FAQ

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1. What is High Strain Dynamic Pile Testing ?

High Strain Dynamic Pile Testing or PDA testing is a method to determine STATIC PILE CAPACITY using a dynamic impact. The method involves measurement of force and velocity response of the pile on field under the impact of a hammer of predetermined weight falling from a known height. The test is used in lieu of conventional static load testing. The test is conducted using Pile Driving Analyzer (PDA) and with its allied strain sensors and accelerometers. The entire equipment conforms to ASTM and other relevant standards worldwide. 

2. Is PDA testing based on any Empirical Formulae?

The method is based on the Smith algorithm developed in 1960. In 1964 research was initiated in Case Western Reserve University under funding from Federal Highway Administration. By 1974, Dr. Goble and his associates had successfully demonstrated the use of this method and today it is a standardized test tool used worldwide and a part of various code specifications of various European, Asian and Americas. 

The method is NOT Related with any of the empirical formulae viz. Hiley's Formulae, ENR, etc. It is based on the WAVE EQUATION approach studied by Smith in 1960. Today, such procedures based on Wave Propagation Theory are collectively called the Case Method and are conveniently applied in the field by dedicated electronic equipment called the Pile Driving Analyzer (PDA) system.

3. Can Empirical Formulae be used to determine pile capacity on field ?

Use of empirical formulae such as Hiley's or ENR or any modified formulae has been discarded worldwide due to various limitations and many assumptions involved. Such formulae were in use in 1950s before advent of computers and when not much information or Wave Equation type procedures were available. Using Hiley's or ENR formulae can lead to dangerous situations and should be strictly avoided. 

4. What is CAPWAP Analysis and its need ?

CAse Pile Wave Analysis Program is an analytical method that combines measured field data with pile wave equation type procedures, to predict the pile's static bearing capacity and soil resistance distribution. Measured force and velocity data is directly input from the PDA. Based on the measured velocity data, the program computes force required to induce the imposed velocity. Both measured and computed forces are plotted as a function of time and the iterative analysis is continued till there is good agreement between both the curves. If the agreement is not satisfactory, the soil resistances at the pile point and along the pile are adjusted until a good match is obtained. This gives better estimates of the actual static pile capacity measured during field-testing, and also the friction and end bearing components.

It is essential that CAPWAP be done on piles subjected to PDA test especially for bored piles subjected to Restrike. Some other methods like SIMBAT do not own CAPWAP and hence lack the ability to correctly predict pile capacity and other parameters.

5. Is High Strain Dynamic Pile Testing reliable and a standardized method?

As mentioned earlier, the method is used in more than 30 countries and is a part of code provisions of ASTM, AASHTO in USA, also part of U.K., German, Australian, Dutch, Canadian and also various Asian countries. In India, Geo Dynamics today is the sole agency and leaders in this field. We have conducted atleast 20 co-relation studies with good agreement between High Strain Dynamic Pile Test and Conventional Static Test at various projects all over India to ascertain its applicability in Indian conditions. 

6. What is the nature of data in case of High Strain Dynamic Pile Testing?

The output in case of PDA test is a measured force and velocity curve. A CW analysis that shows match between measured and computed force is also submitted as displayed below. A simulated static test curve and variation of skin friction numerically and graphically also forms part of the report. (not included here).
faq_graph1 

7. What is purpose of Low Strain Pile Integrity Testing ?

The purpose of Pile Integrity Testing is to evaluate potential defects in the pile shaft. Based on field information the type of defect can be identified. It is essential that the equipment used to conduct PIT conforms to ASTM D5882 and the test agency is trained to interpret the data. Geo Dynamics is fully equipped with the latest PIT equipment available worldwide from the Pile Dynamics, Inc., original developers of this technology worldwide. 

8. What is the nature of output from a Pile Integrity Test ?

A typical output from PIT is given below for easy reference.
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