Geoscience Reference
In-Depth Information
CHAPTER 18
SEISMIC RISK ASSESSMENT OF UNDERGROUND STRUCTURES
UNDER TRANSIENT GROUND DEFORMATIONS
Roberto Paolucci
1
and Kyriazis Pitilakis
2
1
Depart. of Structural Engineering, Politecnico di Milano, Milano, Italy
2
Depart. of Civil Engineering, Aristotle University of Thessaloniki, Greece
Abstract.
Some relevant issues concerning the seismic risk assessment of underground structures
under transient ground deformations are dealt with in this paper, mainly referring to: (i) the evalu-
ation of earthquake-induced ground strains and the re-examination of the currently used formulas
fordesign;(ii)theanalysisoftheirspatialvariabilityasafunctionofthelateralsoilheterogeneities,
includingtheroleofsurfacewaves;(iii)theratiobetweenshearandaxialstrains;and(iv)themain
problemstobefacedintheconstructionofhazardmapsforseismicriskassessmentofunderground
structures.Adetailedexampleofapplicationtotheriskassessmentofthewaterpipelinesystemin
thetownofDuzce,Turkey,isprovided,includingthenumericalsimulationofseismicwavepropa-
gation from the source of the Nov. 12, 1999, earthquake to the Duzce basin and the comparison of
1Dand2Dresultsintermsofpeakgroundstrains.Theeffectofdifferentvulnerabilityfunctionson
theriskassessment,eitherintermsofpeakgroundvelocityorpeakgroundstrain,isalsoaddressed.
Finally, a further example of risk assessment of the water transmission system in Thessaloniki is
summarized.
1. Introduction
Itiswidelyrecognizedthat,unlikeabove-groundstructuresthatactasakindof“inertial”
filter on the incident ground motion, the seismic response of underground structures is
predominantly affected by the deformation of the surrounding soil, while soil-structure
interaction effects are generally negligible (St John and Zarah, 1987). Therefore, one of
the critical aspects behind the seismic design and assessment of underground structures
is the proper definition of the input ground motion that cannot be directly deduced from
the standard spectral representation of seismicactions.
Leavingasidethecaseofearthquake-induced groundfailures,suchasfaultruptures,liq-
uefaction or landsliding, that will not be covered in this paper, the procedures for deter-
mination of seismic design actions on underground structures are generally based on a
simplified evaluation of transient ground strains under the assumption of plane waves
propagatinginahomogeneousunboundedmedium(Newmark,1967;Yeh,1974).Refer-
ring to thecomprehensive state-of-art of Hashash et al.(2001) forthe review of different
formulas applicable to the various deformation modes, we limit ourselves here for sim-
plicity to the case of longitudinal strains that are generally considered to be the main
