scholarly journals The criterion of block media strength and geomechanical back-calculation

2020 ◽  
pp. 37-47
Author(s):  
Zhabko Andrei ◽  
Keyword(s):  
Rock Mass ◽  
Fundamental Problem ◽  
Jointed Rock ◽  
Theoretical Research ◽  
Block Medium ◽  
Rock Masses ◽  
Jointed Rock Masses ◽  
Engineering Sciences ◽  
Shear Rupture ◽  
Block Media

Relevance and problematics. The mechanism of block medium and jointed rock mass deformation and breaking differs notably from continuum mechanics ideas, making up the crucial fundamental problem of geomechanics and distinguishing it from other engineering sciences connected with the mechanics ISSN 0536-1028 «Известия вузов. Горный журнал», № 6, 2020 47 of deformable solids. However, due to poor understanding of block media breaking mechanism, rock masses strength is overwhelmingly estimated by means of empirical dependences obtained by simulation in laboratory conditions. It is apparent that this approach does not solve the crucial fundamental problem and the accuracy of predicting mechanical characteristics of jointed rock masses may reach 100%. Research methodology. Based on the earlier theoretical research by the methods of variational, integral, and differential calculus, a new mechanism of block mass breaking at a point was substantiated. It implies translation and rotational character of blocks displacement in a rock mass in the process of its deformation making it possible to substantiate the criterion of jointed rock masses breaking. Research results, analysis and recommendations for use. The research was the first to obtain the block medium strength criterion. It has been shown that block mass strength is made up of the strength along the slip joint and block rotation resistance. Besides, within some range of loads, the ultimate strength of the rock mass is proportional to the tensile strength of a structure block. The work also proposes a range of analytical dependences obtained based on the solid mechanics making which make it possible to back calculate the rock mass strength based on the curvature of the shear rupture surface and assess the full tensor of the plain field of strain by the base axes orientation.

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 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.

Long-wavelength P-wave and S-wave propagation in jointed rock masses

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. E205-E214 ◽  
Author(s):  
Minsu Cha ◽  
Gye-Chun Cho ◽  
J. Carlos Santamarina
Keyword(s):  
Wave Propagation ◽  
Rock Mass ◽  
Normal Stress ◽  
Jointed Rock ◽  
P Wave ◽  
Rock Masses ◽  
S Wave ◽  
Jointed Rock Masses ◽  
Long Wavelength ◽  
Joint Properties

Field data suggest that stress level and joint condition affect shear-wave propagation in jointed rock masses. However, the study of long-wavelength propagation in a jointed rock mass is challenging in the laboratory, and limited data are available under controlled test conditions. Long-wavelength P-wave and S-wave propagation normal to joints, using an axially loaded jointed column device, reproduces a range of joint conditions. The effects of the normal stress, loading history, joint spacing, matched surface topography (i.e., joint roughness), joint cementation (e.g., after grouting), joint opening, and plasticity of the joint filling on the P-wave and S-wave velocities and on S-wave attenuation are notable. The ratio [Formula: see text] in jointed rock masses differs from that found in homogeneous continua. The concept of Poisson’s ratio as a function of [Formula: see text] is unwarranted, and [Formula: see text] can be interpreted in terms of jointed characteristics. Analytic models that consider stress-dependent stiffness and frictional loss in joints as well as stress-independent properties of intact rocks can model experimental observations properly and extract joint properties from rock-mass test data. Thus, joint properties and normal stress have a prevalent role in propagation velocity and attenuation in jointed rock masses.

Rock mass movements across bedding in Kananaskis Country, Alberta

1992 ◽  
Vol 29 (4) ◽  
pp. 675-685 ◽  
Author(s):  
Xian-qin Hu ◽  
D. M. Cruden
Keyword(s):  
Rock Mass ◽  
Key Words ◽  
Sliding Mode ◽  
Sedimentary Rocks ◽  
Jointed Rock ◽  
Mass Movements ◽  
Rock Masses ◽  
Jointed Rock Masses ◽  
Bedding Planes ◽  
Mode A

Rock mass movements in sedimentary rocks across bedding in Kananaskis Country, Alberta, are controlled by discontinuity orientations and topography. When bedding planes dip at less than 50°, small rock masses can slide along strike joints or fall and slope angles remain unchanged. When bedding surfaces dip at 65–70°, large rock masses topple and then slide or simply slide along sheeting joints or combinations of bedding surfaces and strike joints to reduce slope gradients. Block toppling and sliding models of large slope movements in highly jointed rock masses indicate that toppling mode is more critical than the sliding mode. A natural example, the 6 × 106 m3 Elk Ridge landslide, shows toppling from bedding planes followed by sliding can be catastrophic. Key words : topple, slide, landslide, rock, Rockies.

Distinct Element Modeling of the Effect of Joint Persistence on Dynamic Fracturing of Jointed Rock Masses

2014 ◽  
Vol 553 ◽  
pp. 445-451
Author(s):  
Zeinab Aliabadian ◽  
Mansour Sharafisafa
Keyword(s):  
Wave Propagation ◽  
Rock Mass ◽  
Jointed Rock ◽  
Intact Rock ◽  
Rock Blasting ◽  
Rock Masses ◽  
Jointed Rock Masses ◽  
Free Face ◽  
Rock Bridges ◽  
Discontinuous Joints

Rock masses consist of intact rock and discontinuities such as faults, joints and bedding planes. The presence of such discontinuities in rock masses dominates the response of jointed rock masses to static and dynamic loading. These structural weak planes seriously hinder and affect the propagation of stress waves in rock mass. The joints parameters such as persistence, orientation, distribution patterns, spacing and filling material have a significant effect on the response of rock masses against wave propagation. In most studies of blast induced wave propagation in jointed rock mass, it is assumed that joints are continuous. In many situations the rock mass consists of non-continuous joints and rock bridges. Rock bridges and discontinuous joints have a different effect on wave and fracture propagation in a blasting operation. With regard to complexities associated with rock blasting in particular in jointed media, numerical tools are viable alternatives for rock blasting analysis. In this study the DEM methods was employed to investigate the effects of rock bridges on the wave propagation process. A plain strain 2D scenario was assumed and a single blasthole explosion was simulated. Three models with different jointing orientation patterns including jointing pattern parallel to free face, perpendicular to free face and orientated at 45 degree with respect to free face were analyzed numerically to investigate rock mass fracturing while blast wave propagation. The discontinuous joints were considered to be filled with weak materials (open joints) and rock bridges are composed of intact rock. In order to allow material plastic failure, a Mohr-Coulomb material model was used. The analysis results show that the stress concentration at the rock bridge location leads to excessive fracturing. This effect is more visible at the free face where the stress wave reflection occurs. Moreover, the obtained results show that the pattern and orientation of non-continuous joint system has a pronounced effect on rock fragmentation.

Crack Propagation of Jointed Rock and Application

2011 ◽  
Vol 117-119 ◽  
pp. 476-479
Author(s):  
Jing Wang ◽  
Wei Shen Zhu ◽  
Hai Ping Ma
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Failure Process ◽  
Jointed Rock ◽  
Rock Masses ◽  
Stress Strain ◽  
Jointed Rock Masses

Brittle media, such as rock mass, usually contain a great number of joints or cracks, which lead to varying mechanical properties and failure behaviors of different rock masses. In this paper, the DDARF method is adopted to simulate the crack initiation, propagation, coalescence and failure process in rock masses prefabricated with the different crack number and spacing under loading. The corresponding stress-strain curves and strength envelope are obtained. The parameters are applied in a case study. The differences in the failure behaviors of the intact and jointed rock masses after cavern excavation are analyzed and compared.

Sign in / Sign up

Export Citation Format

Share Document