Pile Design and Construction Practice, Fifth edition

268 Pile groups under compressive loading
the maximum end-bearing resistance, where the settlement calculated from the upper limit
curve is likely to be relatively small.
5.3.2 Estimating settlements from static cone penetration tests
Where total and differential settlements are shown to be large and critical to the superstructure
design, it is desirable to make static cone penetration tests (Section 11.1.4) from which
the soil modulus values can be derived and then to use the Steinbrenner (Figure 5.18) or
Christian and Carrier (Figure 5.20) charts to obtain the group settlement. Relationships
between the cone-resistance (qc) values and the drained Young’s modulus for normally consolidated
quartz sands are shown in Figure 5.28. The E25 and E50 values represent the
drained modulus at a stress level of 25% and 50% respectively of the failure stress. In a general
review of the application of cone penetration testing to foundation design, Meigh (5.23)
stated that the E25 values are appropriate for most foundation problems but the E50 values
may be more relevant to calculating settlements of the single pile.
The E values in Figure 5.28 greatly overestimate settlements in over-consolidated sands.
Lunne and Christoffersen (5.24) E�v established a relationship between initial tangent constrained
modulus (the reciprocal of the modulus of volume compressibility mv) and qc for normally
and over-consolidated sands as shown in Figure 5.29.
Drained secant Young's modulus, at 50%
failure stress level, E50 (MN/m2 )
60
50
40
30
20
10
Medium dense, Dr 5 46%
Dense, Dr 5 70%
Very dense, Dr 5 90%
e a
50
s0 E 25 5 2q c
0
0
0 10 20
Cone resistance, qc (MN/m2 30 40 50
)
100
Stress, s 0
E 25
200
E 50
Strain, e a
s9 vo 5 400 kN/m 2
1.5q c
s 0max
0.50 s0max 0.25 s0max 90
75
60
45
30
15
Drained secant Young's modulus, at 25%
failure stress level, E25 (MN/m2 )
Figure 5.28 Drained deformation modulus values (E d) for uncemented normally consolidated quartz
sands in relation to cone resistance (after Meigh (5.20) ), Robertson and Campanella (5.21) ),
Baldi et al. (5.22) ).