a study of foundation scour in the east coast of sri lanka due to ...

A STUDY OF FOUNDATION SCOUR IN
THE EAST COAST OF SRI LANKA
DUE TO TSUNAMI 2004
V. SUTHAGARAN, V. KANDEEPAN,
G. KALATHEEPAN, AND H.N. SENEVIRATNE
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF PERADENIYA
SRI LANKA

TSUNAMI 2004
• WORST NATURAL DISASTER ON RECORD
• OVER 31,000 DEATHS
• OVER 2 BILLION U.S. DOLLARS DAMAGE
• NEXT LARGEST NATURAL DISASTER ON RECORD
CAUSED ONLY ABOUT 1000 DEATHS
• BROUGHT THE REALITY OF NATURAL DISASTERS
TO SRI LANKANS
• IN TERMS OF PER CAPITA LOSS SRI LANKA WAS
WORST HIT

INUNDATION
MAP

AFFECTED
DISTRICTS

BATTICALOA DISTRICT

GEOTECHNICAL SUMMARY
• MAIN CAUSE OF DAMAGE – SCOUR
• SOME OVERTURNING - TILT
• SOME SETTLEMENT FAILURES
• SOME DRAWDOWN FAILURES
• NO RECORDS OF OTHER PHENOMENON

Scouring
Foundation Settlement

Tilting of Foundation
Drawdown Failure of Embankment

Overturning of Building

AIM:
• To study the scour patterns around the foundation of
buildings due to tsunami wave action.
OBJECTIVES:
• To identify and measure the depth, shape and
position of scour holes
• To analysis the effect of environment, wave action
and other factors on scouring
• To study suitable foundation types for low cost
buildings in tsunami areas

DEFINITION OF SCOUR
Scour is defined as the removal of
hydrodynamic force of granular bed material in
the vicinity of coastal structures.
It occurs whenever the hydrodynamic bottom
shear stress is greater than the sediment critical
shear stress.

Scour at vertical wall
S m = H max -or- S m = h
S m - Maximum depth of scouring
H max - Maximum wave height
h - Pre scour water depth at wall

STUDY
AREA

SITE LOCATION
Location
Lat(E)
Coordinate
Long(N)
No. of Houses
Navaladi
081 42 39.7
07 43 38.8
18
Kathankudy
081 42 58.1
07 43 03.0
15
Chettipalayam north
081 47 17.6
07 35 02.6
01
Palamunai
081 44 07.5
07 41 24.1
06
All Divisions
40

GEOTECHNICAL ASPECTS
• NAVALADI AREA CONFINED BETWEEN
LAGOON AND SEA
• ALL AREA FLAT WITH DEEP SAND DEPOSITS
• GROUNDWATER TABLE NOT VERY SHALLOW
(< 2 m)

DATA COLLECTED
• LOCATION OF BUILDINGS – GPS – DISTANCE FROM
SHORELINE
• TYPE OF FAILURE
• SHAPE, DEPTH, AND WIDTH OF SCOUR HOLE
• POSITION OF SCOUR HOLE (SEA/LAND SIDE)
• OBSTRUCTIONS TO BUILDINGS
• TYPE OF SOIL, WATERTABLE POSITION

OBSERVATIONS
OBSERVATIONS
3.4
3.4
10.2
10.2
0.7
0.7
1.2
1.2
40
40
All Divisions
All Divisions
3.0
3.0
9.4
9.4
0.6
0.6
1.2
1.2
06
06
Palamunai
Palamunai
2.5
2.5
5.5
5.5
0.8
0.8
0.8
0.8
01
01
Chettipalayam
Chettipalayam
north
north
4.2
4.2
10.0
10.0
0.6
0.6
1.0
1.0
15
15
Kattankudy
Kattankudy
3.8
3.8
10.2
10.2
0.7
0.7
1.2
1.2
18
18
Navaladi
Navaladi
Average
Average
Maximum
Maximum
Average
Average
Maximum
Maximum
Width (m)
Width (m)
Depth (m)
Depth (m)
No. of
No. of
houses
houses
Division
Division

FACTORS INFLUENCING SCOURING
• Shape of the foundation layout
Circular – or - Elliptical
• Distance from shoreline
50 to 100 m
• Obstructions to the building
Not affect to the scouring

Recommended design
Sample 01

Sample 02

Sample 03

THANK YOU