ABSTRACT
Spoil arising from excavation of the face has to be transported away along the line to the drive pit, and from there to the surface where it is removed from site. Removing this spoil is often the most critical part of the operational cycle and can be the key to the rate of progress in pipejacking. This is not so for microtunnelling. One main limit on increasing the capacity of spoil removal is the small cross-sectional area of the pipe, which allows no opportunity for a by-pass with wheeled systems, except in the largest pipe sizes. For this reason pumped systems of spoil discharge are frequently used, even in situations where ground conditions do not demand a pressure balance chamber.
