Project summary
As part of a warehouse development from Bericote Properties in Haydock, St Helens, EPG were approached to conduct a detailed thorough site investigation. This followed an initial investigation from a third party consultancy.
A more detailed view of the plot helped guide the client during the planning permission stages, giving additional context to what was required on site to progress the development.
Challenges
Following BS8485 guidance, the initial investigation reported that the site held a CS4 class risk due to over 71% methane being present in the ground. The potential sources of gas were mine gas from old coal mine workings and ground gas. In addition to this, the development had mine shafts and drainage which presented risks as with the potential for pathways for the gas to escape to the surface. With only this information to guide progress, the next steps would have been installation of a gas membrane and venting.
The solutions
By undertaking a mine gas risk assessment in accordance with CL:AIRE, conducting a detailed analysis of the ground gas regime and developing a conceptual model to show the client what was occurring under the site, we were able to demonstrate that there was no significant risk to the building and the risk of gas could be managed through additions to the floor slab construction, avoiding the need for a very costly alternative.
The results
The ground gas risk assessment and gas protection design from EPG, saved the client a significant amount of money, as even though the monitoring wells displayed 71% methane, this was only present between a very thin layer and underneath a significant thickness of compacted soil.
Grouting was completed to fill any voids and provided assurance that the mine and ground gas was not a significant risk. This assessment meant planning permission was secured with St Helens Council, and the project could begin.
By taking a unique approach to the challenges, EPG were able to provide a practical and cost-effective solution. All risks were safely managed and the client saved some money – a win-win for all!
