Background

Dorset Council faced a critical engineering challenge at Bridport (West Bay) Harbour, specifically concerning Wall B and adjacent areas. The existing harbour wall, a structure with historical significance dating back to the 1824 design by Francis Giles, was exhibiting significant signs of distress. Ongoing monitoring revealed continued gradual loss of fines, with the footway behind the wall continuing to drop. The area just south of the Harbour Master’s office showed a marked “dish shape,” and a void was present below the steps. Vertical cracks extending into the rear of Wall B further indicated its poor condition. Investigations revealed that every time the tide came in and out, the way the walls moved had caused fines to be washed away from behind and under the wall, leading to void pockets behind the wall. While emergency works in March 2024 had provided a new toe to the wall with steel sheet piles and granular fill as a first step, a more comprehensive improvement was urgently needed to stabilise the wall and harbourside while a long-term scheme design was developed. The scope of the required solution needed to address the voids and improve ground characteristics to inform WSP’s permanent repair designs, extending coverage to the curved section of Wall B and further west behind the sheet pile section.

Cracking and sinking

Customer Alternatives

Traditional methods for addressing ground instability, voiding, and settlement in such a critical and historically sensitive marine environment typically involve extensive and disruptive civil engineering works. Potential alternatives considered for a temporary improvement could include:

• Excavation and Backfilling: This would involve excavating the compromised ground behind the wall, filling voids with conventional granular or concrete materials, and then recompacting. This method is highly disruptive, requires significant plant and personnel, and would necessitate prolonged closures of the harbourside, impacting local businesses and community access. It would also likely involve “dismantling the wall and having to support the ground,” a complex and costly undertaking.
• Mass Concrete Underpinning/Grouting: Injecting large volumes of traditional cementitious grout or constructing mass concrete plinths could be considered. While effective, these methods are often slow, can be messy, and may involve significant dewatering if performed below the water table, adding complexity and environmental risk.
• Piling: Driving new piles to support the wall is a long-term solution but is highly disruptive, noisy, and time-consuming, making it unsuitable for a temporary improvement where minimal disruption is key. A critical concern with traditional piling or other vibratory methods was the risk of further damage; any vibration down through the ground would have lost the wall.

These alternatives often entail substantial logistical challenges, prolonged site occupation, and a higher carbon footprint due to the materials and processes involved.

West Bay Harbour

Why Geobear

Dorset Council opted to engage Geobear due to their expertise and experience in delivering ground improvement at complex sites. Using an engineered design with a specialist geopolymer injection method, Geobear offered distinct advantages over traditional approaches, particularly for a stabilisation solution in a live harbour environment:

• Minimally Invasive & No Vibration: Geobear’s solution is non-disruptive, causing less disturbance to residents and shop owners. Crucially, it involves no vibration, which was a primary concern given the fragile state of the wall and adjacent structures. This eliminated the risk of further damage that traditional vibratory methods would pose.
• Speed of Application: The rapid curing time of geopolymer (less than 60 seconds) and efficient injection process significantly reduce project timelines compared to traditional methods, enabling works to be done in summertime when there is a lot of tourism in the area.
• Environmental Benefits (Low Carbon): Geobear’s solutions are certified to emit significantly less carbon compared to traditional methods. A previous study by Carbon Footprint Ltd and KLH Sustainability found that a Geobear approach for asset maintenance in the rail sector could lead to a 75% reduction in carbon emissions. The geopolymer is also leachate-free and has no impact on aquatic ecosystems, making it suitable for a marine environment.
• Precision and Control: The controlled application of expanding geopolymer allows for precise ground improvement and void filling without imposing additional loads on the existing wall. Dynamic probing (DP30-20) can be used for pre- and post-verification of ground improvement.
• Self-Contained System: The lorry-mounted, self-contained injection unit with a 120m hose minimises the site footprint and logistical requirements.
• Avoids Wall Dismantling: The method avoids dismantling the wall and having to support the ground, a major advantage over more invasive alternatives.
• Collaboration: Geobear emphasises working collaboratively with clients and designers (like WSP), ensuring the solution integrates effectively with broader scheme designs. The client also highlighted that Geobear had worked well together as a team collaboratively with Dorset Council, Dorset Highways, and G. Barrow.

Drilling

The Geobear Solution

Geobear designed a geopolymer injection solution to improve the ground both below and behind the existing harbour wall, addressing the settlement and voiding issues. The solution involved:

Injection Layout: Drilling a series of small holes through the asphalt on a 1m grid pattern for behind-the-wall treatment and through the foundation at seabed level below the wall.

Materials: Two specialist Geobear geopolymers were used for ground improvement and void infill. The choice of geopolymer would be based on specific site conditions, with faster-reacting geopolymers considered for water-filled voids to ensure rapid curing. The geopolymer was injected five metres down into the ground, which is lower in the seabed, to fill all the voids.

Methodology:

• Injection tube locations were marked out as per the injection plan.
• Injection points were pre-drilled to the design depth, and steel injection tubes were inserted.
• Geopolymer was pumped via hoses from the self-contained injection unit to the top of the injection tube, mixing as it was pumped into the surrounding soil.
• Works were planned to utilise low tide for access to the scaffold platform area for injections on the harbour wall foundations, and high tide for works on the upper tarmac surface behind the wall.

Monitoring & Verification: Pre- and post-dynamic probing (DP30-20) were undertaken by Geobear to verify the efficacy of the ground improvement. Dorset Council provided full-time, live monitoring of the harbour wall, with injections halted if any movement beyond an agreed magnitude was observed.

The programme duration was 3 weeks.

Injection tubes

Carbon Savings

Geobear’s geopolymer injection method offers significant carbon savings compared to traditional ground improvement techniques. Geobear’s previous carbon study, certified by Carbon Footprint Ltd and KLH Sustainability, indicates substantial reductions. For instance, a report found that using a Geobear approach for asset maintenance in the rail sector could lead to a 75% reduction in carbon emissions compared to a complete reconstruction.

Traditional alternatives like excavation and backfilling, or extensive concrete underpinning, involve:

• Higher material production emissions: Cement and aggregates have a high embodied carbon footprint.
• Increased transport emissions: More material needs to be transported to and from the site, often requiring larger vehicles.
• Greater machinery use: Excavators, dump trucks, and other heavy plant machinery operate for longer durations, consuming more fuel.
• Waste disposal: Excavated material often needs to be transported to landfill, incurring further emissions.

Geobear’s self-contained, lorry-mounted injection unit and the minimal material volume required for effective ground improvement inherently lead to a much lower carbon footprint, primarily limited to transport and the chemical reaction of the geopolymer itself.

Time Savings

The Geobear solution took 3 weeks to complete, based on a single injection and drilling team working midweek days with a minimum 8-hour window.

In contrast, traditional alternatives would likely involve:

• Excavation and Backfilling: This could easily extend to several months, requiring significant lead time for planning, permits, and coordination of heavy machinery.
• Mass Concrete Underpinning/Grouting: This would also be a multi-month project, factoring in curing times, sequential pouring, and potential dewatering operations.
• Piling: A piling operation would be even more protracted, potentially taking many months to a year or more, depending on the scale.

Impact on the local community and client:

The rapid deployment and non-disruptive nature of the Geobear solution had a profound positive impact:

• Minimised disruption to harbour operations: The ability to work during low tide and from the upper asphalt surface during high tide meant the harbour could remain largely operational, avoiding prolonged closures.
• Reduced impact on local businesses: West Bay Harbour is a commercial and tourist area with a kiosk and the harbour master’s office nearby. A multi-month traditional construction project would severely impact local businesses reliant on harbour access and foot traffic. The ability to perform the work during summer, when there is a lot of tourism in the area, was a significant benefit.
• Faster resolution of safety concerns: The critical nature of the wall’s instability meant that a swift solution was essential to ensure public safety and allow Dorset Council to manage the adjacent area closures more effectively. Geobear’s speed provided this rapid response.

Cost Savings

The indirect cost savings using Geobear are significant:

• Reduced operational disruption costs: For Dorset Council and local businesses, avoiding prolonged harbour closures translates into substantial savings from lost revenue, compensation claims, and public inconvenience.
• Lower temporary works costs: Less need for extensive temporary traffic management, public access diversions, and scaffolding (beyond what was already in place or minimal requirements for Geobear’s specific access needs) due to the non-invasive nature.
• Minimised project management overhead: A shorter project duration (3 weeks vs. several months) reduced the internal project management, supervision, and administrative costs for Dorset Council.
• Avoidance of emergency escalation and catastrophic failure: Avoided the immense cost of reconstructing a collapsed harbour wall, making the Geobear solution suitable for the budget.