Stress-Deformation Behavior of an Embankment on Boston Blue Clay

Ladd, Charles C.; Whittle, Andrew J.; Legaspi, Dante E.; ,

Stress-Deformation Behavior of an Embankment on Boston Blue Clay

by Charles C. Ladd, (F.ASCE), Massachusetts Inst of Technology, Cambridge, United States,
Andrew J. Whittle, (A.M.ASCE), Massachusetts Inst of Technology, Cambridge, United States,
Dante E. Legaspi, Jr., (S.M.ASCE), Massachusetts Inst of Technology, Cambridge, United States,

Document Type: Proceeding Paper

Part of: Vertical and Horizontal Deformations of Foundations and Embankments

Abstract:

An 11 m high I-95 embankment was thoroughly instrumented with piezometers, settlement rods and inclinometers to measure the behavior of the underlying 40 m thick deposit of Boston Blue Clay (BBC) during staged loading and four years of subsequent consolidation. This paper uses updated estimates of the engineering properties of BBC at the site, based on several major in situ and laboratory test programs, in order to perform finite element analyses that incorporate coupled consolidation with two generalized effective stress soil models, Modified Cam Clay (MCC) and MIT-E3. Comparison of predicted versus measured performance during 1967-1973 led to four principal conclusions: (1) The analyses give reasonable predictions of pore pressures and the overall magnitudes of deformations, except in the upper 15 m of the clay crust where uncertainties in the stress history were evaluated using two preconsolidation pressure profiles. (2) Differences between the two soil models lie primarily in the predicted horizontal displacements, for which MIT-E3 gives better agreement with measured behavior. (3) Measurements of outward horizontal displacements (lateral spreading) after the end of construction are predicted as a consequence of anisotropic yield in the MIT-E3 model and are most probably not related mainly to creep of the clay as postulated by others. (4) During consolidation, the analyses predict a significant reduction of centerline vertical total stress due to arching which contradicts the conventional assumption of constant total stress.

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