GNGTS 2018 - 37° Convegno Nazionale

414 GNGTS 2018 S essione 2.2 marine continental shelf deposit, the boundary between the clayey unit (i.e. MVA Formation of CARG sheet 374 Rome) and the underlying sandy unit of (AA.VV ., 2008) (Tab. 1). The adopted depth of the seismic bedrock (H), equal to 550 m bgl, agreed with the estimation of H for the Mef site by applying the formula: f 0 = Vs / 4H, imposing the resonance frequency (f 0 ) equal to 0.30- 0.35 Hz and an average Vs obtained from the available measures (Pagliaroli et al. , 2011). For the soil behaviour the well-known equivalent linear model was adopted. Thus, the shear modulus G and the damping factor D depend on the shear strain γ induced by the earthquake motion and are iteratively adjusted until they match a fraction of the maximum strain caused in each layer by the passing shear waves. The adopted G/G 0 vs γ and D vs γ curves of the soil units were obtained from resonant column tests specifically performed (Fig. 2). Only for the sandy gravel layers we adopted curves from literature (Rollins et al. , 1998) (Tab. 1). Tab. 1 - The subsoil model and seismostratigraphy of the MEF site. CI refers to the curve G/G0 vs γ and D vs γ obtained from the borehole S1 soil samples and reported in Fig. 2. Geological unit Lithology Depth (m) Vs Density Dynamic (m/s) (KN/m3) Behaviour (see Fig.2) Anthropic deposit Sand and clayey silt with 0-6.8 100 17 CI 2 (Holocene) (“h” of brick fragments CARG sheet 374 Rome) Pyroclastics (cinerite Silty-sandy pyroclastics 6.8-9.2 160 16 CI 2 and tuff) of Sabatini Volcanic District (Middle cinerite 9.2-11.4 190 16 CI 2 Pleistocene) (“LTT”, “SKF” of Sandy-silty pyroclastics 11.4-17.4 200 16 CI 2 CARG sheet 374 Rome) Silty clay 17.4-20.3 200 18 CI 3 Silt and sand with 20.3-23 240 19 CI 4 travertine concretions Silt and sand with 23-26.4 310 19 CI 4 travertine concretions Sandy-clayey silt with 26.4-30 340 19.5 CI 4 travertine concretions Sandy-clayey silt with 30-31.7 360 19.5 CI 4 travertine concretions Clayey silt 31.7-39.7 390 19.5 CI 7 Silty sand 39.7-43.7 350 19.5 CI 7 Sandy gravel 43.7-46 360 22 Rollins et al. (1998) mean Sandy gravel 46-51 400 22 Rollins et al. (1998) mean Clayey silt 51-60 (from 360 20 CR 15 (MVA of CARG sheet 374 borehole S1) Rome encountered in the / 550 m (from Circo Massimo borehole) Circo Massimo borehole, 0 and 1D numerical modelling) Sand (seismic bedrock) - 800 23.5 damping (encountered in the = 1% Circo Massimo borehole) Alluvial deposit of Paleo Tiber River (Middle Pleistocene) (CIL of CARG sheet 374 Rome) Pliocene pelite and sand of the Tyrrhenian Sea continental shelf