Page 161 - Moving the Earth_ The Workbook of Excavation

Source: MOVING THE EARTH

CHAPTER 4

BASEMENTS

Excavations for basements may be roughly classified as the dig-and-pile and the dig-and-haulaway
types, which will be referred to in this discussion as residential and commercial, respectively, as
the larger part of them fall into these categories.
Backfilling around the foundation may be a problem. It must be emphasized here that a wet fill
can crumple in a foundation and even move footings, and that this danger is especially severe if
the masonry has not had time to cure.

PRELIMINARY WORK

Tree Protection. In residential excavation, any clearing that may be required is likely to be of
the selective type. Large trees, or trees of desirable species, may determine the location of the
house, and they must be guarded against damage and burial. It may be advisable to wrap the
trunks of such trees in cloth, and protect them by a collar of vertical boards, as in Fig. 4.1. If their
bases may be temporarily buried, the original ground line should be marked on the bark with
paint, so that the fill may be removed accurately, and burial or overcutting avoided.
Topsoil. Topsoil is usually present, and if it will be needed for landscaping, it should be saved.
This involves taking it off the area to be excavated, and preferably from the areas where spoil is
to be piled. This stripping may be a substantial part of the cost of the excavation but is required
in most localities.
In places where there is no well-defined topsoil, or the topsoil makes up one-third or more of
the spoil and the subsoil will mix well with it, stripping may not be needed.
A method of stripping topsoil which is often most economical in the long run is to remove it
completely from all areas to be involved in the digging. Figure 4.2(A) shows one method of doing
this by placing it in compact piles well away from the two corners of the proposed house. This
will usually keep it out of the way of digging, piling, and ditching, and will leave it in a position
for straight-line spreading. But it should not be put in corners where a dozer will be unable to get
behind it.
Figure 4.2(B) shows a more usual method. The digging and piling area is stripped, the topsoil
being pushed into two piles, so placed as to be just beyond the spaces for the piles of spoil. If too
small an allowance is made for the spoil, the topsoil may have to be moved back farther, or may
get buried by the fill and partly lost. In any case it will probably interfere with backfilling.
In (C) the topsoil is pushed to the sides and fill piled to the front and rear.
Topsoil stripping is discussed in Chap. 10. It is customarily done by a dozer, which does the
cleanest work. Backhoe excavators, and to a lesser extent other shovel rigs, will remove topsoil
rapidly, and if the soil is heavy and wet, may be preferred because they do not compact it and
cause it to cake. If large areas are involved, scrapers may be used.
If the topsoil is thin and will be required for finishing off, it may be deliberately mixed with
some fill while stripping to increase its bulk. If the subsoil has a loose texture, little or no harm
will be done to fertility, and regrading will be simplified.

4.1