Laboratory determination of direct shear strength of granitoid rocks; examples from the host rock of the nuclear waste storage facility of Bátaapáti (Hungary) (original) (raw)
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This paper presents results and interpretation of shear strength tests performed on granitoid rocks that were obtained from the National Radioactive Waste Repository in Bátaapáti (south-western Hungary). Direct shear strength tests were carried out under laboratory conditions along clear, and calcite covered granitoid joints, using samples drilled from larger blocks. The shear strength influencing parameters were investigated, and sample groups were distinguished according to surface roughness and joint infill properties. Peak and residual internal angle of friction values and apparent cohesion were determined from the measurements. The results are represented in the form of shear stress – normal stress diagrams.
Shear strength criteria for rock, rock joints, rockfill and rock masses: Problems and some solutions
Although many intact rock types can be very strong, a critical confining pressure can eventually be reached in triaxial testing, such that the Mohr shear strength envelope becomes horizontal. This critical state has recently been better defined, and correct curvature or correct deviation from linear Mohr-Coulomb (M-C) has finally been found. Standard shear testing procedures for rock joints, using multiple testing of the same sample, in case of insufficient samples, can be shown to exaggerate apparent cohesion. Even rough joints do not have any cohesion, but instead have very high friction angles at low stress, due to strong dilation. Rock masses, implying problems of large-scale interaction with engineering structures, may have both cohesive and frictional strength components. However, it is not correct to add these, following linear M-C or nonlinear Hoek-Brown (H-B) standard routines. Cohesion is broken at small strain, while friction is mobilized at larger strain and remains to the end of the shear deformation. The criterion 'c then n tan ϕ' should replace 'c plus n tan ϕ' for improved fit to reality. Transformation of principal stresses to a shear plane seems to ignore mobilized dilation, and caused great experimental difficulties until understood. There seems to be plenty of room for continued research, so that errors of judgement of the last 50 years can be corrected.
2020
Determination of the mechanical behaviour of intact rock is one of the most important parts of any engineering projects in the field of rock mechanics. The most important mechanical parameters required to understand the quality of intact rock are Young's modulus (E), Poisson's ratio (m), the strength of rock (r c) and the ratio of Young's modulus to the strength of rock known as modulus ratio (M R), which can be used for calculations. The particular interest of this paper is to investigate the relationship between these parameters for Hungarian granitic rock samples. To fulfil this aim, Modulus of elasticity (E), Modulus of rigidity (G), Bulk modulus (K) and the modulus ratio (M R = E/r c) of 50 granitic rock samples collected from Bátaapáti radioactive waste repository were examined. Fifty high-precision uniaxial compressive tests were conducted on strong (r c-[ 100 MPa) rock samples, exhibiting the wide
IJERT-A Study on Variation in Mineralogical and Strength Characteristics of Some Granitic Rocks
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/a-study-on-variation-in-mineralogical-and-strength-characteristics-of-some-granitic-rocks https://www.ijert.org/research/a-study-on-variation-in-mineralogical-and-strength-characteristics-of-some-granitic-rocks-IJERTV3IS10170.pdf Rock texture and mineralogical composition is of great importance in understanding engineering characteristics of a rock. In this study thin sections were used to assess the texture and mineralogical composition of some granitic rocks of Jabalpur and Bundelkhand regions of Madhya Pradesh state of India. The Brazilian tensile strength, point load index and unconfined compressive strengths (UCS) of these rocks samples were also found out. The test results showed that there are significant variations in the engineering properties of the granitic rocks. The UCS varies from 120 MPa to 175MPa for dry samples and 119 MPa to 170 MPa for saturated samples. Brazilian tensile strength also has variations from 9.6 MPa to 18.4 MPa for dry sample whereas in saturated the value varies from 8.5 MPa to 17.7 MPasimilarly Point Load Strength Index 6.14 MPa to 9.26 MPa for dry sample and for saturated sample 5.70 MPa to 8.55 MPa conditionsrespectively. The possible reasons for such variations are due to the change in textural, structural and mineralogical composition of such rocks. Introduction:
Strength and dilatancy of jointed rocks with granular fill
Acta Geotechnica, 2010
It is well recognised that the strength of rock masses depends upon the strain history, extent of discontinuities, orientation of plane of weakness, condition of joints, fill material in closely packed joints and extent of confinement. Several solutions are available for strength of jointed rock mass with a set of discontinuities. There is a great multiplicity in the proposed relationships for the strength of jointed rocks. In the present study, the author conceives the effect of increasing stresses to induce permanent strains. This permanent strain appears as micro crack, macro crack and fracture. A fully developed network of permanent deformations forms joint. The joint may contain deposits of hydraulic and hydrothermal origin commonly known as gouge. The joint factor numerically captures varied engineering possibilities of joints in a rock mass. The joints grow as an effect of loading. The growth of the joints is progressive in nature. It increases the joint factor, which modifies the failure stresses. The dilatancy explains the progressive failure of granular media. Hence, a mutual relationship conjoins effectively the strength of jointed rock and a dilatancy-dependent parameter known as relative dilatancy. This study provides a simple and integral solution for strength of jointed rocks, interpreted in relation to the commonly used soil, and rock parameters, used for a realistic design of structure on rock masses. It has scope for prediction of an equivalent strength for tri-axial and plane strain conditions for unconfined and confined rock masses using a simple technique.
Applied Mechanics, 2023
Any rock mechanics' design inherently involves determining the deformation characteristics of the rock material. The purpose of this study is to offer equations for calculating the values of bulk modulus (K), elasticity modulus (E), and rigidity modulus (G) throughout the loading of the sample until failure. Also, the Poisson's ratio, which is characterized from the stress-strain curve, has a significant effect on the rigidity and bulk moduli. The results of a uniaxial compressive (UCS) test on granitic rocks from the Morágy (Hungary) radioactive waste reservoir site were gathered and examined for this purpose. The fluctuation of E, G, and K has been the subject of new linear and nonlinear connections. The proposed equations are parabolic in all of the scenarios for the Young's modulus and shear modulus, the study indicates. Furthermore, the suggested equations for the bulk modulus in the secant, average, and tangent instances are also nonlinear. Moreover, we achieved correlations with a high determination factor for E, G, and K in three different scenarios: secant, tangent, and average. It is particularly intriguing to observe that the elastic stiffness parameters exhibit strong correlation in the results.
Residual strength of granitic rocks
Tunnelling and Underground Space Technology, 2021
When carrying out compressive tests on rock specimens, a stress plateau is typically attained following peak strength within a strain range a few times larger than the strain at peak strength. This stress level is commonly known as residual strength. A large database of these tests on granitic rock specimens has been compiled and analyzed in detail with the aim of improving understanding of the residual strength of this type of rock. It is observed that physical scale does not significantly change this residual strength. This stress threshold is also shown to be independent of the initial level of jointing in the rock volume. The implication of these findings is that residual strength derived from rock specimen testing can be potentially extended to rock mass scale, at least for granitic rocks. Three one-parameter residual strength models have been used to fit laboratory test residual strength data of granitic rocks, and all of them are shown to reasonably approximate the actual data. Additionally, the residual laboratory strength parameters of all the varied studied granitic rocks for varying scale and pre-jointing tend not to be very different, covering a limited range of values. Ultimately, the potential errors in simple excavation analysis that might result from a priori assumptions regarding the residual strength of granitic rock masses are quantified.
Shear Behaviour of Rock Joints
2000
This title covers the fundamental properties of rock joints, the method of laboratory testing of rock joints, and shear strength assessment under different loading conditions. This work is intended as a reference text for students and practitioners in mining and rock engineering.
Shear strength behaviour of rock joint material influenced by different weathering grade
Journal of Physics: Conference Series, 2019
Shear strength parameter is a crucial in designing the rock mass structures such slope and tunnel. Stability of rock mass structure is affected by apparent joint sets and discontinuities present in the rock mass especially when the joint interfaces degraded and physically altered due to weathering effect. The weathered condition imposed on joint surface importantly play the role to control the shear strength characteristic and sliding behaviour. A comprehensive study and focussing on effect of weathering grade to the rock joint surface particularly for granite type of rock was introduced. A set of granite samples were collected from a quarry then been classified into respective grade of weathering based on surface hardness by using Schmidt rebound hammer and rock material density by using PUNDIT test. The standard laboratory testing of direct shear test that accordance to ISRM suggested method were carried out on jointed block samples with different grades of weathering. Detail asse...
The measure of friction angles for different types of granular material
Journal of Mountain Science, 2019
The aim of this research is to deepen the knowledge of the role of friction on the dynamics of granular media; in particular the friction angle is taken into consideration as the physical parameter that drives stability, motion and deposition of a set of grains of any nature and size. The idea behind this work is a question: is the friction angle really that fundamental and obvious physical parameter which rules stability and motion of granular media as it seems from most works which deal with particle dynamics? The experimental study tries to answer this question with a series of laboratory tests, in which different natural and artificial granular materials have been investigated in dry condition by means of a tilting flume. The characteristic friction angles, both in deposition (repose) and stability limit (critical) conditions, were measured and checked against size, shape, density and roughness of the considered granular material. The flume tests have been preferred to "classical" geotechnical apparatuses (e.g. shear box) since the flume experimental conditions appear closer to the natural ones of many situations of slope stability interest (e.g. a scree slope). The results reveal that characteristic friction angles depend on size and shape of grains while mixtures of granules of different size show some sorting mechanism with less clear behaviour.