Improvements in the Construction of Tunnels and in the Appliances Required therefor.
Year: 1890

page_text: Date of Application, 3rd Dec., 1890
Complete Specification Left, 25th Aug., 1891-Accepted, 31st Oct., 1891
PROVISIONAL SPECIFICATION.
Improvements in the Construction of Tunnels and in the Appliances
Required therefor.
I, JOHN WULSTAN TWINBERROW, of 172 York Road, King's Cross, in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this invention
to be as follows :-
The object of my invention is to facilitate the construction of tunnels in such
cases as it is necessary to support the weight of the superincumbent earth, to prevent
injury to the surface above the tunnel and to the property & buildings on it by
reason of the subsequent subsidence of the ground, & to economise material &
labour by the execution of so much excavation only as is required for the actual
reception of the tunnel arch & the poling boards above it.
To attain these ends I proceed as follows:-I employ steel or iron drawing bars
or girders of suitable section to support the ground over the arch instead of the
usual larch bars. These bars are placed at such distances apart as are found
convenient & the weight of the ground to be carried demands. The ground inter-
vening between them is supported by poling boards of the requisite length the ends
of which rest on the drawing bars. The position of the bars is for the most part
within the line of the extrados of the future arch.
The bars or girders are forced forward as the mining becomes sufficiently
advanced for their reception by means of levers, jacks, rams, screws or other
suitable means & are supported at their leading end by a timbered face, whilst the
trailing end rests on the arch of the length of tunnel last keyed.
The leading end of the bar is of such a shape as admits of its resting readily &
without danger of lateral displacement on the props or grooved sweeps provided
at the timbered face for its support.
The trailing end is so shaped by being partially cut away, perforated or grooved
as to admit of the space which the bar previously occupied in the former length
being readily filled up with mortar & bricks, concrete, grout or other suitable
material forced back from the leading end of the arch. In cases where the nature
of the ground admits of the employment of a bar of sufficiently light section, this
space being small may be left unclosed without danger to the stability of the arch
or without incurring the possibility of settlement.
The bars may be provided with holes or studs to enable a grasp to be taken of
them when it is desired to get them forward, & with a fillet to prevent lateral
movement of the boards resting on them.
As the tunnel arch is constructed a chase is left in it immediately around the
bars whilst between them the arch is built tightly up to the poling boards.
Consequently when the bars are drawn forward for the support of the succeeding
length these boards prevent the earth from sinking down behind the bars & closing
up the chases. The depth of the bars & of the chases is such as admits of the
thickness of the arch below the chases being sufficiently great to ensure the perfect
stability of the arch until such time as it is found convenient to close up the chases,
the arch centreing moreover conducing to this object.
In the event of the ground proving so heavy as to require the employment of
bars of inconvenient weight they may be made in two or more pieces & ordinary
taking out timbers are used to support the boards intermediately between bars of
lighter section than would be necessary for the unaided support of the ground. As
the arch is carried up these taking out timbers are removed & the ends of the
drawing bars projecting beyond the arch of the length being lined & over the
timbered face serve to support that portion of the length under consideration until

page_text: the mining of the next length is commenced; & through the sill props which
supported them, to prevent without additional strutting that rising of the sills which
sometimes occurs when taking out bars are alone employed.
Dated this Second day of December 1890.
COMPLETE SPECIFICATION.
Improvements in the Construction of Tunnels and in the Appliances
Required therefor.
I, JOHN WULSTAN TWINBERROW, of 172 York Road, King's Cross, in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
The object of my invention is to facilitate the construction of tunnels, subways,
sewers or other subterranean passages in such cases as it is necessary to support the
weight of the superincumbent earth during the progress of the work and to prevent
injury to the surface above the tunnel and to the property and buildings on it by
reason of the subsequent subsidence of the ground & to economise material & labour
by the execution of so much excavation only as is required for the actual reception
of the tunnel arch and the poling boards above it. By my invention also all
disturbance of the ground in drawing the bars is avoided and an advantage is
obtained in such cases as the head room is limited.
To attain these ends I proceed as follows:-I employ steel or iron drawing bars
or girders of suitable section to support the ground over the arch or the more
central portion of it. These bars are placed at such distances apart as are found
convenient and the weight of the ground to be carried demands. The ground
intervening between them is supported by poling boards of the requisite length the
ends of which rest on the drawing bars. The position of the bars is for the most
part within the line of the extrados of the future arch.
The bars or girders are forced forward as the mining becomes sufficiently
advanced for their reception by means of levers, jacks, rams, screws or other suitable
means and are supported at their leading end by a timbered face, whilst the
trailing end rests on the arch of the length of tunnel last keyed.
The leading end of the bar is of such a shape as admits of its resting readily and
without danger of lateral displacement on the props, crossheads or sweeps provided
at the timbered face for its support, such props, crossheads or sweeps being more-
over grooved or notched out when by so doing a firmer bearing is afforded for
the bar.
The trailing end is so shaped, when the particular section of bar employed
renders it desirable, by being partially cut away, perforated or grooved as to admit
of the space which the bar previously occupied in the former length being readily
filled up with mortar and bricks, concrete, grout or other suitable material forced
back from the leading end of the arch. In cases where the nature of the ground
admits of the employment of a bar of sufficiently light section, this space being
small may be left unclosed without materially affecting the strength of the arch or
incurring the possibility of settlement of the superincumbent ground.
The bars may be provided with holes or studs to enable a grasp to be taken of
them when it is desired to get them forward, and with a fillet to prevent lateral
movement of the boards resting on them.
As the tunnel arch is constructed a chase is left in it immediately around the
bars whilst between them the arch is built tightly up to the poling boards.
Consequently when the bars are drawn forward for the support of the succeeding
length these boards prevent the earth from sinking down behind the bars and
closing up the chases. The depth of the bars and of the chases is such as admits

page_text: of the thickness of the arch below the chases being sufficiently great to ensure the
perfect stability of the arch until such time as it is found convenient to close up
the chases, the arch centreing moreover conducing to this object.
In the event of the ground proving so heavy as to require the employment of
bars of inconvenient weight or of inadmissible dimensions either of the following
expedients may be adopted.
Firstly I use taking-out bars of timber, iron or any suitable material placed to
support the poling boards intermediately between drawing bars of lighter section
than would be necessary for the unaided support of the ground. In this case I
prefer to carry the leading ends of all the bars on timber cross-heads supported by
the face props. Each of these cross-heads being made of sufficient length to receive
two or more bars I am thereby enabled to dispense with the excessive number of
props required when each bar is provided with its own props. The cross heads
abut against one another and their tops are cut to the sweep of the extrados of the
tunnel. They are provided with grooves on the top in which the leading ends of
the drawing bars rest and their trailing face may be cut to a slope or notched out
so as to afford a bearing for the leading ends of the taking-out bars such ends being
cut to a form corresponding with that of the cross-head. As this arch is carried
up these taking-out bars are removed and the ends of the drawing bars projecting
beyond the arch of the length being lined & over the timbered face serve to support
that portion of the length under consideration until the mining of the next length
is commenced; and through the cross heads & sill props which supported them, to
prevent without additional strutting that rising of the sills which sometimes occurs
when taking out bars are alone employed.
:
Secondly I form the bar in two or more pieces each being of such a weight as
may be conveniently manipulated. Great strength combined with lightness may
be obtained by uniting such pieces in the form of a truss. In this case the top or
compression member of the truss forms a complete drawing bar. This bar being
got into position & propped beneath the poling boards & the mining being
sufficiently advanced for their reception, the other members constituting the truss
are introduced and all is tightened up. This is repeated with each drawing bar so
soon as sufficient mining has been executed to enable the excavation to proceed
behind the truss. The centres for the arch are placed beneath the struts of the
truss. The length of these members is adjustable so that the weight of the ground
may be transferred directly by them to the arch centreing. So soon as this has
been done the tension members of the truss may be removed with impunity. The
arch lining is now carried well up to the lowest drawing bar the struts to which are
then slackened out and removed. The arch may be then carried on to the next
bar when the above process is repeated, and so on until all has been completed.
The top compression members of the trusses are thus left in chases in the arch
until drawn forward during the mining of the succeeding length, when the chases
may be closed up.
The following description of a particular example will, with the aid of the sheet
of drawings attached, render my invention sufficiently comprehensible, though it
must be understood that I do not limit myself to the forms or dimensions therein
shown which are merely given by way of illustration and are subject to such
modifications as the circumstances of the case demand.
Referring to the accompanying sheet of drawings
Fig. 1 represents the half cross section of the excavation for a tunnel arch
looking towards the leading end.
Fig. 2 represents the half cross section of the same length during the construction
of the lining arch.
Fig. 3 is a longitudinal section showing a length mined and ready for lining.
A, A..
are the steel drawing bars to which my invention refers. The mining
of a length proceeds as follows: A top heading of the requisite length being
supposed driven the centre bar is drawn forward into it and propped as shown
at D Fig. 3. The position of this bar is such that its upper surface shall be as

page_text: nearly as possible level with the extrados of the arch when it is constructed. The
mining is now proceeded with on both sides, poling boards E being inserted when
necessary as the excavation advances, their one end resting on the centre bar the
other being temporarily supported until sufficient excavation is completed to allow of
the second bar on each side being drawn forward and securely propped at its leading
end. So soon as this has been done mining is recommenced & the above operations
are repeated. In general from 5 to 9 steel bars placed about 2' 6" apart will be
found sufficient for a tunnel for a double line of railway through ordinary heavy
ground, the remainder of the excavation being supported by taking-out timbers in
the ordinary manner. The bars may be efficiently stretched with short blocks of
timber to prevent lateral displacement. It will be seen that the only excavation
beyond the extrados of the tunnel is that required for the head trees of the top
heading and for the poling boards which are afterwards built in. That portion of
a tunnel known as the sweets is thus wholly avoided and a corresponding economy
of excavation and brickwork effected. The excavation being completed the lining
is built in the ordinary manner up to the steel drawing bars. Around these a chase
is left in the arch H as shown at A. Fig. 2, the masonry or brickwork being built
tightly up to the poling boards in the space intervening between the bars--see E
Fig. 2. It will thus be seen that when the bars are drawn forward during the
mining of the next length the ends of the poling boards projecting over the chases
in the arch will prevent any settlement of earth into them. The state of affairs at
this stage is shown at B Fig. 2. No difficulty is found in drawing the bars forward
as by allowing them to drop slightly all weight is effectively transferred from them
to the arch itself. The chases may be closed up at any convenient time during the
mining of the succeeding length as for instance when the excavation is down to
the top sill. This is done by passing bricks and mortar alternately down the chase
on a long handled shovel, removing them thence and forcing them well home with
a punner, or the chases may be closed by ramming back fine concrete with a punner
or by pumping back liquid grout, thus in any case completing the arch to its full
section throughout.
Fig. 4 represents a few convenient sections for the drawing bars, the scantlings
of which should be so chosen as to admit of the chases being worked to brickwork
dimensions.
The method of affording additional support by means of taking-out bars inserted
between the drawing bars will be understood by reference to C Fig. 2 where an
intermediate timber taking out bar is shown supporting the poling boards between
the drawing bars. The brickwork having been carried up as close to the taking-
out bar as possible so as to support the poling boards resting on it, the bar is
removed and the brickwork carried on to the next taking-out bar a chase being left
around the intervening drawing bars just as in the general case.
The method of trussing the bars is most advantageously applied when it is
desirable to carry out the work in long lengths say for example 18' and when the
ground is very heavy.
Fig. 5 represents a half cross section of the excavation for a tunnel arch looking
towards the leading end.
Fig. 6 shows the same length during the construction of the lining arch.
Fig. 7 is a longitudinal section of the length shown in Fig. 5.
Fig. 8 represents a portion of the truss to a somewhat larger scale.
Р
A, A. are the drawing bars. E, E... the poling boards. q, q the struts &
P. p... the tension members of the truss. H is the arch. G, G the centres & B Fig. 7
represents the chase after the bar has been drawn forward out of it. The tie bars
may be provided with union screws to admit of the whole being tightened up, and
they together with the struts are attached to the drawing bar by means of bolts or
pins which can be easily inserted or removed. The length of the struts is adjustable
by forming them in two portions the one screwing into the other, or by means of
wedges or slack blocks as shown at r Fig. 8, or in case it is desired to make the
truss of a greater depth than the arch the struts may be composed of two members

page_text: one passing down each side of the centre ribs & supported from them by a movable
saddle passing over or through the rib & connecting the two members of the strut.
The execution of a length proceeds on the same lines as hereinbefore described
for the untrussed bars, with the exception that the trussing of the drawing bars A..
Figs. 5 to 8 is completed by means of the struts g & ties p so soon as their intro-.
duction will in no way impede the miners, the drawing bars A.. being moreover
supported until such time by one or more temporary props in such cases as it may
be found desirable to do so. The tie bars p p are first removed after the
centres G. G have been set and the struts q. q have been given a firm bearing
on them.
By this means the weight of the ground is at once transferred directly to the
centres, distortion of which by rising of the crown due to unequal loading is thus
avoided. The struts q. q. are slackened out and removed in turn as the arch is
carried up to them.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
(1) In constructing tunnels, sewers, subways or other subterranean passages the
use of drawing bars of steel or iron substantially in the manner and in the position
hereinbefore set forth and as illustrated by the accompanying drawings.
(2) In constructing tunnels, sewers, subways or other subterranean passages the
combined use of drawing bars of steel or iron with taking-out bars in the position
and manner hereinbefore described and set forth.
(3) In constructing tunnels, sewers, subways or other subterranean passages the
use of movable trussing to the drawing bars substantially as hereinbefore described
and as illustrated by the accompanying drawings.
(4) In constructing tunnels, sewers, subways or other subterranean passages the
use of a long handled shovel and punner for closing up the chases with bricks and
mortar as hereinbefore described and set forth.
(5) In constructing tunnels, sewers, subways or other subterranean passages
the groove in the top and the sloping face of the crossheads of the face timbers
whereby the bars are maintained in position as hereinbefore described and set
forth.
Dated this 25th day of August 1891.
J. WULSTAN TWINBERROW, A.M. Inst. C.E.