No description available.

This thesis presents the results of a study into the behaviour of post-tensioned pocket type brickwork retaining walls. An analytical and experimental study was carried out to examine the behaviour of the wall up to failure. The programme of work considered the effect of the following parameters on the perfromance of the wall: (i) vertical concentrated eccentric load; (ii) percentage area of steel; (iii) pocket spacing and wall slenderness; (iv) type of wall bond. The results of the analyses were compared with those based on the Code of Practice, B.S 5628, Part 2, 1985. A computer program was written in Fortran to predict the ultimate moment of the wall panels, using predicted equilibrium equations. Good agreement was found between the theoretical and experimental results. The results show that post-tensioned pocket type brickwork retaining walls have a large nominal strength, largely due to the presence of prestressing forces and the behaviour of the walls as homogenous cantilevers. The most effective pocket spacing was found to be h/3, and the maximum spacing should be limited to give an aspect ratio which is greater than 1.15. The study confirms the applicability of prestressed brick masonry for structures such as slabs and retaining walls irrespective of the type of brickwork bond.

In this study, I use the cross-hole method to examine the relationship between fractures in limestone reservoirs, where the presence of fractures has been determined by <I>a priori </I>information, and the shear-wave anisotropy of the rockmass. I process and interpret multicomponent seismic data from two producing areas: the East Fitts field Oklahoma, where a multi-azimuthal cross-hole survey is used to image the Hunton and Viola reservoir formations at depths of 3000-4000 feet; and the Iatan East Howards field, Texas, where two cross-hole azimuths are used to image the Clearfork reservoir formation at a similar depth. I apply a numerical method to measure the shear-wave splitting parameters, <I>qS1</I> polarization and time delay between <I>qS1</I> and <I>qS2</I> arrivals, and best-fit parameters for reservoir crack strike and crack density are determined by forward modelling. The observed <I>qS1</I> polarizations at three azimuths from the East Fitts site can be related to propagation through two thin layers, representing the Hunton and Viola reservoir zones, each containing distributions of micro-cracks with a best-fit strike of N35°E. The observed time delays between <I>qS1</I> and <I>qS2</I> arrivals can also be modelled by lower crack densities distributed throughout the layered model. Polarization measurements at one cross-hole azimuth from the Iatan site agree with <I>a priori </I>reservoir fracture direction of N60°E-N85°E. Results from the second azimuth fall within the expected zone of behaviour for cracks striking ±12.5° of N170°E. A measured <I>qS1</I> polarization direction of N170°E from near-offset VSP data at the Iatan site also disagrees with the known reservoir fracture direction. The Iatan measurements are incompatible with hexagonal anisotropic symmetry with a horizontal axis of symmetry. No improvements in the resolution of the anisotropic parameters of fractured rocks and reservoirs was achieved by using the cross-hole method although propagation through the near-surface is avoided. Acceptable model solutions have been found for the observations, however, the problems of non-uniqueness are inherent in the forward modelling approach.

The observed fractal nature of both fault length distributions and earthquake magnitude-frequency distributions suggests that there may be a direct relationship between the structure of active fault systems and the resulting seismicity. In much previous theoretical work, a positive correlation between the exponent D from the fracture length distribution and the seismic or AE b-value has been inferred from a simple dislocation model of the seismic source. The main aim of this project was to test this relation quantitatively, for tensile fracture, using results from controlled laboratory experiments. Field work on natural tensile fracture systems was also carried out to test that the results from the artificial fracture in the laboratory were relevant to the natural fractures that were being simulated. First, a series of double torsion tensile tests on crystalline rock, carried out at the Fracture Mechanics Laboratory, University College London, is described. A program of tests was carried out on two rock types, granodiorite and granite of different grain size, to test the effects of rock type and specimen size on the laboratory results. The main controlling variables, used during the tests, that affect the results, are the presence or absence of fluid, at ambient temperature and pressure, in the crack tip environment, and stress intensity (and hence crack velocity). Microseismic acoustic emissions (AE) were monitored during subcritical crack growth under controlled conditions of constant stress intensity, K<SUB>I</SUB>, and quantitative structural analyses of the resulting fracture patterns were carried out on the same specimens. AE microseismicity is found to reflect different aspects of microcrack propagation in the laboratory. AE b-values range form 1.0 to 2.4 and vary depending upon fluid presence at the crack tip. The greater the fluid-rock interaction, the higher the relative proportion of smaller seismic sources (thus producing a higher b-value).

No description available.

No description available.

No description available.

No description available.

An attempt was made in the course of this investigation, to introduce some modern laboratory and 'in-situ' techniques of Experimental Stress Analysis to mining configurations, and in particular, to the design of underground pillars. Chapters I and II are both introductory ones. In the former, the basic problems associated with the design of structures in rock are briefly outlined whereas in the latter, a detailed and up to date discussion is given, on the behaviour of underground pillars and their design considerations. In Chapters III and IV two modern and sophisticated photoelastic techniques are described, with particular reference to their application to mining. The Scattered Light technique of three-dimensional photo-elasticity, and the special polariscope on which this method can be executed, are described in Chapter III. In Chapter IV, an Image De-rotation technique has been specially adapted, to enable gravity loading simulation in 'real time'. The application of the Scattered Light technique to the field of Rock Mechanics, is given in Chapter V, where two cases of underground pillars are examined photo-elastically, in three dimensions. In order to examine the underground behaviour of pillars as well as establishing the degree of reliance of the photoelastic results, two 'in-situ' investigations were carried out, and are described in detail in Chapter VI. Finally, the important problem of developing improved methods of 'in-situ' measurements was not ignored. The design and laboratory testing of two instruments capable of triaxial measurements at a point 'in-situ', from a single borehole, is discussed in Chapter VII.

No description available.