VS Profile Inversion in Heterogeneous Granular Soil Deposits: Implications for Structural Design in a Study Site (Italy)

Many urbanised areas of the Apennines, in Italy, have complex soil stratifications. A typical example is the outskirts of the city of L’Aquila, which is founded on highly heterogeneous soil layers and was severely affected by a strong earthquake in 2009. In such conditions, shear wave velocity profiles (VS) obtained from in situ tests such as the Seismic Dilatometer Marchetti Test (SDMT) provide reliable analyses of the local seismic response. This article presents the mono-dimensional (1D) and two-dimensional (2D) seismic response analyses conducted to characterise the soil foundation of the hospital complex and adjacent university buildings in L’Aquila before their seismic retrofitting. This study emphasises the importance of accurate soil characterisation prior to repair interventions, especially in deposits where there are VS inversions and in the presence of geometrically irregular and large structures. Under these conditions, estimating the motion amplitudes of the deposit’s higher modes beyond the fundamental level is essential in accurately characterising the seismic response, especially for buildings where higher structural modes play a significant role. The results show that approximating the VS profile with simplified procedures, as proposed by the Italian Building Code of 2018 (equivalent VS, similar to average), leads to incorrect estimates of seismic action.