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 superstruc-
ture 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 con-
solidated quartz sands are shown in Figure 5.28. The E 25 and E 50 values represent the
drained modulus at a stress level of 25% and 50% respectively of the failure stress. In a gen-
eral review of the application of cone penetration testing to foundation design, Meigh(5.23)
stated that the E 25 values are appropriate for most foundation problems but the E 50 values
may be more relevant to calculating settlements of the single pile.
The Evalues in Figure 5.28 greatly overestimate settlements in over-consolidated sands.
Lunne and Christoffersen(5.24)established a relationship between initial tangent constrained
modulus (the reciprocal of the modulus of volume compressibility mv) and qcfor normally
and over-consolidated sands as shown in Figure 5.29.

Ev

60

50

40

30

20

10

0

90

Medium dense,

Dense,

Very dense,

Dr 5 46%

Dr 5 70%

E 2552 qc

E 25 E 50

1.5qc

200

100

50

Stress,

s^0

s (^0) max
0.50 s (^0) max
0.25 s (^0) max
Strain, ea
s 0
ea
Dr 5 90% s9vo 5 400 kN/m^275
60
45
30
15
0
01020
Cone resistance, qc (MN/m^2 )
Drained secant Young's modulus, at 25%failure stress level,
E^25
(MN/m
2 )
Drained secant Young's modulus, at 50%failure stress level,
E^50
(MN/m
2 )
30 40 50
Figure 5.28Drained deformation modulus values (Ed) 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)).