Sonic drilling is a subsurface exploration technique that strongly reduces friction on the drill string and drill bit due to liquefaction, inertial effects, and a temporary reduction of the porosity of the soil generated by a high-frequency vibration applied directly to the drill stem at the drill head. In addition to vibration, sonic drilling uses both the rotation and downforce of the drill rig and drill casing to advance the borehole. Sonic drill stems incorporate both an inner core barrel and an outer sonic drill casing to penetrate the substrate, stabilize the borehole, and collect continuous, relatively undisturbed soil samples.
Sonic drilling techniques can recover a fairly large sample specimen (depending upon the casing diameter employed), successfully sample large-diameter granular soils (gravel and cobbles), and are somewhat effective at recovering in-tact samples of frozen soils. Sonic drilling is also fairly efficient, results in limited ground disturbance, and is devoid of drill cuttings. Sonic drill rigs can also be equipped with standard geotechnical sampling equipment (SPT/MPT, Shelby tubes, etc.). However, sonic drilling is a fairly new, equipment-intensive technology, and therefore, is generally fairly cost-prohibitive for moderate to small-scale geotechnical exploration projects.