Claus Wisser

Doctor of Philosophy, Brasenose College, University of Oxford, Trinity Term, 2002

Numerical Modelling of Tunnel Installation and Compensation Grouting

Abstract

The work in this thesis covers two areas of research: three-dimensional finite element modelling of tunnel installation and compensation grouting. Research into numerical models for tunnel installation deals with improving existing methods of 3-dimensional finite element simulation of tunnel construction. previous analysis resulted in uneven settlement profiles. The causes for this behaviour are investigated and possible solutions examined.

The main focus on this thesis lies on the second area, the development of a numerical model for compensation grouting. Compensation grouting is a useful technique of protecting surface structures from damaging settlements arising from tunnel construction. Radiating out from an access shaft, pipes are inserted into the grout between the tunnel and the over laying structure. The building on the surface is instrumented and movements are carefully monitored. Once the deformations exceed a certain trigger level, grout is injected into the ground to prevent damage to existing structures. In the finite element model compensation grouting is modelled by inserting zero-thickness interface elements into the ground and applying an internal pressure to these interface elements. An “observational algorithm” is used, where the deformations of the surface are monitored and used to control the injection process. Example analysis of compensation grouting consist of three-dimensional tunnel construction underneath a Greenfield site (meaning no surface structure is present) and underneath a three-dimensional model of a masonry structure. Different strategies are used to control the injection process and their effectiveness in preventing damage is assessed.

Also the possibilities of a refined method are explored where the grout is injected at discrete injection points and the program, using a simple algorithm, determines the direction and distance of the grout flow.

It seems that compensation grouting is highly complex and difficult to model using a simple algorithm to control the injection process in response to measured surface deformations

(no thesis available)