Analysis of Improved Ground and Reinforced Soil Systems Performance during the 1999 Turkey and 2001 Nisqually Earthquakes - Part 1 Reinforced Soil Structures

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0201508, James R. Martin, Virginia Polytechnic Institute"Analysis of Improved Ground and Reinforced Soil System Performance During the 1999 Turkey and 2001 Nisqually Earthquakes: Reinforced Soil Structures"Reinforced soil structures, such as soil-nailed walls and mechanically-stabilized embankments, have been shown to be feasible alternatives to conventional earth retaining structures. They are becoming increasingly popular, and designs are becoming more challenging with taller walls and a wider variety of reinforcing and facing materials. Design methods for static conditions are fairly well established; however there is a lack of knowledge regarding seismic performance, and a corresponding lack of comprehensive seismic design procedures. Current guidelines are very limited and are based on generalized assumptions due to the scarcity of documented seismic field performance data. Also, there are no simplified methods that can be used to predict permanent wall displacement - often the controlling serviceability criterion. Although some centrifuge and shake table model experiments have been performed to simulate seismic loadings, these experiments were not designed to assist in the development of improved design procedures. There is a need for case history analysis, parametric numerical study, and additional model experiments to fully understand the seismic behavior of reinforced soil structures and to develop improved seismic design guidelines.A unique opportunity to evaluate the behavior of these systems under a range of ground shaking levels and for a variety of soil conditions and performance levels is provided by the more than sixteen reinforced-soil structures located within the affected region of the M (7+) 1999 earthquakes in Turkey, and four walls associated with large earthquakes in Taiwan and Seattle, WA. Through field reconnaissance studies, the principal investigator collected required performance data, construction details, and subsoil data, providing a comprehensive database of wall performance.The objective of this research project is to: 1.) perform a detailed case history analysis of the most promising and potentially instructive reinforced soil systems identified, and document the findings; 2.) use the field cases to calibrate and/or assess the predictive capability of the numerical models; 3.) perform dynamic parametric numerical analyses to establish behavioral trends and effectively extend the database of wall performance under seismic loading; and, 4.) use this data to develop improved seismic design guidelines for reinforced soil structures.The project ivolves a collaboration between Virginia Tech and Turkish researchers at Bogazici University and Zetas, Inc, and interfaces with a collaborative microzonation project in Turkey involving Virginia Tech, the Swiss Federal Institute of Technology, Bogazici University, and Yokohama National University. It also addresses limitations in current seismic design methods for reinforced-soil systems that have been identified by the Federal Highway Administration in Demonstration Project No. 82 (1999).