Layout 6 ANNALS OF GEOPHYSICS, 61,2, SE221, 2018; doi: 10.4401/ag-7706 1 “STATIC AND DYNAMIC PROPERTIES OF SOILS IN CATANIA (ITALY)„ Francesco Castelli1, Antonio Cavallaro2, Antonio Ferraro3, Salvatore Grasso4,*, Valentina Lentini5, Maria Rossella Massimino6 (1) Faculty of Engineering and Architecture, University of Enna “Kore”, Enna (Italy) (2) CNR - IBAM (Italian National Research Council - Institute for Archaeological and Monumental Heritage), Catania (Italy) (3) University of Catania - Department of Civil Engineering and Architecture (DICAr), Catania (Italy) (4) University of Catania - Department of Civil Engineering and Architecture (DICAr), Catania (Italy) (5) Faculty of Engineering and Architecture, University of Enna, Enna (Italy) (6) University of Catania - Department of Civil Engineering and Architecture (DICAr), Catania (Italy) 1. INTRODUCTION Site characterization is a crucial point in the evalu- ation of site response analysis of soils [Castelli et al., 2016d; Castelli and Maugeri, 2008; Castelli et al., 2008a, 2008b; Castelli and Lentini, 2013; Castelli and Lentini, 2016; Castelli et al., 2017; Cavallaro, 2006b, 2008a, 2008b]. In order to study the dynamic characteristics of soils in three Catania test sites, laboratory and in situ investigations have been carried out to obtain soil pro- files with special attention being paid to the variation of the shear modulus G and damping ratio D with depth. Seismic Dilatometer Marchetti Tests (SDMT) have been also carried out in the area of the “National Institute of Geophysics and Volcanology” building (INGV) and in the “Madre Teresa di Calcutta” building school (CD MTC), with the aim of an accurate geotechnical charac- terisation, including the evaluation of the shear wave velocity Vs profile, as well as the profile of the hori- zontal stress index Kd. Shear wave velocity has been measured by different tests. The soil profiles in terms of the shear modulus G0 and in terms of the shear wave velocity Vs have been evaluated and compared by different in situ tests. The redundancy of measurements is very useful, for in- stance, for site response and liquefaction analyses of the city of Catania [Castelli et al., 2016c], which can be based either on Vs values or Kd values. Boreholes were driven and undisturbed samples were retrieved for lab- oratory tests. Because of their relevance on the estima- tion of local ground shaking and site effects, data from in-hole geophysical surveys (Down-Hole and Seismic Article history Receveid June 8, 2017; accepted February 2, 2018. Subject classification: Dynamic soil characterisation; In-situ tests; Laboratory tests. ABSTRACT The analysis of the historical reports and previous research projects allowed us to describe high-level seismic risk scenarios for the city of Catania, located on the eastern coast of Sicily (Italy). The geotechnical zonation of the subsoil of the city of Catania suggests a high seismic hazard added to a soil amplification of the ground motion. To this aim field and laboratory tests allowed the definition of a geotechnical characterisation in the city of Catania. For the site characterisation of soils deep site investigations have been undertaken. Borings and dynamic in situ tests have been performed in some selected test sites with the aim to evaluate the soil profiles of shear wave velocity and to retrieve undisturbed samples for laboratory tests. The testing programme consisted of standard classification tests, Oe- dometer tests, Direct shear tests, Resonant Column and Torsional shear tests. Two equations to draw the complete shear modulus degra- dation with strain level and the inverse variation of damping ratio with normalized shear modulus respectively have been also proposed. Shear wave velocity profiles experimentally obtained were compared with both in situ and laboratory tests. Dilatometer Marchetti Test) have been examined with special attention, particularly for S wave velocity mea- surements. It must be noted that the shear wave veloc- ity Vs was evaluated on the basis of both empirical correlations with in situ or laboratory tests and a few direct measurements. Moreover, the following investi- gations in the laboratory were carried out on undis- turbed samples: direct shear tests, triaxial tests, Cyclic Loading Torsional Shear Tests (CLTST) and Resonant Column Tests (RCT). This paper tries to summarize the geotechnical information in a comprehensive way in order to provide a case record of data for site charac- terization and for the mitigation of seismic risk within structural improvement of buildings [Abate et al., 2016; Abate et al., 2017a; 2017b; Grassi and Massimino, 2009]. Similar geotechnical studies were also successful performed for significant historical test sites (Castelli et al. 2016a, 2016d, 2016e; 2016f; Cavallaro et al. 1999b, 2003, 2004a, 2004b, 2013a). 2. GEOLOGY AND SEISMICITY OF THE AREA The study was performed in eastern Sicily, which is characterized by the presence of Mount Etna Volcano. This rests on top of two major structural units [Lentini et al., 1982; Pappalardo et al., 2016]: the Foreland Iblean plateau and the Apennine-Maghrebian Chain. The Foreland Iblean plateau is the northern edge of the African plate and is characterized by a succession of Meso-Cenozoic, mainly carbonate, repeatedly inter- spersed with basic volcanic rock. The city of Catania is located on the east coast of Sicily, which is one of the most seismically active areas in Italy. Various disastrous earthquakes struck the east coast of Sicily, with a (MSK) intensity from IX to XI in the last 900 years [Postpischl, 1985; Azzaro et al., 1999; Locati et al., 2016]. In partic- ular, the seismic events of February 20, 1169 and Jan- uary 11, 1693 destroyed almost completely the city of Catania with intensity X-XI MSK and estimated magni- tude between 7.0 and 7.4 [Boschi et al., 1995; Gizzi, 2006]. The earthquake of January 11, 1693 is considered one of the biggest earthquakes occurred in Italy. It is sup- posed that more than 1500 aftershocks occurred along a period of more than two years after the main shock. This earthquake, with an intensity of XI degree on the MSK scale in many centers, struck a vast territory of south- eastern Sicily and caused the partial, and in many cases total, destruction of 57 cities and 40,000 casualties. From 1000 A.D., just four other earthquakes in the area exceeded an estimated local Richter magnitude 5.8: the July 7, 1125, the December 10, 1542, the January 9, 1693 and the February 20, 1818 events [Barbano et al., 2010], see Figure 1. Some of these events probably pro- duced historical tsunamis (1693 and 1908 events) along the Ionian coast of Sicily [Barbano et al., 2010]. The other seismic events, which damaged the city of Catania, such as the March 1536, the April 1698, the December 1716 and the December 1990 earthquakes, generally produced minor effects, with collapses in de- graded buildings. The recent earthquake on December 13, 1990 namely “the St. Lucia earthquake” struck East- ern Sicily with a local Richter Magnitude ML = 5.6 and caused 19 victims and severe damages to buildings and infrastructures [De Rubeis et al., 1991]. Seismicity is mainly distributed in two sectors: along the coast, where the events have also reached a surface Richter Magnitude MS ≥ 7.0, and inland with earthquakes with MS ≤ 5.5 [Panzera et al., 2011a]. Graph 1 shows the seismic history of the city of Catania in the Italian Macroseismic Database DBMI15 [Locati et al., 2016] during the time window of years 1000-2014, starting from the fixed macroseismic inten- sity of VI MCS. Intensity data of DBMI15 derive from studies by authors from various institutions, both in Italy and bordering countries. For these reasons several examples of site response analyses by 1-D modeling and microtremor measure- ments have been performed in the urban area of Cata- nia [Lombardo et al., 2001; Panzera et al., 2011b, 2015; Sgarlato et al., 2011]. 3. SITE CHARACTERIZATION PROGRAMME AND BASIC GEOTECHNICAL SOIL PROPERTIES The static and dynamic geotechnical study of soils in the city of Catania was performed in three investiga- tion tests sites: the “National Institute of Geophysics CASTELLI ET AL. 2 GRAPH 1. Seismic history of the city of Catania in the Ital- ian Macroseismic Database DBMI15 during the time window 1000-2014. and Volcanology” (INGV) in the central area of the city, the “Nazario Sauro building School” (IC NS) in the west- ern area of the city and the “Madre Teresa di Calcutta School” (CD MTC) in Tremestieri Etneo Municipality in the northern area of the city. The investigation studied depth reached a maximum depth of 80 m for INGV, of 40 m for IC NS and of 30 m for CD MTC. Laboratory tests have been performed on undisturbed samples re- trieved by means of a 101 mm tube sampler [Cavallaro et al., 2007]. To evaluate the geotechnical characteristics of soils the following in situ and laboratory tests were per- formed in the tests located in the city of Catania: - INGV: n. 3 Boreholes, n. 3 Standard Penetration test (SPT), n. 2 Down-Hole tests (DHT), n. 1 Cross- Hole tests (CHT), n. 1 Seismic Dilatometer Marchetti Test (SDMT), n. 6 Direct Shear Tests (DST), n. 2 Consolidated Undrained Triaxial Tests (CUTXT), n. 2 Unconsolidated Undrained Triaxial Tests (UUTXT), n. 2 Cyclic Loading Torsional Shear Tests (CLTST), n. 4 Resonant Column Test (RCT). - IC NS: n. 2 Boreholes, n. 2 Seismic Dilatometer Marchetti Tests (SDMT), n. 6 Direct Shear Tests (DST), n. 3 Unconfined Uniaxial Compression Tests. - CD MTC: n. 1 Boreholes, n. 1 Seismic Dilatometer Marchetti Test (SDMT), n. 3 Direct Shear Tests (DST), n. 1 Unconfined Uniaxial Compression Tests. The “National Institute of Geophysics and Volcanol- ogy” (INGV) area mainly consists: S1: a paving slabs of basalt (to 0.00 - 0.15 m depth), a layer of backfill (to 0.15 - 1.50 m depth), a layer of brown to dark yellow sandy silt slightly clayey with included centimeter limestone (to 1.50 - 5.10 m depth), a layer of yellow - orange sand with included sandstone gravels (to 5.10 - 5.40 m depth), a layer of brown to dark yellow sandy silt slightly clayey with included centimeter lime- stone (to 5.40 - 6.70 m depth), a layer of yellow ochre to grey clay slightly silty (to 6.70 - 9.50 m depth), a layer of grey - blue clay slightly silty with included decimeter dark black sand lenses (to 9.50 - 60.00 m depth). S2: a paving slabs of basalt (to 0.00 - 0.15 m depth), a layer of backfill (to 0.15 - 1.50 m depth), a layer of brown to dark yellow sandy silt slightly clayey with included centimeter limestone (to 3 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 1. Map of seismotectonic features of South-Eastern Sicily, with indication of 1693 and 1908 historical tsunamis, after Barbano et al. [2010]. 1.50 - 6.00 m depth), a layer of yellow - orange sand with included sandstone gravels (to 6.00 - 6.90 m depth), a layer of yellow ochre to grey clay slightly silty (to 6.90 - 8.50 m depth), a layer of grey - blue clay slightly silty with in- cluded decimeter dark black sand lenses (to 8.50 - 80.00 m depth). S3: a paving slabs of basalt (to 0.00 - 0.15 m depth), a layer of backfill (to 0.15 - 2.60 m depth), a layer of brown to dark yellow sandy silt slightly clayey with included centimeter limestone (to 2.60 - 8.60 m depth), a layer of yellow ochre to grey clay slightly silt (to 8.60 - 12.00 m depth), a layer of grey - blue clay slightly silty with in- cluded decimeter dark black sand lenses (to 12.00 - 60.00 m depth). The “Nazario Sauro building School” (IC NS) area mainly consists: S1: a layer of topsoil (to 0.00 - 1.00 m depth), a layer of fractured basaltic rock with included dark grey vacuoles (to 1.00 - 4.50 m depth), a layer of smoke grey sand and volcanic breach (to 4.50 - 13.30 m depth), a layer of compact basaltic rock with included light to dark fractures (to 13.30 - 25.20 m depth), a layer of sand and volcanic breach with included highly oxidized basaltic blocks (to 25.20 - 32.20 m depth), a layer of sand and smoke grey volcanic breach (to 32.20 - 40.00 m depth). S2: a layer of backfill (to 0.00 - 2.80 m depth), a layer of fractured basaltic rock with included dark grey vacuoles (to 2.80 - 7.80 m depth), a layer of compact basaltic rock with included light to dark fractures (to 7.80 - 23.40 m depth), a layer of yellow - brown tufites with medium- fine grain size ochre to grey clay slightly silty CASTELLI ET AL. 4 FIGURE 2. Layout of tests sites geotechnical boreholes: a) “National Institute of Geophysics and Vol- canology” (INGV): S1, S2, S3; b) “Nazario Sauro building School” (IC NS): S1, S2; c) “Madre Teresa di Calcutta School” (CD MTC): S1. a) b) c) (to 6.90 - 8.50 m depth). The “Madre Teresa di Calcutta School” (CD MTC) area mainly consists: S1: a layer of topsoil (to 0.00 - 1.00 m depth), a layer of sand and dark grey volcanic breach (to 1.00 - 8.00 m depth), a layer of compact basaltic rock with included light grey to dark grey fractures (to 8.00 - 14.00 m depth), a layer of sand and dark grey volcanic breach (to 14.00 - 22.50 m depth), a layer of compact basaltic rock with in- cluded light grey to dark grey fractures (to 22.50 - 25.00 m depth), a layer of sand and dark grey volcanic breach (to 25.00 - 29.30 m depth), a layer of compact basaltic rock with included light grey to dark grey fractures (to 29.30 - 30.00 m depth). Using information made available from in situ bore- holes, soil profiles of the ground beneath the Catania test sites could be designed (Figure 3). Trying to sum- marize the borehole results it is possible to define four soil classes, namely: basaltic rock, sand, volcanic breach and silty clay. 5 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 3. Soil profiles of: a) S1, S2, S3, on INGV; b) S1, S2 on IC NS; c) S1 on CD MTC. a) c)b) Based on the laboratory tests typical range of phys- ical characteristics, index properties and strength pa- rameters of the deposits mainly encountered in these areas are reported in Table 1, 2, 3. On the basis of SDMT the INGV deposits mainly con- sist of over-consolidated sandy silt slightly clayey and clay slightly silty soil. The value of the natural moisture content wn prevalently CASTELLI ET AL. 6 Site H [m] γ kN/m3 Wn (%) Gs e n Sr (%) DST CUTxT UUTxT c’ (kPa) ϕ’ (°) cu (kPa) ϕu (°) c’ (kPa) ϕ’ (°) cu (kPa) S1C1 4.00 - 4.50 20.01 16.99 2.74 0.57 0.36 81.60 11 29 - - - - - S1C2 9.00 - 9.50 19.71 26.21 2.76 0.74 0.42 98.45 38 16 55 12 32 17 - S1C3 34.00 - 34.50 19.61 22.65 2.76 0.69 0.41 90.15 51 20 - - - - 226 S2C1 5.00 - 5.40 18.24 15.78 2.76 0.72 0.42 60.59 14 26 - - - - - S2C2 7.20 - 7.70 19.22 24.45 2.79 0.77 0.44 88.41 28 22 104 13 69 19 - S3C3 26.50 - 27.00 19.12 26.35 2.72 0.76 0.43 93.97 50 20 - - - - 106 Site H [m] γ kN/m3 Wn (%) Gs e n Sr (%) DST CUTxT UUTxT c’ (kPa) ϕ’ (°) cu (kPa) ϕu (°) c’ (kPa) ϕ’ (°) cu (kPa) S1C2 7.00 - 7.50 16.57 8.69 2.74 0.77 0.43 31.12 20 37 - - - - - S1C3 11.50 - 12.00 16.48 12.36 2.82 0.89 0.47 39.17 30 37 - - - - - S1C1 5.00 - 5.50 16.87 3.76 2.74 0.65 0.39 15.78 18 39 - - - - - TABLE 1. Mechanical characteristics for INGV of Catania areas. Where: c' = Cohesion and ϕ' = Angle of Shear Resis- tance; Direct Shear Test (DST), CU Triaxial Tests (CUTXT), UU Triaxial Tests (UUTXT). TABLE 2. Mechanical characteristics for IC NS of Catania areas. Where: c' = Cohesion and ϕ' = Angle of Shear Resis- tance; Direct Shear Test (DST), CU Triaxial Tests (CUTXT), UU Triaxial Tests (UUTXT). TABLE 3. Mechanical characteristics for CD MTC of Catania areas. Where: c' = Cohesion and ϕ' = Angle of Shear Re- sistance; Direct Shear Test (DST), CU Triaxial Tests (CUTXT), UU Triaxial Tests (UUTXT). Site H [m] γ kN/m3 Wn (%) Gs e n Sr (%) DST CUTxT UUTxT c’ (kPa) ϕ’ (°) cu (kPa) ϕu (°) c’ (kPa) ϕ’ (°) cu (kPa) S1C1 3.00 - 3.50 16.18 6.50 2.71 0.75 0.43 23.46 20 44 - - - - - S1C2 6.00 - 7.00 16.77 4.32 2.72 0.66 0.40 17.87 11 38 - - - - - S1C4 15.00 - 16.00 16.97 1.82 2.75 0.62 0.38 8.08 0 10 - - - - - ranges from between 16 - 26 % for INGV, 4 - 12 % for IC NS and 2 - 6 % for CD MTC. Characteristic values for Gs (specific gravity) ranged between 2.72 and 2.79 for INGV, 2.74 - 2.82 for IC NS and 2.71 - 2.75 for CD MTC. Figure 4 shows index properties of INGV, IC NS and CD MTC areas. The water level is of 3.50 m from the ground surface for INGV, 0 m for IC NS and CD MTC areas. As regards strength parameters of the deposits mainly (Tables 1, 2, 3) encountered in this area c' from DST ranged between 11 kPa and 51 kPa for INGV, 18 kPa and 30 kPa for IC NS and 0 and 20 kPa for CD MTC while ϕ' from DST ranged between 16° and 29° for INGV, 37° and 39° for IC NS and 10° and 20° for CD MTC. The laboratory results of unconfined compres- sion tests performed on sample retrieved on IC NS and CD MTC areas are reported in Table 4 together the dy- namic results of nondestructively Ultrasonic Tester Tests (UTT). 4. SHEAR MODULUS BY IN SITU TESTS It was also possible to evaluate the small strain shear modulus in the investigated Catania test sites by means of the results deriving from the following seismic tests based on Down Hole (DH) and Cross Hole method (CH). In Figure 5, the shear and compression wave veloc- ities against depth have been reported. In Figure 6 the dynamic Poisson ratio variation with depth, obtained from Down Hole (DH) and Cross Hole (CH) tests, is plot- ted to show site characteristics. It is clear that the val- ues oscillate around 0.36 - 0.45 for CH and 0.45 - 0.49 for DH. In Figure 7 the coefficient of earth pressure at rest Ko variation with depth, obtained from a Down Hole (DH) and Cross Hole tests, is plotted to show site char- acteristics. It is clear that apart from the top 5 m, the values oscillates around 0.60 - 0.75 from CH and 0.90 7 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA (b) Site Borehole H(m) γ kN/m3 Rc (MPa) Vp (m/s) Vs υ G (MPa) E (MPa) IC NS SICL1 1.10 - 1.50 25.62 97.24 - - - - - IC NS SICL4 16.00 - 17.00 27.59 132.93 2812 1773 0.17 8779 20544 IC NS SICL2 5.60 - 6.00 27.51 135.77 3427 2076 0.21 12000 29041 CD MTC SICL3 1.00 - 11.50 26.26 146.08 2621 1668 0.16 7393 17152 TABLE 4. Test Results of nondestructively ultrasonic tester tests (UTT). Where: Rc = Compressive Strength. FIGURE 4. Index properties of INGV, IC NS and CD MTC areas. CASTELLI ET AL. 8 FIGURE 5. Vs and Vp from Down Hole and Cross Hole tests in INGV area. FIGURE 6. Poisson ratio from Down Hole and Cross Hole tests. - 0.95 from DH. A comparison between Go values obtained from in situ test performed on the area under consideration is shown in Figure 8. The Down Hole and Cross Hole tests performed in INGV area showed Go values increasing with depth. Very high values of Go are obtained for depths greater than 30 m. According to these data, it is possible to assume that Go values oscillate around 50 - 250 MPa. The SDMT [Marchetti 1980; Marchetti et al., 2008; Monaco et al., 2009] provides a simple means for de- termining the initial elastic stiffness at very small strains and in situ shear strength parameters at inter- mediate level of strains in natural soil deposits [Castelli et al., 2016b; Cavallaro, 1999c; Cavallaro et al., 2012, 2015]. This apparatus was also used in offshore condi- tion by Cavallaro et al. [2013b, 2013c]. 9 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 7. The coefficient of earth pressure at rest Ko from Down Hole and Cross Hole tests. FIGURE 8. Go from Down Hole and Cross Hole tests. Vs may be converted into the initial shear modulus Go by the well-known relationships: (1) where: r = mass density. The combined knowledge of Go and of the one-di- mensional modulus M (from DMT) may be helpful in the construction of the G-γ modulus degradation curves [Cavallaro et al., 2006a; Castelli et al., 2016c]. A sum- mary of SDMT parameters are shown in Figure 9 where: - Id: Material Index; gives information on soil type (sand, silt, clay); - ϕ': Angle of Shear Resistance; - M: Vertical Drained Constrained Modulus; - Cu: Undrained Shear Strength; - Kd: Horizontal Stress Index; the profile of Kd is similar in shape to the profile of the overconsolidation ra- tio OCR. Kd = 2 indicates in clays OCR = 1, Kd > 2 indicates overconsolidation. A first glance at the Kd profile is helpful to “understand” the deposit; - Vs: Shear Waves Velocity. Figure 10 shows results of the SDMTs performed in the test sites in terms of shear wave velocity profiles. It was also possible to evaluate the small strain shear modulus Go in the Catania test sites by means of the following empirical correlations available in literature based on laboratory test results, Standard Penetration Tests (SPT) or seismic Marchetti dilatometer tests results: a) Jamiolkowski et al. [1995] (2) where: σ'm = (σ'v + 2 σ'h)/3 effective medium stress with σ'v = effective vertical normal stress and σ'h = effective horizontal normal stress; pa = 1 bar is a reference pressure; e = void ra- tio index; Go, σ'm and pa are expressed in the same unit. The values for parameters, which appear in Equation (2) are equal to the average values that result from lab- oratory tests performed on quaternary Italian clays and sands. A similar equation was proposed by Shibuya and Tanaka [1996] for Holocene clay deposits. b) Ohta and Goto [1978] (3) where: Vs = shear wave velocity (m/s), N60 = number of blow/feet from SPT with an Energy Ratio of 60%, Z = depth (m), FG = geological factor (clays=1.000, sands=1.086), FA = age factor (Holocene = 1.000, Pleistocene = 1.303). c) Hryciw [1990] (4) where: Go, σ'v and pa are expressed in the same unit; pa = 1 bar is a reference pressure; γD and Ko are respec- tively the unit weight and the coefficient of earth CASTELLI ET AL. 10 G0 = Vs 2r FIGURE 9. Results of the SDMTs in terms of geotechnical parameters for INGV area. Go = 600⋅ m '0.5pa 0.5 e1.3 σ Vs = 69⋅ N60 0.17 ⋅ Z0.2 ⋅ FA ⋅ FG Go = 530 σv ' / pa( ) 0.25 γD / γw −1 2.7 − γD / γw Ko 0.25 ⋅ v ' ⋅ pa( ) 0.5 σ pressure at rest, as inferred from SDMT results ac- cording to Marchetti [1980]. Figure 11 shows the Go values obtained by SDMT and those obtained by means of the empirical corre- lations. On the whole, Equations (2) and (4) seems to provide the most accurate trend of Go with depth, as can be seen in Figure 11. A good agreement exists be- tween empirical correlations and SDMT. However, as can be seen in Figure 11, the method by Hryciw [1990] was not capable of detecting the SDMT results for sandy soil as reported in Figure 11. Figure 11 shows also the value of Go measured in the laboratory from RCT per- formed on undisturbed solid cylindrical specimens. In the case of laboratory tests, the Go values are deter- mined at shear strain levels of less than 0.001 %. At the depth of about 7 m high values of Go are registered by 11 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 10. Shear wave velocity profiles obtained from SDMT for CD NS a), INGV b) and CD MTC c) areas. FIGURE 11. Go values obtained by SDMT, by D-H and by empirical correlations for INGV site. a) b) c) SDMT probably due to the presence of a layer of grey - blue clay slightly silty with included decimeter dark black sand lenses. High values of Go were obtained for levels higher than 25 m depth. In Figure 12 it is proposed a comparison between the values of Vs obtained from SDMT and Ultrasonic Tester Tests UTT. Up to a depth of 15 m higher Vs val- ues are obtained in the laboratory by nondestructively ultrasonic tester tests (UTT) rather than those obtained in situ from SDMT tests. 5. SHEAR MODULUS AND DAMPING RATIO BY LABORATORY TESTS Shear modulus G and damping ratio D of Catania tests sites deposits were obtained in the laboratory by Resonant Column Tests (RCT) and by Cyclic Loading Torsional Shear Tests (CLTST) performed by means of a Resonant Column/Cyclic Loading Torsional Shear Ap- paratus [Cascante et al., 1998] (Figure 13). A Resonant Column test consists in exciting one end of a confined solid or hollow cylindrical soil spec- imen. The specimen is fixed at the bottom (fixed-free test) and it is excited in torsion or flexure at the top by means of an electromagnetic drive system. Once the fun- damental resonant frequency is established from mea- suring the motion of the free end, the velocity of the propagating wave and the degree of material damping are derived. The shear modulus is then obtained from the derived velocity Vs (in case of torsion) and the density r of the sample [Cavallaro et al., 1999a; Maugeri and Cavallaro, 1999]. The equivalent shear modulus Geq is the unload- reload shear modulus that is evaluated from RCT in function of velocity Vs and density r of the sample, while Go is the maximum value or also “plateau” value as observed in the G-log(γ) plot; G is the secant mod- ulus [Castelli et al., 2016c; Cavallaro, 2016; Lo Presti et al., 1999a]. Generally G is constant until a certain strain limit is exceeded. This limit is called elastic threshold shear strain (γet) and it is believed that soils behave elastically at strains smaller than γet. The elastic stiffness at γ<γ e t is thus the already defined Go [Capilleri et al., 2014; Lo Presti et al., 1999b]. For CLTSTs the damping ratio (D) was calculated as the ratio between the area enclosed by the unloading- reloading loop and represents the total energy loss dur- ing the cycle and W is the elastic stored energy. For RCTs the damping ratio was determined using the steady-state method during the resonance condition of the sample. The apparatus used is a fixed-free resonant column apparatus [Hall and Richart, 1963]. It enables the spec- imen consolidation under both isotropic and anisotropic stresses. It is composed of a drive system, a support sys- tem, and a base plate. The solid or hollow cylinder spec- imen is fixed at the bottom and its constraint at the base CASTELLI ET AL. 12 FIGURE 12. Vs from SDMT, UTT and by empirical correlation for IC NS and CD MTC sites. is due to the friction existing between the specimen and the porous synthesized bronze stone [Drnevich et al., 1978]. Torsional forces are applied at the top by means the drive system, realized in aluminium. It is an electri- cal motor constituted of four magnets connected with the top of the sample and eight coils placed on the inox steel annular base, which is strictly linked to the support system. The weight of the motor is counterbalanced by a spring. A programmable function generator (PGF) ex- cites the electrical motor of Stokes. Solid cylindrical specimens were built by using tap- ping [Drnevich et al., 1978], in order to obtain the re- quired relative and a good uniformity during the deposition. The mold is assembled and a little depres- sion is applied to let the membrane adhere to the inside surfaces. The material is placed in the mold using a fun- nel-pouring device. The soil is placed as loosely as pos- sible in the mold by leaving the soil from the spout in a steady stream, holding the pouring device upright and vertical, and maintaining constant the fall height. It is possible to obtain different values of relative density changing the height of deposition. In order to realize high values of relative density it could be necessary to beat delicately the mold surface during the deposition. Each sample was reconstituted with fresh sand. Each specimen was subjected to an isotropic load achieved in a plexiglas pressure cell, using an air pressure source. The axial strain was measured by using a high-resolu- tion proximity transducer, which monitors the alu- minium top-cap displacement. Shear strain was measured by monitoring the top rotation with a couple of high-resolution proximity transducers. During a resonant column test, the proximity trans- ducers are not able to appraise the value of the targets displacements, because of the high frequency of the os- cillations. Then rotation on the top of the specimen is measured by means of an accelerometer. The laboratory test conditions and the obtained small strain shear mod- ulus Go are listed in Table 5. The undisturbed specimens were isotropically reconsolidated to the best estimate of the in situ mean effective stress. The same specimen was first subject to RCT, then to CLTST after a rest period of 24 hrs with opened drainage. CLTST were performed un- der stress control condition by applying a torque, with triangular time history, at a frequency of 0.1 Hz. The size of solid cylindrical specimens are Radius = 25 mm and Height = 100 mm. The Go values [Go (1) and Go (2)], re- ported in Table 5, indicate moderate influence of strain rate even at very small strain where the soil behaviour is supposed to be elastic. In order to appreciate the rate effect on Go, it is worthwhile to remember that the equivalent shear strain rate (γ⋅ = 240 ⋅ f ⋅ γ [%/s]) experienced by the specimens during RCT can be three orders of magnitude greater than those adopted during CLTST. The effects of the rate and loading conditions become less relevant with an in- crease of the shear strain level, as can be seen in Figure 13 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 13. Resonant Column/Cyclic Loading Torsional Shear Apparatus. Borehole H (m) σ’vc (kPa) e CLTST RCT Go (1) (MPa) Go (2) (MPa) Go (3) (MPA) γmax(%) S1C1 4.75 75 0.57 U 95 - 126 0.098 S3C1 5.70 90 0.76 U 62 46 58 0.114 S2C3 14.25 170 0.76 U 30 28 78 0.501 S2C5 72.25 475 0.75 U 47 - - 0.361 TABLE 5. Test condition for INGV area specimens. Where: U = Undrained. Go (1) from RCT, Go (2) from CLTST after 24 hrs, Go (3) from Down-Hole. 14 where the G-γ curves obtained from CLTST and RCT are compared. It is possible to notice that the lowest decay of G with γ is observed in CLTST, while the max- imum decay occurs during RCT. Finally higher values of the initial shear modulus [Go (3)] have been obtained from Down - Hole tests. In general (Figure 15) higher values of D are obtained by RCT than CLTST. The damp- ing ratio values obtained from RCT by steady-state method increases with the strain level, higher values of D have been obtained from strain level higher than 0.02 %. Greater values of D are obtained from RCT for strain level higher than 0.2 %. The experimental results were CASTELLI ET AL. 14 FIGURE 14. G-γ curves from RCT and CLTST tests. FIGURE 15. D-γ curves from RCT and CLTST tests. used to determine the empirical parameters of the eq. proposed by Yokota et al. [1981] to describe the shear modulus decay with shear strain level (Figure 16): (5) in which: G(γ) = strain dependent shear modulus; γ = shear strain; a, b = soil constants. The expression (1) allows the complete shear modulus degradation to be considered with strain level. The values of a = 22 and b = 1.05 were obtained for INGV area. As suggested by Yokota et al. [1981], the inverse 15 DYNAMIC CHARACTERISATION OF SOILS IN CATANIA FIGURE 16. G/Go- γ curves from RCT tests. G(γ) G0 = 1 1+aγ (%)b FIGURE 17. D/Go curves from RCT tests. variation of damping ratio with respect to the nor- malised shear modulus has an exponential form as that reported in Figure 17 for the INGV area: (6) in which: D(γ) = strain dependent damping ratio; γ = shear strain; η, l = soil constants. The values of η = 10 and l = 1.05 were obtained for INGV area. The Equation (5) assume maximum value Dmax = 10 % for G(γ)/Go = 0 and minimum value Dmin = 3.50 % for G(γ)/Go = 1. Therefore, Equation (5) can be re- written in the following normalised form: (7) 6. CONCLUSIONS The paper represents a report about static and dy- namic properties of soils in the city of Catania. A great availability of borehole data, geophysical surveys and laboratory tests have been carried out from various campaigns of geological surveys. In order to study the dynamic characteristics of soils in three Catania test sites, laboratory and in situ investigations have been carried out to obtain soil profiles with special attention being paid to the variation of the shear modulus G and damping ratio D with depth. Therefore a site characterisation of “National Insti- tute of Geophysics and Volcanology” (INGV), “Nazario Sauro building School” (IC NS) and “Madre Teresa di Calcutta School” (CD MTC) areas for seismic response analysis was presented. Using information made avail- able from in situ boreholes, soil profiles beneath the Catania test sites have been proposed. Trying to sum- marize the borehole results it is possible to define four soil classes, namely: basaltic rock, sand, volcanic breach and silty clay. Available data permitted to define the small strain shear modulus Go profile variation with depth. On the basis of the obtained results it is possible to draw the following conclusions: - the influence of strain rate at very small strain is so negligible; - a degradation phenomenon occurs during RCT; - damping ratio values obtained by RCT are greater than those obtained by CLTST; - higher values of Go were obtained by Down-Hole tests; - different Go values are obtained by SDMT than Down Hole and empirical correlations. On the basis of in situ test results, it is possible to stress that the small strain shear modulus measured in the laboratory is smaller than that obtained in situ by means of DH tests; this is probably due to a disturbance phenomenon occurred during sampling. Moreover three empirical correlations available in literature based on laboratory test results, Standard Penetration Tests (SPT) and Seismic Dilatometer Marchetti Tests (SDMT) results were proposed. On the whole, equations proposed by Jamiolkowski et al. [1995] and by Hryciw [1990] seem to provide the most accurate trend of Go with depth. Finally two empirical expressions have been pro- posed to describe the complete shear modulus degrada- tion with strain level and the inverse variation of damping ratio with respect to the normalised shear modulus. Moreover, analysing the shear wave velocity profiles as well as the profiles of the horizontal stress index Kd of the test sites “National Institute of Geophysics and Vol- canology” (INGV) and the school “Madre Teresa di Cal- cutta School” (CD MTC), it is possible to observe that: - higher values of shear wave velocity Vs in the (CD MTC) site have been obtained by tests in the upper 30 m of soil, so that slight soil amplification phe- nomena can occur; - lower values (<400 m/s) of shear wave velocity Vs in the (INGV) site have been obtained by tests in the upper 30 m of soil, so that considerable soil amplification phenomena can occur. REFERENCES Abate, G., Massimino, M.R. (2017a): “Numerical mod- elling of the seismic response of a tunnel–soil– aboveground building system in Catania (Italy)”. Bulletin of Earthquake Engineering Volume 15, Issue 1, 1 January 2017, Pages 469-491. Abate, G., Massimino, M.R. 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