| Urbanisation is a phenomenon that has continued undisturbed since the rise of the industrial era. As the populations of cities increase so do the needs and demands associated with urban expansion. These include the provision of adequate infrastructure to support and sustain the current quality of life, while also planning prudently for future growth. However this continued intensified land use progressively presents challenges to planners and operators alike. It is for this reason that engineers are opting to use underground space as an alternative means of meeting societal needs without significant disruption to activities it the surface. Tunnels are therefore becoming increasingly useful for inspecting and retrofitting buried facilities; buried transportation routes can be seen in subway lines and tunnelled highways. However these services cannot exist without adequate knowledge of the ground in which they exist. It is therefore imperative that studies be done in order to understand as much as possible the intricacies of soil-tunnel interaction.;A review of the literature has shown that overwhelming attention has been placed on modelling tunnels in isotropic, homogeneous media, whether those models be empirical, analytical, physical or numerical. However soils in nature are neither homogeneous nor isoptropic. Therefore the objective of this thesis was to examine the soil-tunnel interaction within an excavation in layered ground. A flexible aluminum lining sleeve was placed inside of a cavity excavated out of a cohesive medium for the purpose of monitoring the reaction stresses and bending moments arising from contact with the encroaching soil. A granular stratum was introduced within the cohesive soil at varying elevations above a fixed tunnel position in order to study the effect of proximity of this layer on the soil-lining response. It was found that the presence of the sandy stratum had an effect on the response when it was located at an elevation of two or less equivalent excavated diameters. At elevations greater than this, the effect was negligible. Stresses and bending moments were reduced by 90% when a layer of sand was introduced at one equivalent excavated diameter above the tunnel as opposed to having no sand layer. Further results involving a numerical model were similar; when the granular layer was one excavated diameter above the tunnel the axial forces were found to be 53% of those calculated when no such layer was present. Soil displacement patterns revealed a related trend, with an increase in soil movement of 17% as the sand layer was moved from one excavated diameter away from the opening to the case where no granular material existed. |
