Pile integrity test


Staff member

2.1 Sonic echo testing has been used successfully for quite sometime now for
checking the integrity of piles after installation.

2.2 It has been established that cast in situ piles in majority of the cases fail
because of defective pile shaft necking, discontinuity of concrete, intrusion
of foreign matter and improper toe formation due to contamination of
concrete at base with soil particles, washing of concrete due to high water
current, adoption of improper construction method, poor quality control on
concreting etc.. Cracks developed while handling of precast piles can also
be a cause of failure. If pile integrity can be assessed before completion
of pile caps, then this will go a long way towards certification of pile

2.3 Integrity testing is relatively quick and simple and enables number of piles
to be examined in a single working day. The method does not identify all
imperfections in a pile, but provides information about continuity, defects
such as cracks, necking, soil incursions, changes in cross section and
approximate pile lengths ( unless the pile is very long or the skin friction is
too high ).

2.4 Integrity testing result for a particular area may not be necessarily valid for
another area. Detailed results in a particular area for a number of sites
have to be collected and evaluated before interpretation of tests result of a
new site in that area. Integrity tests provide an indication of soundness of
concrete but they should be undertaken by persons experienced in the
method and capable of interpreting the results with specific regard to

2.5 In this test, a small metal / hard rubber hammer is used to produce a light
tap on the top of the pile. The shock traveling down the length of the pile is
reflected back from the toe of the pile and recorded through a suitable
transducer / accelerometer ( also held on the top of the pile close to the
point of impact) in a computer disk for subsequent analysis.

2.6 The primary shock wave which travels down the length of the shaft is
reflected from the toe by change in density between the concrete and the
sub strata. However, if the pile has any imperfections or discontinuities
within its length these will set up secondary reflections which will be added
to the return signal.

2.7 By a careful analysis of the captured signal and a knowledge of the
conditions of the ground, age of the concrete etc. a picture of the location
of such problems can be built up.

2.8 Normally more than one recording of signals is done until repeatability of
signals is achieved.

2.9 In case of large diameter piles, the tests are conducted at 5-6 places to
cover the entire section of the pile.

2.10 General Requirements of the tests -
i) Pile shall be trimmed to cut off level or sound concrete level before
the test with all laitance removed.
ii) The area surrounding the pile should be free from standing water
and should be kept dewatered during the tests.
iii) The cast in situ piles should not normally be tested before 14 days
of casting.
iv) The test piles, if available at site can be used for determination of
pulse velocity and characteristic or reference signal generated. This
can also be done from those piles whose depth is accurately

2.11 The following are the complimentary tests to the low strain integrity test
method. These can be used to check the soundness of concrete at test
level and to assess the stress wave velocity of pile concrete depending on
concrete density and its in situ condition.
a) Ultrasonic Pulse Velocity Test – This test is carried out at the head
of the pile in order to arrive at the speed of sound propagation through the
cast concrete of the pipe.
b) Penetration Test – The test is used to assess the strength of the
concrete at the pile head to ensure that the pile is sufficiently cured
and ready for NDT.
c) Density Testing Of Cast Cubes – In order to determine the density
of concrete used each cube should be measured for density by
weighing in air and water.

2.12 Limitations
i) The present experience of NDT of piles is upto diameter of 1500
ii) This is applicable to cast in situ concrete bored and driven piles.
The test cannot be conducted after provision / casting of pile cap.
iii) This method is not suitable for piles surrounded by water as it may
not give correct results.
iv) It does not provide information regarding verticality or displacement
(in position) of the piles.
v) Local loss of cover, small intrusions or type of conditions at the
base of piles are undetectable.
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