During the works, careful logistical traffic management was implemented by RJ Power Rail, with all deliveries being pre-planned and sequenced in accordance with a Traffic Management Plan. All vehicles accessing the site had to be in line with the directives given by the site Traffic Marshals.
All plant/pedestrian interfaces had to be managed around the nominated site storage and parking areas too. To combat this, segregated walking zones were created and a Banksman was present during the transportation and lifting into position of all materials for the works.
RJ Power Rail faced challenges with the timescale of this project due to the number of different project interfaces during the course of these works. With the works being of a multi-disciplinary nature and with multiple contractors needing to negotiate access arrangements, RJ Power Rail’s team needed to be extremely flexible and work collaboratively with others, when approaching and delivering key milestones in their programme.
This liaison was particularly important, as the electrical and water supply services were still required to be available within the depot. RJ Power Rail carefully interfaced with the Colas Rail team, Heathrow Express and GWR in order to programme and plan a phased decommissioning and diversion of the services, so as to ensure as little disruption as possible.
Unknown Buried Services
The project was further challenged, when it was found that the civils design through the depot access road was not achievable, due to the presence of a large amount of unknown buried services and the radius bend of the existing waterpipe.
RJ Power Rail proposed to move the excavation to one side of the access road, away from the middle of the road, allowing the road to remain partially open, which also gave enough distance from the existing buried surfaces and allowed the excavation to run straight rather than stagger around other buried services. This in turn made the installation of the water pipe easier, due to the fact that it could only change direction by an angle of either 45° or 90°.
The road plates were required to sit flush to the road to eliminate tripping hazards. To achieve this the design showed a 45mm recess to be broken out either side of the excavation, with a 20mm cementitious grout laid for the steel road plates to sit on. Due to the composite construction of the road this proved to be unachievable due to the amount of re-bar present.
RJ Power Rail provided a solution that involved excavating the full width of the road plates, applying shuttering to either side of the trench width and then building back up to the recess level, in order to achieve a flush road plate.
The design also showed the excavation connecting onto an existing oil/diesel pipe trench, however, during the works, the trench was found to be full of diesel and oil.
RJ Power Rail resolved this by core drilling through the walls of the existing trench to allow the waterpipe and 6.6kv HV cables to divert over the diesel and oil. This enabled the excavation to continue and run parallel with the oil trench, until such a time when it could be diverted and then connected back to the originally designed route.
6.6kv Ring Main and 25kv HV System
The diversion of the 6.6kv ring main and 25kv OHL high voltage system was an extremely challenging undertaking.
Old Oak Common Depots’ electrical distribution is fed from a vast network of 6.6kV substations (B5, B1, T, S, D and E) in the form of a ring main derived from an 11kV Scottish and Southern Energy (SSE) supply. The ring main is operated with a normally open point as two radial 6.6kV circuits of which the HV switching equipment was locally controlled/operated with no indication or operation control from the railway electrical control room.
The two traction 25kv OHL feeder cables originated from Kensal Green Feeder Station and terminated at structure J/05/125 in the Hex depot and were affected by the Stage 3 works, with both cables running in parallel for the entire length.
One of the two 25kV cables is a feeder cable carrying traction current from Kensal Green Feeder Station section KAGA/805/HV/L and terminated to the sealing end of structure J/05/125.
The other 25kV cable is a traction return cable from Kensal Green Return Current Bus Bar (RCBB) section KAGA/HV/805/N and terminated on spider plate SP/05/101.
This complex HV power arrangement, necessitated the need for alternative HV feeds for both the 6.6kv ring main and 25kv OHL HV circuits to enable continuous supply to the railway infrastructure while the diversions/slewing of the HV cables were also undertaken.
RJ Power Rail’s highly qualified substation level `A`, liaised closely with the substation maintainer, electrical control room and Scottish and Southern Energy, to produce a clear and defined sequence of HV switching operations, for both the 6.6kv ring main and the 25kv traction cables, which enabled a continuous high voltage supply to the operational railway whilst works were undertaken.