Managed by AECOM, with Abe Newmark as the Executive Team Lead for Bridge Engineering and Civil Infrastructure, the rehabilitation of the 13.4 km road from Ashton to Montagu through Cogmanskloof was a significant project undertaken by the Western Cape Government’s Department of Transport and Public Works that completed in August 2022.
The objective of this rehabilitation is improving traffic and pedestrian safety as well as improve flood capacity of bridges and resistance to overtopping of the road by the adjacent Cogmanskloof River. This involved the construction of three new bridges, including the Ashton Arch Bridge, two bridge rehabilitations, stormwater and services improvements and reinforced earth walls within Cogmanskloof. A key feature was the New Ashton Arch Bridge, a single-span tied arch bridge spanning 110 meters, designed to eliminate debris build-up and provide a shallow deck depth.
AECOM’s multidisciplinary expertise
Heritage and environmental aspects were a major consideration in the design and construction of the project’s execution. The use of recycled materials from the old bridge’s demolition for foundational works reduced the carbon footprint. Stone masonry and landscaping elements were integrated to honor the region’s historical and aesthetic values.
AECOM’s multidisciplinary expertise ensured the project addressed its many challenges, including tight construction timelines, complex geotechnical conditions and logistical hurdles of working in a confined, environmentally sensitive area. AECOM provided expertise from feasibility to detailed design, tender documentation and construction monitoring, ensuring a quality outcome for the client. Key solutions included:
- Leveraging local and international expertise for specialized components.
- Implementing advanced concrete technology for a service life exceeding 100 years.
- On completion of the project, 42% of the contract value had been allocated to the creation of economic opportunities and entrepreneurial capacity in the surrounding areas over five years.
Key considerations for the latest upgrading were to minimize flow restriction and improve the available free board within the restrictions of adjacent properties and road alignment levels. Through an economic analysis, the technical options for the river crossing and construction strategy, were evaluated with due consideration of the impact of construction strategy on road user costs.
Sustainability consideration
The old concrete from the demolished bridge was crushed and screened by the contractor. 400 m³ of coarser material was incorporated in the grouted rock fill layers of the eastern abutment while the remainder reserved for maintenance of the contractor’s excavation drainage system during construction of the engineered-fill layers.
Accordingly, the New Ashton Arch can be considered as being founded on the recycled material salvaged from the demolition of the original bridge – incorporating a legacy of at least 90 years. This reduced the carbon footprint and improved sustainability aspects of the project through the maximised utilisation of waste materials and resulted in a lower embodied energy by avoiding the use virgin selected fill material.
Achievements and recognition
The project was recognized with multiple industry accolades, including the 2022 Fulton Award for Best Infrastructure Project over R100 million. It also received two Highly Commended Awards in 2021 from the Construction World Best Projects Awards in the Civil Engineering and Consulting Engineer categories.
The project also marked the first use of the transverse launching method for a complete concrete tied-arch road bridge in South Africa. The client was highly responsive and collaborative, ensuring the project was delivered on time and to a high standard, without compromising safety and environmental considerations.