FOR BRIDGES G S YADAV Professor Bridge 2 BASIC PARAMETERS Design discharge Design discharge for foundations and protection works Depth of scour Maximum depth of scour Depth of foundation ID: 807498
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Slide1
DEEP FOUNDATIONS
(PILE FOUNDATION)
FOR BRIDGES
G S YADAV
Professor
Bridge
2
Slide2BASIC PARAMETERS
Design discharge
Design discharge for foundations and protection works
Depth of scour
Maximum depth of scour
Depth of foundation
(
1.33 times the maximum depth of scour )
Slide3DESIGN DICHARGE
Five Methods :
From stream flow records( yearly peak discharges) available for the desired recurrence interval or more
Statistical analysis
Unit hydrograph drawn on basis of limited observations of rainfall and discharge
Synthetic unit hydrograph
From stage discharge relationships established from gauging of the stream
Slide4DESIGN DISCHARGE FOR FOUNDATION
Design discharge for foundations , protection works and training works except free board , shall be shall be computed by increasing Q as below
Catchment Area(
Sqkm
)
Percentage Increase
Upto
500
30%
500
upto
5,000
30% to 20%
5000 to 25,000
20%
to 10%
More than 25,000
Less than 10% ( at the discretion of chief engineer)
Slide5NORMAL DEPTH
OF
SCOUR (D)
In case of natural channels flowing in alluvial beds where width of waterway provided is not less than
Lacey’s
regime width
D = 0.473 (
Q
f
/ f)
1/3
Where
D is scour depth in meters
Q
f
is design discharge for foundation in cusecs
f is
L
acey’s
silt
factor
(
f = 1.76 √m
)
m is weighted mean diameter of the bed material
particles
in mm
Slide6NORMAL DEPTH
OF SCOUR (D)
If width of waterway provided is less than
Lacey’s
regime width for Q ( not
Q
f
) or where it is narrow and deep as in incised rivers and has sandy bed , the normal depth of scour is given by
1/3
Where
q
f is the discharge intensity in cumec per meter width
Slide7MAXIMUM DEPTH OF SCOUR
Normal depth of scour D is increased to obtain maximum depth of scour for design of foundations, protection works and training works :
Nature of river/ location
Depth of scour
In a straight reach
1.25D
At the moderate bend conditions e.g.
along apron of guide bund
1.5D
At a
s
evere bend1.75DAt a right angle bend or nose of pier2.0DIn severe swirls e.g. against mole head of a guide bund
2.5D to 2.75D
Slide8‘D’
in CLAYEY BEDS
In clayey beds, wherever possible , maximum depth of scour shall be assessed from actual observations at site
Slide9CLASSIFICATION OF PILES
BROAD CALSSIFICATION
DRIVEN (DISPLACEMENT PILES)
BORED (REPLACEMENT PILE)
ON THE BASIS OF MATERIAL
TIMBER
STEEL
PCC
RCC
PSC
COMPOSITE
Slide10CLASSIFICATION OF PILES
METHOD OF CONSTRUCTION
DRIVEN PRECAST PILES
DRIVEN CAST IN SITU PILES
BORED PRECAST PILES
BORED CAST IN SITU
PILES
MODE OF LOAD
TRANSMISSION
END BEARING PILES
FRICTION PILES
FRICTION CUM END BEARING PILES
Slide11CLASSIFICATION OF PILES
SECTIONAL AREA
CIRCULAR
SQUARE
TUBULAR
OCTAGONAL
H-SECTION
SIZE
MICRO (MINI) PILES (<150 mm)
SMALL DIAMETER PILE (>150 mm < 600 mm)
LARGE DIAMETER PILE (>600 mm)
Slide12CLASSIFICATION OF PILES
INCLINATION
VERTICAL PILES
RAKER (BATTER PILES)
Slide13END BEARING PILE
Slide14FRICTION PILES
Slide15Slide16SELECTION OF TYPE OF PILE
Availability of Space : Driven Piles require large areas and head room since it needs larger and heavier driving rigs
Proximity to Structures : driving cause vibrations in ground which may cause damage to nearby structures
Reliability : Precast driven piles ensure good quality of material, uniform section of piles
Compaction of cohesion less soils affected if driven piles are used
Cast in situ piles can be formed to any desired length and no cutting of pile or addition to length required
Slide17SOCKETTING IN ROCK
FOR THE END BEARING PILES
SOUND RELATIVELY HOMOGENOUS ROCK INCLUDING GRANITE AND GNEISS --
1
TO 2D
MODERATELY WEATHERED CLOSELY FORMED INCLUDING SCHIST & SLATE ----
2 TO 3D
SOFT ROCK ---
3
TO 4D
Slide18SPACING OF PILES
FOR END BEARING PILES
GOVERNED BY
COSISTENCY
OF BEARING STRATA
NOT LESS THAN
2.5 D
FOR FRICTION PILES
SUFFICIENTLY APART TO AVOID OVERLAPPING ZONES
NOT LESS THAN
3
DMAX SPACING 4 D
Slide19INSTALLATION OF PILEs
( BORED CAST in SITU)
Pile installation in stiff soil strata not requiring side stabilisation :
Wide range of piling rigs are now available. Type of rig to be used depends upon type of soil strata and depth of drilling
Power driven rotary augur drills are suitable for installing piles in clay soils
Piles can be installed from 300 mm
dia
to over 5000 mm
dia
and depths
upto
100 m
Slide20INSTALLATION OF PILEs
( BORED CAST in SITU)
Pile installation in soil strata requiring side stabilisation :
One option could be to drive MS casing
upto
full depth.
Mud circulation method
Continuous Flight Augers method
Slide21TREMIE CONCRETING
Slide22LOAD CARRYING CAPACITY OF PILE
Ultimate load carrying capacity of a Pile may be assessed by :
(
i
)
Dynamic pile formula, using data obtained during driving of piles, or by
(ii) Static formula on the basis of soil test results, or by
(iii) Load Test ……only after 4 weeks of installation of pile
For Non cohesive soils
Hiley’s
Formula is more reliable than other formulae ( Appendix B of IS 2911
pt 1/sec1)Hiley’s Formula not reliable in cohesive soilsWhere scour is anticipated , resistance due to skin friction will be available only below scour level
Slide23LOAD CARRYING CAPACITY OF PILE
When pile is installed through compressive fill or sensitive clay into underlying hard stratum, a downward drag down force is generated in the fill. This must be added to the load
The drag force can be roughly estimated as cohesion of the remolded clay multiplied by the surface area of pile shaft
Slide24FACTORS INFLUENCING PILE CAPACITY
SURROUNDING SOIL
INSTALLATION TECHNIQUE
SPACING OF PILES
SYMMETRY OF THE GROUP
LOCATION OF PILE CAP
DRAINAGE
CONDITIONS IN SOIL
Slide25(
Appendix B IS2911pt1/sec2
)
Slide26Slide27Slide28(Appendix
B
IS2911pt1/sec2)
Slide29Slide30BEARING CAPACITY OF A PILE GROUP
MAY BE
EQUAL TO THE
BC OF SINGLE PILE X NO. OF PILES
LESS/MORE
THAN THE ABOVE
FRICTION PILES, CAST OR DRIVEN INTO PROGRESSIVELY STIFFER MATERIALS & END BEARING PILES – EQUAL
FRICTION PILES INSTALLED IN SOFT AND CLAYEY SOILS – LESS
DRIVEN PILES IN LOOSE SANDY SOILS – MORE DUE TO EFFECT OF COMPACTION
Slide31BEARING CAPACITY OF A PILE
GROUP
(para 2.6 of well& pile foundation code)
STRATA
TYPE OF PILE
BC PF PILE GROUP
1. DENSE SAND NOT UNDERLAIN BY WEAK DEPOSITS
DRIVEN
NO. OF PILES X
SPC*
2. LOOSE SANDY
SOILS½ (NO. OF PILES X SPC*)3. SAND NOT UNDERLAIN BY WEAK DEPOSITSBORED⅔ (NO. OF PILES X SPC*)
*SPC
– SINGLE PILE CAPACITY
Slide32PERMISIBLE TOLERANCE FOR PILES
ALIGNMENT CONTROL
VERTICAL PILES – DEVIATION OF 1.5%
RAKER PILES – DEVIATION OF 4%
SHIFT
FOR PILES LESS THAN OR EQUAL TO 600 MM DIA
NOT MORE THAN 75 MM OR D/4 WHICHEVER IS LESS
FOR MORE THAN 600 MM. DIA. PILES
75 MM OR D/10 WHICHEVER IS MORE
EXCESS DEVIATION BEYOND DESIGN LIMITS –PILE TO BE REPLACED OR SUPPLEMENTED BY ADDITIONAL PILES
Slide33PILE LOAD
TEST
Two types of tests for each type of loading (
ie
vertical, lateral, pullout )
Initial test, &
Routine test
Slide34PILE LOAD TESTING
(IS-2911 PART-IV)
Initial
Test
For small size projects ( total piles less than 1000) , a minimum of two tests.
For large projects ( piles more than 1000), a minimum of two tests for first 1000 piles and additional one test for every additional 1000 piles and part thereof.
Initial test piles should be installed by the same technique, same type of equipment as that proposed for working piles.
Purpose
To check safe load calculated by static or dynamic formulae
Arrive at safe
load
Slide35PILE LOAD TESTING
(IS-2911 PART-IV)
Routine Test
On 0.5
percent of
total number piles subject to a minimum one test,
can be increased to 2% depending
on nature of strata.
Purpose
It is carried out on a working pile with a view to check whether pile is capable of taking the working load assigned to it
Detection of any unusual performance contrary to the finding of initial test.
Workmanship
Slide36PILE LOAD TESTING METHODS
Maintained Load Method
: applicable for both initial and routine test
Cyclic Method
: this method is used in case of initial test to find out separately skin friction and point bearing load on single piles
CRP Method
: this method is used for initial test only
Slide37MAINTAINED LOAD METHOD
Test should be carried out by applying a series of vertical downward incremental load, each increment being about 20 percent of safe estimated load on pile
Each stage of loading shall be maintained till the rate of movement of the pile top is not more than 0.2mm/h or until 2h have elapsed, whichever is earlier subject to a minimum of 1 h
The test load is maintained for 24 hours
Slide38MAINTAINED LOAD METHOD
Vertical loading on single pile shall be continued till one of the following takes place :
(a)
In case of Initial Load Test:
Applied load reaches 2.5 times the safe estimated load; or
Max settlement of pile exceeds a value of 10 percent of pile diameter in case of uniform
dia
piles and 7.5 percent in case of bulb
dia
of under-reamed piles.
Slide39MAINTAINED LOAD METHOD
In case of routine load test :
Applied load reaches 1.5 times the working load ; or
Max settlement of pile exceeds a value of
12 mm for piles
dia
up to and including 600mm and 18 mm or maximum of 2 percent of pile
dia
whichever is less for piles of
dia
more than 600 mm.
Slide40MAINTAINED LOAD METHOD
Vertical loading on
group of piles
shall be continued till one of the following takes place
:
(a)
In case of initial load test:
Applied load reaches 2.5 times the safe estimated load ;or
Maximum settlement of pile exceeds a value of 40 mm
(b) In case of routine load test :
Applied load reaches the working load
Maximum settlement of pile exceeds a value of 25 mm
Slide41SAFE LOAD-INITIAL
TEST
THE SAFE LOAD ON A SINGLE PILE WILL BE LEAST OF THE
FOLLOWING
(A) FOR PILES UPTO 600 MM DIA :
Two third of the final load at which total displacement attains a value of 12 mm
50 % of the final load at which the total
displacemnt
equals 10 % of the dia. Of pile for uniform
dia
piles and 7.5 percent of bulb
dia for under-reamed piles.
Slide42SAFE LOAD-INITIAL TEST
(B)
FOR PILES UPTO 600 MM DIA
:
Two-thirds of the final load at which the
totakl
displacement attains a value of 18mm or maximum of 2 percent pile diameter whichever is less.
50 % of the final load at which the total
displacemnt
equals 10 % of the dia. Of pile for uniform
dia
piles and 7.5 percent of bulb dia for under-reamed piles.
Slide43SAFE LOAD – INITIAL TEST
THE SAFE LOAD FOR GROUP OF PILES
FINAL LOAD AT WHICH TOTAL DISPLACEMENT IS 25 MM
TWO THIRD OF FINAL LOAD AT WHICH DISPLACEMENT IS 40 MM
Slide44Selection of piles for Routine Test :
Abnormal variation in concrete consumption
Sudden drop in concrete level during construction of pile
Problems encountered during boring and
tremie
operation
Significant variation in depth of pile with respect to other adjoin piles and boring record
Slide45The
routine test
shall be carried out for a test load of at least
1.5 times the working load
; the maximum settlement at the load being
not greater than 12 mm for piles up to 600 mm
dia
and
18 mm or 2 percent of pile
dia
whichlever less for piles of dia more than 600mm
Slide46OVERLOADING OF PILES
10% of the pile capacity may be allowed on each pile
Max overloading on a group shall be restricted to 40% of the allowable load on a single pile
Shall not be allowed at initial design stage
Slide47LOAD TEST – ROUTINE TEST
TEST LOAD WILL BE ATLEAST 1.5 TIMES THE WORKING LOAD
MAX. SETTLEMENT SHOULD NOT > 12 MM
FOR GROUP OF PILES MAX. SETTLEMENT SHOULD NOT > 25 MM
Slide48STATIC LOAD
TEST ( Maintained Load Method)
Slide49PILE LOAD TEST
(
KENTELEDGE ARRANGEMENT
)
Slide50PILE LOAD TEST
(
WITH ANCHOR PILES)
Slide51DEFECTS IN CAST IN SITU PILES
HONEY COMBING DUE TO INADEQUATE VIBRATIONS
SEGREGATION DUE TO IMPROPER CONCRETE PLACEMENT METHODS
WASHOUT OF CEMENT DUE TO GROUNDWATER FLOW
CRACKS IN PILE SHAFT DUE TO SHRINKAGE
INCLUSION OF FOREIGN MATERIAL
NECKING DUE TO COLLAPSE OF SIDE WALLS DURING WITHDRAWAL OF TEMPORARY CASING
Slide52NECKING IN PILE
Slide53NECKING IN PILE
Slide54DESIGN OF PILES
Slide55RELEVENT STANDARDS
Manual on the Design and Construction of well and pile Foundations issued by RDSO
IS 2911- Part I
Section I – Driven cast in situ piles
Section II- Bored cast in situ piles
Section III- Driven precast concrete piles
IS 2911- Part IV- Load test
Slide56RELEVENT STANDARDS
Concrete Bridge code- For structural design
IRC- 78- For Road bridge foundations, can be referred for guidance
Slide57STEPS OF DESIGN
From soil data, depth of scour – fix length of pile
Based on thumb rules, fix dia of pile
Calculate load carrying capacity of single pile using static formulae
Do rough design for selected group of piles. Spacing to be based on thumb rules
Check design for load carrying capacity, settlement, depth etc.
Revise design if required
Conduct load test to confirm capacity of pile
Slide58THANK YOU
Slide59IMP. CODAL PROVISIONS
DIA. OF PILE
Bridge Manual- > normally 1 m
IRC-78
Bored piles on land- min. 1 m
Bored pile in river bridge- min. 1.2 m
IS 2911- Part I, Section 2
Provisions are for max. dia of 2.5 m
For Railway bridges dia. Of 1 m to 1.5 m be normally adopted
Slide60IMP. CODAL PROVISIONS
SPACING OF PILE
IRC-78
Friction- min. 3 D
End bearing- Can be reduced to clear distance= D that is c/c 2D
IS 2911- Part I, Section 2
End bearing- hard soil- Min. 2.5 D
End bearing- hard rock- Min. 2.0 D
Friction- Min 3.0 D
RDSO Manual
Friction – min. 3 D
End bearing- Min. 2.5 DMax. 4 DFor Railway bridges spacing of 2.5 D to 3.5D be normally adopted
Slide61IMP. CODAL PROVISIONS
GROUP BEHAVIOR
IRC-78
End bearing- If spacing > 2.5 D, no reduction
Friction- If spacing > 3 D, no reduction
Check for block failure
Settlement of group/single pile given for different width of group/pile dia
IS 2911- Part I, Section 2
Bored piles- end bearing- No reduction
Other cases – descriptive guidelines given
RDSO Manual
Dense sand not underlying by weak soil – driven pile – No reductionLoose sand soil – 50% reductionSand not underlying by weak soil – bored- reduction 33%
Slide62IMP. CODAL PROVISIONS
PILE CAP
IRC-78
Min. thickness 0.6 m or 1.5 times dia of pile, whichever is more
max offset of 150 mm beyond outer face
Pile to project 50 mm into pile cap
IS 2911- Part I, Section 2
Offset of 100-150 mm beyond outer face
Pile to project 50 mm into pile cap
Should be rigid enough
Can be designed by taking dispersion at 45 degrees both from substructure and pile upto centre line
RDSO ManualNIL
Slide63IMP. CODAL PROVISIONS
CONCRETE AND STEEL
IRC-78
M 35, Min. cement 400 kg/m3, Max. W/C 0.4, slump 50mm (150-200 for tremie)
Min. long reinforcement 0.4%, links min. 8 mm @ 150 mm c/c.
Min cover 75 mm.
IS 2911- Part I, Section 2
M 20, Min. cement 400 kg/m3, 10% extra cement when under water, slump 100- 180 mm (150-180 for tremie)
Min. long reinforcement 0.4%, Min. spacing 100mm, links min 6 mm @ 150 mm c/c.
Min cover 40 mm.
RDSO Manual
NILCBC to be followed based on environment condition
Slide64IMP. CODAL PROVISIONS
FOS
IRC-78
2.5 if derived from static formulae for soil. 5 for end bearing on rock and 10 for socket resistance.
IS 2911- Part I, Section 2
Appendix given for calculating strength with static formulae
RDSO Manual
3 if derived from static formulae.
2 if derived from load test
Slide65LAYOUT
Accuracy of prime importance
Should always be cross checked by at least two independent surveys
Permanent theodolite stations with the base line on the bank will be established to mark reference points
Slide66CAISSONS
In case where the velocity of water in the river is high making it difficult to construct either an island or cofferdam to construct a well, caisson type construction has been used.
The caisson is pre cast at the shore with the bottom which is generally provided with openings which are plugged, and toed to the required position by tugs and then plugs are removed to permit the caisson to reach the bottom of the ocean bed.
Sinking can also be by concreting in pockets
Slide67Example of caisson foundation in India are -
Ganga bridge at Mokameh,
Brahmaputra bridge in Assam
Mahanadi Bridge at Cuttack
CAISSONS
Slide68Well v/s Pile
Wells have a large cross sectional area and hence more bearing capacity of soil.
q=5.4 N
2
B
+ 16(100+N
2
)D
Well are hallow and most of the material is at periphery. This provides a large section modulus.
Useful in controlling deflection against high horizontal force
it is possible to sink a well through soil having boulders, logs of wood, whereas Piles can not be driven
Slide69In case of wells, it is possible to visually examine the strata through which sinking is done and material on which it is finally resting, hence the bearing capacity of a well is certain. On other hand bearing capacity of pile is generally uncertain
Concreting in the staining of wells is done under dry conditions and the quality of concrete is much better than in case of cast in situ piles.
Well v/s Pile
Slide70Size of well foundation cannot be reduced indefinitely and hence it uneconomical to use well foundation for very small loads, pile foundations are more suitable.
Well v/s Pile
Slide71THANK YOU