Proceedings of Indian Geotechnical Conference December 15-17,2011, Kochi (Paper No. F- 379) SEISMIC DESIGN CONSIDERATIONS FOR PILE FOUNDATIONS A. Murali Krishna, Assist Prof, Dept of C E, IIT Guwahati, Guwahati-781039, Assam, India. Email: [email protected]S. Bhattacharya, Sr.Lecturer in Dynamics, Dept.CE, UniversityofBristolBS81TR,UKEmail: [email protected]ABSTRACT: Pile foundations are adopted commonly for various types of multi-storeyed structures when the founding soil is weak and soft; and also in industrial structures, bridges, offshore structures. With increasing infrastructural growth and seismic activities, designing the pile foundations for seismic conditions is of considerable importance for the efficient function of the structures especially, the lifeline structures like bridges etc. Several studies were conducted by various researchers on the seismic analysis and design of the pile foundations and evolved different theories on the same. Codes of practice available in different countries suggested some procedures for seismic design of pile foundations. This paper presents a short discussion on the various theories evolved on seismic pile performance concepts followed by outlines of suggested procedures by selected international and Indian codes on the subject. A soil profile is selected from Assam, Dibrugarh area as an exemplary case to demonstrating the seismic design of pile foundations. From this paper it can be summarised the points that need to be amended to Indian codes of practice to meet the state of the art developments in the subject. INTRODUCTION Following 1995 Kobe earthquake many pile supported structures collapsed which led to extensive research on seismic behaviour and analysis of pile foundations and the supported structures. 2001 Bhuj earthquake is another exemplary for many pile failures and associated damage. Fig. 1 present a typical damage of the building due the failure of pile foundation during 1995 Kobe earthquake [1]. Fig. 2 shows a revealed picture of pile foundation after 20 years of 1964 Niigata Earthquake highlighting the formation of plastic hinges during earthquake loading [2, 3]. Many researchers explored different mechanisms that pile foundations undergo during seismic event especially, liquefaction. Some of the international codes adopted these research contributions and are in the process of continuous updating. In India, billions of money is being spent for new infrastructure constructions involving huge numbers of pile foundations of different types in different locations and for different loading conditions. But the codal provisions are not included the recent state of the art findings. This is the high time to review the codes of practice and incorporate the lessons learnt from the Japan and elsewhere. This paper presents a short discussion on the various theories evolved on seismic pile performance concepts followed by outlines of suggested procedures by selected international and Indian codes on the subject. Critical comments are made on the need of the revisions of the Indian codes of practice (IS 1893, IRC 78 etc.). A simple design case study is also presented in explaining various points to be considered to avoid the dynamic failure. SEISMIC PILE PERFORMANCE: EVOLVED THEORIES Studies on seismic pile behaviour can be broadly divided into two categories: Piles in liquefiable soil; and Piles in non-liquefiable soil. In general, saturated loose to medium dense cohesionless soils subjected to dynamic excitation under undrained condition may liquefy depending on the excitation level and depth of the soil layer with respect to ground level. Fig. 1 Tilting of building due to pile foundation damage during 1995 Kobe earthquake and schematic of its failure [1] Fig. 2 Exemplary earthquake damage of piles [2] 321
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Proceedings of Indian Geotechnical Conference
December 15-17,2011, Kochi (Paper No. F- 379)
SEISMIC DESIGN CONSIDERATIONS FOR PILE FOUNDATIONS
A. Murali Krishna, Assist Prof, Dept of C E, IIT Guwahati, Guwahati-781039, Assam, India. Email: [email protected]
S. Bhattacharya, Sr.Lecturer in Dynamics, Dept.CE, UniversityofBristolBS81TR,UKEmail: [email protected]
ABSTRACT: Pile foundations are adopted commonly for various types of multi-storeyed structures when the founding
soil is weak and soft; and also in industrial structures, bridges, offshore structures. With increasing infrastructural growth
and seismic activities, designing the pile foundations for seismic conditions is of considerable importance for the efficient
function of the structures especially, the lifeline structures like bridges etc. Several studies were conducted by various
researchers on the seismic analysis and design of the pile foundations and evolved different theories on the same. Codes of
practice available in different countries suggested some procedures for seismic design of pile foundations. This paper
presents a short discussion on the various theories evolved on seismic pile performance concepts followed by outlines of
suggested procedures by selected international and Indian codes on the subject. A soil profile is selected from Assam,
Dibrugarh area as an exemplary case to demonstrating the seismic design of pile foundations. From this paper it can be
summarised the points that need to be amended to Indian codes of practice to meet the state of the art developments in the
subject.
INTRODUCTION
Following 1995 Kobe earthquake many pile supported
structures collapsed which led to extensive research on
seismic behaviour and analysis of pile foundations and the
supported structures. 2001 Bhuj earthquake is another
exemplary for many pile failures and associated damage.
Fig. 1 present a typical damage of the building due the
failure of pile foundation during 1995 Kobe earthquake [1].
Fig. 2 shows a revealed picture of pile foundation after 20
years of 1964 Niigata Earthquake highlighting the
formation of plastic hinges during earthquake loading [2,
3]. Many researchers explored different mechanisms that
pile foundations undergo during seismic event especially,
liquefaction. Some of the international codes adopted these
research contributions and are in the process of continuous
updating. In India, billions of money is being spent for new
infrastructure constructions involving huge numbers of pile
foundations of different types in different locations and for
different loading conditions. But the codal provisions are
not included the recent state of the art findings. This is the
high time to review the codes of practice and incorporate
the lessons learnt from the Japan and elsewhere.
This paper presents a short discussion on the various
theories evolved on seismic pile performance concepts
followed by outlines of suggested procedures by selected
international and Indian codes on the subject. Critical
comments are made on the need of the revisions of the
Indian codes of practice (IS 1893, IRC 78 etc.). A simple
design case study is also presented in explaining various
points to be considered to avoid the dynamic failure.
SEISMIC PILE PERFORMANCE: EVOLVED
THEORIES
Studies on seismic pile behaviour can be broadly divided
into two categories: Piles in liquefiable soil; and Piles in
non-liquefiable soil. In general, saturated loose to medium
dense cohesionless soils subjected to dynamic excitation
under undrained condition may liquefy depending on the
excitation level and depth of the soil layer with respect to
ground level.
Fig. 1 Tilting of building due to pile foundation damage
during 1995 Kobe earthquake and schematic of its failure
[1]
Fig. 2 Exemplary earthquake damage of piles [2]
321
A. Murali Krishna & S. Bhattacharya
Different researchers focussed on these two different
categories: For example, [3-7] on piles in liquefiable soil
and [8-10] on piles in non-liquefiable soil. Bhattacharya
and Madabhushi [4] presented a prim review of the research
work on mechanism of pile failures. Major failure
mechanisms/modes can be outlined as: Bending mechanism
due to permanent lateral deformations or lateral spreading,
buckling instability, settlement failure mechanism and
dynamic failure.
Fundamental failure Mechanisms
The fundamental failure mechanism for pile foundations
are: 1. Bending mechanism–I (Inertial interaction due to
superstructure]; 2. Bending mechanism – II (Kinematic
interaction due to wave propagation]; 3. Bending
mechanism – III [Kinematic interaction due to soil flow]; 4.
Buckling failure mechanism in liquefiable soils; 5.