The research described in this thesis concerns the use of transparent soil in physical modelling to better understand theoretical and analytical analyses of a geotechnical engineering problem. One of the more recent evolutions in the field of geotechnics is the use of geosynthetic materials as reinforcement to improve the shear resistance of soil, and ultimately provide reinforcement to earth structures. Their application in engineering earthworks has increased significantly in recent years. When designing reinforced earth structures, a vital aspect is to understand the interaction between the reinforcement and the compacted soil as this governs the overall stability. The main function of the reinforcement is to redistribute the stresses within the soil structure in order to enhance the internal stability of the reinforced soil structure. The reinforcement undergoes tensile strain as it transfers loads from unstable to stable zones of the soil. The most common example of soil-geogrid interaction research is to investigate pull-out capacity. The lack of knowledge of interaction mechanics between soil and reinforcement has considerable impact on the ability to implement rigorous analytical solutions, or to assign suitable parameters for interface elements in numerical modelling. By using classical pull-out, previous researchers have indicated that the interface factors vary between 0.6 - 0.8 (FHWA-NHI-00-043, 2001); hence, it is likely that many designs over predict the possible resistance that may be generated. Furthermore, in the absence of field validation, there is uncertainty as to how representative small scale pull-out tests reflect the likely behaviour that would prevail in the prototype structure. The transparent soil utilised here is representative of coarse soil and allows nonintrusive measurement of soil displacement on a plane highlighted by a sheet of laser light, captured by a digital camera. This enables the measurement of the displacement of the soil on the target plane by using the image process technique “Particle Image Velocimetry”. This technique allows the observation of the interaction between soil and geogrid, and the shear and pull-out boundary which is mobilised around the geogrid. The principal aim of this research is to investigate the detailed interaction between granular soil and geosynthetics, and to provide a better understanding of the interaction both analytically and numerically. To achieve this aim, this research is separated into two key areas: 1. Analytical modelling of the interaction between soil and geogrid to assess the degree of uncertainty inherent in the methods; 2. Advanced visualisation element tests using transparent soil technology and Particle Image Velocimetry (PIV) to directly observation of the patterns of strain between the soil and reinforcing material.

Soil-filled wire and geotextile gabions are commonly used to construct defensive infrastructure in military bases, where the attenuating properties of soil are used to protect personnel and key assets from the effects of blast and fragmentation. The behaviour of soils in these extreme loading regimes is not well understood, and so designers require data at these high pressures and strain rates in order to develop robust soil constitutive models and adapt to new threats. The one-dimensional compression of three sandy soils was compared under quasi-static loading to axial stresses of 800 MPa. Trends in behaviour were identified with respect to the particle size distributions of the soils, and were found to correspond to the relationships observed at lower stresses. Split Hopkinson pressure bar (SHPB) experiments were used to investigate the strain rate dependence of this behaviour. Measurements of radial stress indicated that an increase in the axial stiffness of the soils between strain rates of 10^-3 s^-1 and 10^3 s^-1 was likely due to radial inertial effects. Potential sources of error were identified in the SHPB experiments, leading to the implementation of a dispersion-correction algorithm, which improved the measurement of axial stresses. Analysis of the electromagnetic activity around the specimen isolated the cause of erroneous radial stress measurements. Quasi-static experiments were used to investigate the effect of moisture content on soil stiffness at high pressures, and SHPB experiments at the same moisture contents were used to consider the effect of strain rate on the quasi-static behaviour. Recovery SHPB experiments were designed to enable reliable post-test particle size analyses to be performed, and the range of moisture contents was expanded to investigate the change in soil behaviour on reaching full saturation. Reduced triaxial compression experiments were used to define the yield surface of a sand to a mean stress of 400 MPa. The high-pressure compression and yield strength data was used to calibrate LS-DYNA soil models, and the performance of the models was assessed through modelling of the SHPB experiments.

The application is based on works carried out in 5 distinct phases throughout a career at the University of Surrey spanning 36 years but with a 20 month gap in 1982 where I worked at Wimpey Laboratories undertaking research work on lightweight concretes. Initially, I was employed on an EPSRC NETCEM contract awarded to Prof Dave Hannant and Dr Jeff Keer where I developed and tested a replica of the Big 6 asbestos cement sheet. There was then a period where I was then employed on an advanced polymer composites contract awarded to Prof Len Hollaway. Although I had no specific technical knowledge of advanced polymer composites at this time I did have considerable expertise in conventional engineering materials and in experimental techniques. Within the period of this contract I gained sufficient knowledge and understanding to co-author a follow up contract. Additionally, I was able to contribute to the supervision of experimental techniques and the numerical modelling of structures undertaken by the PhD students in the research group at that time. Once taken on as a member of staff, albeit on a contractual basis, I undertook supervision and co-supervision of contracts that I had co-authored. I also applied for EPSRC starter funding available at the time. Whilst the application was not successful, Prof Len Hollaway and I were invited to take the principles of the application for reinforcing and strengthening conventional construction materials further and to expand them into a full application where we were subsequently awarded an EPSRC contract. Prof Len Hollaway and I were also requested by Prof Chris Clayton (then Head of Civil Engineering) to include other members of staff onto our contract applications. The first application included Prof Gerry Parke (then Reader in the Department of Civil Engineering) and the second application included a new member of staff Dr Toula Onoufriou (Reader in the Department of Civil Engineering). Both EPSRC applications were successful and resulted in fruitful contracts. We further included other new members of staff, albeit not successfully, on EPSRC applications for novel composite concrete beam configurations for which I took the principal investigator roll. I have since taken a proactive roll in investigating new areas of research, firstly with a PhD studentship in Electronic Engineering with Prof Graham Reed (then Reader in Silicon Wave Guide Applications in the Department of Electronic and Electrical Engineering) and then with the Composites Group in the Materials Department. This link with Prof Steve Ogin incorporated Graham’s expertise for our investigations into measurements in composite materials and then damage detection in composite materials. The major thrust in all of the work throughout this latter period of my career has been in the development and application of FRP composites through research into aspects of applied physics, optoelectronics, materials science and engineering and structural mechanics. It has been made possible through grants and contracts to which I have acted as co-investigator and co-supervisor of PhD students. This has been through both my own research effort and through my participation in an inter-disciplinary research group of staff in the Faculty of Engineering and Physical Sciences spanning across the underpinning engineering disciplines. For the first 16 years, I was the primary member of this group with specific expertise in numerical modelling and simulation of engineering structures under mechanical and environmental loading conditions. Whilst I have been the primary lead in these areas over this period it has always been necessary to choose the Principal Investigator carefully to suit the funds applied for. In this early stage of the development into the research area we have been investigating fundamental materials research based on the formative crack density work conducted by Prof Steve Ogin, Prof Paul Smith and Dr Lynne Boniface. It was thus necessary to install Steve as the Principal Investigator over either Graham or myself for the applications to be successful.

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Although numerical simulation of concrete has a significant background in the framework of simplified one- and two-dimensional elements, a full triaxial description of the structural behaviour of this material is still subject to active research. High fidelity modelling has only been enabled once the required computational capacity achieved an appropriate threshold, and it is precisely of such computational nature that there are diverse drawbacks the material model has to overcome. For concrete, an existing model combining plasticity and isotropic damage is chosen in this work, and this choice over multi-surface plasticity is duly justified. Additionally, an extension to anisotropic damage is proposed. Focus is set on a series of algorithmic enhancements that significantly increase robustness in stress evaluation, in particular from stress states that pathologically associate to a singular Jacobian matrix and stress-returns that lead towards sensitive areas of the failure surface in principal stress space, where plastic flow is undefined. Reinforcing steel is modelled as embedded bars inside the corresponding concrete parent elements, with solely axial stiffness. An arbitrary orientation inside the concrete elements is allowed but otherwise the discretised bars share the parent element morphology, order and degrees of freedom, resulting in a perfect bond interaction. An improved and systematic linearising procedure is presented to track the intersections of each bar segment with its embedding parent element, which can be readily applied to any element type and order. This facilitates an accurate calculation of this constituent’s contribution to the parent element’s stiffness matrix and nodal force vector. The robustness of the enhanced material model is verified by means of numerical tests, highlighting the convergence ratio, and validation ensues via simulations of established benchmark tests. Finally, some case studies are presented to illustrate the performance of the model at structural level, with insight into various issues of computational nature.

Elevated water tanks are used within water distribution facilities in order to provide storage and necessary pressure in water network systems. During the occurrence of a severe seismic event, the failure or severe damages in the reinforced concrete shaft could result in the total collapse of the structure. In a reinforced concrete shaft, plastic hinge formation only occurs at the base of the shaft and nonlinear resources of the rest of the shaft remains unexploited. This research presents an innovative technique for the assembly of shafts for elevated water tanks, using the slits in the reinforced concrete shaft design, which reduces the stress concentration at the shaft base and distributes stresses uniformly along the height of the shaft. The main aim of this study was to investigate the nonlinear seismic performance of the innovative RC slit shaft of the elevated water tanks by means of a finite element approach. The capacity spectrum and time history analyses were carried out to understand the nonlinear behaviour of the proposed support system. The results revealed that the slit width in the reinforced concrete shaft directly affected the failure mode and stiffness of the elevated water tanks. It was concluded that, with an appropriate design, the conversion of a solid shaft into a slit shaft can significantly increase the ductility of a reinforced concrete shaft, but there would be a slight reduction in the lateral strength. Furthermore, the results revealed that crack propagation was more uniform along the height of the slit shafts in comparison to the solid shaft and the ductility of the shafts increases as the slits become wider. Conclusively, this study showed that introducing the slits in the shaft could result in a significant reduction in the seismic response values of the elevated water tank, resulting in an economical design of the shaft structure and the foundation system.

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The thesis presents a study of frost action in unbound and in cement stabilised colliery shale. Frost susceptibility was assessed using the Road Research Laboratory frost heave test, employing either a cold room or a deep freeze cabinet. Of the 17 unbound, unburnt shales tested, only four samples were classified as frost susceptible whereas 11 of the 12 unbound, burnt shales tested were frost susceptible. This difference in behaviour has been attributed, particularly, to differences in absorption and in the amount and nature of the fine material in each shale. The addition of cement generally reduced the heave, but certain fine-grained shales showed increased heave when so treated. Both effects can be explained in terms of the relative changes in pore size, in permeability and in tensile strength which result from cement stabilisation. Measurements of the pressures generated when heave was restrained were also undertaken. For the unbound, unburnt shales heave was related to heaving pressure and with the cement stabilised shales significant heave occurs only when the heaving pressure exceeds the tensile strength of the material. Thus, although this approach provided data which assists in building-up a mechanistic picture of frost action, it does not provide a basis for directly predicting frost susceptibility. However, it is suggested that the criteria for assessing the frost susceptibility of cement stabilised materials should be based on dimensional changes and on tensile strength. Frost action, in both unbound and cement stabilised shale, is explained in terms of an energy balance between the work done in heaving and the energy liberated by supercooled freezing, this concept being related to changes in the nature and properties of the various materials.