Enhancing geotechnical investigations using drilling parameters
Résumé
Since the 1970's measuring while drilling (MWD) has been used mostly for qualitative description of the subsurface. The techniques consist in observation and recording the drilling process in terms of advance rate, penetration thrust, rotation rate, torque, drilling pressure and flow to provide a fairly accurate representation of the stratigraphy while advancing a borehole in soils and in rocks. A study at a specially constructed test embankment was used to evaluate the potential of drilling parameters to deliver quantitative rather than qualitative data from instantaneous drilling logs. The
embankment, composed of 8 distinct areas of different soil types and materials, allowed measurements of MWD parameters under various drilling and soil conditions. Drilling variables studied included drilling methods (rotary drilling and rotary percussive drilling), drilling procedures and use of different drilling tools. Subsurface conditions included gravel, sand, clayey sand, silt, clay, reconstituted chalk as well as a buried layer of concrete and a layer of hollow polymer blocks. The measurements were analyzed as individual drilling parameters or combination of parameters known as compound parameters. The compound parameters also allowed to determine the most efficient drilling techniques to advance boreholes in different materials. Using
histograms and frequency distributions, the results obtained at the test embankment in these different geological conditions, suggest that MWD measurements have the potential to provide geotechnical engineers with reliable stratigraphic details necessary to build an accurate geological model of the subsurface.