By Nikki Smith, Regional Engineering Manager
In densely populated urban areas, such as London, space is at an all-time premium. As a result, your options are often limited to building downwards and upwards, meaning that large basement excavations are an increasingly common occurrence for contractors. In this blog, Nikki explores the challenges large basement excavations can present and the role that temporary works play in ensuring their safe and efficient delivery.
As space in city centres becomes tighter and our buildings get taller, the basement excavations required for their construction become larger and more complex, with building substructures also being used to house car parks, plant rooms and even resident gyms. In fact, basements can be three to four storeys deep, just for residential properties. Their location can also provide additional challenges, with busy urban areas, such as London and other major cities, presenting project teams with unique factors to consider in order to ensure the groundworks are delivered safely.
Available space is perhaps the biggest restriction on basement excavation projects. Naturally, architects and developers will want to utilise every available square metre for the new building, with piling often being carried out all the way up to the party wall boundary. However, the effect of this from a practical perspective is that the construction site itself can be smaller and highly constrained, with less available space to store materials and equipment. As a result, developers have to plan carefully, including the management and scheduling of deliveries.
With every available inch being utilised, basement excavations, unlike other typical groundworks projects, rarely feature a standard rectangular excavation. Instead, the reality is that the site geometry will be incredibly complex, requiring a bespoke groundworks support scheme to match.
The challenges of basement excavations do not end there. As well as requiring more bespoke detailing than a standard groundworks project, their large size, high shear loads, complex geometry, detailed connections and proximity to neighbouring structures can also result in the associated risk being higher. It is for this reason that liaising with a temporary works supplier early on in a project’s construction sequence can be so valuable, providing the design experience and expertise to deliver the works safely, correctly and within programme.
Given the potential size and complexity of basement groundworks projects, the use of Building Information Modelling (BIM) and digital design technology at the scheme design stage can also be invaluable, providing the 3D visualisation and high levels of accuracy you need to help bring the project to life, safely. At Mabey Hire, digital engineering is embedded in everything we do, with our engineers often using BIM software at all stages of a basement excavation project, from the early concept design through to final scheme detailing. Our EVE solution helps to take this even further, providing our engineering team and the client with the opportunity to explore the site and proposed temporary works solution in a virtual and immersive way – a digital rehearsal of the works.
As well as providing peace of mind that the groundworks support scheme will perform as required on site, working with a temporary works supplier with design expertise can also enable you to better value-engineer the scheme of works. Helping to reduce the amount of steel required but without affecting the overall performance, value engineering can help to cut costs and lessen the project’s environmental impact.
The early consideration of temporary works is something that we at Mabey Hire frequently advocate to our customers. Not only does it deliver a great number of benefits for the contractor, but this approach can also be instrumental in the successful delivery of the overall project.
While important on all construction projects, early engagement is perhaps especially valuable on basement excavations. Given its complexity and the additional factors and neighbouring properties to consider, these projects can require high levels of collaboration between numerous technical parties, with the party wall designer and the permanent works designer just two examples. As a result, considering the groundworks at an early stage can enable the scheme to be better designed and with all stakeholders in mind.
Put simply, early engagement enables the most efficient build plan, dig sequence and scheme design – all things that, when working on a high-risk project, are invaluable.
The challenges and risks of basement excavations don’t end once the design has been signed off. A seamless installation is just as critical.
Here, combining design expertise with in-house install capabilities can deliver very real benefits. As well as helping to streamline the overall construction process, it can also have a positive impact on the groundworks scheme design. With in-house knowledge on implementing and installing schemes on site, our install team can offer practical insight at the design stage – for example, whether a complex connection would be feasible on site. This knowledge can help to ensure that the scheme is constructible in the real world, not just in the computer.
The conversation around basement excavations isn’t limited to just groundworks equipment.
Given the tight site restraints and neighbouring buildings and infrastructure seen on city centre sites, both structural monitoring and environmental monitoring can be invaluable on basement excavation projects. As well as providing the assurance that any neighbouring buildings remain structurally safe, such technology can also be used to ensure that the construction works are complying with the agreed levels, often set by the local authority. With excavation projects and their early piling works potentially generating a large amount of noise, dust and vibrations, it’s vital that these levels are closely monitored and managed, especially given the likelihood of businesses, offices and homes being in close proximity, if not next door, to the construction site.
Structural monitoring can also be used on the groundworks props themselves, providing contractors with the assurance that the support scheme is performing as intended, as well as providing advanced warning should additional supports be required.
At Mabey Hire, we have everything you need for a successful basement excavation project delivery; from our expert and experienced people, digital design capabilities, in-house install team, wide range of groundworks support equipment including hydraulic pre-loaded struts, and monitoring solutions. We can also offer support in other ways, such as supplying a means of site access with our versatile and modular temporary bridging, which can be ramped down to basement level.