Browsing by Author "Uotinen, Lauri"
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- Characterization of hydro-mechanical properties of rock fractures using steady state flow tests
A4 Artikkeli konferenssijulkaisussa(2020-11-13) Uotinen, Lauri; Torkan, Masoud; Janiszewski, Mateusz; Baghbanan, Alireza; Nieminen, Ville; Rinne, MikaelCharacterization of Hydro-Mechanical (H-M) properties of rock fractures is the initial and important step in modeling of fully H-M coupled processes in fractured rock masses. Fluid flow in the fractured rock mass is an important aspect when evaluating the safety of geological disposal of high-level nuclear waste. Many attempts have been taken to measure and model fluid flow in rock fractures in different stress field conditions. However, still study about the scale effect of fracture properties and confinement stress on the conductivity of rough rock fractures remains a challenging topic of research. As a part of an ongoing research project about fluid flow modeling in fractured rock mass (RAKKA), and as an initial step one rock slab pair with sizes of 250 mm x 250 mm of Kuru grey granite halves was prepared. It has a horizontal mechanically induced tensile fracture. The surface roughness of the fracture was mapped using a conventional profilometer and structure-from-motion photogrammetry before each fluid flow test. The fractures were subjected to different normal stress and then fluid flow within the fractures was conducted linearly from edge to opposite edge with perpendicular edges sealed, and conductivity of the fractures under steady-state condition was measured. Then the test is repeated with all three sides open. The results show anisotropic behaviour in permeability. The diagonal components of the permeability matrix are significantly stress-dependent. Together the new fracture digitization method and the new three-way fluid flow test allow the contactless characterization of hydro-mechanical properties of rock fractures and the validation of the results. - Characterization of hydromechanical properties of a rock fracture using numerical modelling
Insinööritieteiden korkeakoulu | Master's thesis(2022-06-13) Nieminen, VilleThe hydromechanical processes of a single rock fracture are dependent on the properties of that single rock fracture as well as the properties of the rock fractures that are connected to it, and their geometry, orientation and the effective stress of the fracture walls. Hydromechanical properties of a single rock fracture are governed by several parameters such as contact area, roughness, tortuosity, aperture, channeling, matedness, sample sizes, normal stress, flow regime, and flow boundary conditions. Numerical modelling was used to compare the influences of roughness, aperture, water pressure, and different flow boundary conditions on fluid flow in an artificial granite fracture. Comprehensive fluid flow analyses were made to better understand the flow behaviour, including the streamlines, flow velocities and inner water pressure distributions. A simulation model for fluid flow in a single rough fracture was developed with the COMSOL Multiphysics finite element method software. The resulting model was numerically simulated with COMSOL using the Navier-Stokes equations. In this thesis, 20 fluid flow simulations were performed on fracture model created from photogrammetry of rock block with the size of 250 mm × 250 × 110 mm containing artificial tensile fracture. Laminar fluid flow inside the fracture was simulated with fluid flow through x- and y-axis at increasing water pressure level at normal stress conditions of 0 MPa. Simulated water pressures were from 5 kPa to 50 kPa with 5 kPa interval. The numerical model was successfully verified against experimental laboratory work. The numerical simulation results show that the relationship between water pressure gradient and the flow rate is nonlinear indicating turbulent flow behaviour. The channelling effect of the fluid flow as well as the pressure distribution along the fracture increase with the increase of water pressure. The growth of fluid flow velocity inside the fracture with the increase of water pressure is nonlinear and the growth rate of the fluid flow velocity decreases as the inlet water pressure increases. Comparison between the numerical modelling results and the experimental solution confirms that the 3D roughness geometry has a crucial role in defining the transmissivity, especially for nonlinear flow. The presented method can be used to characterize to flow properties of fractured rock and in evaluating different methods and implementation of underground rock engineering applications. - Correlation of Rock Mass Characterization Measurements in Virtual Reality and in Real Tunnel Environments
Insinööritieteiden korkeakoulu | Bachelor's thesis(2019-09-15) Helko, Ville - Design of shotcrete rock reinforcement in hard rock according to Eurocode
A4 Artikkeli konferenssijulkaisussa(2011-06-06) Uotinen, LauriShotcrete was invented in the 1900’s and first used in rock spaces in the 1930’s. The design of shotcrete is currently (2011) mainly based on empirical rules. This paper explores the feasibility of designing shotcrete structures according to the methods allowed in the Eurocodes. The shotcrete material parameters are derived according to the Eurocode and presented for shotcrete grades up to C50/60. The EFNARC panel test (EN 14488-5) and ASTM round panel test (C1550) are used in conjunction with the Yield Line Theory (YLT) to produce the cracking limit of the bending resistance. The shotcrete failure process and failure modes are described. Linear elastic theory is used to calculate the crack initiation capacity. The means on how to calculate the shotcrete capacity for the most common failure modes are presented. Finally, notes on how to apply these results into practical design work are given. - Kalliotunnelien ratarakenteiden tärinänvaimennuksen mitoituksen ja suunnittelun perusteet
Helsinki University of Technology | Master's thesis(2008) Uotinen, LauriTyössä esitetään tärinänvaimennuksen suunnittelun ja mitoituksen lähtökohdiksi sekä työkaluiksi tärinän eteneminen ja vaimeneminen, kirjallisuustutkimus kansainvälisistä raja-arvoista, stokastisesti perusteltu suositus raja-arvoista sekä mallintamisen lähtökohdat ja perusteet. Tavoitteena oli selvittää ratarakenteiden tärinänvaimennuksen suunnitteluprosessin vaatimat lähtötiedot ja esittää optimaalinen suunnitteluratkaisu. Tuloksena syntyneen materiaalin avulla voidaan määrittää tärinänvaimennusrakenteelle vaadittu vaimennuskyky (syöttöhäviö) ja mallintamalla suunnitella rakenne, jolla se saavutetaan. Kaavoituksessa tai alustavassa suunnittelussa, kun käytössä on vähemmän lähtötietoja, voidaan käyttää työssä esitettyjä materiaaliominaisuustaulukoita sekä tärinän etenemisen teoreettista mallia, jolloin saadaan suuruusluokka-arvio odotettavissa olevasta tärinä- ja/tai runkomelutasosta. Työssä on tutkittu myös pyörähdyssymmetrisen (aksisymmetrisen) FEM-mallin, diskretoidun yksiulotteisen etenemismallin ja teoreettisen etenemismallin tarkkuutta verrattuna todellisiin mittaustuloksiin, joita saatiin Kampin metroaseman itäpuolella suoritetuista tärinämittauksista. Ratarakenteen osien yksityiskohtaista mallintamista varten on luotu katsaus erilaisiin osarakennemalleihin sekä niiden vahvuuksiin ja heikkouksiin. Näiden rakennemallien ja valmistajan ilmoittamien materiaaliominaisuuksien avulla on mahdollista analysoida paras mahdollinen vaimennusratkaisu kutakin ratarakennetyyppiä ja häiriölähdettä varten. Menetelmä soveltuu myös raitiovaunuliikennettä ja rautatieliikennettä varten, kun raideajoneuvon aiheuttama heräte tunnetaan. - Determination of joint mechanical parameters for stability analysis in low stress open pit mines
A4 Artikkeli konferenssijulkaisussa(2016-05-12) Iakovlev, Daniil; Sirkiä, Joni; Kallio, Pauliina; Uotinen, LauriFor low stress mining and civil engineering projects, slope stability is an essential part of safety and financial considerations. While large-scale stability can be modelled using equivalent rock mass properties, at smaller scale the local variations become significant and failure along the fracture planes is possible. The relevant boundary condition for low stress conditions is the Constant Normal Load (CNL), which allows for dilatation to occur. For deep mines the corresponding condition is the Constant Normal Stiffness, which restricts the dilatation. When dilatation is supressed the normal load is increased. This may lead to shearing of the asperities. If both the vertical and horizontal displacement are recorded during CNL testing, the dilatation may be calculated and numerically removed to provide a CNS estimate. In this paper three rock joint samples from the Siilinjärvi open pit mine were tested in a CNL shear box using displacement resetting at three different low normal loads. Profilometer and photogrammetry were used to measure the roughness of the surfaces. The results show poor match between the expected behaviour and observations. One possible cause is the reduced matedness often associated with natural near-surface rock joints. The potential weaknesses of the method are discussed and future research topics are suggested. - Digitisation of hard rock tunnel for remote fracture mapping and virtual training environment
A4 Artikkeli konferenssijulkaisussa(2020-11) Janiszewski, Mateusz; Uotinen, Lauri; Baghbanan, Alireza; Rinne, MikaelThe knowledge of geometrical properties of discontinuities is of crucial importance in the rock mass characterisation process. Recent advances in photogrammetry allow for an easy digitisation procedure of rock surfaces so that digital 3D models can be used for remote site characterisation. This paper presents a methodology to digitise tunnel rock surfaces using Structure from Motion digital photogrammetry for remote measurements of discontinuities. The proposed method is applied on a 12 m long and 4 m high tunnel section of an underground research tunnel at Aalto University in Finland, which is scanned using Canon 5Ds R DSLR camera and Canon 14 mm f/2.8 and 35 mm f/1.4 lenses. The photos are then processed in commercially available photogrammetric software – RealityCapture. As a result, a high-resolution 3D point cloud of the tunnel wall is produced. The point cloud is used for semi-automatic measurements of fracture orientations. In addition, a digital twin of the tunnel section with photorealistic surface texture is created and implemented into virtual reality (VR) system – Virtual Underground Training Environment (VUTE) developed for training of rock mass characterisation. The VUTE system enables remote visual inspection of the rock surface and virtual measurements of the orientation of discontinuities with designated virtual tools. The semi-automatic measurements extracted from the 3D point cloud using a discontinuity extractor software are compared with measurements performed in VR as well as with manual measurements performed in the tunnel. The results demonstrate that all three mapping methods identify three major joint sets with analogous orientations. The automatic fracture mapping method achieves the highest density of the measurements, allows repeatability, and enables other parameters to be extracted automatically, such as persistence and spacing of the discontinuities. This confirms the advantage of automatic analysis of discontinuities on 3D point clouds of tunnel rock surface digitised using photogrammetry. - Effect of anisotropy of fracture surface on fluid flow
A4 Artikkeli konferenssijulkaisussa(2023-01-10) Torkan, Masoud; Hosseini Khorasgani, AMIR; Uotinen, Lauri; Baghbanan, Alireza; Rinne, MikaelCharacterization of fluid flow through rough fractures is an important issue in designing underground excavations, such as nuclear repositories or geothermal applications. Fluid flow could be influenced by several parameters such as contact areas, aperture, hydraulic and mechanical conditions. Contact area and aperture could be two crucial geometrical factors which control hydraulic and mechanical behaviors of fractures. These factors are rarely isotropic, and anisotropy is observed in different directions. In this research, photogrammetry, as a high precision method, was used to analyze morphology of a tensile fracture induced in granite. Experimental and numerical stress-flow tests on rock fracture were conducted in two different directions with diverse normal stresses and water pressures. Analyzing the regenerated 3D model of the fracture and hydromechanical tests predicts the anisotropy in flow rates in different directions. Numerical and experimental results are well fitted particularly in low-stress conditions. The obtained results show that anisotropy affects permeability since outlet flow rates in the different directions with the same initial water pressures differ by 7 % in experiments and 4% in numerical modeling. - Elastoplastic Modelling of an In Situ Concrete Spalling Experiment using the Ottosen Failure Criterion
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-01-31) Uotinen, Lauri; Siren, TopiasAn in situ concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin concrete liner on prestressed rock surface, when the stress states in both rock and concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin concrete liner from level -3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the liner is 3.2 MPa and the tangential stress of rock is reduced by -33 %. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week 9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin concrete liner significantly reduces the amount of damage. - Eurocodes in Hard Rock Engineering in Finland
A4 Artikkeli konferenssijulkaisussa(2011-05-22) Uotinen, Lauri; Nuijten, Guido; Siren, Topias; Stöm, Jesse; Hakala, Matti; Rinne, MikaelThe Eurocodes are a set of European design principles, rules, and guidance intended for the design of load carrying structures. The codes have been compiled by the CEN Technical Committee 250 (CEN/TC250). The intent of the Eurocodes is to unify the design methodology. Parallel use with existing national building codes is allowed during the transition period (2007–2010) to ensure a smooth transition and enough time to make the necessary changes. In Finland (and Sweden and Norway), there is no formal procedure on how to design rock spaces. The design is based on a designer’s expertise, experience, views, and specific procedures. The problem here is that identical initial data could generate very different results depending on the way the initial data is interpreted and which design methods are used. The Eurocodes do not explicitly state how to design rock spaces, but they define the minimum requirements on how to design structures. The Eurocodes are divided into 10 areas. Of these ten, only a part will affect how to design rock spaces. Eurocode 0 defines the main principles concerning the whole design process. Eurocode 1 defines the loads. Eurocode 2 defines the design of concrete structures (e.g. design of reinforced concrete structures, shotcrete, and grouted rebars). Eurocode 3 defines the design of steel structures (e.g. design of non-grouted bolts, steel columns, and pillars). Eurocode 7 defines the design of geostructures. Eurocode 8 would define the design against earthquakes, but it is not required in Finland, unless otherwise stated. - Evaluation of surface roughness of rock-like joints using close range photogrammetry method
A4 Artikkeli konferenssijulkaisussa(2023-01-10) Momeni, Amir Hossein; Torkan, Masoud; Azhari, Amin; Uotinen, Lauri; Baghbanan, AlirezaThe surface roughness of the joints affects their hydraulic and mechanical behavior. There are various methods for assessing the surface roughness of discontinuities. With the development of photography technology and the release of powerful software, a photogrammetric analyzer has been introduced as a non-contact surface evaluation method. In this research, a three-dimensional model of the fracture surface was constructed using the close-range photogrammetric procedure and the joint roughness coefficient (JRC) is derived from the surface profiles. Also, the surface profiles were surveyed using the Profilometers (Barton Comb) and the JRC values were obtained using the Z2 method. Calculations were performed in two sampling steps of 0.42 and 1.27 mm. Ultimately, the results of the two methods were compared. A Sony Cybershot HX1 digital camera was used to capture the images. To process the images and build the 3D model, they were loaded in the "Agisoft metashape" software. A point cloud data was obtained with very high accuracy with a distance of 0.13 mm between points in the 3D model. The results show that the JRC values obtained from the photogrammetry method, for the upper surface of the joint, recorded 8% and 11% difference from the joint surface for sampling intervals of 1.27 and 0.42 mm, respectively. While for the bottom surface of the joint, these differences were 6.1% and 10% for sampling intervals of 1.27 and 0.42 mm, respectively. - Excavation quality and statistical evaluation of laser scanned tunnel cross-sections
School of Engineering | Master's thesis(2013) Matikainen, Antti JohannesThe reason to undertake this subject was to find out, if the true excavation quality can be explained by statistical means derived from laser scanned tunnel cross-sections. The purpose of this thesis is to introduce indicator parameters for statistical evaluation of true excavation quality and apply them for quality assurance, economical inspection of excavated tunnel and risk analysis of costs. The true excavation quality has been determined in this thesis as follows: excavated mean cross-sectional area, continuance within excavation tolerances, excavated total volume, roughness of the excavated rock surface and mean circumference of the excavated cross-sections. These quality factors are explained by statistical indicator parameters, that have been derived from laser scanned tunnel cross-sections by random variables c and r. Random variable c illustrates the length of tunnel periphery. With mean and standard error of the sample mean, the mean length of circumference and shotcrete consumption can be determined. Random variable r illustrates excavation deviations, measured perpendicular between theoretical profile and realized excavation. With mean and standard error of the sample mean, the mean cross-sectional area can be determined and if multiplied with tunnel length the total volume. Standard deviation illustrates roughness of the realized tunnel periphery and quality. With confidence intervals the continuance within tolerances can be determined. Results presented in this work are obtained from Kalliorakennus-Yhtiöt Oy's Ring Railway (Kehärata) and Western Metro (Länsimetro) projects. The results suggest, that true excavation quality can be explained by statistical means. It is reasonable to point out that none of the distribution fittings could explain the data in all cases, therefore best fit was used. The total volume was calculated with statistical means and then result compared to modelled total volume (calculated with TMS Tunnelscan program) giving 0.1 % difference between the results. When studying quantity related costs, including: loading & hauling, post removal of under breaks and shotcreting with statistical means, the results suggested post-removal of under breaks as a determining cost factor. Methods presented in this work offer tools for calculating accurately the quantity of under breaks and even controlling them. Therefore, if under breaks can be controlled and their removal on the job can be done, calculations suggest to accepting the risk of under breaks. This means lowering the mean of random variable r, and same time increasing the risk of under breaks. In other words optimizing the excavation towards smaller over break as the profit gained from the loading & hauling cost changes was significant enough for controlling under breaks and making the best profit. According to calculations, by lowering the mean with 20 cm, and same time accepting the risk of under breaks, which increased from 0 to 0.6 % of the total excavation, the profit gained from the loading & hauling cost changes was 100 000 EUR / 1 km. - Experimental and numerical characterization of hydro-mechanical properties of rock fractures : The effect of the sample size on roughness and hydraulic aperture
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2025-02) Torkan, Masoud; Uotinen, Lauri; Baghbanan, Alireza; Rinne, MikaelThis paper investigated fluid flow in low-stress conditions through rock fractures in Kuru granite measuring 25 cm × 25 cm. Physical aperture and roughness were measured using high-precision photogrammetry. Anisotropy in roughness was observed in two perpendicular directions. Physical aperture under normal stresses was measured, and fracture closure was compared with linear variable displacement transducer (LVDT) measurements, showing good agreement. Hydromechanical tests exhibited nonlinear behavior between fluid pressure gradient and flow rate, following the Forchheimer equation. Applying normal stress resulted in decreased hydraulic aperture and increased nonlinearity of fluid flow. Experimental hydromechanical tests also revealed anisotropy in perpendicular directions, aligning with fracture roughness measurements. Photogrammetric models, aided COMSOL simulations, closely matched the experimental results. Increased stress induced channeled flow and greater tortuosity. Validation of the numerical model allowed simulations on larger fractures. A 2 m × 1 m granite fracture studied scale effects, with the rough surface duplicated and shifted by 350 μm to align with initial aperture measurements of 25 cm × 25 cm samples. Fluid flow simulations assessed subsample sizes (5 cm–100 cm), showing size-dependent variations in roughness, hydraulic aperture, and non-Darcy coefficient, stabilizing beyond 30 cm. This underscores sample size's role in parameter stabilization beyond a 30 cm scale. - Feasibility of underground seasonal storage of solar heat in Finland
A4 Artikkeli konferenssijulkaisussa(2016-09-29) Janiszewski, Mateusz; Kopaly, Antoni; Honkonen, Mikko; Kukkonen, Ilmo; Uotinen, Lauri; Siren, Topias; Rinne, MikaelThe global challenge of climate change is urging for renewable energy sources to reduce greenhouse gas emissions. One of the applications of renewable energy is the solar district heating plant, which uses solar heat for space heating on a community scale. Seasonal storage of solar heat is crucial in solar district heating plants as a solution to the mismatch between the energy supply and demand. This is especially important in countries located in high latitudes with high levels of solar insolation and low heating demand in the summer, and low sun insolation and high heating demand in the winter time. This study investigates the selection of the most feasible method for seasonal storage of solar heat at high latitudes. The aim is to identify the key aspects of method selection and design of underground solar heat storage. Practices of underground thermal energy storage in Finland and other countries with similar ground conditions are reviewed. Five heat storage methods are evaluated based on their efficiency, cost, construction method, and suitability for typical ground conditions in Finland. The available methods of seasonal heat storage are compared, and the most promising method for solar heat storage in Finland is proposed. In addition, the potential provided by a combination of two or more methods is examined. The borehole storage method is proposed for storing solar heat in Finland. The combined method with a rock pit used for short-term heat storage and boreholes for long term storage is also an attractive and technically feasible option for Finnish ground conditions. - Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2015) Siren, Topias; Uotinen, Lauri; Rinne, Mikael; Shen, Baotang - Geotechnical risk management concept for intelligent deep mines
A4 Artikkeli konferenssijulkaisussa(2017) Mishra, Ritesh; Janiszewski, Mateusz; Uotinen, Lauri; Szydlowska, Martyna; Siren, Topias; Rinne, MikaelDeep mining, driven by the increasing need of the sustainable use of mineral resources, yields a chance to exploit untapped resources. Nevertheless, large depths remain challenging and complex environment, posing geotechnical risks such as stress driven damage. The violent damage mechanisms in deep mines are spalling and strainburst in their most severe forms. Real-time monitoring can not only assist in preventing a failure, but can also assist in post failure mitigations. It can help identify the possible systemic failure of adjacent areas and can therefore help is evacuating people and machinery from these areas. The long-term goal is to develop a real-time risk management concept for intelligent deep mines. The objective of this paper is to summarize the outcomes of I2Mine and DynaMine, formulate a risk concept suitable for real-time analysis and to produce a tangible measure of the risk levels. In this paper the Fault Tree – Event Tree methodology is proposed and an example is worked out using strainburst as an example risk case. The proposed methodology seems to work well and using a scenario with both property damage and ore loss, the risk expressed as financial consequences multiplied with probability drops from $128,621 to $25,766 corresponding to a -80% reduction in risk. The financial consequences together with the associated risk level can be expressed visually using a modified FN graph with financial loss on x-axis and probability on the y-axis. The developed geotechnical risk management concept suits the need of semi-automated or fully automated risk management. It would fit well in the analysis stage of the raw data and would produce a stress state change, which could be used as input in the risk management chain for intelligent deep mines. - Helsingin maanalainen yleiskaava
Insinööritieteiden korkeakoulu | Bachelor's thesis(2019-04-21) Tanskanen, Nina - High-resolution photogrammetry to measure physical aperture of two separated rock fracture surfaces
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-08) Torkan, Masoud; Janiszewski, Mateusz; Uotinen, Lauri; Baghbanan, Alireza; Rinne, MikaelPhotogrammetry, reconstructing three-dimensional (3D) models from overlapping two-dimensional (2D) photos, finds application in rock mechanics and rock engineering to extract geometrical details of reconstructed objects, for example rock fractures. Fracture properties are important for determining the mechanical stability, permeability, strength, and shear behavior of the rock mass. Photogrammetry can be used to reconstruct detailed 3D models of two separated rock fracture surfaces to characterize fracture roughness and physical aperture, which controls the fluid flow, hydromechanical and shear behavior of the rock mass. This research aimed to determine the optimal number of scale bars required to produce high-precision 3D models of a fracture surface. A workflow has been developed to define the physical aperture of a fracture using photogrammetry. Three blocks of Kuru granite (25 cm × 25 cm × 10 cm) with an artificially induced fracture, were investigated. For scaling 3D models, 321 markers were used as ground control points (GCPs) with predefined distances on each block. When the samples were well-matched in their original positions, the entire block was photographed. Coordinate data of the GCPs were extracted from the 3D model of the blocks. Each half was surveyed separately and georeferenced by GCPs and merged into the same coordinate system. Two fracture surfaces were extracted from the 3D models and the vertical distance between the two surfaces was digitally calculated as physical aperture. Accuracy assessment of the photogrammetric reconstruction showed a 20–30 μm digital control distance accuracy when compared to known distances defined between markers. To attain this accuracy, the study found that at least 200 scale bars were required. Furthermore, photogrammetry was employed to measure changes in aperture under normal stresses. The results obtained from this approach were found to be in good agreement with those obtained using linear variable displacement transducers (LVDTs), with differences ranging from 1 μm to 8 μm. - Improving teaching methods of rock mass classification parameters
A4 Artikkeli konferenssijulkaisussa(2014) Barbens, Paula Torres; Uotinen, Lauri; Toivanen, Tiina-Liisa; Edelbro, Catrin - In Situ Experiment and Numerical Model Validation of a Borehole Heat Exchanger in Shallow Hard Crystalline Rock
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-04-17) Janiszewski, Mateusz; Caballero Hernandez, Enrique; Siren, Topias; Uotinen, Lauri; Kukkonen, Ilmo; Rinne, MikaelAccurate and fast numerical modelling of the borehole heat exchanger (BHE) is required for simulation of long-term thermal energy storage in rocks using boreholes. The goal of this study was to conduct an in situ experiment to validate the proposed numerical modelling approach. In the experiment, hot water was circulated for 21 days through a single U-tube BHE installed in an underground research tunnel located at a shallow depth in crystalline rock. The results of the simulations using the proposed model were validated against the measurements. The numerical model simulated the BHE’s behaviour accurately and compared well with two other modelling approaches from the literature. The model is capable of replicating the complex geometrical arrangement of the BHE and is considered to be more appropriate for simulations of BHE systems with complex geometries. The results of the sensitivity analysis of the proposed model have shown that low thermal conductivity, high density, and high heat capacity of rock are essential for maximising the storage efficiency of a borehole thermal energy storage system. Other characteristics of BHEs, such as a high thermal conductivity of the grout, a large radius of the pipe, and a large distance between the pipes, are also preferred for maximising efficiency.