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Subsiding building threatened with demolition stabilised

Client: Herefordshire Housing Ltd
Location: Hereford
Reference No: PR221

Disraeli Court in Hereford, a sheltered housing development, owned by Herefordshire Housing Ltd, was suffering from subsidence problems so severe that the facility had to be closed and the residents moved out. Several repair schemes were investigated and rejected and even demolition and rebuilding was being considered until structural repair specialist, Helifix, proposed a cost-effective scheme that would restore structural integrity and also be covered by a 10 year warranty.

Disraeli Court comprises a communal building of 30 flats plus two self-contained annexe bungalows, all constructed with vibro pile foundations on a land fill site. Investigations showed that the foundations had started to fail as organic fill within the ground had decayed, causing the buildings to subside and generating widespread external and internal cracking, distortion of openings and settlement of the floor slabs. By 2008 the damage was so great that it was no longer suitable for residential purposes.

With the approval of project managers and engineers, G Fulford & Co, the Helifix repair scheme proposed a combination of foundation stabilisation and super-structure masonry repairs, undertaken by a Helifix Approved Installer working to main contractor, E G Carter & Co. Foundations beneath all external and internal load bearing walls were stabilised by installing 417 Helifix micro piles, between 3m and 7m in length, at approximately 2.5m centres. To minimise disruption to the internal floor slab, external walls were supported by piles installed on the outer face fitted with foundation support brackets jacked up beneath the existing footings. The internal walls were supported either by foundation support brackets or new reinforced concrete needle beams cast onto the pile head, spanning beneath the walls to provide support.

Access to internal load-bearing walls was severely restricted but the portability of the Helifix micro pile system made it ideal as the pile sections and hand-held hydraulic drive head could be easily manoeuvred through doorways. No large equipment is required and excavations are minimal. The correlation between pile driving torque and pile bearing capacity makes the Helifix micro pile system a very accurate means of structural support. This was important as ground conditions across the site varied considerably, so the ability to accurately assess the bearing capacity of each pile, as it is installed, avoided the potential risk of installing into unsuitable material.

To reinforce and secure the superstructure and spread the loads between the micro piles, masonry beams were created from the existing brickwork by bonding pairs of stainless steel HeliBars into the mortar beds. Further single HeliBars were used to undertake extensive crack stitching on both the internal and external walls, with well over 6,000m being installed in total.

The cost-effective Helifix repair scheme, with 10 year warranty, fully secured Disraeli Court, avoiding demolition and enabling refurbishment of the lift and fixtures and fittings prior to redecoration and the reoccupation of this sheltered housing facility by elderly residents.