Detection and geometric characterization of rock mass discontinuities using a 3D high-resolution digital outcrop model generated from RPAS imagery – Ormea rock slope, Italy

Abstract The use of a remotely piloted aircraft system (RPAS) and digital photogrammetry is valuable for the detection of discontinuities in areas where field mapping and terrestrial photogrammetry or laser scanner surveys cannot be employed because the slope is unsafe, inaccessible, or characterized by a complex geometry with areas not visible from the ground. Using the Structure-from-Motion method, the acquired images can be used to create a 3D texturized digital outcrop model (TDOM) and a detailed point cloud representing the rock outcrop. Discontinuity orientations in a complex rock outcrop in Italy were mapped in the field using a geological compass and by manual and automated techniques using a TDOM and point cloud generated from RPAS imagery. There was a good agreement between the field measurements and manual mapping in the TDOM. Semi-automated discontinuity mapping using the point cloud was performed using the DSE, qFacet FM, and qFacet KD-tree methods applied to the same 3D model. Significant discrepancies were found between the semi-automatic and manual methods. In particular, the automatic methods did not adequately detect discontinuities that are perpendicular to the slope face (bedding planes in the case study). These differences in detection of discontinuities can adversely influence the kinematic analysis of potential rock slope failure mechanisms. We use the case study to demonstrate a workflow that can accurately map discontinuities with results comparable to field measurements. The combined use of TDOM and RPAS dramatically increases the discontinuity data because RPAS can supply a good coverage of inaccessible or hidden portions of the slope and TDOM is a powerful representation of the reality that can be used to map discontinuity orientations including those that are oriented perpendicular to the slope

Geological Structures and Roof Profiles in a Myra Canyon Tunnel Mapped from High Resolution Digital Rock Surface Models

Nearly 100 year old tunnels once used by the Kettle Valley Railway are now popular destinations for hikers and bikers in the Myra-Bellevue Provincial Park in British Columbia. These tunnels have never undergone detailed geotechnical mapping and remain largely unsupported and subject to freeze-thaw cycles and gradual deterioration resulting in some loose rock and small rock falls. Stereo photographs are being taken to establish high resolution digital rock surface models of the tunnel interiors and tunnel portal areas. These models permit accurate mapping of important geological structures and form an archive that can be used to identify changes in the tunnel conditions over time. The capability to monitor changes in the tunnel surface could become critical in detecting and managing possible rock fall hazards.Applied Science, Faculty ofEngineering, School of (Okanagan)UnreviewedFacult

Geohazards in the South Okanagan

Applied Science, Faculty ofEngineering, School of (Okanagan)UnreviewedFacult

Guidelines for Mine Haul Road Design

Applied Science, Faculty ofEngineering, School of (Okanagan)UnreviewedFacult

Frac Sand Crushing Characteristics and Morphology Changes under High Compressive Stress and Implications for Sand Pack Permeability

Sand consisting of round quartz grains is widely used as a proppant during hydraulic fracturing to produce natural gas from tight shale formations. This paper presents results from sand characterization and crushing tests on Jordan Formation frac sand. It includes an assessment of grain size reduction, changes in particle shape, and reduction in void ratio. It also examines the implications for permeability reduction through a sand pack caused by the closure stress on a hydraulic fracture. The sand from two size ranges (0.6 to 0.71 mm and 0.5 to 0.6 mm) was tested dry under applied compressive stresses of up to 40 MPa in a crushing cup. The overall sand pack stress-strain response becomes softer as grains are crushed. The particle shape shifts from nearly spherical grains to diametrically split grains and then to small elongated and angular fragments for the smaller particle sizes. The permeability reduces by over 70% at a 40 MPa stress, which is primarily caused by void ratio decrease, reduction in particle size, and a shift away from spherical particle shapes. This paper demonstrates more information can be extracted from sand crushing tests and that sand pack permeability can be assessed to optimize frac sand selection.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Low-Altitude Aerial Methane Concentration Mapping

Detection of leaks of fugitive greenhouse gases (GHGs) from landfills and natural gas infrastructure is critical for not only their safe operation but also for protecting the environment. Current inspection practices involve moving a methane detector within the target area by a person or vehicle. This procedure is dangerous, time consuming, labor intensive and above all unavailable when access to the desired area is limited. Remote sensing by an unmanned aerial vehicle (UAV) equipped with a methane detector is a cost-effective and fast method for methane detection and monitoring, especially for vast and remote areas. This paper describes the integration of an off-the-shelf laser-based methane detector into a multi-rotor UAV and demonstrates its efficacy in generating an aerial methane concentration map of a landfill. The UAV flies a preset flight path measuring methane concentrations in a vertical air column between the UAV and the ground surface. Measurements were taken at 10 Hz giving a typical distance between measurements of 0.2 m when flying at 2 m/s. The UAV was set to fly at 25 to 30 m above the ground. We conclude that besides its utility in landfill monitoring, the proposed method is ready for other environmental applications as well as the inspection of natural gas infrastructure that can release methane with much higher concentrations.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult

Effect of proppant distribution in hydraulic fractures on coalbed methane extraction

Fracturing with proppants is often used to improve the permeability of coalbed methane (CBM) reservoir. The fracture is easy to close under the closure stress and the proppant distribution in fractures greatly influences the extraction efficiency of CBM. The past research mainly considered the impact of fracturing damage on the coalbed methane extraction but rarely investigated the influence of the proppant distribution forms on CBM extraction. Therefore, based on the theory of dual-porous media, this paper establishes a theoretical model of CBM extraction with different proppant distribution forms, which considers the proppant compaction, embedment, and fracture aperture change. The model is implemented numerically and is validated against field results of CBM production. The research results show that the extraction efficiency of CBM from high to low is the pulse proppant injection, continuous proppant injection, no proppant injection, no fracturing. The continuous proppant injection should ensure that the proppant placement rate is more than 60 %. The CBM extraction efficiency is the highest when the proppant column length is 0.2 m–0.3 m and the void area length is 0.5 m. The research results provide a theoretical basis for improving the extraction efficiency of coalbed methane using fracturing with sand injection

Investigation of Hydraulic Fracturing Behavior in Heterogeneous Laminated Rock Using a Micromechanics-Based Numerical Approach

Understanding hydraulic fracturing mechanisms in heterogeneous laminated rocks is important for designing and optimizing well production, as well as for predicting shale gas production. In this study, a micromechanics-based numerical approach was used to understand the physical processes and underlying mechanisms of fracking for different strata orientations, in-situ stresses, rock strengths, and injection parameters. The numerical experiments revealed a very strong influence of the pre-existing weakness planes on fracking. Geological models for rock without weakness planes and laminated rock behave very differently. Most simulated fractures in the rock without weakness planes were caused by tensile failure of the rock matrix. In an intact rock model, although a radial damage zone was generated around the injection hole, most of the small cracks were isolated, resulting in poor connectivity of the fracture network. For rock models with pre-existing weakness planes, tension and shear failure of these structural planes formed an oval-shaped network. The network was symmetrically developed around the injection well because the strength of the pre-existing weakness planes is generally lower than the rock matrix. The research shows that the angular relations between the orientation of the structural planes and the maximum horizontal stress, as well as the in-situ stress ratios, have significant effects on the morphology and extent of the networks. The strength of the pre-existing weakness planes, their spacing, and the injection rate can dramatically influence the effectiveness of hydraulic fracturing treatments.Applied Science, Faculty ofNon UBCEngineering, School of (Okanagan)ReviewedFacult