City Research Online

Abstract

The Forepole Umbrella System (FUS) uses steel pipes installed from within a tunnel to provide a canopy above the tunnel heading that both increases stability and reduces tunnelling-induced ground movements. Although the system is known to be beneficial and has been used in a number of projects, there is little information on how key parameters including length and forepole stiffness combine to produce effective support. To investigate this, centrifuge tests incorporating the three-dimensional geometry of a tunnel heading in clay and the model FUS have been undertaken. The tunnel heading was supported by a pressurised rubber bag lining with excavation being simulated by a reduction in air support pressure. Image analysis was used to obtain subsurface ground movements and a newly developed 3D imaging system was used to measure accurately the soil surface deformations. The performance of the FUS and the influences of key FUS parameters were quantified via the settlement reduction factor. The results showed that the FUS, arranged in various settings, reduced the maximum surface settlement by 35-75%. The effects of the FUS parameters to the reinforcing effectiveness is dependent on the ratio of cover depth to tunnel diameter. An optimum design arrangement of the FUS is suggested.

Publication Type:	Article
Additional Information:	© Canadian Science Publishing or its licensors.
Publisher Keywords:	Centrifuge modelling; Ground improvement; Tunnels & tunnelling
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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