Lee, J. G. (Korea Infrastructure Safety Corporation) | Jang, B. S. (Korea Infrastructure Safety Corporation) | Bae, S. W. (Korea Infrastructure Safety Corporation) | Moon, J. S. (Kyungpook National University) | Sin, H. J. (Ministry of Land, Transport and Maritime Affairs) | Park, J. H. (Ministry of Land, Transport and Maritime Affairs)
Large slopes constructed during road or building construction contain a number of potential risk factors, and consequently they require a more detailed inspection. In Korea, large slopes more than 200m long and with a cut height of more than 50m have been designated as large-scale slopes for special inspections. The total number of large-scale slopes located on the national highways is 146 and their average lengths and heights are 329m and 64 m, respectively. The safety inspection for large-scale slopes consists of an assessment of their stability and condition and an evaluation of the level of damage and potential risk factors. The final safety rating for slope stability is determined based on these assessment results and the future plan for periodic inspection is decided based on the final safety rating. In this study the safety ratings for all 146 large-scale slopes were evaluated and the economic efficiency of operating the current inspection system was assessed.
As approximately 60% of the national land in Korea consists of mountainous areas, it is essential to form a cut slope or an embanked slope as a prerequisite to construction work in many cases. In particular, more cut slopes are being formed for road construction than for other construction work as these construction zones are long, with most passing through mountainous areas. Most road slopes are distributed along expressways and the national highway, and their number is increasing year by year.
Currently, Korea has 4789 km of expressways along which approximately 7000 slopes are distributed. In addition, there are 13,797 km of national highway, more than twice the length of the expressways that have 29,757 slopes, which is more than four times the number of slopes as on the expressways.
The Ministry of Land, Transport and Maritime Affairs has been operating the Cut Slope Management System since 1997 in order to prevent slope disasters on the national highway and to minimize any damage. A complete enumeration of the slopes on the national highway through the Cut Slope Management System was conducted and a master planwas established based on the result and is in operation. Continued observation of these slopes is required, but only 124 sites on which it is difficult to apply reinforcement methods remain under real-time monitoring.
Of these cut slopes, slopes more than 200m long and with a cut height of more than 50m are designated as large-scale slopes under the “SpecialAct on the Safety of the Facility”, regular safety inspection and maintenance must be conducted. The Cut Slope Management System includes safety inspections of the large-scale slopes that are distributed on the national highway, which contributes to reducing the damage that can result from slope collapse and also secures the safety of roads through safety inspections and maintenance.
Prendes-Gero, M. B. (Department of Construction and Manufacturing Engineering, Engineering Polytechnic School of Gijón) | Suárez-Domínguez, F. J. (Department of Construction and Manufacturing Engineering, Engineering Polytechnic School of Gijón) | González-Nicieza, C. (Department of Mining Engineering, Mining Engineering School, University of Oviedo) | Álvarez-Fernández, M. I. (Department of Mining Engineering, Mining Engineering School, University of Oviedo)
There are several factors that affect the formation of localized rockfalls in self-supporting underground mines. Between these factors we can point out the type of material, the environmental conditions, the process of exploitation or the redistribution of stresses. All of them contribute to the alteration of the rock and the formation of cracks, and their spreading produces rockfalls and increase in the temperature of the surrounding material. The measure, all through the time, of the temperature of the rock with thermic images allows us to identify variations in it. These changes in the thermic conditions of the rock mass identify areas with a high probability of rockfalls. Following this principle, researchers of the University of Oviedo have developed a methodology for the prevention of localized rock falls in self-supporting underground mines using infrared thermography techniques. To test its goodness, they have applied it in an underground mine of limestone located in the north of Spain. This work has been realized in the last year and it has realized that the infrared thermography technique is a quantitative way to know the risk of rockfalls, that lets to prepare the adequate proceedings in order to avoid accidents or situations of risk within the exploitation. In this paper the methodology developed and its application on a real mine, as well as the results of the job are described.
The purpose of this article is to develop and validate a procedure for quantitatively determining the location and probability of localised detachments of material in self-supporting underground excavations through the evaluation of thermal alterations to reduce the risk of accidents in such situations.
When an excavation is made inside a fractured rock mass and the spacing of joints is considerable, large blocks of rock may appear. If these blocks are unstable, may come loose inside the excavated cavity, causing significant personal and material damages. For this reason it is important to have analytical tools for identifying such blocks before or during the execution of work.
For straight galleries with a constant cross-section and tetrahedral blocks made up of three families of joints and the surface of the gallery itself, the problem of identifying blocks has been widely studied and solved (Goodman & Shi 1985, González et al. 2005). For pentahedral blocks made up of four families of joints and the surface of the gallery, both the problems of identification and support have also been studied in considerable depth and solutions found (González et al. 2005).
Ishida, T. (Kyoto University) | Nagaya, Y. (Kyoto University) | Inui, S. (Kyoto University) | Aoyagi, K. (Kyoto University) | Nara, Y. (Kyoto University) | Chen, Y. (Kyoto University) | Chen, Q. (3D Geoscience, Inc.) | Nakayama, Y. (3D Geoscience, Inc.)
Use of carbon dioxide (CO2) as a fluid for hydraulic fracturing has been considered to stimulate oil production, to enhance shale gas recovery and to extract hot dry rock geothermal energy. In these projects, CO2 is usually injected into rocks at a depth more than 1,000 m. In the temperature and pressure at that depth CO2 usually becomes a supercritical state (SC-CO2), and viscosity of the SC-CO2 is very low around 5% of that of water. So, it is important to understand the behavior of SC-CO2 in rock. Thus, we made hydraulic fracturing experiments using SC-CO2 and water in two granite specimens for each fracturing fluid under a true tri-axial loading condition. The results of the experiments suggested that low viscosity fluid like SC-CO2 is expected to induce more three dimensionally and widely spreading cracks under considerably lower breakdown pressure than water.
Carbon dioxide (CO2) is injected into the underground rock for a variety of purposes. It is often used for miscible flooding to enhance oil recovery in depleted petroleum reservoirs, and the use of CO2 as a frac- turing fluid for well stimulation has been considered because it eliminates formation damage and resid- ual fracturing fluid (Sinal & Lancaster 1987, Liao et al. 2009). Using CO2 as fracturing and circulat- ing fluid has also been proposed in hot dry rock geothermal energy extraction, because it eliminates scaling in the surface piping due to the inability of CO2 to dissolve mineral species (Brown, 2000). Recently, since shale has a greater affinity for CO2 than methane (Nuttall et al. 2006), the CO2 injection to enhance shale gas recovery has been considered as well (Kalantari-Dahaghi 2010). For all of these pur- poses, it is necessary to understand the behavior of CO2 in rock. It is also important to know how injected CO2 infiltrate into the surrounding rock mass in CO2 capture and storage projects (Xue et al. 2006, Nooner et al. 2007).
In these projects, CO2 is usually injected into rocks at a depth of more than 1,000 m. The temperature and pressure at that depth usually makes CO2 a super- critical state, while the lower temperatures in special geological conditions create a liquid state. The viscos- ity of liquid CO2 (L-CO2) is one order lower than that of normal liquid water, while that of the supercritical state (SC-CO2) is much lower still. To clarify fracture behavior induced with injection of the low viscosity fluid, we have already conducted hydraulic fracturing experiments using SC- and L-CO2 in granite speci- mens under hydrostatic loading, and have discussed differences in the results between the two fluids (Ishida et al. 2012). In this paper, we report the hydraulic fracturing experiments using SC-CO2 and water in granite specimens under a true tri-axial loading condi- tion. From the results, we discuss differences between the two fluids focusing on the breakdown pressure and distribution of located acoustic emission (AE) sources, adding data of our experiments with injection of oil having a few hundred times larger viscosity than water.
The paper presents a numerical study of the elastic response of laterally loaded rock sockets. Sockets are loaded at the top with transverse forces and bending moments and the corresponding displacements and rotations are calculated. 3D finite element analyses are carried out to investigate the effects of shaft length, relative stiffness of socket to rockmass and the ratio of the applied moment to shear force. The rockmass is assumed to be linearly elastic, as rock sockets rarely reach the rockmass strength. However, socket-ground interface elements are used along the periphery and at the socket base in order to simulate separation and lift-up effects on the response. The results of the analyses are compiled in semi-empirical dimensionless relationships giving the socket stiffness in terms of the important parameters. The produced results showsignificant differences compared to the results of numerical analyses reported by Carter & Kulhawy (1992) where separation and lift-up effects were not included.
Rigid sockets are nowadays an effective foundation type of structures founded with tall piers. The specific foundation undertakes significant horizontal loads and bending moments, thus it undergoes considerable horizontal displacement and rotation on its head.
Two different approaches are met in common engineering practice for the estimation of the aforementioned socket head deformation. One approach involves the subgrade reaction methods, including numerous methodologies of p-y curves for rock that serve the presence of non-linear, horizontal springs along the socket (Reese 1997, Gabr et al. 2002). On the other hand stands the elastic continuum theory, which treats the rigid socket as an equivalent spring with three independent degrees of freedom for the prescribed loading conditions (Douglas & Davis 1964, Carter & Kulhawy 1992).
The scope of the present paper is the evaluation of the socket head deformation predictions proposed by the most recent methodology of the latter approach. Furthermore it is attempted to derive corresponding closed-form equations through 3D finite element analyses, taking into account the frictional behavior and the possible separation between the laterally loaded rock socket and the surrounding rockmass.
Wojtecki, L (Bielszowice Coal Mine, Kompania Wêglowa) | Mendecki, M. J. (Faculty of Earth Sciences, University of Silesia in Katowice) | Talaga, A. (Faculty of Earth Sciences, University of Silesia in Katowice) | Zuberek, W. M. (Faculty of Earth Sciences, University of Silesia in Katowice)
Coal exploitation in the Upper Silesian Coal Basin is associated with rockburst hazard. This hazard is minimalized by active rockburst prevention, where torpedo blastings in roof-rocks take very important place. The estimation of the torpedo blasting effectiveness becomes significant under exploitation in difficult geological and mining conditions, where the high danger of rockburst occurs.
Pioneer investigations lead to estimate of the torpedo blastings effectiveness on the basis of an analysis of focal mechanisms of the induced mining tremors. The study has been carried out in the Bielszowice coal mine in cooperation with the Faculty of Earth Sciences of the University of Silesia. The torpedo blastingswere performed during exploitation of the seam 507 with the longwall 307b. Each blasting provoked a tremor immediately. The parameters of the focal mechanisms for each provoked event were estimated by the FOCI software.
Beside tremors foci with an explosive mechanism, related only to the detonation of an explosive, the occurrence of tremor foci with a shear mechanism has been confirmed. Shear mechanism in provoked tremors proves that blastings caused the motion of rock masses, what is connected with stress drop in the rock mass. The results have been associated with geological and mining conditions.
Coal exploitation under condition of a rockburst hazard determines active rockburst prevention applying, where torpedo blastings occupy a prominent place.An estimation of the blasting efficiency becomes particularly important during the exploitation in difficult geological and mining conditions.
The focal mechanism studies with seismic moment tensor inversion method were performed for the tremors induced by torpedo blastings in the longwall 307b during exploitation of the seam 507 in the Bielszowice coal mine. Focal mechanisms were calculated by the seismic moment tensor inversion based on the analysis of seismic waves generated in the focus and registered by the appropriate number of seismometers surrounding the source.
Lacking appropriate mathematical, mechanical, investigation and testing methods to realistically characterize the ground and predict the ground and system behaviours, for many centuries purely empirical methods for tunnel design have been used. Initially the used experience was bound to single persons. Later, formalized procedures have been developed, using a few, relatively easily collectable parameters, and by weighting them, arrive at a ground quality indicator. It is obvious that the complex properties of the ground cannot be adequately described by a single number or expression. Basis for the selection of parameters and weighting and rating is experience under specific conditions, making a use under other conditions questionable. The authors of some of the systems extended their classification systems to tunnel design tools by including additional parameters and input in the system. The assignment of e support measures is strongly biased, and does not consider different behavioural modes of the ground and its interaction with excavation and support. Thus tunnel designs based on such systems necessarily are inaccurate and sometimes even entirely wrong. From the legal point of view, the sole use of “classification systems” for tunnel design is inacceptable, as there is no proof of stability or serviceability. Due to the reasons mentioned above and a number of other shortcomings, like oversimplification, so called “classification systems” are not adequate to the problem, leading to inadequate designs, and thus to uneconomical construction.
1 Why Classification?
The reasons for establishing a classification system can be manifold. The main purpose generally is to group items with similar features or properties into one category. This requires the definition of classification criteria. Those criteria need to be clear and meaningful. It is quite obvious that a small number of classification criteria leads to a quite heterogeneous distribution of individual members of one category.
As an example the classification of children, which should enter school may serve. The main criterion in most countries is that they are six years of age. If this is the only criterion applied, any six year old kind falls into the category of school beginners, regardless of their origin, mother tongue, weight and height, and what other differences might exist among that group.
To arrive at a more homogeneous group, additional criteria are required. Naturally the single criteria are not of the same importance, thus the different criteria need to be weighted. The weight of each criterion again depends on which specific requirements the target group should meet. It is quite clear that different persons would put different weights on the single criteria due to their personal preferences or experience. With adding more criteria to apparently arrive at a more homogeneous group the bias increases. There is no guarantee that the group eventually fits together, as one group member may have strong qualifications with respect to some criteria, while another group member has high qualification in other aspects.
The question arises why we need classification at all if the result probably is not satisfying? The answer is quite simple: to enable also inexperienced people to forma group, meeting certain requirements with some degree of probability of success. But while an expert can correct unwanted results from the classification process, a layperson uncritically has to believe that the result is appropriate.
Lemaitre’s viscoplastic model is widely used to model the long-term behavior of rocks, especially argillaceous rocks that are being considered as host rocks for radioactive waste repositories. However, this model has marked disadvantages, such as pressure independency and no volumetric viscoplastic strain, which greatly limit its ability to reproduce the complex phenomena in underground structures. In view of these, based on thermodynamic principles, Lemaitre’s phenomenological viscoplastic model is extended in this paper. Two equivalent surfaces are introduced in the p-q stress plane in order to consider the contribution of hydrostatic stress on the viscoplastic strain and damage respectively. The inherent concept is that the stress points located on the same equivalent surface share the same intensity for both viscoplastic strain and damage. Moreover, in this model, the non-associated flow rule is assumed and a hyperbolic viscoplastic potential is used to reproduce volumetric viscoplastic deformation. The time dependent damage evolution law is also modified to rely on inelastic strain. In order to verify the constitutive model and to study the newly added parameters, several numerical procedures were performed corresponding to quasi-static tests, creep tests and relaxation tests. Finally, a detailed discussion about the influences of these parameters on both compression and tension cases is presented.<./p>
Lemaitre’s viscoplastic model is widely used to characterize the long-term behavior of argillite (Souley et al. 2011) as well as to model the time dependent evolution of the Excavation Damage Zone (EDZ) around underground openings (Pellet et al. 2009). However this constitutive model assumes that the hydrostatic stress has no influence on the viscoplastic behavior and it imposes no volumetric viscoplastic strain. These are obvious drawbacks in its ability to model geomaterial behavior.
In this paper, an extension of Lemaitre’s model that will overcome these drawbacks is presented. Based on thermodynamic principles, two equivalent surfaces are introduced to take into account the influence of hydrostatic stress on both the evolution of viscoplastic strain and damage. In addition, the volumetric viscoplastic strain is introduced by using a hyperbolic viscoplastic potential. The time dependent damage evolution law is also modified to be dependent on inelastic strain. This model is implemented into the finite element software ABAQUS 6.10, and detailed studies of the new parameters are performed by modeling quasi-static tests, creep tests and relaxation tests.
Righetto, G. L. (ATHENA) | Lautenschläger, C. E. R. (Computational Geomechanics Group, GTEP) | Inoue, N. (Group of Technology in Petroleum Engineering, PUC-Rio) | da Fontoura, S. A. B. (Pontifical Catholic University of Rio de Janeiro)
Aiming to increase hydrocarbon production, the oil industry has developed recovery methods whose purpose is to get more production. Thus, several problems may be encountered when making use of these techniques, mainly the conventional one. In addition, consideration of geological structures in reservoir engineering, such as fault zones, has fundamental character for determining realistic response for the production of hydrocarbons. In the case of faults zones, its consideration in the model has significant importance currently, especially with regard to the possibility of reactivation and possible loss of tightness of the reservoir. Thus, the aim of this study was assess reservoir models with a fault zone using partially coupled hydro-mechanical simulations. The methodology considers a fault zone whose behavior is given by the Mohr-Coulomb yield criterion. The plasticity model showed consistent results with the process of reactivation for the models. Thus, for the case where the objective is to determine the maximum flow rate of injection as well as its spatial configurations aimed at maintaining the field production, it is possible to establish the flow rate that may result in the initiation of the fault reactivation. Furthermore, the effect of surrounding rocks had a great influence in the time required to initiate the process of reactivation. As a general conclusion, it is stated that the consideration of fault zones in reservoirs, as well as surrounding rocks, must be taken into account to obtain more accurate response to the field behavior.
The exploitation of petroleum began from the drilling of the first well of petroleum in the XIX century in the United States. From this point, aiming increase the petroleum recovery, the oil industry developed recovery methods whose objective is to obtain a higher production than that which would be obtained only as a result of the natural energy of the reservoir (Thomas 2001). In this context, several problems can be faced when one uses recovery techniques, mainly through the fluid injection, in geologically complex reservoirs.
Besides that, the consideration of geological structures in the reservoir engineering, for instance faults, has fundamental importance for determining realistic responses related to oil recovery factor, compaction of reservoir, seafloor subsidence, among others. In the specific case of faults, its consideration and analyses has been reported for several authors (Morris et al. 1996, Wiprup & Zoback 2000, Mildren et al. 2002, Streit & Hillis 2004, Chiaramonte et al. 2006, Færseth et al. 2007, Rutqvist et al. 2007, 2008, Soltanzadeh & Hawkes 2008, Zhang et al. 2009, Cappa & Rutqvist 2010, Ducellier et al. 2011, Jain et al. 2012, McDonald et al. 2012; Leclère & Fabbri 2012), due, mainly by its reactivation possibility. In the fault reactivation perspective during the field development, the objective is to prescribe the highest injection flow rate or the highest bottom hole pressure that can be applied in injector wells in order to maintain the reservoir pressure, without the failure of the faults. The process of fault reactivation, due the stress state variation, can result in an emergence of a preferential path for the hydrocarbon, implying in the most critical cases, in the leakage of fluid and possible loss of tightness of the reservoir.
The paper begins by noting that many of the contributions to the EUROCK2013 Symposium deal directly with risk. An explanation of epistemic and aleatory uncertainty then follows with further notes on risk analysis techniques and ‘black swan’ events. Three illustrative rock engineering application examples are discussed in some detail: shale gas extraction, CO2 storage, and radioactive waste disposal—with the emphasis being on successfully achieving the project objectives. The paper concludes with ten recommendations, concentrating on the further development of the subjects of uncertainty and risk as they apply to rock mechanics and rock engineering. Especially important is the need to validate coupled numerical modelling and to make the programs more accessible to practitioners. This, together with the wider application of the techniques used for the design of radioactive waste repositories, will significantly reduce the impact of uncertainties and risks inherent in all rock engineering modelling, design and construction.
1.1 Uncertainty in rock engineering modelling, design and construction
In order to be able to coherently design an underground rock engineering project, one has to be able to predict the future. For example, what will happen when a tunnel of this diameter, at this depth, excavated in this direction, in this rock mass, is constructed?Will rock blocks fall into the tunnel, will the concentrated rock stress damage the tunnel, will the tunnel encounter any major faults? If one is unable to answer questions such as these, indicating that the future cannot be predicted, the design of the project is subject to some level of uncertainty and risk. Since, we cannot yet obtain full information about any rock mass, all rock engineering projects are subject to uncertainty and hence risk. Reduction of the risks is directly related to reduction of the uncertainties and so, for improved rock engineering design, we must concentrate on the uncertainties involved. In the worst case, lack of attention to this subject could endanger lives and prejudice the functionality of the completed project.
The program for the final disposal of low and intermediate level radioactive waste was established by Paks Nuclear Power Plant, Hungary. Preparation for final disposal of radioactive wastes has been done as part of a national program since 1993. The Central Nuclear Financial Fund and the Public Limited Company for Radioactive Waste Management (Puram) have been established to coordinate organizations and activities for all tasks in connection with nuclear waste treatment. The project started with a geological screening in order to find the most suitable formation for the radioactive waste disposal. The selected potential host rock is a granite complex in the Mórágy Granite Formation in the south-western part of Hungary, close to the village of Bátaapáti. The goal of this paper is to present the newest modeling results of the Excavation Damaged Zones around the Bátaapáti radioactive waste repository. The following zones are thoroughly investigated and modeled in both 2D and 3D: EdZ: Excavation Disturbed Zone; EDZ: Excavation Damaged Zone and HDZ: Highly Damaged Zone.
These Excavation Damaged Zones (EDZs) are very important for understanding the hydromechanical and geomechanical behavior. Therefore the EDZs were analyzed by hydrogeological, filed-survey, geophysical and Borehole Television (BHTV) methods. Our modeling was using both high number of laboratory rock tests and the field measurements. The correlation between the computed and measured values, were verified.
Due to the latest studies of excavation damaged and disturbed zones three different zones are distinguished (see Figure 1):
• Excavation disturbed Zone or Excavation Influence Zone (EdZ or EIZ), which is a zone with hydromechanical and geomechanical modifications, without major changes in flow and transport properties. Stress and/or strain in EdZ zone involves only elastic change and EdZ is situated beyond the EDZ. The pore volume may be affected close to the EIZ-EDZ transition by the elastic strain.• Excavation Damaged Zone (EDZ), is a zone with hydromechanical and geomechanical modifications inducing significant changes in flow and transport properties. The damage in this zone is in the form of grain scale fractures and minor interface dilation from the EIZ-EDZ transition to interconnected at the EDZ-HDZ. This zone could be subdivided into outer – EDZo and inner EDZi zones. • Highly Damaged Zone (HDZ), is a zone where macro-scale fracturing or spalling may occur. The EDZ and HDZ in different cases: homogeneous rock mass_ (a), modification of EDZ and HDZ due to one pre-existing fracture (b), modification of EDZs in jointed rock mass (c) (after Lanyon et al. 2009).
fractures are typically interconnected which results in a significant increase of the effective permeability in this zone.