PANAJI
Soil strata variations
Initially, few bore logs were taken and the foundation was designed based on these strata. However, during execution, it was noted that the strata varied in each pile, hence, the work had to be stopped and more bore logs were taken and the entire foundation was redesigned based on fresh bore logs.
Piling in tidal waters
Based on earlier strata, a piling methodology was planned with a manual winch placed on a platform supported on temporary piles, later in fresh bore logs, hard rock was found and the entire piling methodology was changed and floating pontoons / high-capacity piling rigs were used.
Pile cap concrete
Temperature control during concrete pouring: Even after splitting the pile cap into three parts, 3,585 cum of concreting has to complete in a single stretch. The code proposes that the temperature variation between concrete and ambient temperatures shall not be more than 20 degrees Celsius and without control, it may have resulted in a very high temperature of this mass concrete which might have resulted in cracks and brittleness in concrete.
Temperature control was initiated during the mix design process itself.
1. Cement quantum was replaced with GGBS in an optimum way to reduce the heat of hydration and provide the desired strength to the structure.
2. Coldwater with less than 5-degree Celsius was used during batching of the concrete.
3. A cooling system was deployed at the site during the pouring of concrete which consists of the following (a) Sacrificial GI pipes were provided in the pile cap in layers and a grid of a metre in both directions to circulate cold water in concrete up to the completion of curing period (14 days)
(b) Cooling towers were installed at the site which circulates fresh cold water from the inlet up to the completion of the curing period (14 days)
(c) Sacrificial sensors were installed in the pile cap to monitor the temperature during and after the pouring of the concrete.
Cable stay construction
The Chinese bridge expert Prof Dewai Chen was deployed for the construction stage analysis which is crucial during bridge erection, but due to Covid and the Indo“ China standoff in the past years, he could not be deployed on-site during bridge erection.
Later, Indian designers were appointed and this was successfully done for the first time in the nation for a bridge of this magnitude
Fabrication of steel segment
The structure being composite, involved a large quantity of structural steel of 10,500 MT and the big challenge was quality control/timely delivery and transportation to the site due to its very large size and weight.
To overcome challenges, a state-of-the-art fabrication unit was set up of more than 10,000 sqm building area with high tech following major equipment imported from various countries.
