Manuel Rocha Medal Recipient Simulating the Time-dependent Behaviour of Excavations in Hard Rock |
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| Authors: | D F Malan |
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| Institution: | (1) CSIR Mining Technology, Johannesburg, South Africa, ZA |
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| Abstract: | Summary
Although hard rock is not usually associated with large creep deformation, data collected from the tunnels and stopes of the
deep South African gold mines illustrates significant time-dependent behaviour. Apart from application in mining, a better
understanding of the time-dependent behaviour of crystalline rock is required to analyse the long term stability of nuclear
waste repositories and to design better support for deep civil engineering tunnels in these rock types. To illustrate the
subtle problems associated with using viscoelastic theory to simulate the time-dependent behaviour of hard rock, a viscoelastic
convergence solution for the incremental enlargement of a tabular excavation is discussed. Data on the time-dependent deformation
of a tunnel developed in hard rock further illustrates the limitations of the theory, as it is unable to simulate the fracture
zone around these excavations. To simulate the rheology of the fracture zone, a continuum viscoplastic approach was developed
and implemented in a finite difference code. This proved more successful in modelling the time-dependent closure of stopes
and squeezing conditions in hard rock tunnels. A continuum approach, however, has limitations in areas where the squeezing
behaviour is dominated by the time-dependent behaviour of prominent discontinuities such as bedding planes. To overcome this
problem, a viscoplastic displacement discontinuity technique was developed. This, combined with a tessellation approach, leads
to more realistic modelling of the time-dependent behaviour of the fracture zone around excavations.
Received January 15, 2002; accepted June 3, 2002 Published online September 2, 2002 |
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