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Title: The role of fill strength in the stability of embankments on soft clay foundations
Authors: University of California, Berkeley. College of Engineering. Office of Research Services.
Chirapuntu, Suphon.
Duncan, J. M. (James Michael)
Keywords: Earth fills
Slices method
Embankment foundations
Soil strength
Soil mechanics
Embankment stability
Stability analysis
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Contract Report
Abstract: This investigation was performed to study the role of fill strength in the stability of embankments on soft clay foundations. It covered four areas: (1.) methods of stability analysis of embankments on soft foundations, (2.) effects of progressive failure on the stability of embankments on soft foundations, (3.) the development of cracks in embankments and their effect on stability, and (4.) a preliminary study of the effectiveness of steel reinforcing in prevention of cracking in embankments on soft foundations. Among several methods of stability analysis, the Ordinary Method of Slices appears to be most suitable for total stress analysis of embankments on soft foundations. Numerical difficulties occur in the Bishop's Modified method when the ends of the slip circle are steeply inclined, as they often are in embankments on soft foundations, and convergence difficulties arise frequently when Spencer's method and Morgenstern and Price's method are applied to this type of problem. Results from nonlinear finite element analyses show that when an embankment is stronger and stiffer than its foundation, the percentage of strength mobilized in the embankment is smaller than in the foundation. These studies showed that the "equal strain" concept of progressive failure is invalid; the strains in a stiff embankment are inevitably smaller than those in the foundation. The more severe the stress-strain incompatibility between the embankment and its foundation, the smaller is the portion of the embankment strength which can be mobilized before failure begins in the foundation. These studies were used as a basis for a simple method to allow for progressive failure effects in analyses of stability. Finite element analyses indicate that tension develops in embankments due to a tendency for clay to be squeezed from beneath the center of the embankment out toward the edges, and that cracks tend to propagate from the bottom to the top of the embankment. An experimental study, using flexure tests on beams of compacted soil, showed that once a crack developed, it continued to propagate and the beams eventually collapsed under their own weight. From the results of a parameter study on the effects of several factors affecting the development of tension in embankments, an empirical equation was developed which can be used to estimate the height at which an embankment will crack. The results of the studies of progressive failure and cracking were employed in developing a rotational method for estimating whether cracks will develop in an embankment, and for determining what portions of the embankment and foundation strengths should be used in evaluation of the stability. A preliminary study was made to investigate the effectiveness of steel reinforcing in preventing cracking of cohesive fills on soft foundations. The results indicate that reinforcing can be very effective, and that further studies of reinforcing would be desirable. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Contract Report

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