The first horizontal jet-drilling machines were imported to Germany in 1986. Since then they have increasingly been used to lay pipes and cables into the ground without trenching. The main features of the horizontal jet-drilling process are illustrated in Figure 1. First a pilot drilling is done (Fig. la); then the expansion and insertion operation takes place (Fig. Ib). Figure lc shows the drilling principle. A high pressure jet of mud excavates the microtunnel. The antisymmetric shape of the drilling head allows the direction of the drilling path to be controlled. Most horizontal drilling projects take place within a depth range of 2 m. A transmitter built into the drilling head allows precise location of the position of the head.


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