Regional-scale assessment of the damage caused by earthquakes to structures is crucial for post-disaster management. While remote sensing techniques can be of great help for a quick post-event structural assessment of large areas, currently available methods are limited to the detection of severely-damaged buildings. Furthermore, remote sensing-based assessment methods typically provide only qualitative results, as they lack integration with information on the building's behaviour in response to seismic-induced ground shaking. In this study, we developed a new methodology that uses airborne Light Detection And Ranging (LiDAR) data in combination with structural indicators of building response to provide a quantitative assessment of earthquake-induced damage at a regional scale. LiDAR datasets collected before and after an earthquake are used to measure residual displacements of building roofs. The resulting lateral drift estimations are used to quantify the level of damage for a specific building typology. Application to the LiDAR datasets collected before and after the 2014 earthquake in Napa Valley, California, demonstrates the capability of the proposed method to detect moderate levels of structural damage, proving its potential for faster and more accurate support to post-disaster management.

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Failure of tall slender masonry structures during earthquakes often involves partial collapse of the structure well-above ground level. Consequently, the elastic response of the structure needs to be considered, which often requires modal analysis using finite element models — the generation of which can be labour-intensive and time-consuming. This paper presents a new integrated modelling approach which combines finite element analysis with rocking dynamics to model the seismic response of complex structural geometries in a computationally-efficient manner. The modelling strategy is implemented within the open-source computational framework COMPAS and is incorporated within the broader framework of a tool being developed for the seismic collapse assessment of masonry structures. The framework of this tool is first outlined, and the utility of the new modelling approach then demonstrated through application to the seismic assessment of a three historic masonry towers in North-Eastern Italy. The importance of accounting for elastic amplification effects, as well as the influence of varying boundary conditions on the dynamic response, is also illustrated.

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In fast growing cities, tunnels are increasingly adopted solutions to meet the demand for more effective transportation. As settlements caused by tunnel excavations can damage buildings along the tunnel alignment, a large portion of investments in underground construction projects is typically devoted to the assessment of settlement-induced damage to buildings. To contain the project costs, only a limited number of buildings is usually included in the monitoring scheme, and therefore damage assessment procedures are traditionally based on highly conservative assumptions. Modern space-borne Synthetic Aperture Radar (SAR) missions can provide monitoring data over large areas, guaranteeing high spatial resolutions and short revisit times. Persistent Scatterer Interferometry (PSI) [1,2] can be used to extract building deformations over time from long temporal series of InSAR images, providing measurements with an accuracy comparable to traditional in-situ monitoring, i.e. of the order of millimetre, and at a much lower cost. However, without an integration with structural models, PS-InSAR data cannot provide meaningful information on the building conditions. This integration is particularly demanding for large excavation projects, where hundreds of buildings need to be assessed. In this research, we present a new methodology for the integration of PS-InSAR-based building deformations within damage assessment procedures to estimate the level of vulnerability of buildings adjacent to tunnel excavations. The methodology combines in an automated workflow PS-InSAR data, GIS (Geographical Information System)-building databases and semi-empirical models of the building response to tunnelling, to provide a more accurate estimate of each structure damage level. We tested the proposed methodology on the Crossrail tunnel alignment in London, UK. Crossrail tunnelling activities started in May 2012, and resulted in the excavation of 21 km twin tunnels below central London. We used as an input historical PS-InSAR data obtained by processing 72 COSMO-SkyMed descending images from 2011 to 2015 [3]. The processing led to the identification of 228,000 PSs over the monitored area, which correspond to an average density of about 9000 PS/km2. The map in Figure 1 shows the distribution of cumulative displacements along the Crossrail tunnel alignment, revealing the settlement caused by the excavation. In the region above the tunnels, line of sight (LOS) displacements between -2 cm and -3.5 cm were observed. PS points were automatically associated to the buildings along the tunnel route, and for each building, the corresponding PS-InSAR-based displacements were used to estimate the actual building settlement profile, using the fitting model described in Giardina et al., 2019 [4]. Figure 2 shows an example of a specific building, for which the PS-InSAR measurements were used to reconstruct the settlement below the structure. Then, the actual building settlement curves were analysed through a semi-empirical model of the building response to tunnelling [5] to estimate the maximum building strains. On the basis of its maximum strain, a level of damage was assigned to each building, and damage maps showing the distribution of building damage levels were the output of the proposed methodology (Figure 3). The developed algorithm enabled the identification of the structural damage of 858 buildings, highlighting its capability as a city-scale assessment tool. Additionally, the application of the proposed algorithm made available for the first time a large dataset of field observations of the building response to tunnelling. This allowed the identification of relationships between building construction materials, foundation typologies and global building behaviour. The findings can help improving current damage assessment procedures and advance the understanding of building response to tunnelling, with an impact on future excavation projects all over the world.@en

Structural deformation monitoring is crucial for the identification of early signs of tunnelling-induced damage to adjacent structures and for the improvement of current damage assessment procedures. Satellite multi-temporal interferometric synthetic aperture radar (MT-InSAR) techniques enable measurement of building displacements over time with millimetre-scale accuracy. Compared to traditional ground-based monitoring, MT-InSAR can yield denser and cheaper building observations, representing a cost-effective monitoring tool. However, without integrating MT-InSAR techniques and structural assessment, the potential of InSAR monitoring cannot be fully exploited. This integration is particularly demanding for large construction projects, where big datasets need to be processed. In this paper, we present a new automated methodology that integrates MT-InSAR-based building deformations and damage assessment procedures to evaluate settlement-induced damage to buildings adjacent to tunnel excavations. The developed methodology was applied to the buildings along an 8-km segment of the Crossrail tunnel route in London, using COSMO-SkyMed MT-InSAR data from 2011 to 2015. The methodology enabled the identification of damage levels for 858 buildings along the Crossrail twin tunnels, providing an unprecedented number of high quality field observations for building response to settlements. The proposed methodology can be used to improve current damage assessment procedures, for the benefit of future underground excavation projects in urban areas.

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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

Structural monitoring of surface building displacements is a significant component of the total financial investment for underground construction projects in urban areas. While traditional monitoring requires in-situ (terrestrial) measurements and trigger levels based on preliminary evaluation of vulnerable structures, very recent advances in Interferometric Synthetic Aperture Radar (InSAR) techniques enable remote monitoring over extensive areas, providing rapid, semi-automatic, and dense measurements with millimetre accuracy. Despite the well-established use of InSAR in geophysical applications, only a few studies are currently available on the use of satellite-based monitoring for the assessment of building deformations and structural damage. The aim of this project is to investigate the potential of InSAR monitoring data as an input to post-tunnelling damage assessment procedures. First, InSAR-based measurements of building displacements, induced by the excavation of Crossrail tunnels in London, were acquired and processed. Then, following the definition of a step-by-step procedure, the satellite-based building displacements were used to evaluate structural deformation parameters typically used in extensive damage assessment procedures. Results show that the number of available measures per single building can enable the estimation of deformation parameters, a capability that is not economically feasible for large scale projects using traditional monitoring systems. The comparison with greenfield predictions offers new insight into the effect of soil-structure interaction and demonstrates the suitability of InSAR monitoring for post-tunnelling damage assessment of structures. The outcome of this work can have a significant economic impact on the construction industry and can advance the knowledge of building and infrastructure response to ground subsidence.

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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 expansion of modern cities causes a growing demand for efficient transport facilities, motivating the realization of large urban tunnelling projects. A major concern during tunnelling operations is the evaluation of the response of existing buildings to induced ground movements, with a considerable economic impact on the total project cost. Since traditional monitoring is based on costly in-situ installations, only a limited amount of observations is typically provided for each structure. Without a systematic increase in the availability of monitored building deformations, lesson learned from previous projects cannot be effectively used to improve existing damage assessment procedures. Satellite Interferometric Synthetic Aperture Radar (InSAR) techniques, providing high quality measurements of building deformations, have been recently validated to be used in combination with damage assessment procedures. In particular, Multi-Temporal InSAR can provide cumulative displacement maps for a high density of monitoring points with millimetric accuracy, enabling to assess buildings nearby the excavation. In this paper, results from post-tunnelling damage assessment of hundreds of buildings along the Crossrail route in London are presented. By exploiting InSAR-based displacements, a semi-automated assessment tool is used to investigate the structural response to tunnelling-induced settlements. Results are compared to the ones obtained through the greenfield-based assessment, enabling to evaluate their accuracy. The application of the proposed method to real case studies highlights its potential for the quasi-real time identification of building damage levels over extensive area. This semi-automatic procedure can positively impact the construction industry, enabling to improve traditional damage assessment strategies and to complement ground-based monitoring systems.@en

The increasing demand for underground infrastructure should be supported by innovation in monitoring and damage assessment solutions to minimise damage to surface structures caused by ground settlements. This paper evaluates the use of multitemporal synthetic aperture radar interferometry (MT-InSAR) to calculate tunnelling-induced deformations of buildings. The paper introduces a step-by-step procedure to use InSAR displacements as an input to the structural damage assessment. After a comparison between traditional and InSAR monitoring data for the London area during the Crossrail excavation, the high resolution, high density InSAR-based displacements were used to evaluate the building deformations for a number of case studies. Results demonstrate the quality of information provided by InSAR data on soil-structure interaction mechanisms. Such information, essential to evaluate current damage assessment procedures, is typically only collected for relatively few buildings due to the cost of traditional monitoring. A comparison between damage indicators derived from greenfield assumptions and building displacements quantifies the practical benefit of the proposed step-by-step procedure. This work aims at filling the gap between the most recent advances in remote sensing and the civil engineering practice, defining the first step of an automated damage assessment procedure which can impact large scale underground projects in urban areas.

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Building monitoring and protection are important components of underground projects in urban areas. Typically the procedures applied for the assessment of settlement-induced damage to buildings are based on simplified assumptions that do not take into account soil–structure interaction. Assessment methods based on the relative stiffness between the structure and the soil exist, but they are rarely applied in practice due to concerns about the accuracy and reliability. The primary aim of this work is to use the large amount of monitoring data provided by the Crossrail project in London to improve understanding of building performance and existing damage assessment methods. The paper gives an initial overview of the available monitoring data by presenting four representative case studies for load-bearing masonry buildings on shallow foundations. Structural data are then used to evaluate the consistency of predictions produced by different relative stiffness formulations. The results show the effect of building stiffness on the soil surface settlements and clarify the effects of various assumptions made during prediction. The conclusions highlight opportunities to improve prediction procedures and the need for more detailed monitoring data for future tunnelling projects.

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Spaceborne multi-temporal interferometric synthetic aperture radar (MT-InSAR) is a monitoring technique capable of extracting line of sight (LOS) cumulative surface displacement measurements with millimeter accuracy. Several improvements in the techniques and datasets quality led to more effective, near real time assessment and response, and a greater ability of constraining dynamically changing physical processes. Using examples of the COSMO-SkyMed (CSK) system, we present a methodology that bridges the gaps between MT-InSAR and the relative stiffness method for tunnel-induced subsidence damage assessment. The results allow quantification of the effect of the building on the settlement profile. As expected the greenfield deformation assessment tends to provide a conservative estimate in the majority of cases (~71% of the analyzed buildings), overestimating tensile strains up to 50%. With this work we show how these two techniques in the field of remote sensing and structural engineering can be synergistically used to complement and replace the traditional ground based analysis by providing an extended coverage and a temporally dense set of data.

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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

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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Current procedures for the assessment of buildings response to tunnelling take into account the effect of soil-structure interaction through the definition of the building stiffness relative to the soil stiffness. Limitations of these procedures are uncertainties in the evaluation of structural parameters and inconsistent results between different methods. In this paper, three existing formulations of the Relative Stiffness Method (RSM) have been critically evaluated by analysing the governing factors in the building stiffness calculation and their effect on the structural damage assessment. The results of a sensitivity study on building height, eccentricity, opening ratio, tunnel depth, soil and masonry stiffness, and trough width parameter quantified the effect of these factors on the considered RSMs. The application of different RSMs to a real masonry building adjacent to the Jubilee Line tunnel excavation underlined the significant effect of window openings, façade stiffness and neutral axis position on the building stiffness calculation and deformation prediction. These results highlight the need for a consistent and robust damage assessment procedure.

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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

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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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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