Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~2~423
PLANT for DIGGING and SHORING UP the WALLS
of TUNNELS DURING EXCAVATION
BACKGROUND of the INVENTION
The present invention relates to plant designed for
use in digging and shoring up excavations during
tunnelling works.
In recent times, a number of different techniques
05 have been employed in the construction of tunnels,
for road or rail, for utilities such as sewers or
underground canals, and for the routing of water
courses generally.
One such technique involves the use of mechanical
shields to carry the excavation forward while
installing pre-cast lining sections (tubular or
segmental) as dig~ing proceeds. These shields can
be driven forward by hydraulic jacks from outside,
using the pre-cast tunnel linings already installed
as intermediate elements in a growing chain.
2 ~2~
The distances obtainable using this expedient are
not great, however, given that friction increases
progressively with length, and impossible demands
are put on the strength of the intermediate linings
05 as greater and greater thrust is applied.
The shield can also be driven forward utilizing the
previously installed section of the tunnel lining
(pre-cast or cast-in-situ) as a fixed bearing.
In this instance, however, limitations are imposed
on forward progress by the capability of the lining
to withstand the thrust of the hydraulic jacks;
more exactly, on encountering a degree of lateral
friction or resistance to penetration greater than
the mechanical strength of the lining, the shield
obviously can no longer operate, inasmuch as the
force required to produce increased thrust would
destroy the lining.
This drawback is partly overcome in the majority of
cases by installing intermediate stations as shown
in German patent application n¦ 3 032 856, against
which to exert the necessary thrust, though the
reaction force from such stations is transmitted
just the same eit~er to adjacent sections that are
not designed to withstand high pressures, and thus
will be in danger of brea~ing up, or to a lining
cast in-situ, which becomes subject to considerable
stresses.
In addition, increased friction must be overcome in
driving forward where the bore has to follow a
05 gentle bend; in this particular situaticn moreover,
the direction of thrust no longer coincides with
the bore axis, and there is no means of altering
the direction except by way cf the jacks, which are
located remotely from the section that is required
to change course.
An apparatus for tunnelling through soft stratum
illustrated in UK patent application nl 2 180 867
comprises a body portion having a plurality of
cylindrical members connected together, a head
portion connected to one of the cylindrical members
at one of its ends, a waterproof frame disposed
between the head portion and cylindrical member, a
plurality of pneumatic cylinders disposed between
each two of the cylindrical members and a plurality
of grouting pipes mounted at the tail end of the
body portion. With this apparatus the reaction
~orce is transmitted to cement grout.
Another apparatus and method for continuously or
intermittently advancing tunnel supports against
surrounding earth pressure is shown in US patent
4 2 ~'3 ~
n¦ 3 613 384. The cutting edge and trailing shells
are interconnected by a longitudinal frame or cage
structure. Intermediate the forward and trailing
shell are overlapping intermediate shells connected
05 individually to the cage structure by hydraulic
cylinders so that each intermediate shell can be
moved longitudinally relative to the others and
relative to the tunnel wall while the other inter-
mediate shells engage the tunnel wall and advance
the cage as well as the forward or support shell
and the trailing shell. The intermediate shells are
moved forward sequentially by releasing pressure
exerted against the wall, as by contracting the
shell.
Where the tunnelled ground is clay, or other loose
soil lacking in consistency, conventional prior art
methods involve manual or mechanical excavation,
shoring and installation of temporary supports or
centers, then driving forward, consolidating the
exposed walls, and ultimately casting the tunnel
lining.
In this type of procedure, consolidation consists
generally in driving piles into and jet grouting
the entire supporting wall of the tunnel; needless
to say, the piles remain embedded, and will be
7/ ~ 3
concealed behind the lining of the tunnel once in
place.
Methods of the kind in question are also beset by
certain limitations and drawbacks, namely:
05 -high costs deriving from the slow rate of progress
and the high manning requirement which accompanies
the various steps of the procedure;
-dangerous operating conditions (risk of collapse
at the workings), for those occupied in excavation
and erecting temporary centerings;
-waste of materials produced in erecting temporary
structures pending installation of final linings.
The object of the present invention is to permit of
excavating a tunnel of any given diameter or cross
section, and of whatever length, without subjecting
pre-cast linings to high thrust stresses.
A further object of the invention is to achieve a
considerable reduction in the cost of shoring up
the tunnel walls during the course of excavation.
Another object of the invention is to provide a
temporary shield structure during excavation and
subsequent casting/lining works such as will ensure
maximum safety during the construction of tunnels
of any given size and length, undertaken in loose
or unstable ground.
2 ~
Yet another object of the invention is to enable
excava~~ion of the tunnel using conventional and
readily available digging equipment, thus bringing
the advantages of low running costs and the option
05 of varying excavation and spoil-removal methods in
such a way as will best adapt to the type of ground
encountered in the course of tunnelling.
An additional object of the present inven~ion is to
render the steps of excavation, driving and .~ining
independent of one another.
SUMMARY of the INVENTION
The stated objects are realized comprehensively in
plant according to the invention, which relates to
a shield of the type used in tunnel excavation, and
consists in a self-propelled modular structure
affording temporary support to the excavated tunnel
walls and housing the tunnelling equipment, which
is extendible, and designed to advance and/or drive
through the ground without the assistance of fixed
thrust bearings, but exploiting exclusively its own
mass and/or lateral friction generated between each
element of the modular structure and the adjacent
tunnel wall to provide the force of reaction.
BRIEF DESCRIPTION of the DRAWINGS
The invention will now be described in detail, by
way of example, with the aid of the accompanying
drawings, in which:
-fig 1 shows the plant disclosed in longitudinal
05 section, viewed in the initial stages of excavating
a tunnel;
-fig 2 shows the plant in the same section as that
of fig 1, seen fully inside the tunnel;
-fig 3 shows a detail of the plant on larger scale.
DESCRIPTION of the PREFERRED EMBODIMENTS
With reference to the drawings, plant according to
the invention consists in a plurality of modular
structures or cylindrical elements 1, by which the
wall of the tunnel 2 is completely masked.
Each modular element 1 consists substantially in a
first ring 3 of 'I' section, to which the rear ends
of a plurality of hydraulic cylinders 4 are hinged,
and a second ring 3a through which the rod ends of
the cylinders are inserted, the rods 5 themselves
being mounted by way of respective pivots 6 to the
first ring 3b of the adjacent element.
a 2~
The hydraulic cylinders are encompassed by an inner
annular sheet member 7 and an outer annular sheet
member 8, of which the outer member lies in direct
contact with the excavated bore.
05 Propulsion of the structure is brought about by
operating the cylinders in such a way that each
modular element is driven forward by the cylinders
anchored to the element behind.
With the leading element and successive elements
thus linked in a chain and generating friction with
the tunnel wall, the reaction necessary for forward
progress is ensured; as regards the development of
thrust, in short, the structure is self-anchoring:
accordingly, the first elements in sequence, i.e.
those farthest from the work face, are drawn toward
the excavation area, and the entire structure edges
forward as the result of the combination of thrust,
generated at the leading end, and the pull exerted
on the rear end.
In a preferred embodiment, each modular element
will be some 2 metres in length, and the number of
elements utilized will be such that the length of
the assembled structure is substantially equal to
the diameter of the bore at least, or twice the
diameter at most.
9 7~2~f' ~;i
Given that operating the cylinders of one modular
element has the effect of distancing the element in
front, a space is opened between one element and
the next which leaves the cylinder rods exposed.
05 To avoid this eventuality and ensure the continuity
of the shield, the structure further comprises
plates 9 rigidly associated with the annular sheet
members 7 and 8 of one element and slidable over
those of the next, thereby encapsulating the space
occupied by the extended rods 5 as illustrated in
fig 3.
The plant will carry a work platform 11 from which
excavators 12 have access to the face, the spoil
being removed by ordinary trucks 13 that enter and
leave via a tiltable ramp section 14 connecting the
platform 11 with the part of the tunnel already
lined or otherwise prepared, which is denoted 10.
15 and 16 respectively denote the operator's cab
and the hydraulic power unit.
Plant thus embodied provides a temporary shoring
structure that is self-propelled and extendible,
capable of passing along the entire length of the
bore and emerging at the far end.
Use is made of n modular elements of cross section
equal to or greater than that of the finished
1 0
tunnel, and of length 1, where n and 1 are variable
according to the dimensions of the bore and the
type of ground throuqh which it is to be driven.
The elements are fastened and/or hinged together by
05 way of hydraulic cylinders, as illustrated, and/or
of other suitable propulsion and steering means.
The extendible structure thus embodied accommodates
all such excavating equipment and transportation as
may be utilized, carrying them along as it edges
10 forward; moreover, the plant advances and pushes
through the soil without the aid of any additional
fixed bearing, whether placed externally or to the
rear, given that the hydraulic cylinders (or other
suitable propulsion means such as worm drives) are
15 able to bring about the movement and penetration of
one or more elements with no expedient utilized to
counteract thrust other than the mass of the single
elements and/or the effects of lateral friction.
What is more, by exercisinq uniform and/or suitably
20 proportioned control over the hydraulic cylinders
or other suitable drive means interconnecting the
rings, if becomes possible to steer the structure
accurately through bends, of which the radius will
vary according to the number of modular elements
25 incorporated and their individual length.
The invention thus affords several advantages:
-the excavation site is made safe, since digging
and lining operations are carried on entirely from
within the structure, functioning as a shield by
05 shoring up the excavated walls; any collapse of the
earth at the work face can be avoided or attenuated
by penetrating deeper with the leading end, given
that the structure is extendible through a distance
of m metres (dependent on the number n of elements
incorporated and the travel permitted to each one),
and can therefore penetrate the necessary depth at
front while the rear end remains in position until
the relative stretch of lining is in place;
-an extendible tunnelling shield brings operational
flexibility, with excavation, removal of spoil and
casting/assembly of linings becoming independent of
one another;
-the capacity of the plant to act as a temporary
shoring structure renders conventional centering,
shuttering and consolidation works unnecessary,
signifying notable advantages from the standpoints
of time-saving and cost reduction;
-propulsion is effected without additional fixed
bearings to accommodate thrust, enabling unlimited
progres~; through any type of ground;
12
-the shield is easily set in motion, requiring no
reaction pillars or tracks, but simply the laying
of blocks and the preparation of a starting ring at
the tunnel mouth:
05 -with the assembly of modular elements operating as
a self-propelled structure, and no need to exploit
the installed tunnel lining as a reaction bearing
for propulsion jacks, linings can be proportioned
without any provision for additional loading.
