(A Must read for solid / structural mechanics Lovers)
I don't know how far I can write, but I will try. The probability of any information being wrong is very low, 1%. If there is any unintentional mistake, I apologize in advance.
Much of the writing is written from my site visit experience. That is why it is not possible to give references in that way. During the creation of any civil engineering structure, due to various challenges, changes are made in the design. Such a change may occur in the future, then there may be a slight inconsistency with this writing.
Padma. There are very few people in Bangladesh who do not seem to have seen the Padma face to face. When you see Padma, what do you see? Its width ?? Width of course. Because the depth and the magnitude of the current are 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 the language of civil) 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.
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.
However, how much do you have to pay for the piles of the Padma river bridge?
When there are excess currents in 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 soil under 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!
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!
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 shape. 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.
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.
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 is removed? 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 bent into the ground, the feet of 6 of them will be far, far away on that side. The soil on these 6 sides will not be washed (scour) together in sha Allah. 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 both sides, far apart. 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 more resistant. 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 push of the current, that is.) Again, just being inclined, a 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, the higher the head of the ladder will go down. 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 6 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 normal 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.
Piles 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 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.
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. The 150 meter span was the most efficient. So in reality a span of 150 meters has been installed.
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 railway 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.
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.
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 bridge above. 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.
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.
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 needed at the junction of Jazira. Adding the length of these bridges alone, it stands at about one kilometer.
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 highest water level.
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 vehicles are 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 yard. For this huge construction yard and approach road, huge amount of land has to be acquired. About 13,000 homes, home to about 64,000 people, have been damaged by the project. Seven resettlement areas have been allotted for these people on both sides of the river. Their houses, mosques, schools, markets have all been built there.
Many trees have been cut down in the vicinity of Padma river for this construction yard, approach road, resettlement area and service area. For this, afforestation has also been done. As of December 2015, 80,452 trees were planted. This was the responsibility of the forest department.
I heard in a news report that during the breeding season of hilsa fish, their piling work was stopped so as not to disturb their normal environment! I don’t know if there is such a beautiful project in any other country, where such a sincere effort is made to compromise with nature.
Another very important work of the Padma Bridge is the work of river management. Let's first see what river governance is, why it is needed.
The river breaks. The river changes its course. Now the bridge is on Mawa Jajira, the river may have changed its course and gone somewhere else. Then the Padma Bridge will become so simple like the broken bridge of Jamalpur. (There is a bridge in Jamalpur called Bhanga Bridge, where the river bank is broken and the river has moved away, but the bridge has remained in its previous place.) That is why the work of river governance is being done so that the car can get the way down from the bridge.
Now let's see what the river system is! I mean, what a job!
River governance refers to the structural work done to protect the course and banks of a river. This means that when bricks or stones or something like that is used to save the edge, to protect the edge.
By analyzing the flood data of different years, it is estimated that 140,000 cubic meters of water could flow into the sea every second for the next 100 years through the Padma. (This means that if we could stop the flow of water in the Padma for 20 seconds, then 16 million people in the greater Dhaka city would have a day's drinking water.) This is the second highest amount of water that flows into the sea through the Padma. First Amazon. Padma is number two. This water has to be taken through the bottom of the bridge. That arrangement should be made so that the water can flow through the bottom of the bridge and go to the Bay of Bengal. If this water gets stuck in any way it will simultaneously flood upstream (west-north side of the river) and at the same time this water will put a lot more pressure or push on the bridge. As a result it would be very normal for the bridge to fail.
These are the challenges of river governance. There are very few contractors in the world who can do this job. When tenders were called for river management work on the Padma Bridge, only 3 companies submitted tenders.
1. Hyundai Engineering and Construction Ltd of South Korea
2. Jan De Nul N.V. of Belgium
3. Sinohydro Corporation Ltd of China
Sinohydro received the tender in July 2014.
This work includes river dredging. Dredging means removing the clay from the bottom and moving it elsewhere. So that there is less obstruction in the movement of water. So that more amount (more volume of water) water can go. This is expected to reduce the water pressure on the shore. 10 million cubic meters will be dredged at the end of Mawa. And 40 million cubic meters will be dredged at the end of Jazira.
Dredging in this river is more than 100 feet. Under water. It has already been calculated how the river bank will be sloping under the water. According to him, the soil on the banks of the river has to be cut. He has to use a special dredger for that. Which is GPS controlled, the underwater soil can be calculated and cut by itself.
Another part of the river system is the dumping of stones, concrete blocks and geo-bags along the river banks. 8.5 lakh tonnes of stone is required at the end of Mawa and 3 million tonnes at Jajira. 3,906,500 Geo bags weighing 600 kg will be thrown away. 16,26,500 Geo bags weighing 125 kg will be thrown away. The total number of cc blocks (cement concrete blocks) is 13,301,248.
River management work will be done at the end of Mawa covering 1.6 km. And 12.4 km at the Jazira end. The reason why there is so much work at the Jazira end can be understood by looking at the map of Bangladesh. The reason is that the water comes from the northwest at a very high speed and pushes the Jazira side more. The water goes to the south-east by pushing here.
Again the soil type at Mawa site is somewhat clay or clayey soil. There is no clay on the Jazira site to the south. There is silt, sand and sandy loam. The higher the current, the more likely it is to erode. So this river has been managed for about 10 and a half kilometers on the site of Jajira. And Mawa site is only one and a half kilometers. In 2017, an unexpected sudden eruption was seen at the Mawa site. Then some more work is done.
River governance is very difficult. Because the square in the river (soil washing) can go so deep that maybe some protection is given upwards. It was seen that the soil was washed away from below. Then the edge will break from the top. Because there is no support below, the soil of support has been washed away. For this, stones, concrete blocks and some new technology geo textile bags have been used from far below.
However, I am confused as to whether a gigantic river like the Padma can scour 85 meters, how much it can be ruled, or what is the benefit of ruling. However, the effort can not be stopped. We have to keep trying.
The river management work may have to continue for all time now. The contract will be renewed or a new tender will have to be issued. Otherwise this bridge is difficult to survive. Take care of every structure. Otherwise it will not survive. I read somewhere long ago that the national parliament is like petting the elephant of the poor in Bangladesh. It costs a lot to maintain. New elephants are coming to the country now! However, these prove that the country is no longer so poor!
Now let's look at some back events. A report called Prefeasibility Study of this project was given in 2000. The initial feasibility study of the entire project was reported in 2005. Feasibility study can be said in very simple language, to calculate how much money will be poured behind it, how profitable it is, or not profitable at all. Or where and how to get the most benefits for the least money.
The purpose of the Prefeasibility Study was to find the most suitable location for the Padma Bridge. In this study, during the planning of Padma bridge, preliminary survey was conducted in two places - Paturia-Daulatdia, another is Mawa-Jajira.
The consulting firm was told, our main objective is to cross the river. So that vehicles can go up or down the river. The consulting firm first studied the bridge and the tunnel. It turned out that the tunnel cost a lot more in terms of investment. Then the tunnel was left, there was a bridge to cross the river.
Feasibility Study started in 2001 with JICA funding. New site selection has started again. A study from Goalanda to Chandpur showed that Mawa-Jajira site is the best.
There are many things to consider in a feasibility study, one is হলো which direction will attract more vehicles, which means exactly where the road needs people the most, or more people. The second is where the course of the river is relatively less variable. The Padma can move a couple of kilometers in some years. If you want to select a site for this, you have to see which one is stable for a long time, which means the river has been in the same place for a long time. In this case also Mawa-Jajira was found to be a suitable place. The Feasibility Study (FS) recommended a preliminary design comprising a prestressed concrete extradosed bridge with railway provision.
However, the whole project is divided into two parts.
Phase 1: From project design to tender
Phase 2: Construction
Phase 1, meaning the work of designing this Padma Bridge started in 2009. A team of national and international experts was formed to design the Padma Bridge in detail, headed by AECOM. The team also included SMEC International, Northwest Hydraulic Consultants and ACE Consultants, with additional assistance from Aas Jakobsen and HR Wallingford.
The Bangladesh Bridge Authority formed a panel of 5 national and 5 international level experts. The task of this panel was to review the design of the Padma Bridge from time to time.
The BS 5400 (British bridge design code) code has been weighed to design. Because its load and other things match the traffic condition of Bangladesh.
A shipping study is done while designing the bridge. The study is that if there is enough space under the bridge, all the ships plying in Bangladesh will be able to pass under the bridge. The Bangladesh Inland Waterway Transport Authority (BIWTA) reports that the water rose to a record high of 18.3 meters (60 feet), with a minimum of 3 spans. But there was trouble here too.
Padma is an unpredictable river. The Padma sometimes carries a huge amount of soil from the bottom with the current. Sometimes a lot of sediment comes with the current and accumulates. Sometimes the river breaks its banks and changes its course. It was seen that the bridge remained in one place, the river broke and diverted to the other side. As a result, the construction of the bridge was almost in vain. Again the river sometimes wakes up suddenly. It was seen that the three spans that were made 60 feet high for the ship to go, the char woke up there, the way to the ship was closed. Because all the other spans are not so high. It is not possible for ships to pass under them.
That's why if you span a ship to go somewhere high for the next 100 years (design life of Padma Bridge), it will survive, the pirates will not wake up under it, the ship will be able to go, it was very critical to gass the matter.
It was later decided that the number of spans as high as ships would be increased. All spans will be raised high enough to cover a distance of about 4.6 km in the middle of the river so that ships can pass under any of them.
Again, the Padma River is a very fast flowing river. With its propensity to scour the bottom of the river as well as its location in places like an earthquake, the design and construction of the bridge has been, or continues to be, quite a challenge.
During the design of the Padma Bridge, detailed research was done on earthquakes. This was done by BUET. Two levels of earthquakes are studied.
1. Operating level earthquake: The probability of it happening once in 100 years is 75%. It is more terrible than a small earthquake in Dhaka or the country, but less harmful than the next level.
2. contingency level earthquake: This earthquake is of a very severe level. It comes once in 475 years. The probability of this happening in the 100 years design life of the bridge is 20%.
(These are all probability, data analysis. It may or may not be. But it will be, mathematics says so.)
A three dimensional non linear time history dynamic analysis, using a modified Penzien model was adopted.
By selecting suitable / efficient seismic parameters from this study, the bridge has been designed with them.
This is the Padma Bridge. Padma Multipurpose Bridge. The main challenges of this bridge were:
- River governance work
- Floods every year
- It's in an earthquake-prone place
- Deep Pile Foundation
- Soft clay at the bottom of the river
- extreme scour depth
- Rehabilitation of people who will be affected
- To take care that the nature / environment is not damaged for the project
- Land acquisition
- After awarding contracts to so many companies, to maintain coordination among them
- To build Padma bridge with own funds
Seeing the challenges, it seems that the people of Bangladesh are up and running just to build a bridge! What has started a constant war with nature, just for a bridge. This bridge is actually a lot of sacrifice, a lot of love. The Bridge of Pride, Padma Multipurpose Bridge!
Wow very nice writing.... Thanks