"Richard J." wrote in message
. uk...
I should have realised that! But to me it had seemed unlikely that they
would go to the trouble and risk of digging shafts in the river bed rather
than sink them on the adjacent dry land. Did they decide to do the former
(a) because they couldn't dig the tunnels unless they had shafts less than
x yds apart (where x is shorter than the width of the river), or (b)
because they couldn't gain access to suitable shaft sites on land?

I don't think (a) holds true as the distance from Borough to King William
Street wasn't particularly long, and certainly much longer sections of the
C&SLR were built without intermediate shafts (e.g. Oval to Stockwell). I
think (b) is the more plausible, combined with the possible ease of removal
of spoil by barge and the lack of disruption to streets (remember that the
earliest Tubes had to follow the streets). I seem to remember reading
somewhere that no working sites were permitted within the City of London,
but that might have been in respect of the W&CR.

Looking through some books...
For the sake of ready disposal of the excavated material, and to avoid
the delay generally attending the acquisition of property, it was determined
to commence the tunnels in the river itself from a temporary shaft sunk into
the bed, clear of the foreshore and wharves. Piles were driven into the
gravel overlying the clay; and a working stage having been formed 100 feet
long by 35 feet wide, the iron rings of a 13-foot diameter shaft were bolted
together and sunk, without pumping, through the fravel and into the clay by
means of a grab. To maintain a uniform level between the water in the shaft
and that of the river, which rose and fell with the tide about 19 feet, a
valve was provided in the shaft lining below low-water level. In this way
the material surrounding the shafr was not disturbed by the inflow and
outflow of water during the sinking, and the valve was not closed uintil the
shaft was well into the solid clay. The lower portion of ths shaft was
completed in brickwork in cement with four openings of "eyes" from which to
start the two tunnels northwards and southwards. [...] The temporary shaft
was sunk to a total depth of 82 feet below high water; and the lower 9 feet
of the shaft were and are used as a sump for the collection of the drainage
from the two tunnels, both northwards and southwards. The upper portion
above the bed of the river was removed after the length immediately over the
tunnels had been closed and made watertight with concrete, asphalt and
puddle.
(Greathead, James "Greathead on City and South London Railway" in Minutes
of the Proceedings of the Institution of Civil Engineers (don't have volume
number). Paper No. 2873, 19 November 1895.)

By choosing the river to sink a shaft, Greathead was able to avoid the
outcry that would have ensued had ha attempted to dig up a public highway.
In the City of London, such an act would have been impossible as the narrow
streets were so tiny that they would have been entirely blocked by any shaft
that was dug within them. North of the river, the only highway of any size
which the railway passed beneath was King William Street, and as this formed
part of the main approach to London Bridge the City Fathers would obviously
have obstructed any plans to block it. The river also offered one other
advantage in that spoil from the works could be removed by boat thus
avoiding an increase in traffic on the streets. Later, additional shafts
were constructed on the sites of stations but when work commenced the
purchase of these sites had not been finalised and they were not available
for use."
(Holman, Printz "The Amazing Electric Tube", London Transport Museum).

Hope that's of interest.

DS.