Geopolymer Injection at the Dock: Ground Improvement to Facilitate Loads
Overview
A prestigious yacht manufacturer faced significant challenges at their dockyard. Accustomed to handling the increasing size and weight of super yachts, their facility began experiencing uneven sinking of concrete slabs due to water ingress and the subsequent softening of soils. This issue threatened the structural integrity of the facility and posed a risk to the valuable yachts under construction.
A key issue was the movement of the yachts in their cradles. Where the ground was uneven due to the sinking concrete slabs, there was a significant risk to the yachts as the cradles traversed the site. The client required an immediate solution to mitigate this risk and also to improve the ground strength throughout the site.
The Issue
An independent site investigation was completed to assess the load capacity of two shipyards. One shipyard featured a 300mm-thick concrete slab cast in bays, which had numerous cracked areas, particularly at the edges and corners of slabs. The second shipyard had a 150mm depth of block paving over a 200mm concrete slab, with various depressions where mobile cranes had been positioned.
Due to the varying construction, the load capacity of each shipyard differed, with cradle capacities ranging between 100-250 tonnes, assuming the underlying soils could support the loads. Three boreholes were commissioned which revealed soft to very soft layers, inadequate to support the loadings without potential for significant movement, which could cause failure of the concrete slabs. The recommendation was ground improvement with Geobear.
The Solution
The client needed a solution that would address the immediate ground instability and allow for continuous operation without disrupting their yacht production. An alternative piled solution would have required the facility to be inoperable for many months to accommodate a piling rig, whereas Geobear uses a minimally disruptive ground improvement method using expansive geopolymer resin injected through steel tubes.
Injection with minimal disruption
The design was delivered in multiple phases and used Geobear’s geopolymer injection technique to improve the ground. Several areas were targeted in each of the two shipyards, with a requirement to provide verification of ground improvement by dynamic cone penetrometer testing.
Geobear’s ground improvement solution was designed by their in-house engineering team using the site investigation data provided. Prior to the full scope, a trial area was treated to verify the design solution was fit for purpose. Following the successful trial, Geobear moved onto the delivery of the full scheme of works.
Water forced out of ground by expansive geopolymer
The full scope of works would see geopolymer injections at multiple depths down to 4.5m below the slabs in a designed matrix. The site delivery teams followed the pre-determined injection plan across and used a number of different geopolymer materials. This approach takes into consideration the ground conditions and uses varying material specifications to ensure competence is achieved.
During the delivery phase the slab is monitored for movement. Laser levels recorded movement in increments of 0.5mm and provided visual verification of improvement.
Benefits
Using the Geobear solution ensured operational continuity. The project was planned to ensure no interruption to the yacht manufacturing process, allowing the client to maintain its delivery programme.
Furthermore, there were several environmental aspects to consider. The chosen solution had to be environmentally friendly, with quick curing times to prevent leakage into the surrounding water bodies. The Geobear geopolymer resin expands almost immediately on installation, meaning no excess material will migrate into the surrounding water bodies. Additionally, the geopolymer resin has been tested by the Environment Agency and proved to be inert.
No disruption, holes filled.
Results
Dynamic cone penetrometer (DCP) testing was used to understand improvement in ground strength. In completing tests before and after Geobear treatment, the DCP results provided an insight into the underlying ground conditions and also clarified the allowable bearing capacity of the soil at 100mm increments.
DCP testing was carried out using Pagani penetrometers with 30kg falling weights. By measuring how many “blows” are required to drive a rod 100mm into the soil to be tested, a measurable indication of strength can be gained.
The DCP results across two locations showed ground improvement of 28% – see figure 1.
In summary, the Geobear design resulted in:
- Immediate Ground Improvement: The injection process led to significant improvements in soil stability, with an increase in bearing capacity.
- Operational Efficiency: By avoiding the need for extensive excavation and construction, the client could continue its operations without any downtime.
- Environmental Benefits: The environmentally friendly nature of the geopolymer injection method ensured compliance with regulatory standards and safeguarded the surrounding marine ecosystem.
DCP result indicate 28% improvement
