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Centrifuge Modeling of Seismic Soil-Structure-Interaction and Lateral Earth
Pressures for Large Near-Surface Underground Structures
Modélisation en centrifugeuse de l'Interaction sol-structure sismique et des pressions de terre
latérales pour les grands ouvrages souterrains proches de la surface
Dashti S., Hushmand A., Ghayoomi M., McCartney J.S., Zhang M.
University of Colorado Boulder
Hushmand B., Mokarram N., Bastani A.
Hushmand Associates, Inc.
Davis C., Lee Y., Hu J.
Los Angeles Department of Water and Power
ABSTRACT: The Los Angeles Department of Water and Power (LADWP) is planning the construction of a new buried reservoir in
Southern California. The current state of practice for evaluating the seismic response of underground structures relies heavily on
simplified procedures or numerical tools that have not been verified adequately against physical model studies or detailed case
histories. A series of eight centrifuge tests are currently being conducted at the University of Colorado Boulder (CU Boulder) to
produce well-documented model “case histories.” The data from these tests help better understand seismic soil-structure-interaction
(SSI) and the distribution of lateral seismic earth pressures on the walls of a buried structure restrained at top and bottom. This paper
provides a brief overview of a centrifuge physical modeling investigation into the influence of the relative stiffness of the
underground structure and the characteristics of the input motion on the seismic response of buried structures.
RÉSUMÉ: Le "Los Angeles Department of Water and Power" (LADWP) prévoit la construction d'un nouveau réservoir enterré, une
centrale hydroélectrique, et une station de régulation de débit en Californie du Sud. L'état actuel de la pratique d'évaluation de la
réponse sismique des structures souterraines repose en grande partie sur les procédures simplifiées ou des outils numériques qui n'ont
pas été comparés de manière adéquate à des des modèles physiques ou des études de cas. Une série de huit essais en centrifugeuse
sont actuellement en cours à l'Université du Colorado, Boulder pour produire des données complètes de prototypes. Les données de
ces essais aident à mieux comprendre l'interaction sol-structure sismique et la distribution des pressions des terres latérales sismiques
sur les murs d'une structure enterrée maintenue en haut et en bas. Ce document donne un aperçu d'une modélisation physique en
centrifugeuse de l'influence de la rigidité relative de la structure souterraine et des caractéristiques du signal source sur la réponse
sismique de la structure enterrée.
KEYWORDS: Physical modeling ; Centrifuge modeling ; Seismic soil structure interaction; Underground structures.
1 INTRODUCTION
In order to better understand the seismic response of buried
water reservoirs, a series of centrifuge tests are being performed
on scale-model underground structures in a new, transparent
flexible shear beam (FSB) type container developed by
Ghayoomi et al. (2012a,b). The data from these tests serve two
important purposes: 1) to better understand seismic soil-
structure-interaction (SSI) and the distribution of lateral seismic
earth pressures on the walls of a buried structure restrained at
top and bottom; 2) to calibrate and improve numerical models.
Specifically, the goal of the tests is to provide validation data
for two-dimensional (2-D) and 3-D finite element analyses of
the dynamic response of equivalent model underground
structures with a range of stiffnesses.
In addition to describing the testing program on buried
structures, we briefly discuss the results from a preliminary
centrifuge test performed on a free-field soil specimen with no
structure. The goal was to initially investigate the dynamic
response of uniform dry sand and simultaneously evaluate the
performance of the newly designed container in simulating 1-D
conditions with minimum boundary effects. The next
experiments, which are currently underway, evaluate the
seismic response of three different tunnel structures with
varying stiffnesses and soil conditions. Accelerations,
displacements, and axial strains as well as the distribution of
lateral earth pressures on the restrained walls are being
measured during a suite of input earthquake and sinusoidal
motions in flight. The influence of the relative stiffness of the
underground structure to soil and the characteristics of the input
motion (i.e., amplitude, frequency content, and duration) on the
seismic response of the buried structures are being studied. The
insight gained from this investigation is aimed at improving the
design and safety of the Los Angeles reservoirs and similar
buried water storage structures in seismically active areas.
2 RESEARCH PROGRAM
2.1
Background
In order to comply with new water quality regulations in
California, the Los Angeles Department of Water and Power
(LADWP) is planning to cover or bypass each of its open
reservoirs and replace them with buried reinforced concrete
reservoirs. The proposed buried Headworks Reservoir includes
35 to 40-foot high walls that will be buried and restrained
against rotational movement at the bottom and top by the
reservoir floor and roof. The current state of practice for
evaluating the seismic response of underground structures relies
heavily on simplified procedures or numerical tools that have
not been verified adequately against physical model studies or
case histories, leading to significant uncertainties. Hence, a
series of dynamic centrifuge tests were planned to evaluate
seismic lateral earth pressures on a range of reduced scale
underground structures.
2.2
Experimental Plan
A series of eight centrifuge experiments were planned to
investigate the seismic response of relatively stiff buried
