Geotechnical Engineering

DHARM

COMPACTION OF SOIL 437

penetration of the needle and the penetration resistance (load applied) may be shown on a
graduated scale on the shank and the stem of handle respectively.

Spring

Handle

Movable

ring

Interchangeable needle point

Needle scale

(to read penetration)

Barrel Calibrated scale

(to read handle pressure)

Fig. 12.8 The proctor needle

A sample calibration curve is shown in Fig. 12.9.

Water content %

Penetration resistance N/mm

2

Dry unit weigth kN/m

3 Penetration resistance

Compaction curve

Fig. 12.9 Calibration curve for proctor needle
The procedure for the use of the Proctor ‘plasticity’ needle, as it is called, is obvious. The
spring-loaded plunger is pressed into the compacted layer in the field with an appropriate
plasticity needle. The penetration resistance is recorded for a standard depth of penetration at
a standard time-rate of penetration. Against this penetration resistance, the corresponding
values of water content and dry unit weight are obtained from the calibration curve.

The size of the needle to be chosen depends upon the type of soil such that the resistance
to be read is neither too large nor too small.

The Tennessee Valley Authority (TVA) engineers had devised a similar device, which is
called the TVA ‘Penetrometer’.

*12.7 Compaction of Sand

The compaction characteristics of cohesionless and freely draining sands are somewhat differ-
ent from those of cohesive soils.

A typical pattern of the moisture-density relationship for a cohesionless, freely-drain-
ing sand from a laboratory test will be somewhat as shown in Fig. 12.10.