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1.
The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial asperity angles, initial normal stresses and ratios of infill thickness to asperity height. 相似文献
2.
Laboratory modelling of shear behaviour of soft joints under constant normal stiffness conditions 总被引：1，自引：0，他引：1
Shear behaviour of regular sawtooth rock joints produced from casting plaster are investigated under constant normal stiffness (CNS) conditions. Test results obtained in this investigation are also compared with the constant normal load (CNL) tests. It is observed that the peak shear stress obtained under CNL conditions always underestimates the peak shear stress corresponding to the CNS condition. Plots of shear stress against normal stress show that a nonlinear (curved) strength envelope is acceptable for soft rock joints subjected to a CNS condition, in comparison with the linear or bilinear envelopes often proposed for a CNL condition. Models proposed by Patton (1966) and Barton (1973) have also been considered for the predictions of peak shear stress of soft joints under CNS conditions. Although Patton's model is appropriate for low asperity angles, it overestimates the shear strength in the low to medium normal stress range at higher asperity angles. In contrast, while Barton's model is realistic for the CNL condition, it seems to be inappropriate for modelling the shear behaviour of soft joints under CNS conditions. The effect of infill material on the shear behaviour of the model joints is also investigated, and it is found that a small thickness of bentonite infill reduces the peak stress significantly. The peak shear stress almost approached that of the shear strength of infill when the infill thickness to asperity height ratio (t/a) reached 1.40. This paper also introduces an original, empirical shear strength envelope to account for the change in normal stress and surface degradation during CNS shearing. © Rapid Science Ltd. 1998 相似文献
3.
循环剪切荷载作用下含二阶起伏体模拟岩石节理力学特性研究 总被引：1，自引：0，他引：1
利用人工材料浇注含二阶起伏体的模拟岩石节理试样,进行常法向荷载循环剪切试验,研究节理剪切力学特性在循环剪切过程中的劣化规律。试验结果表明：二阶起伏体对节理循环剪切力学特性有重要影响,剪切强度、剪切刚度、剪胀角随剪切循环次数增大而衰减,衰减趋势随着二阶起伏度的增大而加快;法向应力、二阶起伏度较大时,二阶起伏体对剪切力学特性的影响主要体现在第1轮剪切循环中,在随后的剪切循环中影响不明显;法向应力、二阶起伏度较小时,二阶起伏体的影响在前几轮循环剪切过程中均有较清晰的体现。基于Hertz接触力学理论,提出了节理面微凸体球面接触细观模型,揭示了节理循环剪切宏观试验现象的力学机制 相似文献
4.
Study of rock joints under cyclic loading conditions 总被引：11，自引：3，他引：11
Summary A conceptual model for the behaviour of rock joints during cyclic shear and under constant normal stresses was proposed according to results from shear tests with 50 concrete replicas of rock joints. The shear strength and deformability of joint samples were found to be both anisotropic and stress dependent. Based on these experimental results, a two-dimensional constitutive model was developed for rock joints undergoing monotonic or cyclic loading sequences. The joint model was formulated in the framework of non-associated plasticity, coupled with empirical relations representing the surface roughness degradation, appearance of peak and residual shear stresses, different rates of dilatancy and contraction, variable normal stiffness with normal deformation, and dependence of shear strength and deformability on the normal stress. The second law of thermodynamics was represented by an inequality and used to restrict the values of some of the material parameters in the joint model. The new joint model was implemented into a two-dimensional Distinct Element Method Code, UDEC, and its predictions agreed well with some well-known test results. 相似文献
5.
M. K. Jafari F. Pellet M. Boulon K. Amini Hosseini 《Rock Mechanics and Rock Engineering》2004,37(1):3-23
Summary Evaluation of the effects of small repetitive earthquakes on the strength parameters of rock joints in active seismic zones is of interest of the designers of underground constructions. In order to evaluate these effects, it is necessary to study the behaviour of rock joints under dynamic and cyclic loadings. This paper presents the results of a systematic study on the behaviour of artificial rock joints subjected to cyclic shearing. More than 30 identical replicas have been tested using triaxial compression devices under different conditions of monotonic and cyclic loading. At the first stage a few samples have been tested in monotonic loading modes under various confining pressures and rate of displacement. In the second series of tests, small cyclic loads were applied on the samples for increasing number of cycles, frequency levels and stress amplitudes. These were then followed by monotonic loading again. The variations of maximum and residual shear strengths for each test have been studied. The results show increase of shear strength as a result of the increase in confining pressure and they display decrease of shear strength due to the increase of rate of loading, number of cycles, frequency levels and stress amplitudes. 相似文献
6.
《Geomechanics and Geoengineering》2013,8(3):237-244
An infilled rock joint is likely to be the weakest plane in a rock mass. The presence of infill material within the joint significantly reduces the friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill, the smaller the shear strength of the rock joint. Once the infill reaches a critical thickness, the infill material governs the overall shear strength, and the joint walls (rock) play no significant role. Several models have been proposed to predict the peak shear strength of soil-infilled joints under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a). CNS models provide a more realistic picture of the soil-infilled joint behaviour in the field. This paper presents a critical review on the existing mathematical models for predicting the shear strength of soil-infilled rock joint and verifies the normalised peak shear stress model with further laboratory investigations carried out on idealised saw-tooth rock joints at the University of Wollongong. Based on the prediction of the experimental data, the normalised peak shear stress model is slightly modified by the authors. A simplified approach for using this model in practice is presented and a new expression for prediction of dilatation at peak shear stress is suggested. 相似文献
7.
This paper presents a review of recent developments made by the authors into the modelling of rock joints in direct shear. Careful observation of laboratory direct shear testing on concrete/rock joints containing two-dimensional roughness has allowed theoretical models of behaviour to be developed. The processes modelled include asperity sliding, asperity shearing, post-peak behaviour, asperity deformation and distribution of stresses on the joint interface. Model predictions compare extremely well with laboratory test results. These models were then applied to direct shear tests on rock/rock joints, and although behaviour in general was well predicted, the strength of rock/rock joints was over-predicted. Direct shear tests have also been carried out on samples containing both two- and three-dimensional roughness to test the accuracy of the two-dimensional approximation to roughness adopted in the theoretical models. 相似文献
8.
Hydraulic Characteristics of Rough Fractures in Linear Flow under Normal and Shear Load 总被引：19，自引：3，他引：19
Summary
A hydro-mechanical testing system, which is capable of measuring both the flow rates and the normal and shear displacement
of a rock fracture, was built to investigate the hydraulic behaviour of rough tension fractures. Laboratory hydraulic tests
in linear flow were conducted on rough rock fractures, artificially created using a splitter under various normal and shear
loading. Prior to the tests, aperture distributions were determined by measuring the topography of upper and lower fracture
surfaces using a laser profilometer. Experimental variograms of the initial aperture distributions were classified into four
groups of geostatistical model, though the overall experimental variograms could be well fitted to the exponential model.
The permeability of the rough rock fractures decayed exponentially with respect to the normal stress increase up to 5 MPa.
Hydraulic behaviours during monotonic shear loading were significantly affected by the dilation occurring until the shear
stress reached the peak strength. With the further dilation, the permeability of the rough fracture specimens increased more.
However, beyond shear displacement of about 7 to 8 mm, permeability gradually reached a maximum threshold value. The combined
effects of both asperity degradation and gouge production, which prohibited the subsequent enlargement of mean fracture aperture,
mainly caused this phenomenon. Permeability changes during cyclic shear loading showed somewhat irregular variations, especially
after the first shear loading cycle, due to the complex interaction from asperity degradations and production of gouge materials.
The relation between hydraulic and mechanical apertures was analyzed to investigate the valid range of mechanical apertures
to be applied to the cubic law.
Received June 12, 2001; accepted February 26, 2002 Published online September 2, 2002 相似文献
9.
A Constitutive Model for Shear Behavior of Rock Joints Based on Three-Dimensional Quantification of Joint Roughness 总被引：1，自引：1，他引：0
Jung-Wook Park Yong-Ki Lee Jae-Joon Song Byung-Hee Choi 《Rock Mechanics and Rock Engineering》2013,46(6):1513-1537
A new constitutive model to describe the shear behavior of rock joints under constant normal stiffness (CNS) and constant normal load (CNL) conditions is proposed. The model was developed using an empirical approach based on the results of a total of 362 direct shear tests on tensile fractured rock joints and replicas of tensile joints and on a new quantitative roughness parameter. This parameter, the active roughness coefficient C r, is derived from the features of the effective roughness mobilized at the contact areas during shearing. The model involves a shear strength criterion and the relations between stresses and displacements in the normal and shear directions, where the effects of the boundary conditions and joint properties are considered by the shape indices C d and C f. The model can be used to predict the shear behavior under CNS as well as CNL conditions. The shear behavior obtained from the experimental results is generally in good agreement with that estimated by the proposed model, and the effects of joint roughness, initial normal stress, and normal stiffness are reasonably reflected in the model. 相似文献
10.
11.
Hui Zhou Fanzhen Meng Chuanqing Zhang Dawei Hu Jingjing Lu Rongchao Xu 《Acta Geotechnica》2016,11(4):925-939
Shear failure of rockmass along a weak plane occurs frequently in rock slopes and in underground tunnels. To study the shear behaviour and acoustic emission (AE) characteristics of joints under different experimental conditions (asperity height, shear rate, and normal load), irregular artificial saw-tooth joints with different asperity heights were sheared in the laboratory, and the AE signals were detected and analysed. The results demonstrated that the strength of the joints increased with increases in normal load and asperity height, while the strength of the joints first increased and then decreased when the shear rate was elevated. The ideal curve of the cumulative hits could be divided into a quiet period, a slow rise period, and a sharp growth period, which could be used to monitor and predict the potential shear failure of the joints. The higher the asperity was, the higher the peak energy rate and the lower the peak hit rate, and cumulative hits at failure were because of differences in asperity size and number. The peak hit rate and cumulative energy tended to increase gradually with the decrease in shear rate, and the minimum peak hit rate and energy rate at failure were both attained at the maximum shear rate. In addition, curves of the energy rate and hit rate showed large fluctuations at higher shear rates. The peak energy rate and cumulative energy under low normal stress could be greater than the peak energy rate and cumulative energy under high normal stress, and the peak hit rate and cumulative hit number under high normal stress could be larger than that of under low normal stress. 相似文献
12.
循环剪切荷载作用下岩石节理变形特性试验研究 总被引：1，自引：0，他引：1
以水泥砂浆为相似材料,制备3种岩壁强度、5种起伏角度的锯齿型节理试样;利用试验设备,进行了在4种法向应力下的循环剪切试验。根据试验结果,结合循环剪切试验特点,定义剪胀角来表征节理循环剪切的法向变形特性,以及剪切刚度来表征节理循环剪切的切向变形特性。基于不同起伏角、不同强度等级和不同法向应力下的节理试样循环剪切试验结果,分析了循环剪切过程中剪胀角和剪切刚度的变化规律;并利用不同条件下的试验结果,对比分析初始起伏角度、法向应力、岩壁强度对节理循环剪切变形特性的影响规律。研究发现：剪胀角、剪切刚度均随着剪切循环次数的增加而呈现先快、后慢的降低趋势,并且中低起伏角度节理的剪胀角、剪切刚度的降低趋势随着初始起伏角度、法向应力的增加而加快,随着岩壁强度增加而变慢,高起伏角度节理的剪胀角、剪切刚度的降低趋势基本保持不变。 相似文献
13.
Mazouz El Hadi Hamimed Messaoud Yahiaoui Abdelouahab Benzagouta Mohamed Said Khodja Mohamed Achi Nada Duplay Joëlle 《Arabian Journal of Geosciences》2020,13(9):1-11
The creep property of rock under cyclic loading is very important in civil engineering. In order to establish a novel constitutive equation for rock under cyclic loading, a fractional-order viscoplastic body under cyclic loading was constructed based on fractional-order viscous element. A fractional-order visco-elastoplastic model (FVEPM) for rock was established by connecting constructed fractional-order viscoplastic body with Burgers model. The model was a Burgers model when the maximum value of cyclic loading was less than the critical strength of rock; otherwise, it was a FVEPM which can be used to reflect the transient, steady-state, and tertiary creep phases of rock. The cyclic loading was decomposed into a static load and a cyclic loading with a zero average stress. According to rheological mechanics theory, the rheology constitutive equation of rock under the static load can be derived. According to viscoelastic mechanics theory, the constitutive equation under cyclic loading with a zero average stress was established by introducing the variation parameters of energy storage and energy dissipation compliance caused by rock damage and fracture. Finally, a new dynamic constitutive equation of rock cyclic loading can be obtained by superimposing the constitutive equation under static load and cyclic loading with a zero average stress. Compared with existing test results of rock under cyclic loading, the proposed constitutive model can be used to describe the creep characteristics of rock under cyclic loading and reflect the presented fluctuation of strain curve of rock under cyclic loading. 相似文献
14.
Modelling cyclic behaviour of granular soils under both drained and undrained conditions with a good performance is still a challenge. This study presents a new way of modelling the cyclic behaviour of granular materials using deep learning. To capture the continuous cyclic behaviour in time dimension, the long short-term memory (LSTM) neural network is adopted, which is characterised by the prediction of sequential data, meaning that it provides a novel means of predicting the continuous behaviour of soils under various loading paths. Synthetic datasets of cyclic loading under drained and undrained conditions generated by an advanced soil constitutive model are first employed to explore an appropriate framework for the LSTM-based model. Then the LSTM-based model is used to estimate the cyclic behaviour of real sands, ie, the Toyoura sand under the undrained condition and the Fontainebleau sand under both undrained and drained conditions. The estimates are compared with actual experimental results, which indicates that the LSTM-based model can simultaneously simulate the cyclic behaviour of sand under both drained and undrained conditions, ie, (a) the cyclic mobility mechanism, the degradation of effective stress and large deformation under the undrained condition, and (b) shear strain accumulation and densification under the drained condition. 相似文献
15.
岩石节理剪切变形对岩体工程的安全性和稳定性具有重要影响。为研究常法向应力下岩石节理剪切变形本构关系,采用RDS-200型岩石直剪仪对非规则砂岩节理进行了不同法向应力下的直剪试验。根据岩石节理剪切应力?位移全程曲线形状特征,将其依次划分为峰前压密阶段、线性阶段、屈服阶段和峰后软化阶段;根据剪切应力在峰后软化阶段降低幅度和速率大小,将岩石节理剪切应力?位移曲线划分为3种类型：峰后平台型、峰后缓降型和峰后跌落型。基于岩石节理剪切应力?位移曲线各阶段剪切变形特征,采用分段函数建立了岩石节理剪切变形本构模型。与其他模型相比,新提出的岩石节理剪切变形本构模型对试验数据拟合精度更高,更好地描述了岩石节理剪切应力?位移全程曲线。另外,在通过岩石节理直剪试验由经验公式确定模型参数之后,所提出本构模型可在不同法向应力下实现对不同粗糙度岩石节理剪切应力?位移曲线的预测。研究结果对岩石节理剪切变形的数值模拟和工程估计具有一定的实用价值。 相似文献
16.
This paper presents a joint constitutive model that considers separately the mechanical contribution of waviness and unevenness of a joint to shear behaviour. The critical asperities for waviness and unevenness are determined from geometric properties in a lab-scale joint. The wear process is employed to model the degradation in dilation and strength during shear. From dimensional analysis, asperity degradation constants are developed using geometric parameters including asperity angle, wavelength, and amplitude as well as rock strength and stress. The applicability of the proposed model was assessed by performing direct shear tests on three joint roughness coefficient (JRC) profiles and providing its correlation with experimental results. Additionally, experimental data taken from literature were used to validate the model’s performance. 相似文献
17.
节理在固定法向压力刚度（CNS）条件下的剪切过程比较复杂,剪切中由于剪胀的存在使得法向压力增大,而法向压力的增加又限制了剪胀的发生。根据CNS剪切过程中某一瞬时状态下法向压应力大小,以节理在该法向压应力下法向剪胀位移与剪切位移的关系为基础,建立一个楔形物理模型。通过循环迭代求得CNS剪切过程中每一步的法向压应力值,进而得到整个过程的剪切应力值。通过该模型,讨论了节理各参数对CNS剪切过程的影响,结果表明,其剪切应力值受法向压应力刚度与节理法向变形参数共同协调控制（包括单轴压缩变形及剪胀角的磨损）,节理在剪切过程中越不易发生压缩变形,其剪切应力值越大。 相似文献
18.
The behaviour of dry and cohesionless granular material during quasi-static cyclic shearing under a constant normal stiffness (CNS) condition is theoretically studied. A particular attention is laid to the volumetric strain change and the degradation of the shear resistance in the course of shearing. Numerical calculations are carried out for several shear cycles under boundary conditions which are relevant to investigate the shear interface behaviour. The global and local evolution of deformation, stress and density within the granular material is investigated with a finite element method on the basis of a hypoplastic constitutive model extended by micro-polar quantities: rotations, curvatures and couple stresses. A mean grain diameter is used as a characteristic length of micro-structure. The constitutive equations for stresses and couple stresses take also into account the effect of the evolution of the void ratio, pressure dependent relative density, direction of rate of deformation and rate of curvature. The numerical results are qualitatively compared with corresponding laboratory tests on direct wall shearing performed by DeJong, Randloph and White. In addition, the results for cyclic shearing of an infinite granular layer between two very rough boundaries under CNS conditions are also enclosed and discussed. 相似文献
19.
A Laboratory Shear Cell Used for Simulation of Shear Strength and Asperity Degradation of Rough Rock Fractures 总被引：2，自引：2，他引：0
Different failure modes during fracture shearing have been introduced including dilation, sliding, asperity cut-off and degradation. Several laboratory studies have reported the complexity of these failure modes during shear tests performed under either constant normal load (CNL) or constant normal stiffness (CNS) conditions. This paper is concerned with the mechanical behaviour of synthetic fractures during direct shear tests using a modified shear cell and related numerical simulation studies. The modifications made to an existing true triaxial stress cell (TTSC) in order to use it for performing shear tests under CNL conditions are presented. The large loading capacity and the use of accurate hydraulic pumps capable of applying a constant shear velocity are the main elements of this cell. Synthetic mortar specimens with different fracture surface geometries are tested to study the failure modes, including fracture sliding, asperity degradation, and to understand failure during shearing. A bonded particle model of the direct shear test with the PFC2D particle flow code is used to mimic the tests performed. The results of a number of tests are presented and compared with PFC2D simulations. The satisfactory results obtained both qualitatively and quantitatively are discussed. 相似文献
20.
The application of energy principles to the determination of the sliding resistance of rock joints 总被引：3，自引：3，他引：3
Summary Energy principles have previously been applied to the analysis of rock joints in order to determine the shear strength of dilatant joints (Ladanyi and Archambault, 1970). This work was based on the analysis of regular triangular asperities and assumed that the asperities were rigid. In recognition of the difficulty of measuring a representative asperity angle in natural, complex rock joints, Ladanyi and Archambault extended their results to natural joints by assuming the equality of joint dilation rate and the effective joint asperity angle. It is shown that the assumption of this equality is not universally valid, and that it may lead to an underestimation of joint shear strength. Further, the effective friction angle for joints in an elastic rock mass, for joints comprising asperities of varying inclination, for post-peak shear displacements and for joints in degradable rock are all analysed using extensions of Ladanyi and Archambault's approach. 相似文献