| Construction surveying is the translation of construction plans
into physical points on the ground that can be used as a basis for
the actual construction. The results of construction surveying are
seen in almost any urban, suburban, and even rural setting. Almost
any roadway, building, or other man-made improvement probably had
some amount of construction surveying involved. Construction surveying
provides not only the horizontal location of new improvements, but
also the vertical information required to ensure that surfaces drain
or pipes flow as required.
The stakes and points set during the process of construction surveying
are not usually set at the actual construction point, but usually
on some sort of offset. This is done so that the survey stake is
not disturbed by excavation or other activities that will take place
at the actual point of construction. The stakes are marked with
an "offset" and a "grade", which provides the
construction crew with the spacial relationship of the construction
stake to the actual point of construction. The "offset"
is the distance from the survey stake to the horizontal position
of the actual point of construction, and would typically be three
feet for curb and gutter to ten feet for underground pipes. The
distance of the offset should be coordinated with the contractor
to accomodate any specific needs due to existing field conditions
or special equipment, and should be clearly marked on the survey
stake (usually by a number enclosed in a circle). The "grade"
represents the change in elevation that needs to be obtained from
the reference point to the actual construction point, expressed
as a "cut" (lower in elevation) or a "fill"
(higher in elevation). The grade should also indicate the vertical
feature that the grade is referencing, usually a flowline or finished
floor elevation.
The need for accuracy is inherent in all of the surveyor's tasks,
but especially evident in construction surveying. It is not only
important to perform all calculations correctly, but also to communicate
clearly with the contractor about the distance of offsets and reference
points for grades. If the surveyor provides grades to the flowline
of curb and gutter and the contractor uses those grades as top of
curb elevation, the net result is a construction site that is not
going to work as planned! Additionally, scheduling should be coordinated
in a manner that minimizes the risk of the stakes being damaged
by human or natural activities, as any disturbance to the survey
stake may carry over to actual construction. (http://www.flatsurv.com/construc.htm) |
