DHARMINDEX PROPERTIES AND CLASSIFICATION TESTS 37
∴ w =WWW
Ws
s21 −− = ()WW
Ws21 − – 1=()
()WW()
WWG
G21
34− 1
−−- 1
∴ w =WW
WWG
G21
34− (^11)
−
F −
HG
I
KJ−
L
N
M
O
Q
P × 100% ...(Eq. 3.6)
It may be noted that this method is suitable for coarse-grained soils only, since W 3
cannot be determined accurately for fine-grained soils.
3.5.3 Rapid Moisture Tester Method
A device known as ‘Rapid Moisture Tester’ has been developed for rapid determination of the
water content of a soil sample. The principle of operation is based on the reaction that occurs
between a carbide reagent and soil moisture. The wet soil sample is placed in a sealed con-
tainer with calcium carbide, and the acetylene gas produced exerts pressure on a sensitive
diaphragm placed at the end of the container. This pressure is correlated to the moisture
content and is calibrated on a dial gauge on the other side of the diaphragm.
However, the reading gives the moisture expressed as a percentage of the wet weight of
the soil. It may be converted to the moisture content expressed as a percentage of the dry
weight by the following relationship:
w =
w
w
r
()1− r
× 100% ...(Eq. 3.7)
where wr = moisture content obtained by the rapid moisture tester, expressed as a decimal
fraction.
The method is rapid and results may be got in about ten minutes.
The field kit consists of the moisture tester, a single small pan weighing balance, a
bottle of calcium carbide and a brush.
This method is becoming popular in the filed control of compaction (Chapter 12) where
quick results are imperative.
Even nuclear approaches have been developed for the determination of moisture con-
tent. Sometimes, penetration resistance is calibrated against water content and is determined
by a penetrometer needle. (Chapter 12).
Density Index
Density Index (or relative density according to older terminology) of a soil, ID, indicates the
relative compactness of the soil mass. This is used in relation to coarse-grained soils or sands.
In a dense condition, the void ratio is low whereas in a loose condition, the void ratio is
high. Thus, the in-place void ratio may be determined and compared, with the void ratio in the
loosest state or condition and that in the densest state or condition (Fig. 3.5).