Civil Engineering Reference
In-Depth Information
2
3
D
D
4
1
Fig. 10.11
Transfer of load in friction piles.
For bearing piles the total foundation load is assumed to act at the base of the piles on a foundation
of the same size as the plan of the pile group. With this assumption it becomes a simple matter to examine
settlement effects.
With friction piles it is virtually impossible to determine the level at which the foundation load is effec-
tively transferred to the soil. An approximate method, often used in design, is to assume that the effective
transfer level is at a depth of 2D/3 below the top of the piles. It is also assumed that there is a spread of
the total load, one horizontal to four vertical. The settlement of this equivalent foundation (Fig.
10.11)
can then be determined by the normal methods.
Exercises
Exercise 10.1
A single test pile, 300 mm diameter, is driven through a depth of 8 m of clay which
has an undrained cohesive strength varying from 10 kPa at its surface to 50 kPa at a
depth of 8 m. Estimate the safe load that the pile can carry.
Answer
60 kN
Exercise 10.2
Three static load tests were carried out on CFA piles and gave the following results:
Test No.:
1
2
3
Measured load (kN)
1210
1350
1490
A ground investigation has revealed that the resistance of the soil increases rapidly
with depth, such that the base resistance may be considered equal to four times
the shaft resistance.
Determine the design compressive resistance of the ground in accordance with
both Design Approach 1 and Design Approach 2.
Answer
(DA1: 794 kN; DA2: 1023 kN)
