No description available.

The stress state at the boundary of any underground mine opening is that of plane stress. This planar state of stress can be simulated in laboratory by subjecting a cubic rock specimen to a biaxial loading condition. Thus, research on the behaviour of biaxially loaded rock is important for better understanding of the stability of mining fronts such as crown pillar skin, drift face or shaft floor. / The objective of this research is to study the geomechanical behaviour of biaxially loaded rock. Three rock types were selected, namely limestone, granite and sandstone. / The laboratory work was conducted using a newly developed, 500-tonne biaxial loading frame, that is equipped with a servo-controlled load and displacement system. Recently patented in China, the new biaxial loading frame is spatially symmetric and equally rigid in both directions. Steel brush platens and solid platens with and without MoS2 were developed to help examine the end friction effect on biaxial strength. It is found that the biaxial strength can decrease up to 26.7% with the increase of cubic specimen size from 75 mm to 150 mm. The biaxial strength increases by 29.3% with the increase of loading rate from 1 MPa/s to 10 MPa/s, for granite. The biaxial strength of granite specimen decreases by nearly 6% when either solid platens with MoS 2 lubricant or brush platens are used. A comparison of the sigma 1-sigma2 failure envelopes reveals that the shape of the envelope and the location of the peak biaxial strength are dependent on the rock type. / Varying intensities of rock spalling generally initiate at the free faces of the specimen when sigma1 and sigma2 exceed sigma c/2. Ultimate failure occurs in the form of an out-of-plane shear failure, which splits the rock specimen into two or more wedges. / It is shown that both Mohr-Coulomb and Hoek-Brown criteria underestimate the biaxial strength of the rock. The Drucker-Prager failure criterion appears to provide poor correlation with experimental results. A new empirical biaxial rock failure criterion for intact rock is derived and another, accounting for rock mass characteristics through the Geological Strength Index (GSI), is then proposed.

The development of a petroleum reservoir would inevitably induce a rearrangement of the in-situ stress field. The rearrangement of the stress field would then bring about a deformation of the reservoir rock and a change of the permeability. This experimental study was carried out to investigate rock deformation and its impact on axial permeability. Triaxial compression tests were conducted on Berea sandstone, Indiana limestone, Westerly granite and tuff specimens. Axial permeability was continuously measured for Berea sandstone and Indiana limestone during triaxial compression tests. The axial permeability of fractured Westerly granite specimens was also measured during hydrostatic compression tests. Acoustic emission (AE) monitoring was performed to help improve the understanding of rock deformation. Results showed that Berea sandstone and Westerly granite were relatively brittle, while Indiana limestone and tuff were relatively ductile. Rock deformation altered pore structures and the change of pore structures considerably impacted fluid flow through rock. For porous Berea sandstone and Indiana limestone, the destruction of the pore structure by rock deformation led to a decrease in axial permeability. For tight Westerly granite, fractures created by rock deformation significantly improved the ease of fluid flow. Acoustic emission response was found to be strongly dependent on rock type. Brittle Berea sandstone and Westerly granite produced high AE rates during compression tests, while ductile Indiana limestone and tuff generated very low AE rates.

A biostimulation field trial was conducted to determine the effect of nutrient addition on microbial populations in a fractured rock environment. The ultimate goal of this research is to induce bioclogging in rock fractures as a method of in situ containment and remediation of contaminated groundwater. This trial focused on biostimulation of indigenous bacteria in a single fracture through the addition of bioavailable carbon, nitrogen and phosphorus sources. Bench-scale experiments were conducted to determine the optimal source and concentration of nutrients for microbial growth. The final mixture selected for the field trial consisted of sodium lactate plus two liquid fertilizers, resulting in a 100:9:4 molar solution of bioavailable carbon, nitrogen, and phosphorus with a carbon source concentration of 8.9 g/L. The field trial was conducted in an uncontaminated area adjacent to an abandoned quarry in southern Ontario, Canada. The geology of the site consists of flat-lying dolostone pervaded by bedding plane fractures, with minimal overburden. An arrangement of three boreholes isolated a single fracture at a depth of 17m using straddle packer systems. A groundwater recirculation system was created with groundwater withdrawal at BH7 and reinjection of amended water at BH9. Throughout the three-week biostimulation experiment, general groundwater parameters, including temperature, dissolved oxygen and electrical conductivity, were monitored frequently. Geochemical and microbiological conditions including available electron acceptors, biochemical oxygen demand, heterotrophic plate counts, and microbial diversity were evaluated before and after the experiment. Monitoring results for the withdrawal well confirmed that nutrient delivery was occurring, albeit with substantial mass loss due to incomplete flow field development. Numerical modelling of the system estimated a nutrient mass loss of 29%. Geochemical monitoring of key electron acceptors suggested that redox conditions in the isolated fracture were greatly affected by nutrient addition. Biological data indicated significant changes in the microbial populations, with heterotrophic plate counts increasing significantly in the isolated fracture. Changes in microbial diversity were also observed through 16S rDNA analysis. Denaturing gradient gel electrophoresis results indicated substantial diversification and growth of the microbial community following biostimulation. Further research will investigate the potential for bioclogging at a NAPL-contaminated fractured bedrock site. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-09-17 12:37:48.16

Shallow excavations through variable rockmasses in urban centers present significant design challenges, whether considering small diameter tunnels for utilities or large span underground caverns. In designing shallow excavations in urban environs, it is especially critical to minimize the impact of the excavation on surface. In small diameter projects, minimal surface disturbance is often achieved by the employment of TBMs as the excavation method. While reducing the risk of surface subsidence due to displacements in front of the face, TBM progress is sensitive to variable ground conditions and the TBM design must be appropriately matched to the expected geology. Sufficient understanding of the geology and development of geological models are critical in the selection of an appropriate TBM and cutting tools. In this study, recent projects in Calgary, AB are used to highlight the challenges faced with using TBMs through sedimentary rock with distinct, variable units. In larger scale projects, long term excavation stability is critical in the reduction of surface disturbance. Due to the low confining stresses, structural failure is often the primary failure mode in shallow excavations, especially within fractured, heterogeneous rockmasses. In these cases, numerical methods are often used in excavation design. The ability of numerical methods to capture the expected failure modes of shallow excavations through layered rockmasses is explored, with an emphasis placed on the ability of support elements to reduce shear slip for increased stability. Passive bolt models are analysed using both 2D and 3D numerical models to adequately capture the behaviour of a passive support system in shear. The shortcomings of some current support models are discussed, and modifications are suggested. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-09-25 20:56:52.083

No description available.

No description available.

No description available.

No description available.

No description available.