Page 51 - Moving the Earth_ The Workbook of Excavation

Source: MOVING THE EARTH

CHAPTER 2

SURVEYS AND MEASUREMENTS

GENERAL CONSIDERATIONS

Surveying is a profession in itself, and contractors and their employees seldom have time to master
it. However, it is possible for a layperson to run levels, to reestablish lines and locations obliter-
ated by construction, and to do rough layout work.
If a job involves as much as a day of work for a surveying crew, it is usually economical to hire
professionals. They work more rapidly and efficiently than amateurs, and are less liable to make
costly mistakes. Unfortunately, it is frequently not possible to obtain the services of engineers
exactly when needed, and there are many jobs which are too small, or too simple, to justify calling
them in.
Also, it is sometimes desirable for the owner or contractor to make a rough survey of a project
to determine the amount of work to be done, and possible layouts, before bringing in surveyors to
provide detailed information. A person can usually obtain a much clearer idea of the problems
involved by running his or her own levels than by reading the findings of another.
The methods outlined in this chapter will in some cases be those used by surveyors, but will
often be shortcuts and substitutes which can be used by amateurs with reasonably satisfactory
results, and which generally are easier to learn, but less accurate, than professional methods.
More detailed information about surveying may be found in textbooks on plane surveying.
Work with a survey crew is the soundest training in field methods.

TELESCOPIC LEVELS

The basic surveyors’ tool is a telescopic level mounted on a turntable which in turn is usually based
on a tripod. The entire unit is often referred to as an instrument. There are a great variety, but most
of them may be classified under three headings—level, convertible level, and transit. The differ-
ence is partly that in the first the telescope is always used in a horizontal position; in the second the
telescope may be lifted out of its frame and reset so as to pivot vertically; and in the transit it is
permanently mounted so as to swivel vertically as well as horizontally. However, these general
distinctions are not always true in regard to particular models.
Automatic leveling and laser instruments will be discussed later in this chapter.
Builders’ Level. Figure 2.1 shows a type of builders’ level which is convenient for general con-
tractors’ use. The telescope is held rigidly in a frame that rotates on a vertical spindle, which is
perpendicular to the line of sight of the telescope. A spirit level with a graduated glass is mounted
on the frame.
The leveling head on which the spindle rotates is fitted with a horizontal circle marked in
degrees, in contact with a pointer fastened to the spindle. Many levels do not have this circle, but
it is essential for the location work to be described.

2.1