TESTING OF PILESTESTING OF PILES

Chandrashekhar DamodareChandrashekhar DamodareSr.Engineer (Quality Control)Sr.Engineer (Quality Control)

INTRODUCTIONINTRODUCTION

Pile foundations are one of the types of deep Pile foundations are one of the types of deep foundations. They are used in case of foundations. They are used in case of soft/soft/siltysilty/clayey type of soils. As in such case of /clayey type of soils. As in such case of soils going for normal foundations may not be soils going for normal foundations may not be possible either from economical point of view or possible either from economical point of view or may not be possible at all in case you want to may not be possible at all in case you want to construct near seashore etc.construct near seashore etc.These are the foundations which transfer load to These are the foundations which transfer load to greater depths, where there is strong strata / greater depths, where there is strong strata / load reaching that point is minimal. load reaching that point is minimal.

NEED FOR PILE TESTINGNEED FOR PILE TESTING

Testing of the piles is very much vital as well as Testing of the piles is very much vital as well as important activity during pile foundation. The testing can important activity during pile foundation. The testing can give better insight of the characteristics of the casted give better insight of the characteristics of the casted piles .piles .The load transfer mechanism from a pile to the The load transfer mechanism from a pile to the surrounding ground is complicated and could not yet be surrounding ground is complicated and could not yet be fully ascertained, although application of pile foundations fully ascertained, although application of pile foundations is in practice over many decades. is in practice over many decades. Pile transfers axial loads either substantially by skin Pile transfers axial loads either substantially by skin friction along its shaft or substantially by the end friction along its shaft or substantially by the end bearing. bearing. Piles are used where either of the above load transfer Piles are used where either of the above load transfer mechanism is possible depending upon the subsoil mechanism is possible depending upon the subsoil stratification at the particular sitestratification at the particular site

TESTING OF PILESTESTING OF PILES

PILE TESTING

Pile Integrity Test Dynamic testing Pile load test

Vertical Load test(Compression) Pull out Test Lateral Load test

Maintained Load test

C.R.P.METHOD

Cyclic method

I.S.CODES FOR PILE TESTINGI.S.CODES FOR PILE TESTING

NDT testing WITH LOW STRAINI.S.14893-2001

Pile Integrity test3

Using Modified Hilley’s FormulaI.S.2911

Dynamic tests on pile2

IN-SITU-TESTI.S.2911(Part 4)Pile Load Test1

RemarkRelevant I.S.CodeMethod of the

testSr.no.

NECESSARY INFORMATION for NECESSARY INFORMATION for Testing of PILETesting of PILE

::

Pile type including material and Pile type including material and reinforcement details, group of piles, if any.reinforcement details, group of piles, if any.Method of driving with driving record or Method of driving with driving record or installation.installation.Pile depth(s) and details of crossPile depth(s) and details of cross--section(ssection(s).).Type of test desired.Type of test desired.Layout of the pile(s) Layout of the pile(s) —— space available space available

around and position in the group for single around and position in the group for single pile test.pile test.

ContinuedContinued………………………………

Safe load and ultimate load capacity, and Safe load and ultimate load capacity, and the the method(smethod(s) on which based.) on which based.Availability and provision of type of piles Availability and provision of type of piles or anchors or or anchors or kentledgekentledge for reactionfor reactionNature of loading/loading plan with a Nature of loading/loading plan with a particularly mention of pile(s) particularly mention of pile(s) whichmaywhichmaybe free standing when scour is expected; be free standing when scour is expected; Depth of water table and soil strata details Depth of water table and soil strata details with soil test resultswith soil test results

PILE LOAD TESTSPILE LOAD TESTS

Pile load testPile load test is the most direct method for determining is the most direct method for determining the safe loads on piles including its structural capacity the safe loads on piles including its structural capacity with respect to soil in which it is installed. It is with respect to soil in which it is installed. It is considered more reliable on account of its being considered more reliable on account of its being inin--situ situ test than the capacities computed by other methods, test than the capacities computed by other methods, such as such as static formula, dynamic formulae and static formula, dynamic formulae and penetration test datapenetration test data..

There are widely varying practices followed for load There are widely varying practices followed for load tests on piles. Particularly, the difficulties regarding the tests on piles. Particularly, the difficulties regarding the establishment of an acceptable criterion, for determining establishment of an acceptable criterion, for determining the ultimate and safe bearing capacity of piles, and the ultimate and safe bearing capacity of piles, and predicting the pile group behavior from the test data predicting the pile group behavior from the test data obtained from individual pile.obtained from individual pile.

TYPE OF LOADING CONDITIONS IN TYPE OF LOADING CONDITIONS IN PILE LOAD TESTPILE LOAD TEST

A) VERTICAL LOADING (COMPRESSION)A) VERTICAL LOADING (COMPRESSION)

B) LATERAL LOADINGB) LATERAL LOADING

C) PULL OUT TestC) PULL OUT Test

There are two types of tests for each There are two types of tests for each type of loading type of loading

Initial Load Test Initial Load Test ―― A test pile is tested A test pile is tested to determine the load carrying capacity of to determine the load carrying capacity of the pile by loading either to its ultimate the pile by loading either to its ultimate load or to twice the estimated safe load.load or to twice the estimated safe load.

Routine Test Routine Test —— It is carried out on a It is carried out on a working pile with a view to check whether working pile with a view to check whether pile is capable of taking the working load pile is capable of taking the working load assigned to itassigned to it

VERTICAL LOAD TESTVERTICAL LOAD TEST

In this type of test, compression load is In this type of test, compression load is applied to the pile top by means of a applied to the pile top by means of a hydraulic jack against rolled steel joist or hydraulic jack against rolled steel joist or suitable load frame capable of providing suitable load frame capable of providing reaction and the settlement is recorded by reaction and the settlement is recorded by suitably positioned dial gauges. suitably positioned dial gauges.

Vertical load method again divided in Vertical load method again divided in to three methods as following:to three methods as following:

A) Maintained load MethodA) Maintained load Method

B) Cyclic MethodB) Cyclic Method

C) CRP MethodC) CRP Method

TERMINOLOGY TERMINOLOGY

Kentledge - Dead-weight used for applying a test load on piles.

Test Pile - A pile which is meant for initial test.

Working Pile - A pile forming part of foundation of a structural system which may be used for routine load test.

Safe Load - It is a load on a pile derived by applying a factor of safety on ultimate load capacity of pile as determined by load test.

General requirements and General requirements and preparation required for Vertical Load preparation required for Vertical Load

methodsmethodsPreparation ofPreparation of PILE HEADPILE HEAD -- The pile head The pile head should be chipped off to natural horizontal plane should be chipped off to natural horizontal plane till sound concrete is met. till sound concrete is met. The projecting reinforcement should be cut off The projecting reinforcement should be cut off or bent suitably and the top finished smooth and or bent suitably and the top finished smooth and level with plaster of Paris or similar synthetic level with plaster of Paris or similar synthetic material where required.material where required.A bearing plate with a hole at the centre should A bearing plate with a hole at the centre should be placed on the head of the pile for the jacks to be placed on the head of the pile for the jacks to rest.rest.

Application of LoadApplication of Load( Not for CRP Method)( Not for CRP Method)

The test should be carried out by applying The test should be carried out by applying a series of vertical downward incremental a series of vertical downward incremental load, each increment being of about 20 load, each increment being of about 20 percent of safe load on the pile.percent of safe load on the pile.For testing of For testing of rakerraker piles, it is essential piles, it is essential

that loading is along the axis.that loading is along the axis.

The reaction may be obtained from the The reaction may be obtained from the followingfollowing

a) Kentledge placed on a platform supported clear of the test pia) Kentledge placed on a platform supported clear of the test pile. le. In case of load test below underIn case of load test below under--pinned structure, the existing pinned structure, the existing structure if having adequate weight and suitable construction mastructure if having adequate weight and suitable construction may y serve as serve as kentledgekentledge. The centre of gravity of the . The centre of gravity of the kentledgekentledge should should coincide with the axis of the pile and the load applied by the jcoincide with the axis of the pile and the load applied by the jack ack should also be coaxial with this pile.should also be coaxial with this pile.

b) Anchor piles with centreb) Anchor piles with centre--toto--centre distance from the test pile centre distance from the test pile not less than3 times the test pile shaft diameter subject to not less than3 times the test pile shaft diameter subject to minimum of 2 m. If the anchor piles are permanent working piles,minimum of 2 m. If the anchor piles are permanent working piles,it should be ensured that the residual uplift is within limits. it should be ensured that the residual uplift is within limits. Care Care should be exercised to ensure that the datum bar supports are noshould be exercised to ensure that the datum bar supports are not t affected by heaving up of the soil.affected by heaving up of the soil.

c) Rock anchors with distance from the nearest edge of the pilesc) Rock anchors with distance from the nearest edge of the piles at at rock level being 2 times the test pile shaft diameter or 1.5 m rock level being 2 times the test pile shaft diameter or 1.5 m whichever is greaterwhichever is greater

SETTLEMENTSETTLEMENT

Settlement shall be recorded with minimum 3 Settlement shall be recorded with minimum 3 dial gauges for single pile and 4 dial gauges of dial gauges for single pile and 4 dial gauges of 0.01 mm sensitivity for groups.0.01 mm sensitivity for groups.

The dial gauges shall be placed symmetrically The dial gauges shall be placed symmetrically and at equal distances from the pile(s) and and at equal distances from the pile(s) and normally held by datum bars resting on normally held by datum bars resting on immovable supports at a distance of 3 immovable supports at a distance of 3 D D (subject to minimum of 1.5 m) from the edge of (subject to minimum of 1.5 m) from the edge of the piles, where the piles, where D D is the pile stem diameter of is the pile stem diameter of circular piles or diameter of the circumscribing circular piles or diameter of the circumscribing circle in the case of square or noncircle in the case of square or non--circular PILEScircular PILES

The safe load on single pile for the initial test The safe load on single pile for the initial test should be least of theshould be least of the

following:following:

a) a) For piles up to and including 600 mm diameterFor piles up to and including 600 mm diameter

i) Twoi) Two--thirds of the final load at which the total thirds of the final load at which the total displacement attains a value of 12 mm unless otherwise displacement attains a value of 12 mm unless otherwise required in a given case on the basis of nature and type required in a given case on the basis of nature and type of structure in which case, the safe load should be of structure in which case, the safe load should be corresponding to the stated total displacement corresponding to the stated total displacement permissible.permissible.ii) 50 percent of the final load at which the total ii) 50 percent of the final load at which the total displacement equal to 10 percent of the pile diameter in displacement equal to 10 percent of the pile diameter in case of uniform case of uniform diameterpilesdiameterpiles and 7.5 percent of bulb and 7.5 percent of bulb diameter in case of underdiameter in case of under--reamed piles.reamed piles.

For piles more than 600 mm diameterFor piles more than 600 mm diameter

i) Twoi) Two--third of the final load at which the total third of the final load at which the total displacement attains a value of 2.5 percent of displacement attains a value of 2.5 percent of pile diameter .pile diameter .ii) Load corresponding to a total displacement of ii) Load corresponding to a total displacement of 1.5 percent of pile diameter. 1.5 percent of pile diameter. iii) 50 percent of the final load at which the total iii) 50 percent of the final load at which the total displacement equal to 10 percent of the pile displacement equal to 10 percent of the pile diameter in case of uniform diameterdiameter in case of uniform diameter

The safe load on groups of piles for The safe load on groups of piles for initial testinitial test

For piles up to and including 600 mm diameterFor piles up to and including 600 mm diameteri) Final load at which the total displacement i) Final load at which the total displacement attains a value of 25mm unless otherwise attains a value of 25mm unless otherwise required in a given case on the basis of nature required in a given case on the basis of nature and type of structure.and type of structure.ii) Twoii) Two--third of the final load at which the total third of the final load at which the total displacement attains a value of 40 mm.displacement attains a value of 40 mm.

ContinuedContinued…………..

For piles more than 600 mm diameterFor piles more than 600 mm diameteri) Final load at which the total i) Final load at which the total displacement attains a value of 3 percent displacement attains a value of 3 percent of pile diameter unless otherwise required of pile diameter unless otherwise required in a given case on the basis of nature and in a given case on the basis of nature and type of structure, andtype of structure, andii) Twoii) Two--third of the final load at which the third of the final load at which the total displacement total displacement attainsaattainsa value of 5 value of 5 percent of pile diameter.percent of pile diameter.

MAINTAINED LOAD METHODMAINTAINED LOAD METHODThis is applicable for both initial and routine This is applicable for both initial and routine test. In this method, each stage of loading shall test. In this method, each stage of loading shall be maintained till the rate of movement of the be maintained till the rate of movement of the pile top is not more than 0.2mm / hr or until pile top is not more than 0.2mm / hr or until two hours have elapsed, whichever is earlier. two hours have elapsed, whichever is earlier. If the limit of permissible displacement as given If the limit of permissible displacement as given in in RoutinRoutin and initial tests and initial tests are not exceeded, are not exceeded, testing of pile is not required to be continued testing of pile is not required to be continued further. The test load shall be maintained for24 further. The test load shall be maintained for24 hourshours

SetSet--up for Maintained Load Testup for Maintained Load Test

Maintained Load TestMaintained Load Test

CRP(Constant Rate of Penetration) CRP(Constant Rate of Penetration) TESTTEST

This method which is used for initial test is This method which is used for initial test is generally considered to be more suitable generally considered to be more suitable for determining ultimate load capacity for determining ultimate load capacity than the maintained load test but the than the maintained load test but the load/deflection characteristics are quite load/deflection characteristics are quite different from those of the maintained different from those of the maintained load test and cannot be used to predict load test and cannot be used to predict settlement of the pile under working load settlement of the pile under working load conditionsconditions

PROCEDURE OF THE TESTPROCEDURE OF THE TESTThe load shall be measured by means of pressure of 0.01 mm sensiThe load shall be measured by means of pressure of 0.01 mm sensitivity tivity load gauge. The penetration (deflection) should be measured by mload gauge. The penetration (deflection) should be measured by means of eans of dial gauges held by a datum bar resting on immovable supports adial gauges held by a datum bar resting on immovable supports at a t a distance of distance of atleastatleast 3 3 D D (subject to a minimum of 1.5 m) away from the test (subject to a minimum of 1.5 m) away from the test pile edge where pile edge where D D is defined in is defined in intialintial test. One of the dial gauges will be test. One of the dial gauges will be selected for conducting the test.selected for conducting the test.

With continuous application of pressure on the pile top by operaWith continuous application of pressure on the pile top by operating of the ting of the jack, a person watches the rate of settlement of the dial gauge jack, a person watches the rate of settlement of the dial gauge against a against a stop watch held in his hand and directs the pump operator to pumstop watch held in his hand and directs the pump operator to pump faster p faster or slower or at the same rate as needed to maintain the prescribor slower or at the same rate as needed to maintain the prescribed rate of ed rate of settlement say at every 0.25 mm settlement, he gives an indicatisettlement say at every 0.25 mm settlement, he gives an indication to take on to take readings. Immediately, other persons record the pressure gauge rreadings. Immediately, other persons record the pressure gauge readings eadings and other dial gauge readings. and other dial gauge readings.

The pump supplying the jack may be hand or mechanically operatedThe pump supplying the jack may be hand or mechanically operated. For . For force up to 200 force up to 200 tonnestonnes hand pumping is convenient. If a mechanical pump hand pumping is convenient. If a mechanical pump is used, it should, for preference, have an is used, it should, for preference, have an ‘‘infinite variableinfinite variable’’ delivery, delivery, controlled either by a bleed valve or a variable speed drive.controlled either by a bleed valve or a variable speed drive.

ContinuedContinued…………..

The jack should be operated to cause the pile to The jack should be operated to cause the pile to penetrate at uniform rate which may be controlled by penetrate at uniform rate which may be controlled by checking the time taken for small increments of checking the time taken for small increments of penetration and adjusting the pumping rate accordingly. penetration and adjusting the pumping rate accordingly. Readings of time, penetration and load should be taken Readings of time, penetration and load should be taken at sufficiently close intervals to give adequate control of at sufficiently close intervals to give adequate control of the rate of penetration. A rate of penetration of about the rate of penetration. A rate of penetration of about 0.75 mm per minute is suitable for predominantly friction 0.75 mm per minute is suitable for predominantly friction piles. For predominantly endpiles. For predominantly end--bearing piles in sand or bearing piles in sand or gravel, rate of penetration of 1.5 mm per minute may be gravel, rate of penetration of 1.5 mm per minute may be used. The rate of penetration, if steady, may be half or used. The rate of penetration, if steady, may be half or twice these values without significantly affecting the twice these values without significantly affecting the results. The test should be carried out for the results. The test should be carried out for the penetration more than 10 percent of the diameter of the penetration more than 10 percent of the diameter of the pile basepile base

ContinuedContinued…………..

As the test proceeds a curve between load As the test proceeds a curve between load and penetration should be drawn to and penetration should be drawn to determine when the ultimate load capacity determine when the ultimate load capacity has been reached.has been reached.

ContinuedContinued…………

The curve of load The curve of load versus versus penetration in penetration in the case of a predominantly friction pile the case of a predominantly friction pile will represent either a peak and the will represent either a peak and the subsequent downward trend, or a peak subsequent downward trend, or a peak and then almost a straight line and then almost a straight line

CYCLIC LOAD TEST METHODCYCLIC LOAD TEST METHOD

Alternate loading and unloading shall be Alternate loading and unloading shall be carried out at each stage as in carried out at each stage as in MMaintained load test aintained load test and and andand each each unloading stage shall be maintained for at unloading stage shall be maintained for at least 15 minutes and the subsequent least 15 minutes and the subsequent elastic rebound in the pile should be elastic rebound in the pile should be measured accurately by dial gauges.measured accurately by dial gauges.The test may be continued up to 50 The test may be continued up to 50 percent over the safe loadpercent over the safe load

Graphical AnalysisGraphical AnalysisAssuming that there is no compression in the pile, plot a graph Assuming that there is no compression in the pile, plot a graph relating total relating total elastic recovery and load at the pile top.elastic recovery and load at the pile top.Draw a straight line parallel to the straight portion of curve IDraw a straight line parallel to the straight portion of curve I to divide the to divide the load into two parts and thereby obtained approximate values of pload into two parts and thereby obtained approximate values of point oint resistance and skin friction.resistance and skin friction.From the approximate value of skin friction, and knowing the loaFrom the approximate value of skin friction, and knowing the loads on top ds on top of pile, compute the elastic compression of the pile correspondiof pile, compute the elastic compression of the pile corresponding to these ng to these loads,byloads,by the following formula:the following formula:∆∆ = (= (T T -- FF/2) /2) LLAEAEwherewhere∆∆ = elastic compression of pile, in cm;= elastic compression of pile, in cm;T T = load on pile top, in = load on pile top, in kgfkgf;;F F = frictional resistance, in = frictional resistance, in kgfkgf;;L L = length of the pile, in cm;= length of the pile, in cm;A A = cross= cross--sectional area of the pile, in cm2, andsectional area of the pile, in cm2, andE E = modulus of elasticity of the pile material, in kgf/cm2.= modulus of elasticity of the pile material, in kgf/cm2.

ContinuedContinued…………....

Skin Friction and Point ResistanceSkin Friction and Point Resistance(The value should normally be measured from (The value should normally be measured from an exposed portion of pile stem by means of an exposed portion of pile stem by means of compressometer during the load test itself.)compressometer during the load test itself.)Obtain values of the elastic compression of the Obtain values of the elastic compression of the subgradesubgrade by subtracting the elastic compression by subtracting the elastic compression of the pile from the total elastic recovery of pile, of the pile from the total elastic recovery of pile, and plot the graph relating these new values to and plot the graph relating these new values to the corresponding loads on pile top. the corresponding loads on pile top. When elastic compression of the When elastic compression of the subgradesubgrade works works out negative, the negative value shallout negative, the negative value shall be ignored until the value is positive.

LATERAL TESTLATERAL TEST

The test may be carried out by introducing a The test may be carried out by introducing a hydraulic jack with gauge between two piles or hydraulic jack with gauge between two piles or pile groups under test or the reaction may be pile groups under test or the reaction may be suitably obtained otherwise. suitably obtained otherwise. If it is conducted by jack located between two If it is conducted by jack located between two piles or groups, the full load imposed by the jack piles or groups, the full load imposed by the jack shall be taken as the lateral resistance of each shall be taken as the lateral resistance of each pile or group. The loading should be applied in pile or group. The loading should be applied in increments of about 20 percent of the estimated increments of about 20 percent of the estimated safe load.safe load.

ContinuedContinued…………The next increment should be applied after the rate of displacemThe next increment should be applied after the rate of displacement ent is nearer to 0.1 mm per 30 minutesis nearer to 0.1 mm per 30 minutes

Displacements shall be read by using at least two dial gauges ofDisplacements shall be read by using at least two dial gauges of0.01 mm sensitivity spaced at 30 cm and kept horizontally one 0.01 mm sensitivity spaced at 30 cm and kept horizontally one above the other on the test pile and the displacement interpolatabove the other on the test pile and the displacement interpolated ed at cutat cut--off level from similar triangles where cutoff level from similar triangles where cut--off level is off level is unapproachable and for approachable cutunapproachable and for approachable cut--off level, however, one off level, however, one dial gauge placed diametrically opposite to the jack shall direcdial gauge placed diametrically opposite to the jack shall directly tly measure the displacement. measure the displacement.

Where, it is not possible to locate one of the dial gauges in thWhere, it is not possible to locate one of the dial gauges in the line e line of the jack axes, then two dial gauges may be kept at a distanceof the jack axes, then two dial gauges may be kept at a distance of of 30 cm at a suitable height and the displacement interpolated at 30 cm at a suitable height and the displacement interpolated at load load point from similar triangles.point from similar triangles.

ContinuedContinued…………………………

The safe lateral load on the pile, for both free The safe lateral load on the pile, for both free head & fixed head shall be taken as the least of head & fixed head shall be taken as the least of the following:the following:a) Fifty percent of the final load at which the a) Fifty percent of the final load at which the total displacement increases to 12 mm;total displacement increases to 12 mm;b) Final load at which the total displacement b) Final load at which the total displacement corresponds to 5 mm; andcorresponds to 5 mm; andc) Load corresponding to any other specified c) Load corresponding to any other specified displacement as per performance requirements.displacement as per performance requirements.

SetSet--up for Lateral Testup for Lateral Test

PULLPULL--OUT TEST ON THE PILESOUT TEST ON THE PILESUplift force may preferably be applied by means of hydraulic Uplift force may preferably be applied by means of hydraulic jack(sjack(s) ) with gauge using a suitable pull out set up.with gauge using a suitable pull out set up.

The test pile shall have adequate steel to withstand pulling. The test pile shall have adequate steel to withstand pulling.

In some cases, in order to allow for neck tension in a pull out In some cases, in order to allow for neck tension in a pull out test, it test, it may be necessary to provide additional reinforcement in the pilemay be necessary to provide additional reinforcement in the piles to be s to be tested.tested.

The pull out load increments and consequent displacement readingThe pull out load increments and consequent displacement readings s shall be read as in the case of vertical load test.shall be read as in the case of vertical load test.

The safe load shall be taken as the least of the following:The safe load shall be taken as the least of the following:a) a) For piles up to and including 600 mm diameterFor piles up to and including 600 mm diameteri) Twoi) Two--thirds of the load at which the total displacement is 12 mm or thirds of the load at which the total displacement is 12 mm or the load corresponding to a specified permissible upliftthe load corresponding to a specified permissible upliftii) Half of the load at which the load displacement curve shows ii) Half of the load at which the load displacement curve shows a clear a clear break break

ContinuedContinued………………………………..b) b) For piles more than 600 mm diameterFor piles more than 600 mm diameter

i) Twoi) Two--thirds of the load at which the total displacement is 2.5 thirds of the load at which the total displacement is 2.5 percent of pile diameter or the load corresponding to a specifiepercent of pile diameter or the load corresponding to a specified d permissible upliftpermissible uplift

ii) Half of the load at which the load displacement curve shows ii) Half of the load at which the load displacement curve shows a a clear break (downward trend)clear break (downward trend)

The initial test shall be carried out up to twice the estimated The initial test shall be carried out up to twice the estimated safe safe load or until the load displacement curve shows a clear break load or until the load displacement curve shows a clear break (down(down--ward trend).ward trend).

Routine test shall be carried out to oneRoutine test shall be carried out to one--andand--aa--half times the half times the estimated safe load or 12 mm total displacement whichever is estimated safe load or 12 mm total displacement whichever is earlierearlier

RECORDING OF DATA AND RECORDING OF DATA AND PRESENTATIONPRESENTATION

The pile test data essentially concerns three variables, The pile test data essentially concerns three variables, namely, load, displacement and time.namely, load, displacement and time.

These are to be recorded sequentially for the tests under These are to be recorded sequentially for the tests under consideration and recorded in a suitable tabular form consideration and recorded in a suitable tabular form along with the information about the pile.along with the information about the pile.

The data may be suitably presented by curves drawn The data may be suitably presented by curves drawn between the variables and safe loads shown on the between the variables and safe loads shown on the graphs. Load displacement curve should be there.graphs. Load displacement curve should be there.

Pile Integrity Test

Pile integrity test is used to assess the Pile integrity test is used to assess the continuity of piles. With this test, necking continuity of piles. With this test, necking or bulging and uniformity of quality of or bulging and uniformity of quality of concrete is checked. Piles that are concrete is checked. Piles that are doubtful for integrity are taken up for doubtful for integrity are taken up for Dynamic load testing along with some Dynamic load testing along with some piles which are ok. Typical defects piles which are ok. Typical defects identified by this test are shown below identified by this test are shown below

DEFECTS IN PILESDEFECTS IN PILES

Procedure of the TestProcedure of the TestMethod of Testing : There are Indian Standards for the pile inteMethod of Testing : There are Indian Standards for the pile integrity grity test & the most commonly used worldwide is test & the most commonly used worldwide is Pile Integrity Test Pile Integrity Test as per ASTM as per ASTM –– D 5882 D 5882 –– 00, 00, ““Standard Test Method for Low Standard Test Method for Low Strain Integrity Testing of PilesStrain Integrity Testing of Piles””..Placement of TransducersPlacement of Transducers –– The motion sensor should be placed The motion sensor should be placed at or near the pile head using a suitable, or temporary, bondingat or near the pile head using a suitable, or temporary, bondingmaterial (that is wax, Vaseline etc.) so that it is assured thatmaterial (that is wax, Vaseline etc.) so that it is assured that it it correctly measures the axial pile motion. The motion sensor is correctly measures the axial pile motion. The motion sensor is placed generally near the center of pile. Additional locations splaced generally near the center of pile. Additional locations should hould be considered for piles with diameters greater than 500 mm. The be considered for piles with diameters greater than 500 mm. The low strain impact should be applied to the pile head within a low strain impact should be applied to the pile head within a distance of 300 mm from the motion sensor.distance of 300 mm from the motion sensor.

Objective: Objective: To check the pile for continuity of the shaft of the pile To check the pile for continuity of the shaft of the pile

ContinuedContinued…………..In the sonic test, the top of the pile is hit with a plastic hamIn the sonic test, the top of the pile is hit with a plastic hammer and mer and the reflected waves are recorded by a suitable computerized the reflected waves are recorded by a suitable computerized equipment. equipment. From the resulting signal, or reflectogram, one can determine boFrom the resulting signal, or reflectogram, one can determine both th length and continuity of the pile. Although a powerful tool, thelength and continuity of the pile. Although a powerful tool, the sonic sonic method also has limitations, such as: the test produces no method also has limitations, such as: the test produces no information regarding the pile capacity, and gives only limited information regarding the pile capacity, and gives only limited information about the concrete quality. The sonic system, can oninformation about the concrete quality. The sonic system, can only ly discover material impedance changes. It cannot tell anything discover material impedance changes. It cannot tell anything whether these impedance changes are due to poor concrete or due whether these impedance changes are due to poor concrete or due to reduced cross section. Even then this test is a fast & economto reduced cross section. Even then this test is a fast & economical ical tool for determining discontinuities in the pile shaft.tool for determining discontinuities in the pile shaft.If pile records are available, then the results can be fine tunIf pile records are available, then the results can be fine tuned for ed for greater & more reliable information.greater & more reliable information.

Limitations of the testLimitations of the test

The accuracy of the length determination The accuracy of the length determination depends on the assumed wave velocity. depends on the assumed wave velocity. This factor, which depends on the grade This factor, which depends on the grade and age of the concrete, varies from pile and age of the concrete, varies from pile to pile and may cause an error of the to pile and may cause an error of the order of 10 percent .order of 10 percent .

Graph of velocity signal Vs. Pile Graph of velocity signal Vs. Pile lengthlength

PILE DRIVING ANALYZER (PDA)PILE DRIVING ANALYZER (PDA)

Pile Dynamic TestPile Dynamic Test

Pile dynamic test is used to assess the load Pile dynamic test is used to assess the load bearing capacity of the pile. This test uses a bearing capacity of the pile. This test uses a hammer of a couple of tons to drop on the pile. hammer of a couple of tons to drop on the pile. Displacements are measured using a high tech Displacements are measured using a high tech instrument. instrument. This data is processed to arrive at the pile This data is processed to arrive at the pile dynamic load bearing capacity as per ISdynamic load bearing capacity as per IS--2911(part2911(part--1 section1 section--1). This test is easy to 1). This test is easy to conduct and requires very few site conduct and requires very few site arrangements. arrangements.

AdvantagesAdvantagesAs a supplement to or replacement As a supplement to or replacement for static tests, dynamic testing takes for static tests, dynamic testing takes far less time to perform and thus far less time to perform and thus reduces the costs.reduces the costs.

Can give better insight in terms of Can give better insight in terms of bearing capacity of pilebearing capacity of pile

MethodologyMethodology

The methodology of test is based on a large weight giving a The methodology of test is based on a large weight giving a dynamic impact to the elastic body. It equates the energy of dynamic impact to the elastic body. It equates the energy of hammer blow to work done in overcoming the resistance of hammer blow to work done in overcoming the resistance of the founding strata to the penetration of the ordinary castthe founding strata to the penetration of the ordinary cast--inin--situ piles as well as grouted micro piles. Allowance is situ piles as well as grouted micro piles. Allowance is made for losses of energy due to the elastic compression of made for losses of energy due to the elastic compression of the pile, subsoil as well as losses caused by the impact of the pile, subsoil as well as losses caused by the impact of the pile. the pile.

The The modified modified HileyHiley’’ss formulaformula given in the code I.S. given in the code I.S. 2911 part 1 2911 part 1 –– section 1 is used in estimating the ultimate section 1 is used in estimating the ultimate driving resistance in driving resistance in tonnestonnes. From that with a factor of . From that with a factor of safety as outlined in the code the safe load on pile can be safety as outlined in the code the safe load on pile can be worked out. worked out.

Dynamic Pile Test Methodology:Dynamic Pile Test Methodology:

ContinuedContinued……....

The instantaneous displacements including The instantaneous displacements including rebounds of the pile are precisely recorded in an rebounds of the pile are precisely recorded in an automatic data acquisition system. This is done automatic data acquisition system. This is done for several cycles & then using formulae as in I.S. for several cycles & then using formulae as in I.S. 2911, the safe load capacity of the pile is 2911, the safe load capacity of the pile is calculated.calculated.

An optical instrument is used for position An optical instrument is used for position sensitive measurement by nonsensitive measurement by non--contact contact continuous measurement with the instrument continuous measurement with the instrument placed away from the vibrations due to impact placed away from the vibrations due to impact load. The system is based on combined light load. The system is based on combined light emitting diode transmitters & a position sensitive emitting diode transmitters & a position sensitive detector. The transmitter & receiver are installed detector. The transmitter & receiver are installed so that the light beam forms a reference line from so that the light beam forms a reference line from the transmitter, receiver to the prism group the transmitter, receiver to the prism group reflector. reflector.

ContiConti…………....

The reflected light can be The reflected light can be received & recorded 100 times received & recorded 100 times per second. Using the energy per second. Using the energy transmitted to the pile & transmitted to the pile & accounting for temporary accounting for temporary compression of the pile, ground compression of the pile, ground & dolly occurring during the & dolly occurring during the impact loading the ultimate impact loading the ultimate driving resistance is calculated.driving resistance is calculated.

MODIFIED HILLEYMODIFIED HILLEY’’S FORMULAS FORMULA

R = Whn / (s + c / 2)R = Whn / (s + c / 2)

(As per I.S.2911)(As per I.S.2911)

WhereWhereR = Ultimate driving resistance in R = Ultimate driving resistance in tonnestonnesW = Mass of Ram in W = Mass of Ram in tonnestonnesh = Height of free fall in cm considered at 80% for winch operath = Height of free fall in cm considered at 80% for winch operated ed dropdropn = Efficiency of the blow representing ratio of energy after n = Efficiency of the blow representing ratio of energy after impact to striking energy of ram impact to striking energy of ram

s = Average final set per blow in cms = Average final set per blow in cmc = Average sum of temporary elastic compressionc = Average sum of temporary elastic compression

Applying the factor of safety, the safe load for the pile is theApplying the factor of safety, the safe load for the pile is then n calculated calculated

Arrangements for pile dynamic testArrangements for pile dynamic test

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