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A comparison between tube-�-manchette and lance grouting to assist tunnel excavation through chalk
Abstract
A road tunnel 13.5 m in diameter and 800 m long has recently been constructed, through chalk, as part of the Ramsgate Harbour Approach Road Scheme. For the first time in the United Kingdom tunnelling has involved primary support being provided by a system of prevaults followed by the installation of an unreinforced concrete lining. This paper describes how an iterative grouting solution was evolved in response to unstable ground conditions during the early phases of tunnelling. As the tunnel drive progressed, and greater knowledge of the engineering behaviour of the chalk was gained, decisions were made to carry out trial injections using the tube-a-manchette and lance methods. These were installed from the surface in areas where it was perceived that future problems might occur. A comparison is drawn between the efficiency and relevance of the two systems in the ground conditions encountered on site.
... Ground strata encountered within the tunnel envelope are shown in Newman and Ingle (2002). At the cottages, a buried river valley increases the depth of chalk weathering significantly. ...
... Transverse arrays of precise levelling points in a field to the west of the cottages gave an indication of the 'greenfield' settlement response to the advancing tunnel. However, the ground conditions in this area were distinct from those at the cottages, with loose, blocky chalk of grades C4/C5 encountered in the crown that caused problems of localised failure of the prevault slots, necessitating grouting to be used (Newman and Ingle, 2002 ). No grouting was necessary at the cottages. ...
This paper presents data from a case history of tunnelling using the pre-vaulting method, at low cover and without compensation grouting, beneath a terrace of masonry buildings at Ramsgate, Kent. Surface and building settlements were measured and movements on existing cracks monitored throughout construction. Volume loss was low and the settlement trough quite narrow. Buildings responded flexibly with lower damage level than predicted by assessment using a deep beam analogy. Damage was concentrated in opening of existing cracks, with the only significant new cracks likely to have their origin in three-dimensional effects as the tunnel heading approached the buildings. Assessment of tunnelling effects on buildings is important to confirm the viability of new tunnelling projects and reassure building owners of the possible level of damage, while avoiding excessive conservatism. Numerical modelling shows potential for such assessment, and a procedure for modelling the ground, tunnel and building together using non-linear three-dimensional finite-element analysis has been applied to this site. It was found that, although geometry and other features of the site required simplification due to practical limitations in computing resources, model results still reflected the main features of observed response including the 'greenfield' trough, flexible structure response and damage severity.
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