Pile Dynamics Testing Pte Ltd

[Jenifer Griffard]

The analysis begins with the hammer ram falling and attaining an initial velocity at impact. This method is the best technique for predicting the relationship of pile capacity and blow counts (or set per blow), and the only method available to predict driving stresses. Download the freeware PDI-Wave to visualize wave propagation after ram impact, as well as resulting forces, velocities, stresses and displacements.

When a hammer or drop weight strikes the top of a foundation, a compressive stress wave travels down its shaft at a speed c, which is a function of the elastic modulus E and mass density. The impact induces a force F and a particle velocity v at the top of the foundation. The force is computed by multiplying the measured signals from a pair of strain transducers attached near the top of the pile by the pile area and modulus. The velocity measurement is obtained by integrating signals from a pair of accelerometers also attached near the top of the pile. Strain transducers and accelerometers transmit data to a high strain dynamic testing system such as the Pile Driving Analyzer (PDA), for signal processing and results.

Soil resistance forces along the shaft and at the toe cause wave reflections that travel and are felt at the top of the foundation. The times at which these reflections arrive at the pile top are related to their location along the shaft. The measured force and velocity near the pile top thus provide necessary and sufficient information to estimate soil resistance and its distribution.

The resulting estimated total soil resistance includes both static and viscous components. The static resistance is obtained by subtracting the dynamic component from the total soil resistance. The dynamic component is computed as the product of the pile velocity times a soil parameter called the Damping Factor. The damping factor is related to soil grain size.

High Strain Dynamic Testing encompasses Dynamic Pile Monitoring and Dynamic Load Testing. Both are covered by ASTM D4945. Pile Driving Monitoring consists of performing real-time evaluation of Case Method capacity, energy transfer, driving stresses and pile integrity for every blow. Dynamic Load Testing involves combining field measurements obtained with a high strain dynamic testing system such as the PDA with wave-equation based analytical procedures performed with a signal matching program such as CAPWAP. Dynamic Load Testing predicts soil behavior including static load capacity, soil resistance distribution, pile soil load transfer characteristics, soil damping and quake values, and pile load versus movement plots (e.g. a simulated static load test).

Wave propagation theory can also be applied to situations where a light impact is applied to a pile, resulting in a low strain. A compression wave will still travel down the pile when it is impacted by a small hand held hammer. Much like in High Strain Testing, this wave will travel at a constant speed c. Changes in pile impedance Z produce wave reflections.

The application of the wave equation theory to waves caused by small impacts is the basis for Low Strain Dynamic Integrity Testing. This procedure is performed with a Pile Integrity Tester (PIT), a hand-held hammer to generate an impact, and an accelerometer placed on top of the pile to be tested to measure the response to the hammer impact. Given a known stress wave speed, records of velocity (integrated from the accelerometer signals) at the pile head can be interpreted to reveal pile non-uniformities (changes in impedance). Interpretation is usually done in the time domain (Pulse echo, or Sonic echo) but data can also be evaluated by measuring the hammer force and analyzing in the frequency domain (Transient Dynamic Response). Pile length may also be evaluated. This non-destructive testing method is usually applied to concrete piles, concrete filled pipe piles, drilled shafts, auger cast-in-place (continuous flight auger) piles, and sometimes timber piles. Usually, the method is applied to piles not connected to a structure, but good results are often obtained for piles embedded in structures (such as cell-phone towers, transmission towers, and bridges). This method is covered under ASTM D5882.

Pile Driving Contractors Association (PDCA) in cooperation with Pile Dynamics, Inc. (PDI), has developed a "Dynamic Measurement and Analysis Proficiency Test" for engineers providing high strain dynamic foundation testing services. The test was designed to reflect their level of knowledge and ability, which is then indicated in a "Certificate of Proficiency". To assure a high standard of testing, many organizations or agencies seeking testing services now require a certificate demonstrating some specified level of ability in dynamic testing. PDA Proficiency Test is available in English, Spanish or Chinese. Click here to read about the Need for Quality Testing.

Click here to pre-register and make an online payment. The test fee is $250(USD) per person. Once payment is accepted, you will be entered in the Prometric online system and will receive a Candidate Admission letter with USER ID and PASSWORD to schedule your test time, date, and location/testing center.

Users of the Pile Driving Analyzer (PDA) system and CAPWAP software interested in obtaining a Certificate of Proficiency in Dynamic Foundation Testing, confirming their ability to their clients seeking services, or meeting qualification requirements from agencies or organizations.

Test Format: The test is a 60 question multiple-choice test, to be completed in 90 minutes or less, with only minimal calculations required (simple math by hand calculation). The test is CLOSED BOOK. Cell phones are strictly prohibited.Click here for sample questions.

The last 4 items mentioned above are supplied with PDA purchases. If you do not have access to the PDA manual and examples, or if you do not have the current version of the PDA manual, please contact softwa...@pile.com in advance of the test date.

Test fee: The fee to take the test and receive a Certificate of Proficiency is $250. Those who do not pass the test will receive full credit of test registration fee to be applied towards retaking the test at the next opportunity. An administrative fee of $50 is required to update any Institution information to a different Institution and/or to receive an updated Certificate of Proficiency.

Passing the test, particularly at higher levels, demonstrates good command of dynamic testing concepts. However, it is recommended that everyone attain a higher level rank through additional study and experience within the suggested time listed below from the date listed on their Certificate.

Agencies or organizations specifying a Certificate of Proficiency as a qualification for providers of foundation testing services should set their own requirements for minimum Rank and maximum period of Certificate validity for each level of proficiency. Test takers should be familiar with the requirements of the agencies or organizations that require PDA dynamic testing services in their territory. (Dark red font indicates the date of the Certificate exceeds the suggested validity period.)

The individual named on a Proficiency Certificate has demonstrated knowledge to the rank granted. However, the ability of this individual to apply appropriate knowledge and advice on a specific project is not implied or warranted by the Pile Driving Contractors Association or Pile Dynamics, Inc. The Pile Driving Contractors Association or Pile Dynamics, Inc. assumes no liability for foundation testing and analysis work performed by the bearer of this certificate.

The Pile Driving Analyzer (PDA) system is the most widely employed system for Dynamic Load Testing and Pile Driving Monitoring in the world. High Strain Dynamic Load Tests, also called PDA tests, assess the capacity of several piles in a single day. Pile Driving Analyzer systems also evaluate shaft integrity, driving stresses, and hammer energy when monitoring installation. If you plan to use your PDA to test non-driven piles make sure to read about that application as well.

PDA tests are performed during driving on pilot or production piles, taking advantage of the high strain impact provided by the driving hammer. Re-strike PDA tests are often recommended; if the driving hammer is no longer on location, a drop weight may be used to impact the pile.

The PDA-8G takes data obtained by accelerometers and strain transducers easily attached to the pile and calculates foundation capacity. In addition, it calculates multiple important quantities by the Case Method and iCAP. iCAP computes capacity in real time after every blow by signal matching (similar to CAPWAP). This calculation is often more accurate than Case Method capacity and better evaluates stresses in the pile.

With the PDA-8G, the engineer has the option of being in the field for the pile driving test or of using SiteLink Technology. SiteLink technology transmits PDA test data via Internet to an engineer located elsewhere who follows the test in real time. Test data displays and results are identical in both modes.

The PDA-8G is furnished with the PDA Software Suite, CAPWAP and GRLWEAP. CAPWAP analysis of PDA data is essential for a Dynamic Load Test. It provides the soil resistance distribution along the foundation and simulates a static load test. Extensive correlations between CAPWAP simulated and actual static load tests have proven the reliability of this method of determining pile capacity.

The PDA-8G conforms to ASTM D4945 and many other codes and specifications. The PDA Software Suite, consisting of PDA-S with iCAP, PDIPLOT2 and PDI-Curves, outputs reports that satisfy ASTM 4945 requirements. An SPT Software add-on to the PDA-S enables the PDA-8G to determine the energy transferred to SPT rods (read about this application).

Pile Dynamics recommends that all those who perform dynamic tests using the PDA take the Dynamic Measurement and Analysis Proficiency Test offered by PDI and PDCA. Read about the need for quality testing.

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