A new sounding technique, measurement-while-drilling (MWD) logging, using a rotary percussion drill has been devised for quick in-situ soil profiling work. The logging produces a continuous soil resistance index, called Np-value, calculated from the drilling energy and a conversion facto which makes the Np-value close to the SPT N-value. The conversion factor is found to be affected by difference between conditions with and without percussion. The Np-values are compared with the N-values at six sites. he results show good agreement and demonstrate the validity of MWD logging for profiling soil resistance.
