This paper outlines methods for estimating the jacking forces associated wi
th different types of microtunnelling operations. These methods have been d
eveloped using probably the most extensive database of microtunnelling jack
ing forces assembled to date. These data were collected by questionnaire in
Japan as part of an initiative by the International Society for Trenchless
Technology (ISTT) and coordinated by the Japanese Society for Trenchless T
echnology (JSTT). Methods for predicting jacking force are produced for slu
rry, auger and push-in type microtunneliing operations. Separate methods ar
e suggested for these techniques as it was found that the jacking force is
sensitive to the method of installation. The methods can also take into acc
ount the soil type found on a particular project. However, sensitivity of t
he measured jacking force to other factors, such as soil strength and depth
of installation, were not included in these predictive methods as no disce
rnible relationships could be established due to the variability in the dat
a.
Examples from two case histories, one involving a 1.0 m nominal diameter sl
urry microtunnelling machine in dense silty sand and the second involving a
500 mm nominal diameter microtunnelling machine in sand and gravel, are pr
esented which use the equations proposed in this paper. The results from th
ese examples show that the predicted jacking forces are comparable to those
measured in the field.
This paper therefore presents practical and reliable methods of predicting
jacking forces associated with microtunnelling projects. (C) 1999 Elsevier
Science Ltd. All rights reserved.