‘No decline in strength of existing Zuari bridge piers’
Panaji: The Indian Institute of Technology (IIT), Bombay, in its report submitted to the public works department (PWD) has said that the strength of the concrete piers of the existing Zuari bridge has not degraded and hence there is no need to close the bridge for traffic.
The team has analysed the shear strength of this ageing structure.
It had orally instructed at the time of inspection in March 2017 to restrict the use of the bridge for light vehicular traffic with maximum load capacity of 12-14 tonne and maintain a speed limit of 30 kmph, which was put in force since June 2018 till date.
During the inspection of the bridge in 2018, the team observed corrosion and cracking of piers as well as distortions of expansion joints and cracks in mastic layer on the superstructure indicating uneven loss of external pre-stress, which is expected after 10-15 years, as external pre-stressing was last done in 2005.
However, the IIT team of engineers asked the PWD to take corrective measures by regularly measuring the vertical levels and lateral movements of piers at base, top and tilt. The team said if a change in level difference of 10-15 mm is observed, then immediate attention of PWD engineers would be required. Moreover, if the installed vibration monitoring instruments record high velocity (5-10 mm/sec or more) during construction activities, then all piers need to be inspected immediately for corrosion cracks, the team said.
The team said the early implementation of the given corrective measures can sustain the existing bridge for the duration required for the construction of the new cable-stayed bridge.
As long term measures, the IIT suggested rehabilitation of the superstructure by replacing mastic layer for both lanes, epoxy grouting of all slab cracks, replacement of expansion joints and use of CFRP strips along the traffic direction.
Acting on a media report that highlighted the poor condition of the bridge posing a risk to users and also quoted principal chief engineer’s letter pertaining to weak piers of the Zuari bridge, the Goa Human Rights Commission (GHRC) had taken suo motu cognisance and called for detailed reports from the principal chief engineer and chief secretary.
The PWD has stated that it is not true that the piers are weak. It has said that the bridge is constantly being monitored and any abnormalities if noticed have been reported to the Ministry of Road Transport and Highways.
With regard to the corrosion, the PWD stated that necessary repairs like epoxy coatings, grouting for the pre-stressing cables and additional external pre-stressing to compensate for the loss of pre-stress have been carried out. It is observed that no major cracks are noticed in these years and wherever required, patch repairs with epoxy grout is done regularly for avoiding exposure to reinforcement to atmosphere, the PWD has stated.
In May 2018, some transverse cracks in the wearing coat of the bridge were seen and these were filled with emulsified bitumen to prevent propagation and also at the finger tip of piers 3 and 4, a level difference of one inch was noted. This was reported to the MoRTH (Ministry Of Road Transport and Highways), which suggested engaging the services of IIT, Bombay for a study of the bridge.