Project Brief

South Staffordshire Water are required to divert existing 600mm DI, water mains located along the A51 Tamworth Road, Whittington in order to facilitate construction of the new High Speed Rail 2 railway (HS2). HS2 proposes to construct a new permanent bridge over the railway line which is to be installed within a new cutting.

The existing highway is to be permanently diverted to enable the construction of this overbridge off-line. To enable the construction of this overbridge, the existing 600mm DI water mains will be temporarily diverted along and to the south of the proposed carriageway diversion route.

The mains will then be permanently diverted across the proposed overbridge. The permanent diversion will comprise twin 710mm HPPE mains installed within 850mm internal diameter ducts cast into the overbridge structure.

Challenges and how we overcame them

As the 600mm DI main is a strategic main for SSW the desire was to keep the water running at all times a plan was formulated to achieve this utilising 2 sets of double 24” line stops with 355mm bypass running at each connection point. The Line stops were successfully installed and removed at northern and southern connection points by our in-house team.

Due to the diameter of the pipe being replaced at 710mm Pe, the client requested that the pipeline was built without the use of fusion couplers as they tend to be unreliable at this size. A fully butt welded system was planned. To achieve this the trench had to be excavated to allow enough room to track the Butt welding equipment into the excavation. This also had to be achieved at depths of over 4m so extensive reduction of ground levels etc was required.

Upon excavation of the trench at a depth of over 2m a layer of sandstone was encountered right the way down to our finished level. This required the mobilisation of additional plant and specialist rock breaking equipment to try to mitigate any delays on the delivery of the project.

After starting the scheme HS2 approached us regarding the programme and whether there was a potential to accelerate the programme so they could progress their works at an earlier date. After some careful planning, we were able to come up with a proposal to bring in a secondary cell of labour and plant and work weekends to complete key tasks which would significantly reduce the programme without having a major impact on the overall cost of the project.

Outcome

The scheme was successfully delivered to meet HS2 timescales.  The client noting how well the project was delivered with numerous challenges navigated and overcame to keep the works on target and achieve the delivery date.