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Pile Dynamic Test
Pile dynamic test is used to assess the load bearing capacity of the pile. This test uses a hammer of a couple of tons to drop on the pile. Displacements are measured using a high tech instrument. This data is processed to arrive at the pile dynamic load bearing capacity as per IS-2911(part-1 section-1). This test is easy to conduct and requires very few site arrangements.
Code: Background:
Modified Hiley’s formula is given in IS – 2911, part 1, section 1.

To obtain a reliable capacity prediction from dynamic pile testing, some very basic guidelines must be followed.
Advantages:
As a supplement to or replacement for static tests, dynamic testing takes far less time to perform and thus reduces the costs.
Methodology
The methodology of test is based on a large weight giving a dynamic impact to the elastic body. It equates the energy of hammer blow to work done in overcoming the resistance of the founding strata to the penetration of the ordinary cast-in-situ piles as well as grouted micro piles. Allowance is 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. The modified Hiley’s formula given in the code I.S. 2911 part 1 – section 1 is used in estimating the ultimate driving resistance in tonnes. From that with a factor of safety as outlined in the code the safe load on pile can be worked out. The instantaneous displacements including rebounds of the pile are precisely recorded in an automatic data acquisition system. This is done for several cycles & then using formulae as in I.S. 2911, the safe load capacity of the pile is calculated.

An optical instrument is used for position sensitive measurement by non-contact continuous measurement with the instrument placed away from the vibrations due to impact load. The system is based on combined light emitting diode transmitters & a position sensitive detector. The transmitter & receiver are installed so that the light beam forms a reference line from the transmitter, receiver to the prism group reflector. The reflected light can be received & recorded 100 times per second. Using the energy transmitted to the pile & accounting for temporary compression of the pile, ground & dolly occurring during the impact loading the ultimate driving resistance is calculated.

Modified Hiley’s Formula

R = Whn / (s + c / 2)

Where

R = Ultimate driving resistance in tonnes
W = Mass of Ram in tonnes
h = Height of free fall in cm considered at 80% for winch operated drop
n = Efficiency of the blow representing ratio of energy after impact to striking energy of ram

s = Average final set per blow in cm
c = Average sum of temporary elastic compression


Applying the factor of safety, the safe load for the pile is then calculated.
Some of the significant advantages of this method are:
1. Non-contact
2. Transparent
3. Accurate
4. Easy to Understand
5. Logical
6. Quick
7. No need to cut projecting reinforcement from pile head
8. No need to cast concrete on pile head
9. Greater capacity utilization in design
Standard Setup Diagram
1.Non-contact
2. Transparent
3. Accurate
4. Easy to Understand
5. Logical
6. Quick
7. No need to cut projecting reinforcement from pile head
8. No need to cast concrete on pile head
9. Greater capacity utilization in design
Dynamic Testing Procedure Notes:
1.To the cured pile, to avoid splitting of head due to impact, a steel cap with timber cushioning between steel & pile head is provided.

2. The instrument and laptop computers is set up at a distance away from the vibrations due to impact.

3. The test considers average/best of 4 blows. It is a known fact that during the first blow, the settlement is larger. The results are co-related with other parameters before arriving at a final conclusion.
Dynamic Pile Test Methodology:
Information required before testing from the customer site:
1.Pile records (total length, socketing length etc.), soil profile in the area, pile drawings, plans etc.

2.Mix design (if used) details of grade of concrete.
Facilities required at the client site to conduct the test:
1.Clear approachable test locations with unobstructed view of one meter length of cleaned pile top.

2.Steel Plate & Wooden Cushion.

3.Loading facilities like piling winch along with chisel of known weight with operators installed at the location.
Sample Dynamic testing Report:

Brief Condition Survey NDT and Condition Survey Structural Drawings Structural Design Preliminary Estimation Structural Redesign Detailed BOQ QA and Project Management Structural Re testing post repairs Stability Certificate
UPV Test Rebound Hammer Half cell and Carbonation Reinforcement Mapping Core Testing Pile Integrity Test Pile Dynamic Test
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