Page 121 - Moving the Earth_ The Workbook of Excavation

ROCK, SOIL, AND MUD

ROCK, SOIL, AND MUD 3.15

A piezometer is a pipe gauge that is placed in the fill as it is built. It will indicate any movement
of soil or soil water that would be likely to threaten to damage the embankment.

Too Much Moisture. The material taken from road cuts often contains too much moisture to meet
compaction specifications in the fills.
In dry summer weather, layers of fill may be stirred up with a disc harrow, moved from side to
side by graders, or sprayed into the air by a rotary tiller with the hood up. When moisture is suffi-
ciently reduced, the surface is leveled off and the layer is compacted. If it rains during this operation,
the result will be mud.
If some fill is wet and some is dry, the two types may be built up in alternating layers, that may
or may not be mixed together.
In a wet season, surface drying is impractical, and no dry fill may be found in any of the cuts.
Under such conditions it may not be possible to meet density specifications.
This is a very serious problem that is almost completely overlooked in the literature on com-
paction. It is generally passed off with a paragraph or two on correction by substituting other
material or by kiln drying.
Kiln drying of such quantities would involve setting up huge and expensive plants, drastic
changes in digging and hauling methods, and lengthening of hauls. It is questionable whether such
operations could be included in a highway budget, or even whether improved pavement life would
justify the cost.
The most critical point for the contractor is that in many states the terms of the contract require
her or him to produce a certain density that can be achieved only at or near optimal moisture con-
tent. If the contractor cannot get the soil down to this content, it is unlikely that the density can be
obtained. See Fig. 3.10.
Theoretically the contractor should get no pay for the embankment work, and would probably
go bankrupt. Actually, this does not seem to occur. Field workers in public works departments are
more realistic than the design engineers, and are inclined to pass the work as long as sincere and
intelligent efforts have been made to reach the specification. However, this puts both sides in the
wrong if their actions become the subject of an official investigation.

FIGURE 3.10 Moisture-density curve.