Design of tunnel support for single zones with swelling clay

Abstract: Swelling clay is an important and challenging geological feature in tunnelling projects.The behaviour of swelling clay is influenced by many internal and external factors.This, combined with a lack of experience and knowledge has resulted in challengeswhen accounting for the swelling phenomena. In addition to this, there is a lack ofunderstanding for the calculation of rock support when swelling clay is present. Themain objectives of this thesis were to compare laboratory methods used to measure theswelling potential, identify possible uncertainties when performing oedometer tests,and to provide a model for design of rock support for single zones with swelling clay.To support these objectives, a literature review has been conducted and laboratory testshave been performed to determine swelling properties using clay samples collectedfrom a tunnel failure in Sweden. In addition, a model has been derived for design ofrock support when swelling clay is present in single zones of different widths. Theresults from the laboratory tests showed that the clay sample could be characterizedas active respectively moderately active clay. The results of the model for design of rocksupport showed that the width of the swelling zone and the swelling pressure have asignificant impact on the shotcrete thickness, rebar spacing and reaction forces at therock bolts. However, future research for design of rock support is required as well asdevelopment of a more detailed standard for testing of swelling clay.