Measurements of Side Friction Using Textured CPT Friction Sleeves

Currently, CPT data obtained from the friction sleeve measurement (f_s) is less widely used than the tip measurement (q_c). The "underuse" of the friction sleeve data is related to its high variability and the common sentiment that the sleeve measurement is unreliable. Recent research has quantitatively demonstrated the dominant influence of surface roughness on interface strength. Laboratory experiments have indicated that a change in the surface roughness from the conventional "smooth" configuration can more than double the interface friction. This effect is significant and has yet to be incorporated into geotechnical engineering practice. A research program was undertaken to determine the effect of friction sleeve roughness on the measured sleeve resistance. A series of CPT soundings were performed using a set of roughened friction sleeves in addition to the conventional smooth friction sleeve. Results show the friction measurement to be heavily dependent on the surface roughness of the friction sleeve. The effect of surface roughness is material dependent, but in general the friction sleeve measurement obtained with a textured friction sleeve is about 1.6 to 2.0 times greater than a conventional "smooth" sleeve in granular soils. These results demonstrate the significant effect of surface roughness on f_s and the potential for modifying current in situ practice to account for this effect.