In RocSupport, the characteristics of a support system are represented by two parameters:
Maximum (radial) support pressure
Maximum (average) strain.
There are two additional simplifying assumptions:
The load-deformation curve of the support system is elastic-perfectly plastic.
The support is applied uniformly around the tunnel opening.
The support system acts like a system of springs – support pressure increases with increasing deformation until the capacity of the system is exceeded. It is assumed that after yielding, support starts to show perfectly plastic behavior. Support pressure remains constant with increasing deformation, as illustrated in Figure 1. In reality, support systems might not demonstrate this behavior. Figure 2 shows actual load-deformation tests of several rockbolt types.
Figure 1. Elasto-plastic behavior of support
Figure 2. Results of rockbolts load-deformation tests. From Hoek et al. (1995).
For all predefined support types, RocSupport makes the assumption that support is installed uniformly around the tunnel opening. This means that rockbolts must be installed in the roof, sidewalls and floor of the tunnel, and that steel sets and shotcrete linings are completely circular. Typical support installations are not uniform, which leads to drastic reduction in the overall capacity and stiffness of support. In this case, it is recommended that some reserve capacity is left, and the factor of safety is increased.
RocSupport allows the user to combine all or selected types of support. When combining supports, it is assumed that the maximum support pressure of the resultant system is the sum of maximum pressures of all individual systems, and the maximum strain is an average of their maximum strains as shown in the formulae below:
