Centrifuge modelling of the initiation of cracks in a clay liner subjected to differential settlement with and without overburden pressure

Compacted clay liners are used in the basal and capping layers of landfills to separate the waste material from the environment. These liners are subjected to differential settlement through degradation of the waste or compression of the subgrade. This differential settlement induces cracking in the liner, and reduces the effectiveness of the clay as an en vironmental protection barrier. P hysical model tests were conducted in the geotechnical centrifuge to study the influence of differential settlement on clay liners and observe the crack mechanism using a consolidated kaolin clay beam to model the clay liner . Differential settlement was imposed on the clay beam by means of a trapdoor. Cracking in the clay was monitored through digital analysis of images taken as the tests were conducted using particle image velocimetry. The test investigate d the orientation and types of cracks formed with varying void dimensions and with and without overburden pressure The unconfined clay over the small trapdoor was able to support itself across the void; a punching shear failure occurred in the case of a wider trapdoor or greater overburden pressure

Recreating passenger mode choice-sets for transport simulation: A case study of London, UK

Urban transport infrastructure is under increasing pressure from rising travel demand in many cities worldwide. It is no longer sustainable or even economically viable to cope with increased demand by continually adding capacity to transport networks. Instead, travel demand must be managed by encouraging passengers to adapt their travel behaviour. This approach necessitates a significantly deeper understanding of the seemingly random variations of passenger flows than is afforded by the current travel demand modelling techniques. This study presents a new modelling framework for predicting travel mode choice, through recreating and analysing the choice-set faced by the passenger at the time of day of their travel. A new data set has been developed by combining individual trip records from the London Travel Demand Survey (LTDS), with systematically matched trip trajectories alongside their corresponding mode alternatives from an online directions service and detailed estimates of public transport fares and car operating costs. The value of the data set is demonstrated by comparing two models of passenger mode choice based on stochastic gradient boosting trees, one using only the LTDS data and the other with our full data set. The models are then used to identify the key factors driving passenger mode choice. </jats:p

Structural Performance Monitoring Using a Dynamic Data-Driven BIM Environment

Structural health monitoring data has not been fully leveraged to support asset management due to a lack of effective integration with other datasets. A Building Information Modelling (BIM) approach is presented to leverage structural monitoring data in a dynamic manner. The approach allows for the automatic generation of parametric BIM models of structural monitoring systems that include time-series sensor data; and it enables data-driven and dynamic visualisation in an interactive 3D environment. The approach supports dynamic visualisation of key structural performance parameters, allows for the seamless updating and long-term management of data, and facilitates data exchange by generating Industry Foundation Classes (IFC) compliant models. A newly-constructed bridge near Stafford, UK, with an integrated fibre-optic sensor based monitoring system was used to test the capabilities of the developed approach. The case study demonstrated how the developed approach facilitates more intuitive data interpretation, provides a user-friendly interface to communicate with various stakeholders, allows for the identification of malfunctioning sensors thus contributing to the assessment of monitoring system durability, and forms the basis for a powerful data-driven asset management tool. In addition, this project highlights the potential benefits of investing in the development of data-driven and dynamic BIM environments

Real-time statistical modelling of data generated from self-sensing bridges

Instrumentation of infrastructure is changing the way engineers design, construct, monitor and maintain structures such as roads, bridges and underground structures. Data gathered from these instruments have changed the hands-on assessment of infrastructure behaviour to include data processing and statistical analysis procedures. Engineers wish to understand the behaviour of the infrastructure and detect changes – for example, degradation – but are now using high-frequency data acquired from a sensor network. Presented in this paper is a case study that models and analyses in real time the dynamic strain data gathered from a railway bridge which has been instrumented with fibre-optic sensor networks. The high frequency of the data combined with the large number of sensors requires methods that efficiently analyse the data. First, automated methods are developed to extract train passage events from the background signal and underlying trends due to environmental effects. Second, a streaming statistical model which can be updated efficiently is introduced that predicts strain measurements forward in time. This tool is enhanced to provide anomaly detection capabilities in individual sensors and the entire sensor network. These methods allow for the practical processing and analysis of large data sets. The implementation of these contributions will be essential for demonstrating the value of self-sensing structures. </jats:p

Field observations of settlements during circular shaft excavation in London

Field observations of ground surface settlement during circular shaft construction in LondonEPSRC (Award Reference 1220514) and Geotechnical Consulting Grou

Centrifuge modelling of the initiation of cracks in a clay liner subjected to differential settlement with and without overburden pressure

Compacted clay liners are used in the basal and capping layers of landfills to separate the waste material from the environment. These liners are subjected to differential settlement through degradation of the waste or compression of the subgrade. This differential settlement induces cracking in the liner, and reduces the effectiveness of the clay as an environmental protection barrier. Physical model tests were conducted in the geotechnical centrifuge to study the influence of differential settlement on clay liners and observe the crack mechanism using a consolidated kaolin clay to model the clay liner. Differential settlement was imposed on the clay beam by means of a trapdoor. Cracking in the clay was monitored through digital analysis of images taken as the tests were conducted using particle image velocimetry. The test investigated the orientation and types of cracks formed with varying void dimensions and with and without overburden pressure. The unconfined clay over the small trapdoor was able to support itself across the void; a punching shear failure occurred in the case of a wider trapdoor or greater overburden pres sure

Pile defect assessment using distributed temperature sensing: fundamental questions examined

Thermal integrity testing has been successfully used to assess the quality of cast-in-place piles for the past decade. It employs temperature data measured during concrete curing to identify defects along the piles’ length. However, the uptake of this technology has been rather limited in the piling industry. The main concerns are that the method is not standardised and its reliability is not well understood. In order to address these, there are a number of fundamental questions that need to be explored in more detail, including (a) the optimum time to conduct the assessment, (b) the defect thermal impact, (c) the zone of influence on temperature sensors, (d) the minimum detectable size of a defect and (e) the associated optimum sensor location required. In this paper, experimental and numerical studies were conducted to examine these questions. Fibre optic sensors were employed on model concrete piles in laboratory tests to provide fully distributed temperature data throughout the curing process. The test results showed that the optimum time to assess the defects is approximately at 60% of the time to reach peak temperature and the minimal detectable defect size, using the currently available optical fibre sensor technology, is 4% of the cross-sectional area. In addition, the thermal influence of different defect sizes is presented. Following this, it is shown in the paper that the minimum numbers of sensor cables required to identify defects with cross-sectional areas of 4%, 5% and 8% are eight, six and four cables, respectively. The optimum layout of these sensor cables within a pile cross-section has also been discussed. When specifying pile instrumentation for integrity assessment, the findings of this paper enable practising engineers to make informed judgements in relation to the size of defects they would like to detect (and hence the associated risk this entails) together with the corresponding instrumentation layout required.</p

A Tale of Two Tunnels-Understanding the Performance of Existing and New Tunnels during Construction Works

In many cases, new tunnels in highly populated urban cities like London will need to be constructed underneath a dense network of existing tunnels to avoid them. The construction of new tunnels, however, inevitably results in ground deformations, which are transmitted to adjacent existing structures. The response of existing cast iron tunnels to tunnelling-induced deformation is not well understood and practicing engineers are faced with significant uncertainties about their response. The first part of this paper presents a case study in which distributed fibre optic strain sensing (DFOSS) have been deployed in a section at an existing cast iron tunnel in London underneath which a new, much larger tunnel was being constructed. The DFOSS deployment in this case study provided a detailed response for the cast iron tunnel in a holistic manner that is not encountered in practice. In the second part of the paper, one of the latest case studies being conducted at the Cambridge Centre for Smart Infrastructure and Construction (CSIC), associated with the instrumentation and monitoring of cross-passages in sprayed concrete tunnel linings (SCL) is presented and discussed. The DOFSS provided new data and hence new insights into SCL behaviour that was not available before.This is a metadata record for an article that can't be shared due to publisher copyright