LOW STRAIN IMPACT INTEGRITY TESTING OF DEEP FOUNDATIONS (ASTM D 5882-07)

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WHAT IS INTEGRITY TEST

The sonic integrity test is a nondestructive type of testing in order tocheck the integrity of the pile shaft.

The technique can be used both oncast-in-situ place piles andprefabricated piles

Integrity testing is relatively simpleand quick and enables number of pilesto be examined in a single workingday.

NEED FOR INTEGRITY TEST

For a successful pile foundation it is

imperative that the piles constructed are

of sound quality and of design shape and

dimensions that is structural integrity

The routine vertical load tests carried outon working piles do not provide directinformation on structural integrity of piles.Also, in view of the very limited number oftests ( 0.5 to 2 percent ) carried out at aparticular project site, it is not possible toreliably testify structural quality of piles

However, it is also true that all the pilescannot be tested in this way because ofboth economic and time constraints

NEED FOR INTEGRITY TEST

GOOD SOUNDING PILES GOOD PILES

Qsafe= 100 Ton Qsafe= 100 Ton

S1= 10 mmEx. S1 = 4.0 mm

Improper Toe formation

Bulging effects

Necking effects

1.Choose the rig machine 2.Bentonite 3.Experience

NEED FOR INTEGRITY TEST

POSSIBLE PILE DEFFECT

Discontinuity of Concrete :

The Toe reflection is observed at 2.40mbelow the testing level due to discontinuity

of the pile

POSSIBLE PILE DEFFECT

The sonic integrity test is a non destructivetype of testing in order to check the integrityof the pile shaft. The technique can be usedboth on cast-in-situ place piles andprefabricated piles

It is a firm belief that cast-in-situ piles inmajority of cases fail because of defective like:

Pile shaft necking, Discontinuity of concrete, Intrusion of foreign matter, Improper toe formation due to

contamination of concrete at base with soilparticles,

Washing of concrete due to high watercurrent, adoption of improper constructionmethod,

Poor quality control on concreting or anyother reason,

PREPARATION OF

THE PILE

Preparing the pile for testing is fairlystraightforward. For acquiring good qualitysignals, prepare the pile as described below.

Pile heads must be clean and free fromdebris (e.g. from cracked or looseconcrete, dirt, grit or embedded foreignmaterials),

Free from standing water, accessible,though not necessarily flat and smooth.

Remove soft concrete from the pile headof cast-in-situ piles.

The concrete of cast-in-situ piles shouldpreferably be cured to at least 80% of itsultimate strength.

In general this stage is reached 7 daysafter installation of the pile.

All piles should be on Cut off level.

FINDING PILE DEFFECT

USING PIT

The method does not identify all imperfectionsin a pile, but provides information aboutcontinuity and defects is described below.

Cracks,

Necking,

Bulging,

Soil incursions,

Changes in cross section

Approximate pile lengths (unless the pile isvery long or skin friction is too high).

Improper toe formation due tocontamination of concrete at base with soilparticles.

LIMITATIONS

A Pile Integrity Test cant provide the loadcarrying capacity of the pile.

Minor deficiencies like local loss of cover,small intrusions or type of conditions ofmaterials at the base of piles areundetectable.

Waves cant usually cross gaps. Henceportion beyond mechanical joints or fullsection cracks cant be tested.

Limitations relating to the depths up towhich the integrity tests can be carried onpiles depend on the surrounding strata,change in pile shape and damping withinthe concrete.

Highly non uniform piles producecomplex records which are difficult toanalyse.

RELATION BETWEEN WAVE

VELOCITY AND PILE LENGTH

Based on the time interval on and the wave velocity through concrete c, simplemathematics will reveal the length:

Prior to taking measurements, the usershould specify the approximate pile lengthand the estimated propagation velocity. Thepropagation velocity is directly dependent ofthe concrete quality.

Analysing formula [2] with which thepropagation speed can be calculated, showsthis

After hitting the pile head with a hammer, ashock wave will propagate through theconcrete pile with a propagation speed ofapproximately 4000 m/s.

At the toe of the pile, the shock wave willreflect (partially) and will propagate back tothe pile head at which it is detected by thesensor. The detection of this reflectedhammer blow is called the toe-reflex.

WAVE SPEED CALCULATION

Examples of relation Pile Length, Propagation Speed and Concrete Quality

DIFFERENT BETWEEN SPEED

AND VELOCITY

DIFFERENT BETWEEN SPEED

AND VELOCITY

DIFFERENT BETWEEN SPEED

AND VELOCITY

The reflected stress wave can bemonitored using either processingtechnique, the observed signals areamplified and converted into digitaldisplay as velocity versus length orfrequency versus mobility records,providing information on structuralintegrity of pile.

The stress wave velocity andapproximate pile lengths areprovided as input for the integritytesting.

The stress wave velocity is dependenton the Youngs modulus and massdensity of pile concrete.

FUNCTION OF VELOCITY AND

LENGTH

Expected Length and Velocity of the pile :

Executed Length and Velocity in Field :

HOW TO OBTAIN INFORMATION

ABOUT THE SOIL INFLUENCE

To obtain a good understanding of the influence of soil changes, one can

compare the measurement signals of piles with the same dimension on the same

site (characteristic signal/ Group Pile Average). In general, SIT measurement

signals "respond" to soil changes, according to the following guidelines.

The cross section appears to decrease, if the soil changes from stiff to soft(a decrease in shaft friction).

The cross section appears to increase, if the soil changes from soft to stiff(an increase in shaft friction).

Some cast-in-place piles tend to show a slow increase in diameter withdepth, particularly in soft upper ground.

When the soil changes from soft to stiff, a sudden change from "invertedtaper" to a cylindrical shape of nominal diameter often occurs and is usuallyseen as a relatively large reflection similar to that obtained from a decreasein cross section. Soil stiffness can also influence the shape of cast-in-placepiles.

HOW TO OBTAIN INFORMATION

ABOUT THE SOIL INFLUENCE

The cross section appears to decrease, ifthe soil changes from stiff to soft.

The cross section appears to increase, if thesoil changes from soft to stiff.

HOW TO OBTAIN INFORMATION

ABOUT THE SOIL INFLUENCE

The cross section appears to decrease, ifthe soil changes from stiff to soft.

The cross section appears to increase, if thesoil changes from soft to stiff.

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PILE DEFECTS

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