Papers by Tomas Fernandez-Steeger
IAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018—Volume 6, 2018
The most popular index for the geometrical characterization of rock discontinuities in rock mecha... more The most popular index for the geometrical characterization of rock discontinuities in rock mechanics is the Joint Roughness Coefficient (JRC). Direct shear tests or mechanical index tests such as tilt-and/or push-tests are most suitable to determine the coefficient. In engineering practice, the JRC is often set according to standard-profiles by visual matching or calculation using correlations with statistical or fractal parameters. However, this method implies that profiles can represent a surface. Naturally, different profile directions and starting points on the surface lead to different JRC values even when quantitative statistical or fractal methods are used. This study elucidates the question whether it is possible to determine a reasonable representative JRC for a surface from profiles. For that purpose, fresh mated samples were tested in push-tests from which their JRC was back-calculated. Additionally, 3D models of the surfaces were assembled as a basis for the calculation of the JRC from statistical parameters. Numerous profiles were extracted from the 3D data. The amount of more than 8000 profiles per sample offers the possibilities to define a JRC according to its variation and to assess its variability on the surface. Based on a comparison of the population of JRC values from all possible 10 cm-profiles with the mechanically determined index it can be stated, that it is not feasible to define a reliable JRC from a few profile measurements only. Moreover, there exists no connection between the experimental results of the aforementioned differing measurement approaches.
Rock Mechanics and Rock Engineering, 2021
After the publication of the type-profiles for the estimation of the joint roughness coefficient ... more After the publication of the type-profiles for the estimation of the joint roughness coefficient (JRC) a discussion evolved about how to adequately use these traces. Based on the chart numerous researchers assembled mathematical correlations with various parameters seeking objectivity in the determination of JRC. Within these works differences concerning the database and the mathematical implementations exist. Consequently, each correlation, although predominantly the same parameters are used, leads to different JRC values. In theory, for any arbitrary profile, irrespective of the particular calculation approach, the same JRC should result. This is a requisite because of the referencing of all correlations to the 10 type-profiles. However, it is shown in this study that in most cases equal or even satisfactorily similar results are not obtained. The discrepancies are vast when non-standard profiles are evaluated, in this case, more than 40,000 traces from six different rock surfaces...
Bulletin of Engineering Geology and the Environment, 2019
The roughness of rock discontinuities is an important input parameter for mechanical models of ro... more The roughness of rock discontinuities is an important input parameter for mechanical models of rock masses. To reliably calculate roughness indices, adequate representations of the surfaces are required. Various optical measuring approaches have been applied in the past. However, many studies lack information on resolution and accuracy of the resulting surface meshes. These qualities are yet important, as they explicitly affect the deduced roughness metrics. Often, the sensors do not achieve the given precision and accuracy. Moreover, no technical standards presently exist for roughness evaluation from optical measuring approaches. Therefore, previous studies are difficult to compare. To overcome these issues, this study offers a comparison of four different techniques and sensors. Here, the focus lies on laboratory use and evaluation of micro-roughness, meaning sample sizes up to 20 cm in length. Stationary structured light scanning (SLS) serves as the reference method. As results, the surface models from dense image matching are very consistent with the reference. Their calculated roughness values accord to a high degree, both for 2D and 3D indices. In addition, roughness indices deduced from models acquired with manually operated SLS show deviations from the reference yet within an acceptable range. Instead, terrestrial laser scanning turned out to be not suitable for microroughness evaluation, at least at laboratory scale. Furthermore, in this contribution, an algorithm is applied, which can retrace all possible profile measurements directly from the triangulated surfaces. That way the ambiguity of the profile-based roughness measure joint roughness coefficient (JRC) is made visible.
Applied Sciences
Aiming at the acid-etched freeze-thaw rock for geotechnical engineering in cold regions, chemical... more Aiming at the acid-etched freeze-thaw rock for geotechnical engineering in cold regions, chemical damage variables, freeze-thaw damage variables, and force damage variables were introduced to define the degree of degradation of rock materials, the law of damage evolution, the total damage variable of acid-corroded rock under the coupling action of freeze-thaw and confining pressure was deduced. The continuous damage mechanics theory was adopted to derive the damage evolution equation and constitutive model of acid-eroded rock under the coupling action of freeze-thaw and confining pressure. The theoretical derivation method was used to obtain the required model parameter expressions. Finally, the model’s rationality and accuracy were verified by the triaxial compression test data of frozen-thawed rocks. Comparing the test curve’s peak point with the peak point of the model theoretical curve, the results show that the two are in suitable agreement. The damage constitutive model can be...
Understanding and Reducing Landslide Disaster Risk, 2020
International Journal of Environmental Research and Public Health, 2020
In this work, we explored a novel approach to integrate both geo-environmental and soil geomechan... more In this work, we explored a novel approach to integrate both geo-environmental and soil geomechanical parameters in a landslide susceptibility model. A total of 179 shallow to deep landslides were identified using Google Earth images and field observations. Moreover, soil geomechanical properties of 11 representative soil samples were analyzed. The relationship between soil properties was evaluated using the Pearson correlation coefficient and geotechnical diagrams. Membership values were assigned to each soil property class, using the fuzzy membership method. The information value method allowed computing the weight value of geo-environmental factor classes. From the soil geomechanical membership values and the geo-environmental factor weights, three landslide predisposition models were produced, two separate models and one combined model. The results of the soil testing allowed classifying the soils in the study area as highly plastic clays, with high water content, swelling, and ...
Abstract: Outcrop evidence and shallow percussion drilling in coastal areas proved sedimentary ev... more Abstract: Outcrop evidence and shallow percussion drilling in coastal areas proved sedimentary evidence for paleo-tsunamis along a 50 km long segment of the Atlantic coast of southern Spain. The coast between Barbate and Tarifa yielded several depositional environments to preserve tsunamigenic layers, both on top of rocky cliffs as well as in lagoons, marshlands and along sedimentary beaches. Also, we focused on bays with river inlets, which are most probably sheltered from direct tsunami wave action. In these bays, ...
Facing the ongoing depletion of traditional energy ressources underground coal gasification (UCG)... more Facing the ongoing depletion of traditional energy ressources underground coal gasification (UCG) with combined CO2 storage is a sustainable approach with positive economic potential (KEMPKA et al. 2009). Industrial UCG applications focus the production of a high calorific ...
Materials, 2021
For thermal and loaded rock in engineering structures for some projects, triple-shear Drucker–Pra... more For thermal and loaded rock in engineering structures for some projects, triple-shear Drucker–Prager yield criteria, compaction coefficient K, damage variable correction factor δ, and thermal damage variable DT are introduced in a new thermomechanical (TM) constitutive model for the entire process. The compaction stage of rock in uniaxial compression test and the strain softening of rock caused by thermal attack are considered in this article. The damage evolution of rocks is described by a damage variable and a constitutive equation, which are in agreement with the actual thermal experimental breakage. The uniaxial compressive strength of granite subjected to a TM coupling effect can be predicted properly by this new unified constitutive model. The new TM unified constitutive model considering the compaction stage and post-failure stage is in good agreement with the test curves throughout the entire process. The coupling effect of heat and load in the total damage of rock has obvio...
Materials, 2022
Rocks are natural materials with a heterogeneous microstructure, and the heterogeneity of the mic... more Rocks are natural materials with a heterogeneous microstructure, and the heterogeneity of the microstructure plays a crucial role in the evolution of microcracks during the compression process. A numerical model of a rock with a heterogeneous structure under compression is developed by digital image processing techniques and the discrete element method. On the grain scale, the damage mechanism and microcrack characteristics of a heterogeneous Biotite granite under compression fracture are investigated. First, the process of constructing a digital image-based heterogeneous grain model is described. The microscopic characteristics of geometric heterogeneity, elastic heterogeneity, and contact heterogeneity are all considered in the numerical model. Then, the model is calibrated according to the macroscopic properties of biotite granite obtained in the laboratory, and the numerically simulated microcrack cracking processes and damage modes are obtained with a high degree of agreement c...
Materials, 2021
In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperat... more In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shea...
In view of the global fossil fuel reserves Underground Coal Gasification (UCG) bears the potentia... more In view of the global fossil fuel reserves Underground Coal Gasification (UCG) bears the potential to guarantee long-term energy supply for the future markets by conversion of otherwise non-mineable coal seams. Besides the production of medium to high calorific syngas for various industrial applications (e.g. electricity generation in the frame of the Integrated Gasification Combined Cycle IGCC Concept; or Coal-To-LiquidCTL procedures like Fischer-Tropsch synthesis), UCG provides an option for effective greenhouse gas reduction through CO2 storage in converted coal seams. With regard to long-term economic and environmental sustainability however minimization of tar related organic pollutants in the process gases is a key factor, as past projects were often confronted with organic groundwater pollution issues of BTEX, PAHs and heterocyclic compounds due to condensation of tar-loaded gas losses. With focus on potential tar reducing strategies the present CO2SINUS study thus investigat...
Journal of Marine Science and Engineering, 2021
High temperatures can enhance the chloride diffusion coefficient and this poses a threat to reinf... more High temperatures can enhance the chloride diffusion coefficient and this poses a threat to reinforced concrete (RC) piles. This study intends to propose predictive models that can evaluate the service life and lateral bearing behaviour of reinforced concrete piles subjected to marine environments and varying temperatures. The models show that temperature can accelerate the diffusion rate of chloride and increase the concentration of free chloride in concrete. The distribution law of chloride concentration is obtained by considering the ageing effect as well. Deterministic and probabilistic models are proposed to assess the time to corrosion initiation and propagation. The stiffness degradation coefficient is introduced in the analysis of the lateral bearing capacity of RC piles. The results show that high temperature can decrease the service life of piles and the life spans obtained from deterministic and probabilistic methods are similar; however, the predictions of the latter are...
Materials, 2021
This study compared the effects of the sulfate dry–wet cycle on the properties of ordinary concre... more This study compared the effects of the sulfate dry–wet cycle on the properties of ordinary concrete and nano-TiO2-modified concrete, including the mass loss rate, ultrasonic wave velocity, compressive strength, and XRD characteristics. In addition, a series of compression simulations carried out using the PFC2D software are also presented for comparison. The results show the following: (1) with an increase in dry–wet cycles, the damage to the concrete gradually increased, and adding nano-TiO2 into ordinary concrete can improve the material’s sulfate resistance; (2) after 50 sulfate dry–wet cycles, the mass loss rate of ordinary concrete was –3.744%, while that of nano-TiO2-modified concrete was −1.363%; (3) the compressive strength of ordinary concrete was reduced from 41.53 to 25.12 MPa (a reduction of 39.51%), but the compressive strength of nano-TiO2-modified concrete was reduced from 49.91 to 32.12 MPa (a reduction of 35.64%); (4) after a sulfate dry–wet cycle, the nano-TiO2-mod...
Environmental pollution (Barking, Essex : 1987), 2018
Packed column experiments were conducted to investigate the transport and blocking behavior of su... more Packed column experiments were conducted to investigate the transport and blocking behavior of surfactant- and polymer-stabilized engineered silver nanoparticles (Ag-ENPs) in saturated natural aquifer media with varying content of material < 0.063 mm in diameter (silt and clay fraction), background solution chemistry, and flow velocity. Breakthrough curves for Ag-ENPs exhibited blocking behavior that frequently produced a delay in arrival time in comparison to a conservative tracer that was dependent on the physicochemical conditions, and then a rapid increase in the effluent concentration of Ag-ENPs. This breakthrough behavior was accurately described using one or two irreversible retention sites that accounted for Langmuirian blocking on one site. Simulated values for the total retention rate coefficient and the maximum solid phase concentration of Ag-ENPs increased with increasing solution ionic strength, cation valence, clay and silt content, decreasing flow velocity, and for...
Sensors, 2016
The fast development of wireless sensor networks and MEMS make it possible to set up today real-t... more The fast development of wireless sensor networks and MEMS make it possible to set up today real-time wireless geotechnical monitoring. To handle interferences and noises from the output data, Kalman filter can be selected as a method to achieve a more realistic estimate of the observations. In this paper, a one-day wireless measurement using accelerometers and inclinometers was deployed on top of a tunnel section under construction in order to monitor ground subsidence. The normal vectors of the sensors were firstly obtained with the help of rotation matrices, and then be projected to the plane of longitudinal section, by which the dip angles over time would be obtained via a trigonometric function. Finally, a centralized Kalman filter was applied to estimate the tilt angles of the sensor nodes based on the data from the embedded accelerometer and the inclinometer. Comparing the results from two sensor nodes deployed away and on the track respectively, the passing of the tunnel boring machine can be identified from unusual performances. Using this method, the ground settlement due to excavation can be measured and a real-time monitoring of ground subsidence can be realized.
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Papers by Tomas Fernandez-Steeger