Skempton (1953b, p. 61) reported that the liquidity index, defined by equation 

 17, may be used as a measure of sensitivity. The available data (Fig. 15) indicate 

 that this relationship may be valid if each area is considered separately and correla- 

 tion lines are forced through the origin. Two lines are shown, however, for Area C 

 samples. The two C 16 and bottom C 19 samples plot with those from Area F, while 

 the C 18 and C 20 samples have lower sensitivities and plot separately. The middle 

 C 19 sample (LI = 400) has a high plasticity index that is anomalous compared to the 

 other Area C samples shown in Figure 15. If correlation lines are not forced through 

 the origin, a clear relationship between the logarithm of sensitivity and liquidity 

 index does not exist. 



Discussion — Hvorslev (1936; 1937, p. 148) established that the cohesion of 

 saturated sediments was dependent on the water content and independent of the stress 

 history of the sample. Rutledge (1947, p. 21, 67) showed that the logarithm of co- 

 hesion was a straight- or slightly curved-line function of water content. Trask and 

 Rolston (1950) confirmed this relationship in sediments of San Francisco Bay. Bjerrum 

 (1951, p. 217; 1954a, p. 60, 89, 92) reported the same relationship to be unique for 

 normally consolidated clays. This paper gives further confirmation in deep-sea sedi- 

 ments . 



It is difficult to assess the relative importance of subordinate factors affecting 

 strength, such as grain size and clay type. In laboratory experiments relating clay 

 content and grain size to strength, Trask and Close (1958) and Trask (1959) found: 

 (1) at a given water content, strength increased from kaolin and illite (very slightly 

 stronger than kaolin) to montmorillonite; (2) at a given water content and sand-clay 

 ratio, strength increased as the sand grain size decreased above 2.9 f£ (below 135/u.); 

 and (3) at a given water content and grain size, strength of all clays increased as the 

 ratio of clay to sand increased . Comparison of clay mineralbgy (see Table 6) in the 

 15- to 30-cm (6 to 12 in) samples of cores B 87 and C 18 suggest the reverse of condi- 

 tion (1) above; however, two samples are of little significance . The other two condi- 

 tions cannot be compared because of the variability of parameters held constant by 

 Trask . 



Sediment structure, thixotropy, and salt content of interstitial water also affect 

 strength and sensitivity. Until very recently it was uncertain whether the structure 

 of cohesive sediment was principally honeycomb (Terzaghi, 1925a, p. 10-11; 1925c, 

 p. 914; Casagrande, 1932b, p. 180-186) or cardhouse (Goldschmidt, 1926—cited 

 by Rosenqvist; Lambe, 1953, p. 38; and others) . Rosenqvist (1958, 1960) published 

 stereo photographs, obtained with an electron microscope, of fresh water clay and 

 remolded and undisturbed marine clay that appear to confirm the Goldschmidt -Lambe 

 cardhouse structure hypothesis in undisturbed marine clays. The photographs show a 

 very open mineral arrangement with principal contact between corners and planes 

 (Rosenqvist, 1960, p. 6). 



43 



