KARACHI, Sept 7: Trigger mechanism caused by heavy rains and low tide on August 9 and 10, resulted in the collapse of 50-year old berths at the Karachi Port.
These were the initial findings of a foreign marine engineering consultant, who had been hired by the Karachi Port Trust (KPT) in 2005 for designing berths No 10 to 17A at East Wharf.
Talking to Dawn during his recent visit to Karachi Technical Director Steve Hutchinson of Scott Wilson (consultant) was of the strong view that trigger mechanism of low tide and heavy rainfall resulted in the collapse of berth No 10 and 14.
While explaining his theory he said that heavy rains raised water level behind the quay wall thereby increasing load on the tendon (wire cable tie), which may had been already weakened due to corrosion.
With little support from the sea owing to low tide, he said, the pressure could have multiplied on one of the already weakened tendon, which may have given way thereby throwing weight and force on other tendons, which fell like nine pins and resulted into collapse of berths.
When these berths were built between 1955 and 1960 their design was adopted on modern concept of that time and was considered to be away from traditional anchored bulkhead with king piles and a sheeted face structure.
Mr. Hutchinson said that as per the design of these berths the piles were pre-stressed concrete and were of substantial scantlings with concrete curtain slabs between them.
He further said that tops of the piles and slabs embedded into a heavy concrete capping beam, which distributed the horizontal loads between high-tensile wire-cable ties (tendon) spaced at 32 feet centres and housed in bitumen-filled ducts.
On visiting the collapsed berths, Mr Hutchinson said it could be easily concluded that load and pressure created by heavy rains and little support from the other side due to low tide may have first broken one of the weakest tendon thereby causing stress on other wire-cable ties.
He emphatically said that after getting the designing contact for these berths last year he carried out investigation of the seabed and witnessed holes of dredging beneath the designed specifications. Similarly, Mr. Hutchinson said there was no evidence of scour holes normally created by the movement of propellers of ships, which might be taken as a cause of collapse of berths.
However, he said the accurate cause could only be known once the condition of tendons is examined because the damage caused by corrosion could not be seen at this stage.
He did not agree that adjoining berths have also been damaged due to stress action and added that for such concrete structures there is always expansion joint, which cuts off the continuity. Therefore, if operation of these berths have been stopped it is only due to precautionary measures, he added.