Analysis of NATM and shield tunneling in soft ground

Demand for new underground transportation systems and utility networks has increased the use of tunneling in soft ground. Many of these tunnels have to be constructed in difficult soil conditions, with strict constraints on ground movement control. Technological advances, such as the pressurized shield or the New Austrian Tunneling Method (NATM), have, to some extent, overcome these difficulties. But the complex interaction between tunneling procedure, ground response, and liner support is still not fully understood. In this dissertation, the three aspects of tunneling, face stability, liner design, and ground surface settlement are analyzed for conditions that might be experienced on current projects. The study is intended to clarify some of the phenomena associated with the use of advanced tunneling techniques in soft grounds, and help improve the current design practice. The NATM generally uses "hand-mining" equipment for excavation, and shotcrete as temporary support of the tunnel wall. The amount and timing of support is optimized by continuously adapting the construction procedure to the conditions found at the tunnel face. In the present study, the applications of the finite element method to tunneling are reviewed, and it is used to model NATM tunneling projects. Using parametric studies, a simplified design method is proposed which allows an estimate of the liner forces and settlements associated with NATM tunneling to be obtained. Pressurized shields are used in soils with little to zero stand-up time to support the tunnel face during excavation. In this work, the face stability of shield tunnels in cohesionless soils is examined using limit analysis principles. Upper bound estimates of the critical face pressure are found in good agreement with results from centrifuge model tests. Empirical correlations for settlement estimates are re-examined, in view of case history data for shield driven tunnels. The ground movements observed on the F3 and F4 contracts of the Washington Metro are analyzed. Earth pressure balance shields were used on these projects. It is shown that difliculties were common in mixed face conditions, unless adequate techniques were used to prevent ground collapse to occur.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Civil Engineering

Department dc:contributor.department

Civil Engineering

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1989

Author dc:creator

• Leca, Eric

Chair dc:contributor.committeechair

• Clough, G. Wayne

Committee members dc:contributor.committeemember

• Brandon, Thomas L.
• Duncan, J. Michael
• Kuppusamy, Thangavelu
• Singh, Mahendra

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/54230

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/54230