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Abstract Available measurements of elastic moduli in Copenhagen limestone include several series of field and laboratory tests, corresponding measurements of the sound velocities on laboratory specimens and VSP measurements in the field. A comparative analysis of the results has been conducted. The work is aiming at determining the scaling factors between the moduli obtained on small samples and the moduli for the limestone mass, applicable on the field scale. The interpreted elastic moduli are presented in relation to degree of induration where available, and considering the data set as a whole. Observed variations and scaling between various tests are discussed. Efforts are made to describe the locus of gathered data, as well as the regularity of change of the elastic moduli with respect to the observed and inferred strain level. The article finally lists pitfalls and challenges when evaluating various field and laboratory tests. 1. Introduction 1.1 General background Existence of a scale difference between laboratory and field tests iswell established in scientific and engineering practice. The scaling factor is material specific. In geotechnics, it is often also site-specific, due to variation of depositional, loading and erosional histories. Determining the scale factor, however, demands large sets of data, which are rarely available. As outlined by Clayton (2011), the fact that the data from several tests need to be combined, makes this evaluation likely to be feasible only for major projects. It is therefore of significance to present the data gathered for the Copenhagen Limestone in connection with the construction of the Copenhagen City Ring metro. A comprehensive overview of the history and practice of the small strain stiffness measurements and evaluations for various soils and soft rocks has been presented by Clayton (2011). The current work is based on evaluated drained elastic parameters. However, the following assumptions are considered for the sake of simplicity:
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation > Scaling methods (0.40)
- Reservoir Description and Dynamics > Reservoir Characterization > Near-well and vertical seismic profiles (0.36)
Abstract The aim of this paper are relations between the static (Est) and dynamic (Ed) modulus of elasticity of geologically recognized rocks: fine laminated, compacted silty clay-shales from a depth range 3 to 4 km. The rocks samples were subjected to triaxial compression under confining pressure varying from 5 to 100MPa and temperature 25 to 93°C. The tests were performed on the high-capacity MTS-815 Rock Test System using a thermo-pressure cell and especially designed equipment for the simultaneous ultrasonic wave measurements. The triaxial compression tests shown that the accuracy of the correlations between parameters of elasticity developing under static and dynamic load, is affected by several factors. One of the most important is lack of integrity in detection of a rock structure failure monitored by both methods. An elasticwave may indicate a failure condition of a rock structure with advance or delay, in respect to the stress at the absolute dilatancy threshold, depending on a rock lithology. The non-integrity growths with growing rigidity of the rock. Consequently, with the increase of the non-integrity the discrepancies between Est/Ed increases. An important role plays also anisotropy of tested rocks, which increases incoherence between the static and dynamic data. Despite affecting their directional, laminar compaction, the anisotropy cause directional microcracks distribution at the early stage of structure damaging. Hence, the detection of a true range of the rock elasticity state by static and dynamic measurement becomes more inconsistent. In a result, the matching of the Est/Ed is poorer than the correlation Est with an initial longitudinal wave velocity (Vp0) measured at a stable conditions of confining pressure and temperature. 1. Introduction At great depths, where direct detection of rocks geomechanical parameters is difficult, an evaluation of a stress-strain features of rock masses is mostly basing on geophysical data regarding measurable parameters of elastic wave propagation and rock density. But, the geomechanical rock parameters determined by remote geophysical methods are not very reliable since the essential data of a rock mass lithology, heterogeneity and anisotropy are unknown. Therefore, the best way for improving the quality of geomechanical data on rocks at the high depth, is by correlating the geophysical dynamic parameters with their geomechanical, static equivalents in laboratory tests. The tests should be performed under modelled high pressure and temperature of rocks with precisely identified geological properties (Mogi 1977, Li 1986, Carmichael 1990, Hood & Brown 1999, Barton 2000, Pinińska 2007, Karato 2008). Such laboratory tests are good alternative to time-consuming and expensive in situ testing in underground research laboratories (Martin et al. 1990, Martin & Simmons 1992, Piquet 2001).
- Europe (0.69)
- North America > United States (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.65)
- Geology > Mineral > Silicate > Phyllosilicate (0.63)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.90)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.90)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.75)
Abstract In order to determine relevant post-yield parameters for behaviour modelling applications, accurate estimates of irrecoverable strains from laboratory tests are required. In this study, samples of Blanco Mera granite were tested using a large number of loading-unloading cycles prior to the attainment of peak strength to allow for the determination of irrecoverable strains. Two different strain-measurement setups were tested for comparison. The irrecoverable strain points in volumetric-axial strain space were corrected to account for non-zero stresses in the "unloaded" states, and also to remove the unwanted effects of crack closure. These strain loci were then compared to those calculated by subtracting elastic strains calculated using both a constant and a variable Poisson's ratio. The plastic strain curves were found to be slightly different, with the curve calculated based on a constant Poisson's ratio predicting the greatest volumetric strains and the most conservative (largest) dilation angle values. The corrected cycle data appears to agree very closely with the curve calculated based on a variable Poisson's ratio, and roughly fits a previously proposed dilatancy model. Since continuum models cannot handle the large Poisson's ratio values observed following the onset of unstable cracking, however, it is recommended that a dilation model calculated based on the constant Poisson's ratio be used for numerical modelling applications. Finite difference modelling was performed to evaluate the sensitivity of excavation displacement predictions to the interpretation of the laboratory test plastic volumetric strain curves. The higher dilatancy models produced more conservative displacement estimates, and these were closer to those predicted using a model with lower dilatancy but a variable Poisson's ratio. In general, the models were found to be relatively insensitive to the initial dilation angle in cases where the transition from the initial dilation angle to the consistent decay phase occurred at small plastic strains (<2 mstrain).
- North America > Canada (0.29)
- North America > United States (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.62)
- Health & Medicine > Diagnostic Medicine > Lab Test (0.81)
- Energy > Oil & Gas > Upstream (0.70)
Abstract The basic friction angle of planar rock joints is a parameter apparently easy to estimate from the results of laboratory tilt or pull tests on adequately cut and prepared rock specimens. However, when performing a good number of these tests, results may be surprising in terms of their wide variability and varying trends according to the particular environmental conditions of the carried out tests. By means of various series of laboratory tilt and pull tests on several specimens of different rock types some features have been deduced. First, a reassessment of the technique of tilt testing of rock cores suggests that even if the original formula was not correct, an appropriate interpretation of results could provide realistic basic friction angle values. Then, it has been observed that, in standard conditions and for the same specimens, tilt and pull tests produce comparable results. Additionally, it was noticed that large numbers of test repetitions on the same surfaces tend to produce diminishing values for the sliding angle if the surfaces are cleaned after every repetition. However, if the surfaces are not cleaned and the rock dust remains over the surfaces, a growing trend of basic friction angle values is registered. Finally, tilt tests on igneous rock specimens performed at a particular moment and months to years later, produce decreasing values for the sliding angle, which can be attributed to previous shearing movements or to surface degradation. Introduction 1.1 Background One of the most relevant features of rock masses is the occurrence of natural discontinuities, which very often control the mechanical behavior of these natural materials. Discontinuities found in real rock masses are typically irregularly rough. The shear behavior of these discontinuities has been one of the most relevant topics of research in rock mechanics. Barton and co-workers (Barton 1973, 1976, Barton & Choubey 1977, Barton & Bandis 1980) developed a procedure to estimate the shear strength τ of these joints starting from the basic friction angle of a planar rock joint φb, a roughness index JRC, the strength of rock in the joint JCS and the normal stress to which the joint is submitted according to the well-known expression:
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Abstract Novel rock breakage techniques are becoming more viable and attractive to industry. Microwave energy, as a thermal energy which is capable of inducing micro cracks through differential heating (therefore expansion of Minerals) is a technology gaining considerable attention in mineral processing and ore comminution applications. Recently, use of microwave has been evaluated as a possible avenue for terrestrial and extraterrestrial drilling applications and full face tunneling or rock breaking machines. As part of an overall research on use of microwave in rock breaking systems, the influence of microwave energy on the mechanical properties of some common hard rock types has been investigated. Experimental and simulation results underlined the potential impact of the use of microwave energy in underground or surface excavation applications such as mining and tunneling. This will also contribute economically when mine-to-mill operation is fully considered. It also outlines the potential impact of a future microwave assisted tunnel boring machine enhanced with microwave and its performance. 1. Introduction To date, many methods have been used in rock breakage applications. Some of these methods essentially break rocks by applying heat either directly or indirectly. Using microwave energy is an alternative method of rock breakage that has been introduced since the 1960s but, as yet, it has not proven to be economically viable, as a single method, to become commonly used (Maurer, 1968). Microwaves have since been applied in mineral processing applications to reduce grinding energy (Kingman et al., 2000 & 2004). However, microwave assisted mechanical rock breaker equipment has been recently highlighted with significant potentials in this area. Mechanical rock breaker equipment has limited performance with high level of bit or disc wear and maintenance in breaking hard rocks in mining and civil applications. The performance of an underground excavation in hard rock with mechanical equipment can be estimated through correlating mechanical rock properties with applied forces and machine specifications. Preconditioning the natural rock prior to be broken by the machine is a novel approach that is to be studied. Flame torch assisting rock excavation systems or tunnel boring machines had been taken in consideration (Lauriello et al., 1974) but has not been economically feasible due to huge consumption of fuel.
- Geology > Mineral (0.67)
- Geology > Geological Subdiscipline > Geomechanics (0.66)
- Well Drilling > Wellbore Design > Rock properties (0.48)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.48)
Abstract This paper aims to apply intelligent tools such as artificial neural networks, support vector machines and multiple regression to forecast the main parameters characterizing the compressive behavior of granites, namely the resistance under compression, fc, the crack initiation stress, fci, and the crack damage stress, fcd, based on physical parameters like density, ρ, porosity, η, and ultrasonic pulse velocity (UPV). The granitic rocks selected are from the north region of Portugal existing in ancient masonry structures. Several experiments were performed to build a database of 55 records containing the mechanical and physical parameters mentioned above. The predictive capacity of the models was evaluated using the coefficient of correlation, R, and the root mean square error, RMSE. The results showed a good predictive capacity of the developed models. 1. Introduction The knowledge of the mechanical behavior of the granite is fundamental to solve many engineering problems. Nowadays, the rehabilitation and repair of existing masonry structures require the mechanical characterization of materials and the detection of damaged zones with cracks and other problems. In this framework, the determination of mechanical parameters related with the compressive resistance and cracking under compression is very important. Besides the compressive strength under compression, fc, the cracking state can be characterized by two main parameters namely crack initiation stress, fci, and the crack damage stress, fcd. The crack initiation stress corresponds to the onset of micro-cracking in compression and the crack damage stress corresponds to the initiation of coalescence and damage propagation. These parameters are represented in Figure 1, which shows the typical stress-strain diagrams for granites under compressive loading up to peak stress. There are several works published about the prediction of compressive strength fc and its correlation with other rock properties (Begonha, 1997; Kahraman, 2001;; Begonha & Sequeira Braga, 2002; Kiliç & Teymen, 2008; Sharma & Singh, 2007). However, the literature about the evaluation of stress cracking parameters, fci and fcd, is scarce. Many years ago Brace et al. (1996) determined from laboratorial tests the cracking initiation. They concluded that crack initiation was coincident with dilatancy measured using volumetric strain. Furthermore, they presented values ranging from 0.3 and 0.7 for the ratio of crack initiation stress to peak strength for distinct types of rocks. Nicksiar & Martin (2013) analyzed the effects of geology and loading conditions on crack initiation stress. They examined crack initiation in uniaxial compression and triaxial compressions tests in igneous, metamorphic and sedimentary rocks. A total of 336 tests were evaluated and used to examine the effect of mineralogy, anisotropy, grain size and confinement on crack initiation.
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Neural networks (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (1.00)
Abstract To investigate the deformation behavior and shear wave velocity change under extensional stress state, we conducted true triaxial compression test using Kimachi sandstone specimens of 35×35×70 mm. Shear wave velocities with different shear motion in the σ3 direction were observed during axial loading to the failure of the specimen. The maximum principal stress increased by some amount of stress in changing from compressional stress state to extensional stress state. The brittleness defined as reduction in the maximum principal strain is observed under increasing of the intermediate principal stress, transition characteristics are also observed from compression state to extension state. Under extensional stress condition, shear wave polarization was disappeared and two shear wave velocities decreased in an identical manner during loading. We discussed strain anisotropy and shear wave velocity anisotropy on distribution change of stress induced micro cracks in the specimen during loading. 1. Introduction A fault in geology is defined as a fracture in the continuity of a rock formation caused by a shifting or dislodging of the earth's crust, in which adjacent surfaces are displaced relative to one another and parallel to the plane of fracture. Reverse fault in geological definition is a geologic fault in which the hanging wall has moved upward relative to the footwall. Reverse faults occur where two blocks of rock are forced together by compression. Similarly, normal fault is a geologic fault in which the hanging wall has moved downward relative to the footwall. Normal faults occur where two blocks of rock are pulled apart, as by extension. In laboratory experimental techniques, there are two experimental approaches to realize the situ stress states around underground; the confined triaxial compression test and the confined triaxial extension test. The former corresponds to the stress state in reverse fault in geology and has the limitation that the minimum principal stress is always equal to the intermediate principal stress, similarly the latter corresponds to normal fault in geology and has the limitation that the intermediate principal stress is equal to the maximum principal stress. We have little data relating to confined triaxial extension tests, especially for deformation characteristics under different stress paths. At the beginning of 1960, many experiments were done to investigate experimentally the rheological behaviors of marble and other rocks under high pressure and high temperature under extensional stress state. Ramsey and Chester (2004) carried out confined triaxial extension tests using dog-bone shaped Carrara marble that showed a continuous transition from extension fracture to shear fracture with increasing compressive stress. On the other hand, in engineering geology fields, the stress state, when generating core disking and when excavating an underground open space, is assumed to be an extensional stress state where the three principal stresses are compressive and maximum and the intermediate principal stresses are always equal. However, there is insufficient data related to the confined triaxial extension test. To understand the deformation behavior and shear wave velocity change under extensional stress state, we carried out true triaxial compression test using Kimachi sandstone. Shear wave velocity with different shear motion in the s3 direction were observed during axial loading. We can discuss different manner of stress induced microcracks distribution by different stress state, confined triaxial compression and confined triaxial extension.
- Geology > Structural Geology > Fault > Dip-Slip Fault > Reverse Fault (0.65)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Normal Fault (0.65)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.47)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Textural Anisotropies Characterization of Granitic Rocks using P-Wave Velocities
Calleja, L. (Universidad de Oviedo) | Rodríguez-Rey, A. (Universidad de Oviedo) | de Argandoña, V. G. Ruiz (Universidad de Oviedo) | Camino, C. (Universidad de Oviedo) | Sánchez-Delgado, N. (Fundación Centro Tecnolóxico do Granito do Galicia, O Porriño)
Abstract Three granitic rocks from Galicia, Spain, namely Gris Alba, Albero Granite and Traspieles were petrographically (textural, mineralogy and fractography) characterized. Later, longitudinal waves velocity (Vp) in 3 orthogonal directions was determined; measurements were carried out on cubes 7 cm edge, wet and water saturated, previously oriented according to regional directions. Wet samples shows an anisotropic behaviour of Vp, however, on water saturated samples one of them behaves isotropically. From the obtained data and calculated IQ (quality index) and IF (microfissuration index), models of microcrack network distribution and possible mineral grains orientation were developed; the proposed models were compared with the petrographic studies, showing a perfect agreement between both of them. 1. Introduction The existence of textural elements orientations (mineralogy or fissuration) of rocks is sometimes difficult to detect in a simple and fast way; the small microcrack size or the low orientation grade of one or more mineral phases can make these characteristics difficult to observed with the naked eye. Obviously, microscopic studies (under optical polarizing or fluorescence microscopy and scanning electron microscopy) easily show the existence of preferred orientations. Generally speaking, granitic rocks show microcrack networks originated by their own crystallization and emplacement processes. These processes sometimes originate mineralogical orientations that may affect the entire volume of rock due to the existence of magmatic flow during the cooling processes. In other cases, the orientation is more localized at the pluton borders due to the emplacement and the fractional crystallization processes. Other granitic rocks show microcrack networks without preferred directions, with a disposition that is dense and orthogonal to a degree that depends on the contraction during the cooling process. The rock characterization by the study of the velocity of high frequency waves (ultrasounds) as well as the characteristics of the waves after travelling through the rocks is a usual technique in geological studies both in the laboratory and in the field. These are nondestructive techniques (NDT), easy to apply and very useful for the determination of the dynamic properties of the rocks. Furthermore, they provide information about the existence of anisotropies that can influence some rock properties.
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Mineralogy (0.79)
- Geology > Geological Subdiscipline > Geomechanics (0.67)
- (2 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.69)
- Well Drilling > Wellbore Design > Rock properties (0.67)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.49)
Abstract Kimachi sandstone and Shikotsu welded tuff were tested in single and multistage triaxial tests to determine the Biot's effective stress coefficient (α). Pure water saturated 30mm in diameter and length of 60mm cylindrical test specimens were introduced for triaxial compression, with strain rate at 10s. For Kimachi sandstone, α value for peak strength decreased with effective confining pressure. α values for residual strength were almost constant and larger than the case of peak strength. For Shikotsu welded tuff, only two data points were obtained for peak strength due to pore collapse and α value for residual strength decreased with effective confining pressure. The multistage test has given a fair evaluation of the coefficient for peak strength of Kimachi snadstone. Number of specimens and variation from specimen to specimen can be reduced by using multistage tests although further considerations are required to obtain the coefficient for residual strength. 1. Introduction Experimental determination of Biot's effective stress coefficient, α for peak and residual strengths is very important in rock engineering problems because failure criteria for strengths of rocks are written by effective stress. The concept of effective stress was first introduced by Terzaghi (Terzaghi, 1936) for soil, which is commonly known as the Terzagi's effective stress principle. It states that the effect of the total stress σ and pore PressurePp can be denoted by a single parameter which is known as effective stress σ defined as, Terzarghi's effective stress principle is not always valid for the fluid related rocks. Therefore, the Biot's effective stress coefficient was suggested by Biot and Willis in 1957 to modify the effective stress principle and the effective stress principle finally is given by, where α is the Biot's effective stress coefficient which denotes the ratio of the area occupied by the fluid to the total area in a cross section in the porous material (Bear, 1972) and is the key parameter that quantifies the contribution of pore pressure to the effective stress. For the granular soil, the contact area among grains is very small, thus it is possible to assume that a cross section which is considered is almost occupied by the fluid. Hence, the corresponding effective stress coefficient α approximately equals to 1. In rock materials composed of crystallization or cementation, grain to grain contact is considerably higher and it is not possible to assume that the cross section is almost occupied by the fluid. Consequently the corresponding effective stress coefficient α will be less than 1.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.49)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Abstract This paper describes the analysis performed in order to obtain the relationship between the static and the dynamic modulus of one sedimentary rock (the San Julián's stone) heated at different temperatures. The rocks have been subjected to heating processes at different temperatures (reaching up to 600°C in steps of 100°C), and two cooling methods for each temperature, to produce different levels of weathering on 24 cylindrical samples. The static and dynamic modulus has been measured for every specimen. Two analytic formulae are proposed for the relationship between the static and the dynamic modulus for this stone. The results have been compared with some relationships proposed by different researchers for various types of rocks. Generally low elastic modules imply highly fissured or damaged rocks. The mechanical properties, including static modulus, are highly dependent of the cracks size, orientation, and spatial distribution of these cracks. The ability to adequately detect the physical changes that affect rock mechanical capabilities by studying the propagation of ultrasonic waves has been widely discussed in many scientific papers. In this work, a high correlation between static and dynamic modules has been observed. It is concluded that in the studied range (i.e. Edyn values lower than 50 GPa) and for the soft rocks, static modulus can be obtained from dynamic tests, being the dynamic modulus (i.e. ultrasonic waves propagation velocities) a good indicator of the material degree of deterioration. The obtained relationships will allow the computation of the static modulus of elements of cultural heritage of Alicante city made of San Julián's stone, from non-destructive field tests, for the analysis of the integrity level of historical constructions affected by high temperatures. 1. Introduction Young's modulus, also called elastic modulus, is one of the most important mechanical characteristic parameters of the rocks in relation to its use as a construction material. The dynamically determined elastic modulus (Edyn) is generally higher than that statically determined, and both methods provide high divergent results for low elasticity modulus rocks (Ide, 1936). Several studies (Ide, 1936, Vanheerden, 1987, Al-Shayea, 2004, Kolesnikov, 2009) explain these differences by means of the nonlinear elastic response at different ranges of amplitude of the strains (ε:) involved in the distinct techniques. Other authors (Kolesnikov, 2009, Ciccotti & Mulargia, 2004) consider that the static test is a dynamic test at a very low frequency, and they highlight the nonlinear elastic response to different associated frequencies (f).Kolesnikov (2009) uses the Kjartansson constant Q-model (Kjartansson, 1979) to analyse the effects of intrinsic dispersion of pressure waves velocities in absorbing media (and it is well known that all rocks absorb energy of elastic waves to a greater or lesser extent).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.70)