From Lithological Modelling to Groundwater Modelling: A Case Study in the Tiber River Alluvial Valley

This study presents the results of a research project financed by the Lazio Regional Government. The research focused on defining an integrated model of recent alluvial deposits in the Tiber River. To achieve this objective, geological boreholes were made to monitor the aquifer and in situ and laboratory tests were carried out. The data obtained were used to detail stratigraphic aspects and improve the comprehension of water circulation beneath the recent alluvial deposits of the Tiber River in the urban area of Rome, between the Ponte Milvio bridge and the Tiber Island. The stratigraphic intervals recognised in the boreholes were parameterised based on their litho-technical characteristics. The new data acquired, and integrated with existing data in the database of Institute of Environmental Geology and Geoengineering of the Italian National Research Council, made it possible to produce a three-dimensional model of the lithologies in the study area. The model of the subsoil, simplified for applied reasons, was described in hydrostratigraphic terms: three different lithotypes were subjected to piezometric levels monitoring. Finally, the research generated a numerical hydrological model in a steady state. In general, this study demonstrates how a numerical hydrogeological model calibrated by piezometric monitoring data can support the construction of a geological model, discarding or confirming certain hypotheses and suggesting other means of reconstructing sedimentary bodies

From Lithological Modelling to Groundwater Modelling: A Case Study in the Tiber River Alluvial Valley

This study presents the results of a research project financed by the Lazio Regional Government. The research focused on defining an integrated model of recent alluvial deposits in the Tiber River. To achieve this objective, geological boreholes were made to monitor the aquifer and in situ and laboratory tests were carried out. The data obtained were used to detail stratigraphic aspects and improve the comprehension of water circulation beneath the recent alluvial deposits of the Tiber River in the urban area of Rome, between the Ponte Milvio bridge and the Tiber Island. The stratigraphic intervals recognised in the boreholes were parameterised based on their litho-technical characteristics. The new data acquired, and integrated with existing data in the database of Institute of Environmental Geology and Geoengineering of the Italian National Research Council, made it possible to produce a three-dimensional model of the lithologies in the study area. The model of the subsoil, simplified for applied reasons, was described in hydrostratigraphic terms: three different lithotypes were subjected to piezometric levels monitoring. Finally, the research generated a numerical hydrological model in a steady state. In general, this study demonstrates how a numerical hydrogeological model calibrated by piezometric monitoring data can support the construction of a geological model, discarding or confirming certain hypotheses and suggesting other means of reconstructing sedimentary bodies

A 3D Geological Model as a Base for the Development of a Conceptual Groundwater Scheme in the Area of the Colosseum (Rome, Italy)

Geological models are very useful tools for developing conceptual schemes owing to their capacity to optimize the management of stratigraphic information. This is particularly true in areas where archaeological heritage is exposed to hydrogeological hazards; 3D models can constitute the first step toward the construction of numerical models created to understand processes and plan mitigation actions to improve visitor safety and preserve archaeological heritage. This paper illustrates the results of a 3D hydrostratigraphic model of the site of the Colosseum in the Central Archaeological Area of Rome. In recent years, this area has experienced numerous floods caused by intense meteorological events. A new borehole survey provided the opportunity to update previous maps and cross sections and build a local scale 3D model. The resulting conceptual model was used to identify primary gaps in existing knowledge about the groundwater system and to optimize the planning of a piezometer monitoring network. Further studies can then focus on the development of groundwater numerical models to verify hypotheses regarding inflow-outflow dynamics and facilitate the optimization of water management

The Upper Pleistocene-Holocene fluvial deposits of the Tiber River in Rome (Italy): Lithofacies, geometries, stacking pattern and chronology

[No abstract available

Local seismic hazard assessment in explosive volcanic settings by 1d and 2d numerical analyses

In this study, we face the problem of local seismic response in explosive volcanic setting by using an integrated geological-geophysical-geotechnical approach in the test area of Stracciacappa maar (Sabatini Volcanic District, central Italy). Our aim is to understand if the horizontal and vertical chaotic heterogeneity typical of the volcanic deposits influence site response. The Stracciacappa maar is an active eruptive centre characterised by a crater of about 1 km in diameter and a crater floor of about 30-40 m below the rim (De Rita et al. 1983; Sottili et al. 2012). The ring is mainly composed by the pyroclastic succession belonging to the last phreatomagmatic activity. This pyroclastic succession generally bends outward the rim with low angle dip (10-20°). It consists of at least 25 metres thick alternation of decimetre- to centimetre-thick layers of fine-medium ash and small lapilli. The crater depression is filled by epiclastic debris deposits and by recent and present-day lacustrine muds. The epiclastic debris deposits, of alluvial and delta origin, consist of alternation of cm-thick reworked fine-grained and coarse-grained volcaniclastic material, dipping with low-angle (1s) motions, compared to tectonic events of equivalent magnitude (Jousset and Douglas 2007); the unscaled recording at Bronte Station (BNT in ITACA database, http://itaca.mi.ingv.it) of the ML=4.4 October 27, 2002 event was employed; 2) a high magnitude far-field “tectonic” event (tectonic scenario), whose reference spectrum was built with Ground Motion Prediction Equations (Ambraseys et al., 2005) assuming M=6.5 and distance of 70 km. These conditions are compatible with seismogenic sources located in central Apennines of Italy. Three unscaled recordings of events characterised by magnitude and distance in the range of 6-7 and 60-90 km, respectively, were extracted from ITACA database (http://itaca.mi.ingv.it), matching on average the reference spectrum Two subsoil models have been considered: a detailed model (based on distribution of the lithotypes unravelled by the geological survey) and a simplified one (obtained by grouping interfingering lithotypes resting below the lacustrine silty clays). The result show that the two models have similar response in all range of the interesting period (0.1-1.0s); the damping properties of soft clays and sands deposits in the upper meters reduce the difference in the seismic response at the surface of both models. The results suggest the possibility to simplify the heterogeneous distribution of deposits in this volcanic context for assessment of seismic response purposes. Finally, we carried out both linear and equivalent linear analyses in one-dimensional and bi-dimensional conditions, in order to investigate the bidimensional effects and the role of nonlinearity on the seismic response,. In linear case the behaviour of soils was assumed linear visco-elastic with small strain damping ratio values D0; amplification factors higher than 10 were reached at 2 Hz at soft clays surface in correspondence of the centre and western edge of the maar in bi-dimensional analysis, whereas the 2D/1D ratios were in the order of 2-3 around 2 Hz with maximum values at the maar edges. In the nonlinear analyses, the maximum amplifications dropped below 10 and the 2D effects (i.e., 2D/1D ratios) were generally lower than 2 in the whole range of frequency

LOCAL SEISMIC HAZARD ASSESSMENT IN EXPLOSIVE VOLCANIC SETTINGS BY 1D AND 2D NUMERICAL ANALYSES

In this study, we face the problem of local seismic response in explosive volcanic setting by using an integrated geological-geophysical-geotechnical approach in the test area of Stracciacappa maar (Sabatini Volcanic District, central Italy). Our aim is to understand if the horizontal and vertical chaotic heterogeneity typical of the volcanic deposits influence site response. The Stracciacappa maar is an active eruptive centre characterised by a crater of about 1 km in diameter and a crater floor of about 30-40 m below the rim (De Rita et al. 1983; Sottili et al. 2012). The ring is mainly composed by the pyroclastic succession belonging to the last phreatomagmatic activity. This pyroclastic succession generally bends outward the rim with low angle dip (10-20°). It consists of at least 25 metres thick alternation of decimetre- to centimetre-thick layers of fine-medium ash and small lapilli. The crater depression is filled by epiclastic debris deposits and by recent and present-day lacustrine muds. The epiclastic debris deposits, of alluvial and delta origin, consist of alternation of cm-thick reworked fine-grained and coarse-grained volcaniclastic material, dipping with low-angle (1s) motions, compared to tectonic events of equivalent magnitude (Jousset and Douglas 2007); the unscaled recording at Bronte Station (BNT in ITACA database, http://itaca.mi.ingv.it) of the ML=4.4 October 27, 2002 event was employed; 2) a high magnitude far-field “tectonic” event (tectonic scenario), whose reference spectrum was built with Ground Motion Prediction Equations (Ambraseys et al., 2005) assuming M=6.5 and distance of 70 km. These conditions are compatible with seismogenic sources located in central Apennines of Italy. Three unscaled recordings of events characterised by magnitude and distance in the range of 6-7 and 60-90 km, respectively, were extracted from ITACA database (http://itaca.mi.ingv.it), matching on average the reference spectrum Two subsoil models have been considered: a detailed model (based on distribution of the lithotypes unravelled by the geological survey) and a simplified one (obtained by grouping interfingering lithotypes resting below the lacustrine silty clays). The result show that the two models have similar response in all range of the interesting period (0.1-1.0s); the damping properties of soft clays and sands deposits in the upper meters reduce the difference in the seismic response at the surface of both models. The results suggest the possibility to simplify the heterogeneous distribution of deposits in this volcanic context for assessment of seismic response purposes. Finally, we carried out both linear and equivalent linear analyses in one-dimensional and bi-dimensional conditions, in order to investigate the bidimensional effects and the role of nonlinearity on the seismic response,. In linear case the behaviour of soils was assumed linear visco-elastic with small strain damping ratio values D0; amplification factors higher than 10 were reached at 2 Hz at soft clays surface in correspondence of the centre and western edge of the maar in bi-dimensional analysis, whereas the 2D/1D ratios were in the order of 2-3 around 2 Hz with maximum values at the maar edges. In the nonlinear analyses, the maximum amplifications dropped below 10 and the 2D effects (i.e., 2D/1D ratios) were generally lower than 2 in the whole range of frequency

Integrated subsoil model for seismic microzonation in the Central Archaeological Area of Rome

An integrated subsoil model for seismic microzonation in the Central Archaeological Area of Rome is presented in this study. This model was created in the framework of a research project aimed at evaluating the geohazard level affecting Palatine hill, Roman Forum and Coliseum. A multidisciplinary survey was carried out mainly in 2010 including continuous-coring boreholes, in situ and laboratory geotechnical tests, MASW, Cross and Down-Hole tests, ambient noise measurements, Electrical Resistivity Tomographies, Ground Penetrating Radar surveys. The surveying methodologies adopted in the surveying campaign are also presented here. A three step procedure adopted for creating the integrated subsoil model of Palatine hill and surrounding areas is described in detail. This procedure first involves the construction of a geological model starting mainly from boreholes' data interpretation and correlation. Geological formations are here interpreted in terms of lithofacies following their sedimentological features and then characteri-zed by means of their main physical properties (i.e. grain size distribution, void ratio, unit weight, plasticity index) to define a scheme of lithotypes. The lithotypes represent the "framework" to be characteri-zed in terms of dynamical properties to produce the final inputs for 1D and 2D numerical modeling of ground motion amplification effects aimed at the construction of seismic microzonation maps