Construction Surveying | What is construction surveying?

Construction Survey (otherwise known as “lay-out” or “setting-out”) is the construction of reference points and markers that guide the construction of new structures, such as roads or buildings. These markers are usually arranged in accordance with the appropriate coordinate system selected for the project.

History of construction surveying

• Almost perfect square and north-south view of the Great Pyramid of Giza, c. 2700 BC, confirm the command of the survey of the Egyptians.

 

• Recently Stonehenge’s recent reevaluation (c.2500 BC) indicates that the monument was erected by prehistoric surveyors using peg and rope geometry.

 

• In the sixth century BC, geometric-based techniques were used to build the Eupalinos Tunnel on Samos Island.

Elements of the construction survey

• Survey existing workplace conditions, including topography, existing buildings and infrastructure, and underground infrastructure whenever possible (for example, measuring the inverted height and diameter of drains in manholes);

 

•  Stackout reference points and markers that guide the creation of new structures;

 

• Check the location of structures during construction;

 

• Conduct a built-in survey: A survey conducted at the end of a construction project to verify that the work completed has been completed to the specifications set out in the project.

Coordinate systems used in construction

 

Land surveys and existing conditions surveys are usually conducted according to geodesic coordinates. However, it is often used for the purposes of building a more suitable coordinate system.

During the construction survey, the surveyor will often need to convert from geodetic coordinates to the coordinate system used for that project.

Watch this for a better understanding:

Chainage or Station

In the case of roads or other linear infrastructure, a chain will be established, often with correspondence to the centerline of the road. During construction, the structures would then be located in terms of chainage, offset, and elevation.

Offset is said to be a “left” or “right” relative to someone who is looking for a chain line of increasing direction.

Plans would often show plan views (see above), profile views (a “transparent” section view collapsing all section views of the road parallel to the chain), or cross-section views (a “true” section view perpendicular to the chainage).

In a plan view, the chainage increases from the top to the right, or from the bottom to the top of the plan. Profiles are shown with the chainwise increasing from the left to the right, and the crosssections shown are the direction of the increasing chainage (so that the “left” offset is to the left and the “right” offset is to the right) ).

“Chainage” may also be referred to as “Station”.

Building Grids

In the case of buildings, an arbitrary system of grids is often so established that the columns of rows and columns of major load-bearing walls.

The grids may be identified alphabetically in one direction, and numerically in the other direction (as in a road map). The grids are usually but not perpendicular, and are often not even spaced.

Floors and basement levels are also numbered. Structures, equipment, or architectural details may be located on the floor and the nearest intersection of the arbitrary axes.

Other coordinate systems

In other types of construction projects, arbitrary “north-south” and “east-west” reference lines may be established, that does not necessarily correspond to true coordinates.

Equipment and techniques used in construction surveying

Surveying equipment, such as levels and theodolites, are used for accurate measurement of angular deviation, horizontal, vertical, and slope distances.

With computerization, electronic distance measurement (EDM), total stations, GPS surveying, and laser scanning have supplemented (and to a large extent supplanted) the traditional optical instruments.
The builder’s level measures neither horizontal nor vertical angles.

It simply combines a spirit level and telescopes to allow the user to visually establish a line of sight along a level plane. When used together with a graduated staff it can be used to transfer elevations from one location to another.

An alternative method to transfer elevation is to use water in a transparent hose as the level of the water in the hose at opposite ends will be at the same elevation.

Also Read:

1. Route Surveying.
2. Land Surveying.