In the past, railway track survey for design and construction works was normally completed using ballade survey techniques.

The advances in electronic distance measurement (EDM) and then total stations has increasingly seen the use of co-ordinated systems on CAD. For small railway sites local plane rectangular grids with scale factor 1 satisfies the requirements for p-way design alignment. However, for large "parallel line" projects such as the WCML and ECML understanding the wider picture is crucial.

Severn Partnership have the in depth experience and theoretical knowledge backed up with the necessary qualifications at all levels to advise on the setting up of the correct survey grid for different railway sites. Simply put, if the shape and height of the earth is not taken into consideration over these long narrow corridors then the acquired survey data will be worthless for p-way design and costly if allowed to be used.

Severn Partnership were involved with the inception of the East Coast Mainline (ECMos)
and the Midland Mainline (MMo?) survey grids and the commissioning of 'Snakemaker'
from the Department of Geomatic Engineering, University College London and Dr. J. Iliffe.
Snakemaker defines a best fit solution keeping scale factor accuracies to as close to it as possible and within p-way design tolerances.

Severn Partnership Surveyors have the necessary site experience in setting out these large scale control systems using dual frequency GPS receivers linking into the OS GPS Active network and ultimately transferring these networks trackside in the form of concreted survey monuments or track machine guidance spigots (TMG).

TMGs have been installed on OHLE gantries and coordinated in 3 dimensions by Severn Partnership over many track route miles. To the "spigots" survey prisms can be attached allowing for the accurate surveying of track using the latest high accuracy magnetic drive total stations. Engineering trains position themselves from the spigots in order to set out the through alignment designs or TAD.

The advantages to be gained from a single seamless grid are multiple seen through all the project processes, survey, design, construction and as built.

Severn Partnership also understand the nitty gritty of "parallel lines", exactly what goes into their make up and the associated supporting equipment. Whilst surveying insulated joints is a must, the lesser known items such as lateral and resistant plates are also important - we know what they are and where to find such railway infrastructure detail!

Please see our website and the Buyers Guide for more details or contact:

Mark Combes

01743 874135

E: mark.combes@severn-partnership.co.uk

Nick Blenkarn

E: nick.blenkarn@severn-partnership.co.uk

Article From: www.railtechnologymagazine.com - April May 2008