values of C'c for e0-values less than 0.336. For e0 = 0.336, Eq. 21 yields a value of C'c = 0.097 which appears to be more realistic; this would ac­count for the " c u r v a t u r e " of the data . O the r available non l inea r compression index correlations are shown in Table 6.

The material for portions of this closure was obtained from a study conducted (1981-82) at the Marine Geomechanics Laboratory, University of Rhode Island (URI). The study was funded by a fellowship admin­istered by the National Research Council (NRC) and sponsored by the Ford Foundation. The writer gratefully acknowledges the assistance given by URI, NRC, and the Ford Foundation.

APPENDIX.—REFERENCES

24. Azzouz, A. S., Krizek, R. J., and Corotis, R. B., "Regression Analysis of Soil Compressibility," Soils and Foundations, Japanese Society of Soil Mechanics and Foundations Engineering, Vol. 16, No. 2, June, 1976, pp. 19-29.

25. Beverly, B. E., "Consolidation Characteristics of Deep-Sea Sediments Re­covered with a Giant Piston Corer: Blake-Bahama Outer Ridge Area," thesis presented to the Department of Civil Engineering, at Worchester Polytechnic Institute, in Worchester, Mass., in 1975, in partial fulfillment of the require­ments for the degree of Master of Science.

26. Helenelund, K. V., "On Consolidation and Settlement of Loaded Soil-Lay­ers," thesis presented to the Finland Technical Institute, at Helsinki, Finland, in 1951, in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

27. Koppula, S. D., "Statistical Estimation of Compression Index," Ceotechnical Testing Journal, GTJODJ, Vol. 4, No. 2, June, 1981, pp. 68-73.

28. Peck, R. B., and Reed, W. C , "Engineering Properties of Chicago Subsoils," Bulletin 423, Engineering Experiment Station, University of Illinois, Urbana, 111., 1954.

29. Ostle, B., Statistics in Research, 2nd ed.. The Iowa State Univ. Press, Ames, Iowa, 1974.

FRICTION CAPACITY OF PILES DRIVEN INTO CLAY'

Discussion by Kul Bhushan,4 M. ASCE

The authors have presented statistical correlations of available load test data for friction piles in clays using a number of existing pile capacity prediction methods. The writer agrees with the authors view that em­pirical methods based on an examination of a large number of available load test data are likely to be the most successful in predicting pile ca­pacity for design. New theoretical effective stress approaches can be used

"November, 1981, by Leland M. Kraft, Jr., John A. Focht, Jr., and Srinath F. Amerasinghe (Paper 16663).

4Project Mgr., Woodward-Clyde Consultants, 203 North Golden Circle Dr., Santa Ana, Calif. 92705.

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to gain insight into the role of various factors affecting pile capacity. However, some of the parameters required for use in these methods are difficult to obtain and thus require the addition of empiricism to make the predictions fit the observed behavior. The writer has the following observations and comments on the conclusions presented in the paper:

1. All load test data below a depth of 150 ft (46 m)—eight data points— belong to the category "less than full set-up, piles having oversize clo­sure plates at the tip, and piles with sequential testing-redriving-retest-ing." The authors state these data represent a lower bound capacity and after performing the statistical analyses, they limit the minimum values of X and p to 0.14 and 0.23, respectively, to account for the lowered measured capacity in the eight cases. The limiting values of X and p correspond to pile lengths of 130 ft (40 m) and 97 ft (30 m), respectively. Consequently, it appears that for the majority of offshore piles, which are greater than 150 ft (46 m) in length, a constant value of X = 0.14 or P = 0.23 is recommended. These values are about 26%-34% higher than the mean of the eight tests below 150 ft (46 m) and are approximately equal to mean-plus-one standard deviation of the eight data points. Vesic (33) suggested the equation Ns = (1 - sin ()>') tan <(>' for obtaining Ns, in which Ns is defined as a dimensionless factor (same as p) and <(>' is the angle of shearing resistance of remolded clay in drained condition. For 15 < <)>' < 30°, Ns or p ranges between 0.2 and 0.29, and Vesic rec­ommends an average value of 0.24. This recommended value of 0.24 by Vesic compares with the limiting value of p = 0.23 proposed by the au­thors. Vesic suggests that lower values may be applicable to very long piles as is apparent from the eight data points below 150 ft (46 m). A review of data above 150 ft (46 m) indicates that for a number piles with less than full set up or closure plates the measured p values are higher than the mean curve. Based on the available information, it appears questionable whether a 26%-34% increase in the limiting values of p or X over the mean values from the eight data points below 150 ft (46 m) is justified due to the effects cited by the authors.

2. The whole question of pile capacity for deep offshore piles is pri­marily relevant for piles with lengths of 150 ft (46 m) or more where limiting values of X of p are suggested. Consequently, comparisons shown in Table 3 using computed values of X less than 0.14 appear to be of no practical value.

3. Correlations of p with L are statistically as good as correlations of P with TT3 and correlations of X with ir3 are statistically slightly better than correlations of X with L. However, calculations of TT3 are based partly on assumed parameters. It is the writers opinion that correlations of p or X with L should be preferred over correlations with ir3 which is based on assumed parameters. Furthermore, limiting values of X or p are likely to be applicable for most practical cases.

APPENDIX.—REFERENCE

33. Vesic, A. S., "Design of Pile Foundations," Synthesis of Highway Practice 42, National Cooperative Highway Research Program, Transportation Research Board, National Research Council, Washington, D.C., 1977, pp. 12-22.

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