19-20 Garlick Hill, London

Nick Langdon

Nick Langdon

Company Chairman and Director

Tel: 01483 310600
Email

Client

Walsh Associates

Services

  • Site Investigation Review
  • Ground Movement Assessment
  • Basement Impact Assessment
  • Planning Support

 

Ground movement assessment

CGL provided geotechnical advice for a development at a sensitive and unusually historical site in central London,100m from the Thames. The site will be developed into a new hotel. The existing structure was demolished with a proposed new basement structure to extend almost 7m below street level.

CGL’s brief was to determine potential ground movement from the construction of the new basement and superstructure, and to identify the potential effect on neighbouring structures. These include the 17th century church of St James Garlickhythe, which was rebuilt by Sir Christopher Wren after the Great Fire of London and is a Grade I listed property. The church is approximately 3m to the south of the site and has been historically subject to ground movements and remedial works.

A CGL investigation into the ground conditions on site showed London Clay at the site was relatively shallow at 6m above the Ordnance Datum. However, beneath the church the top of the clay was much lower, at 2m below the Ordnance Datum – a 4m drop over a horizontal distance of approximately 3m. A further desk top review revealed the Roman bank of the old river Thames running between the site and the church.

CGL created a finite difference model of the ground conditions using FLAC 2D to determine ground movements arising from the proposed construction and taking into account the highly variable ground conditions.The analysis accounted for pile installation movement and vertical/lateral displacements including heave, considering the particularly sensitive marble floor between the aisles and the nave of the church.

The analysis predicted a total settlement of some 4.5mm at the church footing closest to the excavation. The prediction has been validated by monitoring undertaken during construction – showing a total settlement of some 4mm.