Kuwait high-rise goes up with assist from BeiDou

May 9, 2016  - By
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CORS station tracks China’s constellation over three frequencies.

Headquarters for the National Bank of Kuwait, a new 300-meter-tall building under construction, combines concrete, steel, glazing and glass-reinforced concrete in a unique shellfish shape. The engineering challenges behind this building led the engineers of Ahmadiah Company, the contractor, to use GNSS technology to install the core wall structure with millimeter accuracy.

They adopted the core wall control survey method developed by Joël van Cranenbroeck during construction projects in Dubai. To guarantee the precise vertical thrust of a tower during construction, complete control must be maintained of the position of each new element erected on top of the existing core walls. Such new elements, and their formwork structures, must be precisely positioned with respect to the main axis of the design reference frame, defined as the vertical positioned in the tower center. This means that the position of the formwork structures at the top of the tower must be continuously measured during erection of the building.

Core walls are constructed bit by bit, one on top of the other. Each core wall element consists of several concrete pours. The placement of the formwork structure on top of existing core walls must be done precisely, determined from the position of previously placed elements. For this purpose, control points (nails in this instance) are set in the top of the concrete. The basic task of the surveyor is to determine the coordinates of these control points and to compute and stake out the position of the formwork structure in a design reference system based on the main axis of the tower. Dual-axis inclinometers, precise leveling observations and vertical laser plummets complete the method, which is based on a sensor fusion approach.

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Active Control Points

A small network of three to four GNSS receivers and antennas are installed on top of the formwork to provide control points to total station operators. As the construction stages rise, surveyor sightings of ground-based control points decrease.

An active GNSS control point consists of a 360° reflector with a GNSS antenna screwed on its top. The coordinates obtained by post-processing the GNSS observations are transformed in the local datum and are available for any total-station “free station” calculation operating on the building top.

The technique has proven to be successful in several other projects worldwide. Comparisons with resection on ground control points, when made possible by tower height, indicated differences of less than a few millimeters.

GNSS CORS Station

As GNSS can only deliver such performances in differential mode, this requires setup of a local GNSS base station.

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The local GNSS CORS station receiver and a geodetic-grade GNSS antenna were placed near the construction site and connected to an Internet router to provide easy access whenever the data had to be downloaded for post-processing the GNSS receivers placed on top of the building.

To confirm that the GNSS observations by the selected reference receiver match with those of GNSS receivers used in previous similar projects, a zero baseline test was performed by connecting both sets of equipment to the same GNSS antenna. Simultaneously, a temporary GNSS base station was set up using another geodetic receiver.

All the RINEX data collected over an hour was processed using open-source RTK-LIB software. The results showed less than a millimeter variation between the receiver selected for the project and those used on previous projects.

The baseline components between the temporary base station and both receivers showed respectively 1 millimeter in X and Y (WGS-84) and 2 millimeters in Z difference.

BeiDou Role

Up to 11 BeiDou satellites are now visible in the sky over Kuwait. By setting up the selected BeiDou-capable receiver as a local CORS station — processing signals over the three constellation frequencies (B1, B2 and B3) — project operators benefit from additional GNSS signals that aid positioning where obstructions make GNSS use challenging.

The National Bank of Kuwait construction is the first GNSS CORS station tracking Beidou satellite signals deployed in the Middle East area. Surveyors on this job can access remotely via the on-board web server all the information (satellites in view, quality indicators, memory, RINEX files and so on), and can evaluate the impact of new signals and new frequencies within the context of an exceptional architectural project.

Manufacturers

The GNSS M300 Pro from ComNav Technology (Shanghai, China), a multi-purpose GNSS receiver for a range of applications, has 256 channels tracking GPS, GLONASS and BeiDou, with Galileo capability.

Joël Van Cranenbroeck established Creative Geosensing Belgium as an engineering geodesy consultancy company specialized in high-definition positioning, positioning infrastructures (CORS network) and monitoring.

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