Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates generally to a method and
a device for building in the ground ver-tical-walled tunnels or
the like star-ting from a subterranean conduit, and also to the
underground structures, such as tunnels or the like, obtained
by the said method.~
Already known in the art is the making of underground
vertical walls by first providing -trenches lined with sheet
metal and then fil]ing the same with concrete or with s-tone-
work or brickwork. Such trenches are usually excavated by the
open-cut method, starting from ~he surface of -the ground or
from an open excavation.
Where such walls must be cons-tructed on a surface-built
urban site or at a location where communication facilities such
as streets, roads 9 railway tracks, airpor-t runways, etc, are
established and the activities taking place at the surface
must not be interfered with, the trenches may be started from
underground horizon-tal propped galleries made by known conven-
tional means.
The horizontal galleries, the excavation of which is
started from an access shaf-t, serve as a s-tar-ting poin-t for
making -the trenches in-tended to ~orm the vertical walls. The
galleries also serve as condui.ts for ventilating, carrying away
the excavated materials, conveying props, rein~orcements and
concrete.
;
- . : :.
. . . -~ .: ~ .
,
.
This known methQd is usually ernployed for making -tunnels
for -the passage of sub-terranean -transpor-ta-tion means such as
underground railways in large urban centres. With such a me-thod,
the inconveniences caused to surface activi-ties are minimlzed.
On the other hand, a major drawback to this method is
that it is extremely expensive owing to the considerable and
highly skilled labour required for making -the propped galleries.
The purpose of the present invention is precisely to
obviate this drawback o~ -the known method.
To this end, the inven-tion is direc-ted to a method and a
device for constructing structures with underground walls, the
excavation of which is s-tarted from subterranean horizontal
conduits ob-tained simply, reliably and rapidly and requiring
very lit-tle labour.
The invention -therefore provides a method of construc-ting
in the ground vertical-walled s-truc-tures starting :~rom sub-ter-
ranean conduits, consisting in excavating vertical trenches
underneath the said conduits, lining -the said -trenches with
sheet metal, placing reinforcing elements in the said -trenches
and then filling -them wi-th concre-te or wi-th masonry, charac-te-
rized in that it consists in forming the said conduits of -tubes
driven horizontaLly in-to the ground at the desired level and
thereaf-ter excavating -the said trenches starting from openings
provided in the underside of the tubes.
Thus, the labour which formel~ly was necessary to excava-te
and fit up the propped galleries is dispensed wi-th.
According to ano-ther characterizing fea-ture of the
invention, the said me-thod consists in opening an access shaft
from the surface down to the desired level, and then, s-tarting
from the said access shaft, in driving the said conduits hori-
zontally into -the ground by pushing them behind one another by
means of hydrau:Lic ac-tuators bearing agains-t a wall of the sald
access sha~-t, in wi-thdrawing -the ear-th en-terin~ the said con~
duits as they are driven in-to the ground and in removing i-t
through the access shal-t.
The inven-tion also provides a device for carrying ou-t -the
above method, characterized in -tha-t it comprises tube sec-t;ions
of a mechanic~lly resistant material and me~ns for horizon-tally
z
driving into -the ground the said -tube sections behind one
ano-ther, such as for example hydraulic ac-tua^tors placed at the
bottom of an access shaft and bearing against a wall of -the
said shaft.
The invention also relates to a comple-te vaul-t or arched
roof structure for a sub-terranean tunnel oE the aforesaid -type,
and also to a me-thod of constructing the same.
The said vault or arched roof is use:Eul for building
subterranean structures such as highway -tunnels, tunnel sec-tions,
underground railway sta-tions or the like, and can be used be-
neath carriageways, down to at leas-t about 1.20 m below their
level without damaging them.
The said vault is preferably of the type resting on
substantially vertical side-walls of masonry~ particularly of
concrete masonry, extending along the two side edges of the
said vault, the said side walls bein~ advantageously obtained
by filling trenches from horizontal tubes placed along the said
side edges, the said tubes being provided to -this end wi-th
openings in their underside, as mentioned above.
The vault of masonry according -to the inven-tion is
charac-terized in tha-t it is formed of an upper bed cons-tituted
by a series of horizontal half-tubes arranged parallel to and
apart from one ano-ther, with their convexi-ty direc-ted upward
and their opening directed downward, and by connec-ting elements
between the said tubes, the said half-tubes being filled wi-th
concrete or some other masonry material, and of a self-suppor-
~` ting lower bed, preferably of reinforced or prestressed concrete,
in contact, on the one hand, with the said upper bed, and on
-the other hand, wi-th the upper ends of -the said side walls.
According to a preferred form of embodiment of the inven-
tion, the said connec-ting elements be-tween the half--tubes con-
sist of plates forming fluid--tight connectionStherebe-tween.
; ~lthough the said half-tubes and connecting plates may be
of any sui-table ma-terial1 such as for example me-tal, reinforced
concrete, prestressed concrete~ asbes-tos cement, plastics, etc,
they preferably are of metal, thus permit-ting in particular
-the fas-tening of the said plates to -the said -tubes by welding.
ï1~L59~2
'~he inven-tion also provides a method of cons-tructing a
masonry vaul-t or arched roo~ for a sub-terranean tunnel, of the
type comprising -the construction of subs-tantially ver.tical side-
walls laterally delimiting -the said tunnel, -the said side-
walls being preferably ob-tained by filling -two trenches from
two horizontal end-tubes provided -to this end wi-th openings in
their undersid.e, the said method being charac-terized in -tha-t
it consists in setting a system of hori.zontal tubes parallel to
and spaced from one another, the said tubes being dis-tributed
in accordance wi-th the desired profile of the vault between the
said -two horizon-tal end-tubes, -the said setting being prefera-
bly performed by exerting successive horizontal pushes on the
individual sections consti-tuting the said tubes, in placing
connecting elements between the said -tubes, preferably at
substantially -the middle of their height, in filling the upper
half of -the said tubes with concrete by means of a concrete
pump, in cutting off and removing the lower half o~ the tubes
after performing -the earthwork and staying works necessary the~
for , in pro~iding a formwork under the level of the upper half~
tubes remaining in placej and in depositing on -the said form-
work, in contact, on the one hand~ with the upper bed formed of
the said filled upper half-tubes and the said connecting ele-
ments, and on the other hand, with the upper portions o~ the
said side walls, a self-supporting lower bed of masonry,
preferably of reinforced or prestressed concrete.
According to a charac-terizing feature of the invention,
the said connecting elemen-ts are connecting plates which are
brought within the said tubes and pushed through their wall,
between -two successive tubes, after providing longitudinal
r
slo-ts in each of -the tubes or in some of them, until they abut
against the respective adjacent tubes.
According to another characterizing fea-ture of the inven-
tion, a formwork i.s provided subs-tan-tially a-t the level of the
diame-tral plane separa-ting the upper portion from the lower
portion of each tube, before filling the said upper portion
with concrete, and rein~orcing elements such as reinforcing
bars are placed before the said filling of the upper portion.
The said formwork may be cons-titu-ted in par-ticular by a plan-
king or by prefa'bricated reinforced-concre-te slabs preferably
provided with reinforcing metal elements projecting from the
surface of the said slabs and capable o.~ being connec,ted -to
the aforesaid reinforcing elemen-ts.
The aforesaid filling may be advan-tageously performed,
~or each tube, by means of a rigid pipe inserted in-to the
upper portion of the tube or tube section -to be filled, the
said pipe being connected through a hose, preferably of the
same diametre as the pipe, -to -the aforesaid concrete pump9
which discharges high-~luidity concrete, while the tube to be
filled is closed at both ends, the said pipe remaining in place
after the filling.
The inven-tion will be better understood and other purposes,
characterizing fea-tures, details and advantages thereof will
appear more clearly as the following explana-tory description
proceeds with re~erence to the appended diagrammatic drawings
given solely by way of example illustrating several forms of
embodiment of the invention and wherein :
- Figure 1 is a diagrammatic ver-tical cross-sec-tional
view of a buttressed gallery and a sheet-metal lined trench,
according to the prior art ;
- Figure 2 is a longi-tudinal vertical sectional view o~
one stage of the method according to the invention, illus-trating
the driv,ing of the tu~e sec-tions into the ground from an access
shaft ;
- Figure 3 is a ver-tical cross-sectional view of a tube
section and a trench according to the inven-tion ;
- Figure 4 is a longitudinal vertica]. sectional view
corresponding to Figure 3 ;
- Figure 5 is a vertical cross-sectional view correspon~
ding to Figure 3, after -the concre-te r,einforcing means are
placed in the -trench ;
- Figure 6 is a view corresponding to Figure 5, showing
~he trench after -the concreting ;
- Figure 7 is a diagrarnmatic vertical cross-sectional
view of a structure provided with a roof according to -the
invention ;
- Figure ~ is a cross-sec-tional view o~ a subterranean
tunnel provided~ av~lltor arched roof according -to one form
of embodimen-t of the inven-tion ;
Figures 9a -to 9c are de-tailed par-tial cross-sectional
views of -the vaul-t of ~igure 8, illus-trating various stages of
the me-thod of construction of the ~aul-t ;
- Figure 10 is an axial longitudinal sec-tional view of
the whole subterranean tunnel of Figure 8 toge-ther wi-th its
vault, showing the various s-tages of vaul-t cons-truc-tion ;
~ Figure 11 is a cross-sectional view of the said sub
terranean tunnel, upon the line XI-XI of Figure 10 ;
- Figure 12 is a cross-sectional view, upon the line
XII-XII of Figure13, of a lateral end sec-tion of the upper bed
of a vault according to ano-ther form of embodimen-t of the
invention ; and
- Figure 13 is an axial horizontal longitudinal sectional
view of the same bed upon -the line XIII XIII of Figure 12.
Referring -to the drawings, the prior art will first be
described for a better unders-tanding of the inven-tion and i-ts
advantages over the prior art.
In Figure 1, reference 1 deno-tes -the surface of the ground,
e.g.~ a surface~built urban area, -the figure represented on the
right side as a guide being drawn to scale.
According -to the prior-art, a horizontal gallery 2 is
excavated starting from an access shaft (not shown), and -then
propped or bu-ttressed at 3, L~ and 5 in a conventional manner.
From the horizontal bottom of this gallery, a trench 6 is
excavated and lined, as the excavation progresses, by means of
sheet-metal elements 7, 8 of a known -type. The elements 7 con-
sist of rigid plates placed against the ver-tical walls of -the
trench and in-terconnec-ted from one wall -to the o-ther by the
elements 8. The gallery 2 is of course large enough to provide
room for the passage of -the workers and the carrying out of
all -the necessary works : e~cava-tion of the -trench 6, removal
of the earth, supply and placing of reinforcement elemen-ts in
the trench, concre-ting of -the trench, e-tc.
This ls~own me-thod is reliable, but as already pointed out,
its cost is e~tremely high due to -the highly slcilled work -tha-t
is necessary for propping, buttressing or o-therwise supporting
-the walls of gallery Z.
There will now be described, wi-th reference to the
following ~igures, a me-thod and a device according to -the in-
vention allowing the above drawback of the prior ar-t to be
obviated.
According -to the invention, the propped or bu-ttressed
gallery 2 is replaced by a tubular condui-t 10 generally cylin-
drical in shape and formed of prefabrica-ted elements 11 of
appropria-te length which are dri~en horizon-tally in-to the
ground. To this end, and as in -the case of -the bu-ttressed
gallery, an access shaft 12 is sun~ from the surface of the
ground down to -the desired level. Means such as for example
high-power hydraulic actua-tors 13 are arranged at the bo-ttom of
the access shaft so as to bear at one end against a wall 1L~ of
the access shaft. The other end of the hydraulic actuators,
cons-titu-ted by the end of their piston rods, s provided with
a vertical pla-te 15 adapted to bear against the end of a pipe
section 11 so as to push and drive it horizontally .into the
ground. When a p.ipe section 11 is thus comple-tely or almos-t
completely driven horizontally into the ground, the following
section 11 is moved down into the access shaf-t and aligned with
the section 11 already driven in the ground, and is thereafter
pushed against and together with the preceding pipe sec-tion by
means of the actuators 13. The underground tubular conduit 10
represented in Figure 2 is thus obtained.
The sections 11 pushed horizon-tally into the ground are
open and therefore filled with earth while being driven. The
sec-tions 11 are large in diameter, e.g. on the order of 2 m,
and the earth within the tubular conduit 10 can -thus be removed
therefrom and finally carried to the surface through -the shaft
12.
The tube sections 11 are of a sui-table strong material
capable of withstanding without damage the stresses resulting
from the pressure of the earth and the driving force exerted
by the hydraulic actuators 13. The tube sec-tions are prefabrica-
ted elemen-ts made for example of steel, reinforced concre-te~
pre~essed concrete, asbes-tos cemen-t, plastics, e-tc.
They are nnoreover provided, in their underside, with
openings 16 which will permi-t -the excava-tion of a shee~netal
lined -trench 6' for making -the desired ver-tical wall. At the
loca-tions weakened by the said openings~ the -tube sec-tions 11
are s-trengthened by arches 17 of an appropria-te ma-terial,
arranged for exarnple on either side of the openings 16. As
already pointed ou-t, the inner dimension of the -tube sections
11 is enough to provide room for the passage of -the workers and
the carrying ou-t of the necessary works through -the openings
16 : excava-tion of trenches 6', placing of sheet-metal lining
elements 71 and 8', supply and placing of reinforcing means 18
in the -trenches 6', filling of the -trenches 6' wi-th concre-te
or masonry.
In Figure 5 is shown by way of example the trench 6' with
the reinforcing means 18 placed -therein, and in Figvre 6 is
shown the vertical wall 19 obtained after concreting -the
trench 6'.
The method according to the inven-tion may also be used
in constructing the roo~ of a sub-terranean structure e.g. an
underground railway tunnel, as shown in Figure 7.
In -this Figure, the -two tubular conduits 10, each asso-
ciated wi-th a ver-tical wall 19, form part of a set 20 of -tube
sec-tions 21 driven horizontally in-to the ground in parallel
relationship to one another and -to -the -tubular conduits 10 and
intended -to form the temporary or -the permanent roof of~ for
example, a tunnel. The -tube sections 21 are connected wi-th one
another and with the tubular conduits 10 by systems of metal
plates 22 or injections, so as to impart an integral structure
to the whole assembly. It is unders-tood -tha-t the tubes 21 are
driven horizon-tally into -the ground in -the same manner as -the
tubular condui-ts 10,being connected to the adjacent -tubes 21
by the systems of metal plates 22 or lnjections, and tha-t the O
tubes 21 are thereaf-ter filled wi-th concre-te or masonry to
form -the roo:f o:f -the subterranean s-truc-ture.
I-t is unders-tood that -the -tubular condui-ts 10 associa-ted
with -the ver-tica:L walls 19 form two parallel lines of tube
sec-tions and -that -the -tube sectlons 21 form n1utually parallel
intermediate lines connected to thc~ lateral llnes formed by -the
g
-tubular condui-~s 10.
~ The tube sections 11 or 21 may be circular, polygonal, or
; par-tly circular and partly polygonal in cross-section.
The method and dev.ice according to the invention offer
over -the prior art the following additlonal advan-tages :
- there is no need to effect previous injections of con-
crete in-to the ground, for -the combination of the tubes 10 and
21 wi-th the vertical walls results in a perfectl~ fluid--tight
assembly ;
the method according to the inven-tion reduces surface
subsidence or se-ttling and the damages caused by -the construc-
~; tion of such subterranean structures ;
- the method according to the invention is ~uch safer ~or
the workers, who can work sheltered by a continuous tube of
steel, concrete, plastics, etc;
-by reason of the reduction in surface subsi~ence, it is
~ possible to work nearer to the surface of the ground.
s In Figure 8 is shown a subterranean tunnel 111 excavated
in -the ground 102 above the ground surface 103, which~ for
example, is the surface of a carriage-way or road pavemen-t. The
tunnel struc-ture comprises side walls 10~a and 10~b, a floor
105 and a vault or arched roof 106 9 these various elemen-ts of
the structure being preferably of reinforced or prestressed
concrete. The reference numerals 107a and 107b denote the two
horizontal end conduits which have been used for excavating and
filling -the trenches occupied by the side walls 104a and 104b,
respectively.
The vault 106 .is formed of an upper bed 106a and a self-
supporting lower bed 106b, the lat-ter being in contact, on the
one hand, with the upper bed 106a and, on the other hand, the
upper endsof the side walls 104a and 10L~b. The upper bed 106a
is cons-tituted by a seri.es of horizon-tal half-tubes 108 to 115
arranged parallel to and apart from one ano-ther, with their
convexity directed up~ard and -their opening direc-ted downward,
and by connec-ting elements 116 -to 124 be-tween the said half-
tubes 108 to 115, the la-t-ter being ~illed with concrete or
ano-ther appropr.iate masonry ma-terial 125~
Reference is llOW made to Figures 9a to 9c, which illustra-
te the essential stages of the method ~f construc-tin~ the
vaul-t 106. Each o~ the half-tubes ~08 to 113 of Figure 8 re-
sults from the elimination of -the lower half of a series o~
horizontal tubes 111A and 112A shown in Figure 9a. These tubes
have been placed by any appropriate means, preferably as
described in reference to Figure 7.
In Figure 9a are seen the two tubes 111A and 112A which,
at this stage of the construction method, are embedded in the
surrounding ground 102, the transverse dimension of these tubes
being such as to provide enough room for the passage of the
workers. In the example illustrated, all these tubes are of
metal, and so are the connecting elements such as 119, 120 and
121 constituted by metal plates. T~e plates form a fluid-tight
connection between the successive tubes, as seen in Figures 1
and 2a to 2c. The placing of the connecting plates such as 120
and 121 is performed by first providing a longitudinal slot
126 and 127~ respectively, substantially at the middle of the
height of one of the sides of tubes 111A and 1~2A and then
inserting the metal plates 120 and 121, respectively, into the
slots 126 and127, by pushing the same, by any suitable means,
from the interior of tubes 111A and 112A until the said me-tal
plates abut agains-t the outer surface of the adjacent tubes,
i.e. the outer surface o~ tube 112A in the case of the metal
plate 120 brought within the tube 110A and pushed from the in-
terior of this -tube through the slot 126. The plates such as
126 and 127 are welded to the metal tubes from the interior of
which they have been put in place 5 along an internal longitudi-
nal welding line 128 and 129, respectively, in the case of
tubes 111A and 112A.
If desired, water tightness between the successive tubes
o~ the vault can be ensured by inserting plastics sections, e.g.
o~ polyvinylchloride, between the connecting plates extending
consecutively lengthwise of the tubes be-tween two adjacent tubes.
Figure 9b shows the considered vault portion after the
filling of the upper half of the tubes with concrete. This stage
is obtained in the following manner starting from the stage
illustrated in Figure 9a. A ~ormwork illustra-ted diagramma-tical-
ly at 130 is provided to delimit the upper portion of each
æ
1 1
of -the tubes such as 111~ and 112A, and reinforcing elements
such as reinforcemen-t bars 131 are placed, and -then the upper
halves of the said tubes are filled with concre-~.e. Use is made,
to this end, of a concrete pu~p supplying high-fluidity con-
crete so that a single concre-te pump located ou-tside the
structure can ensure the filling of a sufficient tube length
in a single operation. To -this end, the tube section whose
upper portion is to be filled with concrete is obturated at
both ends and supplied with concrete through a pipe extending
throughout substantially the length of the said sec-tion, the
said pipe being rigid in order to supply the said tube section
with concrete throughout its length. The pipe is connec-ted to
the concrete pump through, preferably, the medium of a flexible
conduit or hose of the same diametre as that of the pipe.
If the filling of the upper portion of -the tubes by the
means thus used is no-t considered to be sufficiently complete,
a make-up mortar injection or grout.ing is performed, preferably
by means of small pipes placed vertically, into the portion to
be concreted, the said small pipes being supplied through their
lower portion opening into the lower half of the horizontal
tubes. It is also seen in Figure 9b that -the earth below the
medial level of t~e tubes has been removed and tha-t -temporary
support ~rames, designated generally. by the reference numeral
132, have been provided to transmit the load to the floor (see
also ~igure 10), the said support frames comprising in particu-
lar upper horizontal beams 132a and vertical beams 132b. It is
precisely at this stage that the connection between the hori-
zontal tubes and the connecting plates such as 119 and 120
can be strengthened, if appropriate, by welding to the outside
of the said tubes, the plates abutting thereagainst, along
external longitudinal welding lines, such as 133 and 134 in
the case o~ the connecting pla-tes l19 and 120, respectively,
abutting agains-t -the tubes 111A and 1l2A~
Figure 9c i~lustra-tes a later stage of the vault construc-
ting method, during which the lower halves of the -tubes, such
as 111A and 112A, have been cut off and extracted, so that only
the upper hal~tubes such as 111 and 112 interconnected by the
connec-ting plates such as 120 and filled with concrete 125
~s~ ~
12
have remained in placeO At this stage, suppor-t frames 135
comprising in particular upper horizontal beams 135a and ver-
tical beams 135b transmi-t to -the -tunnel floor the load exerted
by the temporary roof thus cons-ti-tuted.
According -to a modified form of embodiment of the inven-
tion, the earthwork and the s-taying works can be per~ormed by
using, according to another method called -the "Berlin method"~
sheet metal linings instead of the aforesaid frames (which
permit excavation in s-topes by means of earthworking appliances).
In Figure 10 and/or Figure 11 are again seen -the vertical
side-walls 104a and 104b 3 the horizon-tal end-tubes 107a and
107b and the intermediate half-tubes which here are denoted by
the common reference numeral 136, the -tunnel floor being desi-
gnated by the numeral 137. In the right hand portion of E`igure
10 i-t is seen that -the support frames 132 constituted by beams
such as 132a, 132b and 132c have been placed under the intact
tubes denoted by the common reference numeral 136A, the said
portion of Figure 10 corresponding to the stage illustrated in
Figure 9b. In the following tunnel section, located in -the
middle of Figure 10, the lower halves of tubes 136~ have been
cut off (the said lower halves being shown in phan-tom lines)
and eliminated, so that now the load of the s-tructure is trans-
mitted to the tunnel floor 137 by the support frame 135 compri-
sing the beams 135a, 135b and 135c, this portion of the -tunnel
corresponding to the stage illustra-ted in Figure 9c. In the
left-hand portion of Figure 10, the tunnel section that is re-
presented illustrates the stage of constructing the self-suppor-
ting lower bed 106 of -the vault, a formwork cons-tituted by a
planking 138 supported by horizontal beams 139a and vertical
beams 139b, having been previously placed -to this end. Moreover,
suppor-t frames 150 cons-titu-ted by beams 150a, 150b and 150c
help in supporting the concrete bed 106b.
In the form of embodiment illustra-ted in Figures 12 and
13, the general s-tructure of the tunnel vault and the me-thod
of cons-tructing the same are similar to those of the form of
embocliment illustrated in Figures 8 to 14, but the form of
embodiment of the formworks within the tubes is di~ferent.
Fur-thermore, it is clearly seen that the connecting plates,
g3~7~
13
such as 1~0, 141 and 1~2, put in place frorn within a tube such
as 146 and welded thereto along internal welding lines such
as 140a and 141a al-terna-te with connecting plates such as 143,
144 and 145 put in place from within -the adjacent -tube 1L~7 and
welded to this tube along in-ternal welding lines such as 143a.
In Figure 12 are seen the horizontal pipes 160 serving
to supply concrete in-to the upper portions of the tubes, such
as 146, 147 and 148, from -the concrete pump, and also the
small ver-tical pipes 161 for injecting ~ake-up Mor-tar -to com
plete the filling of the said upper portions. The formwork here
is constituted by a planking 162, as shown for -the vault end-
tube 146, or by small prefabricated slabs of reinforced concrete,
such as 163a and 163b for the tube 147. These slabs are suppor-
ted by appropriate support means such as longitudinal wood
beams 16L~ supported by pillars 165, and -those portions of the
cormecting plates that protrude wi-thin -the ~bes, in association
with wood beam lengths, such as 166, alterna-ting wi-th the said
portions lengthwise of the tubes and secured by means of studs
such as 167, welded to -the wall of the said tubes. The planking
162, on the contrary, is supported at its centre only by the
beam 16L~, at its right-hand edge by the protruding portions of
the connecting plates, and at i-ts left-hand edge b~ a longitu-
dinal wood beam 166a secured to -the -tube 146 by studs 167a.
The reference numeral 16~ denotes the reinforcement of
the concrete mass (not shown) to be introduced in-to the upper
portion of the tubes, such as 146, 147 and 148 .
It would be noted that each prefabricated reinforced-
concrete slab, such as 163a, may be provided with metal reinfor-
cement elemen-ts protruding at 169, on the upper surface of the
said slabs,and therefore capable of being assembled to the
reinforcemen-t 168.
Of course, the constitution and construc-tion of -the sel.f-
supporting lower bed depend upon the par-ticular characteristics
of the whole struc-ture to be obtained and the descrip-tion just
given is only an example thereo~.
Of course, the inven-tion is by no means limited to the
forms of embodiment described and .illus-trated which have been
~59~7Z
14
given by way of example only. In particular, it comprises all
means constituting technical equivalents to the means described
as well as their combinations, should the latter.be carried
out according to its gist and used within the scope of the
following claims.
,
~.
