In general, the in-situ ground stress reduces with an increase in inward radial displacement in an unloaded ground/tunnel. The major factors affecting ground-support interaction in tunnels are as follows:
(i) The relative stiffness of ground and linings plays an important role in ground-support interaction. For instance, a stiff support could support the unloaded ground at lower deformation than a flexible support.
(ii) Delay of support to tunnels results in the ground to be deformed by a certain degree before the installation of linings. Consequently, the linings take up less loads subsequently owing to less deformation of ground generated after the action of delay of support.
(iii) As the ground is unloaded, stress is redistributed during excavation. In case the ground is delayed in support and the ground respond from elastic region to yielding region, it results in larger displacement and supporting load.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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