A comparison between tube-à-manchette and lance grouting to assist tunnel excavation through chalk

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-àmanchette 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.