Site characterisation for tunnels in jointed rock masses

Site characterisation for tunnels in jointed rock masses

235A Rock block analysis Stress analysis 914282 Probabilistic stability analysis of block toppling failure in rock slopes Scavia, C; Barla, G; Bern...

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Rock block analysis

Stress analysis

914282 Probabilistic stability analysis of block toppling failure in rock slopes Scavia, C; Barla, G; Bernaudo, V lnt J Rock Mech Min Sci V27, N6, Dec 1990, P465-478

See also: 914081, 914484

Two dimensional limit analysis of rock blocks resting on a stepped failure surface is carried out. A number of failure paths is generated, taking into account variability of selected input parameters. Statistical distribution of interaction forces for each path is calculated. Both computations utilise the Monte Carlo simulation. The probability of failure of one or more blocks is then assessed according to Markov Chain theory. Two examples are presented. The first is an idealised slope design problem, the second an open pit problem, where instability is indicated, despite acceptable deterministic safety factors. 914283 Finding 3-D maximum key blocks on unrolled joint trace maps of tunnel surfaces Shi, G; Goodman, R E Rock Mechanics Contributions and Challenges: Proc 31st US Symposium, Golden, 18-20 June 1990 P219-228. Publ Rotterdam: A A Balkema. 1990 A practical intuitive method is presented for finding the face of 3-d key blocks on the cylindrical surface of a tunnel unrolled into a plane, reducing the problem to that of finding areas on a 2-d map. Analytical representation of curved tunnel boundaries, the tunnel coordinate system, unrolling of the curved surface and the joint traces, identification of the removable blocks, and applications and examples are described. Computation requires only a PC. 914284 Probabilistic prediction of keyblock occurrences Hoerger, S F; Young, D S Rock Mechanics Contributions and Challenges: Proc 31st US Symposium, Golden, 18-20 June 1990 P229-236. Publ Rotterdam: A A Balkema, 1990 Occurrence of unstable keyblocks in an excavation is related to size and shape of the excavation and the number and geometry of the discontinuities which it intersects. A probabilistic model has been developed which can be used to predict keyblock occurrences once discontinuities have been characterised. Assumptions made in simulation of joint geometry, identification of keyblocks, and keyblock statistics are discussed. Keyblock sensitivity to joint size and spacing is analysed. The information necessary for this modelling is easily available using inexpensive joint mapping.

914286 New finite element formulation for one-dimensional analysis of elastic-plastic materials Yu, H S; Houlsby, G T Comput Geotech V9, N4, 1990, P241-256 Difficulties arise when using conventional finite element displacement methods to analyse incompressible or nearly incompressible solids. This is due to kinematic constraints imposed on nodal velocities by the constant volume conditions. In elastic-plastic analysis, those effects are due to conflict between the plastic flow rule and the finite element discretisation. It is demonstrated that these constraints can be minimized using a new displacement interpolation. Cavity expansion problems are solved in elastic-plastic solids to demonstrate the advantages of the proposed analysis. 914287 Validation of an elastoplastic model for chalk Shao, J F; Henry, J P Comput Geotech vg, N4. 1990, P257-272 Chalk exhibits complex rheological properties. A new elastoplastic model for porous materials (Shao and Henry, 1990) has been developed, which includes 2 plastic deformation mechanisms and Lade's 3-dimensional failure criterion. Validation of the model for chalk is demonstrated using materials from two different sources. Ability to simulate homogeneous tests is first illustrated: proportional loading, reduced triaxial, oedometric, undrained triaxial. Validation for a typical boundary condition problem, the hollow cylinder test, is then shown. Influence of parameter perturbation on numerical simulation is also studied. 914288 Time step selection of 6-noded non-linear joint element in elasto-viscoplasticity analyses Sekiguchi, K; Rowe, R K; Lo, K Y Comput Geotech VIO, NI, 1990, P33-58 The 6-noded isoparametric joint element is required to simulate mechanical behaviour of discontinuities in geological materials. Such a joint is formulated based on elasto-viscoplasticity, so that plasticity of the solid and joint elements can be treated similarly. Stability of the elements is examined using a simple Euler time-marching scheme. Validity of the stability criteria is examined for a number of simple cases (sliding, opening) for which numerical and analytical results are available. Practical applications are described which confirm the effectiveness of the element and the time step selection.

914285 Site characterisation for tunnels in jointed rock masses Dhar, Y R: Choubey, V D; Pandalai, H S Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6-10 August 1990 VI, P593-599. Publ Rotterdam: A A Balkema, 1990

914289 Consistent lumped-parameter models for unbounded soil: physical representation Wolf, J P Earthq Engng Struct Dynam V20, NI, Jan 1991, P11-32

A typical rock mass is cut by several sets of discontinuities, to create a mosaic of systematically interlocked blocks. When excavations are made in the rock mass, kinematic characteristics of the blocks influence support loading and deformation. A method for stability analysis and site characterisation based on block analysis is presented. Rock condition is quantified in terms of rock load factors for a given excavation orientation. The optimum orientation within the rock mass can be determined.

A systematic procedure to develop a consistent lumped parameter model with real coefficients to represent the unbounded soil is developed. Each dynamic stiffness coefficient in the frequency domain is approximated as a ratio of two polynomials, which is then formulated as a partial fraction expansion. Each of these terms is represented as a discrete model, which forms a building block for the lumped parameter model. The model developed can be easily incorporated in general purpose structural dynamic programs working in the

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