• a helical or spiral tool form is used to move material from the subsurface to the surface
• a bit at the bottom cuts into the subsurface material
• spiral augers on outside convey the material to the surface while spinning

HOLLOW-STEM AUGER

• center of auger is hollow like a straw when the inner drive rods and plug are removed
• during drilling or formation cutting, the center is filled with rods connected to a plug at the bottom bit
• once the desired drilling depth is reached, the center plug and rods can be pulled out - leaving the hollow augers in place
• the hollow augers hold the borehole open for sediment sampling and well installation

SEDIMENT SAMPLING

Coring devices are lowered through the hollow-stem augers to allow sampling of the undisturbed sediments below the auger bit

WELL INSTALLATION

Sections of connected PVC casing, screens and bottom cap are put together to create a well. The well is placed within the hollow-stem augers. While each section or flight of augers is lifted, materials are dropped into the region outside the well in the borehole - filter pack sands (adjacent to screened sections), bentonite clay and cement grout for sealing the annulus around solid casing up to the ground surface.

SDSU Hollow-Stem Auger Drill Rig

Trailer-mounted with mast down

Mast up and ready for drilling

Numerous sections or flights of auger

Small-diameter PVC well ready for installation in borehole