Surface Roughness Of Rock Joints Research Articles

Characterization of Joint Roughness Heterogeneity and Its Application in Representative Sample Investigations

Rock joint surface roughness is usually characterized by heterogeneity, but the determination of a required number of samples for achieving a reasonable heterogeneity assessment remains a challenge. In this paper, a novel method, the global search method, was proposed to investigate the heterogeneity of rock joint roughness. In this method, the roughness heterogeneity was characterized based on a statistical analysis of the roughness of all samples extracted from different locations of a given rock joint. Analyses of the effective sample number were conducted, which showed that sampling bias was caused by an inadequate number of samples. To overcome this drawback, a large natural slate joint sample (1000 mm × 1000 mm in size) was digitized in a laboratory using a high-accuracy laser scanner. The roughness heterogeneities of both two-dimensional (2D) profiles and three-dimensional (3D) surface topographies were systematically investigated. The results show that the expected value obtained from conventional methods failed to accurately represent the overall roughness. The relative errors between the population parameter and the expected value varied not only from sample to sample but also with the scale. The roughness heterogeneity characteristics of joint samples of various sizes can be obtained using the global search method. This new method could facilitate the determination of the most representative samples and their positions.

Neutrosophic Function for Assessing the Scale Effect of the Rock Joint Surface Roughness

A new investigation method is proposed for recording large-sized joint profiles and making statistical analyses of the joint roughness coefficient (JRC) values of the 10–300 cm sized profiles. The mechanical hand profilograph is used for joint roughness measurement due to its advantage of easy operation and high accuracy in recording joint traces. Based on the proposed method, it provides sufficient samples from various positions on the large joint profile, which allows the statistical evaluation of JRC values. A neutrosophic number (NN) is employed for revealing determinate and/or indeterminate information as it consists of determinate and indeterminate parts. Due to the uncertainty of JRC in the real world, NN is chosen to represent the JRC value, which is not only random but also a fuzzy indefinite parameter. The neutrosophic function is used to analyze and express the scale effect of joint surface roughness, and its derivative is used to describe the changing trend of the scale effect. The results show that the JRC value of the joint profile is related to the scale and has a negative effect on the surface roughness of the rock joint. The indeterminate information about the scale effect on joint roughness is described by the neutrosophic functions, and the derivative indicated that the JRC values of small samples are more sensitive than those of large-sized examples. When the length of the sample exceeds the stationarity limit of 80 cm, the roughness appears to be almost scale independent.

Neutrosophic Function with NNs for Analyzing and Expressing Anisotropy Characteristic and Scale Effect of Joint Surface Roughness

The shear behavior of rock mass significantly depends upon the surface roughness of rock joints which is generally characterized by the anisotropy characteristic and the scale effect. The large-scale natural rock joint surfaces, at Qingshi Town, southeast of Changshan County, Zhejiang Province, China, were used as a case study to analyze the roughness characteristics. A statistical assessment of joint roughness coefficient (JRC) indicated the roughness anisotropy of different sized rock joints. The lower limit (JRCmean-σ) was regarded as the determinate information, and the difference between lower and upper limits represented indeterminate information. The neutrosophic number (NN) was calculated to express the various JRC values. The parametric equations for JRC anisotropic ellipse were presented based on the JRC statistical assessment of joint profiles of various orientations. The JRC values of different sized joint samples were then quantitatively described by the neutrosophic function. Finally, a neutrosophic parameter ψ for evaluating the scale effect on the surface roughness anisotropy was introduced using the ratio of maximum directional roughness to minimum directional roughness. The case study indicates that the proposed method has the superiority in moving forward from subjective assessment to quantitative and objective analysis on anisotropy characteristic and scale effect of joint surface roughness.

A rapid field measurement method for the determination of Joint Roughness Coefficient of large rock joint surfaces

An accurate measurement of the Joint Roughness Coefficient (JRC) of large rock joints is essential for understanding the mechanical behavior and permeability characteristics of rock mass. Determining the surface roughness of rock joints in situ, however, is time-consuming and depends on sophisticated instruments. This study was carried out to develop a systematic method of measuring the JRC values of large joint roughness profiles. The roughness profiles were accurately recorded by a hand profilograph in the field and then digitized with flexibly adjusted sampling intervals by the grayscale image processing method. The digitized profiles were correlated closely with the original roughness profiles. A computerized approach for JRC quantitative evaluation was proposed based on the roughness amplitude/joint length relationship with JRC. The interval effect analysis showed that this method was effective for estimating the JRC values of different sized rock joints. This JRC measurement method has been successfully used in a case study of killas rock joints in Changshan City, P.R. China.

Evolution Process of Natural Rock Joint Roughness during Direct Shear Tests

AbstractSurface roughness is one of the most important parameters that have significant influence on the mechanical and hydraulic characteristics of rock joints. To investigate the evolution of surface roughness under normal and shear loads, direct shear tests and numerical modeling based on the discrete-element method (DEM) were performed; bright area percentage (BAP), which places emphasis on the contact areas, was used as an index to describe the roughness. The results demonstrate that the surface roughness of rock joints decreased gradually as the shear displacement increased, and then roughness experienced a significant reduction in the residual stage and remained constant. Furthermore, the evolution of surface roughness was found to depend on the normal stress and shearing direction. Reduction in the degree of joint roughness with high normal loads was lighter than that with lower normal loads, and roughness varied with shear directions. The numerical simulation method proposed in this study has the...

Effect of contact state on the shear behavior of artificial rock joint

Rock joint surface roughness, which influences the shear resistance of joints, dictates the stability of rock blocks. However, there is a weakening effect on the shear behavior of a rock joint as it becomes “un-matching” caused by external factors, such as vibration due to nearby blasting, excavation or earthquake. This paper presents an experimental investigation of the shear behavior of artificial rock joints under different matching conditions by direct shear test, modeled by imposing varying magnitude of horizontal dislocation along the shear direction between the upper and lower rock blocks. The peak shear strength decreases with increasing dislocation. However, the effect of dislocation on peak shear strength becomes less pronounced as the normal stress increases. With increasing dislocation, the peak shear displacement increases; the shear stiffness decreases and gradually approaches a constant. The influence of dislocation on shear stiffness is more prominent under a higher applied normal stress. The results also show that the peak shear strength of matching joints is influenced mostly by shear velocity.

직접전단시험에서 절리면의 2차 거칠기가 거칠기 정량화 파라미터에 미치는 영향

절리면의 전단강도를 결정하는 중요한 인자로 알려진 암반 절리면의 거칠기는 여러 가지 방법에 의해 연구되어 왔다. 하지만, 거칠기를 구성하는 요소인 1차 거칠기와 2차 거칠기를 분리하여 거칠기를 평가하려는 시도는 매우 제한적으로 수행되고 있다. 본 연구에서는 인장절리 시험편을 이용하여 직접전단시험을 통해 2차 거칠기 요소를 파괴하고 이를 거칠기 파라미터를 이용하여 정량화 하였다. 거칠기 파라미터는 수직응력과 측정 간격이 증가할수록 감소하였으나, 1.5 MPa 이상의 수직응력에서는 일정한 경향을 나타내지 않았다. 또한 전단 반대방향의 거칠기 면적 감소율은 거칠기 파라미터가 증가할수록 감소하였다. Rock joint surface roughness, which is known to be one of the most important factors for defining shear strength of rock mass, has been researched in various methods. However, approaches to separate a roughness into two groups (primary and secondary) for evaluating the roughness have been rarely performed. In this study, elements of secondary roughness were eliminated through direct shear testing with tensile joint specimen and they were quantified with joint parameters. It is revealed that roughness parameters decrease with increasing the normal stress and sampling intervals, except for the case in which the normal stress is larger than 1.5 MPa. Also it is analyzed that ratio of area reduction in the opposite direction of shearing decreases with increasing the roughness parameter.

Development of a new equation for joint roughness coefficient (JRC) with fractal dimension: a case study of Bakhtiary Dam site in Iran

The joint roughness has a significant effect on the shear behavior of rough joints, which control the shear strength of jointed rock mass. This index plays an important role in the mechanical and hydraulic properties of rock masses. There have been extensive studies in last a few decades. Joint roughness coefficient (JRC) and fractal dimension D are two well-studied and adopted parameters used in estimating the surface roughness of rock joints. This study proposed a new relation between JRC and D, and compared this relation with the previous studies by applying it on JRC profiles. This relation was also introduced into Barton’s empirical equation to assess the shear strength of rock joints, and its performance was estimated by applying it to more than 30 laboratory direct shear tests on natural rock joints from Bakhtiary Dam site. The advantage of this study, when compared to the previous works done by others, is using the results of more than 30 direct shear tests on natural rock joints for the evaluation of reliability of the proposed equation. Therefore, the new obtained relationship between JRC and D seems to capture well the roughness coefficient of natural rock joints.

Modeling surface roughness degradation of rock joint wall during monotonic and cyclic shearing

Based on previously proposed surface roughness description parameters (k a, θs, SRs, DRr, a 0), two generalized rock joint surface roughness degradation models were proposed to predict the variation of joint surface degradation during shearing under both constant normal stress (CNS) and constant normal stiffness (CNK) loading conditions. The first model was developed based on the evolution of secondary roughness (an extension of an existing model) and the second was developed based on the concept of “average asperity probable contact angle.” Model variables can be initial normal stress (σn0; k n ≥ 0), normal stiffness (k n; σn0 ≥ 0), accumulated shear displacement u s-tot (monotonic or cyclic shearing), and surface roughness amplitude a 0. Good agreement between experimental and predicted degradation was observed. The models also allow prediction of surface degradation in large-scale shear fractures. Both models are semi-incremental, readily implemented in a numerical code, and adaptable to existing elastoplastic joint behavior models.

Measurement of Rock Joint Roughness by 3D Scanner

Abstract Many methods have been used to measure rock joint surface roughness more accurately. However, true roughness has been distorted and underestimated by differences in the sampling interval of the measurement methods. Thus, current measurement methods produce a dead zone and distorted roughness profiles. This study proposes a new rock joint surface roughness measurement method by use of a camera-type three-dimensional (3D) scanner as an alternative to current methods. For this study, the underestimation of artificial roughness is analyzed by using the current measurement method of laser profilometry. We then replicate eight specimens from two rock joint surfaces, and digitize them by 3D scanners. Finally, the roughness coefficient values obtained from eight numbers of the 3D surface data sets and from 320 numbers of two-dimensional profiles data sets are analyzed by using the current measurement methods and our proposed measurement method. The artificial simulation confirms that the sampling interval is one of main factors for the distortion of roughness and shows that current methods may not consider the inclination of waviness. The experimental results showed that the camera-type 3D scanner produced 10 % larger roughness values than those of the current methods. The proposed new method is a faster, more precise and more accurate method than the current methods for the measurement of rock joint roughness, so that it can be promising technique in this area of study.

Estimating the relation between surface roughness and mechanical properties of rock joints

Discontinuities in rock masses have an important influence on deformational behaviour of blocky rock systems. For a single rock joint, the roughness of its surface is of paramount importance to its mechanical and hydraulic properties, such as friction angle, shear strength, and dilatancy/aperture. Many methods have been used to characterize the surface roughness of rock joints, such as joint roughness coefficients (JRC), root mean square (RMS) value, structure function (SF) etc. However, most of these methods can only be used in the 2-D models. In this study, we carried out direct shear experiments on rock joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, and measured the surfaces of rock joints before and after shearing, using a 3-D laser scanning profilometer system. By using a 3-D fractal evaluation method of roughness characterization, the projective covering method (PCM) and a direct shear apparatus of high accuracy, the relation between mechanical properties of rock joints under different boundary conditions and the change of their fractal dimensions in both 2-D and 3-D models have been examined, which gives a new approach to accurately evaluate the evolution of roughness of rock joint surfaces and its influence on the hydro-mechanical behaviours of rock joints.

Application of a new in situ 3D laser scanner to study the scale effect on the rock joint surface roughness

Application of a new in situ 3D laser scanner to study the scale effect on the rock joint surface roughness

The scale dependence of rock joint surface roughness

Abstract Accurate determination of surface roughness of rock joints at the large-scale is essential for proper rock mass characterization. Surface roughness of rock joints is commonly characterized using small samples. However, since roughness parameters of rock joints are scale-dependent and their descriptors change with scale, a systematic investigation has been carried out to understand the effect of scale on the surface roughness of rock joints. A silicon rubber replica, 1000 mm×1000 mm in size, was moulded in-situ from a natural rock joint surface and its surface was digitized in the laboratory using a 3-D laser scanner having high accuracy and resolution. The fractal parameters, i.e. the fractal dimension D and amplitude parameter A describing surface roughness of the replica, were calculated on the basis of the Roughness–Length Method. To investigate the scale-dependency of surface roughness of rock joints, ten sampling windows ranging in size from 100 mm×100 mm to 1000 mm×1000 mm were selected from the central part of the replica and their fractal parameters were calculated. The results show that both D and A are scale-dependent and their values decrease with increasing size of the sampling windows. This scale-dependency is limited to a certain size, defined as the stationarity threshold, and for sampling windows larger than the stationarity threshold, the estimated parameters remain almost constant. It is concluded that, for surface roughness to be accurately characterized on a laboratory scale or in the field, samples need to be equal to or larger than the stationarity limit. In this paper we have indicated the methodology for establishing the value for the stationarity limit for rock joints.

Photoelastic study of the contact mechanics of fractal joints

The Earth's crust exhibits numerous fractures and weaknesses which significantly affect the mechanical behaviour of rock masses, such as the deformation, strength and conductivity, in which the surface roughness of rock fractures plays a dominant role. To take the influence of roughness into account, efforts have been made to characterize the surface roughness of rock joints. The brittle elastic properties of rock joints can be approximately simulated by using photoelastic material and an investigation has been performed on epoxy specimens cast against natural rock joints. In order to cntrol the roughness and to display directly the fractal effects on the mechanical behavior, a series of synthetic fractal joints with different fractal dimensions is tested in the present study by using the photoelastic method under uniaxial compression and direct shear.

Fractal effects of surface roughness on the mechanical behavior of rock joints

Extensive studies show that the naturally developed rock joint surfaces have the properties of fractals. The surface roughness of rock joints can be well described within the framework of fractal geometry. To give a better understanding of the roughness of rock fracture surfaces in relation to the mechanical properties and behavior of rock joints in loading, a systematic investigation has been carried out. By means of a laser scanning instrument, the fracture surfaces induced in rocks are measured. The fractal characters of rough fracture surfaces of rocks are analysed according to the variogram method, which elaborates explicitly the importance of the geometric parameters — fractal dimension D and the intercept A. Investigation extends to the anisotropy and heterogeneity of rock fracture surfaces, and the scale effect on the fractal estimation. The shear tests on rock joints show a combined effect of the fractal parameters on the mechanical properties and behavior of rock joints. To control the roughness and show the effects in a direct manner, a series of fractal joints with different fractal dimensions are generated on the basis of the Weierstrass-Mandelbrot function and then manufactured in the polycarbonate plates. By using the photoelastic method, the manners of normal and shear deformation, the stress field in the vicinity of the joint surface and the contact behaviour of the fractal joints have been studied in detail under uniaxial compression and direct shear. Based on the experimental results, the dependence of deformation stiffness on the fractal dimensions of rock joints has been recognized. The empirical criteria of shear strength and the evolution law of surface damage during the shear process are developed.

フラクタルモデルによる岩盤不連続面の表面粗さ評価法について

Based on a self-similar fractal model of JRC profiles, JRC diagram was proposed for a reasonable evaluation of rock joint surface roughness and its size effect. The rock joint surface roughness and its size effect can be evaluated by drawing the fractal model of a rock joint surface profile on the JRC diagram. The fractal model is defined by the steepness and the fractal dimension of the profile. In this paper, variogram method was applied to determine the fractal model and a methodology was proposed to generate the JRC diagram. Moreover, the evaluation method of rock joint surface roughness and its size effect are discussed with considering the interlocking effect of a rock joint.

岩盤不連続面の表面粗さ（ＪＲＣ）とせん断特性

岩盤不連続面の表面粗さ（ＪＲＣ）とせん断特性

Statistical description of the surface roughness of rock joints : Liu, H, Sterling, R L Rock Mechanics Contributions and Challenges: Proc 31st US Symposium, Golden, 18–20 June 1990P277–284. Publ Rotterdam: A A Balkema, 1990

Statistical description of the surface roughness of rock joints : Liu, H, Sterling, R L Rock Mechanics Contributions and Challenges: Proc 31st US Symposium, Golden, 18–20 June 1990P277–284. Publ Rotterdam: A A Balkema, 1990