Predicting the ground movements above twin tunnels constructed in London clay

Hunt, Dexter (2005). Predicting the ground movements above twin tunnels constructed in London clay. University of Birmingham. Ph.D.

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Abstract

This thesis provides an improved understanding of surface and sub-surface movements above twin and triple tunnel constructions in London Clay and puts in place a framework for improving the current semi-empirical predictive methods (i.e. a Gaussian curves) for estimating ground movements.

The thesis reports the results of 2D plain strain undrained tunnel analyses using the ABAQUS finite element modelling package in conjunction with a small strain stiffness soil model (Jardine et al 1986) and a modified gap parameter. The actual and relative changes in displacement are reported for single tunnels with varying diameter, depth and volume loss. These are also reported for twin tunnels (in a side-by-side, piggyback and offset alignment) and triple tunnels (in a side-by-side alignment) using different construction sequences. The multiple tunnels are constructed with a time delay which includes stiffness changes with no consolidation.

The results of a 1/50 small-scale model of twin unlined side-by-side tunnels, constructed using two types of tunnelling procedure (i.e. augering and coring), conducted at 1g in a heavily overconsolidated sample of Kaolin clay are also reported.

Based on the finite element results a Modification Factor is presented which is applied to existing semi-empirical methods in order to improve significantly the prediction of displacements above side-by-side twin and triple tunnel constructions for several published case histories.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):