DHARMINDEX PROPERTIES AND CLASSIFICATION TESTS 65
of the rod so as to have a total sliding weight of (1.48 ± 0.005) N. The rod shall pass through two
guides (to ensure vertical movement), fixed to a stand as shown in Fig. 3.19.
Total sliding
weight
(148 0.5 g)±Graduated
scale30.5 mm
15°30 ± 15¢¢Cylindrical
trough
50 mm dia.
and 50 mm highFig. 3.19 Cone penetrometer
Suitable provision shall be made for clamping the vertical rod at any desired height
above the soil paste in the trough. A trough 50 mm in diameter and 50 mm high internally
shall be provided. The soil sample shall be prepared as in the case of other methods.
In the case of clay soils, it is recommended that the soil shall be kept wet and allowed to
stand for a sufficient time (24 hrs.) to ensure uniform distribution of moisture.
The wet soil paste shall then be transferred to the cylindrical trough of the cone
penetrometer and levelled to the top of the trough. The penetrometer shall be so adjusted that
the cone point just touches the surface of the soil paste in the trough. The penetrometer scale
shall then be adjusted to zero and the vertical rod released so that the cone is allowed to
penetrate into the soil paste under its weight. The penetration shall be noted after 30 seconds
from the release of the cone. If the penetration is less than 20 mm, the wet soil from the trough
shall be taken out and more water added and thoroughly mixed. The test shall then be re-
peated till a penetration between 20 mm and 30 mm is obtained. The exact depth of penetra-
tion between these two values obtained during the test shall be noted. The moisture content of
the corresponding soil paste shall be determined in accordance with IS procedure, referred to
earlier.
The liquid limit of the soil which corresponds to the moisture content of a paste which
would give 25 mm penetration of the cone shall be determined from the following formula:
wL = wα + 0.01(25 – α)(wα + 15) ...(Eq. 3.45)