2. PROJECT BREIFING
This bridge forms a part of a bye-pass project near Ropar
The project is undertaken by B&R division of PWD.
Total cost of the bridge over Sutlej is 63 crs.
The contract is given to the company on the lump sum basis.
Length 982 m
Lanes 4 lane
Spans 28
Length of span 36.5 m ( middle 23 spans)
24 m (end spans)
Formation level 273.5 m
High flood level 264.2 m
3. Alignment
•Alignment of the
bridge passes through :
New I.I.T. Road
Sutlej river
Nwansheher highway
•Alignment crosses river
at an angle therefore it
is a Skew alignment
4. Height of Bridge
Bridge is high level bridge i.e. formation
level is above H.F.L.
Height if bridge is determined by
examining the clearance of bridge over
highway
As per IRC 5:1998
Min. clearance needed = 5 m
Road level =267
Width of beam and slab =1.7 m
Req. formation level= 273.7 m
Actual formation level=274.7 m
5. Extent of exploration
The exploration shall cover the entire length of the bridge and also
extend at either side for a distance of about twice the depth below bed
of the last main foundations i.e. if depth of foundation below bed is
24mts. then exploration will be done up to 48mts away from ends.
The depth of exploration should be at least 1 ½ times the minimum
width of the foundation below the proposed foundation level in case of
open foundations and deep well foundation
Where such investigation end in any unsuitable or questionable foundation
material, the exploration shall be extended to a sufficient depth into firm and
stable soil or rock but not less than four times the minimum depth of
foundation below the earlier contemplated foundation level.
6. Scour depth
Depth of scour below the high flood level.
Scour depth has important in determination depth of
foundation.
Determination
The maximum depth of scour should be measured with
reference to existing structures near the proposed bridge
site, if this is possible. Such soundings are best done
during or immediately after a flood.
Mean scour depth (dsm )= 9.2 m
Max. scour depth for piers = 2 dsm = 18.4 m
7. Depth of foundation
Well foundation are taken up to depth such that min.
grip of foundation below max. scour depth is 1/3 rd
of max. scour depth.
The max. Bearing pressure on the subsoil under the
foundation resulting from any combination of the
loads and forces except wind and seismic forces
should not exceed the safe bearing capacity of the
subsoil, after taking into account the effect of scour.
10. Cutting edge
•Cutting edge is the lowermost
part of a well It is the part
which cuts through the earth.
•The mild steel cutting edge
shall be made from structural
steel sections.
• The cutting edge shall weigh
not less than 40 kg per metre
length and be properly
anchored into the well curb
• sections are bent into shape
by cold bended no heating is
The picture above shows a three 160mm MS
done. Sections curved and welded to form Cutting
Edge.
11. Well curb
•Well curb is a structure with
outer wall of curb being straight
and inner at an appropriate angle
which is fabricated over cutting
edge.
•The internal angle of curb can be
kept between 30O to 37o .
•It serves the purpose of
transferring
•Load from steining to bottom
plug.
•Thickness of well curb is 75mm
more than that of steining to
prevent tilts
A fabricated well curb set atop wooden planks
13. Well steining
It is the longest part of well and it transfers load from
well cap to the well curb at desired depth.
Track of length is taken by marking wells on 4 sides
by gauges.
Steining is built in lifts of 2.15m and each lift is
aligned with previous one.
As per IRC 78:200
1. The amount of vertical reinforcement provided
should not be less than .2% of cross sectional area
of steining.
2. At the inner face reinforcement must not be less
than .06% of area.
3. Transverse reinforcement must not be less than
.04% of volume/unit length of steining.
14. Reinforcements in steining
For wells 12 to 23
Outer dia.= 5.35 m inner dia. = 3.4 m
Area of steining= 13.394
Min. reinforcement for steining (20 dia.
Bars)= .02*area/area of bar = 85.3 = 86
bars
Actual no. =62+26 =88 bars
Min. reinforcements for inner wall(20
dia.)=.oo6*area/area of bar =25.59 = 26
bars
Actual no. =26 bars
15. Well steining
Determination of thickness of steining
The min. thickness should not be less than 500mm and should be
according:
h=kd√l where : h- min. thickness in m
d=external dia. Of well
l=depth of well below well cap
k= a constant = 0.03
At the site: avg. depth of well = 25m
dia. = 5.2m
So Min. thickness required = .78 m
16. Well steining
But some adjustments are needed in thickness according to
the strata as given by the table:
Strata Adjustment
Very soft clay strata -10%
Hard clay strata +10%
Boulder strata or well resting on rock +10%
As the strata is sand with boulders
final thickness is = .858 m
Original thickness =.78 m (well no. 1-11 and 24 -29)
= .88m (well no. 12-23)
17. Bottom plug- transfers the load of structure from well to the
ground. It is cast under water after the final depth of well is
reached. No reinforcement is provided. The mix should have min.
cement content of 330Kg/m3
Sand filling : Sand filling shall commence after a period of 3 days of
laying of bottom plug. It helps in increasing the weight of the
foundation which provides more stability to the structure. It also
counteract buoyant force of water.
Intermediate plug :The function of the plug is to keep the sand
filling sandwiched & undisturbed. The concrete used for
intermediate plugging is also M25.
Top plug :After filling sand up to the required level a plug of
concrete is provided over it as shown on the drawing. It at least
serves as a shuttering for laying well cap.
Well cap- It is needed to transfer the loads and moments from the
pier to the well or wells below. It is designed as two way slab.
18. Well parameters
Parameters Data
59 n0.
1. Total no. of wells to be sunk
M 30
2. Grade of concrete used for well curb and steinning:
M 25
3. Grade of concrete used for bottom, intermediate
and top plugging
OPC 43-G
4. Type of Cement used
FE 500
5. Grade of steel used for reinforcement:
9m
7. Scouring levels from previous years data:
16 mm
9. Thickness of the cutting edge:
19. Well parameters
Parameters Data
Depth of the wells below ground: Well no. 1 to 11:24.0 m
Well no. 12 to 23: 26.5 m
Well no. 24 to 29: 24.0 m
Height of well curb: well no. 1 to 11 and 24,25: 1.410 m
Well no. 12 to 25: 1.530
Thickness of the well steinning: Well no. 1 to 11: 780 mm
Well no. 12 to 23: 880 mm
Well no. 24 to 29: 780 mm
20. Construction of well
Setting of well curb
Sinking of well
Bottom plugging
Sand filling
Closing of top by well cap
21. Setting of well curb
The centre of the well is marked
accurately with help of theodolite.
Cutting edge is placed on the wooden
sleepers such that centre of cutting
edge coincide with the marked centre.
Reinforcements and formwork for
curb is fabricated on the cutting edge
and concreting is done.
After curing of well curb is complete
the wooden slippers below the curb
are removed by making soil below
them diluted by water and is allowed
to sink under its own weight.
In this picture a well curb is resting
on the wooden slippers
22. Sinking of well/Construction of steinning
1. Fabrication
3. Dredging of
of formwork
earth to
and
support sinking
reinforcements
2. Concreting
23. Sinking of Well
Fabrication of Formwork
Fabrication Concreting
The formwork for
casting are Concreting is done by
supported on the pumping the concrete to
channels bolted with the mould by concrete
steining on both pump.
sides. The concrete is placed
in 400mm thick layers
As per design lap is
along with continues
provided after every
vibrations.
fourth
On avg. about 23m3 of
reinforcement at
concrete is needed for
same section.
casting of one lift.
24. Sinking of Well
Dredging
In order to sink the well,
continuous dredging is done.
Soil is excavated from the
dredge hole inside the well.
The dredging operation is
performed evenly along the
hole circular hole
25. Construction of well
Bottom plugging : it is done after the well
has reached the founding level. Concreting
is done inside water. For this tremie pipe is
used. A tremie is long funnel made of mild
steel . A flap door is provided at its bottom.
Well cap:After water filling, a truss system
consisting of three trusses supported in
well steining and cribs welded with it in
criss-cross manner are used for top
plugging. This system is covered with
strong plywood and sealed with concrete
slurry so that nothing can enter inside the
well. Hence preparing it for the casting of
well cap.
26. Methods to promote sinking
Kentledge -Total of 125 concrete cubes of 1m3 in size
are made for kentledge loading which is
approximately equal to 25t × 125.
Chiseling- When the boulders are very firmly
cemented then chiselling is done. In this soil is hit
hard by sharp end chisel.
Dewatering- dewatering of dredge hole is done to
reduce buyout force on well thus promoting sinking.
Flushing with jet of water on the outside face of well
reducing skin friction
27. Tilt and shift
Tilt and shift are deviation of well from its proposed position
and orientation.
Max. tilt allowed is 1/80
Max. shift allowed is 150mm
Measures to avoid tilt and shift
The outer surface of steining and curb should be kept as
smooth as possible.
The radius of well curb should be kept more than the steining.
The dredging should be done on all sides of well uniformly.
Causes
Eccentric dredging
Can be caused due to boulder under one side
28. Method of checking tilt and shift
Tilt and shift are calculated with the help of
a level and total station.
Method
Difference between height of points (1& 3)=
R.L.(1)-R.L.(3)
Tilt
= [ R.L.(1)-R.L.(3)]/diameter
Shift at bottom from top position
= tilt/ length
Note : this process is repeated on sides (2 & 4)
and in similar manner tilt is obtained and
then combined tilt and shift is reported.
Shift of well at top is measured by total
station.
29. Correcting tilt and shift
Regulation of Grabbing
Eccentric Loading
Strutting The well
Water jetting or Digging Pit outside the higher side
of well
Pulling the well or caisson
Excavation on the higher side outside the well
30. Problems
Sand blowing- This problem occurs when well bottom rests on
sandy strata and dewatering is done below water table. In this
sand from ground gushes into the well and there is sudden
sinking of well. This sudden sinking is very dangerous and is
very difficult to rectify.
Bridge scour -is the removal of sediment from bed such as
sand and rocks from around bridge, abutments or piers.
Scour, caused by swiftly moving water, can scoop out scour
holes, compromising the integrity of a structure.
Sand heaving-When a well passes through soft strata over a
considerable depth, the upward resistance acting on the
outside surface of the well is less than the weight of the well.
In that situation the well sinks down and quite often a heap is
formed inside the dredge hole.
