On the existing M1 between Lofthouse and the new junction at Belle Isle, an underbridge at Thorpe Lower Lane and an overbridge at Sharpe Lane had to be replaced, working around live traffic on the motorway.
Thorpe Lower Lane
The existing bridge carrying the M1 over Thorpe Lower Lane was found to be understrength and required widening to accommodate the additional lanes from the northbound slip roads of the free flow link at the Lofthouse interchange. Since the abutments were found to be satisfactory, only the existing deck and top of abutments were demolished during closures of the motorway in April and August of 1998.
The top of the abutments required removal to accommodate the new bearing shelf, and this was carried out by drilling approximately 200 cores per abutment to facilitate demolition. The new bearing shelf features an inspection gallery to allow easy inspection of the structure. The new deck was constructed from prestressed concrete Y beams with an in-situ concrete slab supported on elastomeric bearings.
A new bridge was required at Thorpe Lower Lane to accommodate the extended southbound slip roads to Lofthouse Interchange. The bridge is of integral construction requiring no joints or bearings and the deck is formed of prestressed concrete Y beams with an in-situ concrete slab.
The new bridge constructed to the east of the existing bridge. The retaining walls to the south were constructed in reinforced earth and the hexagonal facing panels used in construction can be seen before the brick cladding was constructed. Photograph taken 15 August 1998.
This bridge was required to replace the existing structure carrying Sharpe Lane over the M1 which was too narrow to accommodate the proposed widening. The road and footpaths had to remain open throughout construction (with the exception of some short closures), and the new bridge had to be constructed on the same line as the old bridge. Therefore it was originally proposed to construct a temporary bridge alongside the existing structure which traffic would be diverted onto during demolition of the old bridge and construction of the new bridge.
However, the cost of installing, maintaining and dismantling a temporary structure proved to be so high that it was cheaper to construct the deck of the new bridge on temporary supports to the north, divert traffic onto this deck while demolition and construction of the new supports took place and then slide this new deck into position during a closure of the motorway underneath. The slide took place on 31st May 1998.