# Engineering of Padma Bridge:
Maybe very few people will have the patience to read the whole thing, but if you read it, you will know a lot
There are very few people in Bangladesh who have not seen the Padma face to face. When you see Padma, what do you see? Its width ?? Width of course. Because the depth, the vastness of the current is not so easily understood.
Do you know the depth of the river? The bottom of the river is about forty meters below the water. M but. Not fit. Forty meters means about 131 feet. Ten feet is usually the height of a lock. As such, the height of the water surface from the bottom of the Padma River is equal to that of a 13-storey building.
Then the columns of the bridge (which are actually called piers in civil language) should be equal to 13 storey building. But if the column is not tied to the ground, the current of the Padma, the column will be washed away. Do you think that a column equal to 13 floors will not float? Yes, brother. This is Padma.
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So the column has to be built on the ground. How much to build? The soil at the bottom of the Padma is sand type, soft mud type. Not as hard as stone. Bedrock is thought to be about 6 km down. 6 km is the height of Mount Everest! So it is better not to dream of going to Bedrock. In many countries Bedrock is found a little below. Building any structure in their country is much less costly because building their foundation is much easier, less costly. Our fortunes are bad.
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However, how much do you have to pay for the piles of the Padma river bridge?
When there are excess currents during the rainy season, the soil, like the sand at the bottom of the Padma, washes away. This is called scouring.
The highest record of scouring of Padma river is 85 meters (approximately) (or 71 meters). This means that 65 meters of soil has been washed away from the bottom of the river. That means 213 feet. This means that the soil of the same height as the 21-storey building has been washed away. (I don't believe in myself, how so much soil was washed away!) There is no other river that has the record of washing away so much soil or transporting so much sediment (soil particles). In this case, if you want to get the soil under the water, you have to go down 13 + 21 = 34 floors!
Then the columns of the bridge that you have to give, they have to be more than 40 + 75 = 105 meters long! That means a longer column than a 34-storey building!
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Now, somewhere in the river the scour is more, somewhere less. You are not sure, no matter how much you scour the column of your sadha Padma bridge will be exposed (exposed), will not be stuck in the ground, as a result your long sadha column will be washed away!
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For this, an average pile of 120 meters has been given. 120 meters means a 40-storey building! Piles, as tall as this 40-storey building, have been erected. (At first I thought 120 meters was wrong, 120 feet must be. After listening to it many more times, I realized, not 120 feet, meters!)
It went to the depth of the pile! Now let's see what is the size of the pile, what is the sep. The piles are round. Round cylinder equal to 40 storey building! The diameter of this cylinder is 3 meters. That means almost from the floor to the ceiling of your room! This is the diameter!
The piles are made of steel sheets. Quite thick (I don't remember the thickness, 60/70 mm or less / more) these sheets are being rolled to make cylinders. This cylinder will be attached at a geometric rate. That means with one meter long cylinder, one meter long and one part. Now with this two meter long cylinder, and one with a two meter long cylinder. In this way, a pile is being made with a pair of piles equal to the length of a 20-storey building and a pile equal to the length of a 20-storey building!
These huge long piles, do you think, who picked them up? Who put these? Superman? Special hammers have been brought from Germany for these piles. I heard that a hammer was made for the Padma bridge. Special crane, special hammer! Elahi Kand is going on in Mawa-Jajira.
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These piles are hollow. After settling on the ground, they will be filled with sand. Piles can rust, although 10 millimeters will erode in 100 years. 50/60 mm will still be there. (It is tested, how much damage will be caused by rust) The design life of Padma bridge is 100 years. This means that in 100 years, the thickness of the pile will be nothing but a comma. In sha Allah. These piles are actually called caissons. In the language of Pure Civil Engineering
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So much for the story of a pile! Do you think the column of our Sadh Padma Bridge, which we call Pier, will stand on this one pile? What if the ground beneath this pile moves? If the pile is broken! For this there will be 6 piles at the bottom of each column. The piles of this pier (column) will be scattered in the same direction as the spider has 6 feet.
The piles will be placed vertically but not on the ground. By bending, the inclined way will be inserted. Include in 1H: 6V ratio. So the 120-meter-long pile, if inserted in a crooked way, the feet of 6 of them will be far below the ground. The soil on these 6 sides will not be washed together (inshaAllah). The fact that they will be inclined, it will also increase their load carrying capacity a little. The thing is that the reporters who report during the cyclone are seen to be on either side, far away. If you stand up straight, there is a risk of overturning in the air. This is done because the lateral load (wind load) comes when the two legs stand together as easily as it is possible to stand with both legs, it is convenient to stand, the load can be resisted more. But this is also an engineering plan. So, even these 6 piles will take more lateral load just to stay inclined. (Lateral load means that which is coming from the side, such as the current of the current)
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Again, just being inclined, the 120 meter long pile will go 118.3 meters below the ground. Because when we bend a stick, its height decreases even if it is the same length. For example, if I put the ladder on a steep wall, the higher the head of the ladder is, the lower the head of the ladder will be if the ladder is tilted. The same is true of piles.
A program called PIGLET was used to design these piles. The optimum / most efficient pile has been found with this program. This study is done on three types of pile foundations. These three types of foundations are:
1. 6 raking steel tubular piles
2. 8 raking steel tubular piles
3. 12 cast in situ vertical concrete pile
The study shows that the foundation of 6 inclined steel piles is the most efficient. (raking means inclined)
The pile cap will be on top of these 6 piles. You will see this thing floating in the water. But it does not float at all! It is standing with 8 legs (piles). This pile cap is so big, a family of 3/4 people can make a family in such a place! A very rough estimate says there is more than 900 square feet of space here! That means a pile cap is larger than 900 square feet. This pile cap is made entirely of concrete. I have no idea about the thickness / height.
The pile below the two piers will be a little different. to be vertical bored concrete pile. Which will go up to 60 meters deep. This means that these piles will not be inclined, will go straight under water. These will be concrete piles, like ordinary columns in our homes. The funniest part is, these piles will be cast in water! That means pouring concrete in the water! But the concrete will become a column without floating! Yes brother, there is this technology too! In the case of this pile, 12 piles will be given under one pier.
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Pier or bridge columns will stand on this pile cap. This pier is entirely of concrete. reinforced concrete. The whole bridge will be peeled at 41 o'clock. However, the design / number of piles may change as hard soil without mud could not be found at the bottom of the river at the Mawa end. The number of peers may increase to 42/43. I heard such bizarre talk in many news reports. Which will be the most effective, which will be the least cost, will be implemented in practice.
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The span will sit on the head of this pier. The length of each span is 150 meters. That is to say, from the Bata signal to the Kantaban turn, the length of the two spans.
For this span design, 3 types of span analytical models (with computer, with analysis software) are made and checked, which will provide the highest safety at the lowest cost. There were three spans - 120 meters, 150 meters and 180 meters. Of these, 150 m span was the most efficient so in reality 150 m span has been installed.
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These spans are Warren type still truss girder and concrete on upper deck. All the spans together are 6,150 meters. That is, the length of the whole bridge is 6.15 km. This means that the entire Padma Bridge is: the same length from Science Lab bus stand to Kalyanpur bus stand or from Shahbag to Mohakhali flyover. (approximate)
Padma Bridge is a two storey bridge. The train will still pass through the truss. The railway line is a dual gauge. This means broad gauge and meter gauge, two types of trains can cross the Padma Bridge. Broad gauge railway line on the west side of our country (Rangpur Rajshahi, Kushtia Khulna side). And the rest of the country's railway line is meter gauge. One type of rail cannot run on another rail line. But these two types of trains can run with dual gauge. So, in fact, any train in Bangladesh can run through Padma Bridge. There will be an emergency access point so that if there is any problem on the train, people can be taken off the train and taken to their safe place.
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Again, this is no ordinary railroad. Arrangements have been made so that the wagon can go with two containers. In Bangladesh, trains usually take one container. But this is being done here so that in the future the train can go with one container on top of another i.e. two storey containers. The load-bearing capacity of the main bridge had to be increased to accommodate these two-story containers. That load will actually be taken first by the rail line, from the rail to the truss, from the truss to the pier (column), from the pier to the pile. This has made the pile more robust, and as a very normal result, the cost has increased.
A concrete deck will sit on top of this two-story bridge. I mean the roof. The car will run on it. The lightest material that can be used to make the deck will be used. Deck, meaning the road over the bridge will be 22 meters or 72 feet wide. Cars will run in four lanes here.
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Seismic isolation bearing has been used before placing this span. Without it, the energy with which the earthquake would hit the structure would be much less. The technology used here is Base Isolation, which will move the foundation during an earthquake but not the upper bridge. There will be a system of movement. This is called pendulum bearing. That is being used. It can slide. Will be back again. It has been used in many places in the world. But it has never been used in such a big project. Due to this technology the number of piles, the size of the pile cap has been reduced a bit.
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Some utilities will cross the river through the bridge! There will be a gas transmission line. Optical fiber and telephone lines will go. And of course the electric line will go.
This is just the bridge. Only the Padma Bridge. But there is much more left in the project, such as river governance work, approach road work. Now let's look at them.
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What is the approach road? You don't just have to build a bridge. The bridges have to be connected to the roads that are now with that bridge, the roads on which cars are running. This connecting road is the approach road. This approach road to the Padma Bridge is twice the length of the bridge. 12 km Abdul Monem Limited, a company in the country, has done the work of making this approach road.
Among the works of this approach road was the connection from Jazira to the national highway. Similarly, the road near Mawa was brought to international significance. And service area. Which is the main office of this huge construction site. Offices and residences will be built here during construction and when construction is completed. Of these, five bridges are required at the junction of Jazira. Adding the length of these bridges alone, it stands at about one kilometer.
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This task was also difficult from the engineering point of view. The road to Jajira was once a char area. Soft soil. It is a problem to make the road on such soft soil, because it will cause the road to sink in places and as a result the pitch road above will break. Then any road has to be put much higher than the flood level again. In other words, it will be found out from the flood record how much water rose the most. Then we will see how much water can rise in a certain period of time (maybe in the next 100 years). Then the road will be built in such a way that there is a road above the water of that highest height.
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For this purpose, high places like dams have been built by throwing soil. Then an attempt was made to increase the density of soil under the road. The machine had to be brought from Germany for this work. The name is Sand Compaction Pile. It is not very difficult technically. Inserts into the soft soil like a pipe. Pressure is applied inside the pipe with a machine from above. The bottom of the pipe is closed. In this process the soil is pushed down. And when the pipe is lifted again, sand is thrown from it. Thus the density of soil has been increased. It is hoped that this road will not collapse when a vehicle is moving. Many have been tested. The car is also running, there is no problem. The work of this approach road is almost finished now.
Two huge construction yards have been built at Mawa and Jajira, at both ends, to build the Padma Bridge. I have no doubt that it will take a whole day to walk around the entire construction yar.
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