Page 68 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

2.18 THE WORK

The instrument is set up on A and a bearing taken on B. A 36° angle is turned, the line AD mea-
sured, and the stake D placed. An additional angle of 26°15″ is turned, AC measured, and C marked.
The instrument is now set up at B, sighted on A, turned 32°, and BC measured. The end of this
line should be the stake previously driven at C, but if it is not, a second stake C is placed. The
instrument is turned an additional 22°30″, and BD measured in the same manner. If the same loca-
tions are found for C and D from both A and B, and line CD is the required length, the work thus
far is correct. If serious disagreement is found, the work must be rechecked.
The instrument may next be set at C, sighted on D, and turned 90° left. The distance CE is mea-
sured and stake E driven. Point F is located by setting the instrument at D in the same manner. This
part of the work may be checked by setting up on E, sighting C, turning 90°, and measuring EF.
The accuracy of the location of the house in the lot will depend on exactness of the measurement
on the map and the ability to read horizontal angles correctly. Amateurs may be off several feet in such
work, and should do it themselves only when such differences are allowable. Under any circumstances,
it is necessary to get the building walls of proper length and at the proper angles to each other.
The stakes A and B may be used as benchmarks, and elevations taken at the same time as the
bearings and directions.

Recording. If the location of existing stakes is to be recorded so that they can be replaced if
destroyed, the work is the same except that the angles are obtained by sighting the instrument and
are copied from the horizontal circle onto a sketch. Distances are measured in the field and noted
on the sketch, which is most conveniently made on cross-section paper, roughly to scale. This
sketch is used in the same manner as the map in the previous discussion in replacing the stakes.
Results are generally much better, as the field figures are more accurate than those obtained with
ruler and protractor from the map.
If field observations are to be entered on a map, the baseline or points should be related to features
shown on the map, as corner stakes, points measured on a line between diagonal corners, or mea-
sured along a boundary. When the baseline is correctly drawn, angles and distances can be marked
in with protractor and ruler.

Without Instruments. Simple location work can also be done without instruments. Figure 2.16
shows the same square building plot. Lines are drawn on the print or tracing prolonging each side
of the house to the plot boundaries, from where the distance to the corners is measured. These dis-
tances are then measured off on the ground, and stakes are set.
The distances of the house corners from the boundary lines may be scaled from the map and
measured on the ground in directions found by sighting between pairs of boundary stakes.
Sighting may be done by placing a thin straight stake, as at L, and another at Q.
A person may stand behind the stake at L in such a position that, when she or he looks with
one eye, the stake at Q is centered on L and just above it, as in Fig. 2.16(B). Another person, car-
rying a third stake, measures the distance QE, keeping on line LQ in response to directions from
the observer. The measuring is best done by pinning the tape to Q. The stake is set at E so as to
be directly in line between stakes L and Q. The distance EC is then measured, and stake C set in
the same way. Distance CL is measured for a check.
Stakes F and D may be placed according to sighting from M to P, and measurements similar to
the method used for E and C. The four corners of the building are thus located, and in a regular
plot such as this no more work would be needed.
However, as a precaution against error, or in an irregular plot, or one with poorly defined
boundaries, it is wise to prolong the other sides of the house into lines JO and KN, and to sight
and measure the corners again from J and K.

Reference Stakes. If the corner stakes have been set for a building in a plot without definite
boundaries, and the contractor wishes to be able to reset them if necessary, there are several ways
in which markers can be set without instruments.
In Fig. 2.17 the house wall lines are shown continued in straight lines out of the digging area.
These lines may be established by putting sighting poles on the corner stakes and finding a distant