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:
- Simple and robust
- 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
Wall thickness: 3/16
LEAD ROD: Solid hardened alloy steel
DROP HAMMER: Automatic
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
SPINNING SPEED: 60 RPM
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.