# Seismic Performance of Modal Transfer Stations on Soft Clays
## 2 Definition of the Infrastructure Assets
### Soil Profile and Dynamic Properties  
The studied site is located in the so-called Zone IIIb in Mexico City, where high-plasticity clays are found (i.e., PI > 200). The dynamic properties and seismic response of the site have already been calibrated by several authors [23; 24] studying the seismic effects of past strong earthquakes. To continue from the previous research presented by [PERSON] and [PERSON] [22], it was deemed appropriate to use this geotechnical profile to study the seismic interaction effects discussed above (Figure 3). Figure 4 summarizes the soil stratigraphy of the site studied, some index properties, and results of the Cone Penetration Test (CPT). Figure 4 also shows the shear wave velocity distribution, which was  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Interaction** \\ **Longitude** \\ **(Diameters)** \\ \end{tabular} } & \multicolumn{3}{c}{**Position of the Tunnel for**} & \multicolumn{3}{c}{**Position of the Tunnel for the**} & \multicolumn{3}{c}{**Position of the Tunnel for the**} \\  & \multicolumn{3}{c}{**the Tunnel-Building-Bridge Scenarios**} & \multicolumn{3}{c}{**T Tunnel-Bridge Scenarios**} & \multicolumn{3}{c}{**T Tunnel-Building Scenarios**} & \multicolumn{3}{c}{**Building-Bridge Without Tunnel**} \\ \cline{2-10}  & **A** & **B** & **C** & **A** & **B** & **C** & **A** & **B** & **C** \\ \hline
1 & TBU\_A1 & TBU\_B1 & TBU\_C1 & TU\_A1 & TU\_B1 & TU\_C1 & TB\_A1 & TB\_B1 & TB\_C1 & BU\_1 \\ \hline
2 & TBU\_A2 & TBU\_B2 & TBU\_C2 & TU\_A2 & TU\_B2 & TU\_C2 & TB\_A2 & TB\_B2 & TB\_C2 & BU\_2 \\ \hline
3 & TBU\_A3 & TBU\_B3 & TBU\_C3 & TU\_A3 & TU\_B3 & TU\_C3 & TB\_A3 & TB\_B3 & TB\_C3 & BU\_3 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Tunnel–building–urban bridge cases considered.  
Figure 3: Schematic representation of the idealized problem for the tunnel–building–urban bridge interaction.  
obtained in previous research [23] with various techniques including suspension logging and down-hole.  
The key factors that contributed to the large seismic wave amplification observed in past earthquakes in the MCB are the very low shear stiffness (Figure 4), and the quasi-linear elastic range and very low damping exhibited by the soft clay for shear strain as high as 0.1%. These last two characteristics have been associated with very high plasticity (PI > 200), in accordance with the relation found by [PERSON] [27]. To represent this behavior, [PERSON]'s model [28] was used to estimate the normalized modulus degradation and damping curves for clays (Figure 5). Through a series of resonant column and cyclic triaxial tests, the authors related the model parameters to the plasticity index (PI) of the high-plasticity clays. For non-plastic materials such as silty sands, the curves proposed by [PERSON] and [PERSON] [29] were used to characterize their behavior during seismic loading. Figure 5 depicts the normalized modulus degradation and damping curves used in the numerical analyses. It should be mentioned that similar curves have been used in 1D wave propagation analyses to reproduce the measured response during past earthquakes in the MCB, and good agreement was observed when comparing predictions with measured responses [23].  
Figure 4: Soil stratigraphy of the studied site, including index properties and shear wave velocity distribution [23; 24; 25; 26].  
Figure 5: (**a**) Normalized shear stiffness degradation, G/Gmax, and (**b**) damping \(\lambda\) curves [28; 29].