Page 305 - Geotechnical Engineering Soil and Foundation Principles and Practice

Compaction
300 Geotechnical Engineering

Figure 13.16
The expanding
steel mold of the
‘‘K test’’ enables
rapid estimates of
soil strength and
compressibility
parameters from
Proctor density
specimens, but
drainage may be
incomplete.

compressibility in an expandable steel mold (Fig. 13.16). A specimen from a
Proctor density test is inserted in the mold and compressed at the ends, which
causes the mold to expand and automatically exert a gradually increasing lateral
confining stress on the sample.

In geotechnical engineering, K denotes the ratio between horizontal and vertical
stress. In a ‘‘K test,’’ vertical stress is measured and the lateral stress is obtained
from a suitable calibration from expansion of the steel mold. As both stresses
simultaneously increase it is possible to obtain running estimates of both the soil
cohesion and the angle of internal friction, as well as a compression modulus and
soil-to-steel sliding friction. Although the soil is confined between porous stones
to allow drainage, compacted specimens contain sufficient air that little drainage
occurs. K-test results have been used with bearing capacity theory for design of
tamping-foot rollers.

13.10 GRADATION AND COMPACTED DENSITY

Density after compaction is closely related to the range of particle sizes, as
progressively smaller particles fill in the voids, whereas density also is influenced
by the largest particles present, as a solid particle is more dense than a cluster of
many smaller particles.

A variety of moisture-density curves representing different gradations of soil is
shown in Fig. 13.17, where it will be seen that, in general, the coarser the soil, the
higher the compacted density and lower the OMC. However, it also may be noted

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