High Strain Dynamic Pile Testing (HSDPT)
Geo Dynamics for the first time in 1998 demonstrated the application of these tests (HSDPT) to the Indian deep foundation industry by conducting reliability studies on bored concrete piles for the “55 Flyovers Project” in Mumbai.
Today, Geo Dynamics is a market leader and pioneer in this testing and owns sets of Pile Driving Analyzers (PDA) for assessment of bored / driven concrete and steel piles. We have proven experience of more than two decades in almost all types of pile foundations listed below
- Cast-in-place bored piles for diameters from 275mm to 2000mm
- Monitoring of driven pre-cast / pre-stressed concrete piles
- Testing of Steel H-pile and close / open ended steel pipe piles
- Driven and Bored Micro Piles
- Offshore piles for jetties, ports, platforms
The method is widely accepted today for testing of bored piles in the country due to our efforts and because of an extensive database of reliability studies for more than 200 bored piles of various diameters in a variety of soil types all over India. Refer to the LIBRARY of technical papers.
Geo Dynamics now offers turnkey testing all over India including its own sets of guides and hammers for bored piles. Geo Dynamics is an accepted authority in India for these expertise based tests and has executed major projects in India for metro rail corporations at Delhi, Mumbai, Nagpur, Bangalore, Chennai, Ahmedabad, highway bridges, marine, power and real estate projects.
Geo Dynamics has executed projects internationally at Mauritius, Madagascar, Jordan, Saudi Arabia, Kuwait, Qatar, Bangladesh, Nigeria, Gabon, Burma, Vietnam, etc.
The method involves attaching a minimum of two pairs of strain transducers and accelerometers on diagonally opposite sides of the pile. These are fixed at a minimum distance of 1.5 times the pile diameters below pile top. The testing is conducted by impacting a hammer whose weight is typically 1% to 4% of static test load, so that a force which is normally more than the test load is generated and measured.
Strains induced under the impact of a heavy falling hammer from a pre-determined height are measured with the help of strain transducers attached to the pile, whereas accelerometers record the accelerations generated in the pile. The Pile Driving Analyzer then converts strain to force, and acceleration records are converted to velocities. The resistance developed by the pile is then a function of force and velocity and includes few assumed factors such as the quake and damping parameters as inputs based on the soil type. The maximum pile top compression is obtained by integrating the pile top velocity. The testing is continued by continuously increasing the drop height in stages until the test load is achieved or the pile shows a permanent set of atleast 4mm per blow for several blows.
On completion of field testing, a more accurate value of these parameters is then obtained from CAPWAP analysis conducted on field data.
Geo Dynamics inhouse setup arrangements ensure testing of more than one bored pile per day depending on pile location.
The test replaces static load testing for bored and driven piles and our expertise and database in these methods ensure that the results exceed static load testing requirements.
In case of problems for bored piles in several cases we are able to identify if problem is design or workmanship in case of failures. For driven piles, our expertise helps clients to drive piles successfully and helps identify potential problems of hammer, pile or soil.
The testing is conducted as per ASTM D4945 and IRC:78 generally. We also conform to all other international codes and specifications of European and other Asian countries. There is currently no BIS code for this form of testing although a sub-committee has already been formed.
Geo Dynamics conducts all testing as per ASTMD4945.2014 and IRC:78. We are also the committee to form the guidelines for these tests.
The method requires significant expertise and understanding of piling methods, equipments, installation procedures, soil behaviour and wave mechanics.
Merely having a PDA equipment will not make an expert and engaging untrained or not capable testing companies may lead to dangerous consequences for the project.
Thus proper care should be exercised while selecting a testing company including back ground checks, presentations, technical papers, and discussions before high strain dynamic testing is allowed at the project site.
Testing using Hiley formula as done by some companies does not qualify as dynamic testing as it does not conform to ASTM D4945 and neither to IS:2911 as claimed. The IS:2911 Part:3 mentions Hiley formula for capacity calculations for driven piles and not for testing. Results may vary by upto 200% if testing is done using Hiley formula.