by stopping the penetration at any intermediate
i. The airfield penetrometer is light enough
depth, recording the previous readings, and
and compact enough to be readily carried by an
then resume the penetration.
individual as supplemental equipment and is
capable of withstanding rough handling during
Note. Observance of the following rules is important
in obtaining accurate data--
(1) The load indicator (7) registers "0" on the
construction control work.
Scalee (8) when suspended by the handle and 15
when a 150 pound load is applied,
6. Use. a. Remove the penetrometer (fig. 1)
Note.. Do not exceed 150 pounds to handle.
from its carrying case and unscrew and remove
(2) Inspect and clean the cone (6), extension rod
cone cover and handle (2) from the housing
(5) and cone rod (4) prior to each use.
(3), Remove extra cone and wrenches from the
(3) The penetrometer must be kept in a vertical
cone cover and insert handle (2) into head (1).
position while in use.
Remove cone (6) from cone rod (4), then in-
(4) The appropriate rate of penetration is 1/2
stall extension rods (5) to cone rod (4) and
inch to 1 inch per second. However, slightly
install cone (6) to extension rod (5). Be sure
faster or slower rates will not materially
affect the readings.
that all joints are tight, and that the load in-
(5) If it is suspected that the cone is encountering
dicator (7) registers "0" on the scale (8).
a stone or other foreign matter at a depth
b. To use the penetrometer, place the cone
where a reading is desired, make another
(6) on the ground, grasp the handle (2), steady
(6) Readings must be taken at the proper depths.
arms against the body and apply force to the
Carelessness in determining proper depth is
handle until a slow, steady, downward move-
one significant source of error in the use of
c. The load as indicated on the scale (8) is
7. Maintenance. a. General. The penetrom-
recorded at the moment the base of the cone
eter is constructed of durable metals and needs
(6) enters the ground (surface reading) and at
little care other than cleaning and oiling.
desired depths at the moment the corresponding
depth mark on the extension rod (5) reaches
b. Cleaning. Cleaning consists of removing
the soil surface.
dirt, grass and other foreign matter from the
cone (6), the extension rod grooves and rods
d. A reading is made by shifting the line of
(4 and 5) as well as any accumulation of dirt
vision from the soil surface to the scale (8)
around the lower spring cup and bushing hous-
just before the desired depth is reached. Maxi-
ing at the bottom of the penetrometer housing
mum efficiency is obtained with a two-man team
in which one man operates the penetrometer,
informing the other man when the desired
c. Oiling. After cleaning and prior to stor-
depths are achieved. The second man reads the
age, apply a light coat of engine oil (OE10)
load as indicated on the scale and records the
to the surface of the cone (6), extension rods
values. It is also possible for one man to use
(5) and exposed portion of the cone rod (4),
the penetrometer and record the measurements
be sure to lubricate all threads.