REPORT

ON

CONSTRUCTION OF HIGH LEVEL BRIDGE

BY:

CH.HARSHA VARDHAN(1210211216)

K.MANIDEEP (1210211227)

G.MANIKANTA REDDY(1210211224)

T.ABHINAY (1210211258)

CONTENTS:

Acknowledgement

Introduction

Alignment

Well components

Well parameters

Reinforcement

Dredging

Tilt and shift

Methods and corrections

Problems

ACKNOWLEDGEMENTWe are obliged to Sri.Ranavittal ,EE for giving us the opportunity to undergo training at site in Anantapur district.

We are thankful to Sri.D.Madhusudana Reddy ,DEE, PR, for properly guiding us throughout our training period.

We are grateful to Sri.V.Nagasekhara ,AEE, PR, for explaining various concepts and clarifying all our doubts very patiently.

We would also like to thank Sri.Venu Prasad, site engineer, for helping us out regarding technical doubts we had.

At last, but not the least we would also like to thank our HOD, Mr.M.Ramesh for allowing us to undergo training.

INTRODUCTION

Well foundations are quite appropriate foundations for alluvial soils in rivers and creeks where maximum depth of scour can be quite large. In India technology of well foundation for design and construction is quite well developed. Still there are situations where serious problems are encountered at site during construction of well foundations.

In the Indian subcontinent there are many rivers where the depth of alluvial deposits is very high and the scour around the pier foundations can be very deep if the piers are located within the active channel of river. For such condition well foundation is a very appropriate type of foundation.

In India the technology for the design and construction of well foundation is quite advanced. In all rivers, including large rivers with torrential flow of water currents, well foundations were provided. In the foundations of Howrah Bridge in Kolkata giant monoliths were provided. In Second Hoogly Bridge also in Kolkata with one of the longest span cable stayed bridges in the world having the central span of 457 m being same as that of Howrah Bridge, an ingenius solution was adopted. Instead of a monolith for the foundation of each tower of the cable stay bridge, 2 well foundations up to 23 m dia were placed side by side at 30 m center and interconnected by a 14 m deep beam. This solution was construction-wise easier and more controllable and quantity of material used was much less. These wells were constructed purely by gravity sinking method.

PROJECT BREIFING: This bridge forms a part of a bye-pass project near P.kothapalli.

The project is undertaken by Panchayat raj engineering department of Government of Andhra pradesh.

Total cost of the bridge over penna river is 14 crs.

The contract is given to the company on MNT Grant.

Length 453.33m

Lanes 2

Spans 29

Formation level +340.014

High flood level +336.553

Alignment:

Alignment of the bridge passes through :Penna river between p.kothapalli and katrimala village

Alignment crosses river at an angle therefore it is a Skew alignment

Height of Bridge:

Bridge is high level bridge i.e. formation level is above H.F.L. Height of bridge is determined by examining the clearance of

bridge over highway. Road level =340.014 depth of slab = 1.7 m Actual formation level= m

WellComponents:

Cutting edge

Well curb

Well steining

Bottom plug

Sand fill

Top plug

Well cap

Cutting edge:

•Cutting edge is the lower most 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 meter length and be properly anchored into the well curb

• Sections are bent into shape by cold bending no heating is done. Sections are curved and welded to form Cutting Edge.

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 300to 370 .

•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

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 1.5 m and each lift is aligned with previous one.

As per IRC 78:2001. The amount of vertical reinforcement provided should not be less than .2% of cross sectional area of steining.

At the inner face reinforcement must not be less than .06% of area.

Transverse reinforcement must not be less than .04% of volume/unit length of steining.

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 counteracts 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.

WELL PARAMETERS

Total numbers of wells to be sunk 28Grade of concrete used for well curb and steining

M30

Grade of concrete used for bottom and top plugging

M15

Type of cement used OPC

Grade of steel used for reinforcement

FE415

Thickness of cutting edge 10mm

Depth of the wells below ground: pier type-1 :8.6mpier type-2:11mPier type-3:6.6mPier type-4:6.5m

Height of well curb: 1.5m

Thickness of well steining: 0.75m

Reinforcement

Reinforcement in curb(1.5m)(Bottom)

1. Dia of bars used = 12/16mm2. Spacing of curb rods = 0.15m3. Total curb rods = 1404. 12mm links are provided to the curb rod5. centre to centre distance between curbs = 16.79m6. For steining , an offset of 3inches is provided7. curb defines the shape of frustrum8. M20 concrete is used

Steining ( above curb) [1.5m internal]

1. Dia of horizontal bars used is 12mm 2. Spacing of bars = 0.22m3. Dia of Vertical bars=16mm @220mm centre to centre4. Total no of bars = 75. No of vertical bars in steining = 956. No of horizontal bars in steining = 8

CONSTRUCTION OF WELL

Setting of well curb

Setting of well curb

Sinking of well

Bottom plugging

Sand filling

Closing of top by well cap

The center of the well is marked accurately with help of theodolite.

Cutting edge is placed on the wooden sleepers such that center of cutting edge coincide with the marked center.

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.

Sinking of Well Fabrication of Formwork

Fabrication:

The form work for casting are supported on the channels bolted with steining on both sides.

As per design lap is provided after every fourth reinforcement at same section.

Concreting:

Concreting is done by pumping the concrete to the mould by concrete pump.

The concrete is placed in 400mm thick layers along with continuous vibrations.

On average about 23 m3 of concrete is needed for casting of one lift.

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

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

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

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.

2

1 3

4

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

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.