1 Dynamic Behavior of Shallow Rectangular Underground Structures in Soft Soils SERIES Concluding Workshop – Joint with US-NEES "Earthquake Engineering Research Infrastructures" Ispra, May 28-30, 2013 TA Project: DRESBUS II Investigation of the Seismic Behaviour of Shallow Rectangular Underground Structures in Soft Soils Using Centrifuge Experiments Tsinidis G., Rovithis E., Pitilakis K., Chazelas J.‐L. TA Project: TUNNELSEIS Investigation of Several Aspects Affecting the Seismic Behaviour of Shallow Rectangular Underground Structures in Soft Soils Tsinidis G., Heron C., Madabhushi S.P.G., Pitilakis K., Stringer M.
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Dynamic Behavior of Shallow Rectangular Underground Structures in Soft Soils
SERIES Concluding Workshop –Joint with US-NEES "Earthquake Engineering Research Infrastructures"
Ispra, May 28-30, 2013
TA Project: DRESBUS IIInvestigation of the Seismic Behaviour of Shallow Rectangular Underground Structures in Soft Soils Using Centrifuge Experiments
Tsinidis G., Rovithis E., Pitilakis K., Chazelas J.‐L.
TA Project: TUNNELSEISInvestigation of Several Aspects Affecting the Seismic Behaviour of Shallow Rectangular Underground Structures in Soft Soils
Tsinidis G., Heron C., Madabhushi S.P.G., Pitilakis K., Stringer M.
2
Scope
• Seismic behavior of shallow rectangular underground structures in soft soils in transversal direction
• Daikai station, Kobe Earthquake, 1995 – 1st embedded structure to be collapsed under seismic shaking
1.72m 2.19m
Column 10
Vs
ds
Seismic performance
4
• Imposed seismic ground deformations rather than inertial forces dominate the structure’s seismic response
• Crucial parameters controlling the soil – structure system behavior: • Soil to structure flexural stiffness (flexibility ratio)• Soil – tunnel interface conditions (rough or smooth interface ‐ separation)
Mmax=683kNm αmax==0.37gαmax=0.62gMmax=444kNm
αmax=0.20g αmax=0.20g
Seismic behavior
5
Important “Open” Issues
• Input motion intensity and characteristics• Transversal seismic behavior and analysis
• Complex deformation modes (i.e. rocking, inward deformations)• Estimation of seismic earth pressures • Estimation of seismic shear stresses along the perimeter• Estimation of impedance functions • Effect of the soil‐structure relative flexibility• Effect of the soil‐structure interface characteristics
• Longitudinal seismic behavior and analysis• Estimation of the asynchronous seismic motion • Estimation of impedance functions
• Several other issues coming from the design and construction point of view• Joints performance, design and construction, in case of segmented underground
structures (e.g. immersed tunnels)
6
Experimental research within SERIES
• A substantial advancement to the above topics may be accomplished by means of well‐constrained experimental data allowing investigation of crucial response parameters
• SERIES TA projects: DRESBUS II ‐ Investigation of the seismic behavior of shallow rectangular underground
structures in soft soils using centrifuge experiments – IFSTTAR, Nantes, FR
TUNNELSEIS ‐ Investigation of several aspects affecting the seismic behavior of shallow rectangular underground structures in soft soils – Schofield Centre, University of
Cambridge, UK
7
TA Project: DRESBUS II
8
Project partners and research team
TA User team
• Manos Rovithis (Researcher, EPPO‐ITSAK) – Lead User
• Grigoris Tsinidis (Civil Engineer MSc, PhD candidate AUTH) • Kyriazis Pitilakis (Professor, AUTH)• Emmanouil Kirtas (Assistant Professor, TEI SERRES)• Dimitris Pitilakis (Assistant Professor, AUTH)• Anastasios Anastasiadis (Assistant Professor, AUTH)• Konstantia Makra (Researcher, EPPO‐ITSAK)• Roberto Paolucci (Professor, POLITECNICO DI MILANO)
Access Provider: IFSTTAR, Nantes, FR
• Jean‐Louis Chazelas (Researcher, IFSTTAR)
9
• Dynamic centrifuge tests on rectangular tunnels embedded in dry and saturated sands, under centrifuge acceleration of 40g
• The program extends the DRESBUS program (METU) posing a series of original issues
• Investigation of salient parameters affecting the tunnel response
• Tunnel flexibility
• Tunnel external face rugosity
• Soil saturation
• Input motion
Dynamic centrifuge tests
10
• IFSTTAR geotechnical centrifuge
• Actidyn QS80 actuator (sine wavelets, real records)
• Large Equivalent Shear Box (ESB) container
Centrifuge facility
11
Sand• Fontainebleau sand NE34 D50 = 0.2 mm, of relative density of about 70%
Tunnel models• Material: 2017 A aluminum alloy
• 2 pairs of models: flexible and rigid tunnels
• 2 levels of rugosity: smooth and rough tunnels
Materials
6mm
6mm 1.5mm
1.5mm50mm
47mmModel 1
50mm
Model 254mm
6mm
5mm
6mm
5mm
flexible rigid
tw / ts 0.25 0.83
Flexibility ratio 10 ‐ 12 0.4 ‐ 0.6
smooth Rough
δ δalum. φ
AR
R
AR
R
AR
R
12
• Automatic pluvation device
• During the construction, the tunnel and all the embedded transducers are positioned in the model
• Full dynamic time history analyses of the coupled soil‐tunnel systems
• Analyses in prototype scale using ABAQUS
• No slip (solid connection) vs. Full slip conditions for the soil‐tunnel interface
Preliminary numerical analysis
38
• The soil mechanical properties are adopted according to the strain levels introduced by the each earthquake
• Gmax estimation and appropriate G‐γ‐D curves?
0
2
4
6
8
10
12
14
16
100 150 200 250 300
Vs(m/s)
Depth(m
)
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1
γ (%)
G/Go
0714
21283542
495663
0.0001 0.001 0.01 0.1 1
γ (%)
D (%
)
Hardin and Drenvich, 1972
39
Tunnel – roof slab
Soil ‐ surface
‐0.3‐0.2‐0.1
00.10.20.3
6 8 10 12 14 16
t (s)
A (g)
• Acceleration time histories – EQL Full slip analysis
Soil ‐ base
Tunnel – invert slab
40
• Tunnel response – EQL No slip analysis
Diagonal extension
-1.5-1
-0.50
0.51
1.5
Dis
plac
emen
t (m
m)
-1.5-1
-0.50
0.51
1.5
Dis
plac
emen
t (m
m)
F4
F2
-1.5
-1
-0.5
0
0.5
1
1.5
Dis
plac
emen
t (m
m)
41
TA Project: TUNNELSEIS
42
Project partners and research team
TA User team
• Kyriazis Pitilakis (Professor, AUTH) – Lead user
• Grigoris Tsinidis (Civil Engineer MSc, PhD candidate AUTH) • Anastasios Anastasiadis (Assistant Professor, AUTH)• Dimitris Pitilakis (Assistant Professor, AUTH)• Roberto Paolucci (Professor, POLITECNICO DI MILANO)
Access Provider: Schofield Centre, UCAM, UK
• Gopal Madabhushi (Professor, UCAM)• Charles Heron (PhD candidate, UCAM)• Mark Stringer (Dr Civil Engineer, UCAM)
43
• Dynamic centrifuge tests on square tunnels embedded in dry sand, under centrifuge acceleration of 50g
• Larger models than DRESBUS II
• Investigation of tunnel flexibility at extreme ends
Dynamic centrifuge tests
44
• Turner beam centrifuge – Schofield Centre UCAM
• SAM actuator (fixed amplitude and frequency inputs or sine sweeps)
• Large Equivalent Shear Box (ESB) container
Centrifuge facility
45
Sand• Hostun HN31 sand , of relative density of about 50% and 90%
Tunnel models• “Rigid” tunnel
• Extruded section – 6063A aluminum alloy• 100 x 100 x 220 (mm) – walls thickness: 2 mm
• “Flexible” tunnel• 33 swg soft alumimum foil – wrapped to form the section • 100 x 100 x 210 (mm) – walls thickness: 0.5 mm
• Flexibility ratios >>1 (flexible tunnels compared to the soil)
Materials
weld
46
• Automatic pluvation device • During the construction, the tunnel and all the embedded transducers positioned in
the model
Models preparation
Trial poors for
calibration
47
• Avoid sand entrance inside the model without affecting the tunnel plane strain behavior
• PVC plates 110 x 110 x 10 (mm)
Tunnel boundaries
48
Models layout – instrumentation scheme
• Accelerometers
• Pressures cells
• Position sensors (POTs)
• LVDTs
• Strain gauges
• Air hammer
g
ACC10
ACC1160 Air hammer 10mm
POT1 POT2LVDT2
AH5
LVDT1
AH4
AH3
AH2
AH1
ACC12
ACC14ACC15 ACC16
ACC13
ACC9 ACC4
ACC5
ACC6
ACC7
ACC8
PC1
PC2
110
100
85Accelerometer Pressure cell LVDT POT Strain gauge
(Dimensions in mm)
ACC1
ACC3
ACC2
Rough*
Rough*
Smooth
Soil‐tunnel interface
250Rigid1
250Flexible2
90
Soil Dr (%)
Rigid
Tunnel
23
Number of flights
Test #
* Stuck sand
SG‐A2
SG‐A1 SG‐B2
SG‐A3CC1
ACC3
ACC2
SG‐B1
Rigid tunnel
Flexible tunnel
SG‐A3SG‐B2
SG‐A4SG‐B3
SG‐B1 SG‐A2
SG‐A1
SG‐B4
Stain gauges set ups
49
• Calibration factors are derived for simple static loading patterns
• ABAQUS static analysis to estimate internal forces at each strain gauge position and to establish Internal force‐Voltage calibration curves – calibration factors
Strain gauges calibration
qq
fixity
fixityfixity
fixity
fixity
box withsand
supportingframe
supportingframe
SG B1Gauge Factor K=1.5
0
1
2
3
0 1 2 3 4M (Nmm/mm)
Volta
ge(V)SG B1
0
1
2
3
0 3 6 9 12Weigh (kg)
Volta
ge(V)
LC1a
LC1b
(a)
(b)
(c)
(d) (e)
50
• Spin up in steps (1g 50g)
• Air hammer testing during swing up and before each shake
• Out of phase response reproduced by the numerical analyses (Visco‐elastic analysis)
0.2 0.25 0.3−0.2
−0.1
0
0.1
0.2
t(s)
A/5
0g
Experimental data
0.2 0.25 0.3−0.2
−0.1
0
0.1
0.2
t(s)
Numerical predictions
ACC15 ACC16
ACC15 ACC16
68
• Tunnel internal forces
• Differences due to the difference between the assumed and the actual in test mechanical properties of the soil, the tunnel and their interface
0 0.15 0.3 0.45 0.6−4
−2
0
2
4
N(N
/mm
)
SG−A1
0 0.15 0.3 0.45 0.6−4
−2
0
2
4SG−A2
0 0.15 0.3 0.45 0.6−4
−2
0
2
4SG−A3
0 0.15 0.3 0.45 0.6−4
−2
0
2
4
t(s)
SG−A4
0 0.15 0.3 0.45 0.6−12
−6
0
6
t(s)
M(N
mm
/mm
)
SG−B1
0 0.15 0.3 0.45 0.6−12
−6
0
6
t(s)
SG−B2
0 0.15 0.3 0.45 0.6−12
−6
0
6
t(s)
SG−B4
Experimental data
Numerical predictionExperimental data
Numerical prediction
69
Conclusions
70
• Maximum soil horizontal accelerations were slightly amplified within the soil deposit, for the dry tests, while for the saturated tests the amplification effects were less important due to the probable higher variation of the soil stiffness
• The side‐walls horizontal deformations developed in a symmetrical manner
• The diagonal extensometers denoted the plane strain behavior of the model sections
• Rigid tunnels were understandably less deformed during shaking compared to the flexible sections
• The effects of the face rugosity and saturation are still under investigation
Conclusions ‐ DRESBUS II
71
• The horizontal acceleration was generally amplified towards the surface, while the presence of the tunnel affected this amplification
• Vertical acceleration‐time histories recorded on the sides of the roof slab indicated a “rocking mode” of vibration for the tunnels
• Residual values were reported after each shake for the earth pressures on the side walls and the dynamic bending moments due to soil yielding and/or densification
• Smaller residuals were observed for the dynamic axial forces due to the soil densification, soil yielding and a small amount of sliding at the interface
Conclusions ‐ TUNNELSEIS
72
• The research leading to the presented results has received funding from the European Community’s Seventh Framework Programme [FP7/2007–2013] for access to the Turner Beam Centrifuge, Cambridge, UK, and the IFSTTAR Centrifuge, Nantes, FR under grant agreement no 227887 [SERIES]
• The technical support received by the Technicians of both the facilities is gratefully acknowledged
• Tsinidis G., Heron C., Pitilakis K., Madabhushi G. (2013) Physical Modeling for the Evaluation of the Seismic Behavior of Square Tunnels. A. Ilki and M.N. Fardis (eds.), Seismic Evaluation and Rehabilitation of Structures, Geotechnical, Geological and Earthquake Engineering 26 (in press)
• Tsinidis G., Pitilakis K., Heron C., Madabhushi G. (2013) Experimental and NumericalInvestigation of the Seismic Behavior of Rectangular Tunnels in Soft Soils. Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2013), 12‐14 June 2013, Kos Island, Greece
• Tsinidis G., Rovithis E., Pitilakis K., Chazelas J.‐L.(2013) Centrifuge Modeling of the Dynamic Response of Shallow Rectangular Culverts in Sand. SERIES concluding Workshop, Ispra, May 28‐30 (near submission)
• Tsinidis G., Heron C., Pitilakis K., Madabhushi G. (2013) Centrifuge Modeling of the Dynamic Behavior of Square Tunnels in Sand. SERIES concluding Workshop, Ispra, May 28‐30 (near submission)
• Tsinidis G., Heron C., Pitilakis K., Madabhushi G. (2013) Experimental Investigation of the Seismic Behavior of Square Tunnels in Sand. (Journal paper –near submission)
• Tsinidis G., Rovithis E., Pitilakis K., Chazelas J.‐L. (2013) Seismic Behavior of Swallow Rectangular Culverts Embedded in Sand (Journal paper – near submission)