It will incorporate disused hollow steel piers which supported the western edge of the original Blackfriars Bridge which was dismantled in 1985.
Speaking at the ICE on Friday, Network Rail programme engineer for stations and civils Mark Burton said the five sets of piers supporting the bridge’s 55m spans will, "receive support from the spare columns."
Burton explained that the work, designed by consultants Mott MacDonald and Tony Gee, and to be built by preferred contractor Balfour Beatty, requires the bridge to be rebuilt in two distinct halves, to keep the line open during the upgrade.
"Each span currently has 15 [longitudinal, arched] ribs," said Burton.
"This will be extended with three extra ribs on the east side [up to the nearside disused piers] and one extra rib on the west side," he said.
Burton said core samples into the bridge's foundations revealed they were 1m deeper than expected.
"The foundations were really very good, and fingers crossed, we will not need to do any major work there," he added.
The disused piers will be strengthened by infilling with reinforced concrete and their foundations will be connected to those for the bridge abutments by jet grouting beneath the river bed.
The eastern side of the bridge will be closed first, so it can be dismantled and replaced span-by-span with the extra ribs included. Half the glass station box will be erected on the eastern half of the bridge.
Trains will then be diverted onto the new eastern half and the western half of the bridge will be rebuilt, allowing completion of the rest of the station
"The sawtooth roof will be of a modular construction and could include photovoltaic cells to provide up to 75% of the energy for the station," said Burton.
Network Rail programme director for stations and civils Charles Bell described the doubling in size of Farringdon to accommodate 12-car Thameslink trains south of the existing entrance.
He confirmed that the expansion of the station will be designed to allow future modification for the inclusion of a Crossrail interchange.