Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
ABSTRACT One of the interesting features with the ellipsoidal models of anisotropy presented in this paper is their acceptance of analytical solutions for some of the basic elasticity problems. It was shown by Pouya (2000) and Pouya and Zaoui (2006) that many closed-form solutions for basic problems involving linear isotropic materials could be extended by linear transformation to cover a variety of "ellipsoidal" materials. This paper will describe two main varieties of ellipsoidal elastic models and show how well they fit the in situ data for sedimentary rocks; numerical homogenization results for several varieties of fractured rock masses will also be provided. 1 INTRODUCTION In some anisotropic elasticity problems, information is available on the values of an elastic parameter in the various directions, to be used in identifying the elastic tensor.Atypical case in Rock Mechanics involves deducing Young's modulus from simple compression tests in different directions or measuring the acoustic velocity in different directions on a sample (Homand et al. 1993; Francois et al. 1998). Based on the notion that material isotropy corresponds geometrically to the image of a sphere, an expression for anisotropy can naturally be sought through an ellipsoidal variation of a number of parameters in different directions. The uncertainty then lies in how to deduce the anisotropic tensor from this assumption. Saint Venant (1863) studied this specific question intensively by introducing the approximation of ellipsoidal indicator surfaces. The indicator surface of an elastic parameter c is the polar diagram c (n), where n is a unit vector and c (n) the value of parameter c in the material direction n. In recent years, the concept of ellipsoidal anisotropy has been adopted as a guideline for the phenomenological modelling of geomaterials such as soils, rocks and concrete (Peres Rodrigues, 1970; Daley and Hron, 1979). Yet, the concept of anisotropic elasticity has at times been employed erroneously. For instance, Peres Rodrigues (1970) attempted using ellipsoids to fit, for several types of rocks, Young's modulus values measured along different directions. It has been shown (Pouya, 2007a) however that theYoung's modulus indicator surface, i.e. the polar diagram of E (n), can never be an ellipsoid (different from a sphere), hence the parameters fitted by this author do not define any possible elasticity tensor.The correct approach calls for fitting the diagram of _4 E (n) by an ellipsoid; this was performed by Saint Venant in 1863. 3. APPLICATION TO SEDIMENTARY ROCKS For the study of seismic wave propagation in geological layers, Daley and Hron (1979) developed the concept of an "elliptically anisotropic" medium, as distinct from the ellipsoidal anisotropy considered in the present paper.This concept has been widely used in geophysical studies and Thomsen (1986) undertook an examination within the context of "weak anisotropy" for a large variety of sedimentary rocks. Thomsen (1986) defined four dimensionless parameters ε, δ, δ * and γ, in order to characterise transverse isotropic materials, and provided their values for a wide array of sedimentary rocks.
- Geology > Rock Type > Sedimentary Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT The scope of the present study is the characterization of the inherent anisotropy of metamorphic rocks, based on the most widely used laboratory tests for rocks. The proposed classification system is based on data from literature and results from tests carried out in metamorphic rocks. It takes into account the degree of anisotropy as it is determined from:the uniaxial compressive strength, σ ci, the point load strength, Is50 and the longitudinal wave velocity, Vp. A new anisotropy index for point load strength, determined from diametral tests on oriented core specimens, is also presented. 1 INTRODUCTION A number of indices have been proposed for the classification of inherent anisotropy of the intact rock, mainly that of the uniaxial compressive strength and the point load strength. The degree of strength anisotropy is determined as the ratio of the strength perpendicular to the planes of anisotropy (maximum strength) to that in the weakest direction (minimum strength), as described by ISRM (1981). A classification of the anisotropy of foliated rockswas proposed by Tsidzi (1997) based on the ultrasonic velocity. Tsidzi (1986, 1987) also proposed a descriptive petrographic index (foliation index) for the characterization of the development of anisotropic texture of intact rock and a modification of the classification of point load strength anisotropy (Tsidzi, 1990). Other indices that have been used for the characterization of anisotropy are that based on the deformation modulus and the Poisson ratio (Ramamurthy, 1993 and Kwasniewski, 1993), as well as that of the tensile strength of rock. The indices that have been used for the characterization of anisotropy, possess a different classification scale, as they refer to different mechanical properties of intact rock. These properties are influenced to a varying extend by the anisotropic texture of intact rock. The aim of the present study is the proposal of a concise classification scheme of anisotropic rocks, which will take into account the fundamental anisotropy indices of mechanical properties and will characterize the degree of anisotropy of intact rock, by considering also the uniaxial compressive strength, σ ci, perpendicular to the planes of anisotropy. Thus, the strength and velocity anisotropy indices are correlated to the uniaxial compressive strength. 2 EXISTING CLASSIFICATION OF ANISOTROPY 2.1 Uniaxial compressive strength anisotropy The strength anisotropy index has been widely used for the classification of anisotropy. The maximum uniaxial compressive strength occurs when loading is perpendicular to the planes of anisotropy (β = 90°). The strength anisotropy index is given as (Ramamurthy, 1993): The application of uniaxial load relevant to the planes of anisotropy in the direction ofmaximumand minimum strength is shown in Figure 1. Based on the strength data of anisotropic sedimentary and metamorphic rocks, Ramamurthy (1993) proposed the classification given in Table 1.
- Geology > Geological Subdiscipline > Geomechanics (0.89)
- Geology > Rock Type > Metamorphic Rock (0.82)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.47)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.46)
ABSTRACT: The ground response and site effects of a steep valley were verified with a two dimensional plane strain analysis in the time domain against recorded motions.Weak motions (<0.15 g) have been measured on the site with three accelerographs placed at the base and crests of the slopes. The instrument at the base is on rock and the ones towards the crests on soil. Dynamic models were done with the finite element method (FEM), loading at the base the signals recorded on rock. The peak ground accelerations (PGA) obtained with the FEMfit with the ones measured in situ. The comparison between the main frequencies of the events and the fundamental frequencies of the site show resonance effects. The raised amplifications were demonstrated to be caused by geological site effects, related to the upper geotechnical unit and not by the topography. These results show the importance of subsurface structure in causing resonance effects. 1 INTRODUCTION Numerical methods have been recently applied for back and parametric analysis of earthquake ground response and site effects (e.g.Athanasopoulos et al., 1999; Havenith et al., 2002; Lokmer et al., 2002; Paolucci, 2002; Papalou & Bielak, 2004; Bouckovalas & Papadimitriou, 2005; Psarropoulos et al., 2007). There are few attempts to verify measured with modelled data in time and frequency domains accounting for topographic and geologic effects separately (e.g. Semblat et al., 2005; Assimaki et al., 2005). Thimus et al. (2006) present a theoretical verification of wave propagation with finite differences (FDM). Sincraian & Oliveira (2001) had field measurements but could not find a good fit with the 2− and 3D FEMthey used. Geli et al. (1988) found that 2Dmodels underestimate field observations, caused by the simplicity of the models. Only the 3D model in frequency domain showed a good match. They concluded that for peak ground accelerations (PGA) smaller than 0.24 g hills behave approximately linear. Users of these tools should be aware of the limits of their applicability and benchmark results.Weak motions have been validated with field data with a 3Dhybrid approach (indirect boundary elements method) by LeBrun et al. (1999). They found a good correlation on the responses for frequencies lower than 1 Hz. On the other hand, 1 − Danalysis methods have been extensively verified as documented by Kramer & Stewart (2004) with nearby rock-soil signals aswell as vertical arrays. Strong amplifications have been measured in some cases on hills (Bouchon & Barker, 1996) and related to topographical site effects, without quantifying the effects of the local geology. This paper presents the comparison of the ground responses modelled with two-dimensional (2D) linear elastic finite elements (FEM) of a site with field measurements, comparing the site effects of topography and geology. The site is located in a highly seismic region of Costa Rica.
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (0.66)
Selected Geological Factors Impacting Effects of Induced Seismicity On Surface In Conditions of Ostrava-Karvina Coalfield In the Czech Republic
Holecko, Josef (Department of Geomechanics and Geophysics, OKD, DPB, a.s. Paskov) | Konicek, Petr (Department of Geomechanics and Geophysics, OKD, DPB, a.s. Paskov)
ABSTRACT Underground exploitation of hard coal deposit in Ostrava-Karvina Coalfield which is the Czech part of Upper Silesian Coal Basin is accompanied by induced seismicity. This seismicity can be manifested negatively by rock bursts occurrence in underground workings and/or by vibration on the surface. The magnitude of surface vibration can be influenced by several factors. The basic factors are geological properties of rock mass – the thickness and the quality of overburden of Carboniferous strata and the level of underground water. In the paper authors analyse possible impact of these factors on surface vibration in conditions of Ostrava-Karvina Coalfield. The influence of rock burst and seismicity on surface is being observed by a network of standard underground and surface seismic stations and interpreted since late 1990's. In previous few years the particle velocity was measured by mobile seismic stations on Earth's surface in selected localities. These values were compared with those interpreted from the standard seismic network data. The analyses of geological properties, in the sites where the mobile seismic stations were situated and the assessment of differences between measured and interpreted velocities, give an idea how the geological properties influence the magnitude of particle velocity on the surface structures. The results are also discussed in the paper. 1 INTRODUCTION Annually several tens thousands of minor induced seismic events are recorded in Karvina part of Ostrava-Karvina Coalfield (OKR) in Czech Republic. OKR is the southern part of the Upper Silesian Coal Basin (see fig. 1). Energetically significant major induced seismic events are only few tens. Some of these events are accompanied by earth tremor. This fact is affected by several factors. Among basic factors the following ones can be included:The quantity of released seismic energy and the location of seismic focal area activity (epicenter), The physical and mechanical properties of rock mass environment between the seismic focal area and the place of seismic performance on surface, The properties of the strata under the surface (ground water level, geological structure, tectonics etc.). The impacts of induced seismicity on the surface are observed more or less in inhabited regions. 2 NATURAL CONDITIONS Carboniferous rock formation in Karvina part of OKR is created by Karvina and Ostrava strata (see figs 3 and 4). The coal seams of Karvina strata are recently massively exploited. Karvina strata represent a continental coal-bearing molasa in OKR (middle and upper Namur, Westphal A). In contrast to lithological nature of western part of OKR the sedimentary cycles are conspicuously longer and moreover sandstones are prevailing. Compression strength values of such rocks are distinctly higher ones than those of mudstones and siltstones. In thicker banks of rigid rock components then higher stress concentrations occur than in other parts of rock massif. This condition has been manifested most conspicuously in Saddle beds, which are basal part of Karvina series of strata. The Saddle beds are featured by several tens of meters thick banks of rigid rocks (sandstones, sandy siltstones and conglomerates (Dopita et al. 1997).
- Europe > Czechia > Moravian-Silesian Region > Ostrava (1.00)
- Europe > Belgium > Wallonia > Namur Province > Namur (0.24)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (1.00)
- Materials > Metals & Mining > Coal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Europe > Poland > Upper Silesian Basin (0.99)
- Europe > United Kingdom > England > London Basin (0.91)
ABSTRACT Research on energy characteristics of rocks under dynamic loading is initiated by the need to observe these characteristics for better understanding anomalous geomechanical events in the rock mass, mainly rock bursts. To understand these events better, it is necessary to introduce the observation of temperature of the test specimen in the course of testing. From the record of acting force and strain together with the temperature of test specimens is evaluated in detail both the stress-strain characteristics of rocks under study and their energy characteristics. These events go on dynamically by the influence of seismic wave propagation. In the laboratory, rock loading is simulated similarly to seismic wave propagation in the rock mass. The goal of the research is to determine energy characteristics of rocks under dynamic cyclic loading. Some results of that research are in the paper. 1 INTRODUCTION Researches into energy characteristics of rocks under dynamic loading is aimed at better understanding the processes that take place at anomalous geometric events, above all rock bursts. At the origin of anomalous geomechanical events, seismic waves propagate through the rock mass. In the laboratory, rock loading at the spread of seismic waves is simulated by dynamic (cyclic) loading. In the course of observation of energy characteristics, anomalies were found before achieving the ultimate strength.. From the point of view of kind of loading, the tests were done at the following dynamic loads:simple compression, oblique shear. In this article, we are concerned only with the results of simple compression measurements. From the point of view of loading mode, the tests were performed: in the rheological mode at the constant average strain (target set point, henceforth referred to as TSP), about which the cycling load oscillates, in the mode of uniformly increasing load to the failure of test specimen. 2 LABORATORY EQUIPMENT The results of researches may be influenced by the laboratory environment, the parameters of test equipment and the rock material examined. Researches into temperature changes at cyclic loading the rocks require the elimination of other influences that cause, in the course of measurement, changes in temperature. For this reason, the measurements were taken in the air-conditioned laboratory with the constant temperature of 20°C. 2.1 Thermovision ThermaCAM™PM 695 of the company FLIR Systems AB was used. This camera utilises the infrared camera system and consists of IR (Infrared) camera with a built-in 24° lens.The IR camera measures and shows infrared radiation emitted by the object. On the basis of fact that radiation is a function of surface temperature of the object, this temperature (temperature field) can be thus represented and evaluated. The results of scanning can be stored in the PC card. Repeatability-periodicity of storing the images in the PC card can be set. This periodicity can be set from 2 seconds to 24 hours. By option Fast, the image will be stored at the velocity of about 1 image per 1 second).
ABSTRACT This paper presents a numerical method for estimating rock mass strength criteria in underground mines. The method is based upon "measuring" selected rock mass failure events, which are then numerically back analyzed to estimate strength criteria. The basis of the numerical method is the back analysis technique outlined in Martin (1997), where the spatial and temporal distribution of actual "failure events" are numerically back analyzed to estimate the corresponding mining induced stress states. This technique is based on elastic analysis of stress and as a result has certain limitations which are outlined in the paper.A key aspect to the numerical analysis is the statistical estimation of upper and lower bound limits to the derived failure criteria using the error analysis philosophy expressed inWiles (2005). The method is in use by several mining operations and consultancies; the key aim of this paper is to provide a clear overview of the method for others. 1 BACKGROUND The accurate and routine estimation of rock mass strength remains one the greatest unsolved problems in mining geomechanics. It extends to all aspects of rock mechanics including tunnels, mines, rock slopes, waste repositories and bridge and dam abutments. Rock mass strength is a key factor influencing all aspects of excavation design, such as the routine engineering of stable excavations, excavation sequences and ground support systems. In mining geomechanics, a popular approach to estimating rock mass strength is the empirical method proposed by Hoek and Brown (1980), and refined by Hoek and Brown (1998), and Hoek et al. (2002). A brief history of the Hoek-Brown criterion is available in Hoek and Marinos (2006). The 2002 version is widely used by consultants and mine based engineers to design excavations for both new and existing mining projects. An approach typically taken is:Estimate the parameters for the Hoek-Brown criterion, typically using the software package "Roclab". Approximate the Hoek-Brown strength criterion to a Mohr- Coulomb criterion (with tension cut-off) over the confining pressure of interest. In case of 3D inelastic analysis, the Mohr Coulomb criterion is further generalized to a yield surface in principal stress space. The resulting constitutive model is programmed into a stress analysis program, with all the other parameters and constants such as pre-mining stress states, elastic moduli, dilation angle, and strain softening rules. Models and meshes are built and run: the key outputs used to assess the stability or effectiveness of a particular design might typically include:Analyze factors-of-safety of modeled stress states relative to yield surface for development, shafts, ore passes, pillars, and stopes. Quantification of excavation damage, in particular the indicated depth of failure around development and large excavations in terms of plastic strains, or damaged volumes. Computation of displacements and strains induced in long term excavations such as shafts, crushing stations and surface infrastructure such as railway tracks and pipelines.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
Mining-induced Earthquakes Focal Mechanisms In the Khibiny Massif
Melnikov, N.N. (Mining Institute, Kola Science Centre, Russian Academy of Sciences) | Kozyrev, A.A. (Mining Institute, Kola Science Centre, Russian Academy of Sciences) | Fedotova, Yu. V. (Mining Institute, Kola Science Centre, Russian Academy of Sciences) | Reshetnyak, S.P. (Mining Institute, Kola Science Centre, Russian Academy of Sciences)
ABSTRACT The rockbursts and earthquakes take place at the open pit and underground mines of the Kola Peninsula more and more frequently in last time. The most hazardous mechanism of mining-induced earthquakes has been identified with regard to their impact on underground and surface structures resulting from large-scale mining operations in high-stressed rock mass. The focal mechanisms of number mining-induced earthquakes have been analysed, registered over the recent years within the area of underground and open pit mining operations impact in the Khibiny massif. The reasons and distinctions of these events genesis have been considered comparable in energy, though, occurred in different parts of rock mass. 1 INTRODUCTION Registration of kinematical parameters of seismic waves, arising under the dynamical manifestation of the rock pressure enables one to assess its focal mechanism, which peculiarities are determined by the stress state of rock in the mass. For efficient monitoring of the stress-strain state of rocks one can use the technique, based on the statistic analysis of seismic events' focal mechanisms, registered by the network of local seismic stations. 2 ANALYSIS TECHNIQUE The technique is based on summation of tensors being dyads, built according to single vectors of normals versus the front of waves and the single vectors of the first arrival of P-waves seismic events components in the investigated area. That is the reason why to solve the prediction tasks more justified is to use data covering namely the seismic events average focal mechanisms, registered within the area under study, which makes it possible to determine its background stressed state (Yunga, 1990). 3 PECULIARITIES OF THE GEOMECHANICAL STATE OF THE KHIBINY MASSIF The Khibiny massif is located in the central part of the Kola Peninsula in the north-west of Russia. This massif is a highly tectonically stressed one, which is determined by numerous in-situ measurements and confirmed by mining operations practices (Melnikov, 1996). The apatite-nepheline deposits of the Khibiny massif is developed by the Apatit JSC in three undergrounds and four open pits mines. Geomechanical state of the Khibiny massif is characterised by the high heterogeneity of the stress state parameters. Differentiation of these parameters in different parts of apatite mines is confirmed by maps of stresses, compiled for the deepest levels of mines (600–800m from the surface), where the largest number of rockbursts has been registered. The total volume of the excavated and displaced rock mass in the Khibiny mines makes over 3.5 milliard tons the total area measuring about 10 km2. That is why one has a good reason to believe the level of accumulation and discharge of the stresses energy due to displacement of the rock mass has reached a limit at which mining-induced earthquakes are possible. 4 ANALYSIS OF SEISMIC EVENTS FOCAL MECHANISMS AT UNDERGROUND MINING Below you can find the results of implementation of the developed technique for the database of seismic events, registered within the underground mine.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.87)
ABSTRACT Effects of environment and rock fabric on subcritical crack growth in granite were investigated. Double Torsion test was used. It was shown that the relation between the crack velocity and the stress intensity factor was anisotropic. Under the same temperature and humidity, the crack velocity depended on the crack opening direction, and it was the highest when the crack propagated parallel to Rift plane. From the results under different temperature and humidity, it was shown that the crack velocity was higher when the temperature and humidity were higher. The crack velocity in water was higher than that in air. These results agreed well with the concept that stress corrosion is the main mechanism of subcritical crack growth in rock. From the experimental results in this study, it is concluded that subcritical crack growth in granite is affected by water and pre-existing microcracks. 1 INTRODUCTION In the classical fracture mechanics, it was postulated that the crack propagated rapidly once the fracture toughness has been reached. In fact, the crack can propagate even when the stress intensity factor is lower than the fracture toughness. This phenomenon is called subcritical crack growth (Atkinson 1984), which is one of the main causes of time-dependent behavior in rock. Knowledge of time-dependent crack propagation is important to consider the long-term stability of structures in rock mass, such as underground power plants or repositories for radioactive wastes in underground. In this study, subcritical crack growth in granite was investigated. Especially, the relation between the crack velocity and the stress intensity factor was determined experimentally by Double Torsion (DT) test (Williams & Evans 1973, Sano & Kudo 1992), which is the typical fracture mechanics test used to measure subcritical crack growth. Dependence of subcritical crack growth on the environmental conditions and rock fabric was investigated. 2 SUBCRITICAL CRACK GROWTH Under low homologous temperatures and atmospheric pressure, stress corrosion (Anderson & Grew 1977) is considered to be the main mechanism of subcritical crack growth. Stress corrosion is a weakening process due to a chemical reaction between the siloxane bond structure near the crack tip strained by the tensile stress and water (Michalske & Freiman 1982). 3 EXPERIMENTAL METHOD In this study, Double Torsion test was used. The specimen and the loading configuration for DT test are shown in Figure 1. The experimental apparatus was set in the room where the temperature and the relative humiditywere controlled and kept constant.All experimentswere conducted under the controlled temperature and humidity. For the apparatus used in this study, the temperature and the relative humidity can be controlled within 0.1K in the range of 283–333K and within 1% in the range of 40–75%, respectively (Nara & Kaneko 2005). 4 ROCK SAMPLES Oshima granite, Westerly granite, and Inada granite were used as rock samples. It is known that granite has orthorhombic elasticity (Sano et al. 1992). In Table 1, the P-wave velocities in three orthogonal directions are shown.
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Power Industry (0.54)
- Energy > Oil & Gas > Upstream (0.51)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.36)
ABSTRACT Particle cluster routines were tested using PFC software. The numerical specimens matched the mechanical properties of Westerly granite. The results from PFC2D and PFC3D simulations were compared against the actual laboratory data. After the mechanical tests the PFC3D cubic specimens were heated up to 450 °C. During the heating cracking, AE activity and temperature evolutions were monitored. P wave velocity measurements were conducted for each numerical specimen. The responses were compared against similar thermal laboratory data. The results showed similar P wave velocity decrease due the heating up to temperature of about 250°C. 1 INTRODUCTION The paper describes steps taken to implement and test enhanced particle clustering routines in PFC (Itasca Consulting Group, Inc., 2005). The study relates to the underground storage of high-level nuclear waste and the concept of placing fuel canisters in underground cavities. The canisters produce heat due to fission. The thermal changes in rock could potentially lead to the opening of existing cracks and the initiation of new cracking. Such damage may have serious implications such as increasing the permeability of the rock designed to function as a barrier to groundwater contamination for example. Measured macroscopic properties of rock tend to change with changing temperature. (Mahmutoglu 1998, Jackson et al. 1999). Elastic velocity measurement is a way to monitor some of the change, for example, David et al. (1999) used velocity techniques to study La Peyratte granite. Davidge (1981) and Homand-Etienne and Houpert (1989) among others studied thermal cracking at the grain scale and concluded that it is due to the mismatch in the thermal expansion coefficient between adjacent minerals and produces intergranular cracking. The work presented in the paper is part of the research to better understand mechanical damage induced by thermal loading. The numerical results are compared against results from thermal laboratory experiments onWesterly granite. The presented thermal modeling builds on the PFC2D thermal numerical experiments reported by Wanne and Young (2006). 2 MODELING METHOD 2.1 Particle Flow Code Commercially available PFC was used in the particle cluster development and thermal simulations. The numerical approach models the movement and interaction of circular/ spherical particles by the distinct element method. The method represents solid rock by an assembly of particles joined by breakable bonds.The damage occurs by bond breakages, thus the material can evolve from solid to granular. PFC has been used to simulate hard rock in several studies. A thorough description of the method is given in (Potyondy & Cundall 2004). 2.2 Acoustic emission and velocity measurements PFC uses an explicit time-marching calculation scheme to simulate material behavior. This allows dynamic simulations to be performed in which seismic waves propagate across material at a speed that depends on the material properties. The approach permits realistic acoustic emission simulations (Hazzard & Young 2002). The numerical seismic monitoring technique has been used in studies reported by Young et al (2000) and Hazzard andYoung (2004). Seismic velocities of the numerical specimens were measured by propagating pressure waves through them.
- North America > United States (0.30)
- North America > Canada (0.29)
- Geology > Mineral (0.92)
- Geology > Geological Subdiscipline > Geomechanics (0.74)
- Geology > Rock Type > Igneous Rock > Granite (0.70)
Gotthard Base Tunnel: Rock Burst Phenomenon During Construction of a Multifunctional Section In a Fault Zone Area
Hagedorn, H. (Amberg Engineering AG, Switzerland (Amberg Engineering AG is member of the Engineering JV consisting of: POYRY, Lombardi AG and Amberg Engineering AG)) | Rehbock-Sander, M. (Amberg Engineering AG, Switzerland (Amberg Engineering AG is member of the Engineering JV consisting of: POYRY, Lombardi AG and Amberg Engineering AG)) | Stadelmann, R. (Amberg Engineering AG, Switzerland (Amberg Engineering AG is member of the Engineering JV consisting of: POYRY, Lombardi AG and Amberg Engineering AG))
ABSTRACT The Gotthard Base Tunnel, a 57 km long twin tube single track railway tunnel is currently under construction. The aim of the tunnel is to connect the high speed railway systems of Germany and Italy. During the construction (D&B) of one of the three intermediate points of attack a big unknown fault was encountered. A comprehensive drilling campaign revealed a faults kernel consisting of intensively jointed gneiss and kakirites sub vertically dipping over the tunnels and striking at approximately 10° to the tunnel system's axis. In addition to large deformations rock bursts have been occurring mostly at the face after blasting. Other bursts with damaging effect on the support have been experienced at greater distance to the face. By means of a seismic measuring program the hypocenters of the seismic events could be localized. Computational simulations have been carried out in order to recognize the likely failure mechanisms responsible for the bursts causing damages. 1 RAILWAY AXIS THROUGH THE ALPS The longest tunnel of the NEAT (New Alpine Transverse) through the Swiss Alps is the Gotthard Base Tunnel (GBT) with a length of 57 km. The tunnel consists of two parallel single track tubes each with a diameter of 9.2 m. The tubes are connected by cross galleries every 310 to 325 meters (see Figure 1). The maximum overburden is 2350 meters. Three intermediate points of attack divide the tunnel into five sections of approximately equal length. These additional attacks are necessary to attain a reasonable construction time of approximately ten years and for ventilation purposes. The intermediate points of attack at Sedrun and Faido shall serve as Multi Functional Sections (MFS) during operation of the tunnel. These MFS enables the trains to change the tunnel tube in case of maintenance works and the specially ventilated emergency sections serve the rescuing of people in emergency cases (see Figure 1). The MFS Faido had to be accessed by a 2.7 km long gallery declining at 12.7% from the portal. The overburden in the MFS Faido is approximately 1500 meters. 2 GEOLOGICAL PREDICTION FOR THE MFS FAIDO The outcrops from quarries in the area of the MFS Faido, the experiences made during construction of the investigation system for the Triassic Piora basin as well as various vertical exploration drillings confirmed a favorable geological section for the designed location the MFS consisting of Leventina Gneisses with very good quality. 3 GEOLOGY ENCOUNTERED During April 2002 a completely unexpected break down of fine grained quartz occurred in the roof of the top heading approximately at half of the length of the cross cavern forming a cavity of 8 meters in height (see Figure 1).
- Geology > Structural Geology > Fault (0.51)
- Geology > Rock Type > Metamorphic Rock > Gneiss (0.45)