Stress corrosion crack growth occurs when the chemical weakening of strained crack tip bonds facilitates crack propagation. I have examined the effect of chemical processes on the growth of a creack population by carrying out triaxial compression tests on Clashach and Locharbriggs sandstones at temperatures of 25-80 degrees C and at strain rates of 10-5 to 10-8/s. The axial strain, permiability, acoustic emission (AE) activity and the pore fluid chemistry were monitored continuously during these tests. Rock strength is reduced in the presence of water and on the application of a slower strain rate. Elastic modulus also decreases with decreasing strain rate. Microstructural observations indicate that microfracturing is more pervasive in the slow strain rate tests in comparison to the high strain rate tests. Damage parameters derived from the AE data predict the stress-strain curves adequately. The accumulation of damage is more rapid in the slow strain rate tests than in the high strain rate tests. The exit pore fluid silica (Si) concentrations correlate with the main microfracturing domains of the stress-strain curve. In the strain hardening phase of the Locharbriggs tests the Si concentrations and AE damage increase exponentially. The small reactive surface area and the temperature dependance of the Si concentration in the Locharbriggs tests suggest that silica is dissolving actively from the growing crack tips and that reaction rates contribute towards this signal. the Locharbriggs Si signal and damage parameters are strongly correlated by a power law relationship. the obseved strain rate and environment dependance of mechanical properties of Locharbriggs sandstone can be uniquely attributed to crack growth by the stress corrosion mechanism. In the Clashach tests the damage accumulation is best described by a powe-law. The AE activity of both sandstones exhibits clear fore- and aftershock sequences that are well modeled by the Omori law with a power law exponent that is close to unity. The Clashach Omori decay parameter correlates with test temperature, indicating a faster decay of aftershock activity at a higher temperature. The permeability evolution also displays a distinct strain rate dependence. At high strain rates permeability correlates with microcrack damage. At slow strain rate the fluid flow properties correlate with mean effective stress or pore fluid ion concentrations. These observations suggest that brittle fracturing, chemical reaction and hydraulic properties of porous sandstone are strongly coupled processes in the crust.

Rammed earth is an earthen construction material and an ancient construction technique. It is formed by compacting layers of moist sandy loam subsoil into formwork which is then removed, exposing the material and creating a freestanding, monolithic structure. In this thesis, the behaviour of rammed earth is investigated in terms of unsaturated soil mechanics of compacted earthen materials. Basic unsaturated soil mechanics theory is discussed and a method for linking the behaviour and material structure of an unsaturated soil is presented through the development of a model for predicting a soil's water retention curve using the soil pore size distribution and capillary and adsorption phenomena. A series of experiments is then performed in order to explain the behaviour of rammed earth in tension and compression under varying conditions in terms of the material micro-- and macrostructures. An analysis of the sample manufacturing process is presented in order to understand formation of rammed earth's structure in both natural and laboratory-prepared materials. The effects of temperature and humidity, related to a number of sites around the world, on the compressive strength and of changing water content and clay flocculation on the tensile strength of rammed earth are then investigated and combined in order to determine the sources of strength in rammed earth. The pore networks of several rammed earth samples under compression and those of rammed earth samples comprising multiple compacted layers are then investigated using X-Ray computed tomography in order to determine the effects of loading and layering on the material macrostructure and to support results presented in previous chapters. In the final chapter, implications for the design, construction and conservation of rammed earth structures are discussed based on the findings of investigations presented in the preceding chapters.

Climate change has the potential to affect any transportation network that comprises embankments and cuttings built with soil material in an unsaturated state that is exposed to the climate. The BIONICS project (BIOlogical and eNgineering Impacts of Climate change on Slopes) aims to investigate how climate change will affect the serviceability and safety of earth structures. Part of the BIONICS project was to build a full-scale highly instrumented embankment combined with an automated climate control system. Studies on the fill material used in the construction of the BIONICS embankment were carried out to understand the hydro-mechanical behaviour of the material, which is a sandy clay of medium plasticity. This involved the determination of the soil water retention behaviour and the mechanical behaviour under unsaturated conditions. Soil water retention curves (SWRC) were determined by a series of tests performed on compacted samples comprising various techniques (filter paper, psychrometer, high capacity suction probe and pressure plate). Total and matric suction SWRC following primary drying paths from 25% of water content were determined. In addition, a series of tests with the filter paper on samples at lower water contents (15%, 20% and 22%) was also performed. The SWRC following drying paths showed behavior similar to scanning curves intercepting the primary curve around 3000 kPa (11% water content). However, SWRCs that followed wetting paths showed atypical behaviour by intercepting the primary drying curve. For the investigation of the mechanical behaviour a series of constant water content triaxial tests were carried out in double cell triaxial cells on as-compacted samples, and also samples wetted and dried from as-compacted conditions of 15%, 20% and 22%. A test series of samples tested in a saturated state was also performed to provide a reference state for the unsaturated tests. The unsaturated test series showed that the slope of the critical state line (CSL) in deviatoric stress space (M) was found to be similar for all water contents. The slope of the CSL in ν-ln(p-uw) space (λ) was found to be similar for all water contents, however the CSL shifted position due to variation in the intercept, Γ. Since specimens were at high degrees of saturation, calculations based on effective stress showed a reasonable interpretation of the data. However, a better agreement was achieved using the Bishop’s average stress assumption. A new field measurement system to continuously measure pore water pressure at different depths using high capacity suction probes has been developed. This system was installed at the BIONICS embankment in two different panels (well and poorly compacted). In the well compacted panel pore water pressure behaviour had the tendency to increase with depth, always recording values that were slightly negative at shallower depths and positive at greater depths, showing profiles roughly parallel to the hydrostatic line suggesting that the material was close to saturation. In the poorly compacted panel the behaviour was found to be more variable showing abrupt reactions from the probes to weather events. The differences in behaviour between the well compacted and poorly compacted panels could be related to the laboratory investigations. The well compacted panel was more homogeneous and less permeable (10-11 m/s). The poorly compacted panel was more heterogenic, more permeable and hence, during monitoring, showed more dramatic changes in pore pressure compared to the well compacted panel.

This thesis is concerned with the theoretical development and numerical implementation of efficient constitutive models for the analysis of particulate media (specifically clays) in structures undergoing geometrically non-linear behaviour. The Mohr-Coulomb and modified Cam-clay constitutive models have both been examined and extended to provide greater realism. Findings from this thesis will interest engineers working in numerical methods in solid mechanics, along with those investigating continuum mechanics, inelastic constitutive modelling and large strain plasticity. Although focused on soil plasticity, this research has relevance to other areas, such as metal forming and bio-engineering. Initially the concepts of material and geometric non-linearity are reviewed. A general implicit backward Euler stress integration algorithm is detailed, including the derivation of the algorithmic consistent tangent. A framework for the analysis of anisotropic finite deformation elasto-plasticity is presented and a full incremental finite-element formulation provided. The first constitutive model developed in this thesis is a non-associated frictional perfect plasticity model based on a modified Reuleaux triangle. It is shown, through comparison with experimental data, that this model has advantages over the classical Mohr-Coulomb and Drucker-Prager models whilst still allowing for analytical implicit stress integration. An isotropic hyperplastic family of models which embraces the concept of a Critical State is then developed. This family is extended to include inelastic behaviour within the conventional yield surface and a Lode angle dependency on the anisotropic yield function which maintains convexity of both the surface and uniqueness of the Critical State cone. A calibration procedure is described and the integration and linearisation of the constitutive relations are detailed. All of the developed models are compared with established experimental data. Finally the models are verified for use within finite deformation finite-element analyses. The importance of deriving the algorithmic consistent tangent is demonstrated and the influence of varying levels of model sophistication assessed in terms of both global behaviour and simulation run-time.

The concept of progressive shear surface development remains to be fully understood. This study aims to investigate the mechanisms of progressive shear surface development to failure, and the subsequent post-failure behaviour, of deep-seated landslide complexes. Field samples, collected from the Ventnor deep-seated landslide complex, Isle of Wight have been tested in a series of bespoke triaxial and back pressured shear box tests, in which field failure conditions are simulated by elevating pore water pressures under a constant deviator stress. These laboratory simulations have been calibrated with a detailed analysis of ground movement, groundwater and antecedent rainfall relationships from real-time site monitoring records from the site. A model to explain the progressive failure of landslides in cohesive materials is proposed. The model demonstrates that pre-failure movement in landslides occurs during the progressive shear surface development through the development of micro-cracks within the slope. This process is active during periods when porewater pressures are sufficiently elevated in the slope. These micro-cracks eventually lengthen and coalesce as stresses concentrate at micro-crack tips, leading to the development of a singular shear surface which is observed as tertiary creep. The study confirms that the onset of ‘Saito linearity’ in 1/v – t space is associated with this tertiary creep phase. This mechanism can occur through time dependent creep at constant stresses from below the peak strength envelope. The results have been validated against real-world landslide monitoring data to provide a new understanding of the shear surface mechanisms operating within the Ventnor landslide. The results contribute new knowledge regarding the mechanisms of shear surface development and provide an improved understanding of these mechanisms by developing one of the first high quality data sets that combines laboratory and field data. Finally, the study provides a new method to inform future landslide behaviour predictions for deep-seated slope failures.

The use of X-ray texture analysis techniques enables a simplified picture of the microstructure of a rock to be built up. In this thesis it is shown that, in spite of a wealth of evidence on pre-failure rock behaviour, a simple application of Griffith theory to the assumed microstructure can provide an adequate description of the failure characteristics of an anisotropic rock. It is suggested that the crystallite structure within the rock controls the pre-failure activity in such a way as eventually to produce the crack formation initially deduced from that crystallite structure. These conclusions are drawn from work done on two rocks of different character, Penrhyn Slate and Lumley Mudstone.

Hydrological processes are greatly influenced by the characteristics of the domain through which the process occurs. It is generally accepted that earth materials have extreme variations from point to point in space. Consequently this heterogeneity results in high variation in hydraulic properties of soil. In order to develop a reliable predictive model for transport processes in soil, the effects of this variability must be considered. Soil heterogeneity due to presence of macropores (micro-) and to spatial variability in hydraulic properties (macro-heterogeneity) coexists in the real field conditions. The challenge is to incorporate the effects of both types of soil heterogeneity in simulation models. This thesis presents development and application of a 2D/3D numerical model for simulation of advection and diffusion-dispersion contaminant transport considering both types of soil heterogeneity. Stochastic finite element approach is used to incorporate the effects of the spatial variability of soil hydraulic properties on contaminant fate. The soil micro heterogeneity effects are modelled with a dual domain concept in which a first order kinetic expression is used to describe the transfer of the solute between the two domains. Also, the capability of the model in 3D simulation of field problems improves the accuracy of the results, since it is possible to avoid the generally applied assumption in 2D simulations. From comparison of the model results with experimental and analytical results, it is concluded that the model performs well in predicting contaminant fate and the incorporation of the both types of micro- and macro- heterogeneity in the simulation models improves the accuracy of the prediction. Also, capability of the model in evaluation of the concentration variation coefficient as an index of reliability of the model outputs makes it possible to estimate a probable interval (mean concentration minus and plus standard deviation) for the range of oscillations of possible realizations of solute distribution. Moreover, comparison of the results of the proposed method with the results obtained using the Monte Carlo approach yields a pronounced reduction in the computation cost while resulting in virtually the same response variability as the Monte Carlo technique.

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