Finite Element Method (FEM) - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 252

10.5.3 Evaluation of Stress Resultants
In order to design a shotcrete membrane and a concrete lining of a tunnel or an under-
ground opening, the stress resultants must be determined. The required stress resultants
are usually the bending moments M, the normal thrusts N and the shear forces S in
circumferential direction. In three-dimensional analyses the stress resultants in the di-
rection of driving may also be of interest.
To determine the stress resultants in the shotcrete membrane and in the internal lining
from the calculated stresses with sufficient accuracy it needs to be discretized into three
rows of isoparametric elements with the same thickness and 12 nodes each. For accu-
racy reasons, the ratio of the elements' dimensions in the circumferential and radial
directions should not exceed values of 20 to 30.
Figure 10.25 Discretization of the internal lining, sealing and shotcrete membrane of a tunnel