Power Grid on Well Foundation

transcript

Presentation by Sandeep Pattiwar, TANGENT Technical Solutionsto

Power Grid Corporation of India Limited, GurgaonDate: 8th February 2010

Well Foundations in India Introduction

In large parts of India, well foundations are commonly adopted for bridgesadopted for bridgesDesign and construction practices have been progressively streamlined to cater for ever increasing progressively streamlined to cater for ever‐increasing loads and foundation depths With the introduction of large spans the well size also With the introduction of large spans, the well size also increases. For Second Hooghly Bridge, 24 m dia wells have been adopted The deepest well so for have been adopted. The deepest well so for constructed in India is up to 70 m below WL

Well Foundations in India Introduction

Daring efforts are on in different parts of the world to build bridges on a very large scale build bridges on a very large scale Even bridges between continents are in process, America Asia Europe Africa for exampleAmerica‐ Asia, Europe‐Africa for exampleIn India hundreds of thousands of bridges have been constructed during the twentieth century constructed during the twentieth century During the first decade of this century, about R t d t b t B idRs.100,000 cr are expected to be spent on BridgesFoundations cost 50 % or more

Use of Well FoundationIntroduction

Past Experience making it more reliable and dependable by virtue of default choicedependable by virtue of default choiceWell foundations are more suitable for deep water where it is difficult to carry construction equipment where it is difficult to carry construction equipment like River/Creek BridgesIntake Structures offshore as well as riverIntake Structures, offshore as well as riverDeep foundation and suitable for alluvial soil which

i l i t f S dmainly consist of SandyNo special equipment and heavy machineries are

i drequired

Use of Well FoundationIntroduction

Used in India and Indian Sub‐continent onlyW ll F d i i f bl il f d i if i Well Foundation is preferable to pile foundation if it has to resist large horizontal forcesW ll f d i i i bl f d h Well foundation is more suitable for deep water where it is difficult to carry construction equipmentW ll F d i i f d f d i h Well Foundation is meant for deep foundation where the river bed gets scoured and forces need to be t f d t d l ltransferred to deeper level.

Pile Foundation Vs Well Foundation

Item Pile Foundation Well Foundation

Vertical Capacity By Side Friction as well End Bearing

Only End Bearing

Lateral Capacity By Fixity Depth in clay as well Sandy Soil, alternatively Spring Analogy can be used

Net balance of PassiveResistance and Active

Pressure with FOS of 2Pressure with FOS of 2Structure Slender and Flexible Short and Rigid

Construction Difficult under deep water Easy comparativelyConstruction Difficult under deep water Easy comparatively

Construction Equipment Heavy and Costly like Rig and platform

Crane and Grabp

Time Faster Longer

Protection Liner is required up to scour Caisson is required if o ec o e s equ ed up o scoulevel

Ca sso s equ ednecessary for construction requirement

DESIGN ASPECTSDESIGN ASPECTS

Shapes and Sizes

Shape is governed by the requirement of stability during construction and least resistance during service:construction and least resistance during service:Need for effective streamline flowCircular is the most common option availableCircular is the most common option availableD‐Shape well for wider and heavy foundationsRectangular shape is rare unless required for the Rectangular shape is rare unless required for the functionalityCircular diameter is upto 12 m without any diaphragm Circular diameter is upto 12 m without any diaphragm else either diaphragm is provided or extensive study is undertaken for the steining stresses.

Shapes and Sizes

Shape is governed by the requirement of stability during construction and least resistance during service:construction and least resistance during service:

Dredge hole for easy dredging > 2 mD‐Shape well is not to have aspect ratio (length/breadth) 2:1aspect ratio (length/breadth) 2:1

Well Foundation

A Well foundation consist of following components:

Cutting EdgeW ll C bWell CurbBottom PlugSteiningSteiningSand FillingTop PlugTop PlugIntermediate PlugWell CapWell Cap

Input Data

Forces above well foundationHydraulic Parameters like scour depth current Hydraulic Parameters like scour depth, current velocity and DischargeSeismic Zone and Wind PressureSeismic Zone and Wind PressureBore Hole details for assessing depth of soil and rock, if anyyGeo‐technical Investigations including stratification, density, φ and c and weighted mean diameter of bed y gmaterial Bearing Capacity

Special Requirement

Variation of depth of water i.e. HFL and LWLBed Levels and Ground LevelsBed Levels and Ground LevelsWorking Months availabilityFormation LevelFormation LevelAny other feature depending on the location like rock slope type of water and moderate/severe slope, type of water and moderate/severe environment condition Pneumatic Sinking in case of deeper founding level Pneumatic Sinking in case of deeper founding level with boulder strataFloating caisson incase of deep standing waterg p g

Depth of Well Foundation for Soil

Mean scour depth is calculated as per bed material3/1

2 ⎞⎛ 2

34.1 ⎟⎟⎠

⎞⎜⎜⎝

This “mean scour depth” is used to calculate Maximum scour depth to account local scour effect

For Pier foundations : 2 x dsm from HFLFor Abutment foundations: 1.27 x dsm from HFL

Grip Length: The minimum depth of foundation below scour level is 1/3 rd of Maximum Scour Depth

Depth of Well Foundation for Rock

The well foundation shall be taken up to sound rock and rest evenly along the periphery by blasting or and rest evenly along the periphery by blasting or pneumatic sinking, if required.The shear key should be provided inside the rock for a The shear key should be provided inside the rock for a depth of 300 mm in hard rock and 600 mm in soft rockrock.Diameter of shear key must be minimum 1.5 m or 1.5 m to 2 0 m less than dredge holeto 2.0 m less than dredge hole.6 dowel bars of 25 mm diameter with anchored 1.5 m in rock and projected 1 5 m abovein rock and projected 1.5 m above.

Well Steining

Thickness of well steining is governed by following factors:factors:Natural sinking or sinking without excessive kentledgeWithout getting damaged during rectifying excessive Without getting damaged during rectifying excessive tilt and shiftHoop compression for the differential pressure during p p p gconstruction and serviceHoop tension arising out of differential earth pressure gdeveloped during sand blowStructural design at all levels due to external forces

Well Steining

Thickness of well steining is governed by following Thickness of well steining is governed by following factors:The minimum thickness > 500 mmThe minimum thickness > 500 mmThe thickness arrived for self sinking, empirically:

lkdhWhere k is a constant and depends on the type of well

lkdh =

steining In Cement Concrete 0.03

Twin D wells 0.039

d is diameter of well or smaller dimensions in D‐Welll is depth of well below top of well or LWL, which ever p pis higher

Well Steining

Further steining thickness shall be adjusted as per type Further steining thickness shall be adjusted as per type of soil stratum:

Well Steining

Steining thickness can be reduced if the be reduced, if the height of well is more than 30 m However than 30 m. However, the reduced diameter of well should be able to support structure above well foundation.

Well Steining – Structural Design

Plain Concrete WellsV ti l R i f t % f G AVertical Reinforcement = 0.12% of Gross AreaHorizontal Hoop Reinforcement = 0.04% of volume

RC C W llRC Concrete WellsVertical Reinforcement = 0.2% of Gross AreaInner Face, vertical reinforcement = 0.06%Transverse Reinforcement as per column design and h ll b l h % f lshall not be less than 0.04% of volume

Well Steining – Structural Design

Checking of steining stresses at all critical sections and normally these are:normally these are:

Well cap bottom levelAt th l l f h i t i i thi kAt the level of change in steining thicknessBelow scour level where resultant shear is zero

Well steining also shall be checked for ovalisationtmoments

Well Steining – Jack down methodWell Steining Jack down method

l• As per ‐IRC‐78‐2000 Clause‐708.2.3.5If Specialised methiods of sinking such as jackdownmethod are adopted then the steining thickness maybe adjusted according to design and construction

i trequirements.

Check for cohesion‐less soil

IRC 45 recommends checking of well

Side Earth Resistance

Active and Passive Earth Pressure as per Coulomb Active and Passive Earth Pressure as per Coulomb Theory:

In case of c‐φ soil, effect of ‘c’ may be added as per procedure given by Bell:procedure given by Bell:

Bell Correction

Side Earth Resistance – F.O.S.

The Side earth resistance for pier wells is considered below scour levelbelow scour levelThe resistance calculated is ultimate and converted into allowable resistance by dividing FO Sinto allowable resistance by dividing F.O.S.Net pressure of Passive and Active is calculated

FO S i id d f l d bi i i h F.O.S. is considered 2 for load combination without wind or seismicFO S is considered 6 for load combination ith ind F.O.S. is considered 1.6 for load combination with wind or seismic

For cohesionless soil, IRC 45may be used for pier well foundationsfoundationsSide earth resistance may be ignored in case of foundations resting on rockfoundations resting on rockHowever, side resistance of well foundations resting on rock be considered if allowable bearing pressure is less rock be considered if allowable bearing pressure is less than 100 t/m2

Tilt and Shift

In Design of well, tilt of 1 in 80 and shift of 150 mm due to translation both additive in a direction which will to translation both additive in a direction which will cause most severe effects shall be consideredIf the actual tilt and shift exceeds the above limits, ,remedial measures have to be resorted to bring the well within limit. However, if not possible then its effect on bearing pressure, steining stresses shall be examined and if necessary can be sink further down to control the base necessary can be sink further down to control the base pressure.

Cutting Edge

To penetrate easily through the different type of strata cutting edge is provided at the base of well It is cutting edge is provided at the base of well. It is designed to cater resistance which encountered during sinking It shall be anchored properly to well curbsinking. It shall be anchored properly to well curb.Guidelines of IRC 78 stipulate that its weight should not be less than 40 kg/running meternot be less than 40 kg/running meter.When there are partitions, the intermediate cutting edge have been placed 300 mm higher than the outer edge have been placed 300 mm higher than the outer cutting edge to prevent rocking.

Cutting Edge

Cutting Edgeg g

Cutting Edge

Required 40 kg/meter

Well CurbMinimum resistance while being sunk.S h i f f i i h Strong enough to transmit forces from steining to the bottom plug Minimum reinforcement = 72 kg/m3Minimum reinforcement = 72 kg/m3

Internal angle of curb shall be kept in between 30 degree to 37 degree.37 g

Well Curb

Bottom Plug

Is provided to transfer the load from steining to bottom plug and ultimately from bottom plug to bottom plug and ultimately from bottom plug to underneath strata.A suitable sump shall be made below the level of the A suitable sump shall be made below the level of the cutting edge.Before concreting it shall be insured that its inside Before concreting, it shall be insured that its inside faces have been cleared thoroughly.

Bottom Plug

SANDSANDFILLING

Bottom Plug

Well Cap

The bottom of well cap shall be as low as possible taking into account of LWLtaking into account of LWL.Well cap design is as per any rational methodN ll d i i id i l fi i h Normally design is cater to consider partial fixity at the junction to take care large fixity moments.

Filling

Filling if required shall be sand or excavated material free from organic matterfree from organic matter.Incase filling is not done, bottom plug shall be checked for upward thrustchecked for upward thrust.Normally, if vertical pressure is within limit, filling is done upto scour level atleastdone upto scour level atleast.In a high seismic area, filling is avoided above scour l llevel.

Construction of Well Foundations:

Conventional Construction on

Land / Sand Islands

Floating Caissons

k d h dJack down method

P ti Si kiPneumatic Sinking

Conventional Construction on Land / Sand Island Method

Well Sinking – Sand Island Method

GANGA BRIDGE AT PATNA

Floating CaissonsFloating Caissons

Floating CaissongArea for fabrication of steel caisson will be made near the river bank by constructing suitable cofferdam

I i i l lif f l i ill b f b i dInitial lift of steel caisson will be fabricated on a leveled ground in fabrication yardG bbi f il f i hi d d hGrabbing of soil from within and around the caisson will be carried out so as to allow the water to rush in and make the caisson to float Theto rush in and make the caisson to float. The caisson will be held in position with proper guying arrangementarrangement

The caisson will be towed to the desired location and aligned properlyCaisson will be held in position with tethering arrangementConcrete quantity as per design requirements will be poured evenly in the curb portion so that the

i f h i d i hcaisson gets further immersed in the waterNext lift of steel caisson will be built and concrete

i f d i d ill b d i idquantity of designed amount will be poured inside the caisson

This procedure will continue till the cutting edge th i b dcomes near the riverbed

When the caisson is about to get grounded its alignment will be recheckedWater will be poured inside the caisson to ensure its grounding at exact locationWater ballast will be replaced with concrete so that Wate ba ast w be ep aced w t co c ete so t atcaisson gets grounded at its exact locationSteining concreting will be continued further andSteining concreting will be continued further and the well will be taken to its founding level as per normal practicenormal practice

Tethering arrangement

General Details

Caisson Aligned at location

First lift of concrete poured

Shifting of concrete over Bargeg

Concrete placing

Build next lift of Caisson

And place concrete

Checking of alignment with water ballast

Muck removal by grabbing

Sinking in progress

Steining Concreting & sinking

Sinking in progress

Final stage – At founding level

Well Caisson Launching

Caisson Fabrication Yard

Launching of Caisson

Well Caisson Launching

Caisson being towed Caisson being towed to location

Sinking in progress

SECOND HOOGHLY BRIDGE

Enabling works for caisson sinking

JOGIGOPHA BRIDGESlipway for Floating CaissonsSlipway for Floating Caissons

Jogighopa BridgeSlipway for Floating CaissonsSlipway for Floating Caissons

Jogighopa BridgeFloating Gantry for Handling CaissonsFloating Gantry for Handling Caissons

Floating Caisson being g gTowed to Location

Colcrete arrangemenf f d tifor foundation

Jack Down MethodJack Down Method

Well Sinking By Jack Down Method

Pneumatic SinkingPneumatic Sinking

Pneumatic sinkingPneumatic sinking

Pneumatic sinking is resorted to when open sinkingcan not be continued in hard strata and excavation byopen grabbing and chiseling is not possible.When pneumatic sinking is adopted, it is possible top g p , pinspect the well from inside and take the decisionbased on the actual conditions.

Pneumatic Sinking

• In this method airtight cover is fixed on dredge hole and compressed air is pumped in, so that wateris pushed out of well up to cutting edge level.

• Men are sent inside to carryout manual excavation. Muck is removed through shaft withoutreleasing pressure.

. . .Contd.

Arrangement for Pneumatic Sinking

Kali Bridge – Pneumatic Sinking

Limitations

• Pneumatic sinking is very costly and is resorted to• Pneumatic sinking is very costly and is resorted toonly when the well can not be founded safely withopen sinkingopen sinking.

• Men have to work under compressed air pressure of• Men have to work under compressed air, pressure ofwhich depends upon the depth of cutting edge belowthe water levelthe water level.

• Depth up to which pneumatic sinking can be done• Depth up to which pneumatic sinking can be donewithout undue risk to human lives is restricted toabout 30 mabout 30 m.

….contd

Limitations

• Man feels increased pressure on ear drum when insidethe airlock If it is not balanced properly it may resultthe airlock. If it is not balanced properly it may resultin sever pain, bleeding and may cause damage to eardrum.

• Dizziness, double vision, incoherence of speech arequite common and some times man becomesunconscious after coming out of well.

contd. . . contd

Limitations

• Due to the physiological effects on men working insidean air lock effective working hours are generallyan air lock, effective working hours are generallyrestricted to about two hours. This is followed byperiod of gradual decompression and a minimum restperiod of gradual decompression and a minimum restperiod of 5 to 6 hours

CASE STUDYSecond Hooghly Bridge

Second Hooghly Bridge

Second Hooghly Bridgeg y g

Second Hooghly Bridge , CalcuttaTilting Slipway for Floating CaissonTilting Slipway for Floating Caisson

Second Hooghly Bridge , Calcutta

Vidyasagar Setu Culcutta (1992)Vidyasagar Setu, Culcutta (1992)

Sinking a Pylon caisson11

CASE STUDYJogighopa Bridge

CASE STUDYCASE STUDYJogighopa Bridgeg g p g

Brahmaputra Bridge, Jogighopa, 2.28 km

Wells 7 and 13 tilted; more than a year to correctW ll & 8 h d k i li ( ) Wells 17 & 18 on hard rock at steep incline (1:1). 12 x 1500 mm dia anchor piles, provided through steining, extending to 10 m below cutting edge extending to 10 m below cutting edge For well 17 additional 1500 dia, 8 nos, external piles provided integral with the well cap provided, integral with the well cap Two rows of jet grouted piles around periphery of the t i i t i ll steining as curtain wall

WELL CAP ∅ 1.5 m

Brahmaputra Bridge, Jogighopa

3 5 m3.5 m

50 m2.5 m

DRILL PIPE WITH AIR CONTROL VALVES

WORKING PLATFORMRC PLUG

DRILL PIPE STABILIZER

CAISSON STEINING

WORKING PLATFORMCASING

+ 35.00 m

CC PLUG

JET GROUT CURTAIN

AIR - LIFT DRILL PIPESHEAVY DUTY STIFFASSEMBLY

HEAVY DUTY STABILIZER

JET GROUT CURTAIN

∅ 1.5 m PILE

STIFF SPACER PIPE

NON ROTATING DRUMSTABILIZER

- 12.50 m10 m

SECTION

FIG. JOGIGHOPA BR. FOUNDATIONS WIRTH DRILLING RIG

DRILL BIT

Jogighopa Bridge – Caisson Fabrication

JOGIGOPHA BRIDGESli f Fl ti C iSlipway for Floating Caissons

Jogighopa BridgeSlipway for Floating CaissonsSlipway for Floating Caissons

Jogighopa BridgeFloating Gantry for Floating Gantry for Handling Caissons

Jogighopa BridgeFloating Gantry for Handling CaissonsFloating Gantry for Handling Caissons

Jet Grouting

Foundation scheme for wells 17 and 18Foundation scheme for wells 17 and 18Design & construction ofb f d iabove foundations, weregoverned by following mainfactors:factors:(i) Likely scour upto rock

strata.(ii) Uniform support over

steeply sloping strata(iii) Sinking under pneumatic

condition was notfeasible

I i f b f ll iFoundation scheme for wells 17

d 8 In view of above, followingschemewas adopted :

and 18

(i) Sink well upto one metreabove top of rock strata.

(ii) S bili il d ll(ii) Stabilise soil around wellcurb above rock strata byforming grout barrierforming grout barrier.

(iii) Support steining byconstructing six out ofgtwelve 1.5 m diameter RCpiles through 1.65 mdiameter holes kept in welldiameter holes kept in wellsteining, with 10 m anchorlength in rock strata.g

Foundation scheme for wells 17 and 1

(iv) Remove sand in dredge‐holeb bb d l fby grabbing and air‐lifting toclean entire areaincluding that below wellg

curb.(v) Construct concrete bottom

plugplug.(vi) Construct balance six piles

to complete anchoring ofthe foundationthe foundation.

(vii) Construct RC plug over thebottom plug in dry

d f d hp g y

condition after dewatering thewell.

Jogighopa Bridge - Piling

Piling through the Well Foundation

CASE STUDYNepal Bridge

Artesian ConditionsShivganga bridge, Nepal, 8 spans x 32 m

Artesian head encountered at 17 m below GLW ll d i d i h f d i i l b Well redesigned with foundation resting on clay above the artesian layer. Plus bed protection :

U & d & C ff ll Upstream & downstream aprons & Cut‐off walls, Concrete floor

Artesian Conditions - Khara Bridge, NepalWell disappears during sinkingWell disappears during sinking

Artesian BubblesArtesian Bubbles

SAR 6 Y2k

CASE STUDYPassighat Bridge

Passighat Bridge, Arunachal Pradesh Well Foundation

Non availability of formula for scour depth in bouldarystrata; slow sinking in such strata strata; slow sinking in such strata Subsoil with large boulders 2 to 3 m dia; rate of sinking 10 to 20 mm per hour initially p ySinking very difficult due to large size boulders; considerable slow down in overall progress Difficulties in finally deciding the foundation level; decision making body in considerable dilemma ‐R K Dhiman IABSE colloquium 1999 foundations for major bridges

Passighat Bridge, Arunachal Pradesh Well Foundation

Design consultant recommended 50 m deep wellsTh b d i di d h d l i h The bore data indicated hard conglomerate right through the depth up to 50 m except top 10 m C l %Core recovery was close to 90%During execution, impossible to sink the well beyond i h i l h d 10 m with conventional method

Pneumatic sinking used up to 30 m; beyond that it is bl h l ll k d dnot possible physiologically to work under compressed

air, it is not permitted as per code

Well Foundation Delays Passighat Bridge Arunachal Pradesh 703 m longWell Foundation Delays Passighat Bridge Arunachal Pradesh 703 m longPassighat Bridge, Arunachal Pradesh, 703 m longPassighat Bridge, Arunachal Pradesh, 703 m long

Started in 1987 and well sinking continues (2006) sinking continues (2006) Design envisaged, 50 m deep wells. Hard pconglomerate strata with very large boulders did not

it i kipermit sinkingAfter 15 years of struggle including pneumatic Boulder Boulder including pneumatic sinking, the founding level was raised by 22 m.

dredged during i ki

dredged during i kiy sinkingsinking

Pasighat BridgeUnsuitable foundation

designg

B ldBoulder dredged g

during wellwell

sinking

SAR 6 Y2k

Fi 1 PASSIGHAT BRIDGEFig: 1 : PASSIGHAT BRIDGELEGEND

Narmada bridge, Narmada bridge, Constructability Chandod

Well cap 14 m belowChandod

Well cap 14 m belowWell cap 14 m below water

Well cap 14 m below water

SAR 6 Y2kBridge in Nepal

Construction EquipmentsConstruction Equipments

Batching Plant on Shore

4/2/2010

Floating Batching Plant

Concrete cofferdam being towed to location

Cranes for Concreting and Dredging

4/2/2010

Floating arrangement for Batching PlantConcrete pump and placer boom

GANGA BRIDGE AT PATNA

Fl i f ll i kiFloating crane for well sinking

Well sinking by cranes and grabs

Enabling works for caisson sinking

Correction of Tilt and ShiftCorrection of Tilt and Shift

Well sinking ;Tilt correctionConcrete Kentledge blocksKentledge for Well SinkingConcrete Kentledge blocks

W ll i ki Tilt tiWell sinking ;Tilt correctionPlatform for concrete kentledgePlatform for concrete kentledge

Tilt Rectification of WellsTilt Rectification of Wells

Til R ifi i f W llTilt Rectification of Wells

Tilt Rectification of Wells

Tilt Rectification Platform for Well Foundation

4/2/2010

Kandroor Bridge across Sutlej - Badly tilt d ll b i t dtilted well being corrected

SAR 6 Y2k

Kandroor Bridge

SAR 6 Y2k

Select IRC Papers reporting WellSelect IRC Papers reporting Well Foundation Problems

IRC Paper 253 ‐ Rupnarayan Bridge, West Bengal B i C k B id M bi293 ‐ Bassein Creek Bridge, Mumabi

314 ‐ Godavari Bridge, Maharashtra

8 Bh kl B id UP328 ‐ Bhakla Bridge, UP359 ‐ Haldi Bridge, WB400 ‐ Hasdeo Bridge, Champa, MP434 ‐ Tapi Bridge, Idgaon, Maharashtra464 – Kalyani Bridge, WB

Indian Highways, Dec 1982, Arjun Khola Bridge, NepalIndian Highways, Dec 1982, Arjun Khola Bridge, Nepal

Conclusion

The construction of wells have not always been th i t f bl d i t ti h smooth, a variety of problems during construction has

resulted in inordinate delays, increased cost of tifi ti d b d t f ll rectification and even abandonment of wells

With advance methods of geo‐technical investigation, equipments, revised codal specifications and sound engineering practices, we should able to decide the methodology and foundation type in advance.

Comments, queries, suggestions Comments, queries, suggestions q ggwelcomeq ggwelcome

tangent cons@rediffmail.comtangent cons@rediffmail.comg _ @g _ @

Power Grid on Well Foundation

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