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No description available.

This thesis experimentally investigated the changes in the water content and the void ratio of initially slurried highly plastic clays under zero applied stress during the drying process, changes in the water content of compacted unsaturated clay specimens during the wetting process under zero applied stress for laterally confined and free swelling conditions, and the wetting behaviour of heavily compacted bentonite specimens under confined condition. In total three clays were used, namely MX80 bentonite, Yellow bentonite, and Speswhite kaolin. Several laboratory techniques, namely centrifuge, axis-translation, vapour equilibrium, osmotic and chilled-mirror dew-point techniques were used to establish the suction-water content soil-water characteristic curves (SWCCs). The shrinkage paths of the clays were established from Clod tests and wax method. The suction-water content SWCCs in conjunction with the Clod test results enabled establishing the suction-degree of saturation SWCCs and determination of the air-entry values (AEVs). The AEVs of the clays were also determined based on the chemical analyses of Polyethylene Glycol (PEG) solutions and the applied suctions in the osmotic tests. Degradation of PEG molecules and semipermeable membranes were studied using Fourier Transform Infrared (FTIR) spectroscopy and Atomic Force Microscopy (AFM), respectively. Isochoric (constant volume) swelling pressure tests were carried out on compacted bentonite specimens using deionised water. Additionally, a newly developed suction controlled oedometer was used to study the swelling pressure and the water uptake capacities of heavily compacted bentonites under confined conditions. Microstructural changes of compacted bentonites were studied using Environmental Scanning Electron Microscope. X-Ray Diffraction technique was used to monitor the changes in the c-axis spacing of clay specimens equilibrated at several applied suctions. Applications of the Gouy-Chapman diffuse double layer theory and the van der Waals attractive pressure theory in predicting the drying and wetting suction- water content SWCCs were explored. One-dimensional wetting model (Richard's equation) was used to evaluate the elapsed time versus water content relationships for the clays. Chemical analyses of PEG solutions after the osmotic tests showed a clear lack of equalisation of the osmotic suctions due to the expelled and the retained salts on either side of semipermeable membranes. A majority of the salts were found to be retained within the clays during the osmotic tests. The AEVs of the clays determined based on the suction-degree of saturation SWCCs and that from the total suction equilibrium in the osmotic tests were found to be similar. The FTIR studies did not indicate any degradation of PEG molecules. The AFM studies of membranes revealed alterations of the pore-size during the tests that possibly lead to an intrusion of PEG into the bentonite specimens. Both qualitative and in some cases quantitative agreements were noted between the experimental suction-water content SWCCs and those predicted from the physico-chemical theories.

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Small scale centrifuge models were used to study the behaviour of arches repaired using different techniques. The models under test were 1/12th scale replicas of a 6 metre single span three ring arch. Two types of arch geometry, with span/rise of 4 and 2, were studied as a shallow and deep arch geometry. The models were tested in a centrifuge under a steady equivalent gravity of 12g. Two types of 2-D and 3-D arch models were studied which had the same geometry but different in the addition of spandrel walls. The 3-D models were built with spandrel walls but without any wing walls or parapet. Both 2-D and 3-D arch models were tested under rolling and failure loads. The models were usually tested with fourteen passes of a rolling load and then up to the observation of first signs of failure to enable them to be suitable for applying a repair method. The repaired models were tested using the same procedure but up to the full failure load. To understand the behaviour of the arch models under unsymmetrical loads different roller weights were applied at different positions. The arch deflection and the soil/masonry interaction in arch extrados were measured in all the tests and compared with each other. Plastic mesh reinforcement, stitching, and concrete slab on top of the soil backfill were applied as repair methods to the 2-D arch models. A review of the results has shown an increase in arch stiffness, decrease in deflections and a significant improvement in the ultimate load carrying capacity. A significant effect on the pressure distribution on the arch barrel was observed due to the application of the concrete slab on top of the backfill. Stitching of arch barrel and the barrel to the spandrels, applying partial saddle concrete and strengthening of spandrel wall using reinforced concrete were tested in the 3-D arch models. The results showed improvements in the stiffness and ultimate arch load carrying capacity due to these repair techniques. The results provide a valuable data base for validation of numerical models and an initial attempt to use them with a commercial finite element program is included.

No description available.

This study explores issues related to the numerical simulation of moisture migration patterns in the unsaturated zone and in the vicinity of established vegetation. A one- dimensional water-uptake model was first developed to simulate moisture migration beneath uniform vegetation (crop) cover. The main thrust of the research was then to develop a practicable water-uptake model that can be used to simulate moisture migration patterns beneath mature trees. The moisture flow model used is based on Richard's Equation extended to incorporate a sink term and integrated with appropriate water-uptake models (i.e. ID, 2D, and 2D axi-symmetric form). A numerical solution was achieved via the finite element method for spatial discretisation along with a finite difference time-marching scheme. A series of numerical simulations have been presented that demonstrate the newly introduced sink term functioned correctly and that the model is capable of representing typical water extraction processes from a variety of crop types. A new two-dimensional axi-symmetric model was then developed and applied to simulate moisture migration near established trees. In particular, the approach adopted utilizes radial symmetry and assumes a linear distribution of water extraction rate with both depth and radius. The new model has been validated by direct comparison to field measurements recorded (by others) for mature trees located on a clay sub soil. The model has been shown to be capable of representing water-uptake over a full-annual cycle. Time dependent boundary conditions, based on rainfall data, and hysteresis effects have also been explored. Overall, a good correlation between field data and simulated results has been achieved. Hysteresis effects, when the soil has already experienced repeated wetting and drying cycles, were not found to be of great significance for the class of problem considered. The research also provides a preliminary assessment of the significance of tree induced water content (and therefore suction) changes on the stability of unsaturated soil slopes. The 'typical' example considered, indicated that relatively small suction changes (in the order of 10 kPa) can influence the factor of safety against slope failure by approximately 7%. These findings should be considered in addition to the variety of other vegetation related strength effects. In conclusion, a relatively straight forward approach to modelling water-uptake by vegetation has been developed. The resulting model is thought to be valuable for a range of geoengineering problems.

This thesis presents an investigation of the thermo / hydro / mechanical behaviour of saturated soils with cryogenic suction effects. The flow relationships accommodate a number of mechanisms: i) heat transfer by conduction, convection, and latent heat transfer and ii) moisture transfer in the liquid phase due to pressure head, elevation head, and thermal gradients. The mechanical behaviour of the soil is modelled by an elasto-plastic work hardening modified Cam- Clay constitutive model. A numerical solution for the theoretical formulation is presented. Standard finite element methods are used for spatial discretisation and finite difference methods are used for temporal discretisation. Verification of the model is achieved by means of programme of tests to check the following cryogenic components i) coupled thermo-hydraulic response, ii) deformation behaviour of the fully coupled thermo-hydro-mechanical model, iii) transient coupled liquid flow and deformation behaviour, and iv) latent heat of fusion. Validation focused on the impact of the cryogenic related processes included within the proposed theoretical formulation. In particular the development of ice lenses and the movement of moisture under cryogenic suction were investigated. The performance of the proposed model with respect to a number of variables was subsequently explored in order to determine their effect on the magnitude and growth of ice lenses in a freezing soil. The model was then applied to a large scale freezing experiment, namely a fully coupled thermo / hydro / mechanical simulation. The simulated results show a good correlation with the experimental results by predicting the patterns and trends of experimentally observed behaviour and the cryogenic processes that occur during the freezing and thawing of frost susceptible soils. It was therefore concluded that the proposed model is capable of providing a good representation of the fully coupled THM behaviour of saturated soils with cryogenic effects.

The new model ahs then been applied to investigate relevant hydraulic and hydrogeochemical processes in a swelling clay.

A number of earlier researchers investigated the soil structure interaction parameters which affect the structural behaviour of buried flexible pipes. However, it was not until the mid-1990s that the importance of rocker pipe design to accommodate differential settlement raised awareness of the consequent absence in current design procedure [BS EN 1295-3; 1998]. This study widens the understanding of the effect of differential ground movements on the behaviour of flexible pipes to address concerns raised to the Committee European de Normalisation. Many pipeline failures result from the excessive strains developed in the vicinity of the junction between a pipe and a settling structure. Case studies of such failures are presented in this thesis, which demonstrates that it can occur not only in large diameter pipeline but also in small diameter domestic pipeline systems. A method of analysis and the use of developed appropriate rocker pipe length is an industrially useful outcome of this research. Analytical solutions for flexible pipes have been developed based on the concept of beams on elastic foundation approach. Non-dimensional relationships have been developed and are presented in the form of charts. These charts permit hand calculations and rapid verification of structural design of the pipeline and, thus, assess the integrity of the existing pipelines located in areas with ground instability. Knowledge of the soil strength and sub-grade modulus is required, along with pipeline geometry and pipe stiffness, to apply the non-dimensional relationships. The soil parameters can be measured in situ or estimated using empirical correlations. The cause for failure has been investigated with the proposed analytical soil structure interaction approach which identifies the zone of distress in the pipeline. The analysis has been extended to demonstrate how a rocker pipe system can be incorporated to alleviate such distress. The concept of rocker pipes has also been investigated in the study through laboratory scale testing. Soil box tests, with ground conditions defined through plate/pipe load testing, have been developed. Full-scale testing on flexible pipes instrumented with FlexiForce pressure sensors at the pipe invert, strain gauges measuring strain due to induced differential settlement on the pipe crown and deflection transducers measuring deflection profiles along the pipe length due to differential settlement of the end structure, have been used to validate the mathematical modelling. Ile combination of rocker pipes with flexible joints and elastic effects removes the distress imposed by the differential settlement, and provides the possibility for a better comparison with the data obtained from both theoretical analysis and experimental tests. Results from each of these approaches are compared with those from experiments. It is concluded that there is need for a rational design procedure analysis for rocker pipes to be incorporated into codes of practice, such as EN 1295.