Properties adjacent to existing railways makes good business sense, offering purchasers land availability close to railway services. However, developments of this nature are not without their risks and can have severe consequences if they materialise. To avoid this, the design and construction need to be properly assured and controlled.
What are the main risks?
The main risk to developments of this nature is excessive short-term settlement. This often results in the collapse of earthworks, retaining walls, track drainage and railway formation. In a worst-case scenario, this may result in train delays or railways being shut down for repairs, which can be an extremely disruptive and expensive undertaking.
There are other less obvious, but nonetheless significant, risks such as:
1. Long term settlement causing a track alignment fault that is not easily detected visually. The operational railway must be maintained to very tight alignment tolerances in the order of a few millimetres. Should the alignment exceed these tolerances, unacceptable faults such as twist faults (the difference in the two parallel rail levels measured over a distance of three metres) can occur. If this difference exceeds the specified limit even by only a few millimetres, it is enough to derail a train.
2. Lineside equipment, such as signalling or overhead line electrification structures, is installed to operate within very tight geometric tolerances. For example, the aspects (lights) of the signals are positioned in such a way that train drivers see them well in advance and brake at the right time to stop at desired position in the case of a red signal warning. A long-term settlement can affect the sighting distance of a signal. This may cause a driver to miss a signal or brake late, pass the signal and red and resulting in a potential catastrophe.
3. Railway tunnels, such as Crossrail, have been designed and built to withstand the ground and loads above them. Should these loads or ground conditions change significantly, tunnels can get over stressed causing the lining to crack or fail. This runs the risk of collapse or ground water penetration in the tunnels, causing flooding.
What are the mitigation measures?
To mitigate these risks, railway operators and maintainers such as London Underground, Network Rail and Crossrail have put in place asset protection standards and procedures, which impose constraints on property development adjacent to the railways. These constraints ensure that the design and construction do not cause any safety issues to the railway and its surroundings.
Examples of the asset protection constraints are: 1. Structures installed outside exclusion zones of the railways and tunnels. 2. Foundations designed so that the transferred loads do not exceed a specified safe value. 3. Tracks, tunnels and structures monitored before, during and after construction so that the right level of intervention is applied to mitigate any unacceptable level of movements.
How to achieve compliance?
We understand the sensitivity of this subject and have end-to-end in-house capabilities to help clients navigate through and comply with the complex asset protection procedures and standards.
By obtaining the timely relevant approval from the authorities, our team can survey, design, specify mitigation measures and provide site supervision to ensure that the project is compliant from start to finish.
We can also carry out in-depth geotechnical analysis of the ground and railway installations to ascertain the effects of developments on existing assets.
For more information regarding our expertise within the rail industry, you can contact Sen Jay Dookayka at firstname.lastname@example.org or on 020 8538 9555.