High quality and cost effective drilling system for prebored pressuremeter testing

A prebored pressuremeter test (PMT) requires a predrilled vertical smooth surface borehole of a constant diameter. Two methods for the preparation of predrilled boreholes are included in ASTM D4719. The first method is drilling a borehole using a rotary rig. While this method provides a constant diameter and a vertical borehole, it is costly and time consuming. The second method is the drilling of a borehole by a hand auger (Iwan type). While this is a low cost, rapid method, it may not provide a vertical borehole of constant diameter in a variety of soils.An innovative mechanical drilling system (MDS) has been developed for the preparation of vertical smooth surface borehole of constant diameter for the pressuremeter testing. The PMT was conducted in boreholes drilled by MDS, rotary rig (RR) and hand auger (HA) at a site that comprised clayey silt (CL-ML) and sandy silt (ML) deposits. The PMT curves thus obtained were compared in terms of quality, cost and time. The comparison indicates that good quality and cost effective PMT curves can be obtained by using MDS in broader strain range (up to 40%) for the stiffness and limit pressure determination.