Balasingam Muhunthan - US grants

9304506 Muhunthan During an earthquake, the motion of the ground inputs both kinetic and potential energy into a soil mass or structure. The ability of these systems to dissipate this energy when subject to vibration is a key factor in the design of earthquake-resistant systems. Energy principle have traditionally provided methods for the design of earthquake- resistant structures, but for soil dynamics, the approach has been to concentrate on stress-strain based formulations. Thus, this project is motivated to examine the response of soil structures to earthquake loading using energy principles to quantify soil performance up to failure. The objective of this research project is to identify and develop the relationships between relevant energy characteristics in monotonic and cyclic loading leading up to failure and soil liquefaction, and to use the state boundary surface as an energy envelope that provides a unifying link between monotonic and cyclic loading. As part of this development, it is necessary to examine the question of uniqueness of the state boundary surface. The main objectives are: 1. Establish an energy envelope for monotonic soil behavior and its relationship to the state boundary surface. 2. Investigate the hypothesis that liquefaction initiates when the input energy level exceeds the dissipation energy in cyclic loading. 3. Develop a framework to analyze soil failure due to liquefaction, based on energy principles. This is a collaborative research project involving Washington State University and the Georgia Institute of Technology. ***

9309345 Muhunthan The objective of this research is to develop a new technique based on simulation, aimed at building models of real porous media. On the basis of measurements of characteristics made using thin sections of porous media at the microstructural level, an artificial medium that has the same average geometric properties as the original medium will be created. The permeability tensor will be obtained by solving the field equation numerically in a sample of three-dimensional reconstructed soil medium. the results will be compared with experimental data. The possibility of determing the permeability tensor by direct observations on thin sections will be also investigated. ***

9802887 Muhunthan The International Research Fellow Awards Program enables U.S. scientists and engineers to conduct three to twentyfour months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twelve month postdoctoral research visit by Dr. Balasingam Muhunthan of Washington State University to work with Dr. Malcolm Bolton at Cambridge University on the effects of microstructure on mechanical and transport processes in soils. Funding for this award comes from the Hazard Reduction Program in the Division of Engineering. This collaboration will develop a new framework to enable the characterization of nonlinear and unstable materials behavior from the approach of micro-mechanics. Dr. Bolton has made significant contributions in constitutive modeling of soils and centrifuge testing for geotechnical applications. He is director of the Cambridge Geotechnical Centrifuge Center. ***

This proposal requests funding for supplementing the purchase of a servo-hydraulic material testing system. Two-thirds of the funding required has been committed by external sources, namely the Asphalt Paving Association of Washington, Washington State DOT, and internally by Washington State University (WSU). This system is to be utilized jointly by the geotechnical and pavement engineering faculty at WSU in conducting student/technical personnel training and research. It will allow hands-on training of an average of 75 students enrolled in 5 undergraduate and graduate courses to state of the art methods of asphalt concrete and soil testing. These include the resilient modulus of asphalt concretes (AASHTO TP31/ASTM D4123), the fatigue and creep testing of asphalt concretes (AASHTO TP9 and TP-9, resp.) and the resilient modulus of aggregates/soils (AASHTO T294-94). Two particular research studies will be made possible with the proposed servo-hydraulic material testing system. The first will explore the visco-plastic response of the constituents of asphalt concretes to dynamic loads utilizing imaging techniques. The second will study the dynamic response of cohesive soil subgrades to shear stresses of various magnitudes and frequencies, in the light of recent developments in critical state soil mechanics.

OIA-0116793 PI Eyad Masad Institution Washington State University Title "Acquisition of x-Ray Computed Tomgraphy System for the Modeling and Characterization of Materials with Nanostructure Abstract This MRI award is for the acquisition of an X-ray computed tomography (CT) system for non-invasive evaluation of the microstructure of engineering materials. The system is unique for the visualization of three-dimensional of microstructural features in the interior of opaque solid objects. The X-ray CT system will be used to perform detailed observations of the microstructural features associated with granular deformation. It will also be used in the development of new generation ceramics and metal matrix composites. The focus of the first research is on the development of a microstructure based continuum model to study the deformation and locialization in granular materials. The model is based on crystal plasticity but inclused two microstructure length scales; one associated with the plastic curvature (orientation re-distribution) and the other one is related to the porosity re-distribution. This study is unique in that the microstructure model parameters are determined directly from microscopic measurements. The study will lead to analytical methods for modeling strain localization not only in laboratory specimens, but also inpractical boundary value problems in geotechnical engineering. The outcome of this work will also have implications to the modeling of other types of materials that exhibit deformation instabilities and shear banding such as metals and composites. The engineering behavior of ceramics and metal matrix composite materials is controlled by the microstructure of several levels. Therefore, the second study combines microscopic and macroscopic principles and develops multiscale mosels for their description. The multiscale model parameters are determined directly from X-ray CT measurements. Use of such models will enable the design and development of new materials with tailored microstructures. In addition to the above major studies, a host of other research activities from different disciplines at Washington State University will benefit from the proposed system. The unique capabilities of the system will contribute substantially to the extramural funding, and encourage more collaboration with other institutions and research centers.

The deformation of soils in the field and laboratory are commonly observed to concentrate into shear bands formed during strain localization. While this mechanism is widely appreciated by engineers and researchers, it remains difficult to model, predict and analyze. The main difficulty can be attributed to the fact that while classical continuum mechanics models that do not include microstructure length scales can predict the onset of instability, they cannot predict the size and evolution of the shear bands. In particular, the classical theories of plasticity break down in the post-bifurcation regime.

The main objective of this study is to develop a microstructure based continuum model to study deformation and localization in granular materials. The model is based on crystal plasticity but includes two microstructure length scales; one associated with the plastic curvature (orientation re-distribution) and the other related to the porosity re-distribution, both of which can be directly quantified by experiments.

The study is unique in that the microstructure model parameters are determined directly from measurements. Granular specimens are hardened by impregnation with resin and their microstructure captured by means of non-invasive x-ray computer tomography. Evolution of the microstructure model parameters is monitored at various stages of shear deformation. The model will be implemented into a 3-D finite element code and used to identify deformation patterning, softening, and instabilities (shear banding and liquefaction) in boundary value problems.

The experimental and analytical program will lead to a better understanding of the phenomenon of bifurcation and localization and to analytical methods for analyzing strain localization not only in laboratory specimens, but also in practical boundary value problems in geotechnical engineering. The outcome of this work would also have implications to the modeling of other type of materials such as metals and composites that exhibit deformation instabilities and shear banding.

0234103, Balasingam Muhunthan, Washington State University
"Failure of the Teton Dam: A New Theory"

The objective of this research is to verify a new theory regarding the failure of the Teton Dam. The Teton Dam, in Idaho, failed during its first filling on 5 June 1976. It resulted in 14 fatalities and a very large economic loss. Its failure was one of the most publicized events involving a large earth fill dam in recent times. The dam was designed and built using modern standards; therefore its failure received considerable attention from engineering experts. However the failure assessment and prognosis by experts, including the Independent Panel (IP) and the Interior Review Group (IRG), failed to arrive at a consensus. Failure mechanisms suggested, included hydraulic fracture, internal erosion, the wet-seam theory, and defects in the abutment rock. None of the investigations, however, was able to explain satisfactorily why the dam breached when the reservoir reached El. 5301.7 ft and only in the vicinity of Sta. 15+00 on the right abutment.

This investigation is based on a preliminary work using fundamental "state based soil mechanics". It indicates that a deep open transverse vertical crack(s) existed in the core (Zone-1) to EL.5300 ft and the deepest crack(s) occurred only in the right abutment and in the vicinity of Sta. 14+00 to Sta.15+00. When the reservoir rose above El. 5300 ft in the early hours of 5 June 1976, water flowed through the open transverse vertical crack(s) into the pervious downstream Zone-2, which was seated on bedrock at El. 5200 ft. The water flow slowly eroded the crack into a large tunnel leading to the major breach of the dam hours later. This preliminary work is based on the critical state soil mechanics framework. It assumes that the mechanical behavior of soils, such as the compressibility, pore pressure response, shear behavior with respect to yield, rupture and fracture, is dependent on the "state of soil" in q-p-e (shear stress-mean stress-void ratio) space or equivalently the LI - p (Liquidity Index - mean stress) space.

A one-day workshop will be held at the conclusion of the program, at which a panel of experts will meet with the investigators to examine the research results and provide a critique in light of past investigations of the Teton failure. The expert committee will include professionals from the US Bureau of Reclamation, the US Army Corps of Engineers, and academics. The proceedings of the workshop, along with a detailed analysis of the Teton Dam failure and recommendations, will be disseminated via the worldwide web.

Unsaturated soils play an essential role in a variety of natural earth processes and engineered earthen systems. The pore water in an unsaturated soil system forms a complex fabric consisting of saturated pockets of water under negative pressure and a network of liquid bridges formed near the particle contact points. Water influences bulk soil behavior by modifying intergranular stress through negative pressure in the saturated pores, and by providing an intergranular bonding force through the liquid bridges. The magnitude and relevance of each mechanism, however, is highly dependent on the pore water fabric, which is readily altered with changes in suction, saturation, wetting direction, external stress, and global or localized deformation. It is evident that changes to unsaturated soil microstructure under mechanical or hydraulic loading will influence macroscopic soil behavior, but the difficulties associated with its characterization have limited development of microstructure-based frameworks for predicting macro soil response.
This collaborative project seeks to observe and quantify the multiphase fabric of unsaturated soils by making use of recent advances in non-destructive imaging techniques. Microfocus X-ray computed tomography will be integrated with a series of special loading stages designed to image the microstructure of unsaturated sand specimens under controlled suction and stress conditions and over a wide range of saturation and strain. Images will be analyzed to characterize salient features of the multiphase fabric, including 3D grain orientation, particle contact normals, liquid bridge configurations, and the distribution of liquid- and gas-saturated voids. Tensors describing these features will be quantified and their evolution tracked as specimens are subject to controlled changes in suction, wetting direction, compression, and shear. Grain size, density, anisotropy, suction, confining stress, and strain rate will be treated as experimental variables. Microstructural observations will be integrated into a new constitutive framework for unsaturated soil behavior that explicitly accounts for elements of the solid, liquid, and gas fabric.
The research will work to resolve the links between unsaturated soil microstructure and macroscale response, and will implement them through a new constitutive platform for predicting engineering behavior. Observations of fabric evolution with hydraulic and mechanical loading will provide direct evidence to address the bottleneck issues that currently limit our predictive understanding of unsaturated soil behavior, including wetting-drying hysteresis, coupling between suction, saturation and deformation, liquid bridge rupture, dilation, and rate effects. Understanding multiphase interactions in packed particles with wetting fluids is also critical to other scientific fields that deal with physical phenomena such as filtration, drying, pharmaceutical and ceramic agglomeration, and oil recovery. Teaching and diversity will be enhanced through graduate and undergraduate student involvement and educational module development, including activities targeted specifically for women and minorities at the University of Missouri and Washington State University.

Cementitious stabilization offers great advantages, such as beneficial utilization of in-situ materials or waste/byproducts. However, shrinkage cracking associated with stabilized materials limits the widespread use of this technology. The project is focused on the creation of an innovative sequential hydration procedure that could mitigate the development of shrinkage cracking of stabilized mixtures. The study will lead to a deeper understanding of the hydration mechanism of new stabilized mixtures and its effect on strength, shrinkage strain, relaxation, and shrinkage cracking potential. The behavior of stabilized mixtures will be characterized and modeled for optimal design and construction. In addition, the microstructure mechanism of hydration will be verified by the use of X-Ray computed tomography that allows non-destructive visualization of the 3-D microstructure of stabilized mixtures. The performance of the new mixture will be compared to that of traditionally stabilized mixtures.


The successful completion of the project will lead to the development of crack-free stabilized mixtures and thus significantly promote the technology for use in stabilizing in-situ materials and waste/byproducts. This in turn will contribute to the sustainable development by reducing the quarrying of virgin materials. Potential benefits include reduced construction costs, reduced energy consumption and reduced greenhouse gas emission. This project will provide cross-disciplinary educational opportunities for graduate and undergraduate students. The findings and results will be widely disseminated through publications and incorporated into a new graduate course.

One of the key concerns of Geotechnical engineers has been how to improve soil behavior to mitigate geo-hazards. This research addresses the utilization of in-situ microbial biofilm formation on mineral surfaces as a means of soil improvement. Despite extensive research efforts on biofilms in a wide range of engineering applications, current knowledge of biofilm-mineral interactions in geologic materials is still in its infancy. The objectives of the proposed research are to quantify the interactions between biofilms and soil minerals, and to identify the effects of such biofilm-mineral interactions on the mechanical properties of soils. The primary emphasis is to explore the hypothesis that the biofilms produced by soil bacteria coat soil minerals and increase the mechanical strength and stiffness of soils, the extent of which will be dependent on physicochemical properties of the soil mineral, pH and ionic strength of pore water, as well as confining stress. This research will be among the first efforts to investigate biofilm associated soils from a geomechanical point of view, and will use various multi-scale experimentation techniques such as atomic force microscopy, X-ray computed microtomography, geophysical monitoring, and triaxial strength testing. The combination of those techniques will allow examination of the effects of mineralogy and pore water chemistry on adhesion forces of biofilms to minerals, biofilm growth patterns in pore spaces, and shear behavior of soils undergoing biofilm growth. Therefore, the specific aims of the proposed research are to select a model bacterium via characterization of the composition and structures of biofilms grown on mineral surfaces; to quantify the interactions between model bacterium biofilms and soil minerals at the nanoscale; to visualize the three-dimensional morphological patterns of biofilm growth in pore spaces of soils at the microscale; and to identify the effect of biofilm formation on geomechanical behavior of soils at the macroscale. Success of the proposed research will advance the understanding of the roles of biofilm formation in enhancing soil behavior, by identifying the most relevant factor related to mechanical behavior, investigating the extent of enhancement of soil strength and stiffness, and providing experimental data for development of a theoretical mechanistic model of biofilm-associated soils.

Society will benefit from the advancement in understanding of biofilm formation in geo-media and the development of the intelligent use of microbial biofilms to improve ex-situ and in-situ soil properties. The use of biofilms may improve hydrologic engineering barriers; controlled bio-remediation methods of contaminants, and sustainable soil improvement methods for mitigating of soil erosion, debris flows, and slope instability. Moreover, the outcome of the research will have broad impact related to engineering applications to natural and engineered porous media, such as biomass accumulation in near-surface soils of agricultural/farm lands, bio-clogging during natural oil and gas production, microbial enhanced oil recovery using selective plugging, biofilm development in microbial fuel cells, or biofuel processing. The cross disciplinary nature of this research gives graduate and undergraduate students unique experiences and opportunities that integrate bioscience, surface physical chemistry, and geophysics with geotechnical engineering. In addition, the proposed educational and outreach activities with high school teachers will broaden the participation of underrepresented groups and minority students in engineering, strengthen their scientific and engineering foundation, and stimulate their interest in engineering. The research and educational results will be broadly disseminated to the public and scientific community through publications at peer-reviewed journals and professional conferences, exhibition of demo hands-on modules with the high school teachers at regional conferences, and dissemination of the description of the demo hands-on modules through university websites.