How to mitigate one of the largest potential risks to your construction project
Authors
Most construction projects in the UK have a time and cost overrun of 10% or greater1. Overrun is not a unique phenomenon; in fact, in a global study of mega transport projects 9 out of 10 were found to overrun their cost, and a 50% plus cost overrun was actually found to be quite common2.
The main contributing factors to these overruns appear to be design changes, inaccurate initial estimate, complexity of the work, risk and uncertainty. Risk and uncertainty in projects are inevitable in some instances (no one could have reasonably predicted the COVID-19 pandemic and resulting economic impact), but some are more within our control to manage.
As a ground engineering professional, I’ve witnessed how unforeseen ground conditions can significantly attribute to redesign and/or additional costs to deal with during construction. But not all ground conditions have to be unforeseen, we can change these unknowns to knowns, if only more was invested in good ground investigation earlier in the project.
I understand, there can be a myriad of constraints to completing a good ground investigation early in the project; budget, existing buildings and utilities get in the way or sites that are busy and still in use tend to get some push back. Some data is usually better than none, so with all the potential constraints in mind, let’s go back to the basics.
A graph illustrating how much opportunity there is to influence risk reduction during a construction project.
What is it that makes a good ground investigation and what is the real cost of not doing one?
Significant redevelopment requires planning permission from the local planning authority (LPA). Under the National Planning Policy Framework, it is the duty of those bringing the development forward to confirm to the LPA that the site is suitable for its proposed end use. The first stage of proving this is a thorough desk study (or Phase 1 assessment), which will be required for planning and provides the basis for all your other ground-based assessments.
I’m sure you can get a desk study for a decent price that ticks all your planning boxes. It’ll look at the publicly available information on the site’s underlying geology, previous and current site uses, surrounding site uses, potentially sensitive environmental receptors and it'll use all this information to provide you with an idea of the types of potential contamination you could encounter. But why stop at ticking the boxes for planning? Any good desk study will look at all that information and more, and put it in the context of your development, your priorities and your opportunities. If you’re looking at the ground-risk, why only look at contamination? Engineering properties of the ground and geotechnical risks can cause just as much nuisance to a developer during construction as historical contamination could. Not all foundation types will work in all situations, or for all loads. Over designed foundations, although inherently safe, will be more carbon intensive, take longer to construct and ultimately cost more money. It can cost even more money, if you find the foundations you planned on using are unsuitable after you get on site to start building them. It doesn’t have to just be about what you have to do for planning, a good desk study is the start of a good ground investigation and can provide you with so much more insight.
Contaminated pipework being removed during demolition and remediation works, known to be heavily contaminated due to the ground investigation undertaken.
No site is the same
Every site is different. The potential risks are variable and unique depending on its situation and circumstance. Why should the ground investigation be any less unique?
A good ground investigation can only really be achieved off the back of a good desk study as it’ll use the most suitable methodology, not only for the constraints present on site, but also to obtain the right data to disprove, or prove, the risks that were identified at desk study stage. The more accurate, relevant and developed our desk study is, the more accurate and relevant our ground investigation will be.
When we have a good idea of the site’s history and can marry this with the context of the site’s future, our clients get the most bang for their buck. We can drill into what really needs answering. Yes, I’m sure most could tell you that to design a pile, you should probably find out where the bedrock is, but knowing that actually the loads of your building aren’t going to be that high means we might ask “do we need to pile it in the first place?” You probably will need some ground gas monitoring in the vicinity of that infilled pond, but if a building isn’t going to be on top of it, let’s monitor where the building will go to see if any gas would be present there.
There isn’t a crystal ball when it comes to ground investigations
At Cundall we’re not just looking at what you need to do for planning, we want to look at what is best for your project.
As ground specialists, we wish we had a crystal ball as much as our clients. We would love to be able to say “this is all the ground investigation you’re ever going to need” but unfortunately that just isn’t the case. Multiple phases of ground investigation can be required, particularly on complex sites, particularly where there are access constraints or where mobile contamination is present. Sometimes ground investigation is like playing battleships, sometimes there’s strategy, sometimes it’s an educated guess, either way it’s much easier not to play blindfolded with an arm tied behind your back.
The cost of not knowing about potential constraints are hard to quantify, no one ever thinks about the headaches they don’t get. It can range from potentially a couple of extra loads of hazardous waste removed from site (<£10k) all the way up to a stop on site whilst there is a redesign of the foundations because there’s a large obstruction you didn’t know about.
The amount of investigation you’re willing to invest in will be dependent on where you wish the risk to sit within the project. With quite a few design and build projects, you tend to find this uncertainty will be priced by the contractor, and it won’t be a small number. Good ground investigation can help reduce that upfront uncertainty and potentially avoid nasty surprises down the line. It can also reveal opportunities on site such as whether there is potential for material reuse on site, ground source heat pumps or are soakaways a viable option for drainage.
Ground investigation is required under planning for the purposes of contaminated land but has the potential to be so much more than just a tick box exercise.
As a ground engineering specialist, it’s easy to see the value that can be added from good, targeted ground investigation specific to a site and in the context of the proposed development. I hope you can start to see the value in it too.
Ground investigation undertaken in an urban centre pre-demolition.
