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DESIGNING AND MINING-CONSTRUCTIONS WORK
ArticleName Estimation of jacking forces on casings in microtunneling
DOI 10.17580/gzh.2020.02.05
ArticleAuthor Shornikov I. I.
ArticleAuthorData

College of Mining, NUST MISIS, Moscow, Russia:

I. I. Shornikov, Associate Professor, Candidate of Engineering Sciences, shornicovivan@gmail.com

Abstract

In tunneling projects for water-bearing ground using the microtunneling technology with jacking of casings, it is necessary to predict the jacking forces. The regulatory documents in tunneling miss the widely known fact of increase in the jacking forces at restarting after stoppage. It is of the current concern to study the physical processes which initiate the increase in the take-off resistance in the shield–casing system, in particular, in the contact zones of the shield shell–soil and the tunneling machine rotor–bottomhole. The model of end forces in the take-off resistance of a rammed system in straight-line portions during the shield shift is constructed. Both characteristics of the material in the shield clearance, representing a water and support medium mix (a slurry or a muck), and characteristics of counteractions of the support pressure as well as reaction of the tunnel heading in soil are taken into account. These forces are governed by own weight portion of the tunneling machine transferred to the soil skeleton, by the ground pressure, tunnel heading zone stiffness and also friction characteristics at the shifted object–shield clearance material contact. The results both of exact and of numerical solutions of the model problem on quasistatic deformation of the shifted object at the contact with the shield clearance material are presented as the jacking force–displacement dependences. The dependences of the take-off forces and maximal jacking forces on a set of parameters governed by the shear stiffness of the shifted object, bottomhole stiffness in soil and by the support pressure are derived. The obtained results make it possible to analyze more accurately the values of the bottomhole component of the jacking forces and its sensitivity to the change in the ramming parameters.

keywords Ramming force, jacking forces, tunnel casing, stoppages, restarting force, water-bearing ground, take-off resistance, shield clearance material, shield–shield clearance material contact, weakened zone, characteristic length, tunnel heading stiffness, shields series AVN, Herrenknecht AG
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