These two attached terrace houses in Sussex were suffering from subsidence due to the poor bearing capacity of the ground beneath the rear projections, which caused large cracks to form in the walls.
Site Access & Design
The site access to these properties was the first consideration of the project. As they were not only on a tight residential street but were also set significantly below street level, even one of our specialist mini rigs would not be able to gain access. Our engineers opted for a Micropiled solution, as Micropiles can be installed with equipment that can be carried through the property.
Bungaroosh & Shoring
An added complexity (and interest) of this project was the rear wall of the main house was made of Bungaroosh. Bungaroosh is a composite building material used almost exclusively in the Brighton and surrounding areas in the mid-18th and late 19th centuries. It is made of miscellaneous materials in response to the high brick tax at the time. Due to its poor resistance to climatic changes, it was important not to take any chances with the supporting shoring system. We designed a substantial raking shore system, supporting the whole rear of the houses to reduce this risk.
Mitigating Risk Through Innovation
The existing foundations were minimal at this stage of the subsidence process, which posed a significant risk of collapse, added to by the Bungaroosh wall.
To minimise this risk our in-house engineers designed the piled raft to be installed backwards. This entailed building the raft first, creating some initial support for the structure above, then piling through the slab.
This process is rarely done and required original design thinking to allow piles through the slab and create a solid connection between the slab and the raft.
Traditionally in a piling first process, steel fixing would project from the pile to be formed into the raft, creating a solid connection. However, as this was not an option, we created a conical opening in the poured slab. This shape (tapering to the top) not only facilitated the Micropile installation but crucially, once formed, meant that the weight of the structure and raft would create a permanent connection. If left as a traditional circular pile, the poor conditions below would have allowed the possibility that the houses could continue their downwards movement.
The conical voids were formed from wire mesh and infilled with stone to prevent collapse during the concrete pour. Once set the stones were removed leaving a void ready for piling.
Although this was a new underpinning process for our Special Works Crew, the project went smoothly, completing on time and in budget.
Just a quick note to commend you and your teams hard work on the Wendover Woods project. From the beginning of the order process right through to design, construction and signing off the works it was a pleasure working alongside Abbey Pynford on this challenging project.
Michael Hayes, Senior Site Manager, Kier Construction
By using the Housedeck system, we greatly simplified what would have been a complex and expensive approach to the foundations. We look forward to working with Abbey Pynford in the future.
Andrew Crouch, Senior Project Manager, Engie
Abbey Pynford added value at every stage of the development process with a well-designed system for Coram Community Campus.