Building response to tunnelling

AbstractUnderstanding how buildings respond to tunnelling-induced ground movements is an area of great importance for urban tunnelling projects, particularly for risk management. In this paper, observations of building response to tunnelling, from both centrifuge modelling and a field study in Bologna, are used to identify mechanisms governing the soil–structure interaction. Centrifuge modelling was carried out on an 8-m-diameter beam centrifuge at Cambridge University, with buildings being modelled as highly simplified elastic and inelastic beams of varying stiffness and geometry. The Bologna case study presents the response of two different buildings to the construction of a sprayed concrete lining (SCL) tunnel, 12m in diameter, with jet grouting and face reinforcement.In both studies, a comparison of the building settlement and horizontal displacement profiles, with the greenfield ground movements, enables the soil structure interaction to be quantified. Encouraging agreement between the modification to the greenfield settlement profile, displayed by the buildings, and estimates made from existing predictive tools is observed. Similarly, both studies indicate that the horizontal strains, induced in the buildings, are typically at least an order of magnitude smaller than the greenfield values. This is consistent with observations in the literature. The potential modification to the settlement distortions is shown to have significant implications on the estimated level of damage. Potential issues for infrastructures connected to buildings, arising from the embedment of rigid buildings into the soil, are also highlighted

Twin-tunnelling-induced changes to clay stiffness

With urban tunnel construction growing worldwide, the ability to accurately predict the ground and structural response to tunnelling and the associated risks is now more important than ever before. Engineers are expected to consider all aspects of tunnel engineering in order to safeguard existing infrastructure, by employing field monitoring, physical modelling and numerical analysis in developing a detailed knowledge of multiple soil-structure interactions. The Geotechnique Symposium in Print took place at the Institution of Civil Engineers on 14th September 2017 to discuss the wider aspects of tunnelling in urban locales. The papers included here bring together important international research presented at the symposium and featured in Geotechnique . Topics of discussion, amongst others, included - case studies from Crossrail, CTRL and Barcelona metro projects - open-face tunnelling effects on non-displacement piles in clay - influence of building characteristics on tunnelling-induced ground movements - impact of new tunnel construction on structural performance of existing tunnels. Tunnelling in the Urban Environment offers practitioners and researchers alike with important coverage of the increasingly complex and varied challenges engineers have to face when constructing tunnels in urban centres

A cantilever approach to estimate bending stiffness of buildings affected by tunnelling

The evaluation of the effect of tunnel construction on buildings is a problem being faced by engineers around the world. Building bending stiffness is an important parameter in tunnel-soil-structure interaction analyses. The construction of a new tunnel influences an existing building via induced ground movements, and the existence of a building also affects ground displacements due to tunnelling via its stiffness and weight. The magnitude of the effect depends on the properties of the building and foundation as well as the complex soil-structure interactions that occur. In this paper, an approach is proposed in which the building response to tunnelling is related to the bending of a cantilever beam and empirical-type relationships are developed to predict building bending stiffness. This approach is relevant to cases where the building is perpendicular to the tunnel axis and its nearest edge does not overlap more than half of the tunnel cross-section. Rigorous finite element analyses are used to evaluate the response of buildings to ground displacements and expressions are provided which relate three-dimensional building bending stiffness to a simple beam theory expression. The results show that lower storeys have a proportionally higher stiffness effect than higher storeys. In addition, the parameters that affect the global behaviour of the building, such as component stiffness and geometry, are studied. The suggested approach provides a relatively quick and easy way of accurately evaluating building bending stiffness for use within tunnel-soil structure interaction analyses

Pile tunnel interaction: literature review and data analysis

The underground space of densely populated cities contains deep foundations and tunnels. Considering the possibility that a new tunnel can be built close to existing piles it is necessary to assess the possible effects of that interaction. Most case studies have shown limited damage on pile supported structures; however, these constructions deal with great uncertainty as the mechanism of pile tunnel interaction is not completely understood. Physical tests at full and reduced scale are a valuable tool to improve that understanding and validate prediction methods. A descriptive review of studies on that matter is presented followed by a quantitative comparison of the results of tunnelling induced axial forces and settlements on the piles. Gathering and analysing these data provided a deeper understanding of the influencing geometrical and structural parameters as well as indicating where further research is needed

Addressing student models of energy loss in quantum tunnelling

We report on a multi-year, multi-institution study to investigate student reasoning about energy in the context of quantum tunnelling. We use ungraded surveys, graded examination questions, individual clinical interviews, and multiple-choice exams to build a picture of the types of responses that students typically give. We find that two descriptions of tunnelling through a square barrier are particularly common. Students often state that tunnelling particles lose energy while tunnelling. When sketching wave functions, students also show a shift in the axis of oscillation, as if the height of the axis of oscillation indicated the energy of the particle. We find inconsistencies between students' conceptual, mathematical, and graphical models of quantum tunnelling. As part of a curriculum in quantum physics, we have developed instructional materials to help students develop a more robust and less inconsistent picture of tunnelling, and present data suggesting that we have succeeded in doing so.Comment: Originally submitted to the European Journal of Physics on 2005 Feb 10. Pages: 14. References: 11. Figures: 9. Tables: 1. Resubmitted May 18 with revisions that include an appendix with the curriculum materials discussed in the paper (4 page small group UW-style tutorial

TBM pressure models: observations, theory and practice

Mechanized tunnelling in soft ground has evolved significantly over the last 20 years. However, the interaction between the tunnel boring machine (TBM) and the ground is often understood through idealized concepts, focused mostly on the machine actions in detriment of the reactions from the ground. These concepts cannot be used to explain several mechanisms that have been observed during the construction of mechanized tunnels. Therefore, this paper presents the path from field observations to the theoretical developments to model the TBM-ground interaction more realistically. Some ideas on how these developments can be applied into practice are presented. Finally, a discussion is proposed about how an effective collaboration between academia and industry can alleviate the current concentration of knowledge in the state of practice

Ballistic electron spectroscopy

We demonstrate the feasibility of ballistic electron spectroscopy as a new tool for mesoscopic physics. A quantum dot is utilised as an energy-selective detector of non-equilibrium ballistic electrons injected into a two-dimensional electron system. In this paper we use a second quantum dot as the electron injector to evaluate the scheme. We propose an application in the study of interacting 1D and 0D systems.Comment: 3 pages, 4 figure