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 ⎟⎟⎠
⎞⎜⎜⎝
⎛=
sf
bsm k
Dd
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
i i
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:
Side Earth Resistance
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
Side Earth Resistance
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 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
Well Curb
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
Well Sinking – 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
Well Sinking By Jack Down Method
Well Sinking By Jack 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
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 Bridge
Second Hooghly Bridgeg y g
Second Hooghly Bridge , CalcuttaTilting Slipway for Floating CaissonTilting Slipway for Floating Caisson
Second Hooghly Bridge , Calcutta
SECOND HOOGHLY BRIDGE
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
1.5 m
50 m2.5 m
18
DRILL PIPE WITH AIR CONTROL VALVES
WORKING PLATFORMRC PLUG
PLAN
18 m
DRILL PIPE STABILIZER
CAISSON STEINING
WORKING PLATFORMCASING
+ 35.00 m
3 m
CC PLUG
JET GROUT CURTAIN
AIR - LIFT DRILL PIPESHEAVY DUTY STIFFASSEMBLY
HEAVY DUTY STABILIZER
10
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
SECOND HOOGHLY BRIDGE
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 of Wells
Tilt Rectification Platform for Well Foundation
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 [email protected] [email protected] _ @g _ @