Project Aims
Our Engineering Team took on a pivotal infrastructure inspection at a top-tier COMAH installation.
Tasked with evaluating various bridge constructions across the expansive 160-hectare site, our objectives included:
- Carrying out a structural review to identify the various bridge construction types
- Reviewing past inspection reports
- Identifying common defects and rates of deterioration
- Assessing the current inspection standard and proposing improvements
- Proposing effective management strategies
This article delves into our approach, summarising our findings from the inspection and assessment programme and highlighting how sustainability can be factored into ensuring the reliability and safety of critical infrastructure in high-hazard environments.
As with many ageing assets, serious consideration needs to be given to effectively manage these structures, enabling the site to operate seamlessly on a day-to-day basis, minimizing disruptions, and unnecessary expenditures. Some of the bridges date back 80 years and required attention.
Strategy Employed
Our structural inspections revealed that while 84% were in good condition, 10% were deemed substandard and had to be taken out of service or operate under reduced load restrictions.
Accounting for 76% of the inspection failures were two main types of bridges:
- Precast Concrete C-Section Bridges
- Larssen Sheet Pile with Concrete Deck Bridges
Our analysis pointed to two major issues:
- water ingress through bridge decks.
- congestion of service pipework, affecting the ability to effectively maintain both steel and concrete bridges.
Addressing Soffit Spalling and Water Ingress in Precast Concrete C-Section Bridges
Issue: Soffit Spalling
Mechanism: Water Ingress
Addressing the challenges associated with precast concrete C-section bridges necessitates a multifaceted approach.
Focusing on early detection of spalling, implementing targeted interventions to prevent water ingress, and recognising the impact of bridge maintenance on vulnerability are key considerations.
By taking proactive measures, the industry can avoid the progression of seemingly minor defects into extensive and irreversible damage, ultimately extending the lifespan of these critical infrastructure assets.
Bridge Inspection Challenges and Design Considerations
Spalling and exposed reinforcement are recurring issues typically starting along joints and propagating to larger areas of the precast unit’s soffits and abutments. However, recommended concrete repair systems are often not possible to implement due to the congestion of pipework limiting access to the affected areas.
Existing bridges present significant challenges for service maintenance, and we found instances where concrete bridge decks had to be removed or cut to access failed service pipework.
Recognising the importance of access to site pipework and cables needs to be a key consideration in asset bridge design to prioritize accessibility for maintenance of both the structure itself and the services beneath it. This consideration aligns with the requirements outlined in CDM Regulations (HSE, 2015), emphasising the need to not only consider the usability of structures but also how the structure can be appropriately maintained.
Foundation Hurdles: Conquering Soft Clay Challenges on Reclaimed Terrain
The site’s geological history, situated on reclaimed land, presents challenges with soft clays limiting bearing capacities.
Imported spent shale was laid on the reclaimed land to facilitate industrial development, emphasising geotechnical constraints as the soft clay offers minimal bearing resistance for bridge structures.
To address these challenges effectively, two foundation design options are available for significant structures:
- The first involves using a raft foundation to spread loads over a larger area, but the design must ensure sufficient stiffness to counteract potential ground movements.
- The second option is to use piled foundations for cases where more concentrated loads are applied, providing ample bearing resistance.
Delivering Distinction: Reusing Bridge Foundations for Sustainable Solutions
The re-use of foundations addresses two crucial factors:
- circumventing geotechnical risk
- Accelerated deconstruction and construction programmes
- and avoiding the congestion of site services under bridges, reducing risks associated with construction near pipework containing volatile materials.
- Reducing the impact on-site operations.
Our analysis indicates a 25-33% reduction in embodied carbon compared to traditional bridge replacement programs.
Charting a Greener Path: Bridge Solutions for Sustainable Asset Management
Reusing existing bridge foundations offers accelerated construction, cost savings, and reduced hazards. By replacing only the bridge superstructure, traditional construction time is significantly reduced, eliminating potential “hold periods” for in-situ pouring of concrete.
This streamlined approach not only reduces financial costs but also lessens the environmental impact. The scaled-down construction requirements lead to a decrease in heavy plant usage and materials, directly lowering CO2 emissions.
To address geotechnical constraints, IKM utilised foundation solutions that considered both site-specific challenges and environmental impact. By embracing the benefits of reusing existing bridge foundations, the solutions have not only enhanced operational safety and efficiency but also contributed to a significant reduction in embodied carbon.
