(asce)0733-9410(1989)115_2(263)
TRANSCRIPT
CJCC CONCEPT AND K0 DURING SECONDARY COMPRESSION*
Discussion by Balu Iyer3
The writer has read with great interest the paper and wishes to provide additional support to the Ca/Cc concept. This discussion deals with three different types of soils, all from the southern Ontario region in Canada. For the purpose of this discussion, the soils will be identified as soil A, soil B and soil C. Typical properties of the three soils are given in Table 4.
Soils A and B, as shown in Tables 5 and 6, respectively, were subjected to consolidation tests with a load increment ratio of two with each load increment maintained on the soil samples for 24 hours, except for two load increments which were maintained for 48 hours each. For the purpose of calculation of Cc, the e-log a'v plot was prepared using the end-of-primary (EOP) e values. The slope of the e-log ul curve at any particular increment was taken as the Cc value. The Ca value was calculated from the dial reading versus log t plot. The Cc, Ca and CjCc values for the various load increments are given in the tables below. The Ca/Cc value for the organic silt (soil A) varied between 0.028 and 0.072, with an overall average of 0.045. For the silty clay (soil B), the CjCc ranged between 0.029 and 0.058, with an overall average of 0.037. For both of these soils, large variations in CJ Cc values were observed during the recompression range (i.e., at loads less
TABLE 4. Typical Properties of Soils A, B, and c
Soil number
(1)
A B C
Soil type (2)
Organic silt Silty clay Silty clay
Natural water
content (3)
70.0 33.3 19.5
Liquid limit (4)
74.0 41.0 —
Plastic limit (5)
46.2 21.4 —
Initial void ratio (6)
1.884 0.838 0.509
Preconsolidation pressure t.s.f.
(MPa) (7)
0.7 (0.067) 1.2 (0.115) 4.5 (0.431)
TABLE 5. Soil A Soil Type: Organic Silt
Load
t.s.f. (1)
0.25 0.50 1.00 2.00 4.00 8.00
16.0
MPa (2)
0.024 0.048 0.096 0.191 0.383 0.766 1.532
cc (3)
0.05 0.21 0.48 0.50 0.55 0.55 0.55
ca (4)
0.0036 0.0058 0.0195 0.0250 0.0274 0.0216 0.0187
CJCC
(5)
0.072 0.028 0.041 0.050 0.050 0.039 0.034
Note: Overall average C/Cc = 0.045 (for loads greater than preconsolidation pressure average C/Cc = 0.043).
"March, 1987, Vol. 113, No. 3, by G. Mesri and A. Castro (Paper 21323). 3Proj. Mgr., Geocon Inc., Mississauga, Ontario, Canada.
263
J. Geotech. Engrg. 1989.115:263-264.
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TABLE 6. Soil B Soil Type: Silty Clay
Load t.s.f. d) 0.25 0.50 1.00 2.00 4.00 8.00
16.0
(MPa) (2)
0.024 0.048 0.096 0.191 0.383 0.766 1.532
cc (3)
0.064 0.09 0.16 0.155 0.21 0.21 0.21
c„ (4)
0.0037 0.0028 0.0046 0.0055 0.0069 0.0076 0.0076
CJCC
(5)
0.058 0.032 0.029 0.035 0.033 0.036 0.036
Note: Overall average Ca/Ce = 0.037 (for loads greater than preconsolidation pressure average CJCC = 0.034).
TABLE 7. Soli C Soil Type: Silty Clay
Load
t.s.f. (1)
4 8
(MPa) (2)
0.383 0.766
(3)
0.048 0.073
(4)
0.0022 0.0034
CJCC
(5)
0.046 0.047
than the preconsolidation pressure). The variation in the Ca/Cc value was in the range of —21% and +16% from the average, when the load on the sample was greater than the preconsolidation pressure.
The consolidation test for soil C consisted of maintaining each load increment for a few hours (until after the primary consolidation under that load was complete) except for two loads, one on each side of the anticipated preconsolidation pressure, that were maintained on the soil sample for 24 hours each. The Cc and Ca values were calculated as described in Table 6 above and the results are tabulated in Table 7. The CJCC values were 0.046 and 0.047.
The CjCc values fall in the narrow range proposed in the paper. The maximum deviations from the average values were observed for soils A and B when the load on the sample was less than the preconsolidation pressure.
Discussion by Ian S. M. Martins,4 Associate Member, ASCE, and Willy A. Lacerda5
The authors are to be congratulated for presenting a paper with considerable amount of experimental data in a subject that has been object of controversial opinions.
First, the writers want to note for discussion that the statement, "In gen-eral, Ca remains constant, decreases, or increases with time," seems to be
"Asst. Prof., COPPE, Federal Univ. of Rio de Janeiro, Brazil. 5Prof., COPPE, Federal Univ. of Rio de Janeiro.
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J. Geotech. Engrg. 1989.115:263-264.
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