Tunnelling and Shaft Contractor Insurance

The difference between tunnelling and almost every other construction activity is that the damage happens above, to people who are not involved.

Removing ground causes the surface to move. A well executed drive produces predictable, small settlement; a face that loses ground, an over-excavation, a void left behind a lining or a drive through unexpected strata produces more. What sits above is houses, shops, roads, drains, railways and utilities, and the owners are neighbours rather than clients. A terrace with existing cracking will crack further. A sensitive structure will object to movement well within normal tolerance.

So three things carry the weight. A condition survey of every structure within the predicted zone of influence, done before any excavation, with crack gauges, photographs and position references. Monitoring with agreed trigger and action levels so movement is detected and responded to during the drive rather than discovered afterwards. And a policy that genuinely covers damage arising from ground movement, because many wordings restrict exactly that, and a tunnelling contractor with such a restriction is uninsured for the thing most likely to happen.

Every tunnelling contractor knows this and it still causes the surprises, because a tender is priced on a report and driven through reality.

A ground investigation gives boreholes and laboratory results at intervals. Between them can be anything: a lens of sand in clay, an old well, a buried structure, a service nobody recorded, a perched water table, contamination, or ground that is stiffer or softer than classified. The machine finds all of it, at the face, with a drive underway and limited options. A change in ground can mean a loss of face stability, a change in settlement behaviour, a slower rate that threatens a programme, or damage to a machine.

Which makes the contractual position on ground conditions as important as the technical one. Establish who carries the risk of conditions differing from the information provided, in writing, before pricing rather than after encountering it, because it is the single largest commercial variable in the work. Technically, probing ahead of the face where conditions are uncertain, monitoring that reveals behaviour early, and a defined procedure for stopping and reassessing rather than pressing on are what prevent a geological surprise becoming a collapse.

The employers' liability exposure here is as serious as any in construction and it is driven by the environment rather than the activity.

A tunnel or a shaft is a confined space with a single route in and out, containing machinery, electricity, water and an atmosphere that can change. The recognised hazards are inrush of water or ground, loss of face stability, fire and smoke in a space with no second exit, oxygen deficiency and gas accumulation, being struck by machinery in a confined area, and a lifting operation down a shaft. Somebody injured at the face cannot be carried out quickly.

So the controls an insurer asks about are the serious ones: atmospheric monitoring that is continuous rather than spot, ventilation designed and maintained, a rescue capability appropriate to the depth and length rather than a plan to call for help, controlled access with everybody accounted for, fire precautions underground including what is permitted to be taken down, and a defined emergency procedure that has been exercised. A contractor who can describe a tested rescue arrangement is presenting the part of the operation that matters most.

There is a loss specific to tunnelling that does not fit neatly into any single section of a policy.

A tunnel boring machine that cannot be advanced, because of ground, a mechanical failure, an obstruction or a collapse ahead of it, creates several losses at once. The machine itself may be very high value and may not be recoverable without sinking an intervention shaft, which means land, consent, excavation and time. The drive may need realigning or abandoning. The programme fails, downstream contracts are affected, and the client's project stops. None of that is a straightforward property claim.

So the position is worth establishing before a drive rather than during one. Whether the machine is insured at a value reflecting bespoke manufacture, whether recovery and intervention costs are contemplated, whether an abandoned drive and the works already constructed are covered, and how the policy treats a machine that is physically intact but inaccessible. Then the practical mitigation: probing ahead, a realistic view of where an intervention shaft could be sunk if needed, and ground treatment where the risk justifies it rather than where the budget allows.

Ground movement is the clause that decides it. We are an FCA regulated broker and will not tell you we are the best choice. These are the questions that decide it.