Geotechnical Engineering

DHARM

PILE FOUNDATIONS 671

Another method in use for the slow test is to plot both load and settlement values on
logarithmic scale. The results typically plot as two straight lines (Fig. 16.8). The intersection of
the straight lines is taken as failure load for design purposes although this may not be the
actual load at which failure occurs.

Pile settlement (Log scale)

Pile load (Log scale)

Qup

Fig. 16.8 Log-Log of pile load-settlement curve
and determination of failure
The allowable load on a single pile may be obtained as one of the following [I.S: 2911
(Part I)-1974]:

1. 50% of the ultimate load at which the total settlement is equal to one-tenth the
   diameter of the pile.


2. Two-thirds of the load which causes a total settlement of 12 mm.


3. Two-thirds of the load which causes a net (plastic) settlement of 6 mm (total settle-
   ment minus elastic settlement).
   In the case of the cyclic load test, the load is raised up to a particular level, released to
   zero and again raised to a higher value and released to zero. Settlements are recorded at each
   increment or decrement of load. A typical plot of a cyclic load test data will look as shown in
   Fig. 16.9.

Settlement

Se 2

S 2

O Q 1 Q 2

Load

SS

e 1

Sp 1

Sp 2

Fig. 16.9 Cyclic load test on a pile-load vs. settlement