Mike Reeve, geotechnical director at SLR Consulting, believes that an increase in the understanding of what lies beneath the ground is pivotal if we are going meet the UK’s requirements for housing and infrastructure.
The latest guidance from the National House Building Council (NHBC) will undoubtedly raise challenges for landowners, housebuilders, and developers. While the NHBC recognises that there is a lot of good practice in the way that earth works are being carried out on sites, it also found that there is little consistency in how works are being undertaken. There are sites being brought forward where the geotechnical risks are not being fully understood from the outset, nor are solutions being provided.
As such, the NHBC is looking for greater involvement and significantly earlier engagement from geotechnical engineers. For example, in instances where developers want to put simple shallow foundations into earth works fill, that fill needs to be placed under full time supervision of a geotechnical expert. This is of course a seismic change to what has happened previously, which would normally see the contractor carry out this work, before getting it verified by a suitable individual.
Understanding what’s underneath
The release of land for residential development has been well documented as of late, particularly following the government’s 1.5 million homes target. Whether the land being released is green belt, grey belt or brownfield, ensuring it is viable for development can’t be underestimated.
Many of these sites will need to be remediated in some capacity before any works can begin, however, project managers need to consider the need for ground investigation. The process itself will reveal information about things like the condition of the soil, the general geology of an area and ground stability. While investigations and services of this nature will have an initial increase in costs, they will also result in both time and economic savings later down the line as developers will know the foundations of what they are building on. Understanding these constraints at an early stage may also help inform decision around site layout and programme to ensure structures avoid problematic areas or development is phased to make construction as efficient as possible.
Geotechnics to form part of the planning process
One of the main challenges geotechnics faces is that it does not currently form a significant part of the planning process, and it often only comes to the forefront when unforeseen ground conditions are encountered and it becomes a concern of the housebuilders or warranters when they consider what the cost implications will be in five- or ten-years’ time.
The work geotechnical engineers carry out is far more impactful at the outset of a project. Much of the ‘upfront work’ – such as characterising sites and analysing earthworks material sources which will be required – simply can’t take place if they’re not undertaken during a project’s infancy. This in turn is resulting in contractors struggling to meet performance criteria, simply due to a lack of knowledge around the materials available and how best to use them. There needs to be consideration for how these materials will behave as a project progresses and how they will deal with a change in weather.
I think there’s an opportunity in the planning process at the moment where geotechnical experts can almost bolt on to. On the environmental side our colleagues in the land quality team will carry out a phase one desk study for most development projects which are going through planning. This study looks at the geology and history of a site, any public available data and a risk assessment potentially looking at contaminants etc – these findings will then inform the planning application on whether any remediation is required.
By using the exact same information we could carry out a geotechnical risk assessment, identifying those headline risks that are going to bring additional costs beyond a conventional development. Essentially, this would give the developer an understanding of the things they need to anticipate, and when they will start to become problems.
Areas of land that pose more challenges than others
Looking at grey belt for example, by definition these are normally areas of land where there has been some sort of development before and as such, they’re relatively straightforward and innocuous because the foundations and structures in the ground are fairly manageable. However, we work with a lot of minerals operators with former quarries and as these often consist of large deep holes in the ground. Creating attractive development platforms often requires the import of additional material and this is where earthworks become a critical area.
Similarly, when it comes to heavy industrial sites then there could be some historic foundations that need to be demolished and pulled out of the ground which can leave big voids. Again, this will likely leave you with a site that has had an awful lot of disturbance to the ground. So, if the aim is to build a row of terraced houses, then you will potentially run into a number of problems around managing settlement and ensuring you have consistent foundations on which to construct these homes.
In an ideal world we’d be going into a green field every single time and the geology would be exactly what it was three million years ago when it was last touched by a river, but the reality is that so much of our country has been developed during some part of our industrial history so there is always something that needs to be thought about.
Moving forward
We completely understand that cash flow is a little difficult across the built environment and as such, investing in support from geotechnical experts before having even been given planning permission may seem a little excessive. However, highlighting things at the pre planning stage will allow developers to cost accordingly and ensure everything is factored into the cost structure correctly.
The findings from a geotechnical engineer may also help to inform whether a site is actually viable for the planned development, again saving large amounts of time and money.