Kanthasamy K. Muraleetharan

A continuum theory of porous media saturated by multiple immiscible fluids: I. Linear poroelasticity

The mechanical behavior of porous media is largely governed by the interactions among coexisting components. These interactions occur through interfaces. In this paper, a continuum theory of multiphase porous media is developed that can be used to characterize the interactions among various components. Central to the theory is the implementation of the dynamic compatibility conditions microscopically representing the constraints on the pressure jumps across the interfaces. It is shown that capillary relaxation processes are thermodynamically associated with the changes in the volume fractions of fluids. A linear model is developed by a formal linearization of the proposed theory. For fully saturated conditions, the linearized theory reduces to the Biots poroelasticity model. A procedure to evaluate the material constants is presented for the porous media with two fluids. The linear model is utilized to analyze the propagation of acoustic waves in an unsaturated rock. The theoretical results are compared with the experimental data available in the literature.

A continuum theory of porous media saturated by multiple immiscible fluids: II. Lagrangian description and variational structure

Abstract The mechanical behavior of porous media is largely governed by the interactions among coexisting components. In a companion paper [Int. J. Eng. Sci. 40 (2002) 1807–1833], a continuum theory of multiphase porous media has been developed that is capable of rigorously characterizing these interactions. In this paper, the results previously obtained are used to develop a macroscale model where the state of a porous medium is described by macrostate variables measurable through experiments. The variational structure of the proposed theory is investigated. All the formulations of the macroscale model are presented in the Lagrangian setting. It is shown that the volume fractions of fluids can be considered as internal variables that microscopically represent capillary relaxation processes. By virtue of the variational description of the theory, Biots principle of virtual dissipation [Int. J. Solids Struct. 13 (1977) 579] is rigorously recovered, and a link between the mixture theories and Biots theory of porous media is established.

Effects of soil skeleton deformations on hysteretic soil water characteristic curves: Experiments and simulations

[1] Soil water characteristic curves (SWCCs) represent the relationship between suction and water content in unsaturated soils. The SWCCs exhibit hysteresis during wetting-drying cycles; however, the empirical expressions used to describe SWCCs have typically ignored the hysteresis. Additionally, the shape of the SWCC will vary depending on the void ratio of the soil and changes resulting from soil skeleton deformations, which may also show hysteretic behavior under various loading conditions. Therefore, it is important to investigate, both experimentally and theoretically, the relationship between soil skeleton deformations and the SWCC for different soils. There is limited information in the literature that examines, both experimentally and theoretically, the complex coupling between the soil skeleton deformation and SWCC behavior, and generally, this behavior is not well understood. This paper presents laboratory test results of SWCCs determined under different confining stresses on similarly prepared samples of a silty soil; drying, wetting, second drying, and scanning curves were obtained. The influence of soil skeleton deformations on SWCCs is inferred from the curves measured in an oedometer under different stress conditions. An elastoplastic phenomenological constitutive model based on the bounding surface plasticity theory was utilized to simulate the coupled mechanical-hydraulic behavior of measured results. This research demonstrates that the model is capable of predicting hysteresis in SWCCs and soil skeleton deformation and the coupling between the hydraulic and mechanical behavior of unsaturated soils.

Coupled Hydro-Mechanical Elastoplastic Constitutive Model for Unsaturated Sands and Silts. I: Formulation

AbstractUnsaturated soils are three-phase porous media consisting of a solid skeleton, pore water, and pore air. The behavior of unsaturated soils is strongly influenced by the matric suction (pore air pressure minus the pore water pressure). Soil water characteristic curves (SWCCs) describe the relationship between matric suction and water content in unsaturated soils and, therefore, capture the hydro-behavior of soils. SWCCs show hysteretic behavior that not only depends on the wetting or drying history of the soil, but also on the stress-strain history (mechanical behavior) of a soil. The hydro-behavior of unsaturated soils, on the other hand, influences the mechanical behavior through matric suction. To predict the behavior of unsaturated soils, a hysteretic SWCC model is proposed based on the bounding surface plasticity concept. The model for hysteretic SWCCs is then incorporated into a constitutive model for unsaturated sands and silts in the general stress space. The resulting model is a comprehens...

Coupled Hydro-Mechanical Elastoplastic Constitutive Model for Unsaturated Sands and Silts. II: Integration, Calibration, and Validation

AbstractFollowing the comprehensive model formulation given in Part I, a fully implicit integration procedure for the rate equations using a closest point projection method is presented in this paper. The stress-update algorithm and calibration procedure for all the model parameters are discussed in detail. Two sets of laboratory test results, one from unsaturated Minco silt and another one from Toyoura sand, are used to validate the proposed model. The model is shown to have the ability to capture the coupling effects between hydro- and mechanical behavior and predict the laboratory tests reasonably well.

Bridging the Macro and Micro: A Computing Intensive Earthquake Study Using Discovery Net

We present the development and use of a novel distributed geohazard modeling environment for the analysis and interpretation of large scale earthquake data sets. Our work demonstrates, for the first time, how earthquake-related surface deformation measured from satellite images using imageodesy algorithms is coupled with analysis and simulation using finite-element numerical models. Our work realises a real time distributed analytical environment where analysis and simulation are closely coupled; integrating high performance implementations of image mining components executing on dedicated Discovery Net servers at Imperial College London, UK and high performance implementations of finiteelement models executing at specialised servers at the University of Oklahoma, USA. Novel scientific results produced using our data sets provide a valuable insight into earthquake analysis. In addition, our informatics work provides a novel high performance computing framework and methods for the application of complex knowledge discovery methods to understanding earthquake dynamics. Furthermore, the realisation of our distributed computing platform is based on the implementation of a set of open standards, making its results accessible over the Grid to the wider scientific community.

WETTING-INDUCED SETTLEMENT OF COMPACTED-FILL EMBANKMENTS

Many highway embankments experience problematic settlements. Compression of soil under the self-weight of the embankment generally occurs during construction, but postconstruction, wetting-induced collapse can result in more long-term settlement problems, depending on climate and movement of the wetting front. A study undertaken to examine settlement associated with unsaturated soil embankments included centrifuge modeling of compacted silt embankments, laboratory testing of the embankment soil, and data interpretation with the focus on settlement prediction. A silty soil was selected to facilitate the measurement of matric suction using tensiometers. Three model embankments were constructed and tested in the Army Corps of Engineers Centrifuge Research Center in Vicksburg, Mississippi. Embankments 20 m high were simulated using centrifugal acceleration of 165 g. Embankments were constructed to achieve a relative compaction of 90 or 95 percent based on standard effort and moisture content between 2 and 5 percent dry of the optimum moisture content. Instrumentation used during self-weight compression and wetting included linear variable differential transformers and pore-pressure transducers equipped with high-air-entry porous stones. Results demonstrate the importance of the as-compacted water content and dry unit weight on the potential for wetting-induced collapse settlement. Settlement caused by self-weight compression and that caused by wetting-induced collapse are clearly discernable in results of centrifuge tests, allowing for comparison to settlement predictions. Results are discussed in light of typical compaction specifications, oedometer-based predictions, and implications for the design of compacted embankments.

Evaluation of Resilient Moduli of Pavement Layers at an Instrumented Section on I-35 in Oklahoma

ABSTRACT Resilient Modulus (Mr) is an important material property for pavement design and evaluation. The Mr values can be estimated in the laboratory by measuring materials response under simulated field loading conditions. It can also be determined from nondestructive tests such as the falling weight deflectometer. Some previous studies have shown, however, that the Mr values determined from laboratory testing can differ significantly from that determined from the backcalculated resilient moduli using FWD data. This paper presents the results of a site-specific comparison of the Mr values determined through laboratory testing and backcalculation of FWD data. Both laboratory and FWD data are related to an instrumented pavement section on I-35 in central Oklahoma. Unlike most previous studies that focused on FWD testing on the top of asphalt concrete, in the present study FWD tests are conducted on different layers namely, natural subgrade, stabilized subgrade, aggregate base and asphalt concrete. The study indicated increase in backcalculated Mr values due to the construction of overlying layers. For natural subgrade and aggregate base layer, backcalculated Mr values were found higher than corresponding laboratory determined Mr values. In addition, FWD tests were also performed on top of the asphalt strain gauges and earth pressure cells and strains and pressure data were collected simultaneously. A comparison of the pavement response between the predictions from a multilayer elastic program, KENPAVE, and the in-situ sensors was made.

Centrifuge Investigation of Seismic Behavior of Pile Foundations in Soft Clays

The seismic behavior of pile foundations in soft clays is a very complex problem with interacting piles, soils and superstructure. Using ground improvement, for example, Cement Deep Soil Mixing (CDSM), to restrict lateral displacements of piles during earthquakes is a viable, but not fully explored technique. This paper presents experimental methods and procedures for centrifuge tests on single piles with and without ground improvement under both static and dynamic loadings. The data collected from the centrifuge test were used to analyze the differences between piles in unimproved and CDSM-improved soft clay. The test results confirmed that the CDSM can improve the seismic behavior of pile foundations and demonstrated that the pile response is directly related to the size of the ground improvement zone.

Centrifuge Modeling of Laterally Loaded Pile Groups in Improved Soft Clay

AbstractA series of centrifuge tests were performed to investigate the behavior of laterally loaded pile groups in improved and unimproved soft clay. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense layer of sand. The pile groups had a symmetrical layout consisting of 2×2 piles spaced at 3.0 and 7.0 pile diameters (D). After improving the soft clay in situ using simulated cement deep soil mixing (CDSM), pile foundations were driven into the improved ground. Centrifuge tests revealed that CDSM is an effective method to increase the lateral resistance of pile foundations. The lateral resistance of the improved pile group at 7D spacing increased by 157%. Due to pile–soil–pile interactions, the lateral resistance in the 3D pile group increased by only 112%. In both improved and unimproved pile groups with 3D spacing, the leading row of piles carried larger loads and bending moments than the trailing row of piles. No group interaction effects were observed in all pile g...