Services used by the client:
William Hunt Consulting were asked to provide a cost-effective, low-impact solution to a block of flats near Bedford, which was suffering from subsidence as a result of moisture extraction from nearby local authority owned trees.
The trees were located to the rear of the site and had caused category 5 damage to the rear portion of the three-storey structure with cracking of up to 40mm recorded. Although access was reasonable, working space to the rear was limited and, with numerous tenants directly impacted by the subsidence, a scheme needed to be designed and installed quickly without causing disruption to the residents.
Although space was tight to the rear of the building, a root barrier was successfully installed to separate the roots of the implicated vegetation from beneath the building and provide long-term confidence that the property would remain unaffected by these trees.
The barrier was successfully installed within one week. Due to the severity of movement to the property; significant deep-seated desiccation of the clay soils; and likely timescales involved in allowing the clay to rehydrate naturally, stakeholders had been preparing for a period of approximately two years to allow the ground to rehydrate before repairs to the properties could be completed. However, the installation of our Accelerated Rehydration system to the perimeter of the worst-affected section of the building sought to significantly reduce the timeframe of the claim by introducing water constantly to the clay at depth. This approach to encourage the rehydration and as a consequence swell the clay over a truncated timeframe, meant that stability was gained more than 12 months sooner than it would have been with just natural rehydration.
There were a number of benefits resulting from the root barrier and Accelerated Rehydration solution: the implicated trees to the rear of the site that offered a screen from a nearby road were retained; the time period for ground recovery was more than halved; disruption to the tenants was reduced; and the alternative accommodation costs were significantly reduced.
Had the trees remained in situ, the conventional solution would have been to complete an underpinning scheme to the structure. The cost of this work together with all other associated costs would have been in the region of £160,000. The total cost of the dual root barrier and rehydration solution was under £30,000.