Commencement of the Permanent Work.
The positions of the four main piers on Fife being fixed at an early date, a beginning was made with the excavation of the rock upon the site of the two north piers. The natural bedrock of whinstone rose here to a level of from 10 ft. to 20 ft. above high water, and excavation had to be made to the level at which the foundation or holding-down bolts started—namely, at 7 ft. below high water. The rock was then levelled with rubble masonry and the building of the granite courses commenced.
_Fig._31,_Page_17.jpg)
Fig. 31. Raft Used for Survey of Foundations.
Excavation was also started upon the site of the north cantilever pier at a level of about 21 ft. above high water, and upon viaduct piers, 10 and 11, at 25 ft. and 22 ft. above high water respectively. These three piers stand on high ground, while piers 12 and 13 were placed at the bottom of the ancient quarry, and were founded at level 7 ft. below high water. The foundations of the abutment upon the hillside was commenced somewhat later at level 92 ft. above high water. All the piers on the Fife side are founded on the solid whinstone rock, with the exception of piers 12 and 13, these being partly on whinstone, partly on freestone. All the viaduct piers being on land no cutwaters were built. The rock after being cleaned and examined, and worked roughly into steps where necessary, was levelled up with concrete and a bed of concrete laid on from 4 ft. to 11 ft. in thickness—this bed projecting all round the granite masonry some 2 ft. Upon this concrete foundation the first course of granite was set, the form of the piers being rectangular and the curved batter of the pier starting from the bed. (See Plate VIII.) Piers 10, 11, 12 and 13 were built to level 37 ft. above high water, and left, pending the construction of the girders.