Sinkholes have been headline news in the UK in recent months. In Surrey and South Wales they have damaged infrastructure and almost destroyed houses. Alarming events for the residents advised to evacuate their homes. Sinkholes are not new phenomenon, but they are expected to increase in frequency. Climate change is a factor and in particular very heavy rainfall. The saturation of ground and erosion of soluble material below the earth's surface creates voids. When these voids collapse you suddenly have a sinkhole at the surface.
While the risk profile for sinkholes varies nationwide (parts of South Eastern and North Eastern England are considered more vulnerable due to underlying beds of chalk and gypsum) the potential for swift catastrophic collapse in a built-up area, focusses attention on the vital role of geotechnical engineers in investigating ground conditions for development land.
Let's remind ourselves of what geotechnical engineers do. Broadly speaking, they investigate and advise their clients on the composition and engineering properties of below ground material. Their expertise is called upon during the early stages of construction projects, when potential sites and proposed works are being assessed. Their advice interweaves with the development of foundation designs by structural and civil engineers (geotechnical engineering is a subset of civil engineering), and they can be tasked with monitoring works during the groundworks phase. Geotechnical engineers analyse existing geological records as well as the results of intrusive investigations which they design and supervise, such as boreholes, trial pits and dynamic probes.
Where there are risks of differential ground settlement or indeed voids/sinkholes, geotechnical engineers are called upon to investigate and advise on ground improvement works. They also provide expert evidence in professional negligence claims concerning such issues.
The Government is currently shaking up the planning system. The objective is increased development in the newly classified 'grey belt', which essentially relaxes planning policy for some existing green belt sites. The drive to build housing stock and commercial premises on previously undeveloped land could also drive an increase in the number, type and scope of claims involving geotechnical engineering issues.
Projects located in higher risk areas coupled with wetter weather may well lead to an uptick in property damage and construction disputes arising from sinkholes and associated differential settlement issues. There will be an increased focus on ground risk at the outset of projects. However, not every project will be resourced and financed in the same way. Where the extent of a ground investigation is constrained, or something is overlooked, severe consequences may follow.
Take a housing developer who appoints a geotechnical engineer to investigate a grey belt site on the outskirts of a town. The site is underlain by unstable chalk with subterranean voids and cavities (known as dissolution features). Its true risk is undetected before substantive works are carried out. Although, it could have been had the developer not relied on an intrusive ground investigation that was restricted in scope and had its engineers properly appraised existing data available for the site. The project is at an advanced stage. Two sinkholes occur in close proximity following heavy rain. They damage the foundations of several plots and affect drainage installations, placing the project in jeopardy as urgent investigations and remedial works are considered.
The developer sues his geotechnical engineer. Both sides need geotechnical engineers to assist with considering their case on liability regarding the scope of the original ground investigation. But they also need geotechnical advice to appraise quantum and especially the reasonableness of the developer's proposed remedial scheme. In light of the now apparent ground risk, the developer has elected to demolish and rebuild an entire phase of the development due to concern regarding the adequacy of its foundations. Other consequential losses, such as increased financing costs, are also pursued. The developer seeks damages in the alternative for diminution in value of the site, i.e. the difference between the site's value with its ground issues and what it would have been worth without those. This makes for a fraught and complex dispute.
Notwithstanding the input of geotechnical engineers, where pockets of undeveloped land in higher risk areas are being investigated - sometimes at speed, and with costs reductions in mind - one can easily see how such geotechnical claims could proliferate in the coming years. Geotechnical engineers will be in greater demand at the front end of projects to assess the ever-changing landscape of geotechnical risk, but also at the back-end when things go wrong and claims result.
The apparently increasing frequency of sinkhole events has shone a light on the appraisal of ground stability risk by geotechnical engineers. It has brought home the potentially catastrophic consequences for buildings and infrastructure where there is a sudden ground collapse. As we look to the future, the combination of increased levels of heavy rain and development in 'uncharted' territories means geotechnical engineering challenges are set to increase. As such, we anticipate a greater number of disputes in this arena.
