Category: Construction specialty · Reviewed by Amy Price, Account Executive · Last reviewed 2026-06-05
Tunnel construction insurance is the specialist subset of Contractors All Risks cover for tunnelling and underground works, with bespoke wordings reflecting the unique risks of tunnel boring machine (TBM) operations, conventional drill-and-blast tunnelling, sprayed concrete lining (SCL) and other underground construction methods.
Category: Construction specialty Also known as: tunnelling insurance, TBM insurance, underground construction insurance First codified: Lloyd’s wordings from c.1970s; modern wordings refined after the 1994 Heathrow Express collapse and the 1999 Joint Code of Practice for the Procurement, Design and Construction of Tunnels Related legislation: Construction (Design and Management) Regulations 2015 [1]; Borehole Sites and Operations Regulations 1995 [2]; Health and Safety at Work etc. Act 1974 [3]
Tunnel construction is among the highest-risk classes of construction work. The combination of ground uncertainty, complex temporary works, expensive specialist equipment (tunnel boring machines costing £40m–£100m+), substantial third-party exposure (ground movement affecting overlying buildings and infrastructure) and limited room for error in design or execution creates a distinctive risk profile that justifies specialist insurance treatment [4][5].
The principal sections of a tunnel construction insurance policy mirror those of a standard CAR policy but with adapted wordings:
Section 1 — Physical damage to the works: cover for the permanent works (the tunnel structure), the temporary works, and (uniquely for tunnelling) the tunnel boring machine itself as a substantial item of project equipment. The wording typically addresses TBM damage from face collapse, mixed face conditions, TBM jam and water ingress.
Section 2 — Public liability: third-party legal liability for personal injury and property damage arising from tunnelling operations, including ground movement claims from overlying property owners. Limits per occurrence are typically £100m–£250m for major tunnel projects, reflecting the substantial third-party exposure.
Section 3 — Existing structures and surrounding property: cover for damage to overlying buildings, surface infrastructure (roads, railways, utilities) and subsurface infrastructure (existing tunnels, basements, foundations) caused by tunnelling. The cover is often a key contractual requirement.
Section 4 — Equipment and TBM: separately scheduled cover for the contractor’s specialist plant, with the TBM as the highest-value single item.
Section 5 — Delay in start-up: extension responding to the employer’s loss of expected revenue from a tunnel completion delay caused by a physical-damage event.
The Joint Code of Practice for Risk Management of Tunnel Works (TCoP), originally published 2003 and most recently revised 2024, is the industry standard risk management framework expected by underwriters. Compliance with the TCoP is normally a precondition of cover [4][5][6].
The Construction (Design and Management) Regulations 2015 apply to tunnelling as to all construction works, with specific attention to the high-risk character of underground operations. The Health and Safety at Work etc. Act 1974 and supporting regulations (including the Confined Spaces Regulations 1997 and the Work in Compressed Air Regulations 1996) apply to specific tunnelling activities [1][3][7].
The Borehole Sites and Operations Regulations 1995 apply to certain tunnelling operations involving boreholes ancillary to the main tunnel works. The Mines Regulations 2014 apply where tunnelling operations fall within the definition of a ‘mine’ under the Coal Industry Act 1994 (rare in modern infrastructure tunnelling but historically significant) [2][8].
For major infrastructure tunnels (such as HS2, Crossrail, the Thames Tideway Tunnel), the project is typically authorised under specific primary legislation (the High Speed Rail (London - West Midlands) Act 2017 for HS2; the Crossrail Act 2008; specific provisions of the Planning Act 2008 for other NSIPs). The authorising Act may include specific compensation provisions for affected property owners that interact with the third-party liability cover under the CAR programme [9].
The Joint Code of Practice for Risk Management of Tunnel Works (the ‘TCoP’) is the principal industry standard, jointly published by the British Tunnelling Society, the Association of British Insurers and the International Tunnelling Insurance Group. The 2024 revision (TCoP 2024) reflects updated industry practice and lessons learned from recent projects. Underwriters typically require contractual confirmation of TCoP compliance as a condition of cover [4][5][6].
A major tunnel project’s CAR programme is typically arranged at financial close with the cover attaching at start of tunnelling works. For very large projects (HS2 with its multiple tunnel sections; the Thames Tideway Tunnel with its 25km super-sewer beneath London) the cover is arranged on an Owner Controlled Insurance Programme basis with the project promoter procuring the cover. For smaller tunnel projects (utility tunnels, mining access tunnels, road tunnel sections) the cover is typically arranged by the principal contractor [4][5].
Underwriting for tunnel projects is among the most technically demanding in the construction insurance market. Underwriters and their consulting engineers conduct extensive due diligence on the tunnel design, the ground investigation, the selected tunnelling method, the TBM selection (where applicable), the contractor’s experience with similar projects, the risk register and the TCoP compliance plan. Premium is typically expressed as a rate per linear metre of tunnel or per £100 of contract value, with rates significantly higher than conventional CAR reflecting the elevated risk [4][5].
Claims handling for tunnel losses involves specialist construction loss adjusters with tunnelling backgrounds, working alongside the contractor’s project team, the consulting engineers and (often) independent expert panels. Major claims include TBM damage from face collapse or mixed face conditions, water ingress and inundation, sinkholes and surface subsidence affecting overlying property, and (rarely but with severity) tunnel collapse. The 1994 Heathrow Express NATM tunnel collapse and the 2002 Lausanne metro tunnel collapse are landmark losses that shaped market wordings and TCoP requirements [4][5].
TBM tunnelling: the dominant method for major infrastructure tunnels. Wordings address TBM jam, face collapse, mixed face conditions and TBM withdrawal scenarios.
Conventional drill-and-blast tunnelling: typically used for mountain road and rail tunnels and certain civil tunnels in hard rock. Different exposure profile (lower equipment values, higher dependence on ground support).
Sprayed Concrete Lining (SCL) / NATM tunnelling: increasingly common for stations, junctions and intermediate-diameter tunnels. The 1994 Heathrow Express collapse highlighted the specific risks of SCL methods.
Pipe jacking and microtunnelling: for utility tunnels and smaller-diameter works. Lower per-project values but different equipment and method risks.
Cut-and-cover tunnelling: for shallow urban tunnels and station boxes. Combines conventional civil engineering risk with significant third-party exposure to adjacent infrastructure.
Immersed tube tunnelling: for sub-fluvial crossings (e.g. underwater tunnel sections of road crossings). Bespoke wording reflecting marine elements, prefabricated tube manufacture and float-and-sink installation operations.
Compressed air working: increasingly rare in modern tunnelling but where used, requires specific cover for the additional health and safety risks (decompression illness, equipment failure).
Maintenance period and defects liability: cover for the maintenance period following completion, addressing the residual risk of tunnel defects becoming apparent during early operation.
A UK water utility is constructing a 12 km sewer tunnel under London with a contract value of approximately £680m and a construction period of 48 months. The cover is arranged on an OCIP basis with the utility as project promoter procuring the programme. CAR cover provides the full contract value plus £200m for third-party property (reflecting the substantial overlying property exposure in central London), £150m for public liability and £85m for the TBM and specialist equipment. The CAR programme is placed in the London, Bermuda and continental European markets, with annual premium of approximately £18m across the construction period. TCoP 2024 compliance is documented through the project’s risk register and quarterly underwriter review meetings. Figures in this example are illustrative.
This entry is part of the Apex Insurance Wiki. Last reviewed by Matt Bartlett on 2026-06-05. Next review: 2026-12-05.
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