Key Operational Considerations
One of the key difficulties encountered on the site was how to take core samples in an areas with a high denisity of utilities.On this project we were asked to take a core sample from a service subway beneath Southwark Street, SE1 to establish its constructional makeup. The work required the co-ordination of a geophysics team and a confined access team. The complications of working in the area included a major carriageway, a subway, utilities, the need to work in a confined environment with a risk of elevated gas levels and the need to minimise disruption to local trade within an allotted two week window.
The first stage in the project was to consult with the client and the local stakeholders and define the specific risks, produce risk assessments, methods statements and a traffic management plan tailored to the conditions on-site. The northbound carriageway was closed and a contraflow was established. The road was excavated to expose the external surface of the subway. A confined access team, wearing appropriate PPE (Personal Protection Equipment) and carrying escape breathing apparatus, gained internal access to the subway approximately 0.5km to the north to establish the exact position where the external surface of the subway had been exposed, internally.
Numerous vital services were fixed to the internal surface of the subway in the vicinity of the proposed core sample, leaving only a very narrow window to position the core. The preferred position for the sample was established internally by the confined access team and geophysical techniques were used to pinpoint the location externally.
On inspection it was found that the tolerance level that the core sample would have to negotiate was 25mm either side of the hole diameter, running between cabling. A pilot hole was successfully drilled to confirm the location and finally the core sample was taken. All works were completed and reinstated within the allotted two week window, even though at one stage in the investigation the gas monitors indicated a build up of gas and the confined access team had to be withdrawn and the tunnel vented.