SPT Energy Calibration consists of measuring the energy transferred by the Standard Penetration Test (SPT) hammer to the SPT rod. SLP Engineers take these measurements with the Pile Driving Analyzer® (PDA) and using an SPT rod instrumented with strain transducers and accelerometers.
The SPT Analyzer is furnished with a 0.6 m sub assembly (or section) of an SPT rod (AW, NW or other type) instrumented with 2 strain gage bridges, and precisely calibrated by Pile Dynamics. The instrumented section is inserted at the top of the drill string between the hammer and the existing sampling rod. The rod is connected to the SPT Analyzer.
Smart Sensor technology allows the SPT Analyzer to read the rod instrumentation, obtaining the sensor calibration and rod cross sectional area. These quantities are input to the SPT Analyzer automatically without the operator having to enter them. This significantly simplifies the initial test setup. The strain gages and accelerometers obtain the force and velocity signals necessary for the calculation of transferred energy as the SPT hammers drive the instrumented rod into the ground. The energy is displayed in real time on the SPT Analyzer screen.
SLP performs this service in accordance with ASTM D1586-99 Standard Test Method for Penetration Test and EUROCODE requirements for SPT Energy Measurement to evaluate k60.
EUROCODE 7 and The American Society for Testing and Materials (ASTM) recommends standardizing the measured N value by multiplying it by the ratio (k60) between the measured energy transferred to the rod (Emax) and 60% of the theoretical potential energy of the hammer. This compensates for widely variable efficiencies from different SPT hammer types and therefore improves the reliability of the estimates obtained from the test.