Experiments were conducted to study the relationship between the transmission ratio (TR) and normal stress, joint roughness, joint number and frequency of incident waves, respectively, when ultrasonic waves pass across a rock mass with one joint and multiple parallel joints oriented normally. The ultrasonic waves were generated and received by pairs of piezoelectric transducers and recorded by an ultrasonic detector. The specimens were subjected to normal stress by a hydraulic jack and loading frame. The jointed rock mass was produced by superposing rock blocks in the study. Rough joints were produced by grooving notches on the planar joints formed by sawing directly. In the case of multiple parallel joints, the overall thickness of specimens was maintained while the joint number changed. Three pairs of P-wave transducers and one pair of S-wave transducers with different frequencies were, respectively, applied and all transducers emitted signals perpendicular to the joints in the experiment. The results indicate that TR increases with increasing normal stress while the increment rate decreases gradually. This is particularly so when the normal stress is high enough that TR will approximate 1 even if the rock mass has many joints. In addition, the experiments indicate that the higher the wave’s frequency, the lower its TR, and this phenomenon is gradually reduced as the normal stress increases. In response to S-waves, TR increases with increase in joint roughness; however, in response to P-waves, TR decreases gradually with increase in joint roughness. For multiple parallel joints in a fixed thickness rock mass with normally incident P-waves, TR does not always decrease with increase in the number of joints, and there is a threshold joint spacing for a certain incident wave: when the joint spacing is smaller than the threshold value, TR will increase with a decrease in joint spacing. The experimental results support similar conclusions based on analytical results drawn by Cai and Zhao (Int J Rock Mech Min Sci 37(4):661–682, 2000), Zhao et al. (Int J Rock Mech Min Sci 43(5):776–788, 2006b) and Zhu et al. (J Appl Geophys 73:283–288, 2011a).
Propagation of elastic waves in discontinuous media is studied in this paper by the scattering matrix method (SMM). An electromagnetic transmission line analogy is also used to set up the mathematical model. The SMM operates in the frequency domain and allows for all wave polarizations (P, SV and SH). Rock masses are examples of discontinuous media in which the discontinuities (fractures or joints) influence wave propagation. Both elastic and viscoelastic joints are considered and the latter are...
Experiments have been conducted to determine the effects of parallel and variable directional joints on ultrasonic pulse propagation in two 60 × 60 × 360 mm prismatic marble blocks containing no joints, six parallel joints, and six variable directional joints. The results indicated that the attenuation increases with increasing ratio of joints in both models, but the attenuation ratio was higher for the variable directional jointed model than for the model with parallel joints. The relationships...
#1Jianbo Zhu(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 25
#2Andrea Perino(Polytechnic University of Turin)H-Index: 7
Last. Jian Zhao(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 63
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Rock joints are often filled with weak medium, for example, saturated clay or sand, of viscoelastic nature. Their effects on wave propagation can be modelled as displacement and stress discontinuity conditions. The viscoelastic behaviour of the filled joint can be described by either the Kelvin or the Maxwell models. The analytical solutions for wave propagation across a single joint are derived in this paper by accounting for the incident angle, the non-dimensional joint stiffness, the non-dime...
The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat, India have been analyzed to understand the attenuation of high frequency (2–25 Hz) P and S waves in the region. The frequency dependent relationships for quality factors for P (Q P) and S (Q S) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat. The earthquakes recorded at nine stations of Kachchh, fiv...
Abstract In order to investigate the transmission and reflection of stress waves across joints, a fractal damage joint model is developed based on fractal damage theory, and the analytical solution for the coefficients of transmission and reflection of stress waves across joints is derived from the fractal damage joint model. The fractal geometrical characteristics of joint surfaces are investigated by using laser profilometer to scan the joint surfaces. The dynamic experiments by using Split Ho...
Last. Jian Zhao(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 63
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This paper presents an analytical study on normally incident wave propagation across a joint set. Combined with the displacement discontinuity method (DDM), the virtual wave source method (VWSM) is adopted to take account of multiple wave reflections among joints. After theoretical formulation, a comparison between results from VWSM and those from the method of characteristics (MC) is carried out. These results agree well with each other, and the applicability of VWSM into wave propagation study...
Last. Jian Zhao(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 63
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An equivalent viscoelastic medium model is proposed for rock mass with parallel joints. A concept of "virtual wave source (VWS)'' is proposed to take into account the wave reflections between the joints. The equivalent model can be effectively applied to analyze longitudinal wave propagation through discontinuous media with parallel joints. Parameters in the equivalent viscoelastic model are derived analytically based on longitudinal wave propagation across a single rock joint. The proposed mode...
Abstract Dynamic properties of rock joints are of great interest to mining engineers, seismologists and geoscientists in characterizing the dynamic mechanical behavior of discontinuous rock mass. An experimental study of stress wave propagation across filled rock joints has been carried out using a modified Split Hopkinson Pressure Bar (SHPB) apparatus. Two granitic bars cored from a rock site were used as the incident and transmitter pressure bars in the SHPB tests, while a sand layer of differ...
Last. J. Teng(Harbin Institute of Technology Shenzhen Graduate School)H-Index: 1
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Abstract An explosion in a borehole or an accidental explosion in a tunnel will generate a two-dimensional (2-D) compressive wave that travels through the surrounding rock mass. For the problem of 2-D compressive wave propagation in a rock mass with parallel joints in the radial direction normal to the joints, parametric studies on the transmission ratio and the maximum rebound ratio are performed in universal distinct element code. The variation of the transmission ratio with the ratio of joint...
Abstract This paper presents the experimental and theoretical investigation of property of stress wave propagation in jointed rocks by means of SHPB technique and fractal geometry method. Our aim focuses on the influence of the rough joint surface configuration on stress wave propagation. The comparison of behavior of reflection and transmission waves, deformation and energy dissipation of a rough joint surface characterized by its fractal feature with that of a smooth plane joint has been carri...
Last. John R. Bargar(SLAC National Accelerator Laboratory)H-Index: 68
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From geochemical reactions to proppant emplacement, hydraulic fracturing induces various chemo-mechanical fracture alterations in shale reservoirs. Hydraulic fracturing through the injection of a v...
Last. Gabriel Walton(Colorado School of Mines)H-Index: 14
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Abstract Pre-existing discontinuities act as the primary source of damage initiation processes in rock masses, and consequently govern their overall deformational behavior. As laboratory tests are critical for establishing constitutive behavior of rocks, in this study, the impact of a pre-existing flaw on rock damage behavior has been analyzed through laboratory-scale experiments. For this purpose, prismatic Barre granite specimens with an existing flaw were progressively damaged under uniaxial ...
#1Malavika Varma(Indian Institute of Technology Madras)H-Index: 1
#2V. B. Maji(Indian Institute of Technology Madras)H-Index: 7
Last. A. Boominathan(Indian Institute of Technology Madras)H-Index: 13
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Abstract Waves propagating through rocks when intersected with joints gets transmitted or reflected. Joints or discontinuities in a rock affect the amplitude and velocity of the transmitted and reflected waves propagating through it. The changes occurring on a transmitted wave is following the properties of the incident wave namely frequency, amplitude, wavelength and the rockmass properties namely joint angle, joint roughness, joint stiffness, number of joints. In the present work, the effect o...
#1Dongya Han(PolyU: Hong Kong Polytechnic University)H-Index: 3
#2H. Yang(PolyU: Hong Kong Polytechnic University)H-Index: 2
Abstract External stresses, i.e., compressive, shear and tensile stresses, strongly affect seismic wave propagation across rock joints. The present study experimentally investigates the effects of tensile stresses on wave behaviors across single natural rock joints by simultaneously conducting ultrasonic measurements and direct tensile tests. Laboratory results show that increasing tensile stress causes decreases in transmission coefficient and spectral amplitudes for both ultrasonic P- and S-wa...
#1Jian Zhou(CAS: Chinese Academy of Sciences)H-Index: 140
#2Luqing Zhang(CAS: Chinese Academy of Sciences)H-Index: 11
Last. Duoxing Yang(CEA: China Earthquake Administration)H-Index: 12
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Abstract The stiffness coefficient is a key parameter of rock fractures that controls the properties and behavior of a rock mass. According to the displacement discontinuity theory, the dynamic stiffness of rock fractures can be back analyzed using stress wave propagation. This study aims to measure the dynamic stiffness of rock fractures then develop an empirical ratio to describe the relationship between dynamic and static stiffness. Propped artificially fractured shale and granitic rock sampl...
The shear strength of the rock discontinuities under different shear rates is of great importance to evaluate the stability of rock mass engineering, which is remarkably influenced by the size effects induced by both the length and the undulated amplitude of discontinuities. An advanced shear strength criterion taking into account the size and the shear rate simultaneously was proposed. There is an advantage of the dimension unity in terms of the new shear strength criterion in comparison to pre...
Last. Tao Zhou(SZU: Shenzhen University)H-Index: 12
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Damaged rock mass contains a great number of microstructures and defects at various scales, which could influence wave propagation significantly. In this paper, investigation of low-amplitude stress wave attenuation in rocks with different damage degrees was undertaken to determine the effects of parameters including damage degree, heterogeneity and type of waveforms on wave propagation, attenuation and slowness. The numerical method was validated through comparison with laboratory measurements....
#1Yidu Hong(CAS: Chinese Academy of Sciences)H-Index: 6
#2Baiquan Lin(CUMT: China University of Mining and Technology)H-Index: 35
Last. Wen Nie(Jiangxi University of Science and Technology)H-Index: 10
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Abstract Formation microwave heating treatment (FMHT) is a potential method for degassing coalbed methane. Camera pictures and ultrasonic method were used to evaluate the crack propagation on the surface and in the interior of the coal cores, respectively. The results suggest that the fracture induced by microwave energy would remarkably increase with increased heating time. New fractures and pore sizes produced by microwave energy decreased P- and S-wave velocity in coal cores. The amplitude of...
In this study, density, porosity, void ratio, and ultrasonic P- and S-wave first arrival times were measured on limestone, sandstone, and siltstone samples obtained by using mechanical soundings in the city of Zonguldak. Turkey. Fracture and fissure indexes of rocks were calculated from ultrasonic P- (Vp) and S-wave (Vs) velocities. Multi-parameter relationships occurred between ultrasonic velocities with seismic fracture and fissure indexes and physical and mechanical properties of the rocks. R...
