Pipe jacking is a trenchless construction technique for the installation of underground pipelines. Although pipe jacking is widely used, fundamental research is still needed to understand fully the factors affecting the process and to prevent unexpected failure. With the time and financial limitation, it is difficult to explore all aspects of these factors with experiments; and it is also difficult to study them by analytical methods because of the complexity of the problem. This thesis describes the use of the finite element technique to study the pipe performance under different environments and the laboratory tests of several different joint designs. The emphasis of the current research is on the performance of the concrete pipes during jacking under working conditions and to seek possible improvements in the design of pipes and pipe joints by numerical modelling. In the finite element modelling, a simplified two-dimensional model is used for a preliminary study, then the analyses are carried out with three-dimensional models A, B and C representing a complete pipe, a pipe with surrounding soil and a symmetric three-pipe system respectively. Several factors affecting the pipe performance have been examined, for example, the properties of the packing material, the stiffness of the surrounding soil, the misalignment angle at the pipe joint, and the interaction between the pipe and surrounding soil. The numerical results show that the misalignment of the pipe is the dominating factor inducing both tensile stresses and localized compressive stresses in the concrete pipe, especially with a high misalignment angle which results in separation between packing material and the pipe. The packing materials with high Poisson's ratio and high stiffness also induce higher tensile stresses in the pipe, and the influence of Poisson's ratio is significant. Under 'diagonal' loading, both the stiffness of the surrounding soil and the interaction between the pipe and the surrounding soil have a significant effect on the stresses within the concrete pipe. Under 'edge' loading, the greatest potential damage is at the pipe joint due to the tensile stresses in the hoop direction; while under 'diagonal' loading, the damage is most likely the cracking on the external surface of the pipe along a line connecting the two diagonal loaded corners. The results show that the Australian model gives somewhat good prediction about the maximum normal stress and the diametrical contact width at pipe joint. Based on the numerical results, several different joint designs for improving the pipe strength have been proposed and tested in the laboratory. Both the laboratory tests and the back analyses suggest that the local reinforcement and the local prestressed band at the pipe joint will improve the pipe strength.

The mechanisms by which a geogrid acts to reinforce a granular layer over a soft clay were investigated with reference to trafficking of unpaved roads. The research involved a programme of physical testing at both model and full scale. Model tests were carried out for monotonic and cyclic loading of a dual footing on to a layer of granular material that was compacted over a consolidated kaolin sample. The tests were made in conditions of plane strain at a quarter scale, and included a scaled geogrid at the base of the granular layer. Measurements of footing load, displacements and photographic observations through a perspex front face to the test box were used to identify the reinforcing actions of the geogrid. A virtual work procedure was adopted in analysis of the results for both unreinforced and reinforced layers. The procedure accounts for lateral restraint of the subgrade and a membrane action in the reinforced tests, and allows a comparison of the cyclic test results with an equivalent monotonic bearing capacity. Load tests were also made on footing plates at full scale, involving a similar arrangement of compacted granular layers over prepared London clay and including a high strength polymer geogrid. Examination of the test results allowed a qualitative assessment of the model performance and the reinforcing mechanisms attributed to the geogrid.

An instrumented model pile was used to investigate the fundamental behaviour in clay soils of driven cylindrical steel piles used for offshore structures. Four test-bed sites were chosen; two in stiff heavily consolidated clays, and two in normally/lightly overconsolidated clays. Data from these sites confirm that a residual shear surface is formed along the pile during installation, the location of which relative to the shaft surface appears to depend on the shaft roughness. Comparisons with other site investigation data and cavity expansion theoretical predictions indicate that stress relief immediately behind the pile tip during driving gives rise to total radial stresses and pore pressures measured on the pile shaft which are lower than predicted. This stress relief is particulary severe in the stiffer clays. The data did however show that the installation total radial stresses and pore pressures are governed by the initial in-situ stresses and undrained shear strength as is predicated by the theory. During reconsolidation, pore pressures close to the instrument rise initially in all clays, and radial effective stresses drop. The slow recovery in radial effective stress during the later stages of reconsolidation was in some cases insufficient to return it to levels recorded during installation. However, the generation of negative pore pressures during undrained loading increased the radial effective stress and shaft friction at failure. This effect is particularly important in the normally consolidated clays, and is responsible for the set-up of shaft capacity seen in such clays, which might not be observed if the loading were drained. The observed behaviour was therefore quite different from the monotonic increase in radial effective stress during reconsolidation, followed by decrease during undrained loading which was expected from a review of current theory.

The development and implementation of a complex numerical model for the determination of the damage to masonry buildings resulting from tunnelling settlements is described in this thesis. The current methods of damage prediction do not, in general, take into account the stiffness and weight of the surface structure. The model addresses this deficiency by explicit inclusion of the structure. Three-dimensional finite elements are used to model the ground with a non-linear, elasto-plastic soil model based on kinematic hardening. Tunnel linings are modelled using a novel overlapping elastic shell element: volume loss being simulated by shrinkage of linings coincidentally with excavation. Structures are modelled as collections of facades comprised of plane stress elements using a non-linear material model for masonry, similar to elastic-no tension. In developing the three-dimensional model, its two-dimensional counterpart is also studied. While the beam and shell elements used for linings (in two- and three-dimensions respectively) have the advantage of no rotational degrees of freedom the need to model boundary conditions at the element stiffness level complicates implementation. Tests using the shell elements show them to be satisfactory for the purpose of modelling tunnel linings. Results from a small number of analyses are given for construction of a straight tunnel beneath simple masonry structures. It is shown that the effect of the building on settlements depends heavily on its location in plan with respect to the tunnel axis. Predictions of crack patterns using the model for these analyses show that facades which the tunnel passes under first are less damaged than those later in the excavation sequence. Both of these conclusions serve to demonstrate that the problem can only be realistically modelled using three-dimensional methods. At present, however, the computer resources required to run the three-dimensional model are considerable.

The reported work constituted the third phase of a programme of research into the performance of concrete pipes during installation by the pipe-jacked tunnelling technique. This third stage was a continuation of the on-site monitoring of full-scale pipe jacks during construction. Four schemes were monitored in different ground conditions: London clay, dense fine sand below the water table, stiff glacial till and soft alluvial clay. Pipe sizes ranged from 1000mm to 1800mm internal diameter and excavation methods included hand tools, slurry machines and an open face tunnel boring machine. The main objective was to collect information on jacking loads and stresses at the pipe-soil interface to provide a better basis for future designs. This was achieved by building twelve stress cells -capable of measuring total normal stresses, shear stresses and pore pressures - into the wall of a standard concrete jacking pipe that could be inserted anywhere in the pipe string. Jacking loads and forward movement of the pipe string were simultaneously recorded and the results were correlated against site activities, including lubrication operations, and tunnel alignment surveys. Another objective was to monitor the ground response by measuring displacements around the tunnel and ground pressures above the perpendicular to the intended line. Ground movements were measured using conventional surveying techniques for surface settlements, and inclinometer access tubes for sub-surface deformation. On one scheme, electro-levels were employed in a near-horizontal tube to measure centre line settlement as the tunnel bore advanced. Push-in spade cells and pneumatic piezometers were installed on two schemes to measure the change in horizontal pressures with the passage of the shield. Because of the myriad data collected, it has only been possible to present a summary of the results obtained. Jacking force records from all the monitored schemes - including the previous fieldwork stage - are presented. The pattern of jacking load build up and the magnitude of frictional resistance can differ significantly according to the type of ground and use of lubricants. Stress measurements at the pipe-soil interface show that the interaction between jacking loads, pipeline misalignment, stoppages, lubrication, excavation technique etc, is highly complex. Ground movement measurements compared to well established empirical predictive methods show that short-term displacements are related to ground losses caused by closure of the overbreak void between shield and pipe.

Currently, much research is being directed at alternative energy sources to supply power for modern life of today and the future. One of the most promising sources is wind energy which can provide electrical power using wind turbines. The increase in the use of this type of energy requires greater consideration of design, installation and especially the cost of offshore wind turbines. This thesis will discuss the modelling of a novel type of shallow foundation for wind turbines under combined loads. The footing considered in this research is a circular caisson, which can be installed by the suction technique. The combined loads applied to this footing will be in three-dimensional space, with six degrees of freedom of external forces due to environmental conditions. At the same time, during the process of building up the model for a caisson, the theoretical analyses for shallow circular flat footing and spudcans also are established with the same principle. The responses of the soil will be considered in both elastic and plastic stages of behaviour, by using the framework of continuous plasticity based on thermodynamic principles. During this investigation, it is necessary to compare the numerical results with available experimental data to estimate suitable values of factors required to model each type of soil. There are five main goals of development of the model. Firstly, a new expression for plasticity theory which includes an experimentally determined single yield function is used to model the effects of combined cyclic loading of a circular footing on the behaviour of both sand and clay. This formulation based on thermodynamics allows the derivation of plastic solutions which automatically obey the laws of thermodynamics without any further assumptions. A result of this advantage is that non-associate plasticity, which is known to be a proper approximation for geotechnical material behaviour, is obtained logically and naturally. A FORTRAN source code called ISIS has been written as a tool for numerical analysis. Secondly, since there are some characteristics of the geometric shape and installation method which are quite different from that of spudcans and circular flat footing, another objective of this study is to adapt the current model which has been developed in ISIS for spudcans to the specific needs of caissons. The third goal of this research is the simulation of continuous loading history and a smooth transition in the stress-strain relationship from elastic to plastic behaviour. The model is developed from a single-yield-surface model to a continuous plasticity model (with an infinite number of yield surfaces) and then is discretized to a multiple-yield-surface model which can be implemented by numerical calculation to be able to capture with reasonable precision the hysteretic response of a foundation under cyclic loading. This can not be described by a conventional single-yield-surface model. Fourthly, as a method to simplify the numerical difficulties arising from the calculation process, a rate-dependent solution will be introduced. This modification is implemented by changing the dissipation function derived from the second law of thermodynamics. Finally, in order to control the model to capture the real behaviour, many parameters are proposed. A parametric study will be implemented to show the effects of these parameters on the solution.

The construction of underground tunnels in soft ground in urban areas involves the potential for ground movements caused by the tunnelling to affect existing surface structures. Masonry structures are at particular risk of crack damage. Conventional empirical building assessments do not fully capture all aspects of this soil-structure interaction situation. Numerical methods are increasingly used for such problems. It is common practice in empirical and numerical methods to model a building as an elastic beam in 2D. The objective of this thesis is the development of a new approach to the numerical modelling of masonry buildings using surface beams in 3D. In phase one of this project, finite element analyses of elastic and masonry facades are undertaken and the traditional beam method of modelling them is assessed. New equivalent elastic surface beams are developed, the properties of which account for the dimensions and openings in facades which were found to influence the response to settlements. Equivalent masonry beams are also developed which have a constitutive model that accounts for the different response of masonry buildings in hogging and sagging. Timoshenko beams are chosen to model the facades and these beams were implemented into the OXFEM finite element program with full 3D capability along with the new constitutive beam models. Example masonry structures were modelled in 3D using the new surface beams in phase two. Tunnel construction was simulated under the buildings and the response of the beams compared to a full masonry building model. Example analyses included buildings both symmetric and oblique to the tunnel. Results showed that the equivalent elastic beams accurately simulate full masonry building response in sagging regions. Parametric studies confirmed the choice of equivalent beam parameters and the impact of different relative stiffnesses. The equivalent masonry beams displayed the same good agreement in sagging but were less accurate in hogging. In phase three, finite element models are used to compare ground movements and structural response of buildings using the 3D equivalent masonry beam method and observed data from the construction of the London Underground Jubilee Line Extension. The surface beams showed good agreement with the observed building responses in both sagging, where the building response was essentially rigid and in hogging where a more flexible response was observed.

The stress-strain behaviour of unsaturated soils containing discrete bubbles of gas has been studied in a programme of experimental and theoretical research. The research is of particular relevance to the offshore environment, where bubbles of methane, nitrogen and carbon dioxide are formed within the seabed by the decomposition of organic matter. The presence of these gas bubbles can have a major influence on the engineering properties of the soil. As gas bubbles in marine sediments are typically much larger than the normal void spaces, the bubbles cannot be considered as simply changing the compressibility of the pore fluid. Chapters 2 to 4 describe a series of undrained triaxial tests on reconstituted samples of clayey silt from an estuarine site. Bubbles of methane were formed within the soil by using a chemical technique. The test results provide evidence of the effect of gas bubbles on the undrained shear strength, together with useful information on the stress-strain behaviour prior to failure, the generation of pore pressures during shearing, the elastic moduli and the isotropic consolidation behaviour. A theoretical model for soils containing large gas bubbles is developed in Chapter 5. The model consists of spherical bubble cavities surrounded by a matrix of saturated soil. In the following three chapters various aspects of the soil behaviour are examined by analysing the theoretical model. Chapter 6 covers the elastic moduli, Chapter 7 the consolidation behaviour and Chapter 8 the undrained shear strength. In Chapter 9 the predictions of the theoretical model are compared with the experimental results. The agreement between theory and experiment is excellent, suggesting that the theoretical approach developed and analysed in Chapters 5 to 8 is a reasonable model for the behaviour of soils containing large gas bubbles.

This thesis presents the results of an investigation into soil-reinforcement interaction by means of direct shear and pull-out tests. Scale and other factors affecting test results were studied; for this purpose an apparatus able to contain a 1 cu.m sample of sand was designed by the author in order to perform large scale tests. Plastic and metal sheet and grid reinforcements were used in conjunction with Leighton Buzzard sand. Direct Shear tests on unreinforced sand samples showed that soil strength parameters were not affected by the test scale, although the post peak behaviour and the shear band thickness at the centre of the sample were significantly affected by the scale of the test. The presence of a reinforcement layer inclined to the central plane of the box had a marked effect on the strength and behaviour of the sample. The reinforcement increased the vertical stress and inhibited the shear strain development in the central region of the sample. The behaviour of the reinforced sample was found to depend on the type and form of the reinforcement as well as its mechanical properties. Pull-out test results can be severely affected by boundary conditions, in particular by the friction on the front wall of the box. The results obtained in the series of tests showed that interference between grid bearing members is the main factor conditioning the pull-out resistance of a grid reinforcement. The intensity of such interference was quantified on the basis of results obtained in tests using single isolated bearing members and grids with different geometric characteristics. An expression for the bond coefficient between soil and grid, taking into account the degree of interference, was suggested. It was also observed that the maximum bearing pressure exhibited by a bearing member depends on the ratio of the member diameter to the mean particle size.

An understanding of the behaviour of newly deposited soil is important because of its direct applications in fields such as harbour siltation and storage of dredge slurries. In coastal regions the dominant mode for deposition of fine-grained cohesive material is through flocculation- the electrostatic aggregation of mud particles. The present study focuses on the measurement of both flocculation conditions and bed properties, towards the understanding of the influence of the former on the latter. A computerised laboratory setup, complete from sedimentation and flocculation to the long term consolidation allows each of these processes to be observed in instrumented perspex columns without the many variables present in an estuary. The bed deposition rates resemble those found in natural estuaries, and therefore this technique is a much improved method for examining natural processes than the method of slurry deposition, which is normally employed in soil mechanics. An image acquisition and analysis system has been designed specifically for this work. Image sequences are analysed in real time to give information about the dimensions and concentration of the particles, and the particle velocities. Floc sizes increase as the particle concentration increases in the column. Increasing the concentration further leads to an overall hindering of the sedimentation rate and breakup of the flocs. Images of beds formed through slow sedimentation clearly show aggregate features that are not present in slurry experiments. From low to medium sedimentation rates the bed height, normalised by the mass of sediment in the bed, increases. From medium to high rates of sedimentation, however, the normalised bed heights decrease. Overall slurry experiments have lower bed heights than slowly deposited experiments. Image analysis of the bed surface (top 0.5mm) has revealed that aggregates which are present immediately after deposition are broken down over tens of hours. The ISIS instrument has been modified to gather information about the resistance to erosion of the beds. A bed is more easily eroded after it has had a long period of consolidation. X-ray density measurements and imaging techniques are used to link the strength of the bed to biological factors. X-ray bulk density and pore pressure measurements allow calculations of void ratio, porosity, and effective stress. Bender element apparatus has been constructed to measure shear stiffness of the soil, and bed strength measurements are made using a shear vane. It is found that variations in the sedimentation conditions have significant effects on bed density and on void ratio. These effects continue to be visible in the consolidated bed, even after an order of magnitude increase in the total vertical bed stress (equivalent to the range of metres of overburden pressure). The variations in the bed structure can have profound effects on bed strength. Methods to compare floc measurements to bed measurements are complicated by the inherent variation in floc data. Possible techniques include the use of solids volume fraction, fractal dimension and intrinsic sediment properties. The usefulness of each of these is assessed. It is suggested that it is the frequency at which the bed is bombarded by flocs, and not the properties of the flocs themselves, that largely determines the bed properties.