Page 235 - Numerical Analysis and Modelling in Geomechanics

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

Figure 7.9 Idealized ground condition of a subway tunnel in Pusan, Korea.
elastic modulus and strength parameters can be empirically estimated from
correlations with standard penetration test (SPT) N-values. Estimation of the K o
value is even more difficult. Therefore, some typical values using Figure 7.9 are
used as the prior information in this case study. The coefficient of variation of
the SPT N-value is about 0.26 (Harr 1987). The coefficient of variation of E and
K is selected as 0.3, including uncertainty of the SPT N-value.
0
Model identification

In order to assess the best model, three models are introduced. Model I-1 is
adopted directly from site investigation (see Figure 7.9). Since the elastic
modulus of the residual soil selected in model I–1 seems too small, model I–2
adopts a larger elastic modulus for the residual soil layer. The estimated elastic
2
modulus of the granite soil for model I–2 was about 10,000 ton/m , which was
obtained from triaxial tests conducted by Kim (1994). In model II, residual soils
and weathered rocks are considered as a single ‘weathered zone’.