This is a dynamic Cone Penetrometer with no significant side friction to 100-ft depth. The suppression of friction is achieved by spinning the rods continuously during driving.

Objective of the SDPT

The SDPT is a strictly empirical tool with the objective of producing and SPT EQUIVALENT that is:

  • Continuous
  • Accurate
  • Inexpensive


  • Simple and robust
  • Fast
  • Produces a blow count equivalent to SPT N60
  • Provides continuous blow count
  • Eliminates drill hole disturbance and heaving problems that occur with SPT
  • Constant energy delivered by mechanical trip hammer
  • Penetrates formation that CPT can’t handle
  • Cost of SDPT plus a continuous auger hole for sampling is considerable cheaper than a Mud Rotary hole with SPT.

SDPT – Technical Description Cone

Diameter: 2-1/2 – 64mm
Cone angle: 60 degrees from ¾” dia blunt center
Sleeve length: 10-1/2″-267mm
Total length: 12″-305mm

AWJ Equivalent: 5ft length
OD: 1-¾
Wall thickness: 3/16

LEAD ROD: Solid hardened alloy steel

DROP HAMMER: Automatic
Weight: 140lbs
Drop: 30
Efficiency 95%


ROD FRICTION: Monitored by a hydraulic pressure gauge which measures the rod torque while spinning
(50 PSI pressure increase represents a friction of one blow per foot)
HAMMER SPEED: 47 blows / min

NOTE OF CAUTION: This test works very well in Sand, Silt and Fine, to Medium gravel. It is too small to be effective in Course gravel and Cobbles. In Sticky clay; it appears that with spinning, the clay wraps around the rod increasing the friction. Therefore, in sticky clays, spinning is not advised.