M6 - Orrell Footbridge ReconstructionProject Challenges and Background
During the winter of 2017, the Orrell footbridge near the M6 was hit by an articulated vehicle. The footbridge passes over the A577 slip road and main interchange for the M6 and M58, and links Pemberton to the east of the M6 with Orrell to the west. The footbridge plays a strategic part of transporting foot traffic in the area, and the damage sustained required the complete removal of the footbridge and the installation of a new structure along with the construction of new abutments and foundations. The bridge was subsequently removed with a provisional design on the drawing board for a replacement.
The ground engineering design was governed by the ground conditions on either side of the A577. Underlying coal deposits at varying depths meant that a ‘down the hole hammer’ solution and a cased bored pile was required. The project was also hampered by restricted access to site, meaning large crawler mounted rigs typically used for these types of projects, could not be employed. Smaller more accessible rigs had to be utilized, but with a system that still achieves good rates of production and high loading capacities. The Ischebeck TITAN micropile self-drilled system is ideal for these situations.Products Used
Amey were engaged to act as consultant to design a solution for the ground conditions and restricted access. Given the loadings and the overall span of the new bridge, a micropile solution utilising Ischebeck TITAN 103/43 (Ult Load = 4155kN, Yield Load = 3132kN) micropiles was chosen as a permanent solution. The 3.0m TITAN bars were fixed and joined by the Ischebeck coupler and supporting the pile with alignment down and into the casing, were Ischebeck centralisers. Ensuring that the bar remained central to the casing, allowing for adequate cover of grout around the bar. Spherical collar nuts were also used to connect the head plate to the pile cap once the piles were placed and cast.