Overcoming Challenges: The Construction of the Bletchley Flyover on East West Rail Phase 2

The Bletchley Flyover is a part of East West Rail Phase 2 and it allows the East West Rail lines to cross over the West Coast Main Line (WCML) and three roads in Bletchley. During the Phase 2 works, the spans over the WCML had to be reconstructed since the existing viaduct structure had failed the assessment. However, constructing a new span across the WCML was challenging due to various constraints such as the presence of adjacent properties, land boundaries, overhead electrification, and the difficulty of working around the West Coast Main Line without causing disruption. Moreover, designing the foundation for the new span bridge was also challenging since it had to accommodate the existing viaduct foundations consisting of shallow under-reamed piles within the footprint of the new linear foundation for the abutments. Assessing the existing foundation for the new loads in accordance with the current standard and designing a skewed bridge abutment foundation of approximately 90 m in length in REPUTE, which considers the pile cap to be an infinitely rigid structure were also significant design challenges. Additionally, there was little historical information available for the existing foundations, making it harder to design the foundation for the new span bridge. Cross hole seismic testing was carried out as part of the design to determine the size of existing under-reamed piles.