Collaborative Research: SWCC Based Models for Realistic Simulation of Swell Behavior of Expansive Soils

Project: Research project

Description

Current engineering practice for determining the volume change behavior of unsaturated soils, including expansive soils, are mostly based on simplified tests, correlations with index properties, or other empirical methods. Such practices can lead to poor and often uneconomical foundation designs. As a result, distresses to foundations, pavements, and other structures on expansive soils are common, and repairing them can be quite expensive. Costs are reported to be several billion dollars annually. One major limitation for not undertaking advanced experimental characterization studies can be attributed to time consuming and expensive soil testing techniques. Also, the fundamental behavior of expansive soils under various soil compositional and environmental factors is not well-understood, and basic studies to supplement the unsaturated soil property determination research are needed. Hence, there is a strong and fundamental research need to review the current characterization practices in expansive soils and to revise them to reflect the current state of knowledge of unsaturated soil mechanics. The proposed research is aimed for a fundamental change or transformation in the design and practice currently used for the determination of volume change when dealing with expansive soils. It has become a common engineering practice to use the soil-water characteristic curve (SWCC) to interpret strength and flow characteristics of unsaturated soils. The SWCC provides a fundamental relationship between soil suction and gravimetric or volumetric moisture content of unsaturated soils. A similar framework can be extended to develop a sound methodology to characterize volume change properties of expansive soils, by improving the determination of swell strains and swell pressures. Such characterization methods will lead to better, safer and more durable designs of foundations, transportation infrastructure (pavements and bridges) and earth structures built on expansive soils. The intellectual merit of the proposed research is hence related to the development of a new and more mechanistic methodology to provide reliable expansive soil properties and prediction of expansive soil behavior, by utilizing the principles of unsaturated soil mechanics. Two major efforts including experimental and modeling tasks are proposed to accomplish the research objectives. Experimental tasks include comprehensive investigations on eight types of expansive subsoils containing different clay mineralogy. The testing program will include determination of SWCCs over the complete range of soil suction, volumetric swell strain and swell pressure response with explicit consideration of clay mineralogy, moisture content, dry unit weight, and stress history. Particle and pore fabric, specific surface area and other clay mineralogy data of compacted soils will be quantitatively estimated by performing soil chemistry studies, high resolution digital imaging, and environmental scanning electron microscopy studies. These results will be incorporated in the modeling and sensitivity analyses. Modeling tasks include: (1) analytical formulations to predict swell characteristics using SWCC attributes, clay mineralogy, and pore void data, and (2) flow and deformation based finite element modeling to simulate volume change behavior of expansive soils. Based on these modeling studies, methods will be developed to better interpret expansive soil properties, and use of unsaturated soil mechanics principles for expansive soil applications will be demonstrated. The proposed research will be a joint collaboration effort of The University of Texas at Arlington (UTA) and Arizona State University (ASU). These universities are well equipped and the research teams have worked in unsaturated soils and expansive soils area for several years. They will follow a systematic well-defined plan for completing the proposed research. The broader impacts of the re
StatusFinished
Effective start/end date9/1/108/31/14

Funding

  • National Science Foundation (NSF): $163,028.00

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expansive soil
swell
soil water
simulation
volume change
soil
soil mechanics
mineralogy
clay
soil property
modeling
pavement
suction
moisture content
study method
transportation infrastructure
engineering
Earth structure
methodology
soil chemistry