M1-A1 Link Road:
Lofthouse Interchange

This was probably the trickiest element of the whole project as it required the construction of three bridges and two cut and cover tunnels under the M1 and M62, while maintaining traffic flows on the motorways.

The two tunnels comprise reinforced concrete portal structures. They were to be built in a way that minimised disruption to the motorways above as three lanes of traffic had to be maintained in both directions at peak times. As a result construction of the tunnels took place in three stages.

For each stage, the layout of the motorway above was altered to leave sufficient room for the excavation of the tunnel. Fortunately the geology of the site predominantly comprises sandstone with some saturated mudstone and coal measures which allowed excavations to be dug with battered slopes of 2 in 1. The slope running alongside the carriageway of the motorway was excavated to a slope of 4 in 1 and rock anchors were installed to stabilise this slope. Excavation took place in stages to allow for installation of the rock anchors.

Following excavation, the tunnel walls and roof slab could be constructed and the structure was backfilled before the carriageway was reinstated over the top.

Diagram of Lofthouse Interchange
Diagram of Lofthouse Interchange

The two slip road bridges comprise three span composite steel plate girder and concrete slab decks supported on reinforced concrete bankseats at the ends, and steel tube columns filled with mass concrete via reinforced concrete diaphragms at the internal supports. They were built using top down construction to minimise the quantity of temporary works required to support the beams during construction of the deck and diaphragms.

The columns were constructed by excavating shafts lined with segments 2m in diameter to the required level; the steel tubes were lowered into these shafts and filled with mass concrete. Scaffolding was constructed to support the steel plate girders and the falsework for the deck and diaphragms. For the M62 bridge this proved to be quite difficult to construct, as the excavation for phase 1 of the M62 tunnel had removed a significant amount of the level area required to construct a level platform on the rock and so a system of scaffold towers and a grillage of beams spanning onto these towers and the rock platform was devised to support the scaffolding.

After the deck and diaphragms were complete, the parapet cantilever and edge beam were cast onto the side of the deck using falsework, supported off the edge plate girder.