The F-Meter® supports measurement and reporting of both overall and minimum local FF and FL numbers (including the generation of all associated data lists and profile graphs by direct download into Excel®) in full accordance with both ASTM E-1155-96 (2001) and ACI-117. Alternative backup downloading to PC through Hyperterminal® is also provided.

The F-Meter's® non-volatile memory will retain up to 99 run records, even if the unit is turned off or loses power. This feature eliminates all concerns about data loss and fully supports consolidated, back-at-the-office, data processing and report generation.

December 8th,  Savannah, GA           Joseph F Whitaker, Vice President & CFO of Whitaker Laboratory in Savannah, Georgia announced today, the acquisition of new state of the art testing equipment designed to speed the process of Pile Dynamic Analysis.  

Mr. Whitaker said, "Attempts to determine pile capacity using dynamic analysis date back to the 19th century. At that time, a dynamic formula that considered the energy of the pile driving hammer and the set of the pile was developed to find bearing capacity. Dynamic formulae are still used today, in spite of their inaccuracies and of the fact that they cannot predict stresses during driving.

Wave Equation Analysis

In the 1950’s, E.A. Smith of the Raymond Pile Driving Company developed a numerical analysis method to predict the capacity versus blow count relationship and investigate pile driving stresses. The model mathematically represents the hammer and all its accessories (ram, cap, cap block), as well as the pile, as a series of lumped masses and springs in a one-dimensional analysis. The soil response for each pile segment is modeled as viscoelastic-plastic. Mr. Whitaker stated, "The wave equation approach it is an excellent predictive tool for analysis of impact pile driving, but it has some limitations. These are mainly due to uncertainties in quantifying some of the required inputs, such as actual hammer performance and soil parameters."

High Strain Dynamic Testing

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 are connected to a 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.

Total soil resistance computed by the PDA includes both static and viscous components. The static resistance can be 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 an input to the PDA and 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 assures 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 using a PDA to perform real time evaluation of Case Method capacity, energy transfer, driving stresses and pile integrity for every blow. Dynamic Load Testing involves another technique that evolved from Smith’s approach of modeling the wave propagation theory of pile driving, the Case Pile Wave Analysis Program (CAPWAP^®). CAPWAP combines field measurements (obtained with the PDA) and wave-equation type analytical procedures to predict 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). CAPWAP analysis is made on the PDA data after the test is complete.