Flexible slope stabilization systems made from wire meshes in combination with nailing are widely used in practice to stabilize soil and rock slopes (Fig. 1). They are economical solutions and a good alternative to measures based on rigid concrete liner walls or massive supporting structures. Apart from designs using conventional steel wire, meshes from high-tensile steel wire are now also available on the market. The latest can absorb substantially higher forces and transfer them onto the nailing. Special concepts have been developed for the dimensioning of flexible surface stabilization systems for use on steep slopes in more or less homogeneous soil or heavily weathered loosened rock, but also on fissured and layered rock in which the bodies liable to break out are determined by fissure and layer surfaces. Stabilizations implemented in soil and rock, with and without vegetated face, confirm that these measures are suitable for practical application (Cała, et al. 2012). The research work presented in this paper explains the latest verification of the existing dimensioning concept for superficial slope protection system based on test results coming from a large-scale field test setup. Thereby the influence of properties of the facing as well as deformations under loading and forces on the nails are tested and the results will be presented.
Various aspects of slope stability are the subjects of study of many fields of engineering such as road and rail engineering, mining. There are numerous methods for stabilizing slopes that can be chosen depending on the scale of the occurrence, technical conditions and terrain characteristics. To enable the best possible solution it is necessary to take into consideration several variables that could impact the effectiveness of such protection. At the same time the technical and economic aspects of the proposed construction need to be taken into account. Another aspect to be considered is whether the construction is environmentally friendly. It is also important for the slope stabilization to ensure not only its global but also superficial stability.
In many cases the optimum solution is to use nailing in combination with the flexible facing systems. It ensures global stability (nailing) and protects the slope against the possible local instabilities and rockfalls. High effectiveness of such solutions was proved in the recent years’ installations.
It can be claimed that the aspects of nailing are relatively well known, whereas, in the case of slope facing there are still many questions. In order to understand better how the nailing and slope facing work together and what the role of mesh is in bearing and transferring the forces to the nailing system, first results of the full scale tests, setup and equipment that was used will be presented in this article.
The entire project is supported with CTI Swiss funds and lead by Bern University of Applied Sciences with cooperation with Geobrugg AG and AGH University of Science and Technology.
Park, H. (National Institute of Advanced Industrial Science and Technology (AIST)) | Ito, K. (National Institute of Advanced Industrial Science and Technology (AIST)) | Takahashi, M. (National Institute of Advanced Industrial Science and Technology (AIST)) | Osada, M. (Saitama University) | Smolnik, G. (Silesian University of Technology)
It is fundamental to understand the process of crack initiation and propagation of intact rock to clarify the coupled hydro-mechanical properties due to the stress change in underground. We have been working on the study of coupled shear-flow properties on sedimentary rock using pumice tuff, Japan. The changes of shear stress, normal stress, flow rate and process of fracturing on sample surface have been investigated by using a new type coupled shear-flow test apparatus. In this study, we designed a numerical model for the coupled shear-flow test using a discrete element code. We report the comparison between the experimental results and the simulation results. The porosity changes of model showed good agreement with the flow rate behavior of the test.
New fractures due to underground excavation or fault cause mechanical and hydrological problems in underground (Tsang et al., 2005, Mitchell and Faulkner, 2009). The fractures are generated through a variety of mechanisms with various scales (Bossart et al., 2002, Scholz et al., 1993). For the research of underground disposal or geological evaluation, it is necessary to investigate the coupled hydro-mechanical behavior of rock (Olsson and Barton, 2001, Li et al., 2008). We conducted an experimental study on coupled shearflow properties of sedimentary rock, and designed a numerical model for the coupled shear-flow test using a three-dimensional simulation tool, PFC3D (Particle Flow Code3D, Itasca Inc.). The purpose of this study is to examine the performance characteristics of the numerical model. The test system and model are briefly introduced, and the results are compared focusing on stress, permeability and crack propagation.
2 Particle Flow Code3D
PFC3D is classified as a discrete element code (Cundall and Strack, 1979, Potyondy and Cundall, 2004) based on the definition in the review by (Cundall and Hart, 1992). It allows finite displacements and rotations of discrete bodies (including complete detachment), and recognizes new contacts automatically as the calculation progresses. PFC3D can be considered as a simplified implementation of the DEM because of the restriction to rigid spherical particles.
A Thermo-Hydro-Mechanical (THM) model for partially saturated rocks is developed and implemented. The hypothesis of constant air pressure simplifies the equations and improves efficiency of calculation while still allowing the description of vapor flow. The implementation uses a fully coupled approach. Comparison against experimental data is performed. Results are promising, yet additional comparisons are required to fully validate the model and its implementation.
The necessity of THM modeling appeared in the nineties within the framework of nuclear wastes storage in deep geological formations. Models have then been extended to include the effects of temperature on the mechanical and the hydraulic behavior of rocks (Rutqvist et al. 2001, Collin et al. 2002). Accurate description but also the implementation of such coupled phenomena still remains a challenge. After defining a THM model for partially saturated rocks, its implementation is described then compared to experimental results. .
2 Governing Equations
In this section the governing equations of fully coupled thermo-hydro-mechanical analysis are briefly described. This is an extension to the previous work in which fully coupled hydro-mechanical analysis has been implemented (Galavi et al. 2011, Galavi 2011). Here, non-isothermal unsaturated groundwater flow, heat transport and deformation are considered. Similar to the previous work, we assume a constant gas pressure. Therefore, only one independent unknown in the fluid mass balance equation is needed which is pore water pressure. This study is based on the assumption of local thermodynamic equilibrium which means that all phases have the same temperature, i.e. only one equation of total energy is required. Consequently, the four primary variables are displacements (v), pore water pressure (pw) and temperature (T).
Kukutsch, R. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic) | Soucek, K. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic) | Konicek, P. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic) | Ptácek, J. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic) | Waclawik, P. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic) | Šnupárek, R. (Institute of Geonics, Institute of Clean Technologies, Academy of Sciences of the Czech Republic)
This paper addresses the monitoring results in the maingate No. 080 5253 at the Paskov Mine, in the Czech Republic. In the main longwall gate in question, the convergence of the mine affected by longwall mining 080 210, movement from loosening of the rock layers using extensometers, and the load steel frame construction reinforcement by dynamometers is monitored. In addition to in-situ measurements, research laboratory measurements were carried out to evaluate the influence of geological conditions, based on the RQD parameter of boreholes drilled before the extraction. The results show that geology, the character of the overlying rocks, and rock stress ratios play important roles in the effectiveness of the combined rock bolt and steel frame supports. The effective action of the reinforcements also shows significant adverse effects on floor lift, and these factors are reflected in the extension and retraction of anchors in the overburden and significant deformation of the profile.
Even with the existing knowledge and experience of underground excavation of coal seams in the difficult mining and geological conditions of the Ostrava- Karvina coal mining district (the OKR), the installation of high-capacity and high-density support systems is unable to prevent significant deformation of mining gates at large depths (c. 800–1000 m), during the mining operations (Souček et al. 2012). The originating deformations are connected with the redistribution of stresses in the rock mass due to the excavation of the coal seams and consequently, there is deformation and fracturing of the rock mass surrounding the operating longwall gates. This is the reason for the great increase in the use of various types of anchor (e.g. stranded anchors anchored along roots, rock bolts fully encapsulated in resin) Anchoring systems are used both in an independent sense (rock bolts or anchors anchored directly to the excavated surface) and in a combined sense, where:
In this paper we show how the appropriate uncertainty model to apply in an analysis depends on the nature of the available information. We explore this through the analysis of a rock slope using probabilistic models that incorporate alternative subjectively assigned probability distributions. These alternatives mimic the opinion of multiple experts. The results are shown to depend strongly on the shape of the input distributions, and hence the expert opinion utilised. We conclude by showing that an analysis using fuzzy mathematics is more appropriate than a probabilistic approach when objective data are limited or absent, and present a novel technique for decision making using the results of a fuzzy analysis.
In rock engineering, practitioners are often required to make critical decisions based on little or no objective data. This lack of information requires subjective estimation of parameters used in any analysis, and thus introduces uncertainty.
Some have suggested that even with little or no information, stochastic methods can be used to make pragmatic decisions by adopting a subjective view of probability (Aven 2010, Lindley 2000). This forms the basis of the Bayesian approach, which suggests that expert opinion can be applied to assign precise probability distributions (so-called ‘priors’) based solely on the knowledge or judgement of an expert. Within this framework, a probability distribution function (PDF) represents an expert’s subjective degree of belief in a value’s probability of occurrence. However, others argue that the subjective assignment of priors can lead to misinformed decisions and dissonance amongst experts (Ferson & Ginzburg 1996). In this paper, we investigate the latter argument via a case study on slope stability – that of the previously published Sau Mau Ping Road slope in Hong Kong (Hoek 2007).
In this paper we compare the results from Monte- Carlo simulation based on a subjectivist approach to probability and a non-probabilistic approach using fuzzy sets. We show the significant differences in design decisions that may result depending on the model adopted to characterise and propagate uncertainty.
Agan, C. (Harran University) | Yesilnacar, M.Í. (Harran University) | Genis, M. (Bülent Ecevit University) | Kulaksiz, S. (Hacettepe University) | Ulusay, R. (Hacettepe University) | Aydan, Ö. (Tokai University) | Yücel, M. D. (Aydogan Sitesi)
Geoengineering evaluation of man-made antique underground structures improves and provides important information on such structures. Harran City in Şanliurfa Province of Turkey was constructed probably during Sumerian period BC 3000 (5000 years BP). The building stones consisting of limestones of Harran City were extracted from open-pit and underground quarries known as Bazda quarries. Bazda antique underground quarry pillars suffer some structural stability problems in terms of splitting of high pillars, roof falls, plane or wedge sliding and large sinkholes. The authors have initiated a collaborative integrated research program to map the antique underground quarries having working levels up to four floor, in-situ rock characterization, identification of stability problems, some geomechanical properties of surrounding rock. This paper describes the first preliminary studies on Bazda antique underground quarries and discusses its implications in modern geomechanics and geoengineering.
The long-term performance of underground openings is of great importance for civil engineering utilization and also the nuclear waste disposal. Therefore, the geoengineering evaluation of man-made antique underground structures improves and provides important information on such structures. There are several geoengineering studies on such antique underground structures in literature. Turkey also has a number of antique underground openings, such as those in the Cappadocia Region and in Şanliurfa Province. Harran City in the Şanliurfa Province was constructed probably during Sumerian period BC 3000 (5000 years BP). The building stones of Harran City, where there is no rock outcrop, were extracted from open-pit and underground quarries in Tek-Tek Mountain and they are called as Bazda quarries, which are the oldest underground quarry known in Turkey as well as in the world. These quarries are about 7–8 km away from the city and the extracted stones are Eocene aged limestone. Stone blocks from Bazda quarries were used in the construction of Harran ancient city, the temple of Moon and Sun God and the nearby historical Hanel Ba’rür caravanserai and Şuayb City. Underground rooms in Bazda extend more than 50m and pillars are mostly in rectangular or nearly square shape. These quarries have greatest importance for both underground excavation techniques in the past as well as the long-term performance of underground mining.
Rockburst means stress induced violent ejection of rockmass in tunneling and mining. Rockmass comes off under high energy release. To determine this energy, different approaches exist, depending on different countries and regions. Rockburst phenomena mostly occur in deep tunnels and mines but also in regions, where high stress concentrations appear. A major engineering challenge for mines experiencing significant seismicity is the performance of the support systems. The development of an adequate retaining system, such as dynamic rock bolts together with high-tensile steel wire mesh and their behavior during rockburst had been tested and quantified. The special large scale test facility was constructed for that purpose. It allowed the estimation of portions of energy transmitted by rock bolts and wire mesh.
As more and more near surface deposits are mined out, deeper mines are required in order to continue the exploitation of resources. This inevitably leads to the occurrence of more rock bursting, deformation problems and safety issues. Rock burst means stress induced loosening of parts of the rock mass under enormous energy release. It seems to be similar to damage from natural seismic phenomena. Rock burst events occur mostly in deep tunnels and mines but also in regions with high horizontal stresses.
There are different methods to mitigate rock burst risks thus reducing exposure of personnel. Changes include mine design, layout and extraction sequence (Potvin 2012). In addition the ground support needs to be chosen and designed in such a way that it can cope with the conditions. In deep mines the ground support is complex and cost is high. Static ground support is not satisfactory for such a demanding environment. The ground support consists of the rock reinforcement (e.g. bolt), a surface support (e.g. mesh) and the connection between the two (e.g. plate). For dynamic loads it is essential that these components fit and work together as a system (Cala & Roth 2007). The observations of Heal (2007) show that most of the damage done from rock bursting led to the failure of the surface support or the rupture of the reinforcement.
In order to investigate the dynamic behavior of reinforcement elements and surface support, extensive testing was carried out at various test sites. Some tests were done in South Africa, Canada and Australia. Hadjigeorgiou (2011) put the results of the various tests together and tried to make them comparable. However the boundary conditions of the test sites were different making comparison difficult. There are two active test sites at the moment, one is in Canada at CANMET and the other in Australia at WASM (Player et al. 2004). The WASM test site is the best instrumented facility and is based on the momentum transfer concept. It can test reinforcement, surface support and to a certain extent combinations of the two.
Rocks are generally more or less anisotropic, depending on their structure at the scale of interest. The anisotropic rocks in civil and mining engineering projects cause non-symmetric deformation and their behaviour is unpredictable. The authors present the results of Brazilian Indirect Tensile (BIT) strength and Cracked Chevron Notched Brazilian Disc (CCNBD) tests for the determination of the fundamental tensile fracturing parameters of Brisbane phyllite specimens. In general, the influence of orientation angle (ψ) and foliation-loading angle (β) were found to influence both fracturing and the failure load.
Anisotropy is a characteristic of foliated metamorphic rock masses (gneisses, phyllites and schists), and intact stratified or bedded sedimentary rocks (coal, shales, sandstones, siltstones, limestones, etc.). At a larger scale, rock mass anisotropy is found in volcanic formations and in sedimentary formations consisting of alternating layers or beds of different rock types and in rock formations cut by one or several regularly-spaced joint sets. Since the deformation and fracture of these rocks is of importance to engineers concerned with the design of mining excavations or of foundations for civil engineering structures, it is obvious that research into the effects of anisotropy on rock behavior is necessary (Hoek, 1964; Chen & Hsu, 2001; Cho et al., 2012).
As in the case of the original Griffith criterion (Griffith, 1924), it is generally assumed that the specimen contains a sufficient number of randomly-oriented cracks for fracture to initiate from those cracks, which are inclined at an angle. If, however, the cracks are oriented preferentially, as in the case of a highly antistrophic material, it is necessary to consider the inclination of the cracks with respect to the applied stress system (Hoek, 1964). Brace (1961) presented evidence indicating that the cracks, from which fracture of the rock propagates, probably lie within the grain boundaries of the rock. Even in rocks of sedimentary origin, which exhibit marked foliation and planar anisotropy, the constituent bedding planes are made up of grains that are cemented together and hence randomly-oriented grain boundary cracks are likely to be present (Brace, 1960).
This article describes consolidated drained triaxial tests to determine the acoustic and mechanical properties of heavy oil sandstone from shallow, high-temperature boreholes in the Eastern Venezuela basin. The purpose of this laboratory campaign is to create physical correlations between rock under in-situ conditions and the severe temperatures generated during steam injection. These tests will be used for modeling the impact of Steam-Assisted Gravity Drainage (SAGD), in unconsolidated sandstones.
For most oil and gas reservoirs, temperature effects on rocks during the life of the well are incorrectly thought to have aminimal effect, compared to the effects of hydrostatic or injected fluid pressures such as from completion fluids or drilling muds. However, this is clearly not the case where steam is injected for heavy oil reservoir stimulation. In these situations there is a tremendous elevation in the bottom hole temperature, resulting in changes in the rock structure and its elastic properties and rock strength.
Thermal properties of rocks are very complex.Their thermal parameters depend on mineralogy, density, and grain size distribution in addition toporosity and permeability and static and dynamic in-situ temperature effects that include the reservoir geothermal base temperature plus induced by the enhanced oil recovery (EOR) process. Steam-assisted gravity drainage (SAGD) processes generally disturb the stress field, stress direction and rock properties. High thermal conductivity results in a wide range of temperature distribution, improving the porosity, permeability and stiffness of the rock (Rabe et al. 2008).
Among the 9–13 trillion barrels of oil that presently constitute the world oil reserves, 30% correspond to conventional oil (greater than 22.3? API), 15% to heavy oil (between 22.3 and 10? API), and 55% correspond to extra-heavy oil, bituminous sands and bitumen (Alboudwarej et al. 2006). Many thermal processes have been developed to increase the recovery factor of heavy oil and extra-heavy oil reservoirs around the world. Chalaturnyk & Li (2004) concluded that steam stimulation is one of the most successful thermal processes that can affect the rock formations. Indeed, steam stimulation can reduce the effective stresses by varying the pore pressure, inducing oil sands to shear, generating compaction or surface dilation, reducing the strength of the formation around the steam chamber and occasionally causing in rock failure.To properly evaluate the impact of geomechanics on the SAGD process in the Faja del Orinoco study area, itwas necessary to understand the rock properties and porepressure behavior, the stress state as well as the fracture gradient during steam injection to predict wellbore instability, design the casing shoe, correctly locate the well pairs and predict accurately the recovery factor as well as the volume of heavy oil that could be extracted in the studied field (Rabe et al. 2008, Perdomo et al. 2010). The purpose of this paper is to provide a fundamental geomechanical data set of the studied area to optimize and mitigate risks in SAGD projects elsewhere.
The paper deals with formulation and numerical implementation of anisotropic strength condition for micro layered rock. Periodically layered two–constituent microstructure is considered. The failure criterion of the constituents is assumed to be governed by Drucker-Prager strength condition. The macroscopic criterion is derived based on the micro-mechanics approach. It appears that a microstructure failure function can be satisfactory described by the conjunction of Jaeger critical plane condition and Pariseau anisotropic criterion. The formulation derived is then implemented into the commercial codes FLAC and FLAC3D. Numerical integration scheme, i.e. an elastic predictor and a plastic corrector of the failure function proposed are discussed in details, in the paper. Efficiency and numerical stability of the model proposed are verified against a series of numerical examples. The proposed model is also compared with “Ubiquitous Joints”: a classical Jaeger critical plane approach available in FLAC environment. The presented results show that the model in some cases provides more precise description of micro-layered rock then Jaeger criterion.
In many rocks one can recognize a characteristic pattern: two or more constituents appear in a form of thin, periodically repeating layers. These rocks are sometimes referred as “micro layered”. The microstructure especially often occurs in sedimentary rocks: sandstone, claystone and schist are the most typical examples. The main consequence of the presence of micro layers in the material is its strong anisotropy in both elastic and inelastic range.
The micro layered rocks are usually considered in civil engineering practice as a problematic case for foundations. From the other hand necessity of structures foundation in such condition continues to grow. New structures are usually designed based on numerical calculations performed with some commercial codes. Identification and implementation of adequate, numerically efficient model of micro layered rock to one of these codes is an important and complex task.
A number of researchers focused on formulating a macroscopic anisotropic strength criterion for micro layered rocks based, mainly, on a phenomenological approach. Brief review of some of these criteria is presented in a work of Duveau et al. (1997). Two of these criteria are especially worth noting, i.e. Pariseau criterion (Pariseau 1972) which is an extension for the case of anisotropy of Drucker-Prager isotropic criterion, and Jaeger criterion (Jaeger 1960) which can be interpreted as a basis of a so-called critical plane approach.
The above mentioned Jaeger criterion is implemented as yield function for one of the plastic models available in FLAC and FLAC 3D codes. The model referred as “Ubiquitous Joints” is one of the few most popular models of micro layered rock.