Hammer Energy Calibration of Standard Penetration Test

Abstract

The Standard Penetration Test (SPT) is the most widely held in-situ test used for subsurface exploration and investigation. There are number of factors that affect the efficiency of the SPT system. The most dominant of them all is hammer efficiency. This research aims at finding the actual amount of energy transferred by the hammer with respect to the standardized 60 percent. For the purpose of reducing the major variations of the N value due to large differences in the values of energy transferred, it is suggested that N value should be changed to specific energy level by the use of certain correction factors. As per this study, these correction factors are different for the type of equipment used. Keeping in view all the previous work done, a system named as Standard Penetration Test Energy Measurement and Analysis Tool (SEMAT) has been developed which gives the energy ratio of the actual energy transferred to the theoretical energy using accelerometers (for velocity) and strain transducers (for force) which are mounted on indigenously developed instrumented SPT rod. Actual energy transferred is calculated by the SEMAT using force velocity method whereas theoretical potential energy (mgh) is calculated manually and inserted to the software. Study incorporated field tests behind Civil Engineering wing MCE on different borehole depths. Equipment used in the test was the property of MCE Geotechnical laboratory. Major causes of loss in hammer energy in manual method are sliding of hammer and tilting of SPT rods. With each blow of hammer strike data is acquired from the accelerometers and strain transducers which are connected to compact Data Acquisition device which convert analog signal into digital data and gives the output on tough book in the form of acceleration, strain, velocity and force waveforms.