Page 233 - Numerical Analysis and Modelling in Geomechanics

214 I.-M.LEE AND D.-H.KIM

Figure 7.7 Sensitivity of geotechnical parameters on sidewall settlement (a) Elastic
modulus; (b) Initial horizontal stress coefficient; (c) Cohesion; (d) Internal friction angle.
Ground condition
The ground at the site consists of a fill layer (cohesionless soil), residual soil and
highly weathered rock from the ground surface, as shown in Figure 7.9. Below
the overburden, it is composed of Bulkuksa granite. The tunnel was constructed
through the highly weathered rock, which is classified as ‘poor rock’ with a rock
mass rating (RMR) description. A typical cross-section of the tunnel is shown in
Figure 7.10.

Measurement

The crown subsidence and sidewall convergence measured by tape
extensometers are used as the observed data. The location of measurement points
is shown in Figure 7.11. The characteristic lines are obtained from the
extrapolation of the measured data. Figure 7.12 and Table 7.4 show obtained
characteristic lines and absolute displacements. In this case, the ratio of
deformation which occurred ahead of the tunnel face was 45 percent of the