This paper investigates the deformation of buildings due to tunneling-induced soil displacements. Centrifuge model tests of three-dimensionally (3D) printed building models subject to a plane-strain tunnel excavation in dense, dry sand are discussed. The small-scale structures replicate important building characteristics including brittle material properties similar to masonry, a realistic building layout, façade openings, strip footings, and a rough soil-structure interface. Digital images were captured during the experiments, enabling image-based measurements of the building response. Results demonstrate the essential role of the building-to-tunnel position and structural details (i.e., opening percentage and building length). The onset of building cracking and cracking patterns confirms the importance of the building-to-tunnel position and structural details. The tests illustrate that an increase in the façade opening area leads to increased shear deformations while longer buildings caused an increase in bending deflections. An evaluation of the widely accepted framework of treating a structure separately at either side of the greenfield inflection point shows that this procedure can underestimate building damage.@en

This paper evaluates the performance of currently available analytical procedures to assess building response to tunnelling-induced ground displacements. The focus is on methods that account for the interaction between the soil and the structure during tunnelling. These methods relate the soil to the building stiffness and are often called Relative Stiffness Methods (RSMs). Results from centrifuge model tests are used to evaluate the ability of these RSMs to predict building deformations. This evaluation benefits from detailed building models including facade openings, intermediate walls and strip footings. The range of RSM predictions was large, and the accuracy of each RSM was quantified. It was found that no RSM accurately predicts flexural building deformations. Recommendations that consider the building-to-tunnel position to achieve accurate predictions are indicated. This contribution provides a better understanding of the performance of currently available criteria to assess the risk of urban tunnelling.

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The potential damage caused by tunnel excavations to surface buildings can be effectively investigated by centrifuge testing. However, for practical reasons only a limited number of geometrical configurations can be tested in a geotechnical centrifuge. Therefore, numerical modelling provides an essential tool to generalise the laboratory results. This paper illustrates the performance of a 2D finite element model of masonry buildings subjected to tunnelling in sand. The results of the first series of centrifuge tests performed on complex 3D printed masonry structures and presented in the companionpaper were used for the model validation. The model includes nonlinear constitutive laws for both the soil and the building. Differently than previous works, this paper focuses on the accurate simulation of the building response by using structural parameters specifically defined for the assessment of building deformations. The results provide insights into the effect of different building positions relative to the tunnel on the structural response. The validated model can be used to investigate the effect of different building conditions on the soil-structure interaction mechanism.

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Understanding the building response to tunnelling-induced settlements is an important aspect of urban tunnelling in soft ground. Previous centrifuge modelling research demonstrated significant potential to study this tunnel-soil-structure interaction problem. However, these recent studies were limited by simplified building models, which might result in uncertainties when interpreting the building performance to tunnelling subsidence. This paper presents an experimental modelling procedure and the results of a series of centrifuge tests, involving relatively complex surface structures subjected to tunnelling in sand. Powder-based three-dimensional (3D) printing was adopted to fabricate building models with realistic layouts, facade openings and foundations. The 3D printed material had a Young's modulus and a brittle response similar to historic masonry. Modelling effects and boundary conditions are quantified. The good agreement between the experimentally obtained results and previous research demonstrates that the soil-structure interaction during tunnel excavation is well replicated. The experimental procedure provides a framework to quantify how building features affect the response of buildings to tunnelling subsidence.

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In urban tunnelling it is essential to predict the performance of surface structures to tunnelling-induced ground movements. Existing methods to assess potential building damage assume that a building located within the hogging and sagging region of the settlement trough can be subdivided into its sagging and hogging parts, which are then analysed separately. Netzel (2009) importantly identified that this splitting of a building can underestimate the structural damage. This paper examines the effects that both the building length perpendicular to the tunnel axis and the building location relative to the tunnel have on the building response to tunnelling in dry sand. A series of centrifuge model tests, performed on 3D printed surface structures with different building stiffness, are discussed. The findings confirm that potential structural damage caused by tunnelling-induced ground movements significantly depends on the building length and the location of the building within the settlement trough. Importantly, structures that span the sagging/hogging transition zone were found to be more vulnerable to building damage (in the form of cracking) than equal length structures wholly located in either the hogging or sagging region. Longer structures that span the sagging/hogging transition zone were found to be even more vulnerable. As a consequence, experimental results indicated that partitioning a structure into its sagging and hogging parts can lead to underestimation of building damage.@en

Centrifuge modelling necessitates large scale factors due to space and payload limitations. Hence, replicating details of a prototype is difficult. This is particularly true for masonry buildings with highly nonlinear material properties and building features that affect the structural behaviour. This paper discusses powder based 3D printing to replicate masonry structures in centrifuge models. Four-point-bending tests determined the mechanical properties of the 3D printed material. Results reveal a variation in material properties with position and orientation of the 3D printed object in the print bed. After restricting the position of the model in the print bed, repeatable material properties with lower stiffness and higher strength than typical masonry were observed. However, building layout and window opening percentage could be adjusted to create building models with overall bending and axial stiffness typically obtained in the field. These improved 3D printed scale models were subsequently used in centrifuge tests exploring building response to tunnel subsidence. Results show that powder based 3D printed models provide a level of detail not previously simulated in the centrifuge, unlocking new information regarding this soil–structure interaction problem.@en

In urban tunnelling projects, surface buildings interact with tunnelling-induced ground movements. Understanding this interaction aids when predicting the behaviour of buildings above tunnelling works. However, much uncertainty still exists about the impact of structures on tunnelling subsidence and thus current design practice is widely based on empirical methods that neglect this soil-structure interaction. To refine current modelling assumptions and reduce uncertainty, more detailed knowledge of the influence of buildings on tunnelling-induced ground displacements is needed. This paper presents results from an experimental investigation that seeks to provide a more thorough understanding of this soil-structure interaction problem using more realistic surface structures. In particular, it focuses on the effect of surface structures on the ground surface and subsurface soil displacements. Three centrifuge tests with building models placed in different regions of the tunnelling-induced settlement trough were compared to a greenfield case. The ground model consisted of a dense, dry sand and the building was 3D printed. Results showed how the structure alters the vertical and horizontal soil displacements associated with tunnel excavation. Soil deformation mechanisms were notably influenced by the position of the building model relative to the tunnel, causing different magnitudes of vertical and horizontal ground movements above and next to the tunnel, widening of the surface and subsurface settlement troughs and localised failure beneath building corners.

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The interaction mechanisms between surface structures and tunnelling-induced ground movements were investigated through centrifuge testing. Although numerous studies have considered this soil-structure interaction problem, previous experiments have neglected important building characteristics and field data inherently contain numerous uncertainties related to the soil, the structure and the tunnelling procedure. Consequently, the interpretation of results and validation of computational models can be problematic. In this study, tunnelling beneath three-dimensional printed structural models with varying building characteristics (i.e. Position, length and facade openings) was simulated in a centrifuge. The experimental results demonstrate that tunnelling induces soil displacements at the surface and subsurface that are notably altered due to nearby structures. Specifically, different amounts of vertical and horizontal ground movements, soil dilation and widening of settlement troughs were observed. Building distortions and horizontal building strains were also affected by the relative position of the building to the tunnel, the building length and the area of facade openings. The experimental results provide important data for the evaluation of current design methods and verification of computational models.

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Accurate simulation of the building response to soil settlements is useful for the risk assessment of underground excavations in urban areas. Two-dimensional numerical models with coupling between the soil and structure offer a relatively flexible means of investigation for large scale projects, as complete 3D simulation is time consuming. However, the material parameters of the 2D building models need to be adjusted to reproduce the correct building stiffness relative to the soil. Furthermore, 2D models neglect potential torsional effects,which can be relevant during the tunnel advance and due to building orientation with respect to the tunnel. In this work, the responses of 2D and 3D models are compared to evaluate the effect of the dimensional assumption on the accuracy of the prediction of cracking in masonry structures. First, a 2D finite element simulation, which includes both the soil and the structure, is compared to the results of a centrifuge test on a scaled 3D structure subjected to tunnelling in sand. The assumptions employed to calculate the stiffness of the "equivalent" 2D model are highlighted and discussed. Second, a semi-coupled model, where the soil is not modelled directly but the soil displacements are directly applied to an interface which accounts for the soilstructure interaction, is presented. Finally, a 3D semi-coupled model of the structure is used to investigate the 3D boundary effect in the centrifuge sand box. In all simulations, a cracking model is used to account for the structural damage experimentally observed. Comparison of the 3D model and experimental results demonstrates the ability of the model to reproduce the torsional building response.The modelling of cracking in the masonry makes it possible to assess the development of structural damage and its influence on the building response. The comparison between the 2D and 3D results enables quantification of the impact of 2D simplification on the final prediction.

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For urban tunneling projects it is essential to predict and prevent building damage. Although various case studies and experiments have shown that buildings considerably modify greenfield soil movements, widely accepted damage assessment methods neglect this soil-structure interaction and simplify structures as linear elastic beams. This paper summarizes an experimental investigation of the response of more realistic structures to tunneling-induced deformations. Small scale structural models with facade openings and brittle material properties were 3D printed and tested in a geotechnical centrifuge. Soil and structure displacement data were obtained by image-based measurement. Results demonstrate that structures notably mitigate differential greenfield ground displacements. It is also shown that maximum soil settlements, horizontal soil displacements beneath the structure and structural damage in the form of cracking significantly depend on the position of the structure in the settlement profile. The results provide a basis from which to predict building settlement response with greater certainty.@en