Pile Pile Design Design in in Liquefi Liquefiabl ablee Soils Soils Theory Theory & Code Code Defic Deficien iencie ciess Subhamoy Subham oy Bhatta Bhattacharya charya1, Pradeep KumarDammal Kumar Dammala a2 , Piyush Piyush Moh Mohant anty y 3 2Research 3Scientist,
Scholar, IIT Guwahati & Visiting Scholar, University of Surrey CSIR-CBRI, & Research Scholar, University of Surrey
Presented by 1Prof Subhamo Subhamoy y Bhattac Bhattacharya harya Chair in Geomechanics, University of Surrey (UK) Director: SAGE (Surrey Advanced Geotechnical Engineering) Laboratory Adjunct Professor, Professor, Zhejiang University (China)
Failure Failu re of of Piles Piles in Liqu Liquefied efied Soils
Tubul bridge in 2010 Chile (Maule) earthquake Fire House, Kobe Port, 1995 Kobe Earth Earthquak quake e Kandla Port Tow ower er,, 2001 Bhuj Bhuj Earth Earthquak quake e
In this lecture, we will explore why these pile-supported structure stru cturess collaps collapse e in the way they do
What are common in these structures? •They are heavily loaded vertically (bridges/ high rise building buildings) s) •Supported •Supporte d by by piles piles
BUILDING/BRIDGE BUILDING/BRIDGE
GROUNDLEVEL
SOIL SOIL LAYER1 LAYER1
SOIL SOIL LAYER2
SOIL SOIL LAYER3
PILES
Loading on a pile foundation during seismic liquefaction P gravity
V inertial P gravity
P gravity V inertial
H inertial
H inertial
Loose sand
V inertial P gravity
H inertial
Liquefied sand
Liquefied sand
Stage I
Stage II
Stage III
Stage IV
Before earthquakeon levelground
Shaking starts. Soil yet to liquefy
Soil liquefies. Vertical inertial forces act with gravity. Piles may starts to buckle or settle
On sloping ground Soil liquefies. Lateral spreading may combine with behaviour in stage III
B h a t tac h a r y a et al . (2004 ) - G eo t ec h n i q u e
During Liquefaction Different stages of loading during liquefaction process Skin friction diminishes (Axial capacity reduces) Bearing & settlement failure? Additional Forces induced Inertial loading Kinematic loading DYNAMIC CONSIDERATION
Time taken to reach full Liquefaction and the increase In time period of the system
Lombardi & Bhattacharya (2014)
Earthquake Engineering and
Time period increase example: example: SHOWA SHOWA BRIDGE
Bhattacharya et al. (2014) – Soil Dynamics & Earthquake Engg
(b) Variati Variation on of period with with lique liquefie fied d soil layerthickness
(a) Showa Bridge pile configuration for period estimation estimation 6.5
Dead Weight Weight ,
Deck Level Level
M = 74 74 T
6.0
5.5
Air
6m 5.0
4.5
Water
3m
d o i r ) e s4.0 P ( 3.5
Liquefied soil soil layer
Variable
3.0
thickness,L 2.5
Depth of fixity, Fd = 4D
2.0 0
2
4
6
Liquefie Liquefied d soil layer layer thickness (m)
Non-liquefied
stiff stiff soil
8
10
Failure Failu re Mechanism Mechanism/s /s in Lique Liquefiabl fiable e Soil Soils s What we need to design the piles for What for? ? Bending failure [Lateral load acting on the pile due to inertia and/or lateral spreading] spreading ] – needs a bending bending moment moment calculati calculation. on. Buckling failure [In liquefiable region, the pile is laterally unsupported] – Euler type calculation & embedment depth below liquefiabl liquefiable e soils Combined action of bending and buckling (this needs P-delta analysis) Note the time taken taken to to liquefaction liquefaction and change Dynamic failure [ Note in period of the structure structure]]
Bending Failure
Bending Failure
Pile is considered as laterally loaded beam
– the loads are from Inertia loads from superstructure Drag loads from lateral spreading FLOWING SOIL WaterTable
Depth of liquefaction
Non-liquefied stabilised crust
Liquefied layer
Methods for bending analysis 1.
Subgrade reaction approach
2.
Continuum approach
3.
Stiffness of soil defined
Pile & soil are
by mathematical formulation Preferable for small strain analysis (Reese & Matlock, 1965; Poulos 1971)
modelled in continuum Preferable for complex analysis Expensive (Wu & Fin 1997)
Spring approach Beams on Nonlinear
Winkler Foundation (BNWF) (Hetenyi 1946; Matlock 1970; Reese et al. 1974)
Codal Suggestions - Bending JRA(1996, 2002) –
Only code suggesting guidelines for pile design in Lateral Spreading Soil
–
Pressure distribution was formulated by back analysing Kobe earthquake case studies (1995)
IS 2911 (2010) –
In the zone of soil susceptible to liquefaction
the lateral resistance of the soil shall not be considered
JRA, 2002 30% of overburden pressure
Codal Suggestions (contd.) EUROCODE 8 (2003) –
Liquefiable zone should be neglected for lateral resistance
–
Suggests the location of plastic hinge •
2d from pile cap
•
±2d near any interface between two soil layers with
markedly different shear stiffness
Codal Suggestions (contd.)
NEHRP 2000 (FEMA) – USA Bending mechanism (inertia and lateral spreading) Road Bridge Seismic design Rules (JTGTB02-01-2008)-China Pile should penetrate deep into the dense and stable layer below the liquefied layer/s. (No specifications for any kinds of failure)
Can bending explain observations of pile failures?
Failure in sloping ground and level ground Sloping ground
Level ground
REFERENCE: Criticism of theory based on lateral spreading: See Bhattacharya and Bolton (2004)
Showa Bridge
GA-1
G1-2
G2-3
G3-4
G7-8 G4-5
G5-6
G6-7
G8-9
G9-10
G10-11 G11-A
Collapse of Showa Bridge during 1964 Niigata earthquake
Schematic diagram of the failure of Showa bridge, Takata et al (1965)
Factor of Safety based on Japanese Road Association (2002) code: 1.84
Reference: Bhattacharya et al (2005) in Soils and Foundation
Buckling Failure
Structurally piles are columns or beam? Structural nature of pile –
Long and slender •
(L/D = 25 to 100)
93m
Piles of Jamuna Bridge (117m)
Structural nature of pile Once the surrounding soil liquefies, a pile is laterally unsupported. May undergo buckling if the axial load is excessive.
15 m 0.35m dia (L/D) = 43
No lateral support
Before liquefaction
After liquefaction
Failed piles of building(1964 Niigata Eq)
Bending versus Buckling CURRENT UNDERSTANDING (Bending) Bending of the pile due to the lateral loads
FLOWING SOIL
Buckling
Buckling of the pile due to the axial load
Buckling calculation Critical load (Pcr) (Euler’s buckling equation) Slenderness ratio :Leff /rmin
P cr
2
EI
Leff
2
r min
I A
In API (2000) & Eurocode 8 (1997), buckling is only to be considered when I. Driving in soft soil II. Lateral load is excessive (But not in case of liquefied soil)
Different boundary conditions of pile
Non-liquefied crust
Non-liquefied crust
Normalised pile length in liquefiable zone or likely unsupported zone
Non-liquefied crust Liquefiable soil(L0)
Liquefiable soil(L0)
Dense
Dense
Dense
Case 2
Case 1
Liquefiable soil(L0)
P cr
Case 3
Liquefiable soil(L 0)
Liquefiable soil(L0)
Dense
Dense Dense
Case 4
Case 5
Case 6
2
EI
Leff
2
Back Analysis of 15 case histories –
5 from Niigata (1964), 1 from Chubu (1983), 1 from New Zealand, 8 from Kobe (1995) 4 bridges, 1 hospital, 2 Oil tanks, 1 hotel and 7 buildings SA F E A G A I N ST
R E T E M A I D E L I P D E I S L A M R O N
0.7
BUCKLING
0.6
Good performance Poo r performance L/rmin = 50
0.5 ) n
0.4
r (
0.3
i m
0.2 0.1 0
0
20
40
Effective length (Leff )
NORMALISED PILE LENGTH
Bhattacharya et al (2004) – Geotechnique
60
Plotting for concrete piles from the case histories Short Column, can fail only by crushing
1 f
21
1 cr
1
Euler's Theo ritical curve for M 25 concrete
y
Good performance Poo r performance Yield stress line
16
Rankine's formula
) a P10 M (
cr
P cr
A
2
L eff r min
2
E
5
0 0
50
100
Low shear capacity, Hollow RCC pile
150
200
(Leff /r min)
250
300
350
Verification of Buckling instability Centrifuge test and 1-g test
Bhattacharya (2003)
Chong Suck et al (2006)
Knappett and Madabhushi (2005)
Case Study on Buckling failure FOS against buckling =0.81 (Bhattacharya, 2006)
Fire House, Kobe Port, 1995 Kobe Earthquake
Foundation Details
Combined Bending & Buckling interaction analysis
Numerical modelling technique
S ee D as h , B h a t t ac h a r y a an d B l a k eb o r o u g h (2 00 9)
Note the effect of axial load on instability
y
Bhattacharya et al (2008)
Bending and Buckling •
•
•
Bending failure; M>Mp Buckling failure: P>Pcr Bending and buckling failure: M
Axial load and moment acting on a pile in liquefied soil
Shape of p-y curves for liquefiable and non-liquefiable soils Note the shape of p-y curves for Liquefied soils Axial Load Load (p) LateralLoad
Lateralsoil Springs
t-z Liquefiable layer
p-y Displacement (y)
t-z
Bottom of liquefiable layer
p-y Load (p) t-z Non-liquefiable layer
p-y q-z
Displacement (y)
Lombardi, D., S. R. Dash, S. Bhattacharya , et al (2017) "Construction of simplified design py curves for liquefied soils." Geotechnique (2017) – available online and OPEN ACCESS.
Codal provision for liquefied Soils P-multiplier approach JRA (2002), RTRI (1999), Brandenderg (2005) Defined w.r.t. N1(60) Empirically determined Over-predicts the initial stiffness of liquefied Doesn’t model strain hardening
Note the importance of shape of p-y curves A: Small amplitude vibration B: Large differential ground movement
V H
A Lateral soil spring
A
B
pu
pu y u
y u
pu
pu
y u
y u
pu d a o L
B
pu K y u
Displacement Model (a)
y u Model (b)
700
600
Non-liquefiable p-y curve (h=12 m)
) 500 m / N k ( p , 400 e c n a t s i s 300 e r e l i P
Liquefiable p-y curve (h=12 m)
Non-liquefiable p-y curve (h=8 m) Liquefiable p-y curve (h=8 m)
200
100
Non-liquefiable p-y curve (h=4 m) Liquefiable p-y curve (h=4 m)
0 0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Soil-pile displacement, y (m)
0.08
0.09
0.1
Dynamics [Transient]
How does liquefaction effect dynamics?
Before liquefaction Depth of fixity (Df1)
Significant change in natural period due to Increase in depth of liquefaction (D f1
After liquefaction Depth of fixity(Df2)
How does liquefaction effect dynamics? •
•
•
•
Lombardi & Bhattacharya, 2014
•
Inertial forces reduce as elongation of natural period.
a
result
of
As the frequency of the structure decreases, it may get tune with the predominant frequency of the earthquake - RESONANCE Damping also increases, sometimes reaches a value of 20% Spectral displacement increases leading to increased Bending moment demand Significant bending moment due to P- ∆ effect.
Experimental Validation Shake table tests (Lombardi & Bhattacharya 2016) Two single piles Two group piles Monitored behaviour during Transient (0.2
Lombardi & Bhattacharya (2014) in Earthquake Engineering and Structural Dynamics
Experimental Validation BNWF model (p-y) with Proposed liquefied springs P-multiplier approach Compared with shake table results Inferences from strength (BM) criterion Magnitude of BM underestimated In both the numerical models Location of max BM is predicted Using proposed p-y springs
Comparison of bending moment during transient phase
(Lombardi & Bhattacharya 2016) in Earthquake Engineering and Structural Dynamics
Amplification of Bending Moment in Transient phase
1
M maxtransient M preliq
2
M max transient M post liq
Amplification of Bending Moment in Transient phase
1
M maxtransient M preliq
2
M max transient M post liq
Amplification of Bending Moment in Transient phase
1
M maxtransient M preliq
2
M max transient M post liq
Dynamic failure (contd.) The fundamental vibration period of a building is most often estimated using empirical formulae, which only considers the dimensions, type and material of the superstructure. Eurocode 8, IS 1893-Part 1(2002): = 3/4 (H is the height of the building in m, Ct = 0.085 for moment-resistant space steel frames, 0.075 for moment-resistant space concrete frames
Showa Bridge collapse: 1964 Niigata Earthquake
Showa Bridge
G A-1
G 1-2
G 2-3
G3-4
G 7-8 G 4-5
G 5-6
G6-7
G8-9
G 9-10
G10-11 G 11-A
Middle of the bridge fails
Rokko Bridge, 2011 Tohoku Earthquake
Differential settlement at the midspan of the bridge, Juan Pablo II, Chile, 2010 Earthquake
Some more examples…
Shangli Bridge, 1976 Tangshan Earthquake, China
Increase in Natural Period GA-1
P1
G1-2
G2-3
P2
P3
G8-9
G7-8
G3-4
G4-5
P4
P5
G5-6
G10-11 G11-A
G9-10
G6-7
P6
P7
P8
P9
P 10
P 11
Schematic diagram of the collapse of the bridge along with the deflections of the pile caps (Iwasaki 1986)
Soil liquefaction profile (in grey), Hamada and O'Rourke (1992)
Pile Foundation
What is so special about the middle of the bridge?
Increase in Natural Period
IS 1893-Part 1(2002) Eurocode 8- Part 2
Simplified Stiffness = Natural Period =
Tpre
Tpost
PierNo
(in sec)
(in sec)
P1
1.60
2.91
P2
2.31
3.77
P3
2.47
4.50
P4
2.47
5.08
P5
2.47
5.48
P6
2.47
5.88
P7
2.78
4.13
P8
2.95
3.08
P9
3.11
3.25
P10
2.17
2.14
P11
1.60
1.57
P-∆ effect
Pier
%age
No
increasein
Remarks*
P1
Sd 23.15
Not Collapsed
P2
46.66
Not Collapsed
P3
115.3
Collapsed
P4
153.8
Collapsed
P5
190.7
Collapsed
P6
207.6
Collapsed
P7
56.25
Not Collapsed
1
P8
37.5
Not Collapsed
0
P9
34.07
Not Collapsed
P10
37.61
Not Collapsed
7 Sa-post/Sa-pre=0.10 Sa-post/Sa-pre=0.20 Sa-post/Sa-pre=0.30 Sa-post/Sa-pre=0.40 Sa-post/Sa-pre=0.50 Sa-post/Sa-pre=0.60
6 5 e r p d
S / t
s o p d
S
4 3 2
1
1.5
2
T
/T
2.5
3
A Case Study of Dynamics Change – Saraighat Bridge, Assam
Saraighat Bridge, Assam • • •
Location – Guwahati, Assam (North-eastern city in India) Over Brahmaputra river Constructed during late 1950’s (1958 to 1962) - No Indian seismic code used Liquefaction phenomenon was staged in 1964 – after Nigata & Alaska Earthquakes Well/Caisson foundation Length of the entire bridge = 1.292 Km •
• •
Saraighat Bridge – Seismicity of the region • •
•
Classified as ZONE V – (IS 1893-2002) Experienced two great earthquakes (Mw>8.0) and 20 large earthquakes (7.08.0) since 1897 PGA according to GSHAP = 0.24 to 0.48g
N
Saraighat Bridge – Seismicity of the region • •
Seismic Boundaries: Many active seismic faults surrounding Guwahati Seismologists warn of a greater seismic event in the near future in this region (Kayal et al. 2006)
Saraighat Bridge – Structural Details •
Length of the Bridge = 1.292 km
•
Each span length = 122.2m
•
Mass of each span = 2100 ton
Schematic view of Saraighat Bridge
Saraighat Bridge – Foundation Details • • •
Well/Caisson Foundation with Double D cross section Maximum depth of Foundation (at central pier) = 55m Depth of embedment = 40m (considering average scouring depth)
9.75m
Loose to moderately dense silty sand mixed with pebbles Navg = 25, Ø = 30 0, ɣ=16 kN/m3
25 m
16.3m
PierCap Piers 6m
Dense to very dense clayey silty sand Navg = 36, Ø = 330, ɣ=18 kN/m3
6m
Wellcap
5m
10m
Hard & stiff clayey silt with rock type formation 14m
Well Foundation
N > 100, C = 110 kPa, ɣ=20 kN/m3
Saraighat Bridge – Analysis •
Bridge central pier is considered (as it is most prone to liquefaction)
•
Soil-Well-Pier (SWP) modelled by – 1 Dimensional Spring Dashpot
•
•
Distributed shaft springs (rotational & translational) – Novak et al. (1978)
•
Base translational springs Veletsos & Wei (1971)
Liquefiable strata springs are ignored for model after liquefaction
Loss of lateral support
Saraighat Bridge – Dynamics Change • •
Modal analysis performed Natural time period estimated from numerical model • •
Before liquefaction (springs along the depth) After liquefaction (no springs in liquefiable zone) – (different depths of liquefaction considered)
Time period before liquefaction = 1.12≈1.15 agreeable with measured values by Debnath et al. 2010 Liquefaction doesn’t have significant effect on natural time period of well foundations
•
•
10
140 Saraighat
Showa
c e s , d o i r e P e m i T
120
Saraighat
100
Showa
Showa
8
d o i r e P e m i T n i e g n a h C %
6
Saraighat
4
2
80
SlopeShowa>>>SlopeSaraighat
60 40 20
0
0 0
5
10 Depth of Liq, m
15
20
25
0
5
10 Depth of Liq, m
15
20
25
Conclusions / Recommendations Design against bending failure cannot alone avert the failure of pile foundations Should be designed for all the possible failure mechanisms (especially in
liquefiable zones) Bending Buckling Combined bending & buckling Dynamics (Natural time period & fundamental frequency)
Present codal provisions need a revisit considering above mechanisms Old & important structures (built before liquefaction knowledge) should be
requalified for any effects of liquefaction on their performance Note the shape of p-y curves for liquefied soil
Thank you IGC, DFI & organizers
References (Linked online) Lombardi, D., S. R. Dash, S. Bhattacharya, E. Ibraim, D. Muir Wood, and C. A. Taylor. Construction of simplified
design py curves for liquefied soils. Geotechnique (2017). Lombardi, D., & Bhattacharya, S. (2016). Evaluation of seismic performance of pile‐supported models in liquefiable soils. Earthquake Engineering & Structural Dynamics. Lombardi, D., & Bhattacharya, S. (2014). Modal analysis of pile‐supported structures during seismic liquefaction. Earthquake Engineering & Structural Dynamics, 43(1), 119-138. Bhattacharya S (2003) Pile instability during earthquake liquefaction. PhD thesis, University of Cambridge, UK. Bhattacharya S, Madabhushi SPG. A critical review of methods for pile design in seismically liquefiable soils. Bulletin of Earthquake Engineering 2008; 6(3):407 –446: DOI:10.1007/s10518-008-9068-3 Bhattacharya S, Madabhushi SPG, Bolton MD (2004) An alternative mechanism of pile failure in liquefiable deposits during earthquakes. Geotechnique 54(3):203 –213. Bhattacharya S, Bolton MD, Madabhushi SPG (2005) A reconsideration of the safety of the piled bridge foundations in liquefiable soils.Soils and Foundations 45(4):13 –26. S. Bhattacharya, K. Tokimatsu, K. Goda, R. Sarkar, M. Shadlou, M. Rouholamin, (2014), Collapse of Showa Bridge during 1964 Niigata earthquake: A quantitative reappraisal on the failure mechanisms, Soil Dynamics and Earthquake Engineering, 65, Pages 55 –71. Bhattacharya S, Adhikari S, Alexander NA. Simplified method for unified buckling and dynamic analysis of pile supported structures in seismically liquefiable soils. Soil Dynamics and Earthquake Engineering 2009; 29:1220 – 1235. DOI:10.1016/jsoildyn.2009.01.006. Dash SR, Bhattacharya S, Blakeborough A. Bending-buckling interaction as a failure mechanism of piles in liquefiable soils. Soil Dynamics and Earthquake Engineering 2010; 30:32 –39. Bhattacharya, S., (2006), Safety assessment of existing pile foundations in liquefiable soils. ISETJ2006. Bhattacharya, S., Goda, K., (2013), Probabilistic buckling analysis of axially loaded piles in liquefiable soils.Soil Dyn Eart h q Eng, 45:13 –24. Bhattacharya, S., Blakeborough, A., & Dash, S. (2008, November). Learning from collapse of piles in liquefiable soils. In Proceedings of the Institution of Civil Engineers-Civil Engineering (Vol. 161, No. 6, pp. 54-60). Thomas Telford Ltd.
References (Linked online)
Dash, S. R., Govindaraju, L., & Bhattacharya, S. (2009). A case study of damages of the Kandla Port and Customs Office tower supported on a mat –pile foundation in liquefied soils under the 2001 Bhuj earthquake. Soil dynamics and Earthquake Engineering, 29(2), 333 –346. Hamada, M. and O'Rourke, T.D. (editors) (1992). Case Studies of Liquefaction and Lifeline Performance during Past Earthquakes, Volume 1, Japanese Case Studies, Technical Report NCEER- 92-0001, State University of New York at Buffalo, Buffalo, U.S.A. Reese, L. C., Cox, W. R., Koop, F. D.. Analysis of laterally loaded piles in sand. Offshore Technology in Civil Engineering Hall of Fame Papers from the Early Years, 1974, 95-105. Matlock, H.. Correlations for design of laterally loaded piles in soft clay. Offshore Technology in Civil Engineering’s Hall of Fame Papers from the Early Years, 1970, 77-94. Brandenberg SJ, Boulanger RW, Kutter BL, Chang D. Static pushover analyses of pile groups in liquefied and laterally spreading ground in centrifuge tests. Journal of Geotechnical and Geoenvironmental Engineering 2007; 133(9):1055 –1066. Brandenberg SJ. Behavior of pile foundations in liquefied and laterally spreading ground. Ph.D. Dissertation, Univ. of California at Davis, Davis, Calif. 2005. Brandenberg SJ, Boulanger RW, Kutter BL, Chang D. Behavior of pile foundations in laterally spreading ground during centrifuge tests. Journal of Geotechnical and Geoenvironmental Engineering 2005; 131(11):1378 –1391. Knappett JA, Madabhushi SPG (2005) Modelling of liquefaction-induced instability in pile groups. In: Boulanger RW, Tokimatsu K (eds) ASCE geotechnical special publication no 145 on seismic performance and simulation of pile foundations in liquefied and laterally spreading ground, pp 255 –267 Hetenyi, M. 1946. Beams on elastic foundation. Ann Arbor: The University of Michigan Press. Reese, L.C. & H. Matlock 1956. Nondimensional solutions for laterally loaded piles with soil modulus assumed proportional to depth. Proceedings of the VIII Texas Conference on Soil Mechanics and Foundation Engineering, 41 pp. University of Texas, Austin. Poulos, H.G. 1971. Behavior of laterally loaded piles: Il-pile groups. Journal of the Soil Mechanics and datio 97(SM5)
