Unit of measure
mm/blow, read directly from graduated steel rule.
- 60 degree apex, 20 mm diameter, 44 mm long cone, with zero mark at 3mm above cone top end.
- 34 mm (5/8 inch) rod, 8kg (17.6 lb) hammer.
- Stool or sturdy box to stand and hold the apparatus.
- A jack to retrieve the rod after test.
- Spade, pick and auger etc. to make a hold for deeper test.
- Three persons need, (a) first one to perpendicularly hold the DCP by handle, (b) the second lift the drop weight, and (c) the third one read and record mm/blow(DCP).
- Seating drive-drop hammer should be released once to seat the cone in any disturbed material, which may be exited. The technician observes reading on the rule at the top of the hand guard and records this as the zero reading of DCP.
- Operating drive-The drop weight is raised to its maximum height (i.e 575 mm) and released. The readings of penetration are taken with each blow of the weight. If the penetration rate is below 20mm, the frequency of readings may be decreased to-:
- one for every two blows with reading from 10-20 mm
- one for every five blows with reading from 5-9 mm
- one for every ten blows with reading from 2-4 mm
- Penetration depth less than 1 mm and exceeding 20 blow is considered as refusal.
- The test shall be terminated (1) if the desired depth is reached (2) if the rod penetrates less than1/8 inch (31.75 mm) in 10 drop.
Normally, readings are taken to 1.0 m below the contact with the sub-grade. No test should be less than 1.0 m from surface.
Number of blow and depth of penetration reading are recorded.
DCP and CBR Relationships
Log 10 (CBR) = 2.632 – 1.28 Log 10 (mm/blow)
(Kleyn and Van Heerden (60 degree cone))