Quasi-static resonant column (QSRC) method for indirect assesment of natural weathered rock joint surface (original) (raw)
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.
International Journal of Geomechanics
The subtle alteration of surface geometry from a fresh surface to a sheared surface usually results in a considerable variation in the shear strength of jointed rock mass. Through profiling surfaces of the granite joints before and after the shear tests, an evaluation scheme was newly proposed by determining a desirable characteristic index and sampling interval of surface measurement in order to distinguish fresh and sheared joint surfaces quantitatively. The measured data demonstrated that although the mean Z2 (root mean square first derivation) values of all the profile lines were confirmed reasonable for estimating the JRC (joint roughness coefficient) value of the fresh joint surface, it could not completely evaluate the roughness of the sheared joint surfaces. Meanwhile, the distribution of slope angles, as the characteristic parameter, was proved enable to clearly distinguish the fresh and sheared rock joint surfaces incorporating the small sampling scales (<= 0.1 mm). The numerical simulations implemented in a mechanical shear model could confirm the critical effect of a slight change in surface geometry, and further prove that the sampling interval of 0.1 mm could sufficiently capture the evolved "waviness" and "unevenness" of rock joint surfaces. Overall, it was A Self-archived copy in Kyoto University Research Information Repository confirmed that the results of our study provide new clues for evaluating the surface roughness of fresh and sheared rock joints and can be beneficial for understanding the variation of surface geometry during the shear process.
Evaluation of Linearity of First Mode of Vibration in Resonant Column Testing
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2005, 2005
In resonant column testing (ASTM standard), the shear strain distribution along the height of a specimen is assumed linear and fixed at the base. To investigate these assumptions, specimens of dry sand, mine tailings, and cemented sand are tested at different confinement and shear strain levels. The measured mode shapes for dry sands and mine tailings are linear at low and high strain levels; however, for a stiff cemented-sand specimen the first mode shape presents slippage at the end platens. Resonant frequencies decrease up to 50 % while the damping ratios increase up to 200 % because of this slippage. The coupling between the specimen and end-platens is enhanced using three different agents: gypsum cement, portland cement, and epoxy resin. The epoxy resin produces the best coupling, whereas portland and gypsum cements are effective only at low confinements and strain levels. Even after eliminating the slippage at the end-platens, the shear wave velocity of aluminum and PVC probes decreases with the increase in specimen stiffness because of the lack of base fixidity. To correct this apparent reduction, a new model and calibration procedure based on a two-degree-of-freedom system are proposed.
Rock Joint Roughness Measurement and Quantification—A Review of the Current Status
Geotechnics
This paper provides a review of the present status of the topic dealt with. The contact and non-contact methods used for rock joint roughness measurement are summarized including their salient features, advantages, and disadvantages. A critical review is given of the empirical, statistical, and fractal-based methods used for rock joint roughness quantification identifying their salient features, shortcomings, and strong attributes. The surface topography of rough rock joints is highly erratic. Fractional geometry is better suited than Euclidean geometry in representing highly erratic rock joint surfaces. The influence of non-stationarity on accurate quantification of roughness is discussed. The existence of heterogeneity of natural rock joint roughness and its effect on computed roughness parameters are well illustrated. The controversial findings that have been appearing in the literature on roughness scale effects during the last 40 years have resulted from neglecting the effect o...
Lateral Non-Homogeneities Characterization Using Seismic
Seismic surface waves are well-suited for the study of the elastic profile of soils. Therefore this technique was adopted to evaluate the properties of stone columns used for ground improvement. A scaled-down model of typical stone columns in soft clay was constructed. Measurements were made on stone columns, under controlled conditions so that the properties of the materials used in the model under test were within limited ranges. The dispersive curve produced in this study demonstrated an increased phase velocity with increasing wavelength for the measurements on the clay (between columns), and decreased phase velocity with increasing wavelength for the measurements on the column. The results showed that were useful in characterization of the lateral non-homogeneities works such as vibro-stone column. These results pointed to the results can be influenced by the positioning of sensors with respect to the survey target. Benefit of this technique can be applied as a tool in quality control.
Non-Destructive Method for Rapid "In Situ" Characterization of Rocks
Bulletin of the Geological Society of Greece
The effective determination of the field and place of application of the products resulting from stone working is a compulsory requirement in the building activity and is solved by laboratory analyses. This article presents details on the determination, by non-destructive method, of the compression strength of the rocks, both "in situ" (in the deposit) and in a laboratory. The originality of the method consists in simplifying the determination process of this parameter, a method that is in agreement with the systems proposed to be applied in the European Community. The method has the advantage of being applicable in quarries, where knowledge of this parameter leads to a rationalizing of the working and more especially to a selection of the blocks by quality criteria. The method is applicable to all categories of natural consolidated hard rocks, being a viable alternative for deposits with an inhomogeneous composition as to quality and structure.