Abstract
M.Tech.
There is a general lack of understanding of the laboratory compaction test
based on the vibrating hammer method. The impact method of testing soil in
the laboratory is conservatively used by engineers for design and
construction control purposes even when the specified mode of compaction
on site is vibratory. Furthermore, the effects of vibratory compaction are not
fully understood, and hence this mode of compaction in the field has not
always been effectively utilized.
The objective of this research project was to determine whether the vibrating
hammer method could be used in the laboratory for design and control
purposes, through an investigation of its operating characteristics, and a
comparison of its effectiveness against that of the impact method, following a
study of the compaction properties of a range of different soils used in road
and embankment construction.
The results of the study showed that the vibrating hammer can be used in
place of impact in the laboratory for non-cohesive soils and gravels. In one
instance, vibratory compaction produced maximum dry densities for a
decomposed granite which were almost 5 % higher than that for impact
compaction. Cohesive soils reached maximum compaction at moisture
contents which were 7 % wetter under the vibratory mode as opposed to
those for impact, but at lower densities. This showed that field densities under
vibratory compaction would be difficult to achieve when the laboratory control
method was based on impact.
The research showed that electrical power input to the vibrating hammer must
be carefully regulated in order to maintain specified standards which are
based on a fixed frequency. Further study based on operation at different
frequencies would be required to determine whether the vibrating hammer
would be suitable for cohesive soils having natural frequencies lower than the
current standard specified.