Mining near Doyang bridge risks compromising its foundation

DIMAPUR — The rampant sand and gravel mining in the vicinity of the Doyang bridge at Governor’s Camp, Liphayan, Wokha district, is compromising the bridge’s foundation due to the constant lowering of the river bed level.

This was stated in a letter addressed to the convenor of the Nagaland Foothill Roads Co-ordination Committee from the office of the executive engineer, PWD (R&B) Dimapur division.

The letter explained that it is crucial for the stability of the bridge that no river bed mining be carried out for at least one km upstream and downstream of the bridge’s location and that mining would ultimately compromise the overall stability of the bridge in the future, and asked the committee to sensitise the local populace about the same.

The letter, signed by executive engineer Z Inahoto Sema, stated that on August 30, the division and the contractor inspected the bridge site and discovered cracks on the approach slab on the Bhandari side that needed to be repaired. The defects on the approach slab and also on the parapet footing observed were pointed out to the contractor, and the contractor verbally agreed to do the needful at the earliest.

During the inspection, the bridge elements (abutments, midpiers, and superstructure) were visually inspected and found to be stable. The return wall on both sides of the bridge was also found to be stable.

The wing wall on both sides of the bridge was found to be stable, but due to natural consolidation of the backfill material behind the wing wall, settlement of the backfill material was observed, causing cracks on the footing of the parapet, which the office said is not a major concern for the bridge or retaining wall’s stability.

On the issue of vibrations of the bridge, it clarified that vibrations are generally considered in the bridge design and are not necessarily a sign of structural failure and that bridges are designed to be flexible to some extent, allowing them to absorb and distribute the loads imposed by the vehicles

However, it was stated that during the construction of the approach slab, the division imposed strict restrictions on any vehicular movement on the bridge until the completion of all its components and a minimum curing period of 28 days. But complaints were received from the contractor that heavy-loaded trucks forcefully plied the bridge multiple times during the curing period of the approach slab.

“The RCC structure requires at least a 28-day curing period to attain its nominal strength, which in the case of the approach slab towards Bhandari side couldn’t be achieved due to vehicular movements,” it read.

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