Mason Land Surveys have extensive experience of rail monitoring projects; operating monitoring programs above ground and in tunnels. Monitoring is required when construction is taking place close to existing rail lines, or when other factors are suspected of causing ground movement. From a health and safety perspective a robust monitoring program is essential to the safe operation of train and other services within the affected area.

Automatic Monitoring

Where there is space available it is possible to set up an automatic monitoring system. Such a system normally consists of a total station connected to a remote PC. A larger system would involve a series of total stations configured to form a monitoring network. A number of mini-prisms or targets are fixed to the surface to be monitored at spaced intervals. Prisms can be placed into a solid surface adjacent to the track and into the track sleepers. Prisms can also be fixed to the tunnel sides and along the roof.

The total stations are programmed to take readings to the prisms in sequence at a user specified time interval. The readings are recorded and processed by software on the remote PC. Any movement detected can then be graded in terms of severity and alerts automatically sent to other systems and individuals concerned.

Manual Monitoring

Even projects using automatic monitoring systems employ manual methods as a check and fall back. In some instances space is not available to set up automatic systems, such as within smaller tunnels. Under these circumstances only manual checks are possible.

Manual monitoring involves sending a survey team on to the track to take readings to the prisms or targets. Thus,providing an independent check against readings taken via the automatic system.

Whilst the survey team is on-site a number of other checks can be made; such as checking the heights on the rails at intervals down the track. Cant & gauge measurements are also made to identify any changes to line spacing and angles. Temporary targets are sometimes used on tracks where it isn’t possible or necessary to attach prisms or other more permanent targets.

A high precision digital level is used to measure the heights of fixed studs placed track side along a tunnel floor, or hooks placed along a tunnel roof. This provides another data set of heights independent of total station readings which is also used to check for movement.

Tunnel Monitoring

The preceding section covers the use of automatic and manual total station based systems for the monitoring of rails and tunnels.

Dimensions can also be recorded using high precision reflectorless hand held measuring devices. Amongst other applications these are sometimes used to check distances between the lines and overhead equipment, or to measure between targets on the tunnel walls.

Hooks can also be fixed into the tunnel sides for use with extensometers in order to measure distances across a tunnel. Any deformation of the tunnel shape can then be identified and monitored.

Above Ground Surface Monitoring

Mason Land Surveys also provide a service to monitor the ground areas above tunnelling work. Survey nails are placed into the ground and their positions recorded.

A digital level is used to measure their heights at high precision. Any changes in height can thus be identified as tunnelling activities progress beneath. The frequency of checks is related to the amount of underground tunnelling activity. Such checks can be across any surface, often across open ground and within buildings.

Duration

Monitoring programs vary in length and intensity. Mason has provided continuous manual monitoring on projects for twenty-four hours and longer during intense construction phases. Some projects require only readings taken once a day or once a week. The duration and frequency of the monitoring is normally related to the stage of the construction process. A monitoring program can ultimately last many months.

Project Examples

Heathrow Express - Track & Tunnel Monitoring
Various monitoring projects have been completed or are on-going on sections of the Heathrow Express tunnel system. Monitoring was performed during construction of a new airside road tunnel at Heathrow which passed above the Heathrow Express tunnel. Another section required monitoring whilst an extension tunnel was bored close to the existing tunnel. More recently the construction of a new multi-storey car park above a Heathrow Express station has meant a three month monitoring program has been put in place and is on-going. These projects have required monitoring both within in the tunnel and on the ground surface.

Piccadilly Line - Track & Tunnel Monitoring

The new airside road tunnel at Heathrow also passed over the Piccadilly tube line tunnel. Within a section of the line below a tunnel exit, a twelve month monitoring program was completed. Surface level checks were also completed around the airport apron in areas which could have been affected by the new road tunnel.

Alsops Road - Under Track Crossing

Track was monitored over a period of four weeks whilst a new storm water pipe was tunnelled underneath. Track was monitored during tunnelling and grouting. Service provided to Nuttalls.

Finchley Central Viaduct – Structure Monitoring

Targets fixed to viaduct arches and monitored on an annual basis. Service provided to JNP.

Canterbury – Under Track Crossing

Track monitored during tunnelling to place a power cable underneath. Service provided to Balvac Rail.

Robertsbridge – Under Track Crossing

Track monitored during tunnelling of a water pipeline to connect two reservoirs. The site was monitored twenty-four hours a day for thirteen days. Service provided to MBR.

Farningham Road – Under Track Crossing

Track monitored during tunnelling to provide a new water main. The site was monitored twenty-four hours a day for six days. Service provided to Morrisons.

In addition to monitoring Mason Land Surveys also undertake topographic and measured building survey work of track and rail related infrastructure.

For More Information Please Contact

Mason Land Surveys Ltd.
Dickson Street, Dunfermline, Fife KY12 7SL
Tel: 01383 727261 Fax: 01383 739480
Email: info@mason.co.uk

OR

4 The Courtyard, Holmbush Farm, Faygate, Horsham RH12 4SE
Tel: 01293 851 226 Fax: 01293 851 630
Email: info@mason.co.uk