Pipe jacking is a well-recognized method for mechanical excavation of small cross-section tunnels with diameters from 0.25 to 4 m, with limited length from 50 to 1,200 m. The excavation method is suitable in soft soil (clay, silt and sand), soft rock (UCS < 50 MPa) and even hard rock (50 < UCS < 200). The pipe jacking advance is based on applying thrust on pipe elements which are installed from a start shaft, oppositely to typical segmental lining tunneling for larger diameters. The geotechnical conditions form a major factor for the excavation rates which may vary between 50 m per day in favorable conditions and only a few centimeters in worst cases. In unfavorable geotechnical conditions such as varying water pressure, occurrence of boulders or abrasive soil conditions the performance can be highly influenced. The aims of the paper are to (1) give a brief introduction to the pipe jacking methodology, (2) introduce how unfavorable ground conditions can be pre-investigated, and (3) how contractors can adapt the both the tendering and decision taking at site having the necessary information about the ground conditions. The subjects are also relevant to segmental lining tunnelling as well as for EPB and slurry shield TBMs.
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