Page 176 - Moving the Earth_ The Workbook of Excavation

BASEMENTS

4.16 THE WORK

Checking Grade. Cutting the bottom to proper grade is more difficult with a backhoe than with
a dozer, as the backhoe operator looks down at the grade rather than along it; has more difficulty
climbing down to check it; and cannot move the machine back to grade over mistakes.
It is very helpful to the operator to have someone to check the work, although the operator can
manage alone if necessary. The corner stakes, and preferably some other stakes, may be marked
at a certain height, as 9 feet above the bottom. In a level field the marks would all be 1 foot above
the ground; in a sloping one the highest stake should be marked a little above the ground, and the
others with the aid of an instrument or a string level. A stick should be cut 9 feet long.
If the operator is checking the grades alone, he or she may fasten a taut string between two stakes
so that it will go over the spot in question and measure the distance from the floor to the string with
the stick. Spots which cannot be crossed by the string, or measured directly from the height of the
wall, may be checked from a known spot by eye, or with a hand or carpenter’s level. See Fig. 4.15(A).
If two people are doing the work, a string may be stretched between stakes on one side.
Another string fastened to another stake across the excavation may be held in any desired posi-
tion on the first string, as in (B), while the other person holds the stick.
Hand, transit, or laser levels may be used. A long rod is required when the instrument is set
outside the hole.
A backhoe cannot cut a perfect floor to a pit, because of the projection of the teeth and the tooth
bases. The smoothest grade is obtained when the bottom of the bucket is used for finishing, rather
than the teeth.

Irregular Edge. Figure 4.16 shows a basement of the same irregular shape as that in Fig. 4.9.
The principal considerations in doing complicated excavations with a backhoe are to avoid dig-
ging it into a trap; to avoid surrounding it or blocking it from other work by piles of spoil; and to
work either parallel or at right angles to outside edges.
There are several ways in which this basement can be dug. The north side can be dug from the
east end, as in (A) and (B). When the jog is reached it is finished off with a vertical cut, the back-
hoe backed away, and brought back in position to cut along the inner line. If the start is made at

FIGURE 4.15 Checking bottom grade.