The need for foundation improvement works arises when the soil on which the foundation sits is too weak or unstable to support the imposed load and foundations need to be deepened to more stable strata. Traditional underpinning has historically been the default repair method for subsidence-affected properties and is in some instances still required, but with the increased understanding of the behaviour of clay soils and foundation stability, there has been a move towards mitigation and new substructure underpinning solutions. In a practical sense, mitigation generally involves the reduction or removal of vegetation and the repair or replacement of drainage. In a small number of cases, where soils have been so irreparably affected by the external influence that the building continues to move downwards, some form of underpinning will then be necessary and at Optera we specialise in designing solutions using the latest piling, ground-improvement and jacking techniques. The construction industry has also evolved over the same period to acknowledge and address the hazardous nature of the work we do. Traditional underpinning is inherently dangerous and there is an incumbent duty upon every contractor and engineer to reduce or eliminate risk at source. By reducing or eliminating the need to put an operative under the building foundations whilst extending their depth into stable ground, we have improved the safe practice of works.
Piling in its simplest form, involves forming a column of concrete in the ground on which we would typically form a ground beam. This form of foundation construction is appropriate in almost every type of ground condition, although the type of pile is varied to suit the geology and depth. Piling is suitable for both newly built structures as well as existing foundation stabilisation works. Historically, piling has been seen as expensive and disruptive: installation rigs were large and would typically involve the policyholder vacating the property for the duration of works.
Using the latest technology, Optera are able to minimise disruption by installing piles with equipment which can be conveyed by hand through a property or by using smaller piling rigs to install driven steel-cased pile solutions, both of which are quick to install and do not require vacated properties. We also have larger equipment for more technically challenging soil types, offering heave protection where necessary and piles which can penetrate rock and obstructions within the ground where required. Our piling solutions can be offered with insurance-backed warranties depending on client requirements.
Optera specialise in the restoration of subsidence-affected structures by jacking the foundations from specially created reaction points, which are formed from either mass concrete underpinning pads or ground beams connected to deep piles, dependent upon the site investigation findings. This engineering solution is suitable for both commonly occurring conservatory and porch claims as well as larger structures. Using hydraulic lifting equipment placed between the top of our constructed reaction point and the underside of the affected footing, we are able to apply a net upward force, pushing the building back into its original position. The resultant void is packed with concrete to leave a permanent repair. This is particularly beneficial in situations where UPVC structures have become brittle due to UV exposure since it allows us to re-level buildings gently, eliminating the need to demolish and rebuild severely distorted structures.
By jacking from reaction points, openings become freely operational without the previous fouling and cracks in masonry close, allowing less destructive repairs such as masonry reinforcement or simple deep-bed repointing.
Safety is a prime concern whenever conducting repairs of this nature and a full assessment of the risk is carried out and reported before commencing works. We ensure that the repair process conforms to current health and safety legislation and where necessary we work with statutory bodies to gain building control approval for the works.
Optera offer epoxy resin and cementitious grouting as ground improvement solutions. Our trained operatives are able to monitor a property’s reaction to the material in the ground and instead of increasing the depth of foundation to stable strata, we aim to treat the superficial soil depths, increasing the bearing capacity of the material around and below the existing footing. Such techniques are used in non-cohesive soils (sands and gravels) where the resin or grout flows into the ground as a liquid, identifying any voids or areas of weakness. Whilst it is theoretically possible to lift structures in this manner, the process is not without risk and would generally be used to achieve stability only.
In the case of epoxy resin, a chemical reaction takes place between two components within the mix and it expands rapidly exerting a lateral force on the surrounding soil. This increases the shear strength and bearing capacity of the soil. Careful monitoring of the building allows us to identify when the force is equal and opposite to the imposed load and the process is complete. With cementitious grouting, the product is pumped under pressure into the ground below footings or floor slabs and acts to increase the bearing capacity of the soil. Again, using monitoring equipment, we are able to assess when the pressure increases to equal the imposed load and curtail the operation. These processes are particularly useful in arresting settlement of loose fill below solid ground-bearing floor slabs.
Optera have extensive experience in the design and construction of retaining walls, ranging from standard garden walls to large-scale dry-stone walls. Utilising a collaborative approach between our Geotechnical and Structural departments, we can offer a bespoke solution tailored to the site and can bring the latest global engineering practice to the UK through our links with international partners.
Optera have recently completed a 6.0m-high retaining wall, cut into an embankment that had previously suffered slope instability and a slip. The work involved stabilising the slope with rock anchors and geotextile; excavating and casting a toe; and constructing a two-phased wall to retain the slope permanently. The anchors were brought through the wall to provide a long-lasting repair, coupled with additional drainage. The wall was built in advance of the existing slope and back-filled with a free-draining concrete. This allowed us to reclaim 1.5m at the top of the slope and reconstruct the roadway there. This is just one example of the many projects which Optera are engaged to complete daily where a multi-disciplinary team are used to deliver a solution to a complex problem.
Optera have experience in building in many materials including cast-in-situ concrete, hollow block, gabion baskets and dry stone to name but a few.
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