A STUDY OF FOUNDATION SCOUR IN A STUDY OF FOUNDATION SCOUR IN THE EAST COAST OF SRI LANKA THE EAST COAST OF SRI LANKA

DUE TO TSUNAMI 2004DUE TO TSUNAMI 2004

V. SUTHAGARAN, V. KANDEEPAN,V. SUTHAGARAN, V. KANDEEPAN,G. KALATHEEPAN, AND H.N. SENEVIRATNEG. KALATHEEPAN, AND H.N. SENEVIRATNE

DEPARTMENT OF CIVIL ENGINEERINGDEPARTMENT OF CIVIL ENGINEERINGUNIVERSITY OF PERADENIYAUNIVERSITY OF PERADENIYA

SRI LANKASRI LANKA

TSUNAMI 2004TSUNAMI 2004WORST NATURAL DISASTER ON RECORDWORST NATURAL DISASTER ON RECORD

OVER 31,000 DEATHSOVER 31,000 DEATHS

OVER 2 BILLION U.S. DOLLARS DAMAGEOVER 2 BILLION U.S. DOLLARS DAMAGE

NEXT LARGEST NATURAL DISASTER ON RECORD NEXT LARGEST NATURAL DISASTER ON RECORD CAUSED ONLY ABOUT 1000 DEATHSCAUSED ONLY ABOUT 1000 DEATHS

BROUGHT THE REALITY OF NATURAL DISASTERS BROUGHT THE REALITY OF NATURAL DISASTERS TO SRI LANKANSTO SRI LANKANS

IN TERMS OF PER CAPITA LOSS SRI LANKA WAS IN TERMS OF PER CAPITA LOSS SRI LANKA WAS WORST HITWORST HIT

INUNDATION MAP

AFFECTED DISTRICTS

BATTICALOA DISTRICTBATTICALOA DISTRICT

GEOTECHNICAL SUMMARYGEOTECHNICAL SUMMARYMAIN CAUSE OF DAMAGE MAIN CAUSE OF DAMAGE –– SCOURSCOUR

SOME OVERTURNING SOME OVERTURNING -- TILTTILT

SOME SETTLEMENT FAILURESSOME SETTLEMENT FAILURES

SOME DRAWDOWN FAILURESSOME DRAWDOWN FAILURES

NO RECORDS OF OTHER PHENOMENONNO RECORDS OF OTHER PHENOMENON

Scouring Foundation Settlement

Tilting of Foundation Drawdown Failure of Embankment

Overturning of Building

AIM:AIM:To study the scour patterns around the foundation of To study the scour patterns around the foundation of buildings due to tsunami wave action.buildings due to tsunami wave action.

OBJECTIVES:OBJECTIVES:To identify and measure the depth, shape and To identify and measure the depth, shape and position of scour holesposition of scour holes

To analysis the effect of environment, wave action To analysis the effect of environment, wave action and other factors on scouringand other factors on scouring

To study suitable foundation types for low cost To study suitable foundation types for low cost buildings in tsunami areasbuildings in tsunami areas

DEFINITION OF SCOURDEFINITION OF SCOUR

Scour is defined as theScour is defined as the removal of removal of hydrodynamic force of granular bed material in hydrodynamic force of granular bed material in the vicinity of coastal structures.the vicinity of coastal structures.

It occurs whenever the It occurs whenever the hydrodynamic bottom hydrodynamic bottom shear stress is greater than the sediment critical shear stress is greater than the sediment critical shear stress.shear stress.

Scour at vertical wallScour at vertical wall

Sm = Hmax -or- Sm = h

Sm - Maximum depth of scouringHmax - Maximum wave heighth - Pre scour water depth at wall

STUDY AREA

SITE LOCATIONSITE LOCATION

060607 41 24.1 07 41 24.1 081 44 07.5 081 44 07.5 PalamunaiPalamunai

4040All DivisionsAll Divisions

010107 35 02.607 35 02.6081 47 17.6081 47 17.6Chettipalayam northChettipalayam north

151507 43 03.007 43 03.0081 42 58.1081 42 58.1KathankudyKathankudy

181807 43 38.807 43 38.8081 42 39.7081 42 39.7NavaladiNavaladi

Long(N)Long(N)Lat(E)Lat(E)No. of HousesNo. of Houses

CoordinateCoordinateLocationLocation

GEOTECHNICAL ASPECTSGEOTECHNICAL ASPECTS

NAVALADI AREA CONFINED BETWEEN NAVALADI AREA CONFINED BETWEEN LAGOON AND SEALAGOON AND SEA

ALL AREA FLAT WITH DEEP SAND DEPOSITSALL AREA FLAT WITH DEEP SAND DEPOSITS

GROUNDWATER TABLE NOT VERY SHALLOW GROUNDWATER TABLE NOT VERY SHALLOW (< 2 m)(< 2 m)

DATA COLLECTEDDATA COLLECTEDLOCATION OF BUILDINGS LOCATION OF BUILDINGS –– GPS GPS –– DISTANCE FROM DISTANCE FROM SHORELINESHORELINE

TYPE OF FAILURETYPE OF FAILURE

SHAPE, DEPTH, AND WIDTH OF SCOUR HOLESHAPE, DEPTH, AND WIDTH OF SCOUR HOLE

POSITION OF SCOUR HOLE (SEA/LAND SIDE)POSITION OF SCOUR HOLE (SEA/LAND SIDE)

OBSTRUCTIONS TO BUILDINGSOBSTRUCTIONS TO BUILDINGS

TYPE OF SOIL, WATERTABLE POSITIONTYPE OF SOIL, WATERTABLE POSITION

OBSERVATIONSOBSERVATIONS

3.43.410.210.20.70.71.21.24040All DivisionsAll Divisions

3.03.09.49.40.60.61.21.20606PalamunaiPalamunai

2.52.55.55.50.80.80.80.80101Chettipalayam Chettipalayam northnorth

4.24.210.010.00.60.61.01.01515KattankudyKattankudy

3.83.810.210.20.70.71.21.21818NavaladiNavaladi

AverageAverageMaximumMaximumAverageAverageMaximumMaximum

Width (m)Width (m)Depth (m)Depth (m)No. of No. of houseshouses

DivisionDivision

Shape of the foundation layoutShape of the foundation layoutCircular Circular –– or or -- Elliptical Elliptical

Distance from shorelineDistance from shoreline50 to 100 m50 to 100 m

Obstructions to the buildingObstructions to the buildingNot affect to the scouringNot affect to the scouring

FACTORS INFLUENCING SCOURING

Sample 01Sample 01

Recommended designRecommended design

Sample 02Sample 02

Sample 03Sample 03

THANK YOUTHANK YOU