Figure F4. Example of the Casagrande and SED method showing the determination of preconsolidation pressure (Pc′). A. Pc′ for prism sample (Test U291 on Section 343-C0019E-5R-1) using the Casagrande method. In this method, the point of maximum curvature is determined. At this point, a line of constant void ratio (Segment B) and a line tangent to the same point (Segment A) is drawn. The intersection of their bisector (Segment C) and the line parallel to the virgin compression line defines Pc′. B. Pc′ for prism sample (Test U291 on Section 5R-1) using the SED method. In the SED method, a line is fit to the early portion of the data and the virgin compression line. Pc′ is defined by their intersection. C. Casagrande method for underthrust sample (Test U293 on Section 20R-1). D. SED method for underthrust sample (Test U293 on Section 20R-1).
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