Experimental and analytical study of friction forces during microtunneling operations

Friction forces usually constitute the main component of jacking loads. As a result of their increase with jacking length, it is these forces which limit the drive length. Therefore, it seems important to be able to quantify them accurately. The field monitorings, carried out as a part of the French National Project 'Microtunnels', have shown the effects of parameters such as lubrication, stoppages, deviation and overbreak on friction force values. Frictional stress, deduced from field monitoring, is compared with empirical results extracted from the literature and with the results of most frequently used calculation models. (C) 2002 Elsevier Science Ltd. All rights reserved.