The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
- Data Science & Engineering Analytics
The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
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ABSTRACT Rock burst is a violent rock failure process posing a significant threat to human safety in mining and tunnelling construction. This makes it of upmost importance to learn more about this hazard and develop a method to predict it. In the presented paper, a system to record acoustic emission during uniaxial loading and how to evaluate the recorded data in regard to rock burst is explained. The testing equipment and testing procedure are described in great detail and the results are evaluated and classified. Uniaxial compression tests were carried out for rock samples and artificial samples, during those tests acoustic emissions were recorded and evaluated through sophisticated software. By combining the different methods of determining certain crack class indicators, it was possible to classify the results in so-called deformation phases. From the certain properties of those deformation phases conclusion were drawn on the probability of rock burst occurring. The number of acoustic hits and the energy release recorded during the acoustic emission test are evaluated in regard to rock burst as well. 1. INTRODUCTION Modern tunnelling and mining projects are exploring deeper areas than ever before, therefore it is necessary to learn more about the hazard of rock burst. This failure is extremely dangerous, as it can occur very suddenly and is capable of releasing high amounts of energy. This leads to a high risk to the life of workers and the used equipment, consequently it is very important to understand rock burst fully and find methods to predict it. For example, a rock burst in the Sunjiawan Coalmine in 2005 caused 214 deaths and left 30 people injured. Six years later, on November the 3rd 2011, a rock burst due to a fault in the Qianqiu Coalmine caused the death of 10 people and left 75 people trapped underground. (Li et al. 2014)
Gottsbacher, L. (Institute of Rock Mechanics and Tunneling, Graz University of Technology) | Klammer, A. (Institute of Rock Mechanics and Tunneling, Graz University of Technology) | Schubert, W. (Institute of Rock Mechanics and Tunneling, Graz University of Technology) | Marschallinger, R. (University of Salzburg) | Hofmann, P. (University of Salzburg) | Zobl, F. (University of Salzburg) | Ketcham, R. (Jackson School of Geosciences, University of Texas at Austin) | Edey, D. (Jackson School of Geosciences, University of Texas at Austin)
Abstract The failure hazard rock burst is very dangerous as it can occur very suddenly and violently. Due to the fact, that tunnel and mining projects are in deeper areas than ever, the importance of investigating this hazard is more relevant than ever. The Graz University of Technology and the University of Salzburg are investigating rock burst with different laboratory tests to learn more about it. The test methods are uniaxial compression tests, acoustic emission tests, micro computed tomography and object based image analysis of thin sections of rock samples. To simulate the high stress state of rock that is prone to rock burst, stress close to the failure stress is applied on the rock samples. Simultaneously, the acoustic emissions in the sample are measured to investigate acoustic events in the sample, which are generated by micro cracks. After that, μCTscans of the loaded samples are performed to create 3D images of the micro-cracks in the rock sample. Subsequently thin sections are made from the samples for an object based image analysis. To evaluate the results various methods are used, from newly developed MATLAB codes to pattern recognition software to analyze the data. The findings allow a better understanding of the underlying mechanism of rock burst and indicate the usefulness of various testing methods to investigate the hazard. 1 Introduction Modern tunneling and mining projects are exploring deeper areas than ever before, because of this it is necessary to learn more about the hazard of rock burst. This failure is extremely dangerous, as it can occur very suddenly and is capable of releasing high amounts of energy. This is a high risk for the life of workers and the used equipment, it is very important to understand rock burst fully and find methods to predict it. As part of a research project financed by the Austrian Research Promotion Agency (FFG) the Graz University of Technology and the University of Salzburg are investigating this hazard, with the University of Salzburg focusing on the geological aspects and the Graz University of Technology on the rock mechanical aspects.
When shield tunnel boring machines (TBMs) are used, the outer lining is constructed using pre-fabricated lining segments. In hard rock conditions the required gap between the lining and excavation boundary is backfilled with pea gravel. In this case, designers consider only the backfilled material relevant for the bedding effectiveness. Thus, a sound knowledge of the deformation properties of pea gravel is essential. At present these parameters are determined in non-standardized laboratory or on-site tests. Moreover, no validation of the used parameters is performed in situ. Based on the static load plate test a prototype for the in-situ determination of the deformation properties of pea gravel was designed and manufactured at the Institute of Rock Mechanics and Tunnelling at the Graz University of Technology. The testing device allows for a maximum test stress of 1.50 MPa under the load plate. This research focuses on the development process and the detailed design of the manufactured prototype. The recorded measurement data (force and displacement) allows to calculate the stiffness properties (i.e. bedding modulus, static deformation modulus, stiffness modulus) of the material tested. Radial openings in the lining segments serve as measurement locations. Mounting of the testing device in the tunnel is possible without any alterations in the lining elements or the lining design. Determination of the stiffness parameters is shown using the test data of one exemplary test series. INTRODUCTION In mechanized driven tunnels, using single or double shield TBMs (S-TBM/DS-TBM), prefabricated lining segments are used as outer lining. Thereby, the load-carrying rings are assembled within the protection of the shield. Due to the construction method, a gap between lining and excavation boundary (i.e. rock mass) exists after a newly installed ring leaves the shield. This so-called ‘annular gap’ needs to be backfilled using a suitable material in order to allow for load transfer. Ideally, the occurring rock loads are evenly distributed. In hard rock conditions, a fine grained and closely graded gravel, termed as pea gravel, is pneumatically injected through radial openings in the lining. The invert area is backfilled using a pea gravel-mortar-mixture.
Abstract Rock scours after a spillway of a dam can lead to major problems regarding the stability of the structure. The pressures on the floor are dependent on the height of the dam and the water cushion in the pool. They can reduce the effective stress between the rock blocks significantly and hence the friction resistance. This mechanism leads to proper instabilities in the foundation and the structure. A model test at the Institute of Hydraulic Engineering and Water Resources Management should expose the pressures on the bottom floor. The results of the test case show a significant decrease of these pressures due to the evaluated configuration of the model. Further investigations, in a more detailed model, with cracks in the rock for different quantities of the jet velocity and the depth in the stilling basin are planned as well as numerical simulations by means of fluid-foundation interaction for comparison reasons. 1 Introduction Rock scour next to the spillway of dams can influence the stability of the structure significantly. Dynamic pressures on the rock foundation due to the impact of high velocity jets lead to abrasion and hence instability. The increasing accuracy of methods for determining the hydrological data lead to assessment criteria that are more exact (Achterberg et al. 1998). This fact concerns mainly older structures, where additional measurements will therefore be necessary. In addition, newer structures are also affected by rock scour, because the knowledge about theses dynamic pressures is still very limited. Although, more and more papers have been published in this field recently (e.g. Bollaert 2002). However, the foundation at the impact zone will crack eventually and the dynamic pressures induced will propagate through the cracks and possible fault zones. These water pressures can reduce the effective stress between the rock blocks significantly and hence the friction resistance. A model test for a survey at the Institute for Hydraulic Engineering and Water Resources Management at Graz University of Technology led to the idea to investigate this problem more elaborated. Therefore, a more detailed model with a wedge and joints is planned to be evaluated along with different discharges and water depths (water cushion) as well as numerical simulations for comparison reasons.
Abstract Currently there is no uniform and consistent documentation of unexpected standstills available, which can be applied during the excavation of tunnels with tunnel boring machines (TBM). Such a documentation and evaluation would be helpful for the estimation of risks, costs and the advance rate for future tunnels excavated with a TBM. An approach for a documentation of unexpected standstills of hard rock tunnel boring machines, such as open gripper TBM, single shield TBM and double shield TBM, was developed at Graz University of Technology. This paper shows the results as well as the benefits of a detailed and continuous event documentation during tunnel excavation. The new approach can be taken as a basis for future documentation of unexpected standstills in TBM tunnelling. 1 Introduction Nowadays large infrastructure projects with long tunnels, such as the Semmering base tunnel or the Brenner base tunnel in Austria, are in planning state or under construction. The length of such tunnels as well as the advantage of a fast excavation in favourable rock mass conditions make the use of a tunnel boring machine more and more important.. As for conventionally excavated tunnels, an excavation with a tunnel boring machine demands a detailed estimation of costs, risks, advance rates and construction time in advance, too. Boundary conditions have to be identified as exactly as possible in order to choose the most suitable machine type. Therefore, a detailed and continuous documentation of unexpected standstills of the tunnel boring machine applied during excavation would provide a proper basis for the design of future TBM driven tunnels. The documentation needs to be done contemporary. Reasons for standstills must be evaluated and interpreted. In addition to the documentation of the standstill reason, implemented measures to resume excavation again, have to be documented. Figure 1 shows a flow chart of such a documentation and the use of gained experience for future projects.
Abstract This paper discusses the design and construction of the initial tunnel section of the OeBB Koralmtunnel lot KAT3 near the western portal. Based on the experience obtained during the advance of the exploration tunnel nearly nine years earlier very challenging tunneling conditions were expected due to multiple fault zones combined with shallow overburden. During the advance of the exploration tunnel large surface settlements developed rapidly, leading to a situation where the overall stability of the structure was considered as compromised. A thorough analysis of the displacement data from the tunnel and ground surface together with the geological documentation provided a comprehensive understanding of the critical situation and allowed implementing mitigation measures and the tunnel excavation to be continued without major problems. The findings and experience from the exploration tunnel provided the basis for the design for the following tunnel advances. The paper focuses on the lessons learned from the exploration tunnel and their influence on the design. The applied monitoring program is discussed in detail, emphasizing the analysis of the system behavior in the light of the encountered geological conditions. 1 Introduction The 32.9 km long Koralm tunnel connects the cities Graz and Klagenfurt and is the main part of the new Baltic Adriatic high capacity railway. The tunnel alignment crosses Neogene sediments on both sides of the Koralm massif, which is composed of various gneiss subtypes, schists and (to a lesser degree) silicate marbles. The overburden varies from 5 m at the portal area to approximately 1200 m in the central section of the advance. Due to the length and general strategic importance of the project, an extensive geological and geotechnical exploration program was conducted – including the construction of two exploratory tunnels on both sides of the massif. On the Carinthian side (western portal), the exploratory tunnel was constructed as the top heading of the final southern tube, and passed through various faulted Neogene sediments before advancing through the main Lavanttal fault zone into the gneisses of the central massif. The exploratory tunnel Mitterpichling advanced westwards from the intermediate access towards the western portal and over a 300 m section encountered severely faulted rock mass conditions with low overburden. While passing beneath a major regional road both the tunnel and surface deformations increased considerably leading to a critical situation, which due to the rapid on-site analyses of the system behavior and subsequent quick introduction of countermeasures was stabilized without incidence (Moritz et al. 2006). Nevertheless, with measured surface settlements up to 220 mm and visible cracks on the surface the zone was deemed highly critical for the completion of the final tunnel drives.
Abstract This paper presents the application of a novel constitutive model for shotcrete in a tunnelling project. The shotcrete model is based on elastoplastic strain hardening/softening plasticity and can account for time dependent strength and stiffness, creep and shrinkage. The tensile strength and fracture energy are calibrated with results from bending tests on steel fibre reinforced concrete. The tunnelling example is a NATM tunnel with temporary side drift walls, which are subjected to significant bending and are critical to the safety of the tunnel during excavation. Different approaches to model the shotcrete lining are employed and the impact of the features of the shotcrete model is discussed. Introduction As shotcrete linings are loaded at a very early age, the influence of time dependent material properties on the deformation behaviour and bearing capacity is much more significant than in regular concrete structures. Notably, shotcrete strength and stiffness increase rapidly within the first few hours after application, while ductility and creep effects decrease. Shotcrete also exhibits plastic material behaviour before reaching the maximum strength, and material strength reduces after the maximum strength has been mobilised. The current engineering approach to model shotcrete linings in numerical simulations assumes a linear elastic material with a stepwise increase of the (artificially low)Young's modulus in subsequent excavation stages. While realistic lining deformations may be obtained with this method, lining stresses are usually too high, in particular if the lining is subjected to significant bending. Furthermore, capturing the redistribution of forces after cracking of the lining requires the manual introduction of plastic hinges, which is a difficult and time-consuming task in more complex numerical models. Alternatively, the non-linearity of the material behaviour can be taken into account directly by using an appropriate constitutive model for the shotcrete in the numerical simulation. Such a material model has been developed at TU Graz in cooperation with Plaxis b.v. and ILF Consulting Engineers. The calibration of this model and its application in tunnelling simulations is demonstrated in this paper.
Abstract The expansion of the current European infrastructure demands the construction of several major and challenging tunnelling projects, such as Gotthard and Ceneri in Switzerland, Lyon-Turino in Italy/France and Koralm, Brenner and Semmering tunnels in Austria. Due to their length and alignment as "base tunnels", they encounter various geological formations and tectonical faults under high overburden. This leads to a frequent combination of weak ground and high primary stresses, causing high displacement magnitudes. Loads unsustainable by a stiff support, support damage and costly re-profiling are a usual consequence. Over the past decades, various approaches for creation of ductile tunnel linings have been proposed and sometimes successfully applied. While most systems fulfilled their role of "deforming element", the imperatives of costs and operational feasibility, as well as their general interaction with shotcrete and deforming ground are seldom discussed. This publication concentrates on a new yielding element type developed at the Institute for Rock Mechanics and Tunnelling, Graz University of Technology. It is based on the venerable Lining Stress Controllers. Their drawbacks such as relatively large amount of machined parts (load bearing pipe, inner and outer leading pipes) have been addressed and removed, while the already favourable load-displacement relationship has been considerably improved. The new element's interaction with shotcrete lining and its overall influence on the system behaviour is discussed in detail. 1 Introduction Due to the general requirements of high capacity traffic infrastructure, long and deep tunnels in alpine regions are unavoidable. The expansion of the current European infrastructure results in construction of numerous long tunnels, especially in the middle Europe: Lyon-Turin in Italy/France, Gotthard and Ceneri in Switzerland, and Semmering, Koralm and Brenner Tunnel in Austria. This can lead to a combination of weak ground in extended tectonic faults and high overburden. In case the conventional approach of obtaining displacement compatibility by increasing the support stiffness and load bearing capacity is followed, extreme support requirements and an unsafe and uneconomical design are the result. The application of stiff support concepts has proven itself unsafe and uneconomical due to:
Abstract: This paper introduces the use of 3D Light Detection and Ranging (LiDAR) for measuring rock mass discontinuities and tunnel excavation profile details, based on a case study of the Raabstollen tunnel in eastern Styria, Austria. The basic survey procedure involves: creating a comprehensive 3D LiDAR point cloud model (PCM); forming detailed triangulated surface model (TSM) from the PCM; and mapping of fracture network characteristics (discontinuity orientation, size, intersection and termination) using advanced digital processing techniques. The result is an actual discrete fracture network being mapped directly on the excavation surface, which facilitates evaluation of over- and underbreaks and provides a permanent digital archive for further analysis and evaluation. This case study shows that LiDAR surveys can provide high quality data for both geological documentation (especially rock mass structure) and excavation geometry. 1 INTRODUCTION Geo-spatial data representations of rock mass conditions encountered during tunnel construction are becoming increasingly common, as they have been found to facilitate technical and economical project success. However, the immediate installation of ground support at the working face gives the engineering geologist/ tunnel engineer limited opportunity to inspect and document the ground conditions, and rock mass conditions exposed in the crown area are often not directly accessible for close inspection and measurements. The increased application of remote characterization methods has greatly enhanced tunneling documentation. Over the last 10 years, digital photogrammetry soft-ware has evolved into useful mapping tools for underground excavation (e.g. Gaich et al 1998, 2005, Birch 2008). More recently, terrestrial Light Detection and Ranging (LiDAR), also referred to as 3D terrestrial laser scanning (TLS), has seen increased application in rock mass characterization studies (e.g., Kemeny & Turner 2008, Ferre-ro et al 2009, Lato 2010, Sturzenegger 2010, Liu & Kieffer 2011).
Wieser, P. (Institute for Rock Mechanics and Tunnelling Graz University of Technology) | Pilgerstorfer, T. (Institute for Rock Mechanics and Tunnelling Graz University of Technology) | Schubert, W. (Institute for Rock Mechanics and Tunnelling Graz University of Technology)
Abstract: Current laboratory techniques for the determination of Young's moduli or constrained moduli are fraught with restrictions: Typically in rock mechanics laboratories, the Young's modulus is determined on drill cores. For fault rocks this test procedure in many cases is not applicable due to the poor quality of the material. Oedometers, as characteristically used for soil testing are not adequate due to the small sample size and low testing stress levels. To enable testing of fault rocks under realistic conditions a large oedometer test apparatus was developed at the Institute for Rock Mechanics and Tunnelling, Graz University of Technology. The large oedo-meter has an inner diameter of 300 mm. The sample height can be varied between 60 and 100 mm. The main parts of the apparatus are the oedometer ring, a base plate, two filter plates, and a head plate. The test set up is designed to conduct tests with fixed ring as well as with a floating ring. The axial force is measured by a 2 MN load cell, which corresponds to 28.3 MPa. The ring is situated on three 50 kN load cells in order to get the amount of friction between specimen and ring. The vertical displacements are precisely captured by three displacement transducers. The oedometer ring is equipped with three strain gauges at different heights to determine the circumferential strains, allowing accurate calculation of the Poisson's ratio. 1 INTRODUCTION The knowledge of the deformation properties, especially of fault zones, is of tremendous importance for the selection of appropriate support measures and for minimizing risks in tunnelling and underground structures. In order to test fault rocks a large oedometer test apparatus (Fig. 1) was developed at the Institute for Rock Mechanics and Tunnelling at Graz University of Technology.