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School is fully stabilised in just seven days

Client: Cambridgeshire County Council
Location: Holme, Peterborough
Approved Installer: Charterbuild
Reference No: CS153

Built in the mid 19th century, Holme Primary School had developed stepped, tapering cracks to the masonry, which were visible both internally and externally. Investigations established that foundation movement had occurred, caused by the close proximity of trees to this part of the school. The foundations were of corbelled brick type supporting a 13.5" brick wall up to six courses above ground level, where they reduce to 9" for the remaining height of the structure. The foundations needed stabilising and brickwork on the front and right hand side walls required repair and reinforcement.

The Helifix solution

Atkins designed a repair scheme using Helifix Dixie micro-piles, to overcome the subsidence problems, and utilising the Helibeam System to both maximise the pile spacing and secure the damaged masonry.

  • Nine end bearing Helifix micro-piles were driven to a depth of 6m, sufficient for the local ground conditions calculated using the manufacturer's design software. Adjustable 'L' shaped foundation support brackets were fitted to the piles and placed under reinforced concrete beams (resin bolted to the side of the foundations) and then jacked up until the structural load transferred to the piles.
  • Pile performance was verified during installation by taking a torque reading every 500mm using the hydraulic, hand-held drive equipment. The well-established direct correlation between the torque reading and the attained bearing capacity of the pile provides an instant verification test for each installed pile.
  • 6mm stainless steel HeliBars were bonded into mortar joints in the brickwork above the foundation level on the front and flank elevations. This formed a deep masonry beam, using the existing brickwork, which reinforced the masonry and spread the building loads.
  • The tapered cracks were stitched with individual HeliBars, bonded into mortar beds with HeliBond cementitious grout, to restore structural integrity.

The use of Dixie micro-piles enabled the school to remain fully functional during the works. With rotational installation there was minimal noise disruption and no vibrations. Using lightweight equipment, the piles were installed, loaded and the area reinstated in just seven days. Download the case study