Apparatus for centrifuge modelling of twin-tunnel construction

In urban areas it is common for pairs of tunnels to be used as a method for building rapid transit systems. Driven by an increasing population and demand for services, tunnels are more widespread in their use than at any previous time. Construction of any form of tunnel causes ground movements which have the potential to damage existing surface and sub-surface structures. Modern tunnelling practice aims to reduce these movements to a minimum but there is still a requirement for accurate assessments of possible damage to structures resulting from settlements. For tunnels driven in clay, superposition of settlement predictions made by considering a single tunnel is an accepted method used to estimate movements around pairs of tunnels. Previous research, particularly numerical studies, has indicated that this may not necessarily be sufficient. In this paper a series of centrifuge model tests designed to investigate settlements related to twin-tunnel construction are described. The development of the experimental apparatus for sequential twin-tunnel construction with variable centre-to-centre spacing and volume loss is described in detail

Condition assessment of reinforced concrete beams – Comparing digital image analysis with optic fibre Bragg gratings

Reinforced concrete is the most widely used construction material and thus effective condition assessment of reinforced concrete elements forms a significant part of structural health monitoring. An effective structural health monitoring system should be able to give the owner prior warning that structural elements are reaching conditions approaching either serviceability or ultimate limit states. The aim of this investigation is to compare strain data recorded during load testing of a reinforced concrete beam using Fibre optic Bragg Gratings (FBG) and a photographic technique to determine circumstances most suitable for the use of each of the techniques. The test results indicate that FBG sensors can be used to detect small strains as well as large strains in uncracked concrete elements, while optical images can be used to accurately map crack development over the surface area of the structure

Condition assessment of reinforced concrete beams – Comparing digital image analysis with optic fibre Bragg gratings

Reinforced concrete is the most widely used construction material and thus effective condition assessment of reinforced concrete elements forms a significant part of structural health monitoring. An effective structural health monitoring system should be able to give the owner prior warning that structural elements are reaching conditions approaching either serviceability or ultimate limit states. The aim of this investigation is to compare strain data recorded during load testing of a reinforced concrete beam using Fibre optic Bragg Gratings (FBG) and a photographic technique to determine circumstances most suitable for the use of each of the techniques. The test results indicate that FBG sensors can be used to detect small strains as well as large strains in uncracked concrete elements, while optical images can be used to accurately map crack development over the surface area of the structure

The influence of tunnelling on piled foundations

A study of the influence of tunnelling on piled foundations was recently completed at the University of Cambridge. The study focussed on tunnelling near driven piles in dense sand and was carried out by means of centrifuge modelling. This paper presents a summary of the main findings, describing the mechanism controlling tunnelling-induced pile behaviour, a zone of influence around the tunnel where piles might be affected and recommendations for tunnelling near piles in practice. Both single piles and pile groups are considered

Preparations for field testing for the performance validation of piled wind turbine foundations in expansive clays

Field-testing of piles in an expansive clay is required for the validation of the design criteria for wind turbine foundations in such soil profiles. The test programme includes lateral load tests to investigate the horizontal stiffness of the soil and vertical plug pull-out tests to examine the axial capacity of pile-soil interface. These tests will be conducted in both dry and wet conditions to study the range of expected responses of the pile and evaluate how the changing soil moisture condition affects the pile behaviour. In addition, an instrumented pile socketed into bedrock will be used to determine the strain induced in the pile due to soil heave as the soil saturation levels increase. For the execution of these tests, a large open area with expansive clay of a sufficient depth is required; a stable stratum below the clay is desirable for the socketing of the long piles. An important component of the investigation is the characterisation of the expansive clay profile. A preliminary site investigation has been carried out on the field-testing site which will be supported by further laboratory testing. Details of the soil profile and site characterisation which will be used in the future analyses of the field-testing results are presented