ABSTRACT: Physical and mechanical properties of a lithology can be heterogeneous for every points in near distance. The random data in the universe has its typical distribution function, so it is afraid that the data normalization process will not represent the real condition of the material in the field. The present study aims to determine the typical distribution (normal, uniform, triangular, lognormal) of geotechnical parameters: wet density, cohesion, and angle of internal friction of the well GT-1, GT-2, and GT-3 in Kungkilang Block, South Sumatera. The distribution function determination of the parameters calculated and estimated in @Risk7 using Monte Carlo method for the sampling process and Kolmogorov-Smirnov for the fitting process. Ultimately, from @Risk7 calculation resulted that all parameters have a normal distribution function. Furthermore, the stability analyses using Geotudio2007 has FS 1.829 and PF 14.77% for 30 m of height of slope and 37 degree of angle of slope.
The concepts of risk and uncertainty are familiar to geotechnical engineers in geotechnical engineering practice, uncertainty about the subsoil stratification is often the major issue (Wu 2009) Probability is such kind of method to solve problems related to a random data. Recently uncertainties and risks should be expressed in the language of probability and that calculations of risk should be based on inferences made using statistics (Baecher & Christian 2003). The mechanical structure of rock presents several different appearances, depending upon the scale and the detail with which it is studied (Jaeger et al 2007) Regarding geotechnical parameters as a random data for the decision-making related to slope stability expected can approach its original condition in the field. As usual the random data must be normalized using statistical process sequences. While the process of transformation is running to normalize the data, removal process is sometimes considered for the irrelevant data. Normalized all random data cannot be done in every condition, whereas the data in the universe has its typical distribution function.
1.2 Purposes and objectives
A slope stability problem is a statically indeterminate problem, and there are different methods of analyses available to the engineers, by far, most engineers still use the limit equilibrium method with which they are familiar (Cheng & Lau 2008) Furthermore, from this paper will estimate the probability of slope stability, also called Probability of Failure (PF). Determining the distribution function of all parameters must be processed before calculating and estimating Probability of Failure (Muhamad 2015). Ultimately we will get the distribution function of Safety Factor (SF) from the slope and also can estimate the most influential parameter for the stability of slopes from the sensitivity analysis.
ABSTRACT: To investigate the influences of angle between foliation and loading direction on mechanical characteristics for the late-Paleozoic to Mesozoic Takkiri gneiss, this study samples rock specimens from seven inclined boreholes and two vertical boreholes at Bruwan, Hualien, in eastern Taiwan. A series of laboratory tests on gneiss specimens with seven distinct angles between foliation and loadng direction are performed. Experimental results show that these samples have consistent physical indices. Their porosity, water absorption, specific gravity and density change insignificant with a deviation less than 1%. Their uniaxial compressive strength range 58.880.8 MPa and vary limited with the angles between foliation and loading direction, indicating insignificant anisotropy in their strength. However, the wave velocity of these specimens are in the range of 2003-4080 m/s, which obviously change with the angles between foliation and loading direction. Additionally, the measured strains at the specimens reaching peak stress, i.e., the failure strain, are in the range of 0.10-0.45%, with obvious variation in Young’s modulus of these specimens, revealing significantly anisotropic deformation. The Takkiri gneiss has different anisotropic characteristics in their strength and deformation behavior.
Out of the three generic categories of rocks, meta-morphic rocks usually display the highest degree of anisotropy (Ramamurthy 1993). Anisotropic rocks have their mechanical, deformational, and permeable characteristics varying with direction, differing from those of isotropic engineering materials and conventional models used in analysis and design tasks. Therefore, the influence of anisotropy must be considered in design and construction of rock engineering, such as rock tunneling and slope engineering (Wang & Huang 2014). Which is also a long-standing issues in rock engineering, beginning in the early developmental stage of rock mechanics (Amadei 1983, 1996).
Taking the late-Paleozoic to Mesozoic Takkiri gneiss as an example which is one of the eldest rocks in Taiwan, this study investigates the anisotropic characteristics experimentally. Specimens with seven different angles between foliations and loading directions are prepared and tested. Their physical indices, uniaxial compressive strength and mechanical parameters obtained through triaxial compressive tests are determined. The influence of angles between foliations and loading directions, and possible mechanism are discussed.
ABSTRACT: New modifications of the optical scanning technique provide non-contact measurements of rock thermal conductivity and volumetric heat capacity on full-size core samples, core plugs, broken cores and other types of rock samples. Data on formation heterogeneity and anisotropy and rock structure and texture can be obtained from continuous non-contact thermal core logging developed that allows to characterize heterogeneity and structural-textural peculiarities of rocks with a spatial resolution of 0.2-1 mm. Principal axes of thermal anisotropy can be established from several non-parallel optical scannings.Thermal scanning presents information for a reasonable selection of rock samples for following measurements of geomechanical characteristics. The implementation of the technique opens wide possibilities in rock mechanics and rock engineering, because continuously measured thermal properties, and data on heterogeneity and anisotropy reflect variations in rock fabric and composition that also drive the variability of geomechanical properties. Observed correlations between the rock thermal and geomechanical properties confirm that.
Reliable data on rock thermal properties are required when the heat transport is considered jointly with other phenomena in mining, geotechnical, civil and underground engineering, in environmental sensitive projects such as disposal of high-level radioactive waste in deep underground sites and repositories, various engineering projects such as the design and installation of buried high-voltage power cables, oil and gas pipe lines, and other ground modification techniques employing heating and freezing.
The optical scanning (OS) approach and first version of corresponding measuring instrument were developed in 1980s and 1990s for simultaneous determination of thermal conductivity (TC) and thermal diffusivity (TD) (hence volumetric heat capacity (VHC) also) within one experiment (Popov 1997). The noncontact character of the OS measurements removed the influence of thermal resistance between the rock sample and the heater and sensors that results in (1) absence of problems with uncertain quality of the measurements, and (2) absence of requirement for careful mechanical treatment of rock samples under study. The OS technique has also provided continuous profiling thermal properties and thermal heterogeneity of rock samples with flat or cylindrical surface and along the entire scanning line length that allows investigating thermal heterogeneity related to the structural and textural characteristics of rocks. Other important characteristics of the OS method are as follows: (1) absence of contact between the instrument components and the rock sample, (2) ability to measure on full size core, split core, broken core with one smooth surface and core plugs without any additional mechanical treatment, (3) ability to determine TC and TD anisotropy tensor components for every rock sample studied, (4) high speed of operation and short measuring time, (5) flexibility in spatial resolution and penetration depth of measurements by changing the scanning velocity and heater-sensor separation, (8) wide range of sample lengths accommodated. At the same time, necessity to coat the surfaces of the rock samples with a paint restricted the OS technique application as penetration of the paint into rock fractures and pores changing rock properties. Additionally, the OS technique should be adapted to continuous profiling on full size cores for development of the thermal core logging that did not exist until now. It was established also that spatial resolution of thermal heterogeneity profiling should be improved for some OS applications and minimum dimensions of rock samples under study should be reduced to provide the measurements on standard core plugs (1 × 1”) and small pieces of broken cores with a length of 7-8 mm and more. Unique possibilities of the OS technique should be used to help in study of other rock physical properties.
ABSTRACT: The degradation of rocks and associated structural instability problems is a severe problem in preserving the many historical structures in Cappadocia region of Turkey. The well-known causes of degradation are wind, rain, cyclic wetting and drying as well freezing-thawing processes. However, the degradation may also be assumed to be related to biological causes. The authors collected some tuff samples from several historical sites at Cappadocia, Turkey and investigated the existence and type of bacteria in tuff samples. In addition, some needle penetration experiments carried out on samples. The authors present the outcomes of this investigation on the effect of biological degradation of tuff samples from Cappadocia region and discuss its implications.
There are many antique and modern rock structures in Cappadocia Region and they are rare rock structures excavated by mankind. The history of excavation of the underground structures may be more than 2500 years on the basis of archeological evidences. These underground structures in Cappadocia have been excavated in tuffs as they have large spacing of discontinuities and are easily carved. These structures recently suffer some stability problems due to weathering and degradation of surrounding rock due to commonly well-accepted causes of wind, rain, cyclic wetting and drying as well freezing-thawing processes.
There are some new considerations on the degradation of rocks in geo-science and geo-engineering. This degradation is assumed to be related to biological causes. Although the degradation and further fracturing of rocks by the plants and roots of trees are well known, bacteria may be another yet very important cause of degradation of rocks.
The authors collected four tuff samples from several historical sites and investigated the existence and type of bacteria existing in tuff samples. Some index tests also carried out on the samples. This study is probably the first attempt to evaluate the effect of biological degradation of tuff samples from Cappadocia region. The authors describe the outcomes of this investigation and discuss its implications on the longterm performance and stability of historical structures in the region.
ABSTRACT: The aim of this paper is to study the mechanical behavior of a real pillar located in an abandoned gypsum mine in San Lazzaro di Savena (Bologna, Italy) through numerical simulations using a continuum to discontinuum hybrid approach. Continuum numerical simulations based on a Mohr-Coulomb constitutive model cannot represent the observed failure mechanism and estimated limit strength of mine pillars, supporting the need to properly account for their real 3D geometry and rock mass structure. A hybrid 3D FEM/DEM method has been applied to obtain a more realistic mechanical response of a gypsum pillar subjected to a vertical uniaxial load.
The analysis of the mechanical response, failure mechanism and limit strength of mine pillars is a key point for the risk management in underground mine operation and decommissioning. Nevertheless, these analyses are usually performed through oversimplified approaches which do not take into account real 3D geometry and rock mass structure.
The aim of this work is to study the behavior of a real pillar located in an abandoned gypsum mine in San Lazzaro di Savena (Bologna) through numerical simulations using a continuum to discontinuum approach.
The 3D geometry of the pillar has been reconstructed by close-range terrestrial laser scanning (TLS). Structural analyses of the TLS point cloud and detailed field discontinuity surveys allowed the characterization of the pre-existing rock joints. Intact rock mechanical properties have been also evaluated through extensive laboratory testing.
The complex 3D geometry and structural pattern of the pillar suggest to go beyond a typical continuum approach. Thus, a hybrid FEM/DEM method, which allows the transition from continuum to discontinuum through the simulation of cracks nucleation and propagation, has been used. By means of a specific numerical code (ELFEN), the pillar behavior has been simulated from the laboratory test scale to the real in situ scale and geometry. The constitutive model, integrating Rotating Crack Model and Mohr Coulomb failure loci, was calibrated on the laboratory experimental results and in situ observation of real failure crack patterns.
ABSTRACT: Magdalena Colliery is experiencing guttering related fall of ground incidences at some locations that are causing production disruptions and safety concerns. This paper investigates the possible reason(s) behind guttering by taking into account the rolling nature of the coal seam, roof lithology and the cutting direction of the continuous miner. Laboratory strength testing on shale in the immediate roof was done and the test results were used as input parameters into the Examine2D modelling. The numerical modelling results were analysed in an attempt to correlate the modelling results to the guttering locations experienced at the mine. The investigation results suggested that the rolling nature of roof lithology and the sensitivity of the shale layer to water could be possible reasons for guttering. The cutting of the shale layer by continuous miner should also be avoided.
Stress equilibrium exists in all virgin stress environments and the removal rock due to mining results in the redistribution of stresses along the periphery of excavations. Depending on the magnitude of post mining stresses and the strength of the rock mass the stability concerns may arise. Roof guttering is one of the concerns that has been noted as a result of high horizontal stresses inherent with a particular stress grid (Ndlovu & Stacey 2007).
A unique feature of the observed gutters at Magdalena Colliery is their asymmetrical occurrence within the excavated bord of the mechanized bord and pillar operation. An intriguing note is that guttering has only been identified on one side of the bord within affected areas of the mine.
A fundamental note is that the identified roof gutters have resulted in fall of ground incidences which are a safety risk to personnel and extend to being a constraint to production.
Any mining induced void in the rock causes a different state of stresses and induces deformation or displacement of the rock surrounding an excavation. The magnitude of such displacements, amongst other factors, are influenced by the new state of stress, the nature of rock surrounding the excavation, excavation size, and geological features.
In an effort to provide a conclusive understanding of the roof guttering phenomena present at the colliery, it is necessary to take note of the characteristics of the lithological constituents included in the roof. In order to assist the understanding of gutters, a mine-wide borehole profile is shown in Figure 1. A high level of seam undulations exists within the colliery as shown in the Figure 1. The seam undulations make the in-seam mining difficult. They often result in the contamination of the extracted coal at the colliery.
Houshmand, N. (Amirkabir University of Technology (Tehran Polytechnic)) | Shahriar, K. (Amirkabir University of Technology (Tehran Polytechnic)) | Khezri, S. E. (Amirkabir University of Technology (Tehran Polytechnic))
ABSTRACT: Caverns are underground superstructures which their popularity has been increased due to their various and strategic applications, numerous advantages such as low initial and operating costs, and free form designing. The case study in this paper is done on pumped storage cavern in Rudbar, Lorestan, Iran. In this area a power station pumped storage is under construction which has a main cavern with dimensions of 26.8 × 50 × 130.5 meters for width, height and length respectively. The geomechanical data of this cavern was analyzed with empirical method (RMR). Although, implementing this method provides a good outline to the task; but it cannot be an exact method for a definite statement. Therefore, the structural analysis was done through numerical modellings. Comparing empirical and numerical methods implies that numerical results are more reliable. However, proposing a supporting system depends on more factors such as financial issues, construction utilization time and application, etc.
Stress in homogeneous and isotropic rock tunnels and tunnels with specific geometric shape following Kirsh (1898) and after his pioneering research scholars such as Love (1927), Muskelishvili (1953) and Savin (1961) which suggested closed form depending on the drilling of various shapes elastic plates are provided as well known. But most of the underground excavations, have irregular shapes. The first step in designing a space is underground exploratory studies.
Then based on data collected from exploratory studies, project characteristics, including cross-sectional shape, type and number of equipment support and monitoring system, cavern is determined. The most common cross-sectional shape for cavern, arched ceiling and a cross-sectional vertical side walls. But in weaker rocks and high tensions often oval crosssection (horseshoe) can be used. In designing tunnel supports, the RMR rock mass classification system have been employed by many researchers and have gained a universal acceptance (Barton 2002, Ramamurthy 2004, Hoek & Diederichs 2006). In recent years this hypothesis was proposed that in designing of an underground superstructure only numerical studies is not enough to reach a decision, but combination of both numerical and empirical studies could lead to a well decision. Empirical methods do not provide the stress distributions and deformations around the cavern (Gurocak et al. 2007). A power station pumped storage in Rudbar, Lorestan is under construction which has a main cavern with dimensions of 26.8 × 50 × 130.5 meters for width, height and length respectively. The minimum and maximum overburden in the range of cavern are 410 and 460 meters respectively. Due to the problems of water leakage dam reservoir, transformer cavern in the upper level of the power station cavern is allocated. According to the existing plan, the cavern is located lateral about 44 meters and altitudinal about 42 meters away from the power station.
ABSTRACT: This paper attempts to provide a theoretical framework for the determination of the stress state induced in a hollow cylinder (ring) under Hertzian compressions on its outer boundary. The solution is obtained using Airy stress functions, Michell-Fourier series expansions and Fourier-Bessel series expressions in polar coordinates. Parametric studies are also performed to investigate the influence of the loading angle and the geometrical aspect ratio of the ring on the induced stress tensor.
Among the various mechanical parameters needed in rock mechanics, accurate estimation of the tensile strength is critical since rock-like geo- and construction materials are much weaker in tension than compression or shear. The direct uniaxial pulling test (DPT), the split cylinder test also refereed as the Brazilian test (BT), the point load strength test (PLST), and lateral compression of a thin disc with concentric holes (also known as the ring test), are among the well-accepted techniques used to obtain a measure of the tensile strength of brittle rocks and pavement materials (Jaeger 1966). The DPT is theoretically the simplest test method, but is difficult to carry out in practice with geo-materials (Liao et al. 1997). The Brazilian test involves splitting a disc loaded by a compressive line load that generates a tensile stress inside the disc causing failure. However, it has long been evident that the concentration of shear stresses that develop in the vicinity of the contacts can often interfere with the tensile breakage of the disc, through the formation of inverse shear conical plugs and multiple cracking (Hobbs 1964). In harder materials, it has also been shown that following strictly the standard Brazilian test methodology is almost impractical (Serati et al. 2015). Deviations from the standard test methodology with hard and stiff materials arise mainly from the violation of the accepted boundary conditions in the Brazilian test, e.g. three-dimensional stresses are developed in the contact regions (Serati 2014). In the case of the PLST, the available relationships correlating the strength index measured in this test with the tensile strength of the rock are generally either empirical or controlled by the characteristics of the rock, and thus cannot be accepted as universal and fundamental (Broch & Franklin 1972). The ring test, initially suggested by Ripperger and Davids (1947), has attracted more recent attention by investigators mainly for its ease of sample preparation and its unique breakage mechanism in pure tension. Unlike the Brazilian test, in which the tensile rupture initiates at the centre of the solid disc in a biaxial stress field condition, failure in pure tension initiates away from the loading platens at the boundaries of the inner hole in the ring test (points m in Fig. 1). Unwanted shear effects and premature local fractures commonly reported in other mentioned techniques can also be controlled in the ring test by suitably choosing the hole size (Hudson 1969). Among many contributions to the theoretical study of the stresses induced inside the ring, are the work of Hobbs (1965), Jaeger & Hoskins (1966), Timoshenko & Goodier (1969), Mellor & Ivor (1971), Ma (1994) and Kourkoulis & Markides (2014). Other works includes that of Pilkey (2008) and Vullo (2014), covering both theoretical and experimental results. However, despite it being proven that the actual loading condition transmitted at the ring-platen interface follows an ellipsoidal (Hertzian) distribution, the available theoretical solutions (including the author’s previous research) are substantially limited by the contact stresses being simplified as either point (line) forces, uniform radial stresses or a parabolic distribution (Johnson 1987, Kourkoulis & Markides 2014, Serati & Williams 2015). This study attempts to eliminate this limitation by investigating the induced stress field when the ring is under the influence of Hertzian radial compressive stresses at the contacts. The assumed Hertzian loading on the perimeter of the ring is expected to provide a more realistic boundary condition than other contact distributions adopted in previous studies (Fig. 2). To pursue these objectives, boundary conditions are first introduced by means of a Fourier-Bessel expansion, and Michell’s stress functions in the form of a Fourier series are then employed to derive the stress tensor.
ABSTRACT: The paper deals with the total load-bearing capacity of steel arch yielding supports of roadways which is inevitable for design of the roadway support. The authors compared results of a finite element (FE) model they developed with results of experimental tests of steel arch supports in laboratory. Computer modelling of the load-bearing capacity of the steel arch support was performed using the massively scalable strongly nonlinear solver MARC. The finite element models of the arch supports and stirrups were created and assembled according to drawings without shape simplification. An experimental investigation was realized in the Laboratory of Mechanical Devices Testing at GIG Katowice. The computer model of the steel arch support captures very well the strength and deformation behaviour of the arch support. The value of the loading capacity of the yielding arch supports at the moment of first slip represents with sufficient accuracy the total load-bearing capacity of arch supports at the specified loading conditions. The mathematical modelling facilitates reliable parametric studies of the steel arch support’s total load bearing capacity from the viewpoint of construction, shape, material, optimal yielding connections and a scheme of loading.
Design of steel arch support of roadways is important in coal and ore mining and also tunnelling (small size galleries). Geomechanical methods based on empirical and analytical procedures (mostly in coal mining – Junker 2009) and static calculations (in underground engineering) facilitate to specify a loading of support constructions. The assessment of real load-bearing capacity of rigid or yielding steel arch support is necessary for optimal design.
2 THE TOTAL LOAD-BEARING CAPACITY OF YIELDING STEEL ARCH SUPPORT
The total bearing capacity of the support frame is ultimate sum of external forces in the moment of the first slip in yielding joints or non-elastic deformation of some support segment. The ultimate bearing capacity of arch supports depends not only on the construction (it means size, material, construction of yielding joints etc.)
The bearing capacity of steel arch supports is also affected by the way of loading and the quality of a contact of the support with the surrounding rock. Laboratory testing of steel arch supports on big hydraulic frames (which have recently become available in the Central Mining Institute Katowice, Poland and DMT Essen, Germany) gives real data on the behaviour and load-bearing capacity of support constructions. Experimental measurements are significantly expensive and time-consuming and we tried to use computer modelling the task by FEM (Finite Element Method). Methods of computer modelling, with efficient programs, are becoming recognised as suitable for comparison of different constructions of roadway supports under various loadings. Modelling of a whole yielding support construction is exacting and also demands verification based on testing results. The authors here present results from both testing and computer modelling of the standard four-segment steel arch support of roadways.
ABSTRACT:An enriched finite element procedure is proposed for formulating interaction of steel rock bolt along with multiple joints in a rock mass. This numerical method involves analysis of bolt behavior with varying joint dip angle, bolt angle, joint-bolt-grout properties in extended finite element platform. This paper presents the procedures and derivation of stiffness matrices of the bolt crossing multiple joints (BCMJ) at any arbitrary orientation. Multiple joints and a bolt can intersect an element enriching nodal degrees of freedom. In this case, constitutive model of rock, rock-joint rock-bolt and joint-bolt are incorporated into the formulation of stiffness matrix. The proposed method is implemented using 3-noded triangular elements and can be upgraded for higher order elements. This procedure is then applied to evaluate the behavior of a bolted joint sample under direct shear test. The method is also applied to analyze reinforced circular tunnel made in rock mass having multiple intersecting joints at different orientations. The results in terms of displacements and stresses are compared with unbolted rock mass model. The proposed method shows the efficacy of enriched finite element method for incorporating discrete discontinuities and rock bolts in finite element platform.
Rock mass in general contains large number of joint sets, strength of which is characterized by the joint spacing, aperture, joint fill strength and intact rock strength. In underground excavations and sometimes open pit slopes, rock bolt is widely used primary support system to stabilize the rock mass. Accurately modelling the rock bolt in rock mass is complex if interaction behaviour between rock, joint and bolt are to be considered. In general, rock bolt reinforces rockmass through restraining deformation within rock mass (Li & Stillborg 1999) and reduces the yield region around the excavation boundary. For a fully grouted passive rock bolt installed in a deformable rock mass, the axial load distribution along the bolt length indicates a neutral point where the shear stress at the interface between the bolt and grout material vanishes. Closed form elasto-plastic analytical solution of grouted bolt around a circular tunnel have been presented by many researchers (Stille et al. 1989, Cai et al. 2004, Carranza-Torres 2009, Osgoui & Oreste 2010). Modelling of rock bolt in jointed rock mass becomes a challenging task if complex mechanisms of rock bolt behaviour and dowel effects due to joint crossing bolt are taken into consideration. A three dimensional elasto-viscoplastic constitutive model has been derived to take special attention of bolt behaviour at a joint (Chen & Egger 1999).