The document summarizes a seminar on pile foundations in liquefiable soils. It discusses 1) the performance of pile foundations during earthquakes, including case studies from past earthquakes, 2) modes of pile failure in liquefiable soils, including failure mechanisms for single piles and pile groups, 3) current design practices using methods like force equilibrium analysis and p-y analysis, 4) alternative design concepts focusing on effective pile length and buckling resistance, and 5) conclusions that further research is needed but design practices have improved based on observations of past earthquakes.

1. SEMINAR ON “PILES IN LIQUEFIABLE SOIL”
BY
NABAM BUDH
M.TECH. Geotechnical Engineering, Department Of Civil Engineering,
NERIST.
 Roll No- MT/12/GTE/01
 Session- 2012-13
Guide:- Dr. M.M. Hussian.

2. CONTENTS
 INTRODUCTION
 PERFORMANCE OF PILE FOUNDATIONS DURING
EARTHQUAKE LOADING
 SOIL LIQUEFACTION AND LATERAL SPREADING
 PERFORMANCE OF PILE FOUNDATIOS IN PAST
EARTHQUAKES
 CASE STUDIES
 MODES OF PILE FAILURE IN LIQUEFIABLE SOILS
 FAILURE MECHANISM FOR SINGLE PILES
 FAILURE MECHANISM FOR PILE GROUPS
 CURRENT DESIGN PRACTICES
 ALTERNATIVE DESIGN
 CONCLUSIONS

3. Over-
burden
Rock
What?

4. How? …design elements
Side Resistance, RS
Axial Load in
Compression, Qc
W
Base Resistance, RB
Axial Design Shown
• Axial Loads are
resisted by
• Side resistance, RS
• Base resistance, RB
• Force Equilibrium:
QC + W = RS + RB
• Lateral Loads are
resisted by
• Soil strength
• Bending Stiffness of
Shaft, EI

5. PERFORMANCE OF PILE FOUNDATIONS
DURING EARTHQUAKE LOADING
1. Performances of pile in liquefied soil is
based on the observation of pile damage
during the past earthquakes.
2. The Pile performance in liquefied soil may
be influenced by earthquake parameters,
variations in the soil profile and the pile
geometry.
3. A question naturally arises as to how far
these factors are accounted for in this.

6. PERFORMANCE OF PILE FOUNDATIONS
DURING EARTHQUAKE LOADING

7. PERFORMANCE OF PILE FOUNDATIONS
DURING EARTHQUAKE LOADING

8. SOIL
LIQUEFACTION
AND LATERAL
SPREADING

9. PERFORMANCE OF
PILE
FOUNDATIONS IN
PAST
EARTHQUAKES

10. CASE STUDIES
 SHOWA BRIDGE FAILURE
 NIIGATA FAMILY COURT HOUSE
BUILDING
 THE HARBOUR MASTER’S TOWER AT
KANDALA PORT
 HAITI EARTHQUAKE OF 2010

11. SHOWA
BRIDGE
FAILURE
Place-
Niigata,
Japan.
Year- 1964
Magnitude-
7.5 of
Richter Scale.

12. NIIGATA FAMILY
COURT HOUSE
BUILDING
The concrete piles
were 0.35 m in
diameter and
between 6m and 9m
long
The horizontal
ground
displacement was
about 1.5 m close to
the NFCH building
while the building
itself suffered
horizontal
displacement of
about 1m.

13. THE HARBOUR
MASTER’S
TOWER AT
KANDALA
PORT
Location- Bhuj, Gujrat,
India.
Year- 2001.

14. HAITI
EARTHQUAK
E OF 2010.
1. Year- 12th
January 2010.
2. Magnitude=
7.2
3. Death toll=
2,50, 000

15. HAITI
EARTHQUAK
E OF 2010
1. Failure of
bridge due
to hinging
of pile.
2. Failure
mechanism
of
settlement
of bridge
piles.

16. 1. FAILURE MECHANISM FOR SINGLE PILE
2. FAILURE MECHANISM FOR GROUP PILE
MODES OF PILE FAILURE IN
LIQUEFIABLE SOILS

17. FAILURE
MECHANISM
FOR SINGLE
PILES
FAILURE MECHANISM

18. MODES OF
COLLAPSE
FOR SINGLE
PILES IN
LIQUEFIABLE
SOIL
a). Buckling
Failure
b). Bearing
Failure

19. FAILUR OF
PILE UNDER
COMBINED
LATERAL AND
AXIAL LOADS
IN LATERALLY
SPREADING
SOIL
a). Liquefiable
sand only.
b). With
Modified
Crust Layer.

20. Combined loading and settlement
failure of a pile in laterally
spreading ground

21. Damage to pile by 2m of lateral ground
displacement during 1964 Niigata earthquake
(Yoshida et al.1990)

22. FAILURE MECHANISM
FOR PILE GROUPS

23. Bending
failure of pile
groups in
laterally
spreading
ground
a). Bending
failure alone
b).
Combination
of local and
plastic
hinging

24. DESIGN STEPS-
1 . ESTABLISHMENT OF LIQUEFACTION POTENTIAL
OF A GIVEN SITE BY CPT.
2. OBTAIN MAXIMUM CREDIBLE EARTHQUAKE FROM
THE SEISMIC ZONEATION MAPS OF THE REGION.
3. OBTAIN PEAK GROUND ACCELERATION (AMAX)
THAT CAN OCCUR.
4. CALCULATE THE CYCLIC SHEAR STRESS
CURRENT DESIGN PRACTICES

25. Liquefaction Potential
Charts

26. METHODS
1. The force or limit
equilibrium analysis
and
2. The displacement or
p-y analysis.

27. The Force or
Limit
Equilibrium
Analysis
 Origin- Japan, based case histories of
Kobe Earthquake.
 Where- in liquefied soils undergoing
lateral spreading
 The method involves estimation of
lateral soil pressures on pile and then
evaluating the pile response.
 The non liquefied top layer is assumed
to exert passive pressure on the pile.
 The liquefied layer is assumed to apply
a pressure which is about 30% of the
total overburden pressure.
 The maximum bending moment is
assumed to occur at interface between
the liquefied and non liquefied soil
layer.

28. Displaceme
nt or p-y
Analysis
 This method involves making Winkler
type spring mass model.
 The empirically estimated post
liquefaction free field displacements are
calculated.
 These displacements are assumed to
vary linearly (Finn and Thavaraj, 2001).
 Degraded p-y curves may be used for
this kind of analysis.
 In the Japanese practice the springs are
assumed to be linearly elastic-plastic
and can be determined from the elastic
modulus of soil using semi-empirical
formulas (Finn and Fujita, 2004).
 Reduction in spring stiffness is
recommended by JRA (1996) to account
for the effect of liquefaction.

29. Recommendations to Practice
 1. Codes of practice need to include a criterion to prevent
buckling of slender piles in liquefiable soils. The designer
should first estimate the equivalent length for Euler’s
buckling, by considering any restraints offered by the pile cap,
or the zone of embedment beneath the liquefiable soil layer.
It is then necessary to select a pile section having a margin of
factor of safety against buckling under the worst credible
loads.
 2. Designers should specify fewer, large modulus piles, in
order to avoid problems with buckling due to liquefaction.
 3. Cellular foundations of contiguous, interlocked sections
should also be effective

30. ALTERNATIVE DESIGN
 The study of the case histories seems to show a
dependence of pile performance on buckling
parameters.
 As short columns fail in crushing and long columns
in buckling.
 The analysis suggests that pile failure in liquefied
soils is similar in some ways to the failure of long
columns in air.
 The lateral support offered to the pile by the soil
prior to the earthquake is removed during
liquefaction.

31. Concept of
Effective
Length of Pile.
 The parameters in the analysis are
 1. Leff = Effective length of the pile in the
liquefiable region.
 2. rmin = minimum radius of gyration of the
pile.
 3. Slenderness ratio of the pile in liquefiable
region, Leff/rmin.
 4. Allowable load on the pile, P, based on
conventional design procedures, with no
allowance for liquefaction.
 5. Euler’s elastic critical load of the pile (Pcr)
calculated from the well-known buckling
formula as,
 6. Axial stress in the pile is calculated by
dividing P by the cross-sectional area of the
pile, A.

32. HYPOTHESIS
ARISING FROM
THE STUDY OF
CASE
HISTORIES
a). Before earthquake in
level ground.
b). Shaking Starts, soil
yet to liquefy. Pile
acting as a beam.
c). Soil has liquefied.
Inertia forces may act.
Pile acts as a column,
and may buckle.
d). In sloping ground,
lateral spreading may
start.

33. Effect of
Liquefaction
on Bending
Moment.
1. The Bending
moment of pile
due to
earthquake will
be 2.8 times
that of static
loading.
2. Needs higher
factor of safety
for piles in
liquefiable soil.

34. CONCLUSION!
1. The design of pile foundations in liquefying soil
= understanding of soil liquefaction+ behaviour
of soils following liquefaction + the soil-pile
interaction.
2. The practice of pile design in liquefying soil has
progressed considerably in the last decade
based on observations during the past
earthquakes and experimental studies on
centrifuge and large shake table.
3. However, there are several parameters and
questions which need to be examined further in
detail.

35. Thank You for
Your
Attention!!