4.20 LAND MONUMENTS AND ROAD CENTERLINE
4.21 RE-ESTABLISHING ROAD CENTERLINE CONTROL POINTS
Grading Projects
After completion of a grading project, iron pins 375 to 450 mm (15 to 18 inches) long
are to be installed to represent a point of intersection (PI) or point on tangent (POT).
Iron pins should be driven so that top of pin is 125 to 150 mm (5 to 6 inches) below
ground surface. If the PI does not fall within the right-of-way, mark location of point
of curve (PC) and point of tangent (PT) with an iron pin but do not mark the PI location.
The location of each iron pin should be cross-referenced to concrete reference posts set
in or near right-of-way line.
WARNINGS:
When setting reference monuments or land corners, utility companies must be notified
by calling the "One Call" telephone number, 1-800-292-8989.
USE HAND TOOLS WITH WOODEN HANDLES IN AREAS SUSPECTED OF HAVING BURIED POWER LINES.
Portland Cement Concrete Pavement
Above mentioned points should be represented by an "X" chiseled in the hardened pavement surface.
Hot Mix Asphalt Pavement
Above mentioned points should be represented by hinge nails driven in the finished surface.
Land Corners
The District Land Surveyor will reset land corner monuments or supervise the resetting of these
monuments by construction survey crews.
4.22 REPLACEMENT OF FEDERAL MONUMENTS & PRESERVATION OF ENGINEERING DATA
Examples of typical federal markers are shown in Appendices 4-2 and 4-3.
4.23 CENTERLINE POINT REFERENCING
Reference markers and centerline control points, if off the paved area, are to be buried 200 to 250 mm (8 to 10 inches) deep.
Location of Reference Points
Placement of reference markers is critical since they are used to find the centerline
control point at some future date and, more importantly, to restore a control point to its
original position if disturbed. These markers should be kept at a minimum distance from the
control point, preferably less than 30 m (100 feet), but not too close so it might be confused
with the point itself.
Precautions must be taken to preserve control points during construction.
Methods of Referencing Points Using a
Transit
Methods using iron pins placed on a line 90o to the construction centerline or tangent
line are shown in Figures 1, 2, and 3 of Appendix 4-5. Where
it is not practical to reference at right angles to the construction survey line, such as at road
intersections, it may be desirable to transit tie the point as shown in Figure 4,
Appendix 4-5. Angles are to be measured from centerline to
both lines of reference. In all cases, stationing of the point and its physical description are to
be shown in reference box.
Method of
Referencing Using an Electronic Total Station Survey Instrument
The use of advanced survey equipment allows referencing of centerline points with fewer reference
points. While a “transit tied” method may require four to six reference points, the following method
uses only three reference points.
The location for reference points, as previously recommended, also pertains to this method.
Two iron pins are placed in line with the control point to be referenced (one pin on each side of the control point) as shown in Figure 7, Appendix 4-6. A third iron pin is placed at approximately a 45degree angle to the set pins. An aluminum cap should be placed on each of the pins with the center punched at the exact point after being driven.
The angles and distances between the three reference points are measured, as well as the distance from the reference points to the centerline point.
In order to reestablish the centerline point, the surveyor should set on either of the two "in-line" reference points and sight toward the reference point. The centerline point can be located by measuring the recorded distance from the reference point to the centerline point.
If either of the "in-line" reference points are destroyed, the third reference point, which was placed as approximately a 45 degree angle, can be used. In this case, the instrument is set on the existing "in-line" reference point and the third reference point is sighted upon. Using the recorded distance and angle, the centerline point can be reestablished.
Land Corners
A land corner should be referenced as shown in Figure 1, Appendix
4-5, if located near a centerline control point. If there is no centerline point in the
same general vicinity, the land corner should be transit tied as shown in Figure 6,
Appendix 4-6.
Concrete Monuments
While above methods are preferred, concrete monuments are also allowed as reference markers.
4.24 BENCH MARKS
Utility poles, fence posts, ends of drainage pipes, and railroad rails should all be avoided since these objects tend to be disturbed by frost, wind, and farming operations. Casting of a permanent concrete monument within the right-of-way appears to be the best solution in the absence of some other stable, permanent object.
Establishment of permanent bench marks should be considered near the end of every major grading and paving project. Monument location should be at the direction of project engineer. Occasionally, the project engineer will have cast-in-place concrete monuments placed by contractor and paid by extra work order. Standard brass bench mark shall be provided by the project engineer to be set in plastic concrete.
Locations for permanent bench marks in urban areas include fire hydrants, concrete sign bases, and other permanent objects. Interval of bench marks should be established at about one per city block.
Permanent Bench Marks Along Rural
Highways
Permanent cast-in-place concrete bench marks should be constructed using the following guidelines.
These should be considered minimum dimensions:
Monument shall be tied to construction centerline by station and distance and recorded on "as built" plan.