Stratified Rock Mass Research Articles

An overview of the thermography-based experimental studies on roadway excavation in stratified rock masses at CUMTB

This paper presents an overview of experimental investigations conducted at China University of Mining and Technology Beijing (CUMTB) on roadway excavation using large-scale geomechanical model tests. The simulated sedimentary rocks are composed by alternating layers of sandstone, mudstone and coal seam inclined at varied angles with respect to the horizontal including 0°, 45°, 60°, and 90°. During the excavation, infrared thermography was employed to detect the thermal response of the surrounding rocks under excavation. The obtained raw thermograms were processed using denoising algorithm, data reduction procedure and Fourier analysis. The infrared temperature (IRT) characterizes the overall rock response; the processed thermal images represent the structural behavior, and the Fourier spectrum describes damage development in the frequency domain. Deeper understanding was achieved by the comparative analyses of excavation in differently inclined rock masses using the image features of IRTs, thermal images and Fourier spectra.

Analysis of Deformation and Failure Characteristics of Stratified Rock Mass around Underground Opening Based on a Microstructure Tensor Approach

In order to have a good understanding of the geotechnical behavior around underground opening excavated in stratified rock mass, numerical simulation of a gate-shaped cavern excavation was conducted by applying a transversely isotropic model base on microstructure tensor method. The simulations were performed under the assumption that both the beddings and the in-situ middle stress vector run parallel with the cavern. Effect of the dip angle of beddings and that of in-situ major stress vector on deformation and failure of rock mass around the cavern was investigated. The mechanism underneath the image of deformation and failure was also discussed. It is found that the dip angle of beddings has less influence than the in-situ stress on deformation while the dip angle of bedding and the direction of in-situ major stress vector are equally important to the failure of surrounding rock mass.

Estimation of the Strength of Stratified Rock Mass

Stratified rock formations are often encountered in engineering structures with large dimensions, such as tunnels, caverns, etc. In the present work, the question of how and when such materials fail is addressed. It is argued that average values cannot provide appropriate measures for the strength of layered rock, as local stresses and strains differ greatly in the various constituents and one may fail, while others remain intact. The present work attempts, therefore, to formulate a solution covering both elasticity and failure in three dimensions, though simple enough to be easy to use in engineering applications. To this end, the local stress and strain state in each constituent were evaluated, assuming the constituents to be orthotropically elastic up to the point of failure. Subsequently, several failure criteria are considered and an example is presented to illustrate the model’s response. A discussion on the effect of geometry and on the values of local versus global quantities follows.

Deformation of anisotropic rock mass in the vicinity of a long tunnel

The article deals with the stress and strain assessment in anisotropic rock mass in the vicinity of a lateral opening. The authors carry out numerical calculations for sets of elastic constants for orthotropic and transversally isotropic bodies and show that integrating and including more elastic constants allows keener estimation of load distribution in a stratified rock mass whereas minimum constant pool is enough for quality modeling.

The Anisotropy Characteristic of Rock Material Described by the Stress Softening Criterion in Civil Engineering

In this paper, firstly we utilize the elastic model, which provides the simplest representation of material behavior in civil engineering. This model is valid for homogeneous, isotropic, continuous materials that exhibit linear stress-strain behavior with no hysteresis on unloading. The elastic models include both isotropic and anisotropic elastic models. Then the Mohr-Coulomb model is used which can represent shear failure in soils and rocks in civil engineering and geotechnical engineering. After that, the strain- softening model is founded, which allows representation of nonlinear material softening and hardening behavior based on prescribed variations of the Mohr-Coulomb model properties (cohesion, friction, dilation, tensile strength) as functions of the deviatoric plastic strain. Finally, a case study is done for the stratified rock mass, the elastic modulus of the rock sample for different surrounding compressive are obtained, to exhibit the anisotropy characteristic of this type of rock material

Anisotropic behaviour of stratified rock masses in tunnelling

This paper investigates tunnel excavation through stratified rock masses from the engineering geological behaviour to the rock mass properties quantification and finally to the study of tunnel response, based on numerical analyses results. Initially the spectrum of the engineering geological behaviour of stratified rock masses in tunnelling is delimited and the critical failure mechanisms according to rock mass structure are described. Rock mass simulation as an equivalent isotropic geomaterial through the widely used characterisation systems in most cases cannot lead to a realistic prediction of the distribution and the values of total displacements. In addition, the complete and accurate simulation of all discontinuities networks involves high uncertainty. Therefore in the numerical analyses carried out, based on an already applied approach, the stratification planes, which contain less uncertainty than the secondary discontinuities and affect significantly the behaviour of tunnel, were simulated as separate elements and the rock mass parts between them as an isotropic material. Additionally, using simple rock mechanics principles, an approach for the quantification of the rock mass properties involved in the analyses is described, which tries to obtain the equivalence between the stratified rock mass and the sum of the distinct rock mass elements (stratification planes and internal rock mass). The numerical analyses depict the mechanism of convergence development in stratified rock masses and the differences between isotropic, anisotropic and transversally isotropic approaches are clearly demonstrated. Based on the results of the numerical analyses the incorporation of the stratification planes leads to an increase of the convergence mainly due to the bending of the rock mass strata where the stratification is tangential to the tunnel section. This increase depends on the GSI value of the reference rock mass and the discontinuities surface conditions.

Stress arch bunch and its formation mechanism in blocky stratified rock masses

Stress arch is a common phenomenon occurring in continupous materials and has also been proved to have great influences on the self-stabilization of soils or rock masses after excavation. In this paper, based on UDEC simulation, stress redistribution after excavation is investigated for a kind of special discontinuous material, i.e. blocky stratified rock mass. A layered stress arch system is observed with each stress arch lying over another. This special phenomenon is defined herein as “stress arch bunch”. Effects of dip angle of bedding plane, lateral pressure and joint offset on this stress arch bunch are studied. Its formation mechanism is also discussed based on voussoir beam theory.

Computer Aided Understanding for Interaction between Stratified Slope and Bolt

Slope excavations are often constructed in stratified host rock masses in practice. The stratification in a rock mass is generally characterised by its planar geometry and persistence. The mechanical properties of the joints dictate both the deformation and strength characteristics of the stratified rock mass. Thus, it is imperative that the influence of the joints be incorporated in any type of load-deformation analysis of slope excavations in layered rock masses. Rock bolts have been widely used as the primary support system to stabilize the rock masses of slope. In general, rock bolts reinforce rock masses through restraining the deformation within rock masses and reduces the yield region around the excavation boundary. In order to improve bolting design, it is necessary to have a good understanding of the behaviour of rock bolts in deformed rock masses. In the present paper, the numerical analysis method is adopted to built the three springs bolt element; then the excavation in the stratified rock slope is simulated to improve the understanding of the slope deformation and bolt mechanical characteristic.

Physical model test and numerical analysis on the behavior of stratified rock masses during underground excavation

Traditional intensive drilling (or grooving) technology in a roadway destroys the rock mass and supporting structure in the shallow anchoring area while implementing pressure relief. In Dongpang coal mine, it is difficult to avoid the failure of the supporting system and continuous large deformations of the deep roadways influenced by disturbance, despite the application of strong bolt (cable) supporting systems and grouting reinforcements. Therefore, this study proposes a novel “anchoring and pressure relief” synergistic supporting technique to eliminate the dilemma among the anchoring supporting and pressure relief. With strong anchoring supporting in the shallow surrounding rock, this novel technology realizes pressure relief by excavating large-diameter holes in the deep peak stress area, to enable active regulation of the move of the peak stress area to the deep surrounding rock without impairing the shallow anchoring area. The path of coal body rheology and stress move is cut off by large-diameter holes using this novel technology, achieving the purpose of absorbing energy and deformation, decreasing the stress applied on the supporting structure in the anchoring area. The novel technology effectively solves the control problems of continuous large deformation in deep roadway and has a good engineering application prospect. This study findings will add scientific value for the improvement of surrounding rock control of deep roadway.

Primary Engineering Geological for Shuibuya Underground Power Station and their Treatment

The Shuibuya hydropower station is located in Badong County in the middle reach of Qingjiang River. It is the first cascaded project in Qingjiang mainstream. The Project consists of a concrete faced rock fill dam (CFRD), underground power house, chute spillway on the left bank, and the sluice tunnel on the right bank. The dam is 233m high, which is the highest of its kind in the world at present. The installed capacity and annual output of Shuibuya Power Plant are 4×460MW and 3.92 GWh respectively. The rock mass of foundation of Shuibuya project is a type of stratified sedimentation rock mass is composed of interbedded stratum by weak layers and hard layers. To solve engineering geological problem is difficult and challenging. For example, the intake slope of Shuibuya hydropower diversion tunnel was a landslide, and diversion tunnel outlet is located at the toe of Maya slope with 360m high, rock mass of the underground powerhouse caverns are soft and hard rock inter-layered, with multi-structural planes, multi-shear zones, and the lithology of rock is highly krast. Some researchs and geological treatments were performed during the geological exploitation and construction, which is fundamental and primary.

Computer Aided Design for Safety Analysis of Excavation in Stratified Rock Tunnel

Stratified rock mass is widely existing in tunnel engineering. The most relevant feature of stratified rocks is the occurrence of very persistent bedding, which makes the rock-mass highly non-isotropic. A number of techniques for designing underground excavations in stratified media have been described in the literature, like theoretical method and laboratory test, which can only be applied in analyzing the problem with simple geometry and costs much expense. Recently, with rapid development of computer technique, numerical simulation methods have been widely applied in engineerin. Among all the numerical simulation methods, fast lagrangian explicit finite difference code of continua (FLAC3D) is widely used to solve practical problems, especially in field of elasto-plastic characteristic, large deformation analysis and construction procedure. So in the present paper, numerical simulation for the failure mode of stratified rock mass after tunnel excavation is done by FLAC3D, which can give further guidance to understand the anisotropic characteristic of stratified rock mass.

Three Dimensional Numerical Modeling for the Stratified Rock Slope and the Parametric Analysis

Stratified rock mass has been widely existing in geotechnical engineering. With obvious transversely isotropic characteristic, stability of stratified rock mass is not only related to strength of intact rock but also to the inclination and characteristic of structure plane. The parameters of the structure plane have great impact on the stability of stratified rock mass. For the stratified rock mass is no homogenous, the homogenous model is not suitable to describe the characteristic of stratified rock mass. Then building an appropriate becomes necessary. In the present paper, Ubiquitous-joint model is introduced to describe the characteristic of rock mass, and the strength reduction method based on the Ubiquitous-joint model is proposed, which then is used to calculate the safety factor of slope, while the relationships between safety factor, strength properties of structure plane are analyzed, whose results can give guidance for the real practice.

Failure mode and strength anisotropic characteristic of stratified rock mass under uniaxial compressive situation

A stratified rock mass model was founded by FLAC (superscript 3D). The failure mode and anisotropic characteristic of strength for stratified rock mass were analyzed. The analysis results show that the numerical simulation can visually reflect the failure modes of rock samples under different inclination angles β of structural plane. The stiffness of rock sample before peak strength changes in the compressive procedure. With the increase of β, the compressive strength o of rock sample decreases firstly and then increases; when β is in the range of 20°-30° and 80°-90°, ac has the largest sensitivity to β; while β falls in the range of 30°-70°, ac varies little. When O(subscript j)＜β＜90° (O(subscript j) is friction angle of structure plane), the results obtained from numerical simulation and theoretical analysis are in almost the same values; whileβ≤O(subscript j) or β=90°, they are in great different values. The results obtained from theoretical analysis are obvious larger than those from numerical simulation; and the results from numerical simulation can reflect the difference of compressive strength of rock samples for the two situations ofβ≥O(subscript j) and β=90°, which is in more accordance with the real situation.

Allowing for the plastic properties of rock in stability problems for a stratified rock mass

The paper addresses the important issue of allowing for the inelastic properties of rock in stability problems for a stratified rock mass. A three-dimensional nonlinear problem statement is used. An exact method to study the surface instability of a regularly layered semi-infinite medium is developed. New numerical results are obtained

Multi-approach back-analysis of a roof bed collapse in a mining room excavated in stratified rock

Roof bed deformation mechanics is a complex topic in mining practice. There are a number of empirical, analytical and numerical techniques that can be used to analyze and design underground excavations in stratified rock masses. Each has particular drawbacks, however, so the use of just one approach in order to obtain consistent and economic designs is not practical. To deepen understanding of this topic, it is useful to study real failure in mines. In this paper we describe how a roof bed failure in an underground mine, excavated in a stratified rock mass, was back-analyzed using different approaches, namely, the empirical stability graph method, the analytical voussoir techniques, and the numerical discrete element method. The study enabled us to better understand the conditions of failure and to define the most significant parameters affecting the failure. It has also been shown how relaxation or loss of confinement stress can play an important role in roof bed deformation.

The development of a coal measure classification (CMC) and its use for prediction of geomechanical parameters

Many studies have been performed to predict the strength and deformation moduli for both rock masses and discontinuities. However, in most empirical equations in the literature that have been proposed for the estimation of the strengths and deformation moduli, the rock mass is assumed isotropic. Although it is known that the strength and deformation of a stratified rock mass varies depending on the loading direction in relation to the orientation of the lamination planes, there exists at present no commonly accepted method for characterising this anisotropy. This paper outlines the development of a rock mass rating system for coal measure rock masses that can be used to empirically predict the engineering properties of stratified rock masses. The output from the classification system is two numerical ratings representing the different engineering properties of the strata in directions parallel and perpendicular to stratification. A detailed description on the methodology used to develop the classification system has been given and the derivation and rating of the various rock mass parameters is outlined. The methodology of deriving the in situ stratified rock mass input parameters and geomechanical computational analysis is illustrated for the case of two rock bolted roadways within a representative deep UK coal mine. The model predictions were validated against the actual in situ monitoring data of displacements within the immediate roof of the roadway.

Upscaling of elastic properties for large scale geomechanical simulations

AbstractLarge scale geomechanical simulations are being increasingly used to model the compaction of stress dependent reservoirs, predict the long term integrity of under‐ground radioactive waste disposals, and analyse the viability of hot‐dry rock geothermal sites. These large scale simulations require the definition of homogenous mechanical properties for each geomechanical cell whereas the rock properties are expected to vary at a smaller scale. Therefore, this paper proposes a new methodology that makes possible to define the equivalent mechanical properties of the geomechanical cells using the fine scale information given in the geological model. This methodology is implemented on a synthetic reservoir case and two upscaling procedures providing the effective elastic properties of the Hooke's law are tested. The first upscaling procedure is an analytical method for perfectly stratified rock mass, whereas the second procedure computes lower and upper bounds of the equivalent properties with no assumption on the small scale heterogeneity distribution. Both procedures are applied to one geomechanical cell extracted from the reservoir structure. The results show that the analytical and numerical upscaling procedures provide accurate estimations of the effective parameters. Furthermore, a large scale simulation using the homogenized properties of each geomechanical cell calculated with the analytical method demonstrates that the overall behaviour of the reservoir structure is well reproduced for two different loading cases. Copyright © 2004 John Wiley & Sons, Ltd.

Mathematical Models of Block Media in Problems of Geomechanics. Part I: Deformation of Stratified Medium

The mathematical model is constructed for the elastic and elastoplastic deformation of stratified rock mass. The examples are presented for solving the plastic problems on mine working in block massif and indentation of hard die block under various conditions of plasticity.

Geostatistical analysis and hierarchical modelling of a fracture network in a stratified rock mass : Gervais, F; Chiles, J P; Gentier, S Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P158–165. Publ California: Lawrence Berkeley Laboratory, 1992

Geostatistical analysis and hierarchical modelling of a fracture network in a stratified rock mass : Gervais, F; Chiles, J P; Gentier, S Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P158–165. Publ California: Lawrence Berkeley Laboratory, 1992

Three dimensional description of the fracture pattern of a stratified rock mass (In French)

Three dimensional description of the fracture pattern of a stratified rock mass (In French)