Knebworth House

Project Information

Knebworth House is a historic manor house built in Tudor Gothic style around a central square court and surrounded by a historic deer park covering over 250 acres.

The building had a history of movement, having undergone remodeling and restyling by generations of the Lytton family. Monitoring of visible cracking and progressive movement to the to the north-west turret had been ongoing for almost 30 years. More recent inspections had highlighted some considerable advances in movement on the turret showing cracking increases of 8.5mm to just under 16mm in places.

Investigations carried out to the south side of the turret identified a range of possible causes for the movement. A series of boreholes established the ground conditions and a trial excavation uncovered the existence of a considerably shallower turret foundation as compared with foundations to the existing main building and the adjacent cellar.  

Geostructural Solutions was appointed to carryout the structural works to permanently stabilise the turret. Our solution involved increasing the depth of the turret foundations to the same depth and bearing stratum of the main house, through. The increased depth foundations would be constructed using hand excavated underpinning techniques.

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Protective Measures

Elegant stone cornicing above the turrets was closely inspected and any loose stonework carefully pictured, recorded and very carefully removed for later reinstatement. Protection bays were installed until all underpinning excavations had been completed and local gargoyle was wrapped in protective layers for the duration of the works

Excavation and Temporary Works

Excavation to a depth of approximately 3m from ground level exposed the projection of the existing foundation, which was to be carefully cleaned and retained. In-house designed temporary excavation shoring was installed as the excavation continued. Gas monitoring and escape breathing apparatus was introduced at 1.5meters.

Tunnelling

Heading or “tunnelling” below the existing foundation was carried out just beyond the width of the original foundation. Earth work support could then be completed, steel dowels installed, and the exaction prepared.

Sensitive Concrete Placing

Special measures ensured no splashing to the historic stone during concrete placement for the new foundations

Reinstatement

Reinstatement was relatively straight forward involving the compacting of the existing oversite followed by “capping off” with a good layer of pea shingle.

Project
Knebworth House
Engineer
Morton Partnership
Contractor
Bramwell Hall Projects Ltd
Services
Rigs
Duration
Value
Location
Status
Project summary
Project summary
Project
Knebworth House
Engineer
Morton Partnership
Contractor
Bramwell Hall Projects Ltd
Services
Rigs
Duration
Value
Location
Status