Humboldt H-4120HA Corps of Engineers Cone Penetrometer - Manual (Page 2)

GENERAL INFORMATION
The H-4120H and H-4120HA Corps of Engineers Cone Penetrometer is the principal
instrument used in evaluating a soil's trafficability. The COE Cone Penetrometer can also
be used during field investigations for a preliminary estimation of a subgrade treatment.
It is lighter and less difficult to use than the Dynamic Cone Penetrometer. The COE Cone
Penetrometer consists of a 30 degree cone 1/2 sq. in. base area, an 18 in. extension rod,
a proving ring, a dial indicator and a handle.
When the cone is slowly forced into the ground, the proving ring is deformed in
proportion to the force applied. The amount of force required to move the cone slowly
through a given material is indicated on the dial inside the ring. This force is considered
to be an index of the shearing resistance of the soil and is called the cone index of the
soil in that plane. The range of the dial is a 150 pound load and is marked 0-300 pounds
per sq. inch since the cone base is 1/2 sq. inch.
OPERATION
A. Inspect the instrument before using to make sure all nuts, screws and joints are
tight and that the dial indicator stem contacts the proving ring bearing block.
B. Allow the penetrometer to hang vertically from its handle and rotate the dial
face until "0" is under the needle. Note that when the instrument is kept vertical
between the fingertips and allowed to rest on its cone, the dial will register about
2.5 pounds, which is the total weight of the instrument when the 18 in. (457.2
mm) rod is used.
C. If additional extension rods are added, or removed, zero the instrument again, as
described above.
D. Place the hands over each other on the handle, palms down and approximately at
right angles, to minimize eccentric loading of the proving ring and to help keep
the rod vertical.
E. Apply force by pressing the chest against the hands until slow, steady, downward
movement occurs.
F. Take a dial reading just as the base of the cone is flush with the ground
surface. Continue the slow, steady downward movement (18 in. (457.2 mm) in
approximately 15 seconds in very soft soil) and take successive dial readings at
3-in. intervals to a depth of 18 in. (457.2 mm).
NOTE: An assistant should be provided to record the readings taken by the
operator. The operator will quickly learn to shift his vision from the
rod at the ground to the dial at the proper moment, meanwhile
maintaining a constant penetration rate.
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