This new housing development in Ealing consists of 180 flats and houses spread over five sites.
All the locations were Brownfield sites and had issues with ground contamination and ground gas. In addition, the underlying London clay was classified as high plasticity, and due to the location of existing trees, there was a risk of ground heave.
The design for the flats was Reinforced Concrete (RC) frame structure up to 7 stories. The superstructure was designed on 450mm dia. piles, pile caps up to 1.5m thick and cast in situ RC slab, with associated heave precautions. It was anticipated the piling mat would be up to 600mm thick.
Our design team proposed our Housedeck system, using 375mm thick slabs and 350mm dia. piles. A clear void was incorporated to allow for heave and under-slab ventilation, due to the ground gas risk.
Not only were we able to reduce the concrete requirements but by carrying out additional Site Investigation (SI) works, we were able to value engineer the piling mat and reduce the thickness to 300mm. Offering significant savings in contaminated spoil removal and importation of crushed material.
The terrace houses were originally designed on deep trench fill foundations with associated sub-structure masonry and beam and block floor. We proposed our Housedeck system, using 225mm thick slabs and 250mm dia. piles and our Brick Support Units (BSU). A clear void was also incorporated to mitigate the heave risk and allow for gas ventilation.
Due to the depth and diameter of our piles, we were able to use our midi rigs, allowing us to utilise our 50mm Concrete Working Surface (CWS), in place of a traditional piling mat.
In order to propose our value engineered design schemes, we carried out targeted Site Investigations, using Cone Penetration Testing (CPT). This allowed us to reduce the pile diameters and construct the flats on 350mm dia. piles instead of the originally proposed 450mm dia. piles.
We also created 3D FE models incorporating the stiffness of the super-structure into our foundation design. This allowed us to propose a 375mm thick slab throughout, instead of pile caps.
The schemes we provided offered significant savings due to the reduction in materials. By using Housedeck vs a compliant bid we saved:
5,900m3 of contaminated spoil from landfill by reducing level of excavation.
3,155m3 imported granular fill, due to the reduced excavation, 50% thinner piling mats, and using our Concrete Working Surface (CWS).
500m3 concrete and 200 tonnes of reinforcement, by slimming down the piles, negating the need for pile caps and trench fill foundations, less RC concrete was needed.
5,492m2 Cellcore, as we used a voided slab to mitigate the heave risk, Cellore was reduced.
1000m sub-structure masonry work, due to our piled raft design mitigating the need for ground beams and beam and block floors, less masonry sub-structure was required.
1,950m2 of beam and block flooring, as Housedeck is a foundation and ground floor system, beam and block flooring was no longer required.
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 have been collaborative from the outset with design input and assistance with NHBC approvals. The cost-effectiveness of the Housedeck system has simplified the delivery and speed of foundations on our projects. We look forward to working with Abbey Pynford on future projects.
James Dupey, Managing Surveyor, Lovells
Hugely impressed with the Housedeck system, its best described as a quick, mess free build process culminating in a tidy end product.