This thesis assesses the ability of remote sensing techniques to characterise soil moisture in a transport corridor environment. Much of the world’s transport networks are built on earthwork embankments or in cuttings. In the UK, many of these earthworks were constructed in the mid-19th Century and are susceptible to slope instability. Instability in transport corridors is often triggered by an increase in pore pressure, which is directly influenced by an increase in soil moisture. Although a number of studies have investigated the use of remote sensing techniques for estimating soil moisture, they have tended to be conducted under controlled conditions and few have considered their capacity for being operational. This study addresses this point by exploring the use of high spatial resolution digital elevation models (DEMs) and airborne hyperspectral imagery for characterising soil moisture in transport corridors. A number of terrain (topographic wetness index (TWI), potential solar radiation, aspect) and spectral analysis (red edge position estimation, derivative stress ratios, continuum removal analysis, partial least squares (PLS) regression modelling, mapping biological indicator values) techniques were assessed using terrestrial systems over a test embankment, and airborne data for a transport corridor. The terrain analysis metrics TWI and potential solar radiation were found to be highly sensitive to the DEM spatial interpolation routine used, with a thin plate spline routine performing best in this study. This work also demonstrated that Ellenberg indicator values extended for the UK can be mapped successfully for transport corridor environments, providing potential for a number of different applications. Individually, the techniques were shown to be generally poor predictors of soil moisture. However, an integrated statistical model provided an improved characterisation of soil moisture with a coefficient of determination (R2) of 0.67. Analysis of the model results along with field observations revealed that soil moisture is highly variable over the transport corridor investigated. Soil moisture was shown to increase in a non linear fashion towards the toe of earthwork slopes, while contribution from surrounding fields often led to concentrations of moisture in cutting earthworks. Critically, while these patterns could be captured using the data investigated in this study, such spatial variability is rarely taken into account using analytical slope stability models, potentially raising important challenges in this respect.

Chalk is a weakly bonded calcareous rock primarily composed of skeletons of microscopic planktonic organisms. Its sedimentary highly anisotropic nature is reflected in its significant range of porosity, bonding strength and textural variation. These intrinsic properties trigger a complex short-term engineering response that has been the subject of numerous studies, whilst its long-term response has attracted lesser attention. A long-term laboratory test programme of conventional compression and extension tests was carried out (duration: 8 to 22-months) in a purpose built environmentally controlled facility, with specially designed loading frames and modified triaxial cells. Furthermore, index as well as triaxial and unconfined tests were also conducted in order to establish the short-term mechanical response. The results were compared and complimented with those of similar studies. In addition, Scanning Electron Microscope (SEM) techniques were employed in an effort to investigate the micro-mechanical response. This led to the formulation of a conceptual micromechanical model associated with the short and long-term deformation of chalk. It was concluded that each variety of chalk has a differing short-term failure envelope controlled by factors such as grain bonding, mineralogy and fabric texture. It was also demonstrated that chalk is not an ideal elastic material and its pseudo-elastic response was associated with the onset of creep. Creep strains appeared to trigger an ageing process that produces elevated post-creep strength and stiffness irrespective of the applied stress path. This was associated to an increase in the frictional interlock of the material. The SEM study revealed a pervasive fabric evolution throughout the post creep/aged samples. This suggested a more uniform stress distribution within the longterm tested samples, than that occurring in the short-term tested samples. The only .discernable effect that could be attributed to the applied stress paths during creep testing was related to the magnitude of the creep rates.

One-dimensional and isotropic swelling tests, hydraulic conductivity tests and triaxial compression tests have been performed at applied stresses up to 450kPa on sodium bentonite powder, sand and compacted sodium bentonite-sand mixtures (5, 10, and 20% bentonite by dry weight). This was done to investigate the use of bentonite improved soils for waste containment, and study the fundamental geotechnical properties of bentonite-sand mixtures using a classical soil mechanics approach. It was found that air dried bentonite powder swells to reach a state described by a single straight line on a plot of void ratio against the logarithm of vertical effective stress, regardless of preparation technique. The gradient of this line was intermediate between a normal consolidation and rebound line for the same material indicating a different sample fabric when allowed to reach equilibrium from an initially dry state rather than the conventional fully saturated state. Swelling of bentonite-sand mixtures expressed in terms of the clay void ratio show a deviation from bentonite behaviour above a threshold stress which depends on the bentonite content. From this behaviour, a modified principle of effective stress has been proposed. Similar swelling relationships were found for samples under an isotropic confining stress. Hydraulic conductivity data for bentonite and mixtures indicate an approximately linear relationship between the logarithm of hydraulic conductivity and the logarithm of void ratio. Observed differences in hydraulic conductivity between bentonite and mixtures, when represented in terms of the clay void ratio, are attributed to the sand porosity and tortuosity. From a stress-dilatancy analysis of triaxial data, the peak strength of mixtures has been shown to depend on the sand relative density. This parameter indicates how the material will behave during shear. A threshold sand relative density has been postulated, which is dependent on the axial strain. Below the threshold value, it is likely that the stress-strain behaviour will be characteristic of the bentonite alone. A design model based on the clay void ratio, sand porosity and tortuosity, and sand relative density is presented, enabling the hydraulic conductivity or strength of a mixture to be estimated.

This thesis addresses the concept of non-destructive rock mass characterisation using in-situ measurements of the velocity and attenuation of seismic waves. The thesis is divided in to two sections, the first of which considers a comprehensive laboratory study of the phenomena of stress-induced velocity and attenuation anisotropy, whilst the second documents a number of field case studies. In the first section, a review is given of the current experimental evidence and theoretical explanations of the factors that affect the propagation of seismic waves. A description is given of the spectral ratio technique for the laboratory determination of P-wave attenuation in rock core samples. The section concludes with the presentation of the results of an investigation of stress-induced velocity and attenuation anisotropy in intact samples, samples induced to failure, and fractured samples. Experimental results show that in-situ measurements of the change in velocity and attenuation could be used to predict stress change in a homogenous rock mass which contains infrequent, isolated fractures. The prediction would be based on laboratory measurements of stress-induced attenuation anisotropy in intact samples. In the second section, a new variant of seismic tomography called Combined Transmission and Reflection Tomography (CTRT) is fully described. In the chapters following this, a number of field cases are documented to show how the technique can be used to identify geological structure such as general stratigraphy, faults, orebody volumes, and man-made features such as old workings and blast induced fracture zones. The technique is shown to be ideal for surveying inaccessible areas and improving tomograms above those that can be produced by the popular transmission tomography algorithms. A final case study considers the use of seismic measurements in the prediction of rock mass behaviour in the footwall of a mine stope. The simple technique described successfully identified fault zones in two stopes before mining commenced, one of which resulted in the subsequent loss of a stope half way through mineral extraction. In conclusion this thesis comprehensively describes how seismic measurements can be used to characterise a rock mass and lays the foundations for using the same measurements for monitoring and predicting rock mass behaviour in active environments.

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