GNGTS 2021 - Atti del 39° Convegno Nazionale

415 GNGTS 2021 S essione 3.2 JOINT OF SEISMIC REFRACTION SURVEY WITH GEOTECHNICAL IN SITU AND LABORATORY TESTS FOR BUILDING SETTLEMENTS D. Barbero 1 , M. Naldi 2 , A. Maroni 3 , S. Payrot 4 1 Geological, Geophysical and Geotechnical Office of Dr. Diego Barbero 2 Techgea s.r.l. 3 Geology Student and collaborator of Geological, Geophysical and Geotechnical Office of Dr. Diego Barbero 4 Geologist, Freelance professional 1. Introduction An integrated approach with seismic refraction survey first and geotechnical in situ and laboratory tests then, for building consolidation due to settlements is here reported. The aim of the study is: i) to highlight the importance of geophysical survey to detect the presence of unconsolidated lenses of soil beneath the building foundation; ii) to verify the presence of lenses of soil strata with poor bearing capacity with geotechnical in situ tests (SCPT test); iii) to collect samples in exploratory pits of these unconsolidated soils for laboratory tests (soils classification and hedometric tests) in support of engineering design to consolidate the building foundation. The case study here reported is located in a secondary valley of the fluvial plain of San Damiano d’Asti town (central Piedmont Region, Asti Province), where a think colluvial cover and reworked deposits with loose to medium texture develop above blue-grey marl clays of the Lugagnano Clay substrata (Middle-Lower Pliocene) occur. The localized presence unconsolidated soils with poor geotechnical properties give rise to differential settlements on one side of the building causing cracks and fractures on the upper floor with predominant oblique pattern on the walls. 2. Geological setting The study area is located in the western side of the Asti Reliefs (elevation 130-320 m a.s.l.) in the central Piedmont hilly region (Asti Province). The sedimentary succession is defined, in the lower bands of the hilly reliefs, by deep marine clay deposits (Argille di Lugagnano) and littoral sandy deposits (Sabbie di Asti) referred to the Pliocene (Zanclean). These sediments are usually covered by the “villafranchian succession” comprising deltaic deposits (Lower Complex) and fluvial deposits (Upper Complex), referred to the Piacenzian and Calabrian respectively, separated by an unconformity (Cascina Viarengo Surface) (Forno et al., 2015; Gattiglio et al., 2015). Above these sediments a widespread silty and subordinately gravelly fluvial cover of middle and upper Pleistocene occurs. The whole sedimentary sequence is deformed by the Asti Syncline consisting of a wide E-W regional scale fold developed in the central hilly area (Poirino Plateau, Asti Reliefs and Alessandria Plateau). In details, the investigated area is located in the lower band of a hilly ridge along a secondary valley of the fluvial plain of San Damiano d’Asti town, where a think alluvial with colluvial cover with loose to medium texture develop above the marine succession formed by gray-blue clay massive deposits rich in microfossils (Lugagnano Clay, Zanclean Stage of the Pliocene Serie). 3. Methods The geophysical investigations with refractive seismic survey (A in Fig. 1) were performed with the aim to define the local lithostratigraphic context up to the depth of about 10-12 meters from