This paper describes part of the monitoring undertaken at Abbey Mills shaft F, one of the main shafts of Thames Water's Lee tunnel project in London, UK. This shaft, with an external diameter of 30 m and 73 m deep, is one of the largest ever constructed in the UK and consequently penetrates layered and challenging ground conditions (Terrace Gravel, London Clay, Lambeth Group, Thanet Sand Formation, Chalk Formation). Three out of the twenty 1·2 m thick and 84 m deep diaphragm wall panels were equipped with fibre optic instrumentation. Bending and circumferential hoop strains were measured using Brillouin optical time-domain reflectometry and analysis technologies. These measurements showed that the overall radial movement of the wall was very small. Prior to excavation during a dewatering trial, the shaft may have experienced three-dimensional deformation due to differential water pressures. During excavation, the measured hoop and bending strains of the wall in the chalk exceeded the predictions. This appears to be related to the verticality tolerances of the diaphragm wall and lower circumferential hoop stiffness of the diaphragm walls at deep depths. The findings from this case study provide valuable information for future deep shafts in London.

Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. While these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain the values corresponding to the data gaps in between; in practice, these discrete instrumented points could be tens of Manuscript Click here to download Manuscript Pelecanos_et_al_Manuscript_7.2.docx 2 meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin Optical Time Domain Reflectometry fibre optic strain sensing system however is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. In this paper, three case studies are presented where the performance of three concrete bored piles in London is investigated using both conventional vibrating wire strain gauges and distributed fibre optic strain sensing during maintained pile load tests which enabled comparisons to be made between the two instrumentation systems. In addition, finite element analyses were conducted for the three piles and it was found that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behaviour.

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.

This paper presents a three-dimensional nonlinear finite element (FE) model for prestressed concrete girders strengthened in shear with externally bonded carbon fibre reinforced polymer (CFRP) reinforcement. A total strain rotating crack model, where the crack direction changes with the change in the direction of the principal tensile stress, was used for the concrete. In this model, explicit modelling of the concrete shear behaviour after cracking, e.g. via a shear retention parameter, is not required as the crack plane is always a principal plane with no shear stresses. The FE model was validated using experimental results from the literature. An extensive parametric study was carried out to identify the effect of the concrete compressive strength, CFRP width-to-spacing ratio, CFRP thickness, girder effective depth, shear span to effective depth ratio, level of prestress, tendon profile, precracking and CFRP-to-concrete interface model on the predicted shear force capacity. The results suggested that the predicted shear strength enhancement can be significant and increases with the increase in concrete compressive strength, CFRP width-to-spacing ratio, and CFRP thickness but decreases with the increase in girder effective depth and shear span to effective depth ratio.