Tunnelling

Our expertise in Tunnelling includes pre-tender assessments, trouble shooting during construction, and resolution of claims for tunnels throughout the UK and abroad. Experience in this field has been gained from more than 30 drives.

Specific examples include:

Advising the main contractor during shaft sinking through slag with an associated vast ingress of water and the presence of toxic gas. Subsequently we designed and supervised a rescue strategy for an inundated tunnel boring machine (TBM); the strategy involved producing a grout curtain in highly permeable ground without grouting up the TBM. This proved to be highly successful, despite doubts from other specialists.

A scheme in Birmingham was progressing at less than half the anticipated rate due to groundwater problems producing aggressive slurry, which was damaging the TBM and making muck handling at surface extremely difficult. We provided advice to the main contractor and devised an innovative method of horizontal drainage holes up to 400m long. These radical methods greatly increased production by drying out the ground and turning the spoil from slurry to manageable silty sand. We also assisted the contractor in recovering the costs arising due to the unforeseeable ground conditions. This methodology was the subject of a paper published in Tunnels and Tunnelling.

Trouble shooting on construction methodology, alignment and ground investigation requirements for multiple short tunnels and pipejacks in South Wales for a gas pipeline.

Geotechnical consultancy was provided for a main drainage tunnel and shafts in challenging conditions in Barrow in Furness.

Providing geotechnical advice at tender stage for major schemes including crossing of the River Exe, power cable tunnels below London, main drainage tunnels in Belfast, etc.

Assisting with contractual issues for multi million pound schemes involving complex issues. These have been dealt with by detailed investigation including high quality laboratory testing, petrographic analysis, mapping and face inspections.

Advising on settlement issues surrounding tunnelling in built up areas such as London with sensitive structures and sensitive services. This has included tunnelling under optical fibre cables and gas mains with minimal clearance.

Mersey tunnel construction of emergency passages linking the two bores. This scheme involved working only during the night and dealing with low strength highly permeable rock with low clearance to the bed of the Mersey. We devised a scheme that was workable within the possession periods whilst still safeguarding the main bores. This involved the use of grouting and spiling bars. Trial holes were also drilled to measure hydrostatic pressure and flow rates prior to the breakout. These measures were adopted in preference to the more costly approaches of freezing or compressed air proposed by other tenderers. This project was reported in Tunnels and Tunnelling magazine.