NUST MISIS, Moscow, Russia:

E. Yu. Kulikova, Professor, Doctor of Engineering Sciences
I. I. Shornikov, Associate Professor, Candidate of Engineering Sciences, shornicovivan@gmail.com

The method for estimation of jacking force of jacks in driving tunnel casing in micro-tunneling is described. The estimation was carried out for the friction component of jacking force in rectilinear sections at the restart of a jacking plant after stoppages. For driving of casings using lubricants, the time evolution of the sticking phenomenon in permeable rocks at stoppages is taken into account. This phenomenon allows having regard to the observed increase in the jacking forces as pipe jacking is restarted. The calculation model of the contact formation in the casing–bentonite solution–external filter cake–well wall is constructed. It is found how the perimeter size of the contact zone depends on such parameters as compressibility and Poisson’s ratio of soil, size of annular gap, differential pressure and casing diameter. The contact size–stoppage time relationship is determined. The time dependences of the jacking force and stoppage duration are presented for the specific tunneling projects not in the conventional logarithmic form but as the exponential function. This allows reflecting physical processes in the contact zone, namely, seepage of suspension particles in soil, filter cake build-up, increase in the differential pressure and resistance under the action of effective pressure along the length of an end zone at dispersion of pore pressure under the influence of weight of the driven casing head part. The nature of the physical processes makes it possible to consider the observable increase in the jacking forces at restart. The analytical and graphical representations of the increase in time of the static resistance force at the contact during stoppage of tunneling are given. The approximate formula of the friction coefficient is proposed for the design convenience. The obtained results allow a more exact analysis of the friction component of the driving force and its sensitivity to changes in the jacking parameters.

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