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How bridges are built over water?

bridges are marvels of engineering that

stand inconspicuously amongst us we

don't think of them much even when we

are passing over them nowhere of these

structures more impressive than when

they are built over water which brings

us to the question our bridge is built

over water when the water is shallow

construction is easy a temporary

foundation is made on which piers are

built to support the upper structure and

the bridge is then built it's when the

water is deep that other techniques are

needed there are many methods to

complete such a task in deep water but

here we will explore the main three

these three methods of bridge building

are called battered piles coffer dams

and caissons

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let's begin with battered piles these

are poles that are driven into the soil

underneath the water piles are hammered

into the water until they turn outward

or inward at an angle

this makes the piles firm and increases

their ability to carry lateral loads

piles are inserted in the ground using

pile drivers these are mechanical

devices that may be transported to a

location on a floating pile driving

plant pile drivers may also be

cantilevered out over the water from

piles that have been installed in

advance with the use of pile frames pile

hammers and winches pile drivers hammer

the piles into the soil until they turn

outward or inward at an angle the piles

are now ready to carry lateral loads and

can provide the foundation of support

for the bridge the next step is to

construct the pile caps above the piles

once this is done the bridge is ready to

be built next up our coffer dams these

are temporary enclosures made by driving

sheet piling into the bed of a body of

water to form a watertight fence this is

called the coffer dam there's more to

this bridge building technique once the

sheet piles have been inserted in the

water to create a coffer dam the water

is pumped out of the enclosure

now the construction workers can build

the bridge as if they are working on dry

land the process then becomes relatively

easy

finally caissons may be used there are

two types of caissons open and pneumatic

an open case on is a structure that is

usually shaped like a box it is open at

the top and bottom the caisson is

usually constructed on land then floated

into position and sunk so that the upper

edge is above water level the caisson

has a cutting bottom edge so that it

sinks through the soft silt on the bed

inside is a series of large pipes or

dredging wells these are used to dredge

up the bed material as more material is

dredged up the caisson sinks and more

sections are added to the shaft to keep

it above water once the caisson reaches

the correct depth concrete is laid to

seal the bottom and then more concrete

is poured into the caisson to form a

solid post a pneumatic caisson is

similar to an open case on but it has an

airtight bulkhead above the bottom edge

this is fitted with airlocks the space

between the cutting edge and the

bulkhead is called the working chamber

in this space the water is removed using

air pressure construction workers can

then enter the chamber and excavate the

soil it is important that the air

pressure in the chamber be carefully

monitored so the workers do not get the

bends but how do engineers pick which

technique to use this all depends on the

condition of the site and the technology

available these are important decisions

to make that only experts can fully

handle

now that you know a bit more about how

bridges are built you can admire them

even more

after all all bridge building techniques

are impressive feats of Engineering

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