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Short Note on PIle Load Test



Pile Load Test
Pile load test is the most acceptable method to determine the load carrying capacity of a pile. The load test may be carried out either on a driven pile or cast in situ piles. The test can be made either on a single pile or on a group of piles.  Before finalizing the design, load tests are carried out on piles installed for the purpose on the site. These are called initial load tests. They are useful in determining the general suitability of the proposed pile foundation, comparing the load capacity obtained from formulae, and for a general check on the piling equipment to be used as well as on soil properties.

Purpose of Pile load test is:
·         To determine settlement under working load.
·         To determine ultimate bearing capacity.
·         To ascertain as a proof of acceptability.

In general two types of pile load tests are conducted:
·         Initial Test: It is performed before the start of construction, to access the design adequacy. In initial test the test load is about 2.5 times the design load.
·         Routine Test: It is performed during the working time. In this test the test load is about 1.5 times the design load
There are two methods of testing piles

  1. Maintained Load Test: Maintained Load test is the better method. This method provides an idea of both shaft and end resistance. In this method the contribution of each soil layer can be calculated but it is time consuming. The failure load is not clearly defined. In this method the distance of anchor piles from test pile should not be less than 1.5 m.


Process of Load application
·         Load is applied in increment at the rate of 25 % of design load till working load is reached.
·         For each load increment, load constant must be maintained till settlement according to code.
·         Go for next Loading
·         After working load is reached, hold the load for 24 hour and record hourly settlement and unload.
·         Reload from working load to higher load.
The ultimate load is determined by plotting the load settlement curve.


1.      2. Constant Rate Penetration Test:  This test is most suitable for friction pile. In this test, the well defined failure load is obtained and the method is very quick. However, this method doesnot provide elastic settlement at working load. In this method the pile is jacked continuously into soil at constant rate till failure takes place. The jacking rate in clay is 0.75 mm/min and a small movement required for failure. In sands, the jacking rate is 5mm/min and large movement is required for failure.
The failure load is that at which the rate of settlement continues undiminished without further increment of load. It is the load where the load settlement curve has its minimum radius of curvature. The ultimate load is taken as the abscissa of the point of intersection of tangents of initial and final portion of the load settlement curve.



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