IMPROVEMENTS IN CONSTRUCTING TUBULAR TUNNELS OR SUBWAYS, AND APPARATUS FOR THAT PURPOSE
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by James Henry Greathead at tho
Office of the Commissioners of Patents, with his Petition, on the
18th October 1871.
I, JAMES HENRY GREATHEAD, of 63, Trinity Street, Southwark, in the
County of Surrey, Civil Engineer, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN CONSTRUCTING TUBULAR TUNNELS OR
SUBWAYS, AND APPARATUS FOR THAT PURPOSE," to be as follows:—
My improvements relate to a mode of constructing tubular tunnels
or subways and to apparatus used for that purpose.
These improvements are applicable in cases where the tubular tunnel
or subway is near the surface of the ground through which it passes, or
at a small depth below the bed of the river or other water under which
it is carried. In such cases the soil is either sufficiently loose to be
penetrated and pushed upwards by means which will be hereafter
described, or it may be loosened and partly or wholly cleared away by

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excavation on land or by dredging under water, rocks being blasted or
otherwise removed when they interfere with the course of the tunnel.
The tube which constitutes the tunnel or subway is fitted with a
sliding front, which acts at the same time as a shield and as a plough for
penetrating the soil in front of it and clearing a bed for the reception of
the tube. For this purpose it is sloped off so as to present an inclined
face to the soil before it. It overlaps the tube already formed in rings
secured together a sufficient distance to allow for the insertion of a fresh
ring; and the part which so overlaps the tube may be made to slide
tightly thereon by means of leather or other clastic collars inserted
between the shield and the tube. The shield is also provided with
screws or hydraulic presses, which butt against the front of the tube.
The operation of forming the tubular tunnel or subway is as follows:-
The soil in front of the shield being sufficiently loose in itself, or having
been partially excavated or loosened by dredging, blasting, or otherwise,
the shield is caused to advance by working the screws or hydraulic presses
within. When it has been sufficiently advanced, pushing the loose soil
in front of it upwards and so clearing a bed for the tube, an additional
ring of the tube is fixed within it. The scows or hydraulic presses
are made to butt on the new front so presented, and the operation is :
repeated.
I prefer to make the front of the shield when it is used under water
with protected port holes for observation, and with openings for boring
tools, and for pipes for flushing in front or at the sides, and tight doors
may be provided within or behind the shield to prevent the tube from a
boing filled with water in case of accident.
When the soil in front of the shield has to be dredged I prefer to
mount the lower shaft of the dredging machine on arms or brackets
attached to the shield so that as the shield is advanced the dredging
apparatus is guided by it to act immediately in front of it. Or instead 3
of dredging by a floating machine over the tunnel I sometimes mount
in front of the shield screws, blades, or scoops, caused to revolve so as to
loosen and press upwards the soil in front of it, and thereby facilitate its
advance.
When the shield and tubular tunnel are nearly cqual in waight to the o

page_text: or lightened so as to adjust its level. For this purpose I prefer to make
it with compartments, which may be filled with water to give additional
weight, or emptied to render it lighter.
The apparatus above described and the mode of working are
applicable also to the formation and laying of large pipes under water,
as may be readily understood.