报告人：Xiong Zhang
Associate Professor
University of Cincinnati, Cincinnati, OH 45221. Email: zhang4xo@ucmail.uc.edu
报告题目：Rapid characterization of stress-strain behavior for unsaturated soils
报告时间： 2016年6月22日9:00-11:00
报告地点： 综合实验一号楼602
Abstract:
Suction- controlled tiaxial (SCTX) tests are considered to allow researchers to investigate influences of individual variables on unsaturated soils under specified stress path with controls of stresses, pore water and air pressures. In the past fifty years, SCTX testing method has been established as a standard approach to characterize constitutive behavior for unsaturated soils. Most important concepts for modern unsaturated soil mechanics were developed upon results from the SCTX tests. However, SCTX tests require sophisticated and therefore expensive equipment. It is usually laborious and time-consuming. It is not uncommon to take 2-3 years to fully characterize one unsaturated soil. Due to the lengthy testing process, the test results, especially for the water content change, are not reliable or simply not available. As a result, SCTX tests cannot be justified for ordinary engineering projects.
In addition, our recent findings indicated that the SCTX tests in fact cannot control the stress path of an unsaturated soil during loading. This incapability, in combination with complicated loading/collapse behavior of unsaturated soils, makes the long-accepted Divide-and Conquer approach for characterizing unsaturated soil behavior unacceptable. This presentation discusses the limitations of the SCTX tests in the characterization of unsaturated soils. A possible solution to the problem was proposed based on a newly developed modified state surface approach (MSSA). It is proposed that results from undrained (constant water content) tests be used to replace the SCTX tests for the constitutive modeling purpose. Not only can it produce theoretically correct results with much simpler testing equipment, but also significantly reduce the testing time (from 2-3 months/test to 2-3 hours/test). This can potentially leads to extensive applications of unsaturated soil mechanics in routine engineering projects.
Bio:
Dr. Xiong Zhang, P.E., is an associate professor in the Department of Civil Engineering, and Architectural Engineering, and Construction Management, College of Engineering and Applied Science, University of Cincinnati. He received his Ph.D. degree in Civil Engineering from Texas A&M University, M.S. and B.S. degrees in Geotechnical Engineering from China Institute of Water Resources and Hydropower Research (IWHR), Beijing, China, and Tongji University, Shanghai, China, respectively. He has been teaching and conducting research in the field of geotechnical engineering since 1992. His studies focus on development of advanced laboratory techniques to rapidly characterize geomaterials, constitutive modeling coupled hydro-mechanical behavior of unsaturated soils, numerical modeling of climate-soil-structure interaction, slope stability analysis, soil stabilization and ground improvement, and frozen ground engineering. He was one of the two speakers of ASCE GeoInstitute Unsaturated Soils Committee Webinar on “Introduction to Constitutive Modeling of Unsaturated Soils.”
Dr. Zhang is currently serving as an Associate Editor for Geomechanics and Engineering, An international Journal and committee member of several nationwide technical committees such as TRB AFP60 Committee on Engineering Behavior of Unsaturated Soils, TRB AFS20 Committee on Soil and Rock Instrumentation, and ASCE Geo-Institute Pavement Committee and Shallow Foundation Committee. He was secretary general for the 2014 GeoShanghai International Conference and the 2015 International Symposium on Systematic Approaches to Environmental Sustainability in Transportation. He organized several sessions in some international conferences and was an editor of ASCE Geo-Institute Geotechnical Special Publications No.189, 202, and 236.
