Rocscience

- Support Estimation Using Ground Reaction Curves

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RocSupport is an easy to use software tool for estimating deformation in circular or near circular excavations in weak rock and visualization of the tunnel interaction with various support systems. Given the tunnel radius, in-situ stress conditions, rock parameters and support parameters, a ground reaction curve and a support reaction curve are calculated. The intersection of these curves determines a factor of safety for the support system.

RocSupport can be used as a tool for the preliminary design of tunnels and support systems. It can provide valuable information about various tunnel support options, before detailed analysis is carried out with a finite element program such as Phase2.

The program is applicable to tunnels excavated in weak rock under squeezing ground conditions. It is not applicable for excavations in hard rock, where failure is controlled by structural discontinuities or brittle failure.

The ground reaction curve is based on the analytical solution for a circular tunnel in an elasto-plastic rock mass under a hydrostatic stress field. Given the tunnel radius, in-situ stress conditions, rock parameters and support parameters, the ground reaction and support reaction curves are calculated. The intersection of these curves determines a factor of safety for the support system. Rock mass strength can be defined in terms of either Mohr-Coulomb or Hoek-Brown parameters.

RocSupport allows you to simulate the application of rockbolts, steelsets or shotcrete around the circumference of the tunnel. Within each support category, you may select from one of several predefined support types (e.g. 34 mm rockbolts, 203 mm flange I section rib steelsets, or 50 mm thick shotcrete). Different support types can be easily combined (e.g. rockbolts and shotcrete) and the properties of the combined support system will be used to determine the overall support reaction curve.

RocSupport has powerful yet easy-to-use probabilistic analysis features. All tunnel and rock parameters can be assigned statistical distributions. Using Monte Carlo or Latin Hypercube sampling, this results in a distribution of safety factors from which a probability of failure for the support system is calculated. Histograms, cumulative plots and scatter plots can be viewed. Results can be exported to Excel with a single mouse click.

Analysis Options

  • Duncan Fama solution for ground reaction curve (uses Mohr-Coulomb criterion)
  • Carranza-Torres solution (uses Hoek-Brown criterion)
  • plot long term ground reaction curve (specify strength reduction factor)
  • deterministic (safety factor) or probabilistic (probability of failure) analysis

Tunnel Parameters

  • tunnel radius
  • in-situ stress

Rock Parameters

  • elastic properties – Young’s modulus, Poisson’s ratio
  • strength properties – Mohr-Coulomb or Generalized Hoek-Brown
  • equivalent Mohr-Coulomb parameters can be calculated from Hoek-Brown parameters (GSI, mi, intact UCS, D)
  • built-in charts and tables to help estimate suitable values of GSI, mi, intact UCS and D
  • peak and residual strength parameters for Generalized Hoek- Brown criterion

Support

  • pre-defined support types for rockbolts, steel sets and shotcrete
  • combine multiple support types (e.g. rockbolts and shotcrete)
  • simple parametric analysis – add, change or remove support with a few mouse clicks
  • user-defined support
  • support installation – specify distance from face or tunnel convergence
  • interactive positioning of support
  • longitudinal deformation profile – built-in or user-defined function

Probabilistic Analysis

  • Monte Carlo or Latin Hypercube simulation
  • random or pseudo-random sampling
  • random variables – all tunnel and rock parameters can be defined as random variables
  • statistical distributions – normal, uniform, triangular, beta, exponential, lognormal, gamma
  • histogram, cumulative and scatter plots
  • user defined plot variables
  • best fit distribution, regression line
  • highlight support failure on histogram and scatter plots
  • one-click export of charts to Excel

Viewing Options

  • ground reaction view, support reaction
  • tunnel section view, plastic zone radius
  • customize display options
  • export image files
  • Info Viewer summary of analysis results

  • Tunnels
  • Rock

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