ROCK, MINING AND TUNNELLING

Discover why PLAXIS is essential for rock, mining and tunnelling

Due to the broad software capabilities, PLAXIS is essential for rock, mining and tunnelling

With PLAXIS you are able to investigate the behaviour of rock masses as a result of tunnelling processes and mining activities. The material models for a rock mass can vary depending on the rock mass characteristics.

If the rock mass exhibits non-significant anisotropy in strength and deformability, the rock mass can be considered as isotropic in, for example, tunnel design. This assumption is usually acceptable as long as there is no preferred orientation of joints within the rock mass that controls the rock mass behaviour. If the rock mass contains a single dominant joint direction, the behaviour of the rock mass is anisotropic.

Tunnelling or mining may take place in inherently anisotropic rocks configured at least by one direction of stratification planes. Aside from the stratification planes, the geometric layout of the joints and other types of discontinuities in the rock mass are significant contributors to the complex behaviour of the rock mass. In such cases, the behaviour of the rock mass can be studied by using either anisotropic continuum models or discontinuum models. In order to support the tunnel against collapse as a result of excavation, appropriate stability measures are needed. Support alternatives include shotcrete or concrete rings, anchored bolts and cables, blocked steel sets or a combination of support systems.


Applications

PLAXIS for rocks

In terms of material models for rocks and rock masses, both the linear Mohr-Coulomb and the non-linear Hoek-Brown models are commonly used. These models allow users to assess the bearing capacity of isotropic elasto-plastic rocks. To simulate the behaviour of stratified and jointed rock layers, two constitutive models are available, namely the Jointed Rock model and the Isotropic Jointed Rock model with Mohr-Coulomb failure criterion.

Whereas the former is a cross-anisotropic, elasto-plastic model, the latter is the combination of the Jointed Rock model with isotropic elastic behaviour and the Mohr-Coulomb model. In addition to the already stated constitutive models for rock masses, the Swelling Rock model is a user-defined model that can be used to simulate the time-dependent anisotropic swelling of rocks.

PLAXIS for mining engineering

The design of stable stope panels between pillars is of vital importance for safety of underground workers and production in shallow mining operations. PLAXIS accurately estimates displacements and can calculate safety factors to ensure a safe working environment. CAD import in PLAXIS allows users to import mine surface data or cross-sections to quickly generate appropriate geometry in PLAXIS 2D or 3D in order to perform slope stability analysis for intended designs. With the groundwater flow module, users can perform coupled flow-deformation analysis to investigate the safety, pore pressures and time dependent seepage behaviour in open pit mines as well as tailing dams. To perform statistical analysis the command line or remote scripting facility can be used, allowing users to quickly run variations of the same model.

PLAXIS for tunnel engineering

PLAXIS 2D and 3D feature a tunnel designer to quickly model sprayed concrete lining or bored tunnels with shell elements or volume elements. This feature includes additional options to model rock bolts, grout pressures, jack forces, tunnel face pressures and/or volume loss.
Principally, tunnel excavation is a three-dimensional problem. For tunnelling problems that comply rotational symmetry, the three dimensional tunnel advance and pre-relaxation ahead of the tunnel face can be considered in PLAXIS 2D by means of the convergence-confinement method. Otherwise, PLAXIS 3D is necessary for a realistic design of support and appropriate location of support installation. Regarding support, a shotcrete model that takes into account the time dependent strength and stiffness of concrete, shrinkage as well as creep strains is now available. Furthermore, it is possible to model rock bolts in order to stabilize the tunnel excavation. PLAXIS is capable of accurately predicting the response of soil and rock masses as a result of shallow and deep tunnelling processes.