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Exploration, development, structural geology
Abstract Using the MTS815 Full-Digitally Servo-Controlled Rock Mechanics Testing Machine, three different types of brittle rocks retrieved at the 1870 Level of the Kafang Mine are tested in the laboratory experiments under uniaxial compression. Four different failure patterns are observed during this test. Most common failure patterns are axial splitting, V-shaped failure, X-shaped and shear failure as well. The 2-dimensional particle flow code (PFC2D) was used in the numerical simulations because of its capability in modelling the behavior of brittle rock material including fracture propagation. Contact-force distribution, crack distribution, stressโstrain response and damage patterns formed during uniaxial compression tests are observed. The parameters used in the numerical simulations are calibrated when rock parameters such as uniaxial compressive strength, elastic modulus and Poissonโs ratio, are in agreement with the experimental results. Splitting and faulting failure modes frequently observed during laboratory experiments of rocks under uniaxial compression are also reproduced in the simulations. Damage formation during the compression simulations indicated that the PFC2D modeling could simulate the events happening during the laboratory compression tests of rock samples by reproducing similar fracture generation and deformation. INTRODUCTION The study of brittle fracture process under compression is essential for understanding many processes encountered in rock engineering and earth sciences[1]. Laboratory experiments have traditionally been used as a simple and effective way to investigate the progressive failure process in rock material under uniaxial compression. Also, the failure of brittle rocks in laboratory cylindrical compression tests has been investigated by many researchers[2-6]. Meanwhile, numerical models (such as lattice model[7], bonded particle model[8-9], RFPA model based on FEM[6,10-11] and other models[12-15]) were used to model the fracture process of rock under loading. Although the failure model of rock subjected to uniaxial compression has been studied in detail for decades, the failure mechanisms, including the micro-cracks initiation, propagation, coalescence, axial splitting, shearing, etc., are not fully understand and still remain the subject of considerable scientific interest[16]. This paper presents a series of laboratory and numerical tests of different rock under uniaxial compression to investigate the fracture process. The marble, skarn and silicateous marble were chosen as the rock specimens in this study. The two dimension particle flow code (PFC2D) was chosen because of its capabilities in modelling the fracture process including fracture initiation, propagation and coalescences of rocks. Then the results from numerical simulation are presented and compared to those obtained from the laboratory tests. LABORATORY TEST Rock specimens A total of 15 rock specimens consisting of five samples from each type of marble, skarn and silicaceous marbles, were prepared for uniaxial compression tests (Fig.1). All the cylindrical rock specimens are retrieved at the 1870 Level of the Kafang Mine, Yunnan Tin Group Corporation. The marble specimens were of 50mm in diameter and 100mm in length. The skarn and silicaceous marble specimens were of 60mm in diameter and 120mm in length. The density of marble, skarn and silicaceous marble are 2.789, 3.269 and 2.817g/cm3, respectively.
A New Forecast Method of Opening Displacement And Its Engineering Application
Li, Xiaojing (Shandong Jianzhu University, Civil Engineering School) | Yang, Weimin (Shandong University, Geotechnical & Structural Engineering Research Center) | Zhu, Weishen (Shandong University, Geotechnical & Structural Engineering Research Center)
Abstract With the development of western region in China, the underground openings are built in high depth and high in-situ stress brittle rock-mass. Under these special geological conditions, opening displacement is observed during the definite range around the carven sidewall. Based on the energy dissipation and crack extending, the forecasting method of opening displacement which considers the non- continuous displacement of rock is put forward. In the end, the method is applied in the practice engineering. The forecasting result is accordant with the monitoring data preferably. INTRODUCTION The rock material is a kind of special material. There are fractures in it. The conventional analysis methods, such as like elastic, elasto-plastic, elastic-brittle and viscoelastic method, are fit for ideal isotropic and continuous material rather than rock material[1,2]. So, the rock mass displacements obtained through continuum mechanics can not reflect the real situation. In this paper, the author tried to propose a method to predict the displacements of surrounding rock mass, based on the energy analysis method. DISPLACEMENT ANALYSIS INDRUCED BY CRACK OPENING According to the stress-strain curve of brittle rock sample, the deformation before the peak point was composed by elastic deformation and crack opening deformation. Under the lower stress level, the crack closure mainly caused the axial deformation, whereas, the lateral deformation was relatively smaller. However, the deformation was heavily influenced by the crack opening under the higher stress level. It can be noticed from the whole stress-strain curve that the lateral deformation was greatly effected by the split crack more than the axial deformation. (Equation in full paper) DISPLACEMENT PREDICTION METHOD IN CONSTRUCTION SITE Displacement prediction in Erโtan underground power house was carried through by using the new empirical opening displacement formula in this section. Fig.2 showed the curve of the stress difference against the distance from side wall to intact rock mass after excavation. The stress level near the side wall was lower because of stress releasing. However, the stress was transferred to a certain range. Then it was gradually returned to the initial stress value of intact rock mass with the distance increasing from the side wall. Introducing the stress values to Eq.3.1, the corresponding crack density ratio G was obtained. (Figure in full paper) The above graph showed the displacement curves, which were elastic and considering crack propagation respectively. The max displacement was 58mm from this graph. This value was very close to the monitoring value, which was 50mm[7]. So, the displacement prediction considering crack opening was more reasonable and realistic. That was the reason that the calculated value gotten from continuum numerical analysis was always significantly different to the monitoring value. CONCLUSIONS The strain expression was derived applying the energy analysis method in compression case, in which the crack opening was taken into account. The empirical crack density function was proposed according to the experiment result. In addition, the displacement prediction method was presented considering crack opening in construction site.
- Health & Medicine > Consumer Health (0.54)
- Energy > Oil & Gas > Upstream (0.34)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.50)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.34)
Abstract A new statistical derivation system named MERKONT (Marble Control) was developed in this study for the quality control of calcareous natural stone types used as industrial marble. A new classification was made via MERKONT system by taking into consideration the porosity values of 45 different natural stones collected from different parts of Turkey. In the scope of this system, Analysis of Variance: Nested Sampling (Optional) method was used as the statistical system. Natural stones were classified into five different groups on the basis of porosity change. These natural stones were subjected to mineralogicalpetrographical analyses with the aim of examining the relationship between this classification, porosity types and checking the accuracy of porosity change limit values. In these analyses, porosity value of the very small crystalline marbles was found to be low and of the porous travertines to be considerably high. In addition, variance range and standard deviation values of each group were reflected in the quality control curve. It was concluded that variance range increased, in turn, quality decreased in parallel with the increase in porosity values of the natural stones. Introduction Marble industry is one of the most effective actors of crystalline carbonat Turkish mining industry economy. Therefore, the use of marble as a decorative facing material in structures is widespread. In general, marbles in Turkey can be classified into eight main groups. These marble groups are beiges, blacks, whites, cherry colors, pinks and greens. In addition to these groups, there are also travertine, basalt, granite and andesite varieties extracted for also construction industry. Senturk et al, [1] made a research on Turkish marbles and analyzed their characteristics from extraction to application in structures. Marble has many decorative and structural uses: it is used for outdoor sculptures and sculptural bases and it is used in exterior walls and veneers, flooring, decoration, stairways and walkways for architectural purposes. Travertine, limestone, sandstone and slate are other natural stones, which are frequently used in building applications. Travertine is a type of limestone and one of the most popular natural stones used in interior and exterior wall covering, interior and exterior paving, statuary and curbing. Limestone is widely used in buildings since it is readily available and easy to handle. Popular applications include countertops, flooring, interior and exterior wall coverings and exterior paving [2]. Marble is a metamorphic rock formed via recrystallization of limestone. Marble is metamorphic stone composed of calcite (CaCO3) and formed as a result of the re-crystallization of limestone under excessive pressure and heat. At the end of this process, a stone which has a very tight crystalline structure and low-level but definite porosity is created. Limestone is a calcareous sedimentary rock, which turns into marble due to the heat or pressure-induced (or both) metamorphosis. There are several varieties in the limestone group: calcarenite, coquina, dolomite, microcrystalline, oolitic, travertine and re-crystallized [2].
- Asia > Middle East > Turkey (1.00)
- North America (0.94)
Abstract Proper evaluation of geological conditions and stress environment are critical to ground control in underground openings. For a slope entry, the problem becomes more complicated due to the fact that the entry normally digresses through different types of strata before reaching the coal seam. Furthermore, as the depth increases, the stress level changes. Therefore, it is important to determine the stress distribution and evaluate stability of the opening along different slope sections when designing roof bolting plan and long term ground support. Over the past two years, Keystone Mining Services, LLC of Jennmar Corporation Inc. has developed a new methodology, designated as the Stress, Geologic, Support design system (SGSsm), for underground mine openings. This methodology has been successfully applied in various coal mines across USA. Through an application at an underground slope mine, this paper briefs main concepts of the methodology and details the following: (1) Geological evaluation and stress analysis along the slope utilizing numerical modeling and the identification of strong, fair, and weak sections along a slope; (2) Design of primary and supplemental bolting plans for each section along the slope. (3) Design of long term standing support in the form of steel sets based on the current industry standards by the American Institute of Steel Construction (AISC); and (4) Validation and performance evaluation of the designed steel set structure under extreme loading conditions using numerical modeling techniques. INTRODUCTION A recent increase in energy demand has resulted in a booming of U.S. coal mining industry. Some coal companies plan to develop new mines or expand existing ones. Many of these operations, especially in the Appalachia or Midwest region, access the coal seam through slope entries. Since these openings will be in service for the entire life of the operation, mining industry generally installs roof bolts after rock excavation and either steel sets or reinforced shotcrete as long-term roof support. However, ground control for mine slopes has been traditionally practiced based on trial-and-error and prior experiences. There is currently no well-accepted slope design methodology and steel set design guidelines that can help mining industry to develop an economic and technically sound ground control plan for a given mine slope entry. As a major ground control product supplier in the US, Jennmar Corporation, Inc. (Jennmar) is dedicated to providing the mining industry with advanced ground control technologies and professional engineering services. Based on prior experiences and successful cases, Keystone Mining Services, LLC (KMS) of Jennmar developed a practical ground support design methodology [1]. This method, taking into account the actual geo-technical conditions, identifies strong, fair, and weak sections along the slope, recommends primary and supplemental roof bolting plans, designs optimal steel sets for actual field conditions and engineering needs, and verifies the adequacy of the developed steel sets. The method received positive comments from mining industry and governmental agencies. Jennmar and KMS have been involved in various slope projects, and the ground control plan developed using this methodology has helped coal companies to pass the review.
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
Abstract The near surface limestones in Florida have been undergoing cycles of deposition and weathering since their formation. These processes coupled with active karstification have resulted in limestone sequences that are highly variable with respect to weathering state and thus engineering and physical properties. Core specimens of Ocala limestone with varying weathering states were tested to determine relationships between physical and index properties. Each weathering state was associated with either two or three hardness values and as weathering state increased hardness decreased. Results show there is no relationship between unit weight and weathering state but the standard deviation of the unit weight values increases as weathering state increases. In general L-type Schmidt hammer, indirect tension, and point load results increase with increasing unit weight. For weathering states of W4 and above, the Schmidt hammer test becomes a destructive test. For weathering states of W3 and above, point load testing may not be appropriate as indicated by very low Is50 values across a wide range of unit weights. 1. INTRODUCTION The Florida peninsula is extensively underlain by sequences of carbonate-evaporite bedrock. Between depositional cycles, the materials were subjected to weathering both physical and chemical weathering. The weathering produced changes in both composition and texture, including dissolution, lithification, and dolomitization. The dissolution process resulted in signification changes to rock fabric and the development of various types of pore spaces [1]. These sequences of events have produced the karst topography present throughout Florida. Weathering of surficial and near surface limestones is an on-going process. Slightly acidic rainwater infiltrates the surficial soils and dissolution occurs at the bedrock surface and within discontinuities that intersect the bedrock surface. Groundwater may also cause dissolution via preferential flow though fissure and/or bedding planes. Large infrastructure works, including freeways and bridges, are often supported by the weathered limestone. As such, it is imperative to understand how weathering affects the physical and engineering properties of the limestone. The purpose of this preliminary study is to investigate the relationships between index properties and physical properties of a weathered limestone. 2. BACKGROUND The weathering state of in-situ rock has long been a concern for design and construction. Numerous studies have been conducted on many different types of weathered rocks, mostly to determine the relationships between mechanical properties as influenced by weathering state. One such study describes the change in physical and strength properties due to weathering of granite, basalt and quartzite. The work focuses on the relationship between unconfined compressive strength and other measurement such as the point load index, the Brazilian tensile strength, and the Schmidt hammer rebound number.The relationship between compression wave velocity and uniaxial compression strength and Brazilian strength values were positive but not linear. The data also showed a positive relationship between uniaxial compressive strength, Brazilian index and point load value and the Schmidt hammer rebound number [2]. Another study investigated the inter-relationship between mechanical properties of nineteen different rock types from southern Anatolia.
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.47)
Evaluating the Present In-situ Stress-State For the Richton, MS, Strategic Petroleum Reserve Site Using Geomechanical Analyses
Rath, J.S. (Sandia National Laboratories) | Arguello, J.G. (Sandia National Laboratories) | Stone, C.M. (Sandia National Laboratories) | Sobolik, S.R. (Sandia National Laboratories)
Abstract The United States Strategic Petroleum Reserve has selected the Richton Mississippi (MS) salt dome as an oil storage site suitable to increase its current capacity to one billion barrels. In order to confirm that the Richton MS site is adequate for storage of oil deep underground, an evaluation of the present in-situ stress-state was investigated using numerical techniques involving large scale geomechanical analyses. Several Finite Element Analysis (FEA) models were constructed to approximate the complex three-dimensional Richton salt dome formation and surrounding rock in two-dimensions. These FEA models elucidated the significance of a parental salt bed which feeds the Richton salt diapir formation. Using complex creep material models to treat the near-field Richton salt diapir and elastic material models to simulate the surrounding media, the structural response of the Richton salt dome was interrogated for several geometric configurations and initial conditions. Results of these FEA simulations showed a significant difference in vertical, horizontal, and von Mises in-situ stress states, which provide valuable information as to where the salt caverns might best be located within the dome to maximize structural integrity, etc.1. INTRODUCTION1.1. Background The United States (US) Strategic Petroleum Reserve (SPR) is a large complex for stockpiling government-owned emergency crude oil. It was established in the aftermath of the 1973-74 oil embargoes. The SPR currently consists of four sites with deep underground storage caverns created in salt domes along the Texas and Louisiana Gulf Coast that store these emergency supplies of crude oil. The Richton Mississippi site is one of the SPR expansion sites available for reaching the total 1.0 billion barrel SPR capacity, as outlined by the SPR Plan [1] established in June 2007. Knowledge of the stress-state in the vicinity of the Richton Mississippi (MS) salt dome, at present, is critical to understanding the pre-excavation oil storage conditions such that mining and construction operations can be conducted.1.2. Scope Sandia National Laboratories (SNL), as scientific advisor to the Department of Energy (DOE) for the SPR, is assessing the geomechanical stability in and around the Richton, MS salt dome formation. This dome is being evaluated for the potential development of oil storage caverns. The material immediately adjacent to the Richton salt dome perimeter in the salt/non-salt interface has experienced a significant disturbance in its stress-state as the salt diapir formed over time. Results from numerical analyses (e.g., large-scale finite element model simulations) can be used to predict the geomechanical response of the salt dome prior to cavern excavation activities and thereby provide useful insight into the state-of-stress in and around its vicinity at present day. In order to assess the extent of this disturbed regime, several two-dimensional axisymmetric finite element analyses (FEA) were performed using existing near-field material property data. These FEA simulations were completed using modern sophisticated material models and utilize the most current geomechanical material property data.1.3. Objective Results from these two-dimensional (2D) FEA simulations predict, among other things, the subsidence, vertical, horizontal, and von Mises stress state in the Richton.
- Geology > Structural Geology > Tectonics > Salt Tectonics (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Government > Regional Government > North America Government > United States Government (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- North America > United States > Louisiana > Selma Field (0.89)
- North America > United States > Kansas > Rock Field (0.89)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Abstract This paper presents a model for the โplane of weaknessโ theory applied to a deviated borehole that penetrated laminated shale contains numerous bedding parallel weakness planes. Two conditions determine whether the rock fails along a weakness plane: the relative magnitude of the two normal stresses, and the angle between the borehole and the bedding plane. The model is applied to a deviated well that penetrated a tight fold in the northeastern British Columbia foothills belt in Canada. The well was associated with severe borehole failure prior to this geomechanical study. Subsequent drilling operations utilizing results of this study lead to a successful completion of the project. 1. INTRODUCTION Strength properties of bedded rocks have been known for some time. Anderson (1951) presented an early analysis of the phenomenon. Jaeger (1960) gives a thorough analysis of the various loading scenario that explain bedding failure. In particular, Jaeger includes friction in his analysis. A common way to model shear failure using Jaegerโs approach is to use the Mohr Coulomb failure model, but vary the cohesive strength and the angle of internal friction, depending on the loading relative to bedding plane inclination. The plane of weakness was introduced in the oil industry by Aadnoy (1988). In modeling highly inclined boreholes, he investigated the effects of wellbore inclination, anisotropic elastic rock properties, anisotropic stresses, and anisotropic rock strength. It was shown that under certain conditions, the rock would fail along planes of weakness. Because of the geomechanical properties of shale (common high pore pressure, alignment of phyllosilicates due to overburden diagenesis), slip surfaces may exhibit significantly more potential to fail as compared to stronger rock units, such as limestone and sandstone. For this reason, shale instability is an extremely important and potentially costly problem in many foothills drilling operations in western Canada. 2. ROCK SHEAR STRENGTH WITH A PLANE OF WEAKNESS Layered rocks such as shales often exhibit different properties along or across bedding planes. Elastic properties like bulk modulus, Youngโs modulus and Poissonโs ratio, show directional properties. The same can be concluded for compressive and tensile rock strength. Figure 1 shows compressional strength data for Arkansas sandstone. Clearly, rock strength is high when force vectors are applied at a high angle to bedding. At lower angles, on the order of 15ยฐ and 30ยฐ, stratal compressive strength is low. For this case, rock failure will occur along bedding planes. This type of rock behavior is often termed โplane of weaknessโ. Empirical data indicates that core plugs will fail along similar shear planes, despite varying confining loads. Figure 1 is a plot showing typical rock response to applied stress. However, the plane of weakness is not so pronounced, generally. Figure 2 shows strength of a Green River Shale under laboratory applied stresses. Although the minimum strength is at about 30ยฐ to bedding inclination, reduced rock strength is seen at all inclinations except a where principle compress ional stresses are parallel to bedding.
- North America > United States > Arkansas (0.25)
- North America > Canada > British Columbia (0.24)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Advances In Researches Of The Mechanical Behaviors Of Deep Bedded Salt Rocks In China
Chunhe, Yang (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics) | Yinping, Li (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics) | Feng, Chen (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics) | Xilin, Shi (State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics) | Dan'an, Qu (West-east Gas Pipeline Company)
Abstract Salt rocks are commonly utilized as the geologic host rocks for storage of gas and crude oil, and are also being considered for the disposal of radioactive waste due to its low porosity and permeability, self-recovering damage and better plastic deformation ability. The Advances in researches of the mechanical behaviors of deep bedded salt rocks in China are reviewed comprehensively. The engineering mechanical properties of bedded salt rocks were investigated for the purpose of the energy storage in deep bedded salt rocks formation. The compression tests showed that the presence of anhydrite interlayer affects strongly the deformation and failure characteristics of bedded salt rocks. A โstress dropโ phenomenon of stress-strain curves was observed for the low confining pressure cases, denoting the anhydrite layer fractures prior to salt rock. The creep tests on salt rock, anhydrite and composite rock samples implied that the steady-state creep ratio of interlayer was one order lower than that of the salt rock. The creep deformation of surrounding rocks of storage cavern will be controlled by the salt rock layer, while the anhydrite layers will restrict the longterm volume shrinkage. For investigation the mechanical properties of the interfaces between anhydrite and salt rock, the direct shear tests, Brazilian disk tests and SEM tests were carried out. These experiments showed that the interfaces between anhydrite and salt rock are bonded perfectly and are not a weak one as expected. This unique property of the bedded salt rocks would benefit greatly the sealability and stability of the energy storage caverns in bedded salt rocks. Finally, the Cosserat-like medium constitutive theory and its applications to the stability analysis of the salt caverns in bedded salt rock formation were introduced. INTRODUCTION The main characteristic of the salt rocks in China is that it is usually composed by many thin salt layers and interlayers (e.g. anhydrite, mudstone, and glauberite etc.) alternatively [1, 2]. However, the theories suitable for the analysis of the stability and security of storage in such bedded salt rocks are lack so far. Following a brief introduction about the researches on salt rocks, this paper mainly introduces some recent advances of the study on mechanical characteristics of the bedded salt rocks in China. The static and dynamic mechanical characteristics, and creep characteristics of the salt rocks have been studied by Hunsche et al. [3-5], Skrotzki [6], Wu et al. [7,8], and Yang et al. [9-12]. The Cosserat theory, in which the local bending effects caused by discontinuity surfaces can be taken into account, was imbedded into the finite element software or the finite difference software [13- 16]. The anisotropic characteristics have been studied by carrying out a series of model tests of the bedded rocks [17]. Recently, aiming at the bedded salt rocks in Yunying Salt Mine in Hubei province, the uniaxial and triaxial compression tests of three typical kinds of samples (salt rock, anhydrite, and rock salt containing anhydrite) were carried out by Li et al. [1], Liang et al. [18], and Liu et al. [19].
- Geology > Mineral > Sulfate > Anhydrite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Halide (0.80)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.89)
- Well Drilling > Wellbore Design > Wellbore integrity (0.56)
- Reservoir Description and Dynamics > Storage Reservoir Engineering > Natural gas storage (0.55)
Abstract The paper reports a monitoring and computation experience related to geotechnical evaluations on a landslide which developed in a sector of an open pit talc mine. The lithology, rock mass structure and groundwater conditions at the mine site are quite complex and their interaction with the open pit exploitation operations have triggered the landslide. As shown from topographic and inclinometric measurements obtained from the monitoring network, the failure prevailingly develops inside the loose and weathered, near surface, micaschist and likely consists of overlapping movement surfaces, of which one reaches a depth of 20m, but some sub-cm displacements also appear even after a depth of 50m. The results from FEM based SR analyses confirm the role of the different rock mass lithologies and fault zones and their strength on the landslide failure mechanism and size. The open pit slope scheme, although highly simplified, allows a suitable simulation to be made of the adverse effects of the groundwater level and of a further hypothesized lowering of the open pit toe on the development of the slope failure. 1. INTRODUCTION Instabilities and landslides of various sizes and complexity are not uncommon in open pit mines [e.g.: 1, 2, 3]. Singling out these phenomena and the evaluation of the unstable potential they have is relevant for the feasibility and profitability assessments of the industrial mine plan and above all for the safety of the mine operations. Furthermore, the recognition of widespread instability phenomena could suggest a modification of the mining technique, as in this case, where a possible transition from open pit to underground exploitation has been considered. For a consistent evaluation of the interaction that difficult ground condition and relevant instability phenomena have on the exploitation of an ore body, as well as on the construction of large geoengineering structures, an important activity of site exploration, monitoring, and geomechanical analysis is required to characterize the rock mass at a large scale [4], in order to recognize the behaviour of the excavations made to exploit the mineable resource. The most significant features relevant to the characterization and stability of open pit mines, as recognized by many Authors [e.g.: 1, 2, 5, 6, 7, 8], include the geological origin, structure, rock type, hydrogeology, site condition of the mined rock mass, along with the broad context of the mining operation which includes the in situ monitoring plan and geomechanical stability evaluations. According to these guidelines, the proposed case study summarizes the aspects of the geostructural and geomechanical characterization for a stability evaluation of a mined slope, where the monitoring was designed to detect the deformation trend of the open pit slope in the unstable sector while the monitoring results, the FEM models and computations were used to evaluate the possible effect played by the rock mass structure, water condition and excavation on the behaviour of the slope. 2. GENERAL SETTING OF THE MINE SITE Talc and Mg-chlorite mineralisations represent a valuable resource of the mining industry in Sardinia and exploration.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.34)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.69)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.87)
Is Thermal Fatigue a Possible Mechanism For Failures of Some Rock Slopes In Rio De Janeiro, Brazil?
Vargas, E.A. (Dept. of Civil Engineering, Catholic University) | Chavez, E. (Dept of Civil Engineering , Catholic University) | Gusmao, L. (Dept of Electrical Engineering, Catholic University) | Amaral, C. (Dept. Civil Engineering, Catholic University/ Geology Dept. State University of Rio de Janeiro)
Abstract It has been observed along the years that a number of failures in rock slopes in areas of Rio de Janeiro, Brazil occurs in relatively dry periods when little, if any, rain fell. The present paper describes these events and proposes possible mechanisms for their occurrence. It is believed that daily fluctuations in temperature may create thermally induced stresses of magnitude enough to propagate cracks already existing in the rock mass. The paper presents data obtained from laboratory experiments and numerical analysis to verify the proposed mechanisms. 1. INTRODUCTION In Rio de Janeiro there exists a considerable number of very steep man-made cuts. Frequently, the areas at the slope foot and along its top are occupied by a large number of extremely vulnerable houses. In these areas, small volume rockfalls are frequent and are able to produce serious material and human consequences. From 1993 onwards, the number of rock slabs falling from the face of cut slopes or simply rolling down is rapidly increasing on the increase [1]. Slab detachments from abandoned quarry faces, for example, already represent 8% of the occurrences reported in the Local Landslide Inventory. Taking into account that it is virtually impossible to undertake stabilization or to remove all the critical slabs, the Geotechnical Control Office of the Rio de Janeiro Municipality (GEORio for short) has already changed its rockfall risk management procedure. Today, instead of fixing the slabs, GEO-Rio is removing the first line of vulnerable houses and then constructing an impact wall at the site. However, some questions concerning the causes of such movements and their failure mechanisms remain unanswered. This paper focuses on the possibility that daily temperature fluctuations could be influencing the failure mechanisms of rock raveling in Rio de Janeiro. For that purpose, research program consisting of both experimental and numerical analysis work was established. The paper reports on the findings of this research program at the present stage. 2. GEOLOGICAL/GEOTECHNICAL PROPERTIES OF ROCK HORIZONS IN RIO DE JANEIRO A sequence of highly metamorphosed pre-Cambrian rocks lately intruded by Mesozoic diabase dikes and tertiary alkaline rocks compose the bedrock geology of Rio de Janeiro. The most common lithologies are porphyritic to fine-grained gneisses and coarse granites, which have been folded and deeply affected by normal faults, the major structural trends being NE-SW and NW-SE. Alone, the three sets of vertical tectonic joints associated to these large structures, particularly due to their low mean spacing (0.1-4m), could be recognized as sufficient for imposing a high degree of fracturing in any rock slope. However, in the rock escarpments of Rio de Janeiro, another geological feature contributes even more to the great variety of geomechanical properties of rock horizons. Widespread and conspicuous sheet jointing system with extreme varying properties, e.g. 5- 10mm opening; 0,2-5m spacing; random attitude and high continuity, combines with the tectonic jointing to build up rock masses with intense compartmentation. Together they tend to form large unstable in situ rock boulders with an average volume of 4m3.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type (0.89)
- Data Science & Engineering Analytics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.54)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.35)
- Well Drilling > Wellbore Design > Wellbore integrity (0.34)