The Pile Driving Analyzer (PDA) is the most widely employed system for dynamic load testing and pile driving monitoring in the world. It assesses the capacity of several piles in a single day. The PDA also evaluates shaft integrity and investigates driving stresses and hammer energy during pile installation. The driving hammer itself is used to perform PDA tests, or high strain dynamic tests, on pilot or production piles. If necessary, it is possible to perform re-strike PDA tests even after the driving hammer is no longer on location, by using a drop weight to impact the foundation. The PDA software calculates results from velocity and force signals obtained by accelerometers and strain transducers attached to the pile. Sensors may be smart (transmit data using wireless transmitters) or traditional (transmit data via cable).
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 pile driving analyzer conforms to ASTM D4945 and many other codes and specification.
Pile Driving Monitoring Services
Pile Driving Monitoring, also called Dynamic Pile Monitoring, helps achieve a safe and economical driven pile installation. During pre-construction test programs, Pile Driving Monitoring helps formulate driving criteria. During the installation of production piles, it helps check that driving happens in accordance with the established criterion and gives information on soil resistance at the time of monitoring and on driving system performance. Dynamic Monitoring with a Pile Driving Analyzer® (PDA) dynamic testing system also calculates driving stresses, helping reduce the risk of pile damage. If stresses indicate a high potential for pile damage, driving can be stopped and alternative installation procedures evaluated. Pile Monitoring happens during driving in real time, without major delays to construction.
Tethys can perform Pile Driving Monitoring with an engineer on the job site or from their office, using SiteLink®. When the pile driving hammer impacts the pile top, accelerometers and strain transducers attached to it obtain data that is converted to velocity and force readings. Tethys analyzes the measurements with a PDA. Data obtained during Pile Driving Monitoring may be used to estimate bearing capacity during driving with Case Method or iCAP®, or after data collection with CAPWAP®. Tethys Engineers have been trained and certified based on PDCA/PDI Dynamic Measurement and Analysis Proficiency Test. Dynamic Pile Monitoring is based on the Case Method of pile testing and is standardized by ASTM D4945 Standard Test Method for High-Strain Dynamic Testing of Piles.
Dynamic Load Testing
Dynamic Load Testing is a fast, reliable and cost effective method of evaluating foundation bearing capacity. Tethys can perform Dynamic Load Testing on driven piles, drilled shafts, auger-cast piles, micropiles, helical piles, and other cast in place foundations. It is often possible to conduct several dynamic load tests in a single day. In addition to bearing capacity, Dynamic Load Testing provides information on resistance distribution (shaft resistance and end bearing) and evaluates the shape and integrity of the foundation element. The Dynamic Load Test involves a substantial ram mass that impacts the top of the foundation and causes it to experience a small permanent set. Prior to the test.
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 modules. 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. As long as the wave travels in one direction, force and velocity are proportional:F = Zv, where:
- Z = EA/c is the pile impedance
- E is the pile material modulus of elasticity
- A is the cross-sectional area of the pile
- C is the material wave speed at which the wave front travels
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. The energy delivered to the pile is directly computed as the work done on the pile from the integral of force times incremental displacement ( ∫Fdu ) which is easily evaluated as force times velocity integrated over time ( ∫Fvdt ). Maximum compression stresses at the pile top come directly from the measurements. The measurements also allow direct computation of the compression stress at the pile toe and the tension stresses along the shaft. Pile integrity can be evaluated by inspecting the measurements for early tension returns (caused by pile damage) prior to the reflection from the pile toe; lack of such reflections indicates a pile with no defects.
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). Tethys analyzes data in real time with the Pile Driving Analyzer® (PDA) dynamic testing system. Data is further analyzed with the CAPWAP® software. Tethys engineers furnish a detailed report for each Dynamic Load Testing project that includes a simulated static load test in the form of a calculated load-set curve.
Dynamic Load Tests are standardized by ASTM D4945 Standard Test Method for High-Strain Dynamic Testing of Piles. The test may also be configured to meet the requirements of the Rapid Load Test standard ASTM D7383 provided an adequate ram is available.