Browsing by Author "Torkan, Masoud"
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Item Characterization of hydro-mechanical properties of rock fractures using steady state flow tests(2020-11-13) Uotinen, Lauri; Torkan, Masoud; Janiszewski, Mateusz; Baghbanan, Alireza; Nieminen, Ville; Rinne, Mikael; Department of Civil Engineering; Li, C.C.; Odegaard, H.; Hoien, A.H.; Macias, J.; Mineral Based Materials and Mechanics; Department of Civil EngineeringCharacterization 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.Item Characterization of hydromechanical properties of a rock fracture using numerical modelling(2022-06-13) Nieminen, Ville; Uotinen, Lauri; Torkan, Masoud; Insinööritieteiden korkeakoulu; Rinne, MikaelThe 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.Item Deep learning methods for underground deformation time-series prediction(2023-04-12) Ma, Enlin; Janiszewski, Mateusz; Torkan, Masoud; Department of Civil Engineering; Anagnostou, Georgios; Benardos, Andreas; Marinos, Vassilis P.; Mineral Based Materials and MechanicsPrediction is a vague concept that is why we need to conceptualize it specifically for underground deformation time-series data. For this impending issue, this paper employs an advanced deep learning model Bi-LSTM-AM to address it. The results show its applicability for practical engineering. The proposed model is compared with other basic deep learning models including long short-term memory (LSTM), Bi-LSTM, gated recurrent units (GRU), and temporal convolutional networks (TCN). These models cover the most common three forms of deep learning for time-series prediction: recurrent neural networks (RNN) and convolutional neural networks (CNN). This research is supposed to benefit the underground deformation time-series prediction.Item Effect of anisotropy of fracture surface on fluid flow(Institute of Physics Publishing, 2023-01-10) Torkan, Masoud; Hosseini Khorasgani, AMIR; Uotinen, Lauri; Baghbanan, Alireza; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and Mechanics; Isfahan University of TechnologyCharacterization 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.Item Empirical mode decomposition approach to simplify the fracture roughness for numerical models(Institute of Physics Publishing, 2023-01-10) Ma, Enlin; Rinne, Mikael; Torkan, Masoud; Janiszewski, Mateusz; Department of Civil Engineering; Mineral Based Materials and MechanicsThe shear strength of natural, unfilled rock fractures is influenced by surface roughness. The surface curve of a fracture can be viewed as a waveform graph, and in general, it is of the characteristic that high-frequency represents the low amplitude (local variation) and low-frequency represents the high amplitude (general trend). In this work, the signal processing method, Empirical Mode Decomposition (EMD) was employed to decompose the original fracture surface scanned by photogrammetry to several frequency-dependent curves. Low-frequency curves were selected and composed as the element geometry while high-frequency curves were ignored and replaced by parameters related to the roughness in each surface element in Abaqus. The process of push-shear test is simulated using the simplified fracture curve, showing the geometry simplification by EMD can help model the shear failure of rock fractures.Item Evaluation of surface roughness of rock-like joints using close range photogrammetry method(Institute of Physics Publishing, 2023-01-10) Momeni, Amir Hossein; Torkan, Masoud; Azhari, Amin; Uotinen, Lauri; Baghbanan, Alireza; Department of Civil Engineering; Mineral Based Materials and Mechanics; Isfahan University of TechnologyThe 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.Item High-resolution photogrammetry to measure physical aperture of two separated rock fracture surfaces(Chinese Academy of Sciences, 2024-08) Torkan, Masoud; Janiszewski, Mateusz; Uotinen, Lauri; Baghbanan, Alireza; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and MechanicsPhotogrammetry, 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.Item Influence of contact shape and distribution on fluid flow through a fracture(2023-10-09) Torkan, Masoud; Hosseini Khorasgani, Amir; Uotinen, Lauri; Baghbanan, Alireza; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and Mechanics; Isfahan University of TechnologyFluid flow through a rough fracture can be affected by several geometrical parameters such as aperture, roughness, and contact area. Of these, eddy flow can occur around contact areas and change streamline patterns. Fluid flow behavior through a 10 cm × 10 cm square fracture was numerically analyzed with different contact shapes and distributions. The basic shape of the contact area is assumed to be square with a 1 cm2 area. The squares as contact areas through fractures were distorted with different ratios, rotations, and relocations. The total contact area and the physical aperture in all models were 25 cm2 and 1 mm, respectively. The flow rates through the fractures were computed with 5 different water pressures. The Forchheimer equation was adopted to analyze results. The calculations highlight the importance of the parameter β in the Forchheimer equation, which reflects the impact of fracture surface geometry on fluid flow.Item Method to obtain 3D point clouds of tunnels using smartphone LiDAR and comparison to photogrammetry(Institute of Physics Publishing, 2023-01-10) Torkan, Masoud; Janiszewski, Mateusz; Uotinen, Lauri; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and MechanicsRemote sensing methods, for example, photogrammetry and laser scanning can be employed to scan rock masses by digitizing underground spaces or slopes. To reconstruct a 3D model by photogrammetry, plenty of photos should be captured. This process is time-consuming and can be dangerous when the rock mass is unstable. Therefore, rapid capturing methods are needed to reduce the acquisition time. This can be achieved with LiDAR scanners that capture a 3D point cloud with a high-speed pulsed laser beam. However, the cost of laser scanners is high, which limits their usability. Apple’s iPhone 12 Pro Max smartphone is equipped with a LiDAR sensor and is much cheaper than conventional laser scanners. Several mobile applications for 3D models using the smartphone Lidar have been developed, making the scanning process easy. Therefore, smartphones can be used for rapid scanning of unstable surfaces of tunnels and slopes. In this study, 3D point clouds (3DPC) of a tunnel wall of the Underground Research Laboratory of Aalto University (URLA) are obtained by a high-resolution digital camera and smartphone LiDAR. The models are analyzed and compared. The results show the quality of the smartphone LiDAR sensor is adequate for generating 3D models of underground spaces.Item Numerical study of scale effect on fluid flow through a rough fracture(2024-09-17) Torkan, Masoud; Janiszewski, Mateusz; Uotinen, Lauri; Rinne, Mikael; Baghbanan, Alireza; Department of Civil Engineering; Tomás, Roberto; Cano, Miguel; Riquelme, Adrián; Pastor, José Luis; Benavente, David; Ordóñez, Salvador; Mineral Based Materials and MechanicsScale effect on fluid flow and rock joint roughness remains uncertain. Using photogrammetry, the topography of a fracture surface was replicated. A 3D model was reconstructed for a 2 m × 1 m granite sample, extracting a 1 m × 1 m subsample. This model was duplicated and shifted a 350-micrometer along the Z-axis. To study scale effect, different samplesizes ranging from 5 cm × 5 cm to 100 cm × 100 cm were used for roughness analysis and fluid flow simulations in COMSOL Multiphysics. The pressure gradients ranged from 20 to 100 kPa/m, with intervals of 20 kPa/m. As the sample sizes increased, the roughness approached a Joint Roughness Coefficient (JRC) of 10, with no significant change observed beyond approximately30 cm in sample size. Fluid flow simulations showed a nonlinear relationship between pressure gradients and flow rates, following For chheimer equation. Notably, beyond 30 cm sample size, the hydraulic aperture and non-Darcy coefficient reached a relatively stable state.Item Photogrammetric Method to Determine Physical Aperture and Roughness of a Rock Fracture(Multidisciplinary Digital Publishing Institute (MDPI), 2022-06-01) Torkan, Masoud; Janiszewski, Mateusz; Uotinen, Lauri; Baghbanan, Alireza; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and MechanicsRock discontinuities play an important role in the behavior of rock masses and have a high impact on their mechanical and hydrological properties, such as strength and permeability. The surfaces roughness and physical aperture of rock joints are vital characteristics in joint shear strength and fluid flow properties. This study presents a method to digitally measure the physical aperture of a rock fracture digitized using photogrammetry. A 50 cm × 50 cm rock sample of Kuru grey granite with a thoroughgoing fracture was digitized. The data was collected using a high-resolution digital camera and four low-cost cameras. The aperture and surface roughness were measured, and the influence of the camera type and 3D model rasterization on the measurement results was quantified. The results showed that low-cost cameras and smartphones can be used for generating 3D models for accurate measurement of physical aperture and roughness of rock fractures. However, the selection of appropriate rasterization grid interval plays a key role in accurate estimations. For measuring the physical aperture from the photogrammetric 3D models, reducing rasterization grid interval results in less scattered measurement results and a small rasterization grid interval of 0.1 mm is recommended. For roughness measurements, increasing the grid interval results in smaller measurement errors, and therefore a larger rasterization grid interval of 0.5 mm is recommended for high-resolution smartphones and 1 mm for other low-cost cameras.Item Photogrammetric prediction of rock fracture properties and validation with metric shear tests(MDPI AG, 2021-07) Uotinen, Lauri; Torkan, Masoud; Baghbanan, Alireza; Hernández, Enrique Caballero; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and Mechanics; Stress Measurement Company Oy; Isfahan University of TechnologyAn accurate understanding of jointed rock mass behavior is important in many applications ranging from deep geological disposal of nuclear waste, to deep mining, and to urban geoengineering projects. The roughness of rock fractures and the matching of the fracture surfaces are the key contributors to the shear strength of rock fractures. In this research, push shear tests with three normal stress levels of 3.6, 6.0, and 8.5 kPa were conducted on two granite samples with artificially induced well-matching tensile fractures with sizes of 500 mm x 250 mm and 1000 mm x 500 mm. The large sample reached on average a -60% weaker peak shear stress than the medium-sized sample, and a strong negative scale effect was observed in the peak shear strength. The roughness of the surfaces was measured using a profilometer and photogrammetry. The scale-corrected profilometer-based method (joint roughness coefficient, JRC) underestimates the peak friction angle for the medium-sized slabs by -27% for the medium sample and -9% for the large sample. The photogrammetry-based (Z'(2)) method produces an estimate with -7% (medium) and + 12% (large) errors. The photogrammetry-based Z'(2) is an objective method that consistently produces usable estimates for the JRC and peak friction angle.Item Photogrammetry based characterization of hydro-mechanical properties of a rock fracture(Institute of Physics Publishing, 2021-09-06) Torkan, Masoud; Uotinen, Lauri; Nieminen, Ville; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and Mechanics; Department of Civil EngineeringHydro-mechanical properties of a single 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. In this study, photogrammetry with numerical modeling and laboratory measurements were used to investigate the influences of roughness, normal stress, aperture, water pressure, and different flow boundary conditions on fluid flow in an artificial granite fracture. A Finnish Kuru grey granite block was mechanically split, and a 250 mm × 250 mm × 100 mm slab pair sample with a tensile crack in the middle was extracted. A photogrammetry-based method was used to reconstruct a 3D model of the fracture geometry. The resulting model was numerically simulated with COMSOL using the Navier-Stokes equations. Fluid flow experiments were computed with the Forchheimer equation. Comparison between the numerical modeling results and the analytical solution confirms that the 3D roughness geometry has a crucial role in defining the transmissivity, especially for nonlinear flow. On the other hand, normal stress increases fracture closure and increases contact areas, decreasing the hydraulic aperture and changing the flow paths. The presented method can be used in the contactless estimation of fluid flow properties of rock joints.Item Photogrammetry for characterizing rock fracture roughness, physical aperture, and hydromechanical properties(Aalto University, 2024) Torkan, Masoud; Uotinen, Lauri, Staff Scientist, Aalto University, Department of Civil Engineering, Finland; Baghbanan, Alireza, Prof., Isfahan University of Technology, Iran; Rakennustekniikan laitos; Department of Civil Engineering; Mineral-based materials and mechanics; Insinööritieteiden korkeakoulu; School of Engineering; Rinne, Mikael, Prof., Aalto University, Department of Civil Engineering, FinlandUnderstanding 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.Item Rapid photogrammetric method for rock mass characterization in underground excavations(2023-05-24) Janiszewski, Mateusz; Prittinen, Markus; Uotinen, Lauri; Torkan, Masoud; Rinne, Mikael; Department of Civil Engineering; Sigursteinsson, Haraldur; Ingimarsson, Atli Karl; Mineral Based Materials and MechanicsUnderground excavation mapping and rock mass characterization are critical for ensuring the safety, proper design, and maintenance of underground infrastructure. Traditional mapping methods typically involve manual inspections and measurements that require contact with the tunnel surface, which can be time-consuming, expensive, and pose safety risks to personnel. In recent years, photogrammetry has emerged as an alternative method for generating high-resolution digital 3D models of tunnels, enabling rapid and remote rock mass measurements. In this paper, we present a method for tunnel and stope scanning using photogrammetry and remote rock mass mapping from 3D models. Two case studies are presented to demonstrate the effectiveness of the proposed method. In the first case, a multi-camera rig consisting of action cameras is used for videobased photogrammetric reconstruction of underground tunnel excavation. The rock mass data is then extracted from the model and visualized. In the second case, a drone workflow is used to map out rock mass features in stopes. Images taken with the drone are processed to create a 3D point cloud of the stope, which is then used to extract discontinuities from the rock mass surfaces. The orientation and spacing of these discontinuities are measured and visualized on top of the photorealistic 3D mesh of the stope for inspection. The proposed method significantly reduces the data capture process. The advancements in camera and software technologies have made it possible to acquire rapid and accurate 3D models of underground excavations that can be used as a source of rock mass data. Our results demonstrate that photogrammetry is a robust approach for underground rock mass inspection and remote mapping.Item Rapid Photogrammetry with a 360-Degree Camera for Tunnel Mapping(MDPI AG, 2022-10-31) Janiszewski, Mateusz; Torkan, Masoud; Uotinen, Lauri; Rinne, Mikael; Department of Civil Engineering; Mineral Based Materials and MechanicsStructure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry is a viable method to digitize underground spaces for inspection, documentation, or remote mapping. However, the conventional image acquisition process can be laborious and time-consuming. Previous studies confirmed that the acquisition time can be reduced when using a 360-degree camera to capture the images. This paper demonstrates a method for rapid photogrammetric reconstruction of tunnels using a 360-degree camera. The method is demonstrated in a field test executed in a tunnel section of the Underground Research Laboratory of Aalto University in Espoo, Finland. A 10 m-long tunnel section with exposed rock was photographed using the 360-degree camera from 27 locations and a 3D model was reconstructed using SfM-MVS photogrammetry. The resulting model was then compared with a reference laser scan and a more conventional digital single-lens reflex (DSLR) camera-based model. Image acquisition with a 360-degree camera was 3× faster than with a conventional DSLR camera and the workflow was easier and less prone to errors. The 360-degree camera-based model achieved a 0.0046 m distance accuracy error compared to the reference laser scan. In addition, the orientation of discontinuities was measured remotely from the 3D model and the digitally obtained values matched the manual compass measurements of the sub-vertical fracture sets, with an average error of 2–5°.Item Rapid tunnel scanning using a 360-degree camera and SfM photogrammetry(Institute of Physics Publishing, 2023-01-10) Janiszewski, Mateusz; Prittinen, Markus; Torkan, Masoud; Uotinen, Lauri; Department of Civil Engineering; Mineral Based Materials and Mechanics; Department of Civil EngineeringPhotogrammetric scanning can be employed for the digitization of underground spaces, for example for remote mapping, visualization, or training purposes. However, such a technique requires capturing many photos, which can be laborious and time-consuming. Previous research has demonstrated that the acquisition time can be reduced by capturing the data with multiple lenses or devices simultaneously. Therefore, this paper demonstrates a method for rapid scanning of hard rock tunnels using Structure-from-Motion (SfM) photogrammetry and a 360-degree camera. The test was performed in the Underground Research Laboratory of Aalto University (URLA). The tunnel is located in granitic rocks at a depth of 20 m below the Otaniemi campus in Espoo, Finland. A 10 m long and 3.5 m high tunnel section with exposed rock was selected for this study. Photos were captured using the 360-degree camera from 27 locations and 3D models were reconstructed using SfM photogrammetry. The accuracy, speed, and resolution of the 3D models were measured and compared with models scanned with a digital single-lens reflex (DSLR) camera. The results show that the data capture process with a 360-degree camera is 6x faster compared to a conventional camera. In addition, the orientation of discontinuities was measured remotely from the 3D model and the digitally obtained values matched the manual compass measurements. Even though the 360-degree camera-based 3D model's quality was visually inferior to the DSLR model, the point cloud had sufficient accuracy and resolution for semi-automatic discontinuity measurements. The quality of the models can be improved by combining 360-degree and DSLR photos which result in a point cloud with 3x higher resolution and 2x higher accuracy. The results demonstrated that 360-degree cameras can be used to rapidly digitize underground tunnels.
