Quasi-static resonant column (QSRC) method for indirect assesment of natural weathered rock joint surface (original) (raw)
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Resonant Column Tests and Nonlinear Elasticity in Simulated Rocks
Rock Mechanics and Rock Engineering, 2017
Rocks are generally regarded as linearly elastic even though the manifestations of nonlinearity are prominent. The variations of elastic constants with varying strain levels and stress conditions, disagreement between static and dynamic moduli, etc., are some of the examples of nonlinear elasticity in rocks. The grain-to-grain contact, presence of pores and joints along with other compliant features induce the nonlinear behavior in rocks. The nonlinear elastic behavior of rocks is demonstrated through resonant column tests and numerical simulations in this paper. Resonant column tests on intact and jointed gypsum samples across varying strain levels have been performed in laboratory and using numerical simulations. The paper shows the application of resonant column apparatus to obtain the wave velocities of stiff samples at various strain levels under long wavelength condition, after performing checks and incorporating corrections to the obtained resonant frequencies. The numerical simulation and validation of the resonant column tests using distinct element method are presented. The stiffness reductions of testing samples under torsional and flexural vibrations with increasing strain levels have been analyzed. The nonlinear elastic behavior of rocks is reflected in the results, which is enhanced by the presence of joints. The significance of joint orientation and influence of joint spacing during wave propagation have also been assessed and presented using the numerical simulations. It has been found that rock joints also exhibit nonlinear behavior within the elastic limit.
A review of methods, techniques and approaches on investigation of rock anisotropy
An extensive review on the anisotropy of rock samples has been carried out to characterize the velocity and strength behaviors under a variety of geometrical and mechanical conditions. Primarily, the causes and impacts of anisotropy is discussed to further understand the importance of the effect of such material from an engineering point of view. The strength anisotropy is investigated in laboratory using the standard strength testing practices (UCS, Triaxial, direct shear and etc..) to perceive the directional dependence of strength for anisotropic rocks and the velocity anisotropy using the ultrasonic scanning of the samples under destructive tests to evaluate the cracks propagation, density and orientation. Then, thorough literature review is done to highlight the significant observations that have been previously elicited. Furthermore, the mathematical determination methods of the degree of anisotropy are explored. Finally, this paper summarize that the strength and velocity anisotropy might be influenced by almost the same factors; however, the behavior of each anisotropy may not be the same considering the rock matrix and failure criteria.
On the Determination of Rock Anisotropy for Stress Measurements
2008
The traditional methods of in situ stress determination can be seriously affected by rock anisotropy, which necessitates both development of the corresponding interpretation methods and accurate determination of the elastic characteristics of the anisotropic rocks. In this contribution we consider the method of determination of anisotropic moduli by testing small subcores drilled in different directions. Rock anisotropy is often induced by the presence of joints, foliation, schistosity, bedding or similar features. In the case when the spacing between the theses features exceeds the length of the subcores the results of moduli determination in separate subcores shows considerable variability. A mechanism of this variability lies in the fact that a particular subcore may or may not be intersected by a joint. We show that despite this, the averaging procedure used in the method of moduli reconstruction, developed previously by the authors, can still be successfully applied, since the averaging over the subcores recovers the large-scale moduli. However, the standard deviation associated with the randomness of joint-subcore intersection can in some case be very large (potentially unlimited) which explains the observed variability.
Journal of The Acoustical Society of America, 2001
This paper presents the experimental and theoretical results of applying resonant acoustic spectroscopy ͑RAS͒ to determine elastic parameters and losses in such consolidated granular materials as rock and building bricks. First, the theoretical aspects of the RAS method are outlined. A computer code for the rectangular and cylindrical samples was developed and tested. The results of experiments on specimens of rock and ceramic brick are then described. Finally, a modification of the previously published RUS algorithm is presented which permits a significant reduction in computing time for elongated samples.
Materiales de Construcción, 2022
Nondestructive testing techniques have attracted growing interest in the last few years due to their ability to assess material properties without damaging the specimens. The free-free resonance method is a nondestructive testing technique based on the analysis of the natural frequencies of a sample. This study presents and discusses the applicability of this technique, traditionally used on soils, for the mechanical characterization of rocks. With this aim, the free-free resonance method is used to obtain the dynamic elastic modulus and shear modulus of four carbonate rocks that have been widely used as construction materials in southern Spain. The results from the nondestructive evaluation of dry and saturated rocks, in combination with petrographic characterization and uniaxial compression tests, make it possible to assess the existing relationships between the mechanical properties of carbonate rocks and to evaluate the impact of porosity and moisture content on their mechanical...
Resonance-based acoustic technique applied to the determination of Young’s modulus in granites
2007
The natural stone industry plays an important role in construction sector activity, and due to this fact the accurate knowledge of the physico-mechanical properties of this kind of materials is indispensable for the configuration of their quality standards. In this work we have optimized an acoustic technique, based on the measurement of the fundamental mode resonance frequency of the longitudinal wave, to determine Young's modulus in different granite variety specimens. The equipment employed was an Erudite MK3 test system (CNS Farnell) working in the range 1 to 100 kHz. The resonance frequencies obtained ranged from 4 to 10 kHz, depending on the granite variety. Based on these resonance frequencies, we obtained values of the longitudinal wave velocities ranging from 2500 to 6000 m/s and of the dynamic Young's modulus from 20 to 100 GPa. We also compared the dynamic modulus results with the static Young's modulus obtained by destructive techniques, and analysed its rela...
Using Resistivity Measurements to Determine Anisotropy in Soil and Weathered Rock
Engineering, Technology & Applied Science Research, 2013
This study uses electrical resistivity measurements of soils and weathered rock to perform a fast and reliable evaluation of field anisotropy. Two test sites at New Concord, Ohio were used for the study. These sites are characterized by different landform and slightly east dipping limestone and siltstone formations of Pennsylvanian age. The measured resistivity ranged from 19 Ω∙m to 100 Ω∙m, and varied with depth, landform, and season. The anisotropy was determined by a comparison of resistance values along the directions of strike and the dip. Measurements showed that the orientation of electrical anisotropy in the shallow ground may vary due to fluid connection, which is determined by the pore geometry in soil and rock, as well as by the direction of fluid movement. Results from this study indicated that a portable electrical resistivity meter is sensitive and reliable enough to be used for shallow ground fluid monitoring.
Application of P SH-waves for rock anisotropy studies: Genting Highlands case study
Bulletin of the Geological Society of Malaysia
Seismic refraction surveys utilizing P & SH-waves were carried out over an abandoned quarry at Genting Highlands in order to study the anisotropy of the bedrock of that site. Shear (S) and compression (P) acoustic velocities of the subsurface refractor have shown significant variations in their spatial distribution. These variations in velocity values were compiled and then qualitatively correlated with surface fracture surveys conducted during the course of acquiring the field data. Seismic P & SH-wave velocity values obtained from in situ measurements have been used for calculating the anisotropy percentage and slowness factor. The petrophysical parameters computed are then contoured to identify the orientation of fracture zones along the refractor surface.
Assessing cross anisotropy of small-strain stiffness using the resonant column apparatus
2010
Almost all soils exhibit cross-anisotropic stiffness to some extent. However, measuring the cross anisotropic properties of soils is difficult because of the need to determine the 3 independent stiffness parameters E v , E h , G vh , and the associated Poisson's ratios, vh and hh. Current techniques that are employed, for example using bender elements or field geophysics, are not always reliable, whilst preparing specimens in different orientations and subsequent testing using standard laboratory techniques has practical constraints. The resonant column is a laboratory apparatus that has been extensively used to measure the torsional stiffness (G vh). Relatively recent development has also allowed the Stokoe resonant column to measure Young's modulus from flexural excitation of the specimen. The apparatus has also been used to determine E v through axial oscillation. Thus a modified resonant column apparatus can apply four different excitations (flexure in two directions, torsion and longitudinal excitation) to a soil. This paper reports a series of dynamic finite element numerical simulations of physical tests in the resonant column apparatus, carried out to model both the apparatus and a cross-anisotropic soil specimen. Forward modelling has been carried out to determine the impact of different degrees of anisotropy on the resonant frequencies of 'specimens' with their axes of anisotropy aligned in different directions relative to the vertical axis of the apparatus. Methods of determining the elastic parameters from these data are assessed.
On the evaluation of rock integrity around mine workings with anchorage by the shock-spectral method
International Journal of Fatigue, 2018
The goal of this study is to investigate the integrity of gypsum-containing rocks during underground mining using non-destructive testing (NDT) anchors by the shock-spectral method. Studies were conducted in-situ at a gypsum deposit in the roof of the transport drift and cleaning chamber of a mine. Steel-polymer anchors were studied. The anchors were fastened in the hole with polymer resin and were fastened outside the hole with washers and nuts. The anchors were free in the middle. The vibrational response after striking the protruding end of an anchor was recorded, a spectrum was calculated, and the frequency (F) of the spectral maximum and the acoustic quality factor (Q) were determined. Q was calculated as the ratio of F to the frequency band at the 1/ 2 level of the spectrum maximum. With a tensioned anchor, it was determined that at the free length of the anchor, half of the wavelength was placed (F is high) and the outer layer of roof rocks determined the measured data. With a weakened anchor, a quarter wavelength was placed on its length (F is low) and the inner layer of roof rocks determined the measured data. All anchors were divided into two groups. When F ≤ 1050 Hz the inner layers determined the Q-factor, and at F > 1050 Hz the external layers determined the Q-factor. The average value of Q-factors of tensioned anchors (outer layers) were below the average value of Q-factors of weakened anchors (inner layers). Large Q values were assumed to correspond to higher rock integrity and strength. The ratio of the average value of the Q-factors of the external layer to the average value of the Q-factors of the inner layer was used to assess roof rock integrity. Smaller values of this ratio were characterized by lower rock integrity and a tendency to collapse and fall.