Credit: 安琦 王/Adobe Stock

Emilio Linde-Arias

Exponent, London

Tom Smith

Hogan Lovells, London

Mark Crossley

Hogan Lovells, London

Why geotechnical design risks need to be managed differently

This article explains how the uncertainties associated with ground conditions mean that liability for geotechnical engineers is handled differently from that of other designers. It will help construction industry players and their advisers understand how the heightened risks are approached during contract negotiations, live projects and disputes. While these risks need to be addressed wherever construction projects take place, the focus of this article is on risk management in English law-governed design contracts.

What is geotechnical engineering?

Geotechnical engineering concerns the behaviour of earth materials. Geotechnical engineers analyse soil, rock and groundwater conditions and recommend how structures should be designed and built in light of this information. Buildings, bridges and tunnels rely heavily on this specialism and many geotechnical construction disputes involve claims against designers.^[1]

The contractual design standard for professionals

In design contracts, the parties agree the designer’s standard of care. English law has two principal standards: to use reasonable skill and care; and to guarantee fitness for a predefined purpose. One or the other is usually chosen, with reasonable skill and care the most common. The Bolam test (from the case of Bolam v Friern Hospital Management Committee [1957] 1 WLR 582) sets this out as:

‘the standard of the ordinary skilled man exercising and professing to have that special skill. A man need not possess the highest expert skill […] it is sufficient if he exercises the ordinary skill of an ordinary competent man exercising that particular art’.

Falling below this standard will render the designer’s work negligent. Conversely, a design professional will not be negligent if they follow a practice accepted as proper by a responsible body of people skilled in that particular type of design.

A fitness for purpose obligation is stricter. It requires designers to ensure their design achieves a particular result when the completed works are used. If the specified outcome is not reached, designers will be in breach of contract, whether or not they behaved negligently. The English Court of Appeal case of Greaves & Co (Contractors) Ltd v Baynham Meikle & Partners [1975] 1 WLR 1095 shows that if designers are aware of the purpose of works, they assume a duty to warrant they will be fit for that purpose, unless the risk is allocated differently in the contract. In 1980, the House of Lords confirmed in Independent Broadcasting Authority v EMI Electronics Ltd [1980] 5 WLUK 151 that a design and build contractor must carry out any design work for which it is responsible so that the works when used are fit for any purposes made known to it (unless the contract states otherwise).

Liability shaped by the nature of the risks associated with ground conditions

During the pre-construction stage, geotechnical investigations assess the type of ground and its expected behaviour during construction and after final design implementation.

Geological variations make it impossible to eliminate all ground condition uncertainty, especially on projects with a significant underground element. Geotechnical design involves making assumptions to account for incompleteness in the geological information. But what happens when less-favourable-than-assumed geological conditions are encountered? In such circumstances, when will the designer have failed in its design obligations, including its duty to interpret available site data correctly?

The two main types of uncertainty in ground conditions shape the extent and treatment of a geotechnical engineer’s liability.

Ground behaviour

First, even if the geology is reasonably well known, soil and rock behaviour is difficult to predict. Whereas materials like concrete or steel are produced synthetically under controlled conditions, soil and rocks occur naturally and are inherently more variable due to their geological origin and deposition.

The European standard for geotechnical design, Eurocode 7 (EC7), guides the design of structures and foundations in soil. It states that the characteristic value of parameters for the soil required for the design (such as the soil’s strength and deformability) ‘shall be selected as a cautious estimate of the value affecting the occurrence of the limit state’, the ‘limit state’ being when a structure or foundation no longer performs its intended function and so may collapse or fail. The level of cautiousness depends partly on the variability of the geology, and the quality and number of investigations carried out at the site.

As field and laboratory investigations are sometimes limited, obtaining meaningful statistics from them is not always possible. Therefore, they must be combined with knowledge of the actual site, which may be drawn from correlations to sites with similar geotechnical conditions or assessments made by experts. These limitations when choosing soil parameters can result in the same data leading to different characteristic values being selected, depending on the engineer.^[2]

The subjectivity of the process of the selection of parameters could result in contradictory expert opinions and make it hard for a court to apply the Bolam test to decide which assumptions an ordinary geotechnical engineer would make about ground properties. Michael Hyde & Associates Ltd v JD Williams & Co Ltd [2000] 7 WLUK 165 addressed this issue. Williams engaged Hyde for ‘all architectural, clerk of works, surveys, quantity surveying and structural engineering services’ for the conversion of mills into warehouses. After a heating system was installed, the textiles stored by Williams discoloured. The Court of Appeal held that ‘where the profession itself embraces more than one tenable view of acceptable practice, competence will not be measurable by a single forensically determined standard; so that where there is more than one acceptable standard, competence has to be gauged by the lower or lowest of them’.

Therefore, where there is a range of views as to the correct standard of reasonable skill and care, the lower or least strict standard will determine whether a geotechnical engineer’s conduct was negligent.

Inconsistent conditions

The second uncertainty is ‘spatial variability’, meaning that ground conditions are inconsistent and therefore unpredictable across a site. The lack of unfavourable sub-surface material during field investigations does not imply its total absence. This causes geotechnical engineers to be wary of the assumptions they make about the state of the ground, even where test pits have been dug on site. How does this fit with a designer’s obligation to consider how to eliminate or mitigate foreseeable risks, which encompasses a duty to warn of foreseeable risks due to unfavourable conditions that could cause economic loss or physical damage? Several cases provide guidance.

In Mirant Asia-Pacific Construction (Hong Kong) Ltd (No 2) v Ove Arup & Partners International Ltd [2005] EWCA Civ 1585, the owner Mirant claimed that Arup’s negligent power plant design, which had not anticipated adverse site geology, led to two boiler foundations failing, which delayed completion.

The Court of Appeal agreed with the first instance judge’s findings that Arup was negligent because the design agreement required Arup to inspect the soil and rock around the foundations to verify the design assumptions and that therefore:

‘[…] absent an explicit warning and disclaimer, it would not be sufficient for a designer, whose initial design is based on an unverified assumption, to leave it to the client alone to obtain and evaluate the additional information. The designing engineer is responsible for the design, and he should normally see to it that the necessary additional information is conveyed back to him, so that he may judge that it is sufficient for the purpose of his design’.

Crucial was whether Arup’s duty to exercise the reasonable skill and care of an ordinarily competent engineer with experience in this type of work created an obligation to verify design assumptions. The Court of Appeal held that it did. Geotechnical designers must not only verify information but, importantly, also warn of the need for verification.

In Overseas Tankship (UK) Ltd v Miller Steamship Co Pty Ltd [1967] 1 AC 617 (commonly known as the ‘Wagon Mound’), Lord Reid illustrated the extent of the designer’s duty to warn or alert in terms of not only the probability of occurrence of the risk, but also its impact. The duty extends to unlikely events that could significantly affect the project, unless the cost of elimination outweighs the possible impact of the risk:

‘[…] it does not follow that no matter what the circumstances may be, it is justifiable to neglect a risk of such a small magnitude. A reasonable man would only neglect such a risk if he had some valid reason for doing so, eg, that it would involve considerable expense to eliminate the risk. He would weigh the risk against the difficulty of eliminating it… [A] person must be regarded as negligent if he does not take steps to eliminate a risk which he knows or ought to know is a real risk and not a mere possibility which would never influence the mind of a reasonable man’.

Eckersley v Binnie & Partners [1988] 2 WLUK 177 examines the foreseeability of geological and geotechnical conditions. The defendant consulting engineer designed a tunnel aqueduct into which methane had leaked from a 1,000-metre deeper underground reservoir of gas resulting in a fatal explosion. Eckersley successfully argued that the designers were negligent in not having foreseen the risk that methane might leak into the tunnel during or after construction based on the geology of the area and the existing literature. Lord Justice Russell in the Court of Appeal confirmed the applicability of the Wagon Mound:

‘I am satisfied that the risk of its being encountered was such that, following the tests laid down in the Wagon Mound […]
it was incumbent upon the first defendants to eliminate the risk before confirming the design.’

Such judgments mean that geotechnical engineers now routinely include disclaimers that they are not responsible for ground-related uncertainties that might affect progress or risk the integrity of the works.

How the observational method can blur design risk allocation

The observational method, a design technique in EC7, is also used by geotechnical engineers to manage risks stemming from spatial variability. Commonly used in tunnel projects, it allows design to be updated continually during the construction process. Uncertainties are reduced as new information emerges.

The Scottish case of SSE Generation Ltd v Hochtief Solutions AG [2018] CSIH 26 (which has non-binding but persuasive effect in English courts) involved a hydroelectric scheme tunnel collapse and addressed the concurrent duties of fitness for purpose and of reasonable skill and care for a design created by observation.

The drawings in Hochtief’s design and build contract stated that ‘rock supports [were to] be installed to the extent required to meet the rock conditions encountered’ and required that the tunnel lining be selected from a menu of ‘classes of support’ depending on the ground conditions (a fitness for purpose requirement). However, Hochtief’s design duty under the contract terms was one of reasonable skill and care. The first instance judge described this term as ‘an important break on liability’ and held that Hochtief had exercised reasonable skill and care in designing the tunnel and therefore was not liable. This was reversed on appeal, where it was held that Hochtief’s on-site decisions using the observational method (referred to as ‘engineering judgment’ below) amounted to design implementation, which, while not part of the pre-construction design process, were still part of the designer’s design responsibility:

‘What appears to have gone wrong was in the implementation of that design, probably in the failure to identify (at the rock face in the tunnel) rock conditions requiring Class III and Class IV support, resulting, as the judge found, in insufficient support being provided to areas of erodible rock […] [The reasonable skill and care obligation] therefore does not come into play at all. It does not relieve the defenders from liability […] The fact that engineering judgement was to be applied at that implementation stage does not detract at all from the fact that the design itself, as agreed and accepted, specified what measures were to be taken to minimise the risk from the presence of erodible rock.’

The courts are yet to provide guidance on how they determine whether geotechnical design decisions are taken during the design or the design implementation stage. Without this, it is unclear, in the design and build context, who is liable as between a geotechnical engineer producing design drawings (but with a continuing duty to use reasonable skill and care), and a contractor carrying out design continually, using the observational method. To ensure their design is properly implemented and to avoid long and costly disputes with builders, geotechnical engineers should therefore document their design process, including any assumptions made, and be involved throughout the construction stage.