ROTARY-PRESSURE SOUNDING: 20 YEARS OF EXPERIENCE

The rotary-pressure sounding method was developed by the Norwegian Geotechnical Institute (NGI) and the Norwegian Public Road Administration (NPRA) in 1967. The aim was to design a rational and efficient sounding method, adjusted for Norwegian soil conditions, climate and terrain. The equipment is operated by a multipurpose drilling rig. The equipment consists of a bit extended by rods with flush couplings. It is forced into the ground at a constant rate of penetration (3 m/min.) and at a constant speed of rotation (25 RPM). The thrust necessary to maintain the constant speed of penetration is measured and plotted versus depth. After 20 years of experience with this method we may conclude that the aims to a great extent have been achieved. The major part of the Norwegian geotechnical institutions and firms employ rotary-pressure sounding in conventional site investigations. The method dominates because it requires less work effort, reduces costs and provides more geotechnical information compared to traditional methods. The rotary-pressure sounding results give information about the overall ground conditions, and the method is widely used to locate quick clay deposits. Rotary-pressure soundings cannot penetrate through coarser materials such as stone and boulders. Modifications towards a "total sounding" method which may penetrate all sorts of soils, are therefore presently underway.