Summary
An oil line in the cellar was accidentally damaged, causing an oil leakage onto the floor, contaminating the
stonework and underlying soils. During evaluation, it was discovered that the cellar lacked foundations,
necessitating excavation and underpinning to create a stable base for reconstruction. The project aimed to
remove contaminated material, install proper foundations, and implement ventilation measures to mitigate
volatile organic compounds (VOCs).
Methodology
- Initial Assessment
– Identified accidental oil leak and contamination of cellar floor, subsoils and 500mm thick stonework walls.
– Determined absence of foundations, requiring underpinning too allow for the excavation of the floor and removal of the walls. - Planning and Design
– Structural Engineer appointed to design underpinning solution.
– Drawings prepared and approvals obtained.
– Building Control engaged for compliance checks throughout the process. - Execution
– 5 Underpinning bays were set out as per the drawings, excavated and 30-40 high strength concrete as specified was then poured, finishing 75mm below the base of the existing wall structure, using a concrete vibrating poker to maximise the structural strength of the bay. 48 hour stand downs were instigated, then using a 3:1 mix ratio of dry pack. The dry packing approach was chosen to prevent encapsulating any remaining contaminants within the lower parts of the existing walls allowing for safer remediation and future wall removal.
– The floor was excavated to the required depth, removing the contaminated subsoil.
– Samples of the soils at optimum depth were sent to the lab for confirmation the contamination had been removed.
– Installed passive vents behind the underpin bays allowing ventilation of any VOCs from behind the bay, into a void former beneath the gas membrane and directly linked to a ventilation stack that expels any VOCs to a safe outdoor area.
– A gas membrane was installed, which also acts as a damp proof membrane.
– Reinstated the floor and walls according to building control regulations.
Has it been evaluated? How successful has it been?
The project was completed successfully, delivering a structurally sound and compliant solution.
Contaminated soils were safely removed, and robust underpinning foundations were installed to restore
stability to the cellar. The work was executed efficiently. The result was a clean, solid concrete base ready
for reconstruction, with all objectives achieved smoothly and to a high professional standard.