RAIL SURVEYING
Quality hand backs with increased line speeds
Dave Dampier, rail & tunnel consultant at SCCS, the survey equipment company, discusses innovative ways to improve hand backs.
W
ith the ongoing requirements for reduced hand back times and improved
track geometry, the SCCS/Amberg partnership has worked closely with the Network Rail innovation team to produce a survey solution to achieve these aims.
Using the ‘long chord’ survey methodology already used in the UK by the Emsat and the Amberg GRP TMD (track measuring device), also used currently for track survey, Amberg has developed a system that combines the best of both.
The resultant 2 x TMD system uses the long chord survey method to accurately and quickly survey the position of track and calculate deviations from a design. At the request of Network Rail, further development by SCCS/ Amberg Rail was undertaken to include the tolerances relating to line speed, as stated within the Network Rail construction standard.
This additional functionality allows for the track to not only be compared with the design with respect to deviations, but also display the resultant line speed that the track is compliant for. The deviations/line speeds are displayed on site with respect to chainage and which of the deviation parameters is responsible for the resultant line speed. The aim is to provide the required information to the engineers and speed raiser on site to then allow for improvement in track geometry quality and therefore line speed.
Methodology
The Amberg VMS system uses 2 TMDs to carry out the survey of the track using a design string
84 | rail technology magazine Dec/Jan 14
and known offsets to control points adjacent to the track. Amberg has developed two systems, VMS 3000 and VMS 1000, which share the long chord measurement system. The principle difference is the ability of the VMS 3000 system to make measurements to other structures during the measurement run, for example 6ft distances, heights and clearance profi les.
The software can then compute the deviations from design and the speed raiser report created, and can export a front offset fi le if required. All processing is done on site with no need for copying of data to an external computer due to the powerful ruggedised computer used during data collection.
staggers, and
Both systems work using a design that can be either an absolute geometry string or relative geometry design, whilst the offsets can be either known relative to the track (chainage, horizontal/vertical offset) or absolute position (Easting/Northing/Height).
Nick Matthews, senior project engineer, Engineering and Innovation,
said: “The
Amberg VMS has been successfully developed by SCCS and Amberg to help Network Rail and its track construction partners achieve the goal of increasing the opening speeds of track renewals in particular the high quality installation tolerances demanded by switch and crossing installations. The ability of the Amberg VMS to give rapid and highly accurate absolute coordinates fi les to the tamper decreases construction time and offers improved track quality. Furthermore the assurance that the geometry is correct for the hand back speed offers a high degree of assurance for the speed raiser.”
The offsets are measured using either a laser profi le device or a high precision Leica total station from the fi rst TMD. The second TMD is then continuously tracked by the total station between the offsets collecting track position, cant and gauge information.
Neither of the systems requires the total station to be set up or orientated in a conventional geodetic way, allowing for ease of use on site and speed of survey.
The use of the Amberg VMS 3000 system gives a comprehensive solution allowing for all track geometry, OLE and clearance critical structures to be surveyed in a single measurement run.
The VMS 1000/3000 have been further developed with Network Rail for use in S&C and plain line renewals where precise and effi cient surveys are required in short time frames. In addition to this, the VMS 3000 systems are also being used for maintenance surveys where a high level of repeatability is required.
Chris Preston, senior survey engineer in the track & civils engineering team, said: “Network Rail is keen to support innovative ideas that can improve the quality, time and safety of survey activities on our network and this contributes to this.”
SCCS is delighted by the endorsement from Network Rail.
FOR MORE INFORMATION
T: 01480 404888 E:
rail@sccssurvey.co.uk W:
www.sccssurvey.co.uk
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