Chemical remanent magnetisation (CRM) occurs as the result of the acquisition of remanence by a rock through chemical change or mineral growth. Despite the important role CRM plays in rock magnetic and palaeomagnetic processes (as a mechanism by which rocks acquire a primary remanence or as a feature of post- depositional alteration) there are few studies of this process to date. This dissertation investigates the effect of phase and chemical change on the magnetic and remanence carrying properties of some geologically important iron oxide minerals. The mineral systems studied are: the goethite-hematite, the magnetite-maghemile-hematite and the lepidocrocite-maghemite-hematite systems. The mineralogy of these systems is studied using transmision electron microscopy, thermogravimetry and x-ray diffraction methods. A transformation mechanism for the dehydration reaction of goethite is presented. The cation distribution of maghemite and its intrinsic magnetic properties are investigated. The process of CRM is simulated in the systems goethite-hematite and lepidocrocite-maghemite-hematite and the results correlated with theoretical predictions of CRM intensity, blocking volume and their dependence on mineral growth rate. A self-reversal in the maghemite-hematite system is reproduced. The low temperature oxidation of magnetite to maghemite and hematite (for example in basalts) and the low temperature dehydration reactions of goethite and lepidocrocite (as occur, for example, in sediments) are important mineral transformations. The results and conclusions of this study are extrapolated to geological environments and time scales, in particular with reference to red bed palaeomagnetism.

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Stability analysis of rock masses composed of small, discrete rock blocks that are in-place and interlocked should consider four components of failure: (1) Sliding between blocks. (2) Shearing through rock blocks. (3) Rolling blocks in a shear zone. (4) Crushing of rock blocks. Statistical rock mass description is used to define the characteristics of the rock blocks and the block assemblage. Clastic mechanics is one method of predicting stresses produced by the arrangement of rock blocks and the loading conditions. Failure begins at a point of maximum stress behind the slope. Progression of the failure is assumed if the first block fails because adjacent blocks will become overstressed. The location of the point of maximum stress is determined from the shape and arrangement of the constituent rock blocks. Because strength is mobilized block-by-block rather than instantaneously along a continuous shear surface, sliding between blocks shows less stability than a soil rotational shear analysis or a rigid block sliding analysis. Shearing through rock blocks occurs when maximum shear stress exceeds rock shear strength. Crushing of rock blocks is predicted if the normal stress exceeds the compressive strength of the rock block. A size-strength relationship is combined with the rock block size distribution curve to estimate crushing strength. Rotating blocks in a shear zone have been observed in model studies and as a mechanism in landslides. Stability analysis assumes that the rock mass is sufficiently loosened by blasting and excavation to allow blocks to rotate. The shear strength of rolling blocks is dynamic shear strength that is less than static sliding shear strength. This rolling mechanism can explain release of slope failures where there are no other obvious structural controls. Stability of each component of rock mass failure is calculated separately using capacity-demand reliability. These results are combined as a series-connected system to give the overall stability of the rock mass. This probability of failure for the rock mass system explicitly accounts for the four components of rock mass failure. Criteria for recognizing rock mass failure potential and examples applying the proposed method are presented.

The displacements and stresses in layered rock above underground openings can be calculated using a beam model for the rock layers. The traditional approach assumes that interfaces between layers are frictionless and layers can slip past one another freely as they deflect. In contrast, the design of structural laminated beams has traditionally been based on the assumption that the interfaces between layers were welded, with no slip occurring there. In this work, the theory of composite laminated beams, which allows for partial slip on layer interfaces, is applied to the problem of predicting displacements and stresses in layered roof rock. The effects of rockbolt reinforcement are modeled by discrete shear and normal stiffnesses incorporated at locations in the model where the rockbolts cross layer interfaces. Published solutions and results for laminated composite beams are reviewed. Composite laminated beam theory provided a means of accounting for rockbolt reinforcement effects and provided a conceptual framework that was used to develop two FORTRAN programs; one, based on the force method of analysis, that automatically finds shear and tensile interface failures in the system, and the other a finite element program that employs beam elements, elastic interface elements, and rockbolt elements to model a rockbolted layered rock system. Published data together with results from these programs suggest that shear reinforcement may be more effective when placed near the ends of roof layers. The normal interaction between layers tends to be uniformly distributed unless rockbolt forces act on the layers or if partial delamination of layers has occurred. Both shear and normal reinforcement will cause stresses to be redistributed within the system of layers. Analysis of this redistribution of stresses requires that the sequence of interface failure be predicted which, in turn, requires that the properties of the individual layers, of the interfaces between layers, and of the rockbolts be properly taken into account. Laminated composite beam theory and programs based on this theory provide rational and efficient ways to study and analyze the behavior of layered roof rock.

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