Pile Design and Construction Practice, Fifth edition

178 Resistance of piles to compressive loads
Cone resistance (qc ) (MN/M2 ) Cone resistance (qc ) (MN/M2 (a) (b)
)
Depth below ground level (m)
0
5
10
15
20
Lower
bound curve
Average curve
The method generally used in the Netherlands is to take the average cone resistance
over a depth of up to four pile diameters below the pile toe, and the average eight pile
diameters above the toe as described by Meigh (4.25) qc�2 .
The ultimate base resistance is then
q ub � q c�1 � q c�2
2
5 10
Determining q c from average
and lower bound q c /depth
curves
Soft silty clay
Loose
becoming
medium
dense
sand
15 5 10
0
Path for
determining q c–1
Method used in the Netherlands
for obtaining base resistance
(4.19)
The shape of the cone-resistance diagram is studied before selecting the range of depth
below the pile to obtain . Where the qc increases continuously to a depth of 4D below
the toe, the average value of is obtained only over a depth of 0.7D. If there is a sudden
decrease in resistance between 0.7D and 4D the lowest value in this range should be selected
for (Figure 4.18b). To obtain the diagram is followed in an upward direction
and the envelope is drawn only over those values which are decreasing or remain constant
at the value at the pile toe. Minor peak depressions are again ignored provided that they
do not represent clay bands; values of qc higher than 30 MN/m2 qc � 1
qc�1 qc�1 qc�2 are disregarded over the
4D – 8D range.
5
10
15
20
Path for
determining q c–2
Figure 4.18 Use of static cone penetration tests (CPT) to obtain design values of average cone
resistance ( ) in coarse soils.
q c
Pile
D
8D
4D
15
q c�1