The friction forces on tunnel segments during pipe jacking determine to a large extent the capacity of the jacks and the number of intermediate jacking stations. Experience shows significant differences between predicted and actual friction forces. In this presentation we will look into the different factors that contribute to the overall soil friction and lead to the differences between design approaches and actual field experiences.

One of the major contributing factors to the overall friction is the boring of curves. To better understand the behaviour of the tunnel boring machine in curved alignments, a model has been developed, that takes the subgrade reaction and the stiffness of the soil into account. The subgrade reaction in the inner and outer curve of the TBM differs substantially and a reduction factor is introduced to deal with this effect. Especially in soft soils the impact of curved drives can be significant, and this will be illustrated by detailed measurements from several pipe jacking project in soft soil conditions.

◆About Wout Broere

Dr. Wout Broere is a professor of Underground Space Technology at Delft University of Technology, a board member for the Netherlands Society for Trenchless Technologies as well as a Fellow of the ISTT. His research interests range from trenchless technologies, large diameter tunnelling and the use of underground space to site investigation, physical modelling and offshore foundation engineering. He has extensively published on these topics and is currently editor-in-chief for the journal of Tunnelling and Underground Space Technology (incorporating Trenchless Technology Research).