Abstract Tensile strength of rocks is an important parameter in the design of underground structures and for various engineering applications. Lack of literature and rapid development of infrastructure in central region of India calls for a need to characterize the mechanical behaviour of rocks in Deccan trap region which is mainly composed of Basalt. In this paper, characterization of tensile behaviour of Basalt rocks from Deccan trap is done at different loading conditions. Indirect test method namely Brazilian test is used to calculate the static indirect tensile strength at a loading rate of 0.2 kN/s. Tests are performed on different diameters samples and desirable failure modes are recorded. Tensile strength values recorded at slow loading are obtained to be different for specimen having different diameters. However, strength of rock in engineering problems like blasting, mining, rock bursting and breakage are affected by high loading rates. To consider the dynamic loading effect, a modified split Hopkinson pressure bar technique is used. For dynamic tensile experimentation, Brazilian disc specimen are used which are slightly flattened before testing. The flat ended Brazilian discs (FEBD) are placed diametrically in SHPB setup. Dynamic force equilibrium is successfully achieved for the initial stages of fracture propagation till complete failure of sample. The factor for increase in dynamic tensile strength of Deccan Basalt has been evaluated in this work. Scope of further research has been identified for experimentations on soft rocks to determine their dynamic tensile strength characteristics. 1. Introduction Strength characteristics of rocks are one of the most important parameters required for mechanical analysis related to various applications in rock engineering field. This work has been progressed on the idea of extension of various experimental methods available in Rock engineering field. The Deccan trap region in central India, which is mainly composed of Basalt [1], is a type of igneous rock formed from volcanic lava flow. This region is becoming an attractive site for large construction projects like dedicated freight corridor project (DFC), multistoried buildings, large hydropower projects like Koyna Dam, underground tunnels (nearly 20 tunnels exist on the newly built Mumbai-Pune expressway as observed during site visits for this work). It becomes imperative to design such important structures with good understanding of behavior of the rocks under low as well as high loading conditions, as mechanical behavior of rocks is dependent on the loading rate [2, 3, 4, and 5]. Determination of tensile strength of rocks using direct methods like pull test is a difficult task. From various indirect test methods, Brazilian test is widely used and the mechanism behind it has been considered in this work. Split Hopkinson Pressure Bar (SHPB) which is widely used for determination of compressive strength of rocks and other materials [6, 8, and 9], has been extended for tensile testing at high loading.

Abstract The indirect (Brazilian) tensile strength test is commonly used in rock engineering and rock mechanics. Most of the research on how to interpret Brazilian test is only valid for isotropic rock. The load may be applied to disc shaped samples through flat platens or curved jaws and the different load configurations give rise to subtle but important differences to stress distributions throughout samples during testing and at the onset of failure. To reliably obtain the tensile strength accurate stress distributions, especially at the location of the initial crack, must be determined. However, most real rocks exhibit a certain type of anisotropy known as transverse isotropy due to the presence of preferred directions of grains, beddings, microcracks or pores. This study focuses on the failure modes when transverse isotropy is present. Previous studies for transverse isotropy indicate that the exact location of the initial crack is at the disc centre. These studies, however, ignore the effect of the load contact configuration on the stress distribution. This paper overcomes this limitation and applies Amadei's analytical solution to assess the effects of the load contact area on the stress distribution. The stress distribution is coupled with a transverse isotropy failure criterion in a mechanically consistent way to find the exact location of initial crack. It is shown that the location of the initial crack depends on the transverse isotropy orientation and load configuration. 1. Introduction The Brazilian test is a diametrical compression test that is used as an indirect tensile strength measurement. At first, the test was proposed by Carneiro [1] and Akazawa [2] to obtain tensile strength of concrete. In 1978, the International Society for Rock Mechanics (ISRM) officially presented Brazilian test as a standard method to indirectly determine the tensile strength of rock like materials (ISRM 2007). Nowadays the Brazilian test is widely used to determine tensile strength of rock like materials because of its simple specimen preparation, experimental performance and data reduction [3–4]. In the test, a thin disc is diametrically compressed. The corresponding stress field throughout the specimen is highly non-uniform.

ABSTRACT: Microfractures and discontinuities are the common structural features of the rock mass lead initiating and developing the brittle fractures in rocks. Fracture toughness is an intrinsic material property for the pre-exist cracks initiate fracture development and play a significant role in brittle fracturing. The Cracked Chevron-Notched Brazilian Disc (CCNBD) samples were tested to determine the fracture toughness of monsonite and sandstone samples. Since conducting fracture toughness tests are quite hard compared with the Brazilian test, the tensile strength can be determined by using the tensile fracturing parameters of rocks. Moreover, stress analysis obtained from the Extended Finite Element (XFEM) modelling confirmed a comprehensive relationship between tensile strength and tensile fracturing parameters of rocks. Based on the laboratory experiments, the tensile strength of rocks can be used for the modelling of tensile fracturing and this will improve our understanding of rock fracturing behaviour utilising for the rock cutting and mining designs. 1 INTRODUCTION 1.1 Brittle fracturing The implementation of the stress-displacement concept in rock fracture mechanics requires the definition of characteristic properties of rock for the different modes of fracturing behaviors. In many practical applications of rock engineering, rock cutting, slope stability, rock cutting and blasting, arbitrary orientations of cracks are related to the loading directions. Brittle fracturing can occur in three different modes, crack opening mode (tensile fractures, Mode I), sliding cracks (shear fractures, Mode II) and rotating cracks (tearing fractures, Mode III). There are different standards methods widely used to determine fracture toughness of rock that is an important parameter for rock failure analysis in various field of engineering applications (Alehossein & Hood 1999, Aliha & Ayatollahi 2014, Andreev 1991, Atkinson & Avdis 1980, Ayatollahi & Aliha 2007, Erarslan & Ghamgosar 2014, Ghamgosar & Erarslan 2015a, Ghamgosar & Erarslan 2015b, Ghamgosar et al. 2014). Crack initiation, coalescence and specimen failure do not occur at the same phase; rather, each separately forms a particular fracture process zone. However, the crack initiation started by forming a pre-existing crack tip, called the primary crack, does not have to lead to failure, since this initial crack propagation may be arrested at some stress level. It is suggested that the crack propagation in rocks, concrete, etc. is associated with the formation of microcracks at the crack tip, and integrated into interlocking of particles behind the crack tip (also called ligament connection or crack bridging) (Ghamgosar & Erarslan 2015a). 1.2 Mode I fracturing The mode I (tensile) stress intensity factor K I itself is dependent on the crack length, C, applied stress σ A , and geometry factor, ψ (Anderson 2005). (equation) where, fracture initiation from the tip of crack occurs when fracture stress intensity reaches to the critical amount as (equation) Cracks below the critical stress intensity value generate subcritical cracks, which is subjected to either repeating or fatigue load, which reduction in stiffness results in micro-cracks generation and coalescences into the macro-cracks form. Static and cyclic loadings produce a different mode of fracture at the Fracture Process Zone (FPZ) that contains the various scale of micro-cracked density and fracture voids at cracks front. The ligaments connection of subcritical cracks at FPZ is shown in Figure 1 (Ghamgosar & Erarslan 2015a).

ABSTRACT: To eliminate the holding and gluing problems making the direct tensile strength test hard to be applied, a new method of testing rock material specimens prepared using lathe machine to make the dog bone shape is assessed whether it could be applied to determine accurate direct tensile strength values of rock materials. A series of numerical modelling analyses was performed using finite element method to investigate the effect of different specimen and steel holder geometries. A proper physical property of the lathed specimens was suggested and ideal failure of the dog bone shaped specimens was determined according to the results obtained with this study. 1 INTRODUCTION Because the conventional rock tensile strength test is not practical to apply, many different kinds of indirect tensile strength (ITS) methods were suggested by different researchers. Splitting tensile strength (Brazilian) test is the most famous ITS determination method because of its practicality and ability to be carried out using conventional press equipments. Specimen preparation impracticality can be accepted to make some other ITS testing methods be not widely applied. One of the reasons for popularity of the Brazilian test is easy specimen preparation to test under basic loading devices. Although the Brazilian test is applied worldwide, its deficiencies cannot be ignored and have been an important issue to investigate by the community on rock testing (Li et al. 2013, Komurlu et al. 2016, Brisevac et al. 2015, Markides & Kourkoulis 2013). Because the Brazilian discs fail under biaxial stress conditions, including tangential stress (σ θ ) along the horizontal diameter of the disc and compressive radial stress (σ r .) along the vertical diameter of the disc, the Brazilian test has an important problem and cannot be used to determine a tensile strength value to be used instead of uniaxial tensile strength of rock materials (Chen & Stimpson 1993, Fairhurst 1964, Krishnayya & Eisenstein 1974, Erarslan & Williams 2012). To be a standard test, the Brazilian test has additional problems resulting from indefinite contact conditions that significantly change the stress distribution in discs with a change in the disc material. Because important factors for stress distribution in the disc specimen such as contact angle and friction conditions vary depending on the rock deformation characteristics, ITS values obtained with the Brazilian test are not only dependent on the strength of the disc specimen material (Komurlu et al. 2015, Komurlu & Kesimal 2015, Markides & Kourkoulis 2015).

ABSTRACT: In this study, a new apparatus which have new jaw clutch mechanism is designed to determine the direct tensile strength of rocks. The determination of the direct (with new apparatus) and indirect tensile strength as Brazilian test method of travertine rock was carried out in compliance with related standard test methods. In order to analyse rock tensile strength between direct and indirect test methods was conducted and obtained results were compared between them. Dumbbell shape samples were used in direct tensile tests and cylindrical specimens were used in Brazilian test. Stress distribution and the stress intensity within the sample were analysed with Finite Elements Method and numerical modelling techniques using ANSYS R.14 software. The direct tensile test yielded lower strength values than the indirect test. Direct tensile test is affected to a greater degree by the presence of microfractures and microfissures in the rock. For the specimens tested in direct tensile test, failure occurred near the radius of the dumbbell shape sample due to stress intensity factor. Therefore, direct tensile stress should be re-calculated by considering stress intensity factor. Since Brazilian disc test strain value in the diametrical line of the specimen has been found higher than nominal strain value according to FEM, tensile strength value which should be re-calculated by using proposed the coefficient. 1 INTRODUCTION Characterizing the tensile strength of rocks thus is of great importance in many engineering and geophysical applications (Dai et al. 2010). The tensile strength is a key parameter for determining the load bearing capacity of rocks, their deformation, damage and fracturing, crushing, drilling, tunnel boring, and blasting etc., and is used to analyze the stability and serviceability of rock structures (Danet al. 2013, Daiet al. 2013). Rocks are less resistant to tension than to compression or shear. Tension cracks often develop before compression or shear failure (Liao 1997). Rock is a brittle material and because all brittle materials are weak in tension, the tensile strength of rock becomes one of the most important parameters influencing its deformability and fracture toughness (Erarslan&Williams 2012). These phenomena provide evidence of direct tensile failure in rock structures. Thus, an understanding of the rock behavior under tension can be beneficial in the analysis that involves either intact rock or rock masses (Liao 1997). Tensile strength is defined as the failure stress of a rock element in pure uniaxial tensile loading. Thus, the direct pull test appears to be best suited for tensile strength measurement (Dai et al. 2010). However, direct tensile strength and deformability of rocks are difficult in the laboratory, and field. Because of the difficulties associated with experimentation in direct tensile tests, various of indirect methods have been suggested for determining the tensile strength of materials such as the Brazilian disc test, ring tests, and bending tests. These indirect methods aim at generating tensile stress in the sample by far-field compression, which is much easier, cheaper and common method for determining the tensile strength of rock in instrumentation than direct pull tests (Dai et al. 2010).

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. 1 INTRODUCTION 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 mechanical behavior of rock under high-temperature was simulated using a grain-based distinct element model. The microstructure of rock was represented as an assembly of deformable polygonal grains, and the micro-parameters characterizing the deformability and strength of each grain and interface were calibrated based on the experimental results of UCS and Brazilian tests at room temperature. For implementation of the mechanical analysis, a commercial code UDEC based on DEM theory was adopted in the present study. With the microstructures and a set of micro-parameters, the specimen was heated up to a maximum of 250 °C prior to being loaded, and then UCS and Brazilian tests on the heated specimens were numerically carried out. The estimated and experimentally measured behavior of rock showed moderately good agreement, which suggests the ability of the grain-based model combined with UDEC to capture the thermo-mechanical behavior of rock at microscopic scale. 1 Introduction A concern regarding the thermo-mechanical coupled behavior of rock has arisen in many rock engineering projects including thermal energy storage, geothermal energy development and nuclear waste disposal. Spatial and temporal change in temperature can initiate new micro-cracks and propagate pre-existing micro-cracks within rocks, and the micro-cracks can influence substantially the physical properties of the rocks (Homand-Etienne & Houper 1989). Many experimental studies have reported that the mechanical properties characterizing strength and stiffness of rock tend to decrease with increasing temperature at high temperature (Dwivedi et al. 2008). Two mechanisms for thermally induced micro-cracks have been suggested in the literature (Yong & Wang 1980); first, new micro-crack can be generated at the interface between different rock-forming minerals because of a mismatch in the thermo-elastic behavior; and the other is that the thermal stress due to local variations in the temperature gradient in rocks causes the propagation of existing cracks. Thus, the thermo-mechanical behavior of rock, in nature, should be understood be based on the observations at mineral scale. With the rapid progress of computer technology, many attempts have been made to reproduce the mechanical behavior of rock using numerical techniques, such as finite element method, boundary element method, and discrete element method. In terms of explicit representation of heterogeneous material at microscopic scale, it would appear more desirable to make use of a polygonal grain-based micromechanical model to adopt other numerical models assuming obscure constitutive laws including a large number of assumptions and uncertainties. Lan et al. (2010) simulated the behavior of brittle rock using a grin-based geometry generated by the power Voronoi tessellation and a commercial code UDEC (Universal Distinct Element Code). They named the technique as GBM (Grain Based Model)-UDEC model, and demonstrated the feasibility of GBM-UDEC model for the reproduction of the brittle rock's failure process induced by its microstructure heterogeneity. Shin (2010) also successfully applied this technique to the simulation of the spalling failure that was observed around AECL's Mine-by Test Tunnel in Canada.

Abstract Typical sandstone with low strength and multi pores is selected for conducting Brazilian splitting test to investigate the physical and mechanical characteristics of sandstone under sub-zero temperatures. Through analysis of microscopic structures, the failure process of specimen under sub-zero temperatures is studied on acoustic emission apparatus. The results showed that, for frozen rocks, their splitting tensile strength increases as temperature decreases or water content increases, which is different from sandstone at room temperature. The variation of cumulative ringdown counts can be divided into three stages from initial loading period to failure, which can offer useful information for problems of frozen wall breakage and mine flooding in western China. 1 Introduction Because rock fails much easier under tensile stress than compressive stress condition, rock tensile failure is critical for long term stability of underground structures. Brazilian splitting test is convenient and practical for determination of rock tensile strength, while the direct tension test is difficult to perform. The splitting tensile strength of direct and indirect test was discussed by Ojdrovic & Petroski (1985), and they believed the results from two tests were close. Proveti & Michot (2006) concluded the Brazilian test was well suited to measure the fracture resistance of materials at room temperature. However, most of researches were performed at room temperature and the results may be not applicable to field condition. Temperature changes lead to crack generation and extension, strength degradation of rock mass and structures, and also pose a threat to the durability and stability of structures and rock mass. Various relationship between rock strength and temperature, loading rate and water content was studied by Rager et al. (2014), and he indicated the temperature and loading rate had a greater effect on tensile strength than uniaxial compressive strength. The failure process of frozen rock is difficult to understand due to the effect of changing mechanical properties and content of pore ice. Generally speaking, the pore ice content increases as temperature decreases. But there exists a limit balance between frozen and unfrozen water in soil (e.g. Kozlowski et al. 2003 and Liu et al. 2012). The freezing-induced cracking process under compressive shear conditions can be considered as a mixed mode of tensile cracks and shear cracks, and crack initiation criterion, propagation direction and crack length based on Griffith theory were analyzed by Kang et al. (2014).

Abstract A computational method to simulate rock cutting is developed and evaluated. It aims to obtain the forces on the pick during cutting. The explicit FEM is chosen to model the pick-rock interaction. It allows accelerated calculations due to parallelization, a robust contact algorithm and superior material description with constitutive equations. A damage-plasticity law is chosen and modified with user-subroutines. The introduction of an element deletion routine evades the expected critical mesh distortions. Infinite elements model the boundary of the model in order to suppress acoustic wave reflection and unrealistic interference. Fitting the yield function numerically to stress states that cause fracture calibrates the constitutive equations. These stress states are obtained from inexpensive Brazilian tests and uniaxial compression tests. The tensile strength concept is extended to a two-parameter description of tensile strength and loaded volume using the Weibull theory. 1 Introduction 1.1 Principles of Excavation Roadheaders (Figure 1) are widely used for excavation and mining purposes but high material strengths limit their usability (Tockner 1999). Nowadays a challenge is to extend their field of application to harder and more abrasive rock materials. The forces on the pick are of great importance and determine wear and especially the efficiency of the machine. Additionally the cutting capability is naturally limited by the weight of the machine, which makes the reduction of reaction forces by optimizing the process parameters rewarding (Tockner 1999). Cutting brittle materials is a stepwise phenomenon of separation and removal of a large segment, the so-called chip (Chiaia 2001). The basic physical phenomenon during rock cutting is fracturing and fragmentation of the rock induced by the mechanical cutting tool (Rojek et al. 2011). The tool-rock interaction determines the forces on the pick and thus the required work. The reduction of tool forces at steady excavated volume is rewarded with increasing cutting efficiency (Tockner 1999). Three forces are distinguished in rock cutting: The normal force, acting in the direction of excavation, the cutting force which acts in line with the cutting direction and finally the side force which is transverse to both other forces (Su & Akcin 2011). Figure 2 shows the principle of cutting and the predominant forces. Variation of pick geometry, cutting depth or attack angle will result in an alteration of these forces and determine the efficiency of the process (Tockner 1999).

Abstract Rocks are quasi-brittle materials that inherently contain different types of flaws, microcracks and inhomogeneity, which are weak under tensile loading. The tensile strength of rock is significant parameter for rock mechanics designers, which plays the dominant role in rock cutting, fracturing and fragmentation on blasting. In general, fractures in rock initiate from tiny cavities and micro-fractures, then coalescence to form macro-fractures, and finally fail. Most of the well-known failure criteria address only the ultimate stage of failure and ignore progressive damage on loading of the rock. To take account of the effect of micro-fractures in quasibrittle materials such as rocks, Continuum Damage Mechanics (CDM) has been used in this study. Recently, micro-fracture effects in rock and concrete have been investigated by using damage evolution in conjunction with thermodynamics theory. As micro-cracking and damage directly influence the rock elastic properties and elastic wave velocities, the ultrasonic properties of rock under loading provide a clear view of the development of micro-fracturing. The Brazilian test has been used to apply indirect tensile loading and has been coupled with the measurement of ultrasonic P and S-wave velocities. Introduction 1.1 Fracture mechanics and rock mechanics Fracture mechanics is one the most significant key parameter in rock mechanics design analyzing for underground and on the ground civil and road construction projects. The major reason of fracturing and damage in rocks is contributing to a significant degradation of rock road-bearing capability. Furthermore knowledge of rock fracture mechanics and fatigue damage is significant source for rock cutting practices and fragmentation's industry. Unlike the other material in other engineers filed, rock normally suffers from different type of inhomogeneity and discontinuity to be dealt with. These parameters directly effect on rock strength value and hence influence on the rock support size in one hand and size of the rock cutting machinery in the other hand. Since the prior experiments and studying, fracture mechanics has been employed in deep mining hard rock analyzing. The structural parameters are shown to be the other important factor in rock fracturing which includes; rock grain sizes and characteristics, pre induced cracks, micro and macro fractures before loading and during loading process, dimension and physical condition of environment involving in rock testing time. The third and also most significant key role in the rock fracture is studying mechanical behavior induced by different loading that cause different types of fracture pattern in rock matrix. Different approaches have been developed from the linear elasticity and fracture mechanics by (Bieniawski & Tonder 1969) and (Brady & Brown 2006) to the several developed numerical methods to simulate fracturing process in rocks (Anderson 1995). Based on the different numerical methods, FEM is more common methods using different techniques for re-meshing and applying different small elements for modeling fracture initiation and growth through (Jing & Hudson 2002).

Abstract Rock failure can either be referred to as brittle, ductile, or at the brittle-ductile transition. Brittle failure is said to occur when the ability of the rock resist load decreases with increasing deformation. Brittle failure is associated with the materials that undergo little to no permanent deformation before failure and, depending on the test conditions, may occur suddenly and catastrophically. Ductile failure is said to occur when the material can sustain permanent deformation without losing its ability to resist loading (without failing). Brittleness may also be defined in terms of the ratio of specific elastic strain energy at the fracture to total specific strain energy at the fracture when a fracture is accompanied by plastic deformation, it is called a ductile fracture and when plastic deformation is absent it is called a brittle fracture. There are different definitions of rock brittleness in rock mechanics literature; however, Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) values are very important parameters to determine brittleness and ductility of rocks. Thus, the study presents the obtained BTS values of rocks by using standard Brazilian Jaws. As the Brazilian test has been criticized since it was initially proposed by ISRM, the aim of this study to investigate the accuracy of Brazilian jaws to determine the BTS values of brittle and ductile rocks separately. FRANC2D software was used to analyse the stress distribution at the centre of disk specimens by considering ductility and brittleness of rocks. Both experimental and numerical results showed that both BTS values and fracturing of rocks were found depended on the brittleness and ductility of rocks and accuracy of using the proposed standard Brazilian jaws may change depending on ductility and brittleness of rocks. 1. Introduction The indirect Brazilian test is widely used in engineering practice to indirectly determine the tensile strength of rocks. In 1978, the Brazilian test was officially proposed by the International Society for Rock Mechanics (ISRM) as a suggested method for determining the tensile strength of rock materials (ISRM 2007). The Brazilian test (splitting tension test) is performed by applying a concentrated compressive load across the diameter of a disc specimen. The tensile strengths of brittle materials like rock and concrete are generally much smaller than their compressive strengths. As the ratio between tensile and compressive strengths is quite high, determination of the indirect tensile strength of brittle materials under diametric compressive loading seems a disadvantage due to possibility of crack initiation in compression zone under contact points (Mellor & Hawkes 1971). In addition, friction conditions between disc and jaws significantly affect the crack initiation point and its position in a disc specimen (Markides et al. 2010). In addition to analytical solutions that assume the rock material to be isotropic and homogenous, recently many researchers have included the effect of rock heterogeneity, ductility and brittleness in their experimental and numerical studies (Van de Steen et al. 2005, Lanaro et al. 2009, Liu 2004).

Abstract In this paper, firstly, uniaxial compression test and Brazilian test of rock were conducted to investigate the influence of surrounding non-atmospheric environments on uniaxial compressive strength and tensile strength. The environments used in this paper were organic vapor, inorganic gas and water vapor. As the results, it was founded that water vapor is the most effective agent which promotes stress corrosion for rocks. Then, a series of uniaxial compression tests, Brazilian tests and Semi-Circular Bend tests of rocks under various water vapor pressures was conducted to investigate the influence of the surrounding water vapor environment on uniaxial compressive strength, tensile strength and fracture toughness. The rocks used in this paper were Kumamoto andesite, African granodiorite and Korean granite. It was made clear that rock strengths and fracture toughness of these rocks are dependent on the water vapor pressure in the surrounding environment and decrease with increasing the pressure. 1 Introduction Strengths of a rock are dependent on not only the properties of rock itself but also the surrounding environment, such as temperature, humidity, confining pressure and so on. Furthermore, it has been known that fracture of a rock takes place owing to the subcritical crack growth caused by stress corrosion under the stress state below the strengths of the rock. The stress corrosion is the chemical reaction activated by stress concentration at a crack tip. The water vapor is considered to be a chemical reaction agent in the stress corrosion for silicate materials like a rock (Freiman 1984, Atkinson & Meredith 1979). Therefore it is desired that the influence of the water vapor on rock strengths is taken into account based on the results obtained from various experiments. In this paper, firstly, uniaxial compression (UC) test and Brazilian test were conducted on Kumamoto andesite to investigate the influence of surrounding non-atmospheric environments on uniaxial compressive (UC) strength and tensile strength (Jeong et al. 2007). The environments used in this paper were methanol, ethanol and acetone vapor as organic vapor, argon, nitrogen and oxygen as inorganic gas and water vapor, using special vacuum chamber. Then it was found that the water vapor is the most effective environment which promotes decreasing of the strengths, namely stress corrosion for rocks. Secondly, fracture toughness of various types of rock was estimated under various water vapor pressures in surrounding environment, as well as UC and tensile strengths. Semi-Circular Bend (SCB) test (Chong & Kuruppu 1984) was adopted to estimate the fracture toughness of rock for its simplicity of specimen preparation, equipment and testing procedure. The Kumamoto andesite, African granodiorite and Korean granite were used in the SCB test (Kataoka et al. 2011).

Abstract: Rock anisotropy is well-known and is of considerable interest in the field of rock engineering mainly because of difficulties in rock mechanical characterization. A proper understanding of rock mechanical anisotropy is required for the design and construction of foundations, in tunneling and in slope stability investigations. Therefore, mechanical characterization of anisotropic rocks has been and is a subject of research with enormous importance. This study focused on characterization of indirect tensile and uniaxial compressive strengths of schistose rocks from the Singhbhum Shear Zone, India. Applicability of point load and block punch index tests in predicting uniaxial compressive strength of these rocks was also evaluated. For every available angle (β) between foliations and collected core axis (when β≠ 0°), equivalent specimens were tested under Brazilian test condition taking 6 different angles (β/s) between loading direction and traces of foliations on the core end face (when β/ = 0°, 15°, 30°, 45°, 60°, 90°) into account. The study suggests that while characterizing Brazilian tensile strength of schistose rocks, not only β/ is important, the influence of β should also be aptly taken into account. The uniaxial compression test results showed that a positive linear trend of uniaxial compressive strength vs. β is apparent for the available range of β. This was found valid only for the specimens with the most prominent foliations that failed completely along these weakness planes under uniaxial compression. It was experimentally demonstrated that the block punch test could be of similar importance as the point load test in estimating uniaxial compressive strength of schistose rocks. In case of these index tests, the stipulation of a valid specimen failure mode by ISRM does not seem to be accurate for anisotropic rocks like schist. 1 INTRODUCTION Mechanical characterization of rock materials is of significant importance in rock engineering.

In this study, strength and deformation characteristics of rocks were examined at low temperatures. That is, results by the uniaxial tension test and the compression test were compared and discussed. It is supposed that an opening is excavated in a rock mountain to a depth of 100m beneath the ground surface with a diameter of 10m and LNG was stored there in. Using the results of the tests mentioned above, temperature and stress distribution around openings were analyzed. Then the thermal behavior of the rock mass around openings which was analyzed using the results of the uniaxial tension test and by the compression test was compared and discussed. 1. INTRODUCTION The authors have proposed and discussed storage of low temperature materials in openings excavated in rock mountains. The low temperature materials are LNG (−162 °C), LPG (−43 °C) and frozen food (−60 °C). This method has many advantages, such as efficient utilization of land, energy conservation, large scale storage, preservation of the environment, etc. In this case, as the rock mass around the openings will receive effects of low temperatures, it is necessary to consider the thermal behavior and the stability of openings. In this study, strength and deformation characteristics of rocks were examined at low temperatures. That is, results by the uniaxial tension test and the compression test were compared and discussed. It is supposed that an opening is excavated in a rock mountain to a depth of 100m beneath the ground surface with a diameter of 10m and LNG was stored within by using a "water curtain system". Using the results of the tests mentioned above, temperature and stress distribution around openings were analyzed by Finite Divided Element Method (FDEM) (Inada & Shigenobu 1983) and Crack Analysis Method (CAM) (Inada & Taniguchi 1987). Then the thermal behavior of the rock mass around openings which was analyzed using the results of the uniaxial tension test and the compression test, was compared and discussed. 2. EFFECT OF LOW TEMPERATURE ON STRENGTH AND DEFORMATION CHARACTERISTICS OF ROCKS 2.1 Rocks used for the tests The rocks used for the tests were granite, andesite and sandstone. In general, granite has many microcracks which exist parallel to three planes perpendicularly intersecting each other, and the plane which has the largest number of microcracks is called the "rift plane", the second is the "grain plane" the third is the "hard way plane" (Fleischmann 1990). In this study, in agreement with this classification, these planes were determined by measuring elastic wave propagation velocity of the block of rock. Specimens were formed 30 × 100 mm for the uniaxial tension test, 30 × 60 mm for the uniaxial compression test, and 30 × 30 mm for the Brazilian test. Specimens were prepared as "dry" by drying for one week in a desiccator, and as "wet" by being kept in a desiccator filled with distilled water for 5 hours using a vacuum pump. The physical properties of these specimens are shown in Table 1.

Basalts are the most common rocks of the Volcanic Complex of Lisbon. The interest of knowing the mechanical properties of this type of rock lays both in its interference with engineering projects (as tunnels and foundations) and its industrial exploitation (crushed stone for road paving, high resistance concrete and rockfill). Samples of basalt with various shapes (discs, cylinders and prisms) were prepared from quarry extracted blocks and submitted to uniaxial compressive strength, indirect tensile strength tests (point load, Brazilian and bending) and slake durability resistance. Results of that series of experiments are presented, compared and correlated in order to reveal insights about basalt properties and their mechanical characteristics. 1. INTRODUCTION Geomechanical properties of rocks are fundamental to predict rock mass behaviour for the purpose of adequately planning engineering projects. The present work was accomplished for studying basalts from the Volcanic Complex of Lisbon due to it industrial importance and reporting the obtained results from several different testing methods. Another objective was aimed to compare results gathered in the application of different methods in order to obtain a number of correlations that are valid for users who need simpler, faster and more economic ways of characterizing that rock type. 2. SAMPLE CARACHTERIZATION The Volcanic Complex of Lisbon (age 72 MA) is strongly represented by basalts, which cover an area of about 200 km 2 of extension. This formation corresponds to one of the most important igneous activities that occurred during the formation of the Atlantic Ocean. The specimens collected for testing were obtained in the "Moita da Ladra" quarry, located in Via Longa (Alverca), 20 km North of Lisbon. The basaltic rock mass that is being extracted there shows low grade of weathering although frequent networks of irregular fractures with quite low spacing, as it is shown in Fig. 1. An homogeneous matrix with very fine grain characterize the hand samples of this type of rock. An attempt was made to collect blocks large enough to obtain all the test specimens needed. Whenever this purpose was not possible all blocks were chosen with the same orientation and visual characteristics. All samples were inspected for macroscopic defects, such as small fractures, joints and weathering, so that a common standard was imposed and all specimens were prepared in accordance with ISRM Suggested Methods. The subsequent operation of coring mainly used NX (54mm) diameter core bits with carefully prepared parallel bases in the specimens. All samples were tested at their natural water content and with an average of at least 10 measurements for each test (except for uniaxial compressive strength with only 5 results). 3. TEST RESULTS Almost all tests were performed according to ISRM suggested methods, except the bending test that followed the Portuguese Standard NP - 314 (three point bending). 3.1. Uniaxial compressive strength Six basalt samples were tested for obtaining Young's modulus, Poisson's ratio and uniaxial compressive strength. The average value for Young's modulus was 79.2 GPa with a coefficient of variation of 10.28%.

ABSTRACT: The artificial weathering test was conducted to observe the change of the strength of the weathered rock for the purpose of the geotechnical assessment of historical monuments in Korea. It is shown that the largest reduction in tensile strength occurred from specimens experiencing both the crystallisation and heating-cooling cycles. It is suggested that in-door environment should be provided to the weathered historical monuments, especially located near the sea shore. RESUME: Nous avons eprouve la desagregation artificielle en vue d'evaluer Ie changement des roches desagregees des monuments historiques en Coree du Sud. Il en resulte que la grande reduction des valeurs de la force extensible s'est produit dans les echantillons, executes par deux experimentations à la fois, Ie selcristalisation et les cycles de chauffage-congelation. Il s'ensuit qu'on devrait construire l'environnement d'interieur pour prevenir contre la desagregation des monuments historiques, situes en particulier au bord de la mer. ZUSAMMENFASSUNG: Der kuenstiiche Verwitterungstest wurde durchgefuehrt zur Einschatzung der Festigkeitsveranderungen der wettergegerbten Steinen in den historischen Denkmalern. Daraus resultierte, daß die Munster, die durch die SaIz-Kristallisierung und zugleich den Erwarmung-Kuehlung-Zyklen getestet wurden, hinsichtlich der Zugfestigkeit am größten reduziert werden. Diese Resultate zeigten, daß die Zimmerumstande vorgesorgt werden sollen, um die fortdauemde Verwitterung der historischen Denkmaler vorzubeugen, die sich besonders nahe an der Kuste verbreiten. 1 INTRODUCTION In Korea, there exists a number of historical monuments which are made of rocks, especially granitic rocks. Most of them are highly valuable in terms of national history and culture. Older ones among them were built in A.D. 500 and have been weathered for 1500 years (Hur, 1994). The degree of weathering mainly depends on the location of the historical monuments, i.e. much more weathered in urban area and less weathered in rural area. Other factors affecting the degree of weathering are rainfall, temperature, freezing of water during the winter. Although it is known that these monuments have been severely weathered (Lee, 1993), no systematic work has been conducted to assess the weathering states and to suggest any method to slow down the weathering process. The purpose of this study is focused on the assessment of the geotechnical properties of the weathered rocks and the analysis of the main factors affecting the weathering. 2 SELECTION OF ARTIFICIAL WEATHERING TEST METHOD From a literature review, it is generally known that most of Korean historical monuments were made of granite (Hur, 1994). Similar granites from the weathered outcrops in Taejon city were carefully selected based on their similarities, i.e. same composition, same weathering state, because no direct sampling of the historical monuments was allowed. By this, a total number of 20 granite blocks were selected for coring. A total of twelve cores having 50mm diameter and 25mm thickness, were prepared for the Brazilian test which was adopted in this study because tensile failure is more sensitive to the effect of weathering than the compressive failure (Park, 1994). A literature review showed a variety of artificial weathering conditions, i.e. weathering under the slow and continuous flow of acidic solution (Augustithis, 1983), weathering cycles under temperature changes and liquid treatment (Ihalainen and Uusinoka, 1994), combined weathering by cycled process of water soaking, drying, fly ash abrasion, acid dip, salt dip and freezing (Bortz and Wonneberger, 1995). Each process represents the specific weathering condition, e.g. acid dip simulating the acid rainfall in urban area.