Sir: About a kilometre long, the Doolha Dariya Khan Bridge consisting of 27 spans was built over 45 years ago in 1967. The bridge is on the Thatta-Sujawal road crossing over the river Indus in Sindh province. The road links the lower parts of Sindh with Karachi. The bridge was designed to withstand a peak discharge of 1,100,000 cusecs. It was more than a decade ago that the superstructure of the original bridge, i.e. deck slab, started crumbling due to heavy traffic vehicles (HTVs) plying over the bridge, and loosening expansion joints. However, the substructure that consists of decks, girders, rectangular hollow piers and foundations is still intact. The bridge was renovated during January 2005 and January 2007 under the Sindh Rural Sector Development Programme, with the financial assistance of the Asian Development Bank. The works included replacing railings and pedestrian walkways, repairing of damaged deck slab portions at several locations with respect to cracks and craters and casting of in situ New Jersey barriers over deck slabs in order to avoid accidents. As a result of HTVs and their ever increasing intensity, the bridge deck slab is again deteriorating after a few years. It is noticed that the New Jersey barriers were recently removed automatically by the Thar Coal Authority to shed load. It is evident that only the bridge deck slab is decaying, and not the bridge as a whole. The load of barriers is mainly sustained by frameworks fixed below the slab in the substructure. It is believed that removal of these barriers is not wise. Therefore, it is advised to replace the entire deck slab throughout the bridge length including expansion joints. The bridge can survive for at least another 50 years. It is further advised to construct another bridge parallel to the original one to cater for ever increasing heavy traffic.
ABDULLAH MEMON
Hyderabad