EARTHQUAKE GEOTECHNICAL ENGINEERING ASPECTS OF THE 2012 EMILIA-ROMAGNA EARTHQUAKE (ITALY)

Transcription

1 EARTHQUAKE GEOTECHNICAL ENGINEERING ASPECTS OF THE 212 EMILIA-ROMAGNA EARTHQUAKE (ITALY) FIORAVANTE V., GIRETTI D., ABATE G., AVERSA S., BOLDINI D., CAPILLERI P., CAVALLARO A., CHAMLAGAIN D., CRESPELLANI T., DEZI F., FACCIORUSSO J., GHINELLI A., GRASSO S., LANZO G., MADIAI C., MASSIMINO M., MAUGERI M., PAGLIAROLI A., RAINIERI C., TROPEANO G., SANTUCCI DE MAGISTRIS F., SICA S., SILVESTRI F., VANNUCCHI G. Presented by Michele Maugeri, University of Catania (Italy) 7 TH INTERNATIONAL CONFERENCE ON CASE HISTORIES IN GEOTECHNICAL ENGINEERING Chicago, USA April 29- May 4, 213

2 The Emilia Romagna earthquake of May 2 and May 29, 212 with a magnitude M L respectively 5.9 and 5.8 caused 27 deaths, 1,2 damaged buildings, 147 damaged campaniles, 6 damaged industrial buildings. The damage was estimated by the UE in about 12 billions of euros: 3.5 billions for residential buildings, 5.5 billions for industrial buildings, 2 billions for cultural heritage and 1 billion for the infrastructures.

3 Historical seismicity of the area (Castelli et al. 212) (data source: Rovida et al. 211).

4 Maximum PGA at the bedrock = g at Finale Emilia, with a probability of exceedance less than 1% in 5 years (return period 475 years). By the way, the Emilia Romagna region was declared seismic area in 23.

5 SUMMARY GROUND MOTION GROUND PROPERTIES PRELIMINARY SITE RESPONSE ANALYSIS LIQUEFACTION GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS CONCLUSIONS

6 GROUND MOTION ( (a) (b) Shakemaps of the horizontal PGA of the main shocks occurred on (a) May 2, 212 and (b) May, 29, 212 (max registered horizontal acceleration =.2872g and.295g respectively for the 2 and 29 earthquakes.

7 GROUND MOTION Subsoil classification type C at Mirandola. Soil amplification factor Ss = given by Italian Code 28. Expected maximum acceleration.15x1.5=.225g. Maximum recorded horizontal acceleration at Mirandola =.2872g for the May 2 earthquake.

8 GROUND MOTION acceleration (g) a max =.261g EW a max =.264g NS a max =.39g UP time (s) time (s) time (s) a) velocity (cm/s) EW V 4 4 max =47.9 cm/s NS UP V max =29.5 cm/s time (s) time (s) time (s) b) Acceleration (a) and velocity (b) time histories recorded at the Mirandola (MRN) station during the seismic event of May 2, 212. It is remarkable that the vertical and horizontal accelerations are similar because of thrust fault.

9 GROUND MOTION velocity (cm/s) a max =.224g EW a max =.295g NS UP a max =.889 g a) velocity (cm/s) time (s) V max =28.6 cm/s EW time (s) V max =57.1 cm/s NS time (s) a max =27.8 cm/s UP b) time (s) time (s) time (s) Acceleration (a) and velocity (b) time histories recorded at the Mirandola (MRN) station during the seismic event of May 29, 212. It is remarkable that relative velocity reaches 57.1 cm/s, the maximum recorded horizontal and vertical accelerations were respectively.295g and.889 g.

10 GROUND MOTION Spe ectral acceleration, Sa (g) May 2 - MRN EW NS UP ξ = 5% a) May 29 - MRN ξ = 5% b).2 May 29 - SAN ξ = 5% c) Period (s) Period (s) Period (s) Acceleration response spectra (5% damped) of horizontal and vertical components: MRN station for the seismic events of May 2, 212 (a); May 29, 212 (b); SAN station during the seismic event of May 29 (c). It is remarkable that the vertical acceleration shows a period much less than horizontal one

11 GROUND MOTION S a (g) MRN - May 2, 212 MRN - May 29, 212 EW NS NTC8 475 yrs, cat. C 1898 yrs, cat. C ξ = 5% S a (g) EW NS NTC8 475 yrs, cat. C 1898 yrs, cat. C S a (g) MRN May 2, 212 May 29, 212 NTC8 475 yrs, cat. C 1898 yrs, cat. C ξ = 5% ξ = 5%.2 a) b) c) Period, T (s) Period, T (s) Period, T (s) Acceleration response spectra (5% damping) from ground motions recorded at MRN station for: horizontal ( a, b ) and vertical (c) components compared to the Italian Bulding code spectra for 475 and 1898 years return periods.

13 GROUND PROPERTIES Offprint of the geological (1:25.) and geomorphological map (1:1.) of the Ferrara plane.

14 GROUND PROPERTIES Location of in situ tests in the area of S. Carlo.

15 GROUND PROPERTIES q c (MPa) V S (m/s) Altitude above sea level (m) SCPTu1 SCPTu2 SCPTu3 SCPTu4 qc,nc SCPTu1 SCPTu2 SCPTu3 SCPTu D (%) Seismic cone test results: a) cone resistance qc and b) shear wave velocity V S profiles.

16 GROUND PROPERTIES Passing (%) SILTY SAND SANDY SILT SAND CLAY Grain size (mm) Grain size distributions.

17 GROUND PROPERTIES G/G (-) clay G/G sand u sandy silt u D (%) u (kpa) sandy silt G/G sand G/G sand D clay D sandy silt D 8 4 clay u γ (%) Dependence of the shear modulus, damping ratio and excess pore pressure on the shear strains.

19 PRELIMINARY SITE RESPONSE ANALYSIS Ground Model SAND SCPTu1 S1 CPTu2 CPTu3 S4 SILTY SAND CLAY- SILTY CLAY NW m above s.l q c (MPa) z (m) q c (MPa) z (m) 28 3 q 3 c (MPa) z (m) SILT- SANDY SILT - CLAYEY SILT GROUND WATER TABLE S9 SE 5 m Cross-section A-A: qc = cone resistance, z = depth below the ground surface.

20 PRELIMINARY SITE RESPONSE ANALYSIS Ground Model Experimental shear wave velocity values versus elevation above sea level from SCPTU and DH tests and average profiles at San Carlo, SC (a) and Mirabello, M (b) sites. Subsoil class according to the Italian seismic code (NTC-8) is also indicated in brackets.

21 PRELIMINARY SITE RESPONSE ANALYSIS Ground Model 17.7 m (a.s.l.) (A)Channel-levee facies: fine sands and sandy silts (B)Channel-levee facies: fine and medium sands (C)Alluvial plain facies: silty clays and peats (D)Alluvial plain facies: sandy silt and silty sand alternating layers (Pleistocene) EC1 M1C1 EC1 M1C2 S1C1 M1C3 EC1 S1C2 m 4 m 6.5 m 12.3 m 14.3 m 2 m 26.3 m Vs (m/s) γ (kn/m 3 ) m (a.s.l.) (B) Channel-levee facies: sandy silt and silty sand alternating layers (C) Alluvial plain facies: silty clays and peats (D) Alluvial plain facies: sandy silt and silty sand alternating layers (Pleistocene) M1C1 EC1 M1C2 S1C1 M1C3 EC1 S1C2 Vs (m/s) γ (kn/m 3 ) m 3.7 m m 9.4 m 1 16 m m 25 3 m 3 EC2 34 m 35 EC m 4.2 m 4 4 Depth (m) 45 5 Depth (m) 45 5 (E)Alluvial plain facies: mostly sandy layers (Pleistocene) EC (E)Alluvial plain facies: mostly sandy layers (Pleistocene) EC m 75 (F)Clays and silts Bedrock m (a.s.l.) EC3 EC4 79 m 124 m (F) Clays and silts Bedrock m (a.s.l.) EC3 EC m Lithologic units, shear wave velocity and soil unit weight profiles assumed for ground response analysis at the vertical soil profile: a) A (top of the embankment); b) B (base of the embankment).

22 PRELIMINARY SITE RESPONSE ANALYSIS Ground Model Experimental values of normalized shear modulus G/G versus shear strain observed in resonant column tests on fine-grained and organic soils from San Carlo and Mirabello sites.

23 PRELIMINARY SITE RESPONSE ANALYSIS Ground Model Experimental values of the damping ratio D versus shear strain observed in resonant column tests on fine-grained and organic soils from San Carlo and Mirabello sites.

24 acceleration [g] PRELIMINARY SITE RESPONSE ANALYSIS Site Amplification acceleration [g] time [s] time [s] time [s] Acceleration time histories of the input motions (the main parameters are summarized in Table). I1 I2 I3 O1-A O2-A O3-A O1-B O2-B O3-B PGA (g) I a (cm/s) T (s) D T (s) FA(PGA) FA(I H ) acceleration [g] Main parameters (PGA: peak ground acceleration; Ia: Arias Intensity; T : fundamental period; DT: Trifunac duration) of seismic inputs (I1, I2 and I3) and outputs (O1, O2 and O3) from ground response analysis at vertical soil profile A (top of the embankment) and B (base of the embankment) and corresponding amplification factors, FA(PGA) and FA(IH) in terms of PGA and Housner Intensity respectively.

25 PRELIMINARY SITE RESPONSE ANALYSIS Site Amplification Pseudo-acceleration response spectra (5% of critical damping) of the seismic input motions and output signals at the vertical soil profile A (top of the embankment) and B (base of the embankment) compared with the spectra suggested from the Italian seismic code (NTC-8) for subsoil classes C and D.

26 PRELIMINARY SITE RESPONSE ANALYSIS at Mirandola Bell-Tower Damage of bell-tower of the Mirandola cathedral between 2 and 32 m height: (a) east view, (b) west view and (c) south view (adapted from Pesci & Bonali 212).

27 PRELIMINARY SITE RESPONSE ANALYSIS at Mirandola Bell-Tower Schematic shapes of the vibration modes of a tower with higher stiffness along y axis: T1 and T2 fundamental period for bending moment along x and y axis respectively T 3 first torsional mode; T4 second bending mode Computation of 1st resonant period of Mirandola bell-tower and other case studies (Rainieri & Fabbrocino, 211): T 1 =.85s

28 PRELIMINARY SITE RESPONSE ANALYSIS at Mirandola Bell-Tower Comparison between the estimated four resonant periods and the response spectra of the main-shock of the seismic sequence recorded at Mirandola station.

30 LIQUEFACTION Evidences and damaged localities Map of soil liquefaction phenomena observed during the Emilia-Romagna earthquakes of May 2 and 29, 212.

31 LIQUEFACTION Evidences and damaged localities Map of observed liquefaction effects at San Carlo village (continuous lines: soil ruptures; cross: sand boils and volcanoes, vents, flooding from swells, ; hatched rectangles: foundation settlements and rotation). Dashed lines delimit paleo-channels area.

32 LIQUEFACTION Evidences and damaged localities Map of observed liquefaction effects at Mirabello village (continuous lines: soil ruptures; cross: sand boils and volcanoes, vents, flooding from swells, ; hatched rectangles: foundation settlements and rotation). Dashed lines delimit paleo-channels area.

33 LIQUEFACTION Evidences and damaged localities Liquefaction evidences and damages at San Carlo (photos by DICeA Geotechnical team at the University of Florence).

34 LIQUEFACTION Analysis of the liquefaction hazard at San Carlo.6 m 2.9 m Topsoil Yellow silt Medium-to-fine silty sand 7.8 m Grey clay 16.5 m 18. m Grey clavey silt Coarse-to-medium sand rising sand 22.2 m Grey and sligthly silty clay 31.1 m 32. m 33.2 m 34.5 m Sandy silt and grey medium-to-fine sand Clay and silt and clave silt Grey silty medium-to-fine sand liquefied layer Grey clay and silt Soil profile at San Carlo from BH 18513P432 of Regional database. Deep trench (6m depth) at San Carlo (photos by DICeA Geotechnical team).

35 LIQUEFACTION Evidences and damaged localities Liquefaction evidences and damages at Mirabello (photos by DICeA Geotechnical team at the University of Florence)

36 LIQUEFACTION Analysis of the liquefaction hazard at San Carlo 1 SAN CARLO Via 8 marzo (S) 9 SAN CARLO Via Verga (S) 8 SAN CARLO S1 (BH-9.5 m) 7 SAN CARLO S3 (S) 6 SAN CARLO S3 (BH-5.5 m) % finer SAN CARLO S3 (BH-9.5 m) SAN CARLO S3 (BH-11.5 m) SAN CARLO S4 (S) SAN CARLO S4 (BH-4.5 m) SAN CARLO S4 (BH-7.3 m) 1 MIRABELLO Corso Italia (S) diameter [mm].1.1 MIRABELLO Via dell'argine.1vecchio (S) DODICI MORELLI Via Maestrola (S) Grain-size distribution of undisturbed samples from boreholes S1, S3 and S4 (San Carlo) and samples of liquefied ejected sands compared with critical curves suggested by the Italian seismic code (NTC-8).

37 LIQUEFACTION Analysis of the liquefaction hazard at San Carlo LPI 16 CPTU1 CPTU LPI 16 CPTU3 14 CPTU4 14 CPTU5 12 CPTU6 12 CPTU7 1 CPTU8 1 CPTU9 CPTU1 8 SCPTU1 8 Quota (m s.l.m.) z (m) CPTU1 CPTU2 CPTU3 SCPTU1 6 SCPTU2 6 SCPTU2 SCPTU3 SCPTU4 SCPTU3 4 SCPTU4 4 2 Low liquefaction hazard Moderate liquefaction hazard High liquefaction hazard Very high liquefaction hazard Low liquefaction hazard Moderate liquefaction hazard High liquefaction hazard Very high liquefaction hazard -2-4 Liquefaction Potential Index, LPI (Iwasaki et al., 1978) from CPTu tests at San Carlo (a) and Mirabello (b) versus elevation on the sea level.)

38 LIQUEFACTION Analysis of the liquefaction hazard at San Carlo and Mirabello Map of the depth from ground level of the top of the liquefiable layer from simplified procedure based on CPTu tests at the San Carlo and Mirabello area. Liquefaction hazard map from simplified procedure based on CPTu tests at the San Carlo and Mirabello area. Map of the thickness of the liquefiable layer from simplified procedure based on CPTu tests at the San Carlo and Mirabello area.

40 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS The main damage of 5.5 billions of euros among 12 billions of euros, occurred at the industrial buildings. The damage was very severe for the industrial buildings designed and built before 22, before when the area was declared to be a seismic area. By the way no significant damage occurred at the industrial buildings designed and built after 22 according to seismic code. The damage of 5.5 billions of euros takes into account not only the cost of repairing the damaged industrial buildings and re-building the collapsed industrial buildings, but also the amount of the indirect loss of industrial production. For repairing the damaged industrial buildings, two guidelines were edited, one for the structural retrofitting and one for foundation retrofitting. The retrofitting must guarantee that the building will be undamaged with a seismic action up to 6% of that given by the Italian National Code.

41 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS

42 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour Location of the inspected damaged industrial buildings at the Mirabello due to soil liquefaction.

43 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour An inspected building at Mirabello before the occurrence of the earthquakes.

44 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour The occurrence of liquefaction inside the inspected damaged industrial building at Mirabello

45 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour Damage on an industrial building due to hammering on a column by the rigid industrial pavement.

46 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour (a) (b) The industrial building pavement with a typical thickness of 15 cm (a); the corrosion of the steel reinforcement and steel grid of the industrial pavement (b).

47 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Damage due to the foundation behaviour and the soil foundation behaviour Damage on an industrial building due to foundation rotation. Damage on an industrial building due to fractures in the soil.

48 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Ground model, site and laboratory investigations for detecting soil properties Overturning of an apparatus Rotation of an apparatus By back analysis of overturning and rotation of some apparatus inside an industrial building, the estimated acceleration was.38g

49 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Industrial buildings foundation typology Section view of an existing industrial building in the examined area, with shallow foundations.

50 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Underpinning for upgrading the foundation to guarantee that the building will be undamaged when subjected to a seismic action up to 6% of that given by the Italian National Code View of the industrial pavement during construction. Sleeve-footing on reinforced concrete sub-foundation.

51 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS Underpinning for upgrading the foundation to guarantee that the building will be undamaged when subjected to a seismic action up to 6% of that given by the Italian National Code GROUTNG RIVETTING OF PRECAST FOUNDATION AND FOUNDATION SOIL STABILIZED SOIL STABILIZED CONCRETE FOUNDATION (a) FOUNDATION (b) a) Increase of the passive resistance of the soil adjacent to existing footings; b) Improvement of the frictional resistance at the base of footings by riveting the foundation to the sub-foundation

52 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS foundation improvement by enlargement of existing foundation

53 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS BARS THROUGH NEW AND EXISTING FOUNDATIONS EXISTING FLOOR SLAB PARTIALLY D REMOVED NEW STRUCTURAL CONCRETE MICRO-PILES Existing foundation improvement by additional piling and a new footing surrounded to it.

54 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS soil grouting 3 soil grouting 3 densified soil Soil grouting to improve soil density and soil resistance against liquefaction

55 GUIDELINES FOR REPAIRING THE FOUNDATION OF INDUSTRIAL BUILDINGS GRAVEL COLUMNS INDUSTRIAL BUILDING MEDIUM DENSE SAND LOOSE SAND DENSE SAND PLAN VIEW INDUSTRIAL BUILDING Increasing soil drainage by gravel columns to decrease pore pressure build up and liquefaction potential index

56 CONCLUSIONS (1/2) In spite of a moderate earthquake (M= 5.9), the damage was very severe mainly to the industrial building, considering the direct damage to the building (5%) and the indirect damage due to the indirect loss of industrial production (5%). In particular the industrial building damaged are that built before 22, when the area was not yet declared seismic area. By the way, practically undamaged are the industrial buildings built after 22 according to the Italian Regulation Code. As far as concern site effects, the soil amplification was greater than that predicted for soil type C by the European Code (Ss = 1.15) and the Italian Code (Ss = 1.5). The average soil amplification effect was about 2., similar values were found for the Abruzzo earthquake (Ss = 2) while the maximum Ss for Abruzzo earthquake was 2.6.

57 CONCLUSIONS (2/2) As far as concern the vertical acceleration, the maximum recorded vertical acceleration was.89g, due to the normal fault. This value is considerably higher than the horizontal acceleration (about 3 times), so more researches are needed about the prediction of the vertical acceleration in seismic areas prone to thrust fault. The earthquake caused extended liquefied areas (first time in Italy) even if the predicted acceleration was only g. This could be due to the actual river deposits by Reno, Panaro, Secchia. In some parts the rivers were diverted to avoid flooding. So, the flooding risk was reduced, but the liquefaction risk was increased. Guidelines for structural and foundations retrofitting of single-storey industrial buildings damaged by the May 212 earthquakes in the Emilia Romagna Region not designed according to seismic code were made for upgrading it to a seismic action up to 6% of that given by the Italian National Code.