Hazard Location | Southwest rail network

Geophysics Finds Hazard Location


Key facts:

Met is a Link-Up approved company. Utility Surveyors are PTS-qualified and experienced in carrying out surveys on the railways and dealing with the many restrictions that entails.

All equipment we use is Network Rail Approved for use on the railways, allowing for a rapid response time to visit site when required.

Met’s hazard location services revealed a large void directly beneath a proposed subway location. This turned out to be a lift shaft.

Project Overview

Alfred McAlpine Civil Engineering contacted Met Consultancy Group (Met) to inform their maintenance and redevelopment work on the southwest rail network. To aid in the detailed design of the proposed redevelopment works accurate plans of the existing facility apparatus were required by the engineers.

Utility surveys are regularly carried out prior to the start of construction works, to ensure that any excavation work can proceed safely.  However if a survey is carried out earlier in the process it allows engineers to take the in-situ apparatus into account when designing the development, reducing the likelihood of unexpected delays and the need for costly utility diversions. It also allows drainage design to utilise existing routes where possible.

In order to accurately locate existing utility apparatus, combined radio frequency locator (RFL) and ground penetrating radar (GPR) surveys were undertaken at a number of stations and sections of railway embankment. Met were able to provide accurate digital plans showing the location of, and depth to, existing apparatus. Using non-intrusive techniques to obtain this information not only reduces the risk of damaging existing infrastructure or injuring employees, but is generally more cost effective than intrusive investigation. Access is also easier for a survey team, and reduces the need for long disruptions to train movements and the general public.

GPR and geophysics is not restricted to locating utilities, and the techniques can be used to look for a wider range of features that can cause problems for development works if encountered unexpectedly. Carrying out a Hazard Location survey alongside a utility mapping exercise can be a cost-effective way of clearing a site, as Ground Penetrating Radar (a standard technique for utility tracing) can also be used to locate voids, buried foundations or rubble, disturbed ground and many other features provided the operator has the expertise to recognise these in the data. Other geophysical methods can also be used to fully characterise a site and allow works to progress with confidence.

At one station where a new subway was being constructed, we were requested to provide information on sub-surface features that might hinder the construction process or compromise operational safety. A combined GPR and microgravity survey was undertaken which provided an accurate picture of the sub-surface and identified the presence of a large void directly beneath the proposed subway location. Excavation revealed the void to be a lift shaft dating back to the late nineteenth century.

Were this unidentified it would have represented a significant danger to construction vehicles and personnel. The discovery of the feature prior to the platform extension work enabled McAlpine to operate safely and their engineers even incorporated the lift walls into the new building plans, thereby reducing construction costs and preserving railway heritage.