Filled Rock Joints Research Articles

Study on stress distribution and extrusion load threshold of compressed filled rock joints

Abstract The distribution of stress and the normal extrusion load threshold in weak interlayer are crucial for direct shear test of filled rock joints, but there is a lack of theoretical research in this area. First, an analytical solution for stress distribution was derived using a semi-inverse method. Then, it is compared by the numerical simulation method. Finally, the influence of the width and thickness of weak interlayer on the extreme values of stress components was analyzed, and the distribution pattern of the normal extrusion load was discussed. The results show that under the same conditions, the analytical solution and the numerical simulation results are in good agreement. The maximum horizontal stress in the weak interlayer decreases with increasing width and increases with increasing thickness, while the change of the minimum is opposite. The normal extrusion load increases first and then decreases along the width direction of the weak interlayer. By comparing the normal extrusion load with the empirical value, the mechanism of extrusion failure in the weak interlayer is revealed.

Experimental study on the role of clay mineral and water saturation in ultrasonic P-wave behaviours across individual filled rock joints

Understanding wave propagation across rock joints is of great importance in rock engineering, petroleum engineering, and other geophysical applications. Previous studies have shown that wave behaviours across filled rock joints are highly affected by the properties of filling materials. However, how clay minerals and water saturation of the infilling affect wave attributes across filled rock joints is still poorly understood. In this study, ultrasonic tests were conducted on kaolinite- and bentonite-filled rock joints to investigate the roles of clay minerals and the water saturation of infillings on elastic P-wave behaviours across individual filled rock joints. The test results show that the infilling's water saturation and mineralogical compositions have combined effects on P-wave signatures of single rock joints filled with clayey soils. Particularly, for the kaolinite-filled rock joint, P-wave velocity and attenuation first increase and then slightly decline with the increasing water saturation. By contrast, for the bentonite-filled rock joint, an increase in water saturation causes gradual decreases in velocity and attenuation. The integrated interpretation of the experimental results indicates that the difference in heterogeneity saturation due to clay hydration is the first-order reason for the discrepancies in saturation-dependent P-wave attributes between kaolinite- and bentonite-filled rock joints. The findings of this study can help further understand wave propagation and attenuation across rock joints filled with fluid-saturated clayey soils.

Experimental study on normal deformation characteristics of filled rock joints with typical fluctuation morphology

The uneven deformation of filled rock joints subjected to ground stress can easily cause instability in engineering rock masses. Fluctuations in morphology and filling are the main factors affecting the normal deformation of filled rock joints. To study the effect of the degree of filling and the degree of morphology fluctuation on the normal deformation of filled rock joints, we conducted a systematic experimental study. First, rock joints with joint roughness coefficients of 1,5, 9, 13, and 17 were selected based on Barton’s typical curves. Then, filled rock joint samples were made using a self-developed filled rock joint sample mold and three-dimensional engraving technology. Lastly, compression tests were carried out to analyze the effect of the degree of filling and the degree of morphology fluctuation on the normal deformation characteristics of filled rock joints. The results show that the degree of filling significantly affects the normal deformation of filled rock joint samples. The normal deformation of filled rock joints has a nonlinear relationship with normal stress. The power function equation can well represent the normal closure deformation behavior of filled rock joints. Additionally, a relationship between the maximum closure deformation of filled rock joints and the degree of filling was established based on Bandis’s empirical formula. The proposed equation takes into account the effect of the degree of filling by replacing the rock joint opening with filling thickness, and the predicted values are in good agreement with the experimental results.

Experimental study on compression mechanical characteristics of filled rock joints after multiple pre-impacts

The prefabricated artificial filled jointed rock specimens are impacted by a self-made drop hammer impact device for many times, and the specimens with different degrees of cumulative damage characteristics are obtained. Then, the static and dynamic compression mechanical properties are studied by using universal testing machine and SHPB device. Through the static compression test, the strength and deformation characteristics of jointed rock specimens after multiple impacts are obtained, and the influence of the damage degree of jointed rock specimens characterized by wave velocity on the compressive strength of filled joints is analysed. Based on the results of SHPB impact test, the dynamic strength and deformation evolution, wave propagation law and energy dissipation law of filled joints after multiple impacts are analysed. During the SHPB test, the impact failure process of rock specimens is recorded by a high-speed camera. The experimental results show that the damage degree of jointed rock samples increases nonlinearly after multiple impacts. The attenuation laws of static strength and dynamic strength of rock samples under the same damage evolution conditions are different. With the increase of impact times, the failure mode of jointed rock samples after damage is simpler and tends to compression failure.

Ultrasonic S-wave responses of single rock joints filled with wet bentonite clay

Clay minerals are prevalent in rock discontinuities and have significant effects on mechanical, hydraulic and seismic properties of rock masses. Understanding seismic behaviours across individual clay-rich rock joints is of great importance in the fields of geology and earth sciences. However, the wave responses of individual clay-rich rock joints have not been well understood until now. This paper reports a laboratory investigation of ultrasonic S-wave propagation and attenuation across single rock joints filled with bentonite clays with varying degree of water saturation. In this study, a series of acoustic measurements were conducted on specimens of the bentonite clay-filled rock joint using a self-developed ultrasonic pulse-transmission test system that equipped with a S-wave transducer pair with a dominant frequency of 250 kHz. Based on the obtained laboratory data, the wave velocity, transmission ratio and the time-frequency-energy distribution of the S-waves transmitted through the bentonite clay-filled joint were calculated and evaluated. The experimental results show that the degree of water saturation of the bentonite clay greatly affects S-wave responses of the filled rock joint. In particular, an increase in the degree of saturation causes a nonlinear decrease in S-wave velocity. In addition, as the water saturation of the bentonite clay increases, the wave attenuation decreases; the minimum wave attenuation is reached at a saturation degree of 71.4% and then the attenuation increases slightly. Additionally, with the increase of the water saturation, the magnitudes of the S-wave energy transmitted across the bentonite clay-filled joint firstly increases and then decreases. The S-wave energy is mostly stored in the frequency range of 150 - 300 kHz regardless of the degree of water saturation of the bentonite clay. This finding indicates that the frequency partition of the transmitted S-waves rarely changes with the changing water saturation. The present work could not only compensate for the lack of laboratory-based research on wave behaviours across clay-rich rock joints but also provides insights into the interpretation of acoustic data from field tests for detecting, characterizing and monitoring rock discontinuities.

Experimental Study on Static and Dynamic Compression Mechanical Properties of Filled Rock Joints

The static and dynamic compression mechanical properties of the prefabricated artificial filled rock joints specimens with different fillings and different joint thicknesses are tested, respectively. Then, the strength, deformation, wave propagation and energy dissipation laws of the filled joints are analyzed. The experimental results show that the static and dynamic compression strength of filled joints increases with the strength of filling materials while decreases with the filling thickness. The deformation characteristics of filled joints under static and dynamic compression are positively correlated with the properties of filling materials and the thickness of filled joints. With the increasing of the filling thickness, the reflection coefficient increases while the transmission coefficient decreases. With the increase of the strength of the fillings, the reflection coefficient decreases while the transmission coefficient increases. The energy dissipation ratio decreases with the increase of the filliing thickness and increases with the increase of the strength of the filling material.

New peak shear strength model for cement filled rock joints

Grouting can significantly improve the mechanical properties of a fractured rock mass. A set of indoor grouting test systems is designed, and 3D scanning and direct shear tests are carried out for 10 groups of grouted joint specimens. In this study, grouted joints are simplified to unfilled joints and cement stone (including the bulk paste and transition zone). The impact of cement stone on unfilled joints is defined as the filling effect and bonding effect. First, 3D morphological characteristics of unfilled joints are analyzed. Then, a weak-filling joint shear model is derived based on the existing shear strength model for unfilled joints. Finally, the shear model for grouted joints is derived from the shear model for filled joints. Reinforcement mechanisms, failure modes and causes of error in grouted joints are discussed. The effects of roughness, filling degree, rock to filling material strength ratio, normal stress and cohesion on peak shear strength are considered comprehensively in the new model for grouted joints. The new model is consistent with the basic form of the Mohr-Coulomb criterion. The good agreement between test data and calculated results from the new model indicates the new model is suitable for predicting the shear strength of grouted joints.

Propagation of the Stress Wave Through the Filled Joint with Linear Viscoelastic Deformation Behavior Using Time-Domain Recursive Method

The dynamic behavior of filled joints is mostly controlled by the filled medium. In addition to nonlinear elastic behavior, viscoelastic behavior of filled joints is also of great significance. Here, a theoretical study of stress wave propagation through a filled rock joint with linear viscoelastic deformation behavior has been carried out using a modified time-domain recursive method (TDRM). A displacement discontinuity model was extended to form a displacement and stress discontinuity model, and the differential constitutive relationship of viscoelastic model was adopted to introduce the mass and viscoelastic behavior of filled medium. A standard linear solid model, which can be degenerated into the Kelvin and Maxwell models, was adopted in deriving this method. Transmission and reflection coefficients were adopted to verify this method. Besides, the effects of some parameters on wave propagation across a filled rock joint with linear viscoelastic deformation behavior were discussed. Then, a comparison of the time-history curves calculated by the present method with those by frequency-domain method (FDM) was performed. The results indicated that change tendencies of the transmission and reflection coefficients for these viscoelastic models versus incident angle were the same as each other but not frequency. The mass and viscosity coupling of filled medium did not fundamentally change wave propagation. The modified TDRM was found to be more efficient than the FDM.

Analytical Time-Domain Solution of Plane Wave Propagation Across a Viscoelastic Rock Joint

The effects of viscoelastic filled rock joints on wave propagation are of great significance in rock engineering. The solutions in time domain for plane longitudinal ( P-) and transverse ( S-) waves propagation across a viscoelastic rock joint are derived based on Maxwell and Kelvin models which are, respectively, applied to describe the viscoelastic deformational behaviour of the rock joint and incorporated into the displacement discontinuity model (DDM). The proposed solutions are verified by comparing with the previous studies on harmonic waves, which are simulated by sinusoidal incident P- and S-waves. Comparison between the predicted transmitted waves and the experimental data for P-wave propagation across a joint filled with clay is conducted. The Maxwell is found to be more appropriate to describe the filled joint. The parametric studies show that wave propagation is affected by many factors, such as the stiffness and the viscosity of joints, the incident angle and the duration of incident waves. Furthermore, the dependences of the transmission and reflection coefficients on the specific joint stiffness and viscosity are different for the joints with Maxwell and Kelvin behaviours. The alternation of the reflected and transmitted waveforms is discussed, and the application scope of this study is demonstrated by an illustration of the effects of the joint thickness. The solutions are also extended for multiple parallel joints with the virtual wave source method and the time-domain recursive method. For an incident wave with arbitrary waveform, it is convenient to adopt the present approach to directly calculate wave propagation across a viscoelastic rock joint without additional mathematical methods such as the Fourier and inverse Fourier transforms.

Experimental Study of S-wave Propagation Through a Filled Rock Joint

This experimental study proposes a Split Shear Plates model to investigate the effects of a filled joint on S-wave attenuation. A dynamic impact is used to create frictional slip and generate an incident S-wave. The filled joint is simulated using a sand layer between two rock plates. Normal stress is applied to the filled joint, and semiconductor strain gauges are arranged on the two plates to measure the strain. Verification tests are conducted to validate the reliability of the experimental results. A series of tests is performed to investigate the influence of the normal stress, filled thickness and particle size of the filling materials on the S-wave propagation. The transmission coefficients of the filled joints are smaller than those of the non-filled joints because of the attenuation associated with the filling materials. Additionally, the transmission coefficients exhibit a stronger correlation with the normal stress than with the filled thickness or particle size. The transmission coefficients increase at a decreasing rate as normal pressure increases.

Propagation of high amplitude stress waves through a filled artificial joint: An experimental study

This paper investigates the propagation of high amplitude stress waves through a filled joint using a modified steel split Hopkinson pressure bar (SHPB) system. Quartz sand fillings with various thickness are placed in a steel tube and then sandwiched between the incident and transmitted bars to simulate the filled rock joints. Using SHPB, the incident stress waves with similar frequency spectrum but varying amplitude are induced to load the artificial filled joints. The particle size distributions of the fillings after tests are analyzed. It is discovered that as the amplitude of the incident wave increases, the fillings experience three stages of deformation: initial compaction, crushing and crushing and compaction. In the initial compaction stage and the crushing and compaction stage, the fillings are mainly compacted, and thus the transmission coefficient increases with the amplitude of the incident wave. However in the crushing stage, the transmission coefficient decreases with the increase of the amplitude of the incident wave. This is a result of energy consumption due to particle crushing. The observed dependence of the transmission coefficient on the wave amplitude is consistent with the particle size distribution of recovered fillings.

Long Wavelength Propagation of Elastic Waves Across Frictional and Filled Rock Joints with Different Orientations: Experimental Results

A study on long wavelength propagation of shear and compression waves across jointed rocks is important as this condition exists in field. Wave propagation velocities and damping of waves across a jointed rock mass depend on many factors and orientation of rock joints is one of them. The experimental study on influence of joint orientation during wave propagation is carried out using resonant column apparatus. The jointed Plaster of Paris samples with and without infill material have been used to simulate the jointed rock mass with different orientations. The experiments and analyses are centered on propagation of shear and compression waves in jointed rocks with different orientations. Wave velocities and wave attenuations across frictional and filled rock joints are obtained for different strain levels and confining pressures. The results show that propagation of shear waves is dependent on joint orientation. Shear waves are attenuated more than compression waves and confining pressure decreases this influence of joint orientation. Results show that filled joints can damp the waves more easily than frictional joints. The joints oriented perpendicular to direction of wave propagation are more effective in damping compared to joints oriented parallel to the direction of wave propagation.

Shear Wave Propagation Across Filled Joints with the Effect of Interfacial Shear Strength

The thin-layer interface model for filled joints is extended to analyze shear wave propagation across filled rock joints when the interfacial shear strength between the filling material and the rocks is taken into account. During the wave propagation process, the two sides of the filled joint are welded with the adjacent rocks first and slide on each other when the shear stress on the joint is greater than the interfacial shear strength. By back analysis, the relation between the shear stress and the relative tangential deformation of the filled joints is obtained from the present approach, which is shown as a cycle parallelogram. Comparison between the present approach and the existing method based on the zero-thickness interface model indicates that the present approach is efficient to analyze shear wave propagation across rock joints with slippery behavior. The calculation results show that the slippery behavior of joints is related to the interfacial failure. In addition, the interaction between the shear stress wave and the two sides of the filling joint influences not only the wave propagation process but also the dynamic response of the filled joint.

A thin-layer interface model for wave propagation through filled rock joints

The present study essentially employs a thin-layer interface model for filled rock joints to analyze wave propagation across the jointed rock masses. The thin-layer interface model treats the rough-surfaced joint and the filling material as a continuum medium with a finite thickness. The filling medium is sandwiched between the adjacent rock materials. By back analysis, the relation between the normal stress and the closure of the filled joint are derived, where the effect of joint deformation process on the wave propagation through the joint is analyzed. Analytical solutions and laboratory tests are compared to evaluate the validity of the thin-layer interface model for filled rock joints with linear and nonlinear mechanical properties. The advantages and the disadvantages of the present approach are also discussed.

Three‐phase medium model for filled rock joint and interaction with stress waves

AbstractA three‐phase medium model is proposed in describing the dynamic property of filled rock joints and an analytical study on longitudinal wave transmission normally across a three‐phase rock joint is presented. Parameters in the three‐phase medium model were determined by a series of modified split Hopkinson pressure bar (SHPB) tests, where a sand or clay layer was used to represent an artificially filled rock joint. The effect of the unloading path on the transmitted wave was discussed by comparing the analytical and SHPB test results. The derived wave transmission coefficients across the filled joint agreed very well with those from the test results. Both the analytical and the test results showed that the wave transmission coefficients were affected by the mechanical properties of the fillings. Parametric studies with respect to the volume ratios of water and air in the three‐phase medium and the type of filling material have also been performed. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of Wave Propagation Through a Filled Rock Joint

An analytical and experimental study on a longitudinal wave (P-wave) transmission normally across a filled rock joint is presented in this paper. The dynamic property of the filling material for the artificial rock joints is derived from a series of modified split Hopkinson pressure bar (SHPB) tests. The incident and transmitted waves in granitic pressure bars are calculated by wave separations of the strain gauge readings. The incident wave is approximated by a series of half-sinusoidal waves, and an analytical model on wave propagation across a filled rock joint is then deduced. The derived wave transmission coefficients across the filled joint agree very well with those from the test results. Both the analytical and test results show that the wave transmission coefficients are influenced by the mechanical properties and the input energy of the incident waves. Analytical parametric studies with respect to pre-compaction of the filling material, the frequency and amplitude of the incident wave have also been conducted.

Experimental study of stress wave propagation across a filled rock joint

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 different widths and water contents sandwiched between the two bars was adopted to simulate the filled joint. Each pressure bar was mounted with two strain gauges with a specific spacing. A wave separation method was used to process the test data. The dynamic stress–strain relation of the filled rock joints was derived from the separated strain waves. Finally, the dynamic stress–strain relations from the tests were curve-fitted by using the least square regression method and compared with a traditional joint model. It was found that the wave separation method is very effective for the SHPB tests using short granitic pressure bars. It was also concluded that the joint width and water content had significant effects on the dynamic stress–strain relation of the filled rock joints. Existing joint models were not able to sufficiently describe such dynamic properties of the filled rock joints.

Discussion: Laboratory testing and parameters controlling the shear strength of filled rock joints

Discussion: Laboratory testing and parameters controlling the shear strength of filled rock joints

Laboratory testing and parameters controlling the shear strength of filled rock joints : de Toledo, P E C; de Freitas, M H GeotechniqueV43, N1, March 1993, P1–19

Laboratory testing and parameters controlling the shear strength of filled rock joints : de Toledo, P E C; de Freitas, M H GeotechniqueV43, N1, March 1993, P1–19

Laboratory testing and parameters controlling the shear strength of filled rock joints

The shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached. This Paper reviews test results in the literature, and compares them with results obtained by the Authors. The main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given. La résistance au cisaillement des joints rocheux remplis a été étudiée depuis trés longtemps mais le mécanisme et les paramétres contrôlant le processus n'ont jamais été totalement compris. Cet article passe en revue les résultats des essais publiés et les compare avec les résultats obtenus par les auteurs. Les paramétres principaux contrôlant la résistance au cisaillement des joints remplis sont discutés et un cadre pour comprendre les mécanismes de rupture associés au cisaillement de telles discontinuités est donné.