Rib for supporting and consolidating a sequential excavation and method for installing such a rib inside a sequential excavation

Abstract

A rib for supporting and consolidating an excavation, comprises a plurality of structural elements (15, 16, 17) which are connected to each other in a movable manner so that the rib can move from a preassembled, at least partially folded configuration before installation to an intermediate, partially extended support configuration of the crown of a sequential excavation in a crown plane as far as a definitive configuration for support on a plane of the base at a lower height than the crown plane, wherein the structural elements are blocked with structural continuity with respect to each other in a mutual position which generally defines an arched rib.

Description

[0001] RIB FOR SUPPORTING AND CONSOLIDATING A SEQUENTIAL EXCAVATION

[0002] AND METHOD FOR INSTALLING SUCH A RIB INS IDE A SEQUENTIAL

[0003] EXCAVATION

[0004] Field of the invention

[0005] The present invention relates to a rib for supporting and consolidating a sequential excavation and an automatic method for installing a supporting rib inside a sequential excavation .

[0006] The term " sequential excavation" is intended to be understood to be an excavation carried out with a sequential excavation method ( SEM) or NATM (New Austrian Tunneling Method) .

[0007] Technological background

[0008] For supporting excavations , such as , for example , road or rail tunnels , it is known to use consolidation arches which are known as ribs . In particular, a rib usually comprises a plurality of shaped structural elements which are made of steel and which are mutually connected in a vaulted configuration . Such elements are constituted by open profiles with an H-shaped, HEB, HEM, IPE , INP, C-shaped or double T- shaped cross-section . In some cases , the elements can be tubular . In the maj ority of cases , the structural elements of a rib are connected to each other in the region of the excavation to be consolidated after having been shaped in the carpentry workshop . After it has been assembled and installed, each rib is connected to the adj acent ones via connection members , referred to in j argon as "chains" even i f normally they are constructed via rigid elements , the ends of which are coupled to supports which are welded along the body of the profiles of the ribs . The space between two consecutive ribs and the wall of the excavation is consolidated usually via sprayed concrete ( spritz-beton / shotcrete ) which forms a structural covering which also encloses the ribs .

[0009] The excavations can be constructed as full-sections or, more commonly, as sequential excavations . The sequential excavations , which are the field to which the present description relates are carried out , whatever the section thereof , by progressively advancing with di f ferent steps which succeed each other and are repeated . In greater detail , a start is made with the crown plane and the tunnel is attacked starting with that excavation section . The tunnel then proceeds with the conventional methodology of excavation means and means for positioning ribs and sprayed concrete . The excavation then continues , after a distance depending on the geological formation, with the so-called bench excavation, that is to say, with the excavation of the area under the crown . This provides for excavating one of the two portions of the side wall of the excavation, also referred to as the lateral excavation, or bench widening excavation or pier, which gradually proceeds as the excavation of the crown advances . There follows the excavation of the other side wall portion of the excavation, that is to say, the other bench widening or pier, which also advances gradually as the excavation of the crown and the first lateral excavation advances . The excavation of a central ramp for access to the excavation plane also proceeds , gradually advancing as the excavation of the crown advances . The final step which continues sequentially is the formation of the inverted arch .

[0010] The structural elements which form the conventional ribs are j oined together by means of flanged couplings . A development and improvement of this system are described in WO 2015 / 186029 which describes an articulated connection system with automatic blocking of the structural elements which form a rib, which has a vaulted configuration which generally resembles that of the excavation portion which is intended to be consolidated via the rib itsel f . The structural elements which form the rib, which are made of metal material , such as , for example , construction steel , are connected to each other with a rotatable coupling, for example , by means of hinges which are enclosed in the structural j oint so as to move from a first position, in which the structural elements are substantially folded one on the other, to a second position, in which they are arranged to form at least one substantially continuous rib portion .

[0011] Another system of the type is described in WO 2022 / 254325 .

[0012] The systems described in WO 2015 / 186029 and WO 2022 / 254325 have been demonstrated to be ef fective for use in fullsection excavations but have characteristics which limit the use thereof in sequential excavations . The progressive and sequential advance of the excavation does not allow the use of known systems , particularly because the ribs cannot support the crown without being completely open, which is impossible until the excavation of the side walls has been completed, or bench widening excavations or piers . This involves the risk that the wall of the crown, which is not supported over a speci fic length of time , can collapse , with evident and substantial risks for persons and equipment near the front of the excavation .

[0013] Therefore , there is perceived the need for a rib with improved features which can advantageously be used in the construction of the tunnels constructed by sequential excavation .

[0014] Statement of invention An obj ect of the present invention is therefore to provide a rib for supporting and consolidating a sequential excavation, which allows the production of a rapid and safe connection between the structural elements thereof so as to be particularly stable for supporting the walls of the crown, even without it being necessary to wait for the excavation of the corresponding side walls , or bench widening excavations or piers , which in the remainder of the present description will always be referred to as right and left lateral excavations , respectively .

[0015] Another obj ect of the invention is to provide a rib for supporting and consolidating a sequential excavation which can readily be used for supporting the walls of the excavation even when the lateral excavations of a sequential excavation are completed without any need for interrupting the support of the crown portion .

[0016] Another obj ect is to provide a rib which is relatively economical and simple to manufacture .

[0017] Another obj ect is to provide a rib which can be installed rapidly, automatically using only mechanical means or at least mainly automatic means and, particularly, which can be safe for the operators and the employees for the excavation .

[0018] These obj ects and other obj ects are achieved by means of a preassembled rib comprising a plurality of structural elements which are movably connected to each other in such a manner that the rib can move from an initial compact configuration, before the installation, to an intermediate configuration, which is partially extended, for supporting the crown of a sequential excavation in a crown plane , as far as a definitive configuration for supporting and consolidating the entire profile of the excavation, wherein the rib is supported on a plane of the base which has a lower height than the crown plane . The structural elements are blocked with structural continuity with respect to each other in a mutual position which generally defines an arched rib, initially for supporting only the crown and subsequently for totally supporting the walls of the excavation .

[0019] One advantage of the present invention is the fact that it allows the immediate and integrated consolidation of the excavated crown portion before completion of the right and left lateral excavations . Another advantage of the rib of the present invention is the fact that it can support the excavation walls not only independently of the advance of the excavation under the crown excavation, but also independently of the progression of the lateral excavation on the right with respect to that on the left .

[0020] According to a first aspect , there is described a rib for supporting and consolidating an excavation . The rib may comprise a plurality of structural elements . The structural elements can be connected to each other . The structural elements can be movably connected to each other . The connection between the structural elements may be such that the rib can move from a preassembled configuration before installation to an intermediate , partially extended support configuration, as far as a definitive , completely extended installation configuration . The preassembled configuration can be at least partially folded . In the intermediate configuration, some structural elements can be blocked with respect to each other . In the definitive configuration, all the structural elements of the rib can be blocked with respect to each other . The structural elements can be blocked with structural continuity, that is to say, resisting the forces which are applied by the walls of the excavation as i f it were a single element or as i f it were blocked with fixed connection members , such as bolts and the like . The structural elements can be blocked, in the final configuration, in a mutual 5 osition which generally defines a rib with an arched profile .

[0021] According to a particular aspect , the structural elements can be mounted in an articulated state , in a manner hinged or oscillating with respect to each other . The structural elements can be connected to each other by means of j oint members which comprise hinges .

[0022] According to another aspect , there is described a method for installing a rib inside an excavation . The method may comprise the step of providing the structural elements with a rib . The method may comprise the step of connecting the structural elements to each other in order to obtain a preassembled rib . The connection can be a movable connection . The method may comprise the step of folding the rib, preferably at least partially, before the installation thereof . The method may comprise the step of transporting the rib, preferably at least in a partially folded state , inside the excavation . The method may comprise the step of installing the rib in an intermediate configuration, in a partially extended state , which supports the crown excavation of a sequential excavation . The method may comprise an additional step of bringing the rib into an intermediate configuration for supporting the crown in a sequential excavation, with extended support in a lateral excavation zone , which is excavated after the crown excavation . The method may comprise the step of installing the rib in a definitive configuration with extended support in both the lateral excavation zones which are excavated sequentially and after the crown excavation . Preferably, in these steps the structural elements can be gradually blocked sequentially with structural continuity with respect to each other . According to another aspect , the method may provide for the structural elements to be blocked with respect to each other in an irreversible manner .

[0023] Brief description of the drawings

[0024] Additional features and advantages will be appreciated from the following detailed description of a preferred embodiment with reference to the appended drawings which are given purely by way of non-limiting example and in which :

[0025] - Figure 1 is a schematic view of the cross-section of an example of a sequential excavation to be consolidated by means of ribs which incorporate aspects of the present invention;

[0026] - Figure 2 is a perspective view of a rib which incorporates elements of the present invention in an intermediate partially extended configuration;

[0027] - Figures 3 to 6 show a number of steps of the installation sequence of the rib of Figure 2 , in the region of the progressive advance of the sequential excavation of Figure 1 ;

[0028] - Figure 7 shows a detail drawn to an enlarged scale of the adj ustment of a support foot of the rib in the excavation plane of the crown;

[0029] - Figures 8 and 9 show additional steps of the installation sequence of the rib of Figure 2 , in the region of the further progressive advance of the divided excavation of Figure 1 ; and

[0030] - Figure 10 shows a detail drawn to an enlarged scale of the support foot of the rib in the region of the lateral excavation .

[0031] Detailed description In the following embodiments , there are described features which allow the invention to be carried out . The features described can be combined with each other in various manners and are not necessarily limited to the precise embodiment to which the drawings and the relevant description refer . In other words , a person skilled in the art of the field who reads the following description will know how to obtain the information items which are advantageous for knowing the way to carry out one or more of the features described by combining it with one or more of the other features described without the particular formulation of the description, paragraphs , terms or drawings constituting a limitation on the possibility of isolating one or more of the features described and illustrated in order to combine them with one or more of any of the other features described and illustrated .

[0032] Now with reference to Figure 1 , there is schematically illustrated the advance of the sequential excavation of a tunnel to be consolidated by means of ribs incorporating aspects of the present invention . A wall excavation S , for example , a road or rail tunnel , comprises a crown C and a base B which, in the example of the Figures , is planar but which can also be configured with a concave central portion in order to form the so-called " inverted arch" .

[0033] The excavation S progressively proceeds in sections . Initially, the excavation of the crown T advances , followed by the excavation of the portion underneath the crown, wherein initially there advances - in the example of Figure 1 - the right lateral excavation DX (bench widening excavation or pier ) and there follows the left lateral excavation SX . The central ramp zone R also continues progressively, ensuring the access to the crown plane P gradually as the excavation of the crown T advances .

[0034] Figure 2 illustrates a rib 10 for supporting and consolidating the sequential excavation S , incorporating aspects of the present invention . Figure 2 illustrates the rib 10 in an intermediate configuration, preceding the definitive installation . The rib 10 comprises an arcuate portion 15 which terminates at the two ends thereof in two intermediate feet 12 . Two additional rib sections are mounted near the intermediate feet 12 and terminate in two respective end feet 14 .

[0035] Figure 2 shows one of the lateral end feet 14 , in particular the right end foot 14a, in a definitive configuration which is already extended so as to move into abutment against a corresponding right lateral planar zone of the base B of the excavation S when the right lateral excavation DX has been carried out in the region of the position of the rib 10 along the axis of the tunnel . However, the other left end foot 14b of the rib is illustrated in a still- folded position . In this position, the left intermediate foot 12b, which is intended to rest on the crown plane P, is extended and supported and is intended to be supported on the crown plane P when the left lateral excavation SX has not yet been completed . When the left lateral excavation SX is completed, the left end foot 14a can be extended from the folded position, illustrated in Figure 2 , until reaching a final symmetrical position with respect to that of the right end foot 14a so as to move into abutment with the corresponding left lateral planar zone of the base B of the excavation S . In this manner, the rib 10 reaches the definitive configuration, which is completely extended, for supporting the entire section of excavation S, with both end feet 14 which are supported on the base B.

[0036] The rib 10 is formed by a plurality of structural elements, for example, but in a non-limiting manner, three structural elements 15, 16, 17, in addition to the intermediate feet 12 and the end feet 14. The structural elements 15, 16, 17 are preferably made of metal material, such as, for example, construction steel (Fe 430 or the like) . According to a preferred embodiment, each structural element 15, 16, 17 is formed by a member which is constituted by a profile with an open cross-section, for example, H-shaped or C-shaped or double-T-shaped, for example, a standardized European profile, such as HEA, HEB, HEM, IPE, etc. However, it is not excluded that one or more of the structural elements 15, 16, 17 may be made with different profiles, for example, tubular profiles with circular, elliptical, square, rectangular sections, etc.

[0037] The rib 10 has a vaulted configuration which is substantially symmetrical with respect to a vertical plane of symmetry which is defined by one or more structural elements, for example, the three structural elements 15, 16, 17 which form the sides and the top of the rib 10 in the zone of the crown T. The symmetrical vaulted configuration of the rib 10, in the extended configuration in which the end feet 4 are both extended in the manner of the right end feet 14a of Figure 2, generally reproduces the section of the portion of the excavation S which is intended to be consolidated via the rib itself .

[0038] The rib 10 illustrated in the Figures comprises a first lateral structural element 15, a central structural element

[0039] 16 which is connected to the first lateral structural element 15 and a lateral structural element 17 which is connected to the central structural element 15 . In one embodiment which is not illustrated, the rib 10 may comprise an additional base structural element which is or can be preferably connected to the second lateral structural element 17 for reinforcing, where applicable , the inverted arch of the excavation S when provided . As illustrated, the first lateral structural element 15 and the second lateral structural element 17 are arranged in accordance with a substantially specular position with respect to the vertical plane of symmetry of the rib 10 . In other words , in this exemplary configuration of the rib 10 , the first lateral structural element 15 and the second lateral structural element 17 are lateral structural elements of the rib 10 . The central structural element 16 preferably develops symmetrically between the first lateral structural element 15 and the second lateral structural element 17 with respect to the same vertical plane of symmetry . In the example of the rib 10 , the central structural element 16 is an upper structural element , also referred to as the summit or top structural element which is intended to support the upper zone of the crown T .

[0040] The ends of the various structural elements 15 , 16 , 17 are operatively connected to each other, for example , via articulated j unction members . The intermediate feet 12 are also operatively connected to the ends of the respective lateral structural elements 15 , 17 in an articulated manner . The end feet 14 are in turn operatively connected to the intermediate feet 12 . The connection of the end feet 14 to the intermediate feet can be brought about selectively with an arrangement which can occur after the rib 10 has been positioned in support of only the excavation of the crown T . The j unction members between the various elements which form the rib, including the feet , are advantageously articulated, oscillating and / or rotatable j unction members , for example , hinges . The structural elements and the feet which are coupled by means of these j unction members can therefore move from folded positions of one on the other to intermediate positions , in which at least some of them are extended . In an intermediate support position of only the crown T of the excavation S , the rib 10 may not have any end feet 14 , which are connected and extend only when it is necessary to laterally support the rib 10 following the advance of the lateral excavations . It is thereby particularly easy and advantageous to transport inside the excavation S the rib 10 which is folded about itsel f in the installation configuration, wherein the structural elements 15 , 16 , 17 together with the intermediate feet 12 and in some embodiments also the end feet 14 already mounted on the rib 10 are j oined continuously to each other .

[0041] The feet 12 , 14 are preferably extensible and can be extended by an adj ustable quantity in order to be supported on the crown plane P and the base B, respectively .

[0042] Figure 7 illustrates to an enlarged scale an embodiment of one of the intermediate feet 12 which comprises a support element 20 . The support element 20 comprises a movable or telescope-like portion which is mounted in an extensible manner with respect to the fixed structure of the intermediate foot 12 which is fixed to a corresponding lateral structural element 15 or 17 , preferably near the end thereof . The fixed structure of the foot 12 can be fixed to the lateral structural element 15 or 17 by means of any system of known type , for example , by means of welding or with bolts or rivets or other connection members of the type , even i f it is preferable that it is mounted in a movable state , for example , by means of an articulation or hinge 22 .

[0043] The movable structure 20 can preferably be produced with a tubular member, for example , with a square or rectangular cross-section, and in any case is configured and si zed so as to slide linearly with respect to the fixed member of the foot 12 , preferably in a telescope-like manner, without any rotational possibility . The foot 12 is provided with a blocking and non-return mechanism, for example , with a ratchet gear, which allows the movable structure 20 to be fixed at a desired height with respect to the crown plane P . At the lower end of the movable structure 20 , which is intended to be supported on the crown plane P, a support plate 24 is fixed . The support plate 24 has greater dimensions than the cross-section of the movable structure 20 in order to form a support base which is suf ficiently extended to distribute the weight over a relatively extensive surface of the crown plane P . Once the extension operation of the movable structure 20 is completed, the telescope-like tubular section can be filled with concrete so as to generate a monolithic foot 12 which no longer moves in any direction .

[0044] There is provided on the fixed structure of the foot 12 a connection member 26 , to which there is connected a corresponding connection element 27 of the end foot 14 , which is shown to an enlarged scale in Figure 10 , when it is necessary to support the rib following the lateral excavation which removes the crown plane . The end foot 14 also comprises a movable structure 28 having functional characteristics similar to those of the movable structure 20 of the intermediate foot 12 , which terminates with a support plate 30 which is functionally similar to the support plate 24 , which is intended to form a support base which extends suf ficiently to distribute the weight over a relatively extensive surface of the base B of the excavation S . The end foot 14 is preferably connected to the intermediate foot 12 in an articulated manner in order to move from a raised position, which is partially shown with a hatched line in Figure 10 , to the final extended position, in which it supports the rib 10 by being supported on the base B of the excavation S . The connection which is formed by the connection members 26 , 27 of the intermediate foot 12 and end foot 14 , respectively, is preferably formed so as to be able to be blocked in an irreversible manner when the end foot 14 is extended in order to reach the final support position, which is illustrated with a continuous dash-dot line in Figure 10 .

[0045] The installation of the ribs 10 in the excavation S can be carried out automatically or semi-automatically by using known machines which are equipped for the purpose in order to follow the sequential progression of the excavation S .

[0046] The ribs 10 described above are transported to the location of the excavation S in the configuration in which the structural elements 15 , 16 , 17 and the intermediate feet 12 are folded in order to assume a compact configuration, the extent of which in the plane which contains the structural elements and the intermediate feet is less than the extent of the section of the excavation of the crown T . The support elements 20 of the intermediate feet 12 are preferably raised or retracted so as to occupy little space during the storage of the rib 10 and during the first positioning thereof in the tunnel , as can be seen in Figure 3 . The transport is therefore carried out in an easy manner and the elements which constitute the rib are in any case already provided for correct positioning in the definitive configuration . When the rib 10 is in the position provided inside the excavation S which proceeds with the advance of the excavation of the crown T , the central structural element 16 is raised so that the lateral structural elements 15 , 17 rotate in the region of the j unctions which are articulated in order to be brought into progressively open configurations , as illustrated in Figure 4 . With the central structural element 16 arranged in the region of the upper wall of the excavation of the crown T , the lateral structural elements 15 , 17 adj acent thereto are placed beside the vault of the excavation, as illustrated in Figure 5 .

[0047] At the end of the relative rotation, the lateral structural elements 15 , 17 are fixed in the installation position illustrated in Figure 5 as a result of the snap- fit blocking of the j unction members between the structural elements . The construction of the snap- fit j unction members allows it to be ensured that the structural elements remain securely in the desired intended position for completed installation without any risks that they close on each other again .

[0048] In the intermediate position, in which the rib 10 is installed in the excavation of the crown 10 , the intermediate feet 12 are extended and positioned in such a manner as to be supported on the crown plane P, as can be seen in Figure 6 . In this position, the movable portions of the support elements 20 of the intermediate feet 12 can be lengthened so as to be stably supported on the crown plane P . In this intermediate configuration, it is possible to carry out a first application of sprayed concrete to the portion of the rib which occupies the excavation of the crown T . As the excavation S gradually advances , in the zone in which the rib 10 has been installed the lateral excavations begin to be carried out , initially ( as in the non-limiting example of the Figures ) the right lateral excavation DX, followed by the left lateral excavation SX . As can be seen in Figure 8 , in view of the advance of these lateral excavations , there is provision for the connection of the end feet 14 to the intermediate feet 12 . The end feet 14 are initially in a folded position with respect to the extent of the rib in the excavation of the crown so as to be supported on the crown plane P, as precisely illustrated in Figure 8 . When the right lateral excavation DX is completed, as illustrated in Figure 9 , the right foot 14 is extended and lengthened so as to be supported on the base B of the excavation, as illustrated in Figure 9 . Similarly, when the left lateral excavation SX is completed, the left end foot 14 is extended and lengthened in order to reach a similar support position on the base B of the excavation . The support elements of the end feet 13 are therefore arranged laterally and in a lower position with respect to the lateral walls of the excavation and are extended or rotated until touching the ground in the region of the base B . In this condition, the consolidation of the rib with sprayed concrete can be completed in the lateral zone of the excavation which is released by the lateral excavations .

[0049] The installation of the rib is therefore carried out in a rapid and substantially automatic manner .

[0050] Each rib is then connected to an adj acent rib by means of connection members referred to as "chains" or equivalent members of the known type . The connection members are formed so as to allow preferably an automatic connection of one rib to another . The ribs used for supporting and consolidating an excavation can have resilient j oints of the known type which can be inserted between two sections of the structural elements of the rib . The adoption of one or more resilient j oints allows , by resiliently reacting to them, the forces which can be applied by the walls of the excavation to the rib to be absorbed .

[0051] The main inventive concept of the invention is not dependent on the type of profile of the rib which is used to construct the structural elements and / or intermediate feet and end feet . Although profiles with an open cross-section have been mentioned above as being preferable , it is not excluded to use the invention with tubular profiles with which to construct , completely or partially, the total profile of the rib and / or one or more of the structural elements thereof . In general terms , it is possible in any case to use di f ferent profiles for di f ferent portions of the rib, the possibility not being excluded of also using di f ferent profiles for portions of structural elements , with open and / or closed / tubular profiles , which are separated from each other, for example , by the resilient j oints described above .

[0052] Naturally, the principle of the invention remaining the same , the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention .

Claims

Patent claims1. A rib for supporting and consolidating an excavation, comprising a plurality of structural elements (15, 16, 17) which are movably connected to each other so that the rib can move from a preassembled, at least partially folded configuration before installation to an intermediate, partially extended support configuration of a crown (C) of a sequential excavation in a crown plane (P) as far as a definitive configuration for support on a plane of the base (B) which is placed at a lower height with respect to the crown plane (P) , wherein the structural elements (15, 16, 17) are blocked with structural continuity with respect to each other in a mutual position which generally defines an arched rib .

2. A rib according to claim 1, wherein a pair of intermediate feet (12) is mounted in an articulated manner at the ends of the group of structural elements.

3. A rib according to claim 2, wherein the intermediate feet (12) are extensible.

4. A rib according to any one of the preceding claims, comprising a pair of end feet (14) which can be selectively connected to the ends of the structural elements or to the intermediate feet (12) .

5. A rib according to claim 4, wherein the end feet (14) are extensible .

6. A rib according to any one of the preceding claims, comprising at least three structural elements (15, 16, 17) which are mounted in an articulated manner with respect toeach other and which can be blocked in an intermediate configuration, in which intermediate feet (12) can be supported on a crown plane (P) . . A method for installing a rib inside an excavation according to any one of the preceding claims, comprising the steps of:- providing a plurality of structural elements (15, 16, 17) with a rib (10) ,- connecting the structural elements (15, 16, 17) to each other in a movable manner in order to obtain a preassembled rib, folding the rib, at least partially, before the installation thereof,- transporting the rib, at least in a partially folded state, inside the excavation (S) ,- installing the rib (10) in an intermediate configuration, in a partially extended state, which supports the crown (C) of a sequential excavation in a crown plane (P) ,- connecting end feet (14) to the rib, configuring the rib in a definitive configuration for support on a plane of the base (B) which is constructed at a lower height than the crown plane (P) , wherein the structural elements (15, 16, 17) are blocked with structural continuity with respect to each other in a mutual position which generally defines an arched rib.

8. A method according to claim 7, wherein the rib comprises a pair of intermediate feet (12) which are mounted in an articulated manner at the ends of the group of structural elements, wherein the step of installing the rib in the intermediate configuration comprises extending and / or lengthening the intermediate feet (12) and positioning them in support on the crown plane (P) .

9. A method according to claim 7 or claim 8, wherein the rib comprises a pair of end feet (14) which can be selectively connected to the ends of the structural elements (15, 16, 17) or the intermediate feet (12) , wherein the step of installing the rib in the definitive configuration comprises:- connecting the end feet (14) to the ends of the structural elements (15, 16, 17) or the intermediate feet (12) , lengthening the end feet (14) and positioning them in support on the base (B) .

10. A method according to claim 9, wherein during the connection of the end feet (14) to the ends of the structural elements (15, 16, 17) or to the intermediate feet (12) , the end feet (14) take up a folded configuration, the end feet (14) subsequently being extended in order to form with the structural elements (15, 16, 17) an arcuate configuration which will be supported on the base (B) .

Images