the rate of tree root water uptake together with an associated numerical simulation is used in this study. A conical shape is considered to represent the geometry of the tree root zone. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from previously published literature are compared with numerical predictions for further validation. The predicted results compared favourably with the measured results, justifying the assumptions upon which the model was developed. It is desirable to consider the influence zone of tree roots and the improved soil properties in modern geotechnical designs, benefiting from native vegetation.

In the wide array of existing ground improvement schemes, the use of vertical drains with vacuum preloading is considered as the most effective and economical method for improving soft clays (normally consolidated to lightly over-consolidated) prior to construction of infrastructure. Vertical drains installed to significant depths promote radial flow inducing consolidation rapidly enhancing the shear strength of the compressed ground. In this paper, the analytical solutions based on lateral soil permeability (parabolic variation) are discussed considering the variation of vacuum pressure with depth along the prefabricated vertical drains (PVD). Using the Cavity Expansion Theory (CET), the smear zone caused by the installation of PVD by steal mandrel was predicted and compared with laboratory measurements obtained from large-scale radial consolidation tests. The effects of drain unsaturation and vacuum pressure along the drain length are also discussed. The numerical analyses incorporating equivalent plane strain solutions were performed to predict the soil responses based on two selected case histories in Thailand. The research findings provided insight as to which of the above aspects needed to be simulated accurately in numerical modelling. The application of cyclic loading on PVD stabilized ground was also examined using a finite element approach under railway embankment. It is demonstrated that short drains less than 8 m installed beneath tracks are still useful for effective dissipation of cyclic pore pressures and curtailing unacceptable lateral movement immediately below the track level, at the same time avoiding excessive settlement of the track in the short-term.

A coordinated field and laboratory investigation was conducted to evaluate the primary and long-term secondary compression characteristics of organic soils and peat existing under SR 15 / US 98 in northwest Palm Beach County, Florida. The specific objectives were: (i) to conduct Piezocone Penetration Tests (CPTu) accompanied with porewater dissipation experiments for predicting the Coefficient of Consolidation (C_v); (ii) to perform consolidation testing on organic silts and peat collected from various depths at each CPTu location; (iii) to conduct secondary compression tests at constant effective stress representing the in-situ conditions; and (iv) to establish the (C_α / C_c) ratios for Florida organic soils following the well-known Time-Stress-Compressibility concepts. The horizontal coefficient of consolidation (C_h) was predicted from porewater dissipation data, which was subsequently used to calculate the vertical coefficient of consolidation (C_v), and compared with laboratory-derived properties. It was found that the primary consolidation process in laboratory specimens is quite rapid, leading to the secondary compression phase. The Secondary Compression Index, C_α was calculated during the first log cycle after the End-of-Primary (EOP) consolidation, and a unique relationship between C_c and C_α was established. Results indicated that for all practical purposes, the (C_α / C_c) ratio had constant values ranging from 0.03 to 0.05, which were consistent with the values reported in the literature for similar soils.

In recent years full-flow probes, such as the Ball and T-bar penetrometers, have been investigated as alternative in situ tests to the peizocone (CPTu) and the vane shear test (VST). These penetrometers do not require correction for overburden pressure and have the potential to provide more accurate undrained and remolded undrained shear strength measurements in soft sediments. This paper summarizes a portion of a research program that is utilizing a number of highly characterized test sites to comprehensively evaluate aspects of the full flow penetrometers. The results presented herein are used to consider the effect of penetration rate on the determination of the undrained and remolded strength. Twitch and cyclic tests are employed during initial penetration and after cycling. Results are analyzed with respect to normalized velocity for both ball and t-bar full-flow penetrometers.

In this study, properties of soft clay soils (undrained shear strength (S_u) ≤ 25 kPa) from three locations along the Texas Gulf Coast were investigated using laboratory and field tests. The data and samples for this study was obtained from 46 boreholes in three counties along the Gulf coast. The soils were characterized based on their geotechnical properties including undrained shear strength using statistical methods. The field tests were performed using the Texas Cone Penetrometer (TCP), which is a dynamic method using a cone of 3-in (75 mm) in diameter. Both CL and CH soft soils were present in these locations and there was large variation in the index properties of the soils. Physical, index and strength properties of CL and CH soft soils were quantified using mean, variation, coefficient of variation and probability distribution function. The natural moisture content of 95% of the soft clays was lower than the liquid limit and the coefficient of variation for the Su of CH soil was about 25%. Based on available data the undrained shear strength of soft clay soil (S_u) was related to the TCP blow count.

Column-supported embankments provide a rapid means of construction in areas where subsurface consists of fine-grained soft soils. A load transfer platform (LTP) is usually provided at the base of the embankment to even out differential settlement and minimize overall deformation of the embankments. The mechanism of load transfer in geosynthetic-reinforced LTPs (GRLTP) supported on columns is, in general, poorly understood. Especially, the case of soil arching within the embankment fill from which the proportion of the embankment load that is transferred to the columns and to the subsoil is determined. A well instrumented full-scale test embankment incorporating a catenary GRLTP and supported by rammed aggregate piers (geopiers) was built in Malaysia. The results of the numerical analysis and its relation to field data are presented along with implications for arching ratio. Overall, the relatively simple elastic-perfectly plastic Mohr-Coulomb constitutive model was able to capture the essential embankment/load transfer platform behavior based on conventional data regarding material properties and subsurface conditions. The arching ratio assumed in the design of catenary load transfer platform based on the British design method is significantly higher than that indicated by the field-calibrated numerical analysis and the field measurements.

In this study, a 3D numerical modelling of a single vertical drains consolidation incorporating vacuum preloading considering both vertical and horizontal drainage is presented. The effects of nonlinear soil compressibility, varying permeability and vacuum pressure distribution along the drain are examined through the dissipation of average excess pore pressure and associated settlement. A selected case history, using 3D finite element method, is employed to analyse two embankments constructed at the Second Bangkok International Airport, Thailand stabilised with prefabricated vertical drains and vacuum preloading. The behaviour of this embankment including settlements and excess pore pressures is then compared with the numerical predictions. This study reveals a close agreement between the predictions results obtained from the numerical model and the field measurements.

Two soil moisture probes from Decagon Devices were calibrated to measure volumetric water content and salt concentration in the soil's moisture. The probes used were the EC-5 and EC-10 models, and the soil used has a USCS classification of SP or poorly graded sand. The EC-10 probes were found to work well for determining the salt concentration, in parts per million, of the soil if the volumetric water content is already known. The EC-5 probes also proved useful for the determination of salt concentrations, but the EC-10 probes proved to be more accurate. Soil-specific calibration curves were developed for both probes for use in saline soils at a range of volumetric moisture contents. Both probes were found to be useful for determining the volumetric water content of soils with no salt present. The probes have each have a very similar calibration curve in non-saline soils so a single curve was developed for both the EC-5 and EC-10.

The railroad ballast is used to fill in irregular surface topology, distribute and transfer loads from a surface structure or system to the subgrade or subsoils as uniformly and widely as possible in order to provide stable and stiff long-term embankment support for railways. A typical ballast grain sizes range from 30 to 70 mm, which makes large-scale laboratory tests difficult to conduct. The parallel gradation technique is to preserve the particle shape, particle surface roughness, and particle mineralogy, and creates a parallel gradation of soil with a maximum particle size for the available apparatus. This paper presents the result of a series of monotonic direct shear tests for three ballast materials having parallel gradation curves, which are served as background study for the ongoing research on validating it under loading-unloading condition.

Experiments have been performed to study the time-dependent behavior of Antelope Valley sand in triaxial compression. Observations of time effects in tests with constant strain rate, creep tests at different stress levels and stress relaxation tests initiated at different amounts of axial strain are presented. Some of the drained creep behavior was reported previously (Lade and Liu 1998) and based on analysis of this behavior, a model for creep in sand has been presented (Lade and Liu 2001). Additional experiments on strain rate effects and stress relaxation of the same sand are reported here and compared with results for creep behavior in sand. It is found that the classic time effects found in most materials, i.e. increasing stiffness and strength with increasing strain rate and corresponding creep and stress relaxation behavior, are not observed in sand.

Lunar soil (regolith) simulant JSC–1 has been widely used by a variety of investigators. Standard laboratory measurements were conducted to characterize the tensile strengths, grain size distribution and other basic behavior. Direct tension experiments were conducted on JSC–1 to determine its tensile strength, which is significant, at different densities. The specimens were prepared through miniature compaction techniques. The effects of density as well as specimen height on the tensile strength are determined. This paper presents the results from extensive experimental studies to illustrate the tensile behavior of JSC-1 regolith simulant, which may be of importance in future designs of infrastructure and in-situ resource utilization on the Moon.

Non-uniformity of deformations has always been a concern in interpretation of laboratory triaxial test results due to boundary effects. This paper describes the application of a novel inverse analysis framework, SelfSim (Self learning simulations) which permits the extraction of relevant soil (or material) behavior using boundary measurements of load and displacement, to the interpretation of a triaxial test of a dense sand specimen. The specimen is sheared in axial compression with frictional platens, and experiences large dilation and global softening behavior during shearing. SelfSim extracts the non-uniform stress and strain field within the specimen. Soil experiences diverse stress paths arid exhibits a range of mobilized secant friction angles under a variety of loading modes. The approach has the potential to provide greater insights into the sand behavior under previously unexplored complex shear modes than the simple interpretation of behavior using global measurements of force and displacements.

When lubricated end platens are used in axisymmetric testing of clay specimens, radial or side drainage is often used. An experimental study of different radial drainage materials in compression and extension that examines vertical load corrections at confining pressures ranging from low stresses up to approximately 3,000 kPa is presented. As confining pressure increases, the filter paper rapidly loses its flow capacity. Therefore, the drainage materials investigated include filter paper and various non-woven geo-textiles which maintain their flow integrity at higher pressures. The vertical load carrying capacity of drainage materials in different configurations (vertical strips or sheets with inclined slots) was determined to be much higher than expected, even for filter paper.

In this paper, an optimization method is tested on in-situ measurements carried out during the excavation of Bois de Peu tunnel in France. An important monitoring program was foreseen during this excavation because it was decided to apply the "interactive design method" in order to adapt support in real time. An optimization software, SiDoLo, is used. It is coupled with the finite element software CESAR-LCPC to evaluate soil parameters. Only the identification of the argillaceous unit parameters is presented in this paper. Experimental responses used in the inverse analysis approach and presented in this paper are strain measurements of the soil ahead the face by extrusometers. Numerical responses are obtained by 2D numerical models. This article shows the results obtained according to the number of used experimental responses. It shows difficulties which can be met during the identification of several parameters simultaneously.

Using numerical modelling, the main goal of this paper is to identify the underlying mechanisms in the pile soil interaction when a single pile is axially loaded. In addition, the implications of the soil behavior in the prediction of the ultimate shaft and base resistance, as well as in the load settlement curves, are studied in terms of soils's stress paths and load transfer curves.

This paper presents the results of a "modeling-of-models" laboratory exercise conducted in a 1-g environment to investigate the applicability and validity of established similitude laws. The study, which was performed under static condition, considers the behavior of cohesive model slopes at small (stiffness) and large strains (failure). The test program involved three small-scale model slopes tested under different geometry scaling factors. The models were comprised of an artificial, fully saturated "model" clay (3 parts kaolinite to 1 part bentonite). The results indicate that for fully saturated cohesive soils tested under undrained conditions, similitude laws are valid for static conditions provided that three dimensional effects and boundary conditions are properly accounted for.

Linear and nonlinear acousto-electric waves in porous solids in the presence of an electric field are investigated. The pores are filled with an electro-conductive liquid. The resulting self-consistent problem is solved while all the factors accompanying the wave being taken into account. Formulae for the wave's linear and nonlinear speeds and absorbtion coefficients are derived. Both 1-dimensional and 3-dimensional cases have been considered. Nonlinear evolutionary and Schrodinger equations are derived. Their solutions are obtained and investigated in detail. It is shown that there can be soliton-shaped waves in the medium.

As a result of the complexities associated with analyzing and evaluating supported excavations, numerical modeling techniques are often employed. Often, there is a great deal of uncertainty associated with the validity of the assumptions and approaches made regarding numerical modeling. Physical models can be used to evaluate complex geotechnical systems whose performances are highly dependent on construction techniques, nonlinear soil-structure interactions, and variable geometries. Physical model tests can be used as alternatives to numerical models or as supplements. Data from physical model tests is often used to verify the validity of the various assumptions and approaches of the numerical models. The data can also be used to calibrate numerical models to the anticipated loading conditions. This paper presents an evaluation of several efforts that utilized physical modeling to investigate the behavior of excavation support systems and the associated ground deformations. Model test results are compared to the state-of-the-practice ground deformation prediction methodologies and to field observations. The information presented herein shows that scale model test data can be reliably extrapolated to equivalent prototype data. Thus, small scale laboratory tests at normal gravity, centrifuge tests, and small scale field tests can all used to evaluate excavation support system behavior and soil response associated with deep excavations. These findings are particularly important in that often full-scale field test cannot be performed.

This paper introduces an electrical resistivity method into the microstructure study on clayey soils and evaluates its effectiveness. The swelling tests were performed on the undisturbed expansive soil samples with a modified oedometer consolidation cell, the vertical and horizontal electrical resistivity was measured at the same time during swelling. The electrical parameters, such as the average formation factor, the electrical anisotropy index and the average shape factor were then calculated and studied. Experimental results showed the effectiveness of electrical resistivity method in quantitative studying on the microstructure change of expansive soils during swelling.

The relationship between particle size and shape for a given sand plays an important role in generating and reconstructing particle assemblies for micromechanical modeling. However, limited and conflicting knowledge is available in the literature describing the relationship between particle size and particle shape. The present study focuses on verifying any existing relationship between grain size and grain shape using different natural and processed sand samples collected from locations around the world. Though in previous literature strong relationships were documented, it is evident from the current research that there is no relationship between grain size and grain shape. As such, discrete element models of angular particle assemblies can be constructed by randomly selecting shapes belonging to a particular sand sample from its particle shape library, irrespective of size. The findings can also provide important information in understanding the nature of variation — or lack thereof — of shape parameters such as elongation, triangularity, squareness with grain size.

The S-wave velocity in particulate materials depends on the state and history of the effective stresses, void ratio, degree of saturation, and type of particles. Based on experimental evidence and analytical studies, the velocity-effective stress relationship for granular materials is expressed as a power function having two physically-meaningful parameters: a coefficient α and an exponent β. These parameters represent the S-wave velocity at a given state of stress and its variation with stress changes. This experimental study presents velocity-stress power relationship for interpreting the packing and contact behavior of sand. Dry medium sand specimens were prepared by five methods of specimen preparation: (1) scooping, (2) tamping, (3) rodding, (4) vibrating, and (5) pluviating, representing five different packings. The S-wave velocities of these sand specimens were measured using bender elements under isotropic state of stress. Results indicate that the coefficient α correlates fairly well with the type of packing (i.e., void ratio or coordination number) and particles' physical properties and that the values of exponent β agree with the semi-empirical values predicted for rough particle contacts and are within the expected range for loose to dense sand.

A micro-mechanical model was used to study of the dynamic response of unsaturated granular soil deposits (with a degree of saturation around 7%). The discrete element method was employed to idealize the soil skeleton. The effects of interparticle water bridges in a pendular state were modeled using suction and viscous forces. These forces are a function of water content and interparticle distance, along with other material parameters and characteristics. Numerical simulations were conducted to investigate the impact of moisture content on the dynamic response of level and sloping ground deposits when subjected to a dynamic base excitation. The dynamic response of level and sloping ground deposits exhibited similar and mostly linear responses when subjected to a moderate cyclic loading. The outcome of these simulations provided a valuable insight into the response of unsaturated soils.

A limitation of using laboratory experiments to study the micromechanics of soils is that detailed information about the specimen microstructure is typically available at only one state in a test sequence due to the destructive nature of the forensic process. To study microstructure evolution, characterization of replicate specimens tested to various global axial strain levels has been undertaken, but this procedure presents some practical and theoretical problems. Accordingly, a numerical program was undertaken using the discrete element method to model the micromechanical deformation response of particulate assemblies in two dimensions. The simulated assemblies failed via regions of high localized strain. The microstructures of these assemblies were studied as a function of global axial strain to assess evolution of local and mesoscale void ratio distributions and mean free paths. Local void ratio distributions were modeled statistically and mesoscale measurements were used to assess microstructure inside and outside of the shear bands.

A fully coupled continuum-discrete hydromechanical model is employed to analyze the dynamic response of saturated granular soils. The fluid motion was idealized using averaged Navier-Stokes equations and the discrete element method was employed to model the solid particles. Well established semi-empirical relationships were used to quantify the fluid-particle interactions. Numerical simulations were conducted to investigate the liquefaction mechanisms of soil-pile systems when subjected to a dynamic base excitation. The outcome of these simulations was consistent with experimental observations and revealed valuable information on the micro-mechanical characteristics of soil liquefaction and associated loss of stiffness and strength.

A discrete element, analysis can provide much useful information on failure mechanisms for large displacement problems in geotechnical engineering. This study involved a series of 2D distinct element method (DEM) simulations of the penetration of a CPT cone, a closed-ended pile and an open ended pile into a rectangular tank containing over 29,000 disk particles. The objective was to explore the influence of penetrometer geometry on the distribution of disk displacements, rotations, and contact forces. The findings of the study indicated that increasing the penetrometer- soil friction coefficient resulted in a slightly deeper failure mechanism. The penetrometer-pile friction value had a significant influence on the formation of plugs in the open ended piles. In all cases localizations could clearly be identified by considering the particle rotations, with clockwise rotations being more dominant to the left of the penetrometer, and anti-clockwise rotations being more dominant to the right of the penetrometer.

A microstructural fabric model is developed for upscaling interlayer volume changes associated with crystalline swelling in compacted expansive clay specimens. Particle fabric is modeled using lamellar tactoids arranged in a parallelepiped structure comprising both interlayer and interparticle void space. Bulk volume changes resulting from mineral interlayer hydration occur as a result of relative volume changes in the interlayer and interparticle voids. Changes in the interparticle voids are studied by quantifying a parameter alpha defining the internal acute angle of the parallelepiped. Initial alpha values are higher for loosely compacted samples. Significant change in alpha is observed for relative humidity values of 33% and 75.1%, which correspond with the zero-layer to one-layer and one-layer to two-layer hydrate state transitions. Specimens with lower density show smaller changes in alpha values. Results support the general concept that smaller bulk volume changes occur in lower density specimens because interlayer swelling is more effectively adsorbed by the larger scale voids.

This paper presents a numerical technique to simulate the resilient modulus test of aggregate materials based on the discrete element method. This technique enables a realistic modeling that takes into account the nature of the materials and loading conditions, and provides valuable information such as the grain rearrangement at the micro level. Numerical simulations were conducted to idealize the cyclic loading of compacted granular samples. These simulations showed that the discrete element method is capable of reproducing the results of the resilient modulus test and capturing the effect of confining pressure on the resilient modulus observed in actual laboratory testing. The resilient modulus exhibited an increase in value with the increase of the confining pressure. The results also showed that the deviator stress has an effect only at low confining pressures.

This paper aims at bridging molecular mechanics, particulate mechanics and continuum mechanics in order to solve a macro level geotechnical problem. Due to the paramount amount of variations in conditions of each length scale, a simplified condition — the dry spherical shape quartz sand is simulated. This paper adapted a so-called "hierarchical" approach to bridge different length scales, which starts from the molecular level and propagates up to the macro level. Molecular mechanics approach is used to obtain crystal properties, particulate mechanics approach is used to obtain assemblage properties of sand particles, and continuum mechanics approach is used to obtain macro scale behavior. MS-Studio software is used for molecular mechanics simulation, OVAL software is used for particulate mechanics simulation, and a simple slope stability example is solved using continuum mechanics. From this study, it turned out that the slope stability analysis of dry sands may be performed not only with experimental data but also with parameters obtained from a lower level length scale mechanics.

The complex relationship between the mechanical properties of individual particles and the global response of a granular assembly for many geotechnical engineering applications is well acknowledged. When studying the deformation behavior of sands, little experimental research exists in the past literature that reports reliable measurement techniques suitable for evaluating the properties at particle scale. A new experimental technique is presented in this study that can be used to measure deformation behavior of individual particles (crystalline silica in this study) using an instrumented indentation technique for depths of indentation in the range of 50 to 500 nanometers. In this research, two important mechanical properties, hardness and elastic modulus, of individual sand particle with diameter less than 750 microns are determined and analyzed using nanoindentation technique. Since a rigorous study of the nanoindentation technique for finite size particles has not been done to date, a detailed description of the process including techniques used and the analysis methodologies suitable for individual sand particle are described in this research along with initial results. Results on reference material with known properties (fused quartz in this study) are also presented to demonstrate the validity of the experimental procedures. Measurements such as these will have an immediate impact on discontinuous modeling techniques such as Discrete Element Method to realistically represent the deformation behavior of granular materials.

In our prior work we have shown significant particle subdivision in montmorillonite during swelling. Here we describe results of our studies on modeling, the evolution of particle subdivision in clays using discrete element modeling (DEM). Particle subdivision has been incorporated in DEM. Our simulations indicate that particle subdivision has an important effect on swelling volume and swelling pressure. We report that the swelling pressure increased with an increase in number of particle subdivisions. Here the quantitative relationship between particle breakdown and evolution of microstructure, swelling, and swelling pressure is elaborated.

Expansive clays exhibit high potential for volume change when changes in soil moisture occur. It has been estimated that the annual cost of damage to facilities built on expansive clay in the United States exceeds $9 billion. The use of soil suction measurements to predict potential clay volume changes has shown significant promise, yet the currently utilized method to determine soil suction, the filter paper method, has serious drawbacks. First, the test takes approximately 8 days to complete, making it less than practical for broad use by practicing engineers. Second, and more troublesome, the filter paper test is difficult to conduct successfully and the results are significantly affected by small differences in procedure, all allowed by the ASTM standard. The WP4 chilled mirror dewpoint potentiometer has been shown to provide total soil suction measurements that are consistent and repeatable within 24 hours. The WP4 device has the potential of providing a method for all geotechnical engineers to use soil suction for all project situations, thereby, reducing the cost and increasing the reliability of predicting clay soil behavior. The ASTM standard for use of the WP4 device does not specify how it should be used. The potential use of the WP4 dewpoint potentiamenter to determine total suction of expansive clay soils has been substantiated by initial testing as reported by Petry and Bryant in 2002. The project reported here provided further evaluation using a process of Round-Robin testing of specimens of three expansive clay soils at three water content-dry unit weight configurations. One soil was from Texas, one was sampled in New Mexico and the other came from Missouri. Seven geotechnical laboratories evaluated the suction characteristics of the nine specimens provided and returned their results to the UMR Geotechnical laboratory. Involved were three geotechnical companies from Texas and one from each of Colorado and New Mexico, and the geotechnical engineering laboratories at BYU and UMR. The results indicate that the relationships of total suction to soil moisture as defined by the WP4 device had significantly less variance and provided slightly more conservative values of suction, when compared to the filter paper method.

Soil is a particulate material and its constituent particles have a wide range of sizes. Nanoparticles of usually 1 to 100 nm are the smallest particles in soil environments and exist in one of the three different forms: nanoplatelets, nanowires or nanotubes, and nanodots. Due to their tiny size, soil nanoparticles usually exhibit special enhanced surface properties and hence interact more actively with other soil particles and solution. In this paper, some commonly occurring nanoparticles and their properties are briefly summarized, including specific surface area, particle morphology, nanoporosity, and surface charges. Owing to the extremely large specific surface area, surface charges, and sometimes nanoporosity, these particles, even preset at a small fraction, may significantly affect soil's physico-chemical behavior and engineering properties. Soils containing nanoparticles with nanoscale intraparticle voids usually exhibit much higher liquid and plastic limits that usually show irreversible changes upon drying, while the presence of fibrous nanoparticles usually makes the soil more thixotropic and enhances its shear strength. To reflect the difference between nanoparticles and classical clay sized particles, a new type of soil particle "nanosol" is proposed to define soil nanoparticles.

Nanomechanics has huge possibilities in explaining basic materials response such as creep, friction, rate and temperature dependency. Constitutive models based on nanomechanics have distinct advantages over phenomological models in simulating the response of geomaterials under extreme environments. This paper presents a study of the elasticity properties of rock and clay minerals using MD simulations. The interatomic potentials used for these minerals are taken from the published work on the same minerals. Both bonded and non-bonded interatomic contributions and periodic boundary conditions in three dimensions are included in the simulations. The elasticity module of the minerals are calculated from the axial stress versus strain curves. The results show that the elasticity properties of the minerals obtained from the MD simulations agree well with the published data. It is found that the elasticity modulus of kaolinite is even higher than quartz, which is in contrast with their known macroscopic properties. This could be due to the arrangement of the clay particles at the microscopic level, which dominates the macroscopic properties of the clay mass.