Griffith’s Strength Loci for Jointed Rock Masses

1989 ◽  
Vol 111 (4) ◽  
pp. 270-278
Author(s):  
B. A. Chappell
Keyword(s):  
Rock Mass ◽  
Equilibrium Model ◽  
Failure Modes ◽  
Shear Failure ◽  
Soft Rock ◽  
Jointed Rock ◽  
Rock Masses ◽  
Loaded Rock ◽  
Deformation Models ◽  
Composite Moduli

Stress distribution in a rock material containing cracks, without thickness, and joints, with thickness, is controlled by two basic principles, namely equilibrium and compatibility. Two deformation models representing these two basic requirements are used to construct the rock mass’ local composite moduli that are then combined to obtain the rock mass’ global moduli. Deformational modes in the form of compliances give upper and lower value moduli representing the constraints of compatibility and equilibrium, respectively. In a loaded rock mass there is no stress redistribution involved in the application of the equilibrium model, while for the compatibility model there are stress redistributions. For cracks, with no thickness, only the equilibrium model defines the deformation moduli, whereas for joints both the equilibrium and compatibility models are required because of the joint’s volume effects. Using both the joint’s shear strength and the Griffith’s crack initiation criteria, the Griffith’s strength loci for firm-hard and soft rock masses are produced. The strength loci representing normal and shear failure modes for the firm-hard rock mass are significantly different, whereas for the soft rock mass they are similar.

A damage constitutive model for rock mass with persistent joints considering joint shear strength

2015 ◽  
Vol 52 (8) ◽  
pp. 1136-1143 ◽  
Author(s):  
Hongyan Liu ◽  
Xiaoping Yuan
Keyword(s):  
Rock Mass ◽  
Constitutive Model ◽  
Failure Modes ◽  
Shear Failure ◽  
Jointed Rock ◽  
Joint Shear Strength ◽  
Rock Mass Strength ◽  
Damage Constitutive Model ◽  
Joint Shear ◽  
Set Up

Microcracks and joints, two types of flaws that appear in a rock mass, affect both the rock mass strength and deformability. A model that can simultaneously reflect the effect of these two types of flaws on the mechanical behavior of a rock mass with persistent joints is not yet available. This study focusses on a microcracked rock mass with persistent joints and establishes a mechanical model, accounting for the anisotropy in the rock mass strength and deformability induced by the existence of the joints. Firstly, the compound damage variable from the coupling macroscopic and mesoscopic flaws is deduced based on the Lemaitre strain equivalence hypothesis. Secondly, the corresponding damage constitutive model for a jointed rock mass is set up. Thirdly, the joint shear failure criterion is incorporated into the constitutive model to extend the model. Finally, the results of the calculation examples show that the existence of the joint will reduce the strength, enlarge the deformability, and lead to anisotropy of the rock mass. A series of calculation examples and comparisons validate that the proposed model is capable of presenting the joint-induced anisotropy in rock mass strength and deformability, determining its possible failure modes, and reasonably simulating its complete stress–strain relationship.

Study on Failure of Rock Mass around Deep Tunnel

2011 ◽  
Vol 99-100 ◽  
pp. 370-374 ◽  
Author(s):  
Yue Hong Qian ◽  
Ting Ting Cheng ◽  
Xiang Ming Cao ◽  
Chun Ming Song
Keyword(s):  
Rock Mass ◽  
Stress Field ◽  
Failure Modes ◽  
Shear Failure ◽  
Simple Function ◽  
Tensile Failure ◽  
Deep Tunnel ◽  
Main Mode

During excavating the problem of unloading is a dynamic one essentially. Assuming the unloading ruled by a simple function and based on the Hamilton principal, the distribution of the stress field nearby the tunnel is obtained. The characteristics of the failure nearby the tunnel are analyzed considering the shear failure and tensile failure. The results show that the main mode of the shear failure, intact and tensile failure occurs from the tunnel. The characteristic of the shear failure, intact and tensile failure are one of the likely failure modes.

Integrated geophysical and geotechnical monitoring for multiscale rock mass damaging investigation at the Acuto Field-Lab (Italy)

2021 ◽  
Author(s):  
Guglielmo Grechi ◽  
Danilo D'Angiò ◽  
Matteo Fiorucci ◽  
Roberto Iannucci ◽  
Luca Lenti ◽  
...  
Keyword(s):  
Rock Mass ◽  
Monitoring System ◽  
Thermal Stresses ◽  
Central Italy ◽  
Jointed Rock ◽  
Failure Behavior ◽  
Rock Masses ◽  
Geotechnical Monitoring ◽  
Strain Monitoring

<p>Rock mass damaging has become a topic of great interest in the engineering-geology research community during the last decades as it can significantly influence slopes stability. In this sense, the study of mechanics and dynamics of jointed rock masses represents a challenge because it will allow to better understand how external continuous and transient stressors can influence the short- to long-term stability controlling their pre-failure behavior. Consequently, the detection of permanent changes in physical and mechanical parameters, due to periodic or transient stressors, is an important target to mitigate the related geological risk as it can potentially lead rock masses to failure, especially when infrastructures and natural or cultural heritages are exposed elements. In this framework, the Acuto field laboratory (Central Italy) has been designed and implemented in 2016 within an abandoned quarry by employing an integrated geotechnical and geophysical monitoring system, with the aim of investigating how natural and anthropic conditioning factors could lead fractured rock masses to failure. The integrated monitoring system, which is installed on a potentially unstable 20-m<sup>3</sup> jointed rock block, is composed of several strain devices (i.e., strain gauges -SG- and jointmeters -JM-), one fully equipped weather station, one rock thermometer, eight high-sensitivity microseismic uniaxial accelerometers and optical and InfraRed Thermal cameras. The acquisition of long-term monitoring time-series, coupling multimethodological approaches, allowed to establish cause-to-effect relationships among different environmental stressors and induced strain effects, highlighting the continuous action of thermal stresses on rock mass deformations both at the daily and seasonal timescales. In fact, while the analysis of thermal and strain monitoring data allowed to characterize the cyclic contraction and relaxation response of major rock fractures and microcracks to temperature fluctuations, the microseismic monitoring array was able to detect during thermal transient (i.e., freezing conditions) the occurrence of microseismic emissions potentially related to the genesis or progressive growth of pre-existing cracks.</p><p>Starting from 2018, experimental activities at the Acuto field lab are supported by the “Dipartimento di Eccellenza” project of the Italian Ministry of Education Universities and Research funds attributed to the Department of Earth Sciences of the University of Rome “Sapienza”.  In this framework, the Acuto filed laboratory will undergo a structural upgrade that will be aimed at the investigation of two new sectors of the abandoned quarry. These new sectors will be instrumented with innovative thermal profiles probe, fiber Brag grating sensors and traditional SG and JM for detailed stress-strain monitoring, acoustic emission sensors and high-frequency and low-frequency geophones for ambient seismic noise monitoring and microseismic events detection as well as accelerometers for evaluating the rock mass response in the case of seismic shaking. The main goal of such an improvement will be both technical and methodological, and will shed light on the application of integrated geophysical and geotechnical monitoring approaches in investigating the multiscale rock mass damaging process as well as the detection of rock mass failure precursors by using non-conventional combinations and configurations of geotechnical and broad-band geophysical devices.</p>

scholarly journals Primary Investigation on Equivalent Anchoring Method of Jointed Rock Mass Tunnel and Its Engineering Application

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Min Gao ◽  
Shanpo Jia
Keyword(s):  
Rock Mass ◽  
Three Dimensional ◽  
Engineering Application ◽  
Friction Angle ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Surrounding Rock ◽  
Rock Masses ◽  
Reinforcement Effect ◽  
Rock Bolts

Rock bolts, one of the main support structures of the tunnel, can improve the stress state and mechanical properties of the surrounding rocks. The rock bolts are simulated by bar or beam elements in present numerical calculations for most 2D tunnel models. However, the methods of simulating rock bolt in three-dimensional models are rarely studied. Moreover, there are too many rock bolts in the long-span tunnel, which are hardly applied in the 3D numerical model. Therefore, an equivalent anchoring method for bolted rock masses needs to be further investigated. First, the jointed material model is modified to simulate the anisotropic properties of surrounding rock masses. Then, based on the theoretical analysis of rock bolts in reinforcing mechanical properties of the surrounding rock masses, the equivalent anchoring method of the jointed rock mass tunnel is numerically studied. The equivalent anchoring method is applied to the stability analysis of a diversion tunnel in Western China. From the calculation results, it could be found that the reinforcement effect of rock bolts could be equivalently simulated by increasing the mechanical parameter value of surrounding rocks. For the jointed rock mass tunnel, the cohesion and internal friction angle of the surrounding rocks are improved as 1.7 times and 1.2 times of the initial value, which can simulate the reinforcement effect of rock bolts. Comparing with analytical results, the improved internal friction angle is nearly consistent with analytical result. The reinforcement effect of rock bolts is simulated obviously when the mechanical parameters of surrounding rocks are increased simultaneously. The engineering application shows that the equivalent anchoring method can reasonably simulate the effect of rock bolts, which can provide reference for stability analysis of three-dimensional tunnel simulations.

A New Method to Determining the Strength Parameters of Fractured Rock Mass

2014 ◽  
Vol 898 ◽  
pp. 378-382
Author(s):  
Yun Hua Guo ◽  
Wei Shen Zhu
Keyword(s):  
Rock Mass ◽  
Mechanical Response ◽  
Fractured Rock ◽  
Fracture Network ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Constitutive Relationship ◽  
Hydropower Station ◽  
Rock Masses ◽  
Fractured Rock Mass

A Hydropower Station is located in the middle reach of the Dadu River in southwest China. The natural slope angles are generally 40°~65° and the relative elevation drop is more than 600m. Complex different fractures such as faults, dykes and dense fracture zones due to unloading are developed. Many abutment slopes were formed during construction of the abutments. The stability of these steep and high slopes during construction and operation period plays an important role for the safe construction and operation of the hydropower station. According to the statistical distribution of joints and fractures at the construction site, the slope is divided into a number of engineering geological zones. For each zone, a stochastic fracture network and a numerical model which is close to the real state of the fractured rock mass are established by the Monte-Carlo method. The mechanical response of fractured rock masses with different sizes of numerical models is studied using FLAC3D. The REV characteristic scale is identified for rock masses in the slopes with stochastic fracture network. Numerical simulation is performed to obtain the stress-strain curve, the mechanical parameters and the strength of the jointed rock mass in the zone. A constitutive relationship reflecting the mechanical response of the jointed rock mass in the zone is established. The Comparison between the traditional method and the method in this paper has been made at the end.

scholarly journals Mechanical Characteristics and Failure Modes of Low-Strength Rock Samples with Dissimilar Fissure Dip Angles

2021 ◽  
Author(s):  
Y L Wang ◽  
D S Liu ◽  
K Li ◽  
X M Hu ◽  
D Chen
Keyword(s):  
Rock Mass ◽  
Mechanical Characteristics ◽  
Failure Modes ◽  
High Strength ◽  
Rock Masses ◽  
Deformation And Failure ◽  
Deformation Features ◽  
Low Strength ◽  
Dip Angle ◽  
Strength Rock

The mechanical characteristics and failure modes of low-strength rock sample with various fissure dip angles were investigated by conventional uniaxial compression test and three-dimensional (3D) crack reconstruction. The results indicated that compared with high-strength rock masses, cracks had different influences on the low-strength rock mass mechanical deformation features. Thereinto, the dip angle of fissures can cause post-peak failure stage of stress-strain curve change from swift decline to multi-step down, showing obvious ductility deformation and failure characteristics. Peak strength and elastic modulus owned an anti-S-shaped growth tendency with the growth of fissure dip angle, which was positively correlated and greatest subtle to the fissure dip angle α < 21° and α > 66.5°. The axial peak strain reduced first and enlarged rapidly with growing fissure dip angle, suggesting a V-shaped change trend. Increasing the fissure dip angle will change the sample failure mode, experienced complete tensile failure to tensile-shear composite failure, and ultimately to typical shear failure. Also, the crack start angle decreased with enlarging fissure dip angle, larger than that the high-strength rock mass fissure dip angle. The above research findings can complement and improve the study of fissured rock masses.

scholarly journals Numerical Modeling on Dynamic Characteristics of Jointed Rock Masses Subjected to Repetitive Impact Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Jie Liu ◽  
Yan-Bin Song ◽  
Yue-Mao Zhao
Keyword(s):  
Rock Mass ◽  
Impact Loading ◽  
Jointed Rock ◽  
Stress Waves ◽  
Rock Masses ◽  
Jointed Rock Masses ◽  
Numerical Tests ◽  
Repetitive Impact ◽  
Dip Angle ◽  
Energy Dissipated

A discrete element method code was used to investigate the damage characteristics of jointed rock masses under repetitive impact loading. The Flat-Joint Contact Model (FJCM) in the two-dimensional particle flow code (PFC2D) was used to calibrate the microparameters that control the macroscopic behavior of the rock. The relationship between macro- and microparameters by a series of uniaxial direct tension and compression numerical tests based on an orthogonal experimental design method was obtained to calibrate the microparameters accurately. Then, the Synthetic Rock Mass (SRM) method that incorporates joints into the calibrated particle model was used to construct large-scale jointed rock mass specimens, and the repetitive drop hammer impact numerical tests on SRM specimens with different numbers of horizontal joints and dip angle joints were carried out to study the damage evolution, stress wave propagation, and energy dissipation characteristics. The results show that the greater the number of joints, the greater the number of cracks generated, the greater the degree of damage, and the more energy dissipated for rock masses with horizontal joints. The greater the dip angle of joints, the less the number of cracks generated, the less the degree of damage, and the less energy dissipated for rock masses with different dip angles of joints. The impact-induced stress waves will be reflected when they encounter preexisting joints in the process of propagation. When the reflected stress waves meet with subsequent stress waves, the stress waves will change from compressional waves to tensile waves, producing tensile damage inside rock masses.

scholarly journals Classification of Red-Bed Rock Mass Structures and Slope Failure Modes in South China

Geosciences ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 273 ◽  
Author(s):  
Cuiying Zhou ◽  
Xu Yang ◽  
Yanhao Liang ◽  
Zichun Du ◽  
Zhen Liu ◽  
...  
Keyword(s):  
Rock Mass ◽  
South China ◽  
Slope Failure ◽  
Failure Modes ◽  
Hard Rock ◽  
Soft Rock ◽  
Red Beds ◽  
Rock Falls ◽  
Geological Formation ◽  
Red Bed

Red beds are Meso–Cenozoic continental sedimentary strata that are mainly composed of gravel stone, sandstone, siltstone, mudstone, and shale and occasionally have interlayers of limestone, halite, and gypsum. As a typical rock mass, red beds are widely distributed throughout South China. In a typical tropical and subtropical continental environment, red beds are the product of multiple sedimentary cycles, which have resulted in complicated rock mass structures that play an important role in rock mass stability. It is thus of great significance to investigate the influence of different rock mass structures on the stability of red-bed slopes. In this paper, the geological formation history of red beds in South China is described. The main features of red-bed rock mass slopes in South China are discussed. The main combinations of inner geomechanical structures comprise: (1) mega-thick soft rock structures; (2) mega-thick hard rock structures; (3) thick hard rock structures with weak intercalation; and (4) soft–hard interbedded structures. In addition, the features of slope failure are analyzed, and four common failure modes are identified from the statistical data: (a) weathering spalling and scouring; (b) rock falls; (c) landslides; and (d) tensile dumping.

scholarly journals Anisotropic Constitutive Model of Intermittent Columnar Jointed Rock Masses Based on the Cosserat Theory

Symmetry ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 823 ◽  
Author(s):  
Wenbin Lu ◽  
Zhende Zhu ◽  
Xiangcheng Que ◽  
Cong Zhang ◽  
Yanxin He
Keyword(s):  
Rock Mass ◽  
Constitutive Model ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Rock Masses ◽  
Cosserat Theory ◽  
Tunnel Excavation ◽  
Jointed Rock Masses ◽  
Columnar Jointed Rock Mass ◽  
Anisotropic Constitutive Model

In this work, an anisotropic constitutive model of hexagonal columnar jointed rock masses is established to describe the distribution law of deformation and the failure of columnar joint caverns under anisotropic conditions, and is implemented to study the columnar jointed rock mass at the dam site of the Baihetan Hydropower Station on the Jinsha River. The model is based on the Cosserat theory and considers the mesoscopic bending effect on the macroscopic mean. The influences of joint plane inclination on equivalent anisotropic elastic parameters are discussed via the introduction of an off-axis transformation matrix and the analysis of an example. It is also pointed out that the six-prism columnar jointed rock mass changes from transverse isotropy to anisotropy under the influence of the angle. A numerical calculation program of the Cosserat constitutive model is developed and is applied to the simulation calculation of a Baihetan diversion tunnel to compare and analyze the respective plastic zones and stress distributions after tunnel excavation under both isotropic and anisotropic conditions. The results reveal that, compared with the isotropic model, the proposed Cosserat anisotropic model better reflects the state of stress and asymmetric distribution of the plastic zone after tunnel excavation, and the actual deformation of the surrounding rock of the tunnel is greater than that calculated by the isotropic method. The results aid in a better understanding of the mechanical properties of rock masses.

scholarly journals Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Feng Zhu ◽  
Haotian Fan
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Epoxy Resin ◽  
Failure Modes ◽  
Shear Failure ◽  
Fractured Rock ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Compression Tests

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.

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