Development and use of microtunnellers in the UK : Washbourne, J Tunn TunnlgV25, N3, March 1993, P69–71

Abstract

There is a growing demand for the use of tunnelling rather than trenching for ducts which are less than man entry such as those used to install cables and pipes. The article describes the design and development of microtunnellers in general giving details of the Hawker Siddeley Dosco slurry microtunnelling system. This system is capable of being used in a wide range of ground conditions. The system has a specially designed high output crusher that uses a stator and rotor configuration that crushes progressively around the circumference. Auger extraction of spoil is preferable for drives of length less than 80m. A slurry system is used for longer drives, and where there is a head of groundwater at the face. Maximum spoil particle size is limited to one-third of the exit pipe diameter for slurry spoil removal, or one-quarter of the auger pipe diameter. A high flow velocity is needed in the excavation of coarse grained soils to ensure saltation of the largest particles during spoil removal. This causes considerable loss of pressure on long return pipes and the spoil can be mined with a low rate of slurry flow using low charging pump pressure. The consistency of the spoil removal slurry is monitored and flow rates are adjusted accordingly. An efficient lubrication system is vital with small diameter pipes if acceptable jacking distances are to be maintained.