In bored tunnel design, most recent structural design models for tunnel linings concentrate on the behaviour of the tunnel lining in the long-term. The load on the tunnel lining in these models is derived from the original soil stresses, often simplified for a single homogeneous layer. Field observations show that higher loads may occur in the initial hours after the assembly, that might effect the tunnel lining and that soil layers with different stiffnesses may have a negative impact on the internal forces of the tunnel lining. This paper proposes a new model for these early construction stages and also includes a more accurate model which explicitly models the impact of multilayered soils. The change of internal forces in the tunnel lining from the initial construction time to the long-term is investigated with this model. Validations with field observations and other analysis results at time of construction and the long-term confirm that the new structural analysis models can accurately predict internal forces in the tunnel lining. The analysis results also show that internal forces in the tunnel lining have an increasing trend in time and become stable in the long-term and accord with field observations.@en

Generally, studies on structural design for bored tunnels focus on moderate to deep tunnels (cover-to-diameter ratio C/D ≥ 2). Such tunnel design methods cannot be used for shallow-situated bored tunnels because the influence of buoyancy is discounted, and actual loads on the tunnel lining are not taken into account properly. This paper proposes a new model that has more accurate loads on the tunnel lining combined with finite-element analysis for shallow tunnels. Internal forces and deformations of various shallow bored tunnels are investigated. The relationship between the optimal thickness-to-diameter ratio d/D of the tunnel cross section and the cover-to-diameter ratio C/D is also studied.@en

Despite the fact that shallow tunnels have the benefits of low short-term construction costs and long-term operational costs primarily due to the shallow depth of the station boxes, the limited understanding of shallow tunnelling in soft soils is an obstacle to the development of shallow tunnels in urban areas. This study carries out a theoretical investigation of the effects of reducing the cover-to-diameter ratio C/D for shallow tunnels in soft soils. In stability analysis, the uplift, face stability and blow-out mechanisms are investigated. This study investigates interactions between the TBM and surrounding soil in tunnelling process, the stability of the TBM is not taken into account. The relationship between the C/D ratio and the required thickness-to-diameter ratio d/D as well as the required support pressures will be derived in various soils. Ranges of support pressures are also estimated for the TBM. Structural analysis is carried out for the variation of deformations and internal forces of the tunnel lining when reducing the C/D ratio. Since the conventional design models are not suitable in the case of shallow tunnels a new structural analysis model, which includes the difference between loads at the top and at the bottom of the tunnel, is proposed. Optimal C/D ratios with various d/D ratios for shallow tunnels in soft soils are also derived. With respect to ground movement analysis, this research investigates the areas affected by shallow tunnelling with a preliminary assessment of the risk of building damage by investigating surface and subsurface soil displacements. These areas are determined for different tunnel diameters in various soil types and are then compared to recent studies. The total volume loss is estimated at the tunnelling face, along the TBM, at the tail and includes long-term consolidation settlements. By combining empirical models from the literature and the proposed new models, the volume loss components are estimated both for short-term construction and for the long-term consolidation effects. This shows that a no volume loss is feasible in shallow tunnelling with careful control of the support pressure. The boundaries of the influence zones in shallow tunnelling are identified and discussed on the basis of various case studies. The effects of the soil parameters on the influence areas are also investigated. From these calculations, the limits and optimal C/D ratios for shallow tunnelling are deduced and recommendations and solutions for improving the shallow tunnelling process are proposed in this dissertation. @en

In estimating the effect of tunnelling on existing buildings, the value of volume loss, which is often determined by experience, is an important input parameter. This paper proposes a method to predict the volume loss for various cover-to-diameter C/D ratios in case of shallow tunnelling. By applying a number of (empirical) relation, such as the stability number of O’Reilly(1988) and an analysis of the bentonite and grout flows, volume loss at the tunnelling face, along the shield and at the tail is estimated. Long-term volume loss behind the shield is also derived by means of a consolidation analysis. A width band of achievable volume loss for future projects is derived in this way.@en

The extent of the influence zone affected by tunnelling depends on the amount of over-excavation and stress changes induced in the soil, normally represented as a value of volume loss. This paper combines upper and lower estimates of volume loss for different soil conditions and cover-to-diameter ratios in order to identify the zones around the tunnel influenced by tunnelling. These zones are combined with risk categories of damage of existing buildings in order to identify whether applying mitigating methods or taking additional control measures during tunnelling would be needed for a safe and damage-free tunnel construction. The influence of soil parameters on the influence zones is also investigated to identify their impact and quantity of the requirements for mitigating measures.@en

Assessing the impact of underground construction on existing structures in urban areas is an important topic during design. In this paper, the extent of the effect area due to tunnelling is estimated, where existing foundations are influenced based on the investigation of surface and subsurface settlements. The extent of the areas where building deformations exceed allowable settlements is presented, which will provide a preliminary assessment during design on the risk on existing structures, based on allowable settlement umax and slope of building max. A more accurate impact area of shield tunnelling on nearby pile foundations is proposed.@en

The extent of the influence zone affected by shallow tunnelling depends on the value of volume loss which normally represents the amount of over-excavation and stress changes induced in the soil. This paper combines upper and lower estimates of volume loss for different soft soils and cover-to-diameter ratios in order to identify the extent of zones around the tunnel influenced by tunnelling. These zones are combined with risk categories of damage of existing buildings in order to determine whether applying mitigating methods or taking additional control measures during tunnelling would be needed for a safe and damagefree tunnel construction. The effects of soil parameters on the influence zones are also investigated to identify their impact and quantity of the requirements for mitigating measures.@en

The extent of the influence zone affected by tunnelling depends on the amount of over-excavation and stress changes induced in the soil, normally represented as a value of volume loss. This study combines upper and lower estimates of volume loss for different soil conditions and ground movement analysis for various cover-to-diameter ratios C/D in order to identify the zones around the tunnel affected by shallow tunnelling. These zones are combined with risk categories of damage to existing buildings to identify whether mitigating methods or additional control measures during tunnelling would be needed for a safe and damage-free tunnel construction. The boundaries of these influence zones have been derived both for surface and subsurface analyses. Although there is only a small number of available case studies, they show good agreement between the analysis and observed data. The influence of soil parameters on the influence zones is also investigated. This study shows that by improving soil properties, the boundaries of influence zones can be controlled. The results in this paper are also the first theoretical basis for estimating the requirements for mitigating measures in shallow tunnelling in soft soils.@en