Figure 5 : Section and Detail of North Anchorage
4.4 South Pier
Foundation works started with creation of a cofferdam made from sheet piles . After removal of silt and cleaning of the river bed , it was dewatered . Caissons formed of heavy steel were erected . Caisson walls were filled with reinforced concrete . Both caissons were sunk together , in free air . At foundation level both caissons were plumb . The working chambers were filled with concrete , annular space with cement grout and the space between air deck level and -30 O . D . with rock fill and lean concrete .
The pier takes the form of a 40 ft ( 12.2m ) wide block with cutwater ends having a total length of 157 ft 6 in ( 48m ). The sides have sloping surfaces and plinth enclose the tower bases at the upper level . Each tower base is held down by 28 bolts on both its north and south faces .
4.5 North Pier
It is founded on the Mackintosh Rock . Cofferdams were of steel sheet piles , with tremie concrete waling . The tower base arrangements are identical to those for the south pier only with different prestresing cable details .
Figure 6 : Section of South Pier
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