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Fhwa/Tx-09/0-5530-1 Prediction of Embankment Settlement

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Fhwa/Tx-09/0-5530-1 Prediction of Embankment Settlement Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. FHWA/TX-09/0-5530-1 4. Title and Subtitle 5. Report Date PREDICTION OF EMBANKMENT SETTLEMENT OVER SOFT December 2008 SOILS Published: June 2009 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Vipulanandan, C., Bilgin, Ö., Y Jeannot Ahossin Guezo, Vembu, K. Report 0-5530-1 and Erten, M. B. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) University of Houston Department of Civil and Environmental Engineering 11. Contract or Grant No. Houston, Texas 77204-4003 Project 0-5530 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Texas Department of Transportation Technical Report: Research and Technology Implementation Office September 2005 - October 2008 P. O. Box 5080 Austin, Texas 78763-5080 14. Sponsoring Agency Code 15. Supplementary Notes Research performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. Research Project Title: Prediction of Embankment Settlement Over Soft Soils URL: http://tti.tamu.edu/documents/0-5530-1.pdf 16. Abstract The objective of this project was to review and verify the current design procedures used by TxDOT to estimate the total and rate of consolidation settlement in embankments constructed on soft soils. Methods to improve the settlement predictions were identified and verified by monitoring the settlements in two highway embankments over a period of 20 months. Over 40 consolidation tests were performed to quantify the parameters that influenced the consolidation properties of the soft clay soils. Since there is a hysteresis loop during the unloading and reloading of the soft CH clays during the consolidation test, three recompression indices (Cr1, Cr2, Cr3) have been identified with a recommendation to use the recompression index Cr1 (based on stress level) to determine the settlement up to the preconsolidation pressure. Based on the laboratory tests and analyses of the results, the consolidation parameters for soft soils were all stress dependent. Hence, when selecting representative parameters for determining the total and rate of settlement, expected stress increases in the ground should be considered. Also the 1-D consolidation theory predicted continuous consolidation settlement in both of the embankments investigated. The predicted consolidation settlements were comparable to the consolidation settlement measured in the field. Constant Rate of Strain test can be used to determine the consolidation parameters of the soft clay soils. The effect of Active Zone must be considered in designing the edges of the embankments and the retaining walls. 17. Key Words 18. Distribution Statement Active Zone, Consolidation, Embankment, Field No restrictions. This document is available to the Tests, Recompression Indices, Settlement, Soft Soils public through NTIS: National Technical Information Service 5285 Port Royal Road Springfield, Virginia 22161 19. Security Classif.(of this report) 20. Security Classif.(of this page) 21. No. of Pages 22. Price Unclassified Unclassified 210 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Prediction of Embankment Settlement Over Soft Soils Project Report No. TxDOT 0-5530-1 Final Report by C. Vipulanandan Ph.D., P.E. Ö. Bilgin, Ph.D., P.E. Y. Jeannot Ahossin Guezo Kalaiarasi Vembu and Mustafa Bahadir Erten 1994 T C I GMA Performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration June 2009 Center for Innovative Grouting Materials and Technology (CIGMAT) Department of Civil and Environmental Engineering University of Houston Houston, Texas 77204-4003 Report No. CIGMAT/UH 2009-6-1 ENGINEERING DISCLAIMER The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Texas Department of Transportation or the Federal Highway Administration. This report does not constitute a standard or a regulation. There was no art, method, process, or design that may be patentable under the patent laws of the United States of America or any foreign country. v ACKNOWLEDGMENTS This project was conducted in cooperation with Texas Department of Transportation (TxDOT) and Federal Highway Administration (FHWA). The researchers thank the TxDOT for sponsoring this project. Also thanks are extended to the Project Coordinator K. Ozuna (Houston District), Project Director S. Yin (Houston District) and Project Committee Members R. Willammee (Fort worth District), M. Khan (Houston District), D. Dewane (Austin District) R. Bravo (Pharr District) and P. Chang (FHWA). vi PREFACE Settlement of highway embankments over soft soils is a major problem encountered in maintaining highway facilities. The challenges to accurately predict the total and rate of consolidation settlements are partly due to the uncertainties in field conditions, laboratory testing, interpretations of laboratory test data, and assumptions made in the development of the 1-D consolidation theory. Hence, there is a need to investigate methods to better predict the settlement of embankments on soft soils. The objective of this project was to review and verify the current design procedures used in TxDOT projects to estimate the total and rate of consolidation settlements in embankments constructed on soft soils. Methods to improve the settlement predictions were identified and verified by monitoring the settlements in two highway embankments over a period of 20 months. Over 40 consolidation tests were performed to quantify the parameters that influence the consolidation properties of the soft clay soils. Based on the laboratory tests and analyses of the results, the consolidation parameters for soft soils were all stress dependent. Hence, when selecting representative parameters for determining the total and rate of settlement, expected stress increases in the ground should be considered. Also the 1-D consolidation theory predicted continuous consolidation settlement in both of the embankments investigated. The predicted consolidation settlements were comparable to the consolidation settlement measured in the field. This report reviewed the current TxDOT project approach to predict the total and rate of consolidation settlements of embankments over soft soils. Based on the laboratory and field investigations, methods to further improve the embankment settlement predictions have been recommended. vii ABSTRACT The prediction of embankment settlement over soft soils (defined by the undrained shear strength and/or Texas Cone Penetrometer value) has been investigated for many decades. The challenges mainly come from the uncertainties about the geology, subsurface conditions, extent of the soil mass affected by the new construction, soil disturbances during sampling and laboratory testing, interpretations of laboratory test data, and assumptions made in the development of the one-dimensional consolidation theory. Since the soft soil shear strength is low, the structures on the soft soils are generally designed so that the increase in the stress is relatively small and the total stress in the ground will be close to the preconsolidation pressure. Hence there is a need to investigate methods to better predict the settlement of embankments on soft soils. The objective of this project was to review and verify the current design procedures used by TxDOT to estimate the total and rate of consolidation settlement in embankments constructed on soft soils. Methods to improve the settlement predictions were identified and verified by monitoring the settlements in two highway embankments over a period of 20 months. Over 40 consolidation tests were performed to quantify the parameters that influenced the consolidation properties of the soft clay soils. Since there is a large hysteresis loop during the unloading and reloading of the soft CH clays during the consolidation test, three recompression indices (Cr1, Cr2, Cr3) have been identified with the recommendation to use the recompression index Cr1 (based on stress level) to determine the settlement up to the preconsolidation pressure. Based on the laboratory tests and analyses of the results, the consolidation parameters for soft soils were all stress depended. Hence, when selecting representative parameters for determining the total and rate of settlement, expected stress increases in the ground should be considered. Linear and nonlinear relationships between compression indices of soft soils and moisture content and unit weight of soils have been developed. Also the 1-D consolidation theory predicted continuing consolidation settlement in both of the embankments investigated. The predicted consolidation settlements were comparable to the consolidation settlement measured in the field. The Constant Strain Rate test can be used to determine the viii consolidation parameters of the soft clay soils. The effect of Active Zone must be considered in designing the edges of the embankments and the retaining walls. ix SUMMARY The prediction of consolidation settlement magnitudes and settlement rates in soft soils (defined by the undrained shear strength and/or Texas Cone Penetrometer value) is a challenge and has been investigated by numerous researchers since the inception of consolidation theory by Terzaghi in the early 1920s. The challenges mainly
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