No description available.

published_or_final_version / Applied Geosciences / Master / Master of Science

No description available.

No description available.

No description available.

No description available.

No description available.

The fracture of rock during freezing and thawing poses a serious threat to rock slope stability and represents an important geohazard in cold regions. However, mechanistic understanding of microcracking processes, controls and rates, and the transition from micro- to macrocracking during freeze‒thaw is limited. To investigate the mechanisms of cracking, two physical modelling experiments supplemented by compressive tests were performed on specimens of chalk and sandstone, monitoring and imaging micro- and macroscale deformation due to freeze‒thaw cycling. The microscale experiment repeatedly scanned two water-saturated specimens 20 mm in diameter and 30 mm high, subject to downward freezing in a climate cabinet. Successive micro-computed tomography (μ-CT) images quantified the progressive development of structure and strain during 20 freeze‒thaw cycles. The macroscale experiment imposed 12 bidirectional (upward and downward) freezing cycles on three 300 mm cubic blocks over the course of 315 days, simulating an active layer above permafrost. Eight acoustic emission sensors recorded the timing, location and energy released during microcracking events, while rock temperature, surface heave and settlement, and subsurface strain were monitored continuously. The microscale experiment generated different probability functions that correlate points, clusters and linear movements of the progressive fracture phase extracted from scanned images and showed dominantly vertical rather than horizontal microcrack growth. The macroscale experiment brecciated a chalk block near modal depths of the 0oC isotherm during thaw, and indicated high tensional activity and limited shearing. Ice segregation during thawing produced more microcracking events than volumetric expansion produced during freezing. A statistical model is proposed that distinguishes the mechanism of fracture propagation during freezing and thawing.

In an attempt to understand the environment of the Precambrian weathering at Rispond, and compare it with weathering processes taking place at the present time, samples weathered to different degrees have been taken at various distances immediately below the Cambrian Unconformity. These samples have been subjected to chemical analysis by X-ray fluorescence spectometry and wet analysis, and to mineralogical analysis by X-ray diffraction and polarised light microscopy. Interpretation of these results indicate that the samples represent a weathering profile (although not necessarily an unchanged one as these rocks have been subjected to a maximum temperature of 250°C during burial subsequent to the deposition of the Cambrian strata). This is inferred from the minerals present in the soil, the nature of the chemical changes observed, the similarities of the data on the Kronberg weathering diagram to those of present-day weathering, and the position of the profile immediately below the unconformity. Further interpretation of the results in terms of the thermodynamic properties of the minerals present in the profile, the chemical reactions believed to have taken place, the geological evidence and a survey of the chemical composition of present-day surface waters leads to the conclusion that the rocks below the Cambrian Unconformity at Rispond represent a fossil soil profile. These rocks contain pyrophyllite, considered to have been formed by low-grade metamorphism rather than by weathering. Three possible modes of origin have been considered, and that involving the weathering of potassium feldspar to kaolinite alone in an acid environment rejected. The two mechanisms involving the weathering of the feldspar to illite in an arid alkaline environment with restricted drainage are considered to be more likely. The illite produced in these mechanisms was further weathered to produce, in the one case, kaolinite, and in the other one, potassium beidellite as a mixed layer mineral with illite. These two mechanisms can be mixed in any proportion, the exact amount of potasium beidellite present depending upon the relative thermodynamic stabilities of kaolinite and beidellite. As the latter is unknown, further accuracy cannot be achieved at present. The presence of abundant potassium feldspar in the Fucoid Beds, and the existence of trace fossil planolites in such rocks as well as the temperature to which they have been heated (about 250°C) suggested the possible existence of an ammonium feldspar in the area. Therefore, a method to measure the amount of ammonia content in these rocks has been designed. The results of twenty-two samples from the Cambro-Ordovician succession of N.W. Scotland analysed by this method show that the ammonia content is very low. If all the ammonia is present as an ammonium feldspar (buddingtonite), it represents about 0.3% of the mineral in the shales and even less in other rock types.

The objective of this research was to determine the impact of algal colonisation on natural stone masonry. Experimental work was carried out to determine the physical and chemical damage caused by micro-algae using reflected light microscopy, Scanning Electron Microscopy and Inductively Coupled Plasma - Atomic Emission Spectroscopy. Colonisation experiments were performed on individual mineral chips of quartz, calcite, dolomite, siderite, labradorite, orthoclase, a perthitic albite, muscovite and montmorillonite; as well as the Giffnock sandstone, a traditional building stone of the Glasgow area. Work was also carried out to determine the effect of algal colonisation on the absorption of water into a masonry surface. The research determined that algae create an alkaline environment in the areas they colonise. Algal mediated damage to the mineral substrates includes the dissolution and pitting of carbonate surfaces as well as the etching of plagioclase feldspar surfaces. Algal colonisation preferences were noted throughout the experiment with algae preferentially colonising kinks and steps in the topography of mineral surfaces as well as grain edges. Preferences were also seen in the colonisation of the Giffnock sandstone with micas showing heavy colonisation compared to other minerals in the lithology. Algal swelling and contraction cycles were examined in Environmental Scanning Electron Microscopy experiments and the impact that this physical swelling may have on the stone is modelled. Algal biofilms at the surface of the stone lead to an acceleration in the rate at which water enters the surface of the stone, this is important as water is the main weathering catalyst for masonry weathering. The findings of this project implicate algae in the weathering of natural stone masonry through enhanced mineral dissolution, mineral etching and pitting, patina formation, physical weathering through swelling cycles and the alteration of the surface physical properties in relation to water absorption.