The causes of the subsidence needed to be investigated, together with proposals to install temporary and then permanent works.

The main issue for the client, as well as having a compliant design, was to have a design that took account of the extremely restricted nature of the site and only used structural components that could be easily handled in such an area. On top of this, it was vital to the client that the operation of the signal box could continue uninterrupted during the installation of the temporary works, during the construction of the permanent works and during the removal of the temporary works prior to which the load from the lever frame had to be transferred to the permanent works. jnpgroup achieved all of the above.

The design of the temporary works involved using slender steel members to support the lever frame at a level which enabled the existing timber members supporting the frame to be cut off at a lower level to permit the installation of the pile caps and ground beams which would form part of the permanent works. The steel beams in the temporary works were supported either by the existing walls of the signal box or by a timber grillage, with jacks being used to ensure load transfer between the permanent and temporary works. The permanent works themselves involved the installation of 2 No Grundomat piles in each pile cap. These piles were chosen due to them being practical in such a restricted space.

Designing the permanent and temporary works in such a way that the numerous existing cables and ductwork in the signal box did not need to be altered/ repositioned made the job easier to the carry out for the client. The pile cap levels were set at a level which avoiding undermining the existing signal box foundations, which in turn would have resulted in more expense to the client if this had not been considered in the design. As designers, we procured the site investigation and the design of the piles so that the client had more cost certainty at tender stage.