Geotechnics of Artesian Flow – Case Study of River Shivganga, Nepal

1. 117 th AUG. 20037 th AUG. 2003
SANJAY GUPTASANJAY GUPTA
RAVI SUNDARAMRAVI SUNDARAM
Cengrs Geotechnica Pvt. Ltd.Cengrs Geotechnica Pvt. Ltd.
New Delhi, INDIANew Delhi, INDIA

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Geotechnology For NaturalGeotechnology For Natural
HazardsHazards
•• Potential Geotechnical Natural Hazards inPotential Geotechnical Natural Hazards in
AsiaAsia
Natural Hazard
Earthquakes Artesian Floods Volcanic

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Artesian HazardArtesian Hazard
•• Localized phenomenonLocalized phenomenon
•• Results inResults in
–– Loss of shear strengthLoss of shear strength -- Ground SubsidenceGround Subsidence
–– Quick ConditionQuick Condition -- LiquefactionLiquefaction
–– Slope Failure in hilly regionsSlope Failure in hilly regions
•• May causeMay cause
–– Damage to structuresDamage to structures
–– Disruption & loss of lifeDisruption & loss of life

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Engineering SolutionsEngineering Solutions
•• Dissipate the excess pressure by suitableDissipate the excess pressure by suitable
mechanismmechanism
•• Ensure stability of the foundation systemEnsure stability of the foundation system
under the influence of the artesianunder the influence of the artesian
pressurepressure

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Vicinity MapVicinity Map
Kohalpur - Mahakali Highway Project, Nepal

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Failure of Chaumala BridgeFailure of Chaumala Bridge
(near Shivganga)(near Shivganga)

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The Bridge …The Bridge …
•• Foundation failureFoundation failure
•• Excessive settlementExcessive settlement
due to artesiandue to artesian
•• Foundation safeFoundation safe
during load testduring load test
•• Artesian pressure lowArtesian pressure low
•• Test misguidingTest misguiding

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The Engineering ChallengeThe Engineering Challenge
To the Geotechnical EngineerTo the Geotechnical Engineer
To the Structural DesignerTo the Structural Designer
To the Construction EngineerTo the Construction Engineer

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The Artesian PhenomenonThe Artesian Phenomenon

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The Artesian PhenomenonThe Artesian Phenomenon

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Artesian FlowArtesian Flow
•• Continuous processContinuous process
•• Seasonal variations inSeasonal variations in
intensityintensity
•• Function of various factorsFunction of various factors
–– Rainfall in catchment area inRainfall in catchment area in
higher reacheshigher reaches
–– Recharge of aquiferRecharge of aquifer
–– Geology & GeomorphologyGeology & Geomorphology
–– Hydrological conditionHydrological condition

13. 7 th AUG. 20037 th AUG. 2003 1313Bridge across River Shivganga
Site Stratigraphy & Artesian HeadsSite Stratigraphy & Artesian Heads
L1 = 7 to 12 m
L2 = 17 to 20 m
L3 = 33 to 34 m

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ObservationsObservations
•• Higher Artesian Pressures Recorded duringHigher Artesian Pressures Recorded during
rains compared to dry seasonrains compared to dry season
•• Increased surficial flow appears toIncreased surficial flow appears to
increase underground flowincrease underground flow
•• Same layer recorded varying artesianSame layer recorded varying artesian
pressures during investigationspressures during investigations
•• Period of InvestigationsPeriod of Investigations -- Important &Important &
needs careful planningneeds careful planning

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Geotechnical ParametersGeotechnical Parameters
•• Artesian pressureArtesian pressure
•• Artesian layers/depthArtesian layers/depth
•• Erosion/scouringErosion/scouring
•• Discharge/migrationDischarge/migration
of finesof fines
Kohalpur-Mahakali Highway,
Nepal

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The ProblemThe Problem
•• Varying nature of the artesian flowVarying nature of the artesian flow
•• Hydrodynamic aquiferHydrodynamic aquifer
–– Underground riverUnderground river –– change in underground flowchange in underground flow
regimeregime
•• Shifting of artesian pointShifting of artesian point
–– not static but of shifting nature, due to flow regime,not static but of shifting nature, due to flow regime,
scourscour
•• Multiple artesian layersMultiple artesian layers
•• Estimation of max. artesian pressureEstimation of max. artesian pressure

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Foundation Design ConceptFoundation Design Concept
•• Foundation DepthFoundation Depth
–– Foundation depth will depend on number ofFoundation depth will depend on number of
artesian layers and depth of each layerartesian layers and depth of each layer
•• For Deep Artesian LayerFor Deep Artesian Layer
–– pile / well foundation with tip in clayey stratapile / well foundation with tip in clayey strata
sufficiently above strata with artesiansufficiently above strata with artesian
pressurepressure

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Foundation Design ConceptFoundation Design Concept
•• For Shallow Artesian LayerFor Shallow Artesian Layer
•• Shallow foundationShallow foundation
–– Shallow well foundation above artesian layerShallow well foundation above artesian layer
–– Bed protection to avoid quick conditionsBed protection to avoid quick conditions
•• Deep foundationDeep foundation
–– Could be critical safety to be ensuredCould be critical safety to be ensured
–– Well to penetrate beyond shallow artesian layerWell to penetrate beyond shallow artesian layer
–– Sufficiently above underlying artesian layerSufficiently above underlying artesian layer
–– Construction during fair weatherConstruction during fair weather
•• to avoid problems due to upper artesian layerto avoid problems due to upper artesian layer

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Design CriteriaDesign Criteria
Check for “bed boiling” quick conditionCheck for “bed boiling” quick condition
Minimum soil cushion thickness aboveMinimum soil cushion thickness above
artesian layerartesian layer
At artesian layer, effective soilAt artesian layer, effective soil
resistance is greater than pressureresistance is greater than pressure
induced from superimposed loadinduced from superimposed load

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Bed BoilingBed Boiling -- Quick ConditionQuick Condition
•• If OVERBURDEN is insufficient to resistIf OVERBURDEN is insufficient to resist
ARTESIAN PRESSURE QUICK CONDITION orARTESIAN PRESSURE QUICK CONDITION or
BED BOILING will occurBED BOILING will occur
•• If Effective Overburden Pressure < 0,If Effective Overburden Pressure < 0,
BED BOILING will occur.BED BOILING will occur.
–– Effective Overburden Pressure at Artesian LevelEffective Overburden Pressure at Artesian Level
where uwhere u == [(RL of bed[(RL of bed –– RL of Strata withRL of Strata with
artesian pressure) + p]artesian pressure) + p] γγww
River Bed Stability under MaximumRiver Bed Stability under Maximum
Scour ConditionScour Condition
tq a u′ = γ −

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Bed BoilingBed Boiling -- Quick ConditionQuick Condition
Ground Level
Max.Scour Level
Strata with Artesian
Pressure

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Bed BoilingBed Boiling -- Quick ConditionQuick Condition
•• Artesian pressure should be dissipated toArtesian pressure should be dissipated to
avoid quick conditionavoid quick condition
–– by relief valves / wellsby relief valves / wells
–– by bed protection in case of shallow artesian layerby bed protection in case of shallow artesian layer

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How Quicksand FormsHow Quicksand Forms
•• Water bubblingWater bubbling
out of ground atout of ground at
some pointsome point
THE ARTESIANTHE ARTESIAN
POINT SHIFTSPOINT SHIFTS
WITH TIMEWITH TIME

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Quick ConditionQuick Condition
Photograph showing Sink hole developed

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Soil Cushion Thickness AboveSoil Cushion Thickness Above
Artesian LevelArtesian Level
Downward PressureDownward Pressure
= Water head inside well
+ pressure due to soil cushion
=
Uplift PressureUplift Pressure
= Maximum expected artesian
pressure at layer below well tip
=
For stability purposeFor stability purpose
HenceHence
Minimum Thickness of Soil cushion
should be equal to
for factor of safety = 1.0.
( )1 2 w th h+ γ + χγ
( )1 wh p+ χ + γ
( ) ( )1 2 w t 1 wh h h p+ γ + χγ ≥ + χ + γ
( )2 wp h ′χ ≥ − γ γ
( )2 wp h ′− γ γ

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Inadequate Cushion ThicknessInadequate Cushion Thickness
Photograph shows quick condition due to puncturing of
soil cushion above artesian layer

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Effective Bearing Capacity atEffective Bearing Capacity at
Artesian LevelArtesian Level
Effective safe gross bearing
capacity of artesian layer
qga =
Total stress at Artesian level
= Superimposed stress
+ effective overburden
pressure
q =
If effective soil resistance at
artesian level exceeds stress
from superimposed loading,
artesian will not yield
q q
1
q N 0.5B N
F
γ γ⎡ ′ ′ ⎤ζ + γ ζ⎣ ⎦
( )z n t 1I q h u⎡ + γ + χ − ⎤⎣ ⎦

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Concluding RemarksConcluding Remarks
•• Planning for geotechnical investigationPlanning for geotechnical investigation
•• A concept for foundation analysisA concept for foundation analysis
–– Bed boiling / quick conditionBed boiling / quick condition
–– Soil cushion thickness above artesian layerSoil cushion thickness above artesian layer
–– Effective bearing capacity at artesian levelEffective bearing capacity at artesian level

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Further ResearchFurther Research
For detailed study for this problemFor detailed study for this problem
•• Long Term Field ObservationsLong Term Field Observations
–– Enormity of hydrodynamic artesian flowEnormity of hydrodynamic artesian flow
•• Prediction of Maximum Artesian pressurePrediction of Maximum Artesian pressure
under life of structureunder life of structure
•• Geotechnical Response of structures underGeotechnical Response of structures under
artesian pressureartesian pressure

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Artesian FlowArtesian Flow
A pipe installed in
Artesian layer has
been providing
water to the
villagers for the
last 30 years
Site at Hamirpur -
Border of H.P. & Punjab

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Thank You!Thank You!