The purpose of a pile load test is:
- To determine settlement under working load
- To determine ultimate bearing capacity
- To ascertain proof of acceptability
Types of Pile Load Tests:
In general two types of pile load tests are conducted. They are:
- Initial Test – 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
- Routine or Work Test – The routine test is performed on a working pile.
We calculate the load chart and accordingly the load the pile is capable of bearing
as per IS Code requirements.
Methods of Testing
There are two methods of testing piles. They include:
- Maintained Load Test – This is a more reliable method as it provides an idea
of both shaft and end resistance. The contribution of each soil layer can also be
a. Loading – Depending upon the workload, the load is applied by any one of the
i) Directly through a kentledge for smaller loads
ii) By taking reaction against a kentledge for loads upto 5000 kN
iii) By jacking against a beam or truss connecting adjacent anchor piles or loads
higher than 5000 kN
b. Load Application – The load is applied in the pile in the following sequence.
Load applied in increment at the rate of 25 % of working load till working load is
For each load increment maintain the load constant till settlement is 0.1 mm for 5
min as per IS Code, 0.1 mm for 20 min as per BS Code
Begin next loading
When working load is reached hold the load for 24 hr and unload
Reload from working load to higher loads
Hold load constant till settlement is 0.1 mm for 5 min as per IS Code, 0.1 mm for
20 min as per BS Code
Repeat the process for subsequent load increments
Go either up to 5/2 times the working load for initial or routine test or to a
settlement equal to 10 % of pile diameter for straight piles and 7.5 % of base
diameter for belled pile
c. Load Measurement
The load is measured by any one of the following equipment
d. Settlement Measurement
The settlement is measured either by a dial gauge or by a leveling instrument.
e. Ultimate Load – The failure load is taken as either of the followings.
2/3rd of final load casing 12 mm settlement
½ load causing a total settlement of 10 % of pile diameter for straight piles or 7.5
% of base diameter for a belled pile.
- Constant Rate of Penetration Test – This test is most suitable for friction piles.
In this test, a well defined failure load is obtained and the method is very quick.
However, this method does not provide elastic settlement at working load.
Method – The pile is jacked continuously into soil at a constant rate till failure
takes place. The jacking rate in clay is 0.75 mm/min and a small movement is
required for failure. In sands, the jacking rate is 5 mm/min and a large movement
is required for failure.
Failure is defined as follows:
Load at which pile continues to move downwards without any further loading or
Load at which settlement is 10 % of pile diameter