Jet grouting to new depths in the Lambeth Group and Thanet Formation beneath London

A jet grouting trial was undertaken within the Thames Tideway Tunnel shaft at Kirtling Street in Battersea, SW London, to assess the viability of the technique within the Lambeth Group and Thanet Formation sediments up to 60 m below ground level. There was no precedent industry experience of jet grouting in the UK at this depth and in these soil types. Four, separate, upper and lower grout columns were constructed respectively within upper and lower granular zones inside the shaft footprint, and then exhumed for inspection and measurement during ensuing excavation within the diaphragm wall lining. Target diameters for the upper columns were achieved within granular channel sand and Laminated Bed material, with minimal vertical deviation. These were not so successfully achieved, however, within stiff cohesive Laminated Bed and Lower Shelly Clay materials. Formation of the lower columns was severely restricted in dense gravel belonging to the 'Pebble Bed' and stiff gravelly clay, at the top of the Upnor Formation, but target diameters were being achieved in the lower portion of the formation, comprising Upnor sand. At their base, the column diameters were, again, restricted in the very dense sand at the top of the Thanet Formation.