Md. Enamul Hoque Sardar
Substructure Engineer, Supervision Consultant,
Bangabandhu Sheikh Mujib Railway Bridge Construction Project (BSMRBCP),
SMEC-ACE-SJ Ltd.
Former Assistant Resident Engineer (Substructure and Superstructure), Padma
Multipurpose Bridge Project (PMBP)
It was very challenging for me to work as an Assistant Resident Engineer (For Construction Supervision Consultant) at the very beginning of such a project. In the initial stage of the project, I was accompanied by one of my esteemed associates/colleagues, who was about 19 years senior to me and also had experience working on some mega projects but compared to him I was very much a beginner. Even in such a huge project, no guidelines were prepared at the primary stages, therefore several tests were adopted related to the substructure. Besides, all the modern technologies/equipment, were completely new to us. In addition, the influence of strong rules and regulations by the lead consultant of the project made the project more challenging but a platform of achievement for all.
During the rainy season, I used to observe the terrible form of the raging Padma river in the strong current/hostile weather, and sometimes while crossing the river, I thought at least once “If I can cross the river for today, I will quit my job tomorrow, but tomorrow I would actually think again and would decide that I will do a little more work!! More than six years have passed by thinking of the above.
It was the first time we monitored that 4 (four) additional piles were constructed to support the reaction system of static load test [Known as anchor pile] by centering the test pile within those 4 (four). Not only that, experimental skin grouting was applied in these anchor piles, to examine whether there is any possibility to develop skin friction around the periphery of different layers for cast in situ pile, which was successful indeed. As a result, later skin grouting was applied to some of the viaduct piles on Mawa and Janjira side. Skin grouting was also adopted in some steel piles of the main bridge through TAM pipe installation [4 nos TAM welded peripherally along the length of pile] with steel tubular piles, in which grout was injected via small nozzles of the TAM in different layers (perhaps 1 m apart). Thus, strengthening of the surrounding soil of the pile, below the river bed has been achieved and ultimately increased the skin friction of the steel pile. There was technology like base grouting which increases the tip contact of the pile or increases the bearing capacity for bored piles and helps to increase the base preloading capacity in case of river steel piles. Recently, pile-base grouting technology is being applied in many megastructures around the world. For the first time, it was noticed, in a static load test, a test pile load increment was performed in sequence continuously until it fails! Strain gauges were installed in each layer along with the rebar cage of the pile which automatically derives concrete properties (temperature & strain) and by further calculation, converting strain into stress format, derived the bearing capacity of the pile. We saw how a 3.0 m dia steel tubular pile was driven by a German hammer to a depth of about 122 m long pile. Observed, that the steel tubular piles of the river were driven in rake or inverted-V formula to handle the external load. Although previously, in our Bangabandhu Jamuna Bridge, this concept of raking pile was applied. The advantage of this raking pile foundation can be share with a simple example, it can be understood, if we stand upright in a strong wind, the stability will be lesser than if we stand with our legs spread. Of course, you will be more stable if you stand with your legs spread apart…isn’t that right?
Base isolation technology has been used in Padma bearings, where the foundation will move during an earthquake but the superstructure will not. There will be a reaction system for movement. This is called a friction pendulum bearing which can slide with it and will be back again into its position. It is used in many places in the world. However, it has not yet been used in such a mega project.
Only the pile cap of the Transition pier (Pier 01 & Pier 42) at both ends of the bridge was about 3600 cubic meters casting (cast in two rounds), of which only the first round was 2200 cubic meters. Sometimes I imagine if such a large pile cap exists anywhere in South Asia. In fact, these technical excellences and phenomenon of Padma Bridge can’t be expressed by this short writing, this article is just the assertion in my mind.
