Excavations In Jointed Rock Research Articles

Validation of a FEM computer programme for underground excavations in jointed rock

ABSTRACTThe paper discusses the validation of a two-dimensional finite-element Phase2 programme using various approaches to verify and compare for underground excavations in rock and jointed rock. Corresponding to the analysis of underground openings, the behaviour between circular and horseshoe-shaped underground excavation, with and without rock bolt and/or lining supports, is carried out using the numerical modelling software Phase2. The analysis of the model is compared with analytical solutions using two other numerical software packages – Plaxis and Universal Distinct Element Code (UDEC) – as well as a case study using field data recorded from one of the Hong Kong tunnel projects. As Phase2 is not a universal computer programme for solving all soil and rock engineering problems, the key assumptions and theory of the programme and its limitations are discussed. The results of the study show that the Phase2 numerical modelling programme provides satisfactory agreement with different verification cases...

Laboratory Measurement of Two-Phase Flow Parameters in Rock Joints Based on High Pressure Triaxial Testing

The accurate flow measurement of each individual phase is important in unsaturated flow through rock joints, where both air and water phases flow together. An increase in the quantity of one fluid phase decreases the relative permeability of the other phase. The relative permeability is important in numerical models to analyze the risk of ground-water inundation and uncontrollable gas flows in underground excavations in jointed rock. A new apparatus, the High Pressure Two-Phase Triaxial Apparatus (HPTPTA), has been designed for examining the strength and coefficient of permeability characteristics of fractured and intact rocks under two-phase flows. In single-phase triaxial equipment, the rock specimen is subjected to a single fluid flow (either water, oil, or gas) through the fractures. In the HPTPTA, two fluids (e.g., water + air, water + oil, and oil + air) can be forced to flow through the specimen, and the flow rates of the fluids can be measured independently. The scope of tests that can be carried out in this apparatus is wide, including the evaluation of (1) stress-strain behavior subject to internal fluid flow; (2) relative permeability of each fluid phase under different degrees of saturation; and (3) the associated volume change of the specimen. In this paper, the design concepts of the HPTPTA and the results based on the testing of fractured rock specimens are discussed. The laboratory results are compared to a simplified mathematical model developed by the writers. Based on the laboratory results, it is shown that the well-known Darcy's law can be modified for estimating the two-phase flow rates using the relative permeability concept.

Estimating keyblock sizes in underground excavations: accounting for joint set spacing

Abstract A new method is introduced for use in the design of underground excavations in jointed rock. A model of discontinuities in a rock mass provides the basis for a closed-form solution to the expected keyblock occurrences within the excavation. The limitations of the assumptions made about the discontinuities are significant but are also, for the most part, conservative assumptions. Initially a two-dimensional formulation of the expected probability of keyblock formulation is introduced. This is valuable because it provides a simple basis for introducing the method. The two-dimensional method is demonstrated for two different excavation cross sections. The case involving excavations of rectangular cross section is validated using simulation models of tetrahedral keyblock formation. The three-dimensional case is also introduced allowing two different probabilistic formulations. One technique predicts the expected probability of a keyblock forming within a randomly selected excavation cross section. The other technique predicts the number of keyblocks (within a nominated size category) expected to form along a nominated excavation length. Both three-dimensional techniques are validated using numerical simulation. Finally, procedures for application of the unit–cell method in excavation design are provided.

Analysis of the Dynamic Performance of an Underground Excavation in Jointed Rock under Repeated Seismic Loading

Results from field observations of dynamic behaviour of an underground excavation have been compared with numerical studies of the rock deformation history. The field behaviour shows progressive accumulation of rock displacement and excavation deformation under successive episodes of dynamic loading. It is possible to reproduce the modes of rock response quite well using a Distinct Element model of the rock mass, but the way displacements develop is dependent on the joint model used in the analysis. It is suggested that, in rock masses subject to repeated dynamic loading, excavation design may need to take account of the prospect of repeated episodes of transient loading at the excavation site.

Rock reinforcement systems

A terminology for reinforcement practice is proposed based on the idea that a reinforcement device, rock mass and reinforced rock mass are all systems of components. It follows that the force-deformation behaviour of each system is a consequence of the particular physical and mechanical characteristics of the system components and their interactions. Using this systems approach and the associated terminology, a method is proposed for the design of reinforcement for excavations in jointed rock. The design method is based on identifying and stabilising the blocks of rock that may form at the excavation boundary. It uses the early developments in block theory for identification and stability assessment of the blocks. These developments are supplemented with new reinforcement design and stability assessment procedures for the unstable blocks.

Rock reinforcement systems

A terminology for reinforcement practice is proposed based on the idea that a reinforcement device, rock mass and reinforced rock mass are all systems of components. It follows that the force-deformation behaviour of each system is a consequence of the particular physical and mechanical characteristics of the system components and their interactions. Using this systems approach and the associated terminology, a method is proposed for the design of reinforcement for excavations in jointed rock. The design method is based on identifying and stabilising the blocks of rock that may form at the excavation boundary. It uses the early developments in block theory for identification and stability assessment of the blocks. These developments are supplemented with new reinforcement design and stability assessment procedures for the unstable blocks.

Probabilistic stability analysis of excavations in jointed rock : C. F. Leung & S. T. Quek, Canadian Geotechnical Journal, 32(3), 1995, pp 397–407

Probabilistic stability analysis of excavations in jointed rock : C. F. Leung & S. T. Quek, Canadian Geotechnical Journal, 32(3), 1995, pp 397–407

Probabilistic stability analysis of excavations in jointed rock

Excavations in jointed rock may liberate rock blocks that may fall by gravity or slide along the discontinuity. The orientation of discontinuities is one of the major input parameters in the conventional deterministic stability analysis of rock blocks. As the mean orientation of a discontinuity is often derived from a large number of joint-set data obtained from site investigation, Fisher's constant is commonly employed to represent the degree of dispersion of individual discontinuity orientation. However, such dispersion factors are rarely used in the conventional analysis. A probabilistic-based approach is proposed in this paper to incorporate Fisher's constant in the stability analysis of rock blocks. To account for the uncertainty reflected by the sample dispersion, data are generated systematically around each mean discontinuity normal, based on its Fisher's constant. The probability of rock block failure at a certain location and the largest possible block volume are determined in a logical manner. A microcomputer program has been developed to automate the analysis, and illustrative examples are shown to demonstrate the importance of incorporating the Fisher's constant of individual discontinuity in the stability analysis. In addition, risk mapping plots are presented to enable visual selection of an optimal route for excavation from one location to another. Key words : discontinuity, factor of safety, probability of failure, rock block, rock excavation, stability analysis.

A 2D coupled finite element and boundary element scheme to simulate the elastic behaviour of jointed rocks

AbstractIn this paper a coupled finite and boundary element formulation is developed for the analysis of excavation in jointed rock. The presence of joints in the rock mass has been included implicitly by treating it as an appropriate anisotropic elastic continuum. The boundary element formulation for an anisotropic medium is briefly discussed. Good agreement has been found between numerical and analytical solutions for several example problems, demonstrating the accuracy of the present formulation. Numerical solutions are also presented for the problems of a deep circular tunnel and a basement excavated in a variety of jointed rock masses.

Dynamic performance and design of underground excavations in jointed rock : Brady, B H Proc ISRM International Symposium on Static and Dynamic Considerations in Rock Engineering, Swaziland, 10–12 September 1990P1–11

Dynamic performance and design of underground excavations in jointed rock : Brady, B H Proc ISRM International Symposium on Static and Dynamic Considerations in Rock Engineering, Swaziland, 10–12 September 1990P1–11

Application of numerical modelling to the analysis of excavations in jointed rock : Beer, G Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18–20 April 1990P3–9. Publ. Rotterdam: A A Balkema, 1990

Application of numerical modelling to the analysis of excavations in jointed rock : Beer, G Proc International Conference on Mechanics of Jointed and Faulted Rock, Vienna, 18–20 April 1990P3–9. Publ. Rotterdam: A A Balkema, 1990

Discontinuum analysis for deep excavations in jointed rock : Hart, R D Proc International Symposium on Rock at Great Depth, Pau, 28–31 August 1989V3, P1123–1130. Publ Rotterdam: A A Balkema, 1989

Discontinuum analysis for deep excavations in jointed rock : Hart, R D Proc International Symposium on Rock at Great Depth, Pau, 28–31 August 1989V3, P1123–1130. Publ Rotterdam: A A Balkema, 1989

Analysis of tunnel distortion due to an open excavation in jointed rock : Carter, J P; Alehossein, H Comput GeotechV9, N3, 1990, P209–231

Analysis of tunnel distortion due to an open excavation in jointed rock : Carter, J P; Alehossein, H Comput GeotechV9, N3, 1990, P209–231

Comparison between the distinct element method and the finite element method for analysis of the stability of an excavation in jointed rock : Fairhurst, C; Pei, J Tunnlg Underground Space TechnolV5, N1/2, 1990, P111–117

Comparison between the distinct element method and the finite element method for analysis of the stability of an excavation in jointed rock : Fairhurst, C; Pei, J Tunnlg Underground Space TechnolV5, N1/2, 1990, P111–117

A comparison between the distinct element method and the finite element method for analysis of the stability of an excavation in jointed rock

Abstract The stability of a large underground excavation in jointed rock has been analyzed using both the Distinct Element Method and the Finite Element Method. The degree of similarity between the results was found to depend on the joint stiffness. As the stiffness is reduced, the Distinct Element Method is seen to provide a better description of the behavior of a jointed system, including block translation, rotation and collapse.

Computer aided design of underground excavations in jointed rock

Stability analysis of rock blocks that may be formed by excavating jointed rock masses is traditionally performed using the stereographic projection technique. However, such technique is prone to human errors, and existing alternative analytical methods are rather tedious and time consuming. In this paper, a computer aided approach is proposed with the prime objective that the entire analysis is automated on a microcomputer. Computer aided design features such as determination of discontinuity orientation based on borehole data, stability analysis of rock blocks involving multiple discontinuity sets, and determination of optimum excavation direction, optimum plunge of rock reinforcement and the most critical direction of earthquake force are provided.

Analysis of tunnel distortion due to an open excavation in jointed rock

General elastic solutions for tunnel deformations due to a nearby basement excavation are presented for jointed rock masses that contain two orthogonal joint sets. The method used to obtain these solutions involves a boundary element formulation for planar problems in anisotropic elasticity. The numerical solutions presented here allow predictions to be made of the changes in key tunnel dimensions, i.e. measures of the tunnel distortion, as the basement is excavated over a range of depths. Data that is typical for tunnels, basements and rocks in the central business district of Sydney have been used to illustrate the use of these solutions in geotechnical engineering.

Analysis of excavations in jointed rock of infinite extent : Sofianos, A I; Watson, J O Int J Num Anal Meth GeomechV10, N2, March–April 1986, P125–136

Analysis of excavations in jointed rock of infinite extent : Sofianos, A I; Watson, J O Int J Num Anal Meth GeomechV10, N2, March–April 1986, P125–136

A Multiplier Method for Identifying Keyblocks in Excavations Through Jointed Rock

G. H. Shi and R. E. Goodman have recently pointed out the practical importance of the keyblock principle in supporting underground and surface excavations in jointed rock and have given an elegant procedure involving stereographic projection and graphics for identifying the shapes of keyblocks. This paper presents the mathematical analysis of an entirely different keyblock characterisation and identification algorithm. The characterisation rests upon Tucker’s Theorem of the Alternative, and the algorithm requires only the execution of a few linear programming type pivot operations and sign tests.

Analysis of excavations in jointed rock of infinite extent

AbstractThe subject of this work is the development of a code to study the behaviour of stratified and jointed rock masses around underground excavations. The rock mass is divided into two types of regions, one which is supposed to exhibit linear elastic behaviour and which may extend to infinity, and the other which will include discontinuities that behave inelastically. The former has been simulated by a symmetric direct, boundary integral, plane strain, quadratic, orthotropic module, and the latter by quadratic plane strain, membrane and inelastic joint elements. The two modules are coupled in one program. Sequences of loading include static point, pressure, body and residual loads, construction and excavation sequences, and quasi‐static earthquake load. The programe is interactive, with graphics. A numerical example is presented to illustrate the method.