Geotechnical and Ground Investigation Insurance

Everything about geotechnical liability rests on a distinction that is obvious to the author and invisible to everybody downstream.

An investigation produces logs at specific locations, laboratory results on specific samples, and an interpretation. The ground between those locations is inferred. A structural engineer then designs foundations for the whole footprint, a contractor prices the earthworks, and a developer appraises the scheme, all on the interpretation. When a foundation meets soft ground, an obstruction, water or contamination that was not in the report, the question becomes whether the investigation was adequate for the scheme and whether the report made its limits clear.

So the wording of the report is the defence and it has to be deliberate. State the number and location of exploratory holes and that conditions between them are inferred, state the scope and what it was designed to establish, state what was not investigated and why, identify where further investigation is recommended before design or construction, and avoid language that reads as a description of the site as a whole. A report that recommends further work at a specific stage, and is ignored, is a very different document from one that is silent.

Ground investigation is frequently bought on price against a programme, and the consequence of a thin scope lands on the engineer.

A client wants a report quickly and cheaply, so four holes are agreed where the site and the scheme warranted twelve, no groundwater monitoring is installed, laboratory testing is minimal, and the deeper strata relevant to piling are not reached. The engineer reports on what was done. Two years later, when the foundations cost twice the allowance, nobody remembers the conversation about scope, and the report is the document on the table.

So the scope decision has to be recorded as a decision rather than absorbed as an instruction. A written proposal setting out what you recommend for the site and the proposed scheme, a clear statement of what a reduced scope will and will not establish, the client's acceptance of the reduced scope on the record, and a limitation in the report itself referring back to it. Where a scheme changes after the investigation, which is common, say in writing that the investigation was designed for the earlier scheme rather than letting the report be reused silently.

The geoenvironmental side of this profession carries losses measured in land value rather than in construction cost.

A report that concludes a site is suitable for a proposed use, or that a remediation strategy has been completed successfully, is relied on by a developer to build, a purchaser to buy, a lender to lend and a regulator to discharge a condition. If contamination is later found, the consequences are remediation of a developed site, a potential liability to occupiers, a planning condition not discharged, a property that cannot be sold or mortgaged, and in some cases a regulator's involvement. The figures bear no relation to the investigation fee.

So the limits of a conclusion need to be as explicit as the conclusion. What was sampled and where, what contaminants were tested for and which were not, the conceptual site model and the assumptions in it, the use the assessment relates to, and a statement that a change of use requires reassessment. On verification of remediation, be precise about what was verified and by what evidence. And watch reliance letters, because they extend who can sue you and for how long, frequently to parties you will never meet.

Unusually for an advisory profession, the act of gathering the information carries its own physical liability.

A borehole or trial pit can strike a buried service, damage a neighbouring structure through vibration or ground loss, destabilise a slope or an excavation face, and most significantly create a pathway: a hole through a confining layer that allows contamination or water to move between strata that were previously separate. That last one is a liability the investigation created rather than discovered, and it can affect a groundwater body or a neighbouring property. Rigs on site also bring the plant and access exposures of any ground works.

So the physical controls are the same as any intrusive ground work, and they are frequently weaker on an investigation because it feels like a survey rather than construction. Service clearance before every position with records, permits and scanning rather than reliance on plans, boreholes properly backfilled and sealed to prevent pathways, monitoring installations completed correctly, and reinstatement agreed. On a contaminated site, add the controls for working in it, and on a neighbouring structure, record its condition before drilling nearby.

What the report says about its own limits is the defence. We are an FCA regulated broker and will not tell you we are the best choice. These are the questions that decide it.