What is SPT?
The Standard Penetration Test (SPT) is a widely employed soil exploration tool that involves using a SPT hammer to drive a split barrel sampler at the bottom of a drill string to obtain soil samples. The number of blows required to penetrate the last
300mm (1ft) is the “N value”, which is related to soil strength.
Several different types of SPT hammers are used to conduct Standard Penetration Tests. Their varying efficiencies influence the N value. The measured N value is normalized by multiplying it by the ratio of the measured energy transferred to the rod to 60% of the theoretical potential energy. The normalization compensates for the variability of the efficiencies of different SPT hammer types, and improves the reliability of soil strength estimates used in geotechnical applications.
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. Once in the field, two accelerometers are bolted to the rod section. 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. The latest model of SPT Analyzer responds to multi touch gestures and have numerous color schemes available, making things like adjusting time scale or display to better view data in the field much simpler than previously. A pre-programmed set of output quantities tailored to SPT calibration is presented to the user, who can, however, modify it to fit a particular project need. Data quality checks are available.