METHODOLOGY FOR HIGH STRAIN DYNAMIC LOAD TEST ON PILES

 

 HIGH STRAIN DYNAMIC
LOAD TEST ON PILES

1. Scope:

 The work shall consist of Preparation of pile head and Conduct the High strain Dynamic load test on working pile.

2. References:

MoRT & H specifications clause no 1113, IS: 2911( part IV) and ASTM D 4945-96

3. Equipments:

 A tripod, Lifting Mechanism to lift 4.0 MT weight to 3.5 mt height, 7.5 KV DG set with single phase power supply,

4. Tools:

 Measuring steel tape, line rope, sensors.

5. Responsibility:

 Responsibility of Implementation of this procedure lies with Site engineer and in charge of structures

6. Materials

 MT weight hammer, Steel helmet of 40mmthick plate, 40mm plywood cushion,

7. Procedure:

PILE HEAD AND TEST PREPARATION :

The pile top shall be re~built for a length equal to 1.8~2.0 times the pile diameter with an at least 4mm thick steel casing to provide smooth finish. Alternatively shuttering / formwork can be used (to achieve smooth surface). Two openings / windows (300mm x 300mm) diametrically opposite to each other shall be made if casing is used. This is for fixing gages to pile. The opening shall be located about 1.5 times the pile diameter below the pile top.

   Dowel bars shall be kept intact and shall be spliced with additional reinforcement provided in the built~up portion. Minimum cover of 75mm shall be provided even in the built~up portion of the pile.

·       The strength of concrete in the built~up portion shall be equal to or one grade higher than the pile concrete in order to withstand the impact of the falling ram.

·       40 mm plywood cushion with diameter equal to pile diameter shall be placed over pile at the time of testing.

·       Steel helmet of 40mm thick shall be kept ready at the time of testing. Helmet should not be welded to the pile casing.

·       A suitable guide shall be provided to ensure a concentric fall.

·       A 4.0 MT (1-2 % 0f test load) hammer with diameter not more than pile diameter shall be used for testing the pile of capacity approximately 400 MT. The hammer should have 8mm thick liner/casing with 40mm thick base plate. Also steel cage should be welded to liner.

·       Central hook shall be provided for lifting the hammer without ant tilt to avoid eccentric blows.

·       Start the fall of hammer at a height of 1.0 mt and increase to interval of 0.5 mt till test load is achieved. The fall off height is expected to vary from 1.0 mt to 3.5 mt.

·       For each hammer blow, the strain transducers measure strains whereas accelerations are measured by accelerometers connected on either sides of the pile. These signals are then converted to digital form by the equipment and then converted to force and velocity respectively by integration.

~ The force and velocity curve shall be generally as defined in ASTM D4945.

~ A suitable power source supply shall be provided for fixing sensors and for the test equipment.

8. Reports:

The final report shall consists of the following

·       Introduction

·       Over view

·       Equipment Details

·       Methodology

·       CAPWAP analysis

·       Discussion of results

·       Conclusions

The complete CAPWAP analysis report shall be submitted with the final report and shall include the following in addition to above.

·       Total pile capacity in friction and end bearing.

·       Frictional distribution along the sides of the pile.

·       Changes in pile cross section if any.

·       Simulated static test curve.

·       Force and velocity curve obtained on field.

9. Safety Requirements:

~ The work area shall be properly barricaded. Care shall be taken during testing; the sensors shall not be disturbed.

·       Any labour, if being used in the job for surveying shall be screened and trained.

·       All workmen at work area shall wear PPE^·s and reflective jackets, safety belts.

·       During night work sufficient lighting shall be provided.

·       Leveling staff shall be wooden or fiber.