Strength in clay (Su)

Su may be estimated from OCR using SHANSEP (Ladd 1977)

Su at National Site FUCINO – ITALY

Cu-at-National-Site-FUCINO–ITALY

A.G.I., 10th ECSMFE Firenze 1991 Vol. 1, p. 37

CPT: different profiles according to Nc (=14-22)

Su comparisons from DMT and from other tests

Recife – Brazil

Coutinho et al., Atlanta ISC’98

Skeena Ontario – Canada

Skeena Ontario Canada

Mekechuk J. (1983). “DMT Use on C.N. Rail Line British Columbia”,
First Int.Conf. on the Flat Dilatometer, Edmonton, Canada, Feb 83, 50

Tokyo Bay Clay – Japan

Iwasaki K, Tsuchiya H., Sakai Y., Yamamoto Y. (1991) “Applicability of the Marchetti Dilatometer Test to Soft Ground in Japan”, GEOCOAST ’91, Sept. 1991, Yokohama 1/6

Roots Of The OCR AND Su Correlations

The Marchetti 1980 correlation for OCR in clays was OCR = (0.5 KD)1.56. It was obtained experimentally by interpolating a line through the then available high quality KD – OCR datapoints (Fig. 3a) . In 1995 that correlation was experimentally reconfirmed (Fig. 3a) by Kamey and Iwasaki (1995), based on KD – OCR datapoints from various clays they had investigated. In 1993 and in 2004 the correlation was independently confirmed theoretically by Finno (1993) and by Yu (2004), who used two different theoretical methods (Fig. 3b  and 3c). Thus the 1980 OCR correlation has “empirical” and “theoretical” roots, and appears a well founded average, generally able to provide reasonable estimates of OCR in average “textbook” clays.

finno ecc tris
Fig. 3. Correlations between OCR and KD in clay: (a) Experimental (Marchetti 1980 and Kamey and Iwasaki (1995);
(b) Theoretical by Finno (1993); (c) Theoretical by Yu (2004).
By adopting the average value m=0.8 (Ladd 1977 ) and the average value (Cu/σ’v)NC = 0.22 (Mesri 1975), the following 1980 average equation for Cu was obtained
Cu = 0.22 σ’v (0.5 KD)1.25 (7)
Since Eq. 7 is based on an average “m” and an average (Cu/σ’v)NC, and since Ladd and Mesri numbers are average values from a large number of textbook clays, Eq. 7 can be considered an average formula for “textbook” clays. It is recalled that Ladd used to say that the best Cu is obtained not by triaxial UU, but by oedometer, where OCR is determined, followed by SHANSEP, statement clearly referred to average “textbook” clays. In conclusion the original 1980 correlations are not subjective propositions envisioned by the author, but are the consequential outcome of well established empirical and theoretical findings applicable to “textbook” clays.

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