High strain dynamic testing is a method of testing deep foundations to obtain information about their capacity and integrity, and in some cases, to monitor their installation. It is codified by ASTM D4945-12 - Standard Test Method for High-Strain Dynamic Testing of Piles. High strain dynamic testing is called dynamic pile monitoring when it is applied during pile

driving Driving is the controlled operation and movement of a vehicle, including cars, motorcycles, trucks, buses, and bicycles. Permission to drive on public highways is granted based on a set of conditions being met and drivers are required to fol ...

and

dynamic load testing Dynamic load testing (or dynamic loading) is a method to assess a pile's bearing capacity by applying a dynamic load to the pile head (a falling mass) while recording acceleration and strain on the pile head. Dynamic load testing is a '' high str ...

when it is applied following pile installation, regardless of the installation method. The origins of these testing methods date to research conducted in the 1960s and 1970s at what is now known as

Case Western Reserve University Case Western Reserve University (CWRU) is a private research university in Cleveland, Ohio. Case Western Reserve was established in 1967, when Western Reserve University, founded in 1826 and named for its location in the Connecticut Western Reser ...

, with funding of the

Ohio Department of Transportation The Ohio Department of Transportation (ODOT; ) is the administrative department of the Ohio state government responsible for developing and maintaining all state and U.S. roadways outside of municipalities and all Interstates except the Ohio T ...

. The 1972 paper {{url, https://ascelibrary.org/doi/10.1061/JSFEAQ.0001781, ''Soil Resistance Predictions from Pile Dynamics'', by Rausche, F., Moses, F., Goble, G. G., published by the Journal of the Soil Mechanics and Foundations Division,

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transformed the academic research into a process embraced by the engineering community. High strain dynamic testing consists of estimating soil resistance and its distribution from force and velocity measurements obtained near the top of a foundation impacted by a hammer or drop weight. The impact produces a compressive wave that travels down the shaft of the foundation. A pair of strain transducers obtains the signals necessary to compute force, while measurements from a pair of

accelerometers An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accele ...

are integrated to yield velocity. These sensors are connected to an instrument (such as a pile driving analyzer), that records, processes and displays data and results. As long as the wave travels in one direction, force and velocity are proportional and related by the expression 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 The wave assumes an opposite direction (a reflection) when it encounters soil resistance forces along the shaft or at the toe. These reflections travel upward along the shaft and arrive at the pile top at times that are related to their location along the shaft. The sensors near the pile top take measurements that translate what is happening to the traveling waves, and make it possible to estimate soil resistance and its distribution. The data obtained in this fashion permits the computation of total soil resistance, which includes both static and viscous components. The dynamic component is computed as the product of the pile velocity times the damping factor (a soil parameter related to soil grain size). The static component is the total soil resistance minus the dynamic component). Dynamic load testing takes a further step in analyzing the data and computing static capacity and resistance distribution. Dynamic pile monitoring takes advantage of the fact that, for driven piles, it is possible to compute the energy delivered to the pile, compression stresses at the pile top and toe and tension stresses along the shaft. Pile integrity can also be evaluated.

References

*Cannon, J.G., September, 2000. ''The Application of High Strain Dynamic Pile Testing to Screwed Steel Piles.'' in: J. Beim & S. Niyama (Eds), Application of Stress-wave Theory to Piles: Quality Assurance on Land and Offshore Piling: © Taylor & Francis 2000. Used with permission; 393-398. In situ foundation tests

See also

References