DYNAMIC LOAD TEST ON DRIVEN PILE (PDA TEST)

This method statement describes the typical dynamic load test on driven pile (PDA Test) procedure. Dynamic pile testing is performed by well-trained and experienced engineers using a Pile Driving Analyzer (PDA) at site and pile wave analysis will be carried out on the signal acquired by using Case Pile Wave Analysis Program (CAPWAP).  

               Plant and Equipment

The plant / equipment to be used for the works shall comprise of the following:

§  PDI series pile driving analyzer and CAPWAP analysis program to determine the mobilized capacity of a test pile.  Pile Driving Analyzer shall comprise;

·         Pile Driving Analyzer

·         2 Strain Transducers

·         2 Accelerometers

·         1-4 Cable

·         30m Extension Cable

The combination of the calibrated sensors and the latest analysis program provides a high accuracy and reliable test results. 

   Dynamic Load Test Preparation

·            Prior to lifting the pile to be dynamically tested, the Contractor shall provide a minimum of 3 ft (1 m) clear access to 180 degree opposite faces of the pile for pile preparation.

·            The test pile must be exposed at least 1 meter above the existing ground level to avoid any obstruction endangering the sensors or cable during testing.

·            All pre-cast concrete pile must remain uncut for restrike purpose and an appropriate piling hammer is required for testing purpose until the final result is obtained.

·            Most of all, the safety of the test personal shall be ensured.

                  Testing Procedures

•         Drilling 3 appropriate sizes of holes on both side of a test pile (figure 1).  The purpose is to obtain the eccentricity in order to eliminate hammer alignment effect.
•          Two strain transducers and two accelerometers will then attach to the pile at least at a distance of 2 times diameter of the pile or 1.0m from the pile head (whichever comes first) during initial driving or restrike testing (Figure 2). Stress wave generated by hammer impact on pile top will be recorded in terms of force and acceleration.
•       The signal captured will be presented in a graph as force curve and velocity curve and is stored in the pile driving analyzer for later analysis purpose

Result Interpretation and Analysis

·         By computation from the pile driving analyzer on force and velocity curve recorded, a lot of useful information can be provided on site as preliminary results. These results include:

o   Pile capacity at the time of testing by CASE method. (RMX)

§  Capacity predicted by assuming appropriate soil damping factor (Jc), young modulus (Em) and wave speed (Ws).

o   Pile top compression stress during pile driving.

§  In order to limit the possibility of pile top damage at the time of testing, pile top stress must be kept within certain bounds. It can be derived by taking maximum force applied to the pile top (FMX) divided by cross sectional area of the pile. 

§  A representative blow will be selected for further analysis seeking for:

·         Mobilized capacity using CAPWAP signal matching program.

·         Load vs. settlement graph similar to static load test.

·         Portion by portion skin friction distributed at pile shaft.

·         End bearing at the pile toe.

·         Hammer efficiency.

·         Integrity at the pile.