Browsing by Author "Rinne, Mikael, Prof., Aalto University, Department of Civil Engineering, Finland"
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- Dust dispersion in hard rock quarries
School of Engineering | Doctoral dissertation (article-based)(2023) Sitkiä, MarjoOpen-pit quarrying constitutes a core industry in many countries. Significant dust emissions appear when different types of rock products, such as aggregates, are being produced. Dust causes harmful environmental effects. The aim of this study was to define the extent of dust dispersion and to find out critical parameters affecting it in hard rock quarries. The most critical parameters affecting the dust concentration and dispersion appears to be the wind direction, seasonal climatic conditions, number of crushing units and capacity of the drill. In addition, the commercial software AERMOD BREEZE for dust dispersion modelling was tested to find out the usability of short-term modelling results. Dust was measured in eight aggregate quarries and in two natural stone quarries. The measurements were made inside the quarry area with a nephelometer. Performed measurements and modelling results were compared with published data. During the production the dust concentration within aggregate quarries was a few thousand µg PM10/m3. The secondary crushing generated approximately 1 700 μg PM10/m3 and tertiary crushing about 3 400 μg PM10/m3, measured 50 m downwind from the source. Compared to crushing, drilling produced significantly less dust: between a few tens to few hundreds of µg PM10/m3. The background concentration of PM10 was reached at extrapolated distances of 750 m, 350 m, and 100 m from the tertiary crushing, secondary crushing, and drilling of natural stone, respectively. During the wintertime, the PM10 concentration near the secondary crushing was approximately 1 700 µg/m3, whereas during the summertime, it was roughly 170 µg/m3. Modelling performed well for crushing during the summertime as the modelled concentrations were same order of magnitude (93%) with the measured ones. However, modelling was unable to react sufficiently into ground inversion during wintertime and predicted concentrations of crushing were approximately 5% of the measured ones. The modelling was not able to predict reliably the hourly fluctuation of dust dispersion in the vicinity of a quarry. Modelling with on-site weather monitoring data and comparison of measured concentrations should be conducted to verify this conclusion. - Geotechnical classification and Bayesian network for real time risk assessment in mining
School of Engineering | Doctoral dissertation (article-based)(2019) Mishra, Ritesh KumarMining involves the extraction of finite resources for their use in vast number of applications. Depletion of resources over time has required mining to be carried out underground and unprecedented depths. It is therefore important to conduct geotechnical risk assessments in advance to prevent accidents and sustain economic mining operation. Extent of available geotechnical information varies for a mine as the mine progresses from feasibility to operational stage. Geotechnical risk assessment (GRA) can be incorporated into the mine planning process from as early as the pre-feasibility stage. A formal risk assessment can be planned using appropriate scope definition which can help chose from a number of risk assessment tools and parameters. The goals of the research were: design a geotechnical risk classification system, which can be used from preliminary stages of mine planning and to motivate a detailed risk assessment; develop guidelines to prepare the scope of a detailed GRA; define selection criteria to choose the appropriate hazard identification tool and risk assessment parameters; carry out risk assessment in presence and absence of historical incident data; develop a framework to carry out geotechnical risk assessment in real time; represent and communicate the final risk to the work force for mitigation planning. The proposed geotechnical risk classification system (GRC) can be used to identify, rank and communicate the hazardous sections of a mine to the work force. The guidelines developed for defining the scope of the risk assessment and the numerical ranking system for risk assessment parameter selection can be used to define the risk assessment process and choose between deterministic, probabilistic and empirical method of risk assessment. The demonstrated methodology of fault tree and event tree can be used to break down a hazard into its elemental causes and to plan against all possible outcomes following an incident. Bayesian network (BN) based risk assessment can be used to model complex causal relationship of accidents and carry out incident investigation using the same model. It was shown using parameter learning that normal distribution of mine incidents was a better fit for incident forecasting compared to Poisson distribution for the cases studied in the thesis. A new method to combine multiple probability distributions to forecast future incidents has been proposed. It was demonstrated that BN based risk assessment can incorporate expert opinion in absence of data to forecast incidents. Finally, the measured risk can be communicated and monitored graphically using the F-N diagram. - Photogrammetry for characterizing rock fracture roughness, physical aperture, and hydromechanical properties
School of Engineering | Doctoral dissertation (article-based)(2024) Torkan, MasoudUnderstanding rock mass behavior is vital for various applications, including nuclear waste disposal and civil projects. Geometrical properties of single rock fractures, like roughness and physical aperture, significantly affect shear strength and fluid flow. This research aimed to characterize single rock fracture properties such as roughness, physical aperture, or hydromechanical attributes using photogrammetry of Kuru granite. Push shear tests were conducted on two sample sizes (200 cm × 100 cm and 50 cm × 25 cm), revealing a reduction of peak shear strength and friction angle for the larger size. Roughness back-calculated from shear tests for the larger sample was lower than the estimates from profilometer or photogrammetry. Scale adjustment was necessary for the correction of roughness estimation for the larger sample. Experimental differences may also stem from matedness. Using low-cost cameras in photogrammetry was investigated for a sample size of 50 cm × 50 cm. While smartphones show promise, caution is advised due to potential accuracy issues. Notably, the sampling intervals of 3D point clouds could affect roughness and physical aperture measurement results. A high-precision photogrammetric method was developed for measuring the physical aperture of three 25 cm × 25 cm samples. Markers at predefined distances used as scale bars were attached to each sample. The Root Mean Square Error (RMSE) between actual and calculated distances ranged from 20 to 30 µm. This method showed high accuracy compared to linear variable displacement transducers (LVDTs) for measuring fracture closure under normal stresses (0, 0.1, 0.3, and 0.5 MPa), with differences ranging from 1 to 8 µm. Achieving this level of accuracy required using at least 200 scale bars. Hydromechanical tests were conducted with fluid pressure gradients from 20 to 200 kPa/m and under the abovementioned normal stresses. The relationship between fluid pressure gradient and flow rate followed the nonlinear Forchheimer equation. Roughness displayed anisotropy, with greater roughness resulting in lower conductivity. Simulations were performed under different conditions and compared with laboratory fluid flow tests for validation. Scale effects study revealed significant variations in roughness and permeability with sample size changes. Three 100 cm × 100 cm surfaces were extracted from the 3D model of the bottom half of the 200 cm × 100 cm sample. Then, square subsample sizes ranging from 5 to 100 cm were extracted to estimate roughness and permeability. The surfaces were duplicated and shifted 350 µm to match the initial physical aperture of the 25 cm × 25 cm samples. Square subsample sizes below 30 cm showed variations in roughness and permeability, while these properties tended to be relatively stable states beyond this sample size. In conclusion, the study showed the feasibility of using photogrammetry to accurately characterize different rough fracture sizes for different applications. - Prediction of stress-driven rock mass damage in spent nuclear fuel repositories in hard crystalline rock and in deep underground mines
School of Engineering | Doctoral dissertation (article-based)(2018) Uotinen, LauriNuclear plants have existed since the 1950s, and they provide 11 % of the world's electricity production. Worldwide, 30 countries are operating 448 nuclear reactors for electricity generation, and 57 new nuclear plants are under construction in 15 countries. Measured by deaths per terawatt hour, nuclear power is the safest method to provide energy, but it does produce a range of radioactive waste, which must be disposed of safely and responsibly. The deep geological repository is currently the only acceptable long-term solution for high-level nuclear waste. The two most common causes of rock mass failure are structurally controlled gravity-driven failure and stress-induced failure. Usually, surface and near-surface rock excavations are subject to structurally controlled gravity-driven problems, but in deep rock spaces, the in-situ stress of the rock mass increases and the risk of stress-driven problems grows. The five most common stress-driven damage mechanisms are i) rockburst, ii) spalling, iii) convergence, iv) shearing and v) seismic. Excessive convergence is rarely a problem in hard, massive rock mass. In this thesis, the remaining four mechanisms are addressed. The goals of the research were to discover the damage-reducing capability of thin sprayed concrete liners, to define the strength of long rock joints, and to develop a real-time risk management concept. Numerical modelling was used to design an in-situ concrete spalling experiment, the ICSE. Laboratory scale mortar rock joint replicas were used to study the scale effect, and large 2.00 m by 0.95 m (ASPERT) and 0.50 m by 0.25 m rock joints were sheared to validate the methods. A new real-time formulation of the Geotechnical Risk Management (GRM) concept was studied using both example cases and case data. New methods were developed for the photogrammetric capture of rock joint surfaces and shear testing of large rock samples. The numerical modelling predictions for the in-situ experiment show that the thin concrete liner produces up to 3 MPa of support pressure and using polyaxial Ottosen criterion the liner is not damaged during the heating stage. Both the replica shear tests and the large shear tests results show a weak negative scale effect. Based on the initial analyses using example data, Bayesian networks appear compatible with the Observational Method, and the approach is ready to be tested using real data. The three main conclusions each address the stress-driven damage prediction and mitigation. The stress-driven damage can be reduced using support pressure generated by thin concrete liners. A new method was developed to capture rock joint geometry using photogrammetry and to manufacture mortar replicas for laboratory scale shear testing. The use of Bayesian networks, together with the real-time geotechnical risk management concept, was demonstrated. The results contribute towards predicting stress-driven damage in deep underground spaces. - Techno-economic aspects of seasonal underground storage of solar thermal energy in hard crystalline rocks
School of Engineering | Doctoral dissertation (article-based)(2019) Janiszewski, MateuszDue to the current issue of global climate change, certain actions have been precipitated in the global energy sector to increase the share of renewable, clean energy. One example of renewable energy is solar thermal energy, which can be utilised for domestic heating purposes in solar communities. However, in countries located at high latitudes, such as Finland, solar thermal energy is most abundant in the summer when the heating demand is low, and less abundant in the winter when the heating demand peaks. The solution to this mismatch is Thermal Energy Storage (TES). TES allows the collection of energy during the summer, which is accumulated in a storage medium, stored seasonally, and extracted in the winter to cover the heating demand. Rock and water in the subsurface are perfect storage media, and a selection of Underground TES (UTES) methods exist which could be utilised as long-term energy storage solutions for solar communities. The goal of this research was to develop a numerical modelling approach for the simulation of the Borehole TES (BTES) systems by first determining which UTES method would be best to apply in a solar community in Finland. Furthermore, through this development, a method was devised to numerically simulate hydraulic fracturing in fractured rock. To select the best UTES method for a Finnish solar community, a criteria-based feasibility study was implemented. It revealed that the BTES method is advantageous in terms of its ease in gaining large storage volumes, feasibility at a small scale, its cost-efficiency and adaptability. Two numerical modelling approaches for the simulation of borehole heat exchangers were proposed, validated by an in situ experiment and used to simulate the BTES systems. Numerical modelling revealed that low thermal diffusivity of the rock is essential for maximising the efficiency of seasonal storage. Furthermore, a fracture mechanics-based numerical model was proposed to simulate the interactions between hydraulic and natural fractures in Fractured TES (FTES) systems. The hydraulic fracturing model indicated that pre-existing discontinuities with low dip angles modify the propagating path of sub-horizontal hydraulic fracture potentially hindering the thermal performance of the FTES systems. The three main conclusions address seasonal TES in hard crystalline rocks. The BTES method is suggested as the most optimal method for a Finnish-based solar community. The two proposed thermal numerical modelling approaches of borehole heat exchangers can aid in the design of BTES systems by efficiently simulating their seasonal performance. Lastly, the proposed hydraulic fracturing model can simulate the construction process of FTES systems. The results of this dissertation contribute towards the development of the state-of-the-art of UTES in hard rocks.