Precast tunnel lining segment

Abstract

A prefabricated ashlar (1) for a tunnel lining (110) comprising an intrados face (11), an extrados face (12) opposite the intrados face (11) and a peripheral edge (13) which connects the intrados face (11) and the extrados face (12). The extrados face (12) defines at least one recess (30), in which an expandable bag (7) which can expand when it is filled with filler material is received. The ashlar (1) comprises at least one bag-filling pipe (15) in order to inject the filler material into the expandable bag (7) having a first end opening (15A) in the region of the intrados face (11) and a second end opening (15B) in the region of the recess (30) of the extrados face (12), and the expandable bag (7) is in hydraulic communication with the second end opening (15B) of the at least one bag-filling pipe (15) in order to receive the filler material (7). The ashlar (1) further comprises at least one auxiliary injection pipe (25) comprising a first end opening (25A) in the region of the intrados face (11) and a second end opening (25B) in the region of the extrados face (12), the at least one auxiliary injection pipe (25) being defined in a local position at a side (131, 132) which forms the peripheral edge (13).

Description

[0001] PRECAST TUNNEL LINING SEGMENT

[0002] TECHNICAL FIELD

[0003] The present invention generally involves the technical field of constructing natural tunnels . In particular, the invention relates to a precast ashlar for constructing a lining of a natural tunnel .

[0004] PRIOR ART

[0005] As known, one of the fundamental operations in constructing natural tunnels by underground excavation is the generation of one or more lining layers for stabili zing and containing the walls which are exposed by the excavation .

[0006] One known type of lining for natural tunnels is constituted by prefabricated elements which are made from concrete and which are suitably shaped and mutually j uxtapositioned and known by the term "ashlars" . This lining is typically constructed by sequentially generating gradually as the excavation advances lining rings which extend over the entire perimeter of the excavation section, each one formed by a plurality of these ashlars .

[0007] This type of lining is normally used in natural tunnels which are constructed by means of so-called "mechani zed" techniques . In this case , the basic excavation operations underground, removal of the excavated material and lining of the walls of the excavation, are continuously and simultaneously carried out by means of large automated machines , which are suitably configured, so-called TBM ( Tunnel Boring Machines ) . These machines carry out the excavation in an integral and continuous manner and simultaneously provide for the removal of the excavated material from the front of the excavation and the construction of the lining of the tunnel gradually as the excavation front advances . In the case of natural tunnels which are constructed using "mechani zed" techniques , there is normally provided a single lining layer which is particularly formed by prefabricated ashlars as mentioned above .

[0008] More recently, it has also been proposed to use lining structures which are formed by prefabricated ashlars in the field of construction of natural tunnels by means of so- called "conventional" techniques , in which the basic operations of underground excavation, removal of the excavated material and lining of the walls of the excavation are carried out discontinuously, largely in succession, and are repeated cyclically until the tunnel is complete . As known, this technique provides for the construction of two lining layers : a primary lining ( also referred to as the " first phase lining" or "temporary lining" ) which is intended to stabili ze the excavation cavity in the short term in order to allow the workers to work in safety and which is typically constructed by positioning reinforcement ribs and applying proj ected concrete and, in a radially internal position with respect to the primary lining, a definitive lining which is intended to ensure the long-term structural stability of the tunnel and to prevent occurrences of introduction of water inside the tunnel itsel f . In the case of natural tunnels constructed using "conventional" techniques , prefabricated ashlars can be used to construct the definitive lining of the tunnel , as an alternative to a conventional construction by means of casting in situ using suitable formworks . An example of this use is disclosed in the patent application WO 2012 / 114249 A2 .

[0009] In all cases , the construction of a tunnel lining using prefabricated ashlars requires the use of particular measures in order to ensure the correct functionality of the lining itsel f .

[0010] A first aspect to be considered is that the positioning of the ashlars requires a speci fic operating space with respect to the radially external wall , towards which the ashlars face ( that is to say directly the excavation wall in the case of tunnels constructed using "mechani zed" techniques or the primary lining in the case of tunnels constructed using "conventional" techniques ) . Therefore , there remains defined between the lining formed by the ashlars and the radially external wall an annular gap which has to be filled as far as possible promptly and completely so as to generate a direct mechanical contact between the external wall and the ashlars in order to avoid failures or settlements of the external wall which could occur in the short term or long term and which are dangerous both for the integrity of the lining itsel f and for the possible triggering of subsidence phenomena in the surface ground .

[0011] During construction of tunnel linings which are formed by prefabricated ashlars , therefore , it is necessary to provide a so-called backfilling operation by which a filler material , typically a two-component admixture based on cement , is inj ected into the annular gap at the front ( that is to say in the direction of longitudinal development of the tunnel excavation) in the region of the front opposite the advance front of the excavation, gradually as the lining construction advances . In the case of tunnels which are constructed using "mechani zed" techniques , this operation is carried out directly and automatically by the TMB, which is provided to this end with suitable inj ection means which are provided so as to be able to inj ect the filler material simultaneously along the entire perimeter of a longitudinal section of the annular gap .

[0012] Another aspect to be considered in the case of tunnel linings which are formed by prefabricated ashlars is the natural presence of discontinuities in the region of the j oints between adj acent ashlars , which j oints therefore have to be made impermeable in order to avoid introduction of water towards the interior of the tunnel . To this end, it is known to provide the ashlars with peripheral fluid-tight seals . Following assembly of the ashlars , the contact pressure between the ashlars squeezes the mutually facing fluid-tight seals against each other in the region of the j oints , typically bringing about a partial deformation of the fluid- tight seals themselves so that there are formed between adj acent ashlars sealed j oint lines which prevent the passage of water through the tunnel lining formed in this manner .

[0013] In practice , however, it is found that this solution does not allow occurrences of introduction of water through the lining which is formed by ashlars to be completely excluded, not only in the long term, for example , as a result of the deterioration of the fluid-tight seals and / or the lining itsel f near the j oints , but also in the short term, in the case of imperfect contact between the seals of adj acent ashlars . When such introductions occur, repair interventions are necessary and are typically carried out nowadays by inj ecting sealing material through the j oints themselves . Such interventions are di f ficult to carry out and have an uncertain outcome as a result of the di f ficulty of access to the introduction locations , the gaps between adj acent ashlars having a fairly small width ( typically between 1 and 10 mm) and the respective fluid-tight seals normally being positioned near the external wall of the lining and therefore at a considerable distance ( typically between 300 mm and 1000 mm) from the accessible internal wall of the lining .

[0014] SUMMARY

[0015] A main obj ect of the present invention is to provide a novel prefabricated ashlar for constructing a tunnel lining which allows the disadvantages described above to be overcome .

[0016] In the context of this obj ect , an obj ective of the invention is to provide a prefabricated ashlar for constructing a tunnel lining which allows a reduction in the times for constructing the lining itsel f and the definitive consolidation of the tunnel excavation, particularly in the case of an excavation carried out with a "conventional" technique .

[0017] Another obj ect of the invention is to provide a prefabricated ashlar in order to construct a tunnel lining which facilitates and makes any repair interventions more ef fective against introductions of water in the region of the j oints between adj acent ashlars .

[0018] Another obj ect of the present invention is to provide a prefabricated ashlar for constructing a tunnel lining which is easy to manufacture with competitive costs .

[0019] These obj ects are achieved by a prefabricated ashlar for a tunnel lining having the features set out in the independent claim 1 appended .

[0020] In particular, the invention relates to a prefabricated ashlar for a tunnel lining comprising an intrados face , an extrados face opposite the intrados face and a peripheral edge which connects the intrados face and the extrados face , wherein the extrados face defines at least one recess , in which an expandable bag which can expand when it is filled with filler material is received .

[0021] The ashlar comprises at least one bag- filling pipe in order to inj ect the filler material into the bag, having a first end opening in the region of the intrados face and a second end opening in the region of the recess of the extrados face and the expandable bag is in hydraulic communication with the second end of the at least one bag- filling pipe in order to receive the filler material .

[0022] The ashlar further comprises at least one auxiliary inj ection pipe comprising a first end opening in the region of the intrados face and a second end opening in the region of the extrados face , the at least one auxiliary inj ection pipe being defined in a local position at a side which forms the peripheral edge .

[0023] Preferably, the ashlar comprises non-return valve means which are arranged along the at least one bag- filling pipe and / or along the at least one auxiliary inj ection pipe .

[0024] Preferably, the ashlar comprises a plurality of auxiliary inj ection pipes for each side forming the peripheral edge .

[0025] Preferably, for each side forming the peripheral edge the pipes of the plurality of auxiliary inj ection pipes are spaced apart along a line parallel with the corresponding side forming the peripheral edge .

[0026] Preferably, the second opening of the at least one auxiliary inj ection pipe is arranged in a region of the extrados face between the recess and the corresponding side forming the peripheral edge .

[0027] Preferably, the recess has a peripheral shape which geometrically conforms to the shape of the peripheral edge .

[0028] According to one possible embodiment of the prefabricated ashlar of the invention, the extrados face defines a pair of recesses in each of which an expandable bag which can expand when it is filled with filler material is received, and for each expandable bag there is provided a bag- filling pipe which passes through the entire thickness of the ashlar and which is hydraulically connected to the expandable bag in order to allow the expansion thereof for filling following the inj ection of the filler material .

[0029] In this embodiment , the ashlar may advantageously comprise at least one additional auxiliary inj ection pipe having a first end opening which is arranged in the region of the intrados face and a second end opening which is arranged in the region of the extrados face , in a region between the recesses .

[0030] Preferably, the at least one auxiliary inj ection pipe and, i f present , the at least one additional auxiliary inj ection pipe have a rectilinear development .

[0031] DESCRIPTION OF THE FIGURES

[0032] Additional features and advantages of the invention will become more evident from the following detailed description of preferred embodiments thereof which is given herein below by way of non-limiting example with reference to the appended drawings , in which : - Figure 1 is a schematic, longitudinally sectioned view of a tunnel portion comprising a lining which is formed by prefabricated ashlars according to the present invention;

[0033] - Figure 2 and Figure 3 are perspective views , from di f ferent points of observation, of a prefabricated ashlar according to the invention;

[0034] - Figure 4 is a schematic, perspective view of two rings of prefabricated ashlars of the tunnel lining of Figure 1 ;

[0035] - Figure 5 is a schematic, sectioned view in accordance with the plane of section V-V indicated in Figure 3 of the prefabricated ashlar of Figures 2 and 3 ;

[0036] - Figure 6 is a schematic, sectioned view corresponding to Figure 5 , in which the expansion of an expandable bag associated with the prefabricated ashlar of Figures 2 and 3 is schematically depicted;

[0037] Figure 7 is an additional schematic, sectioned view corresponding to Figure 5 , in which the expandable bag which is associated with the prefabricated ashlar of Figures 2 and 3 is expanded;

[0038] - Figure 8 is a schematic, sectioned view in accordance with the plane of section VI I I-VI I I indicated in Figure 3 ;

[0039] Figure 9 is a schematic, sectioned view of two prefabricated ashlars according to the invention which are axially adj acent ;

[0040] - Figure 10 is an enlarged view of the detail X in Figure 9 ;

[0041] - Figure 11 and Figure 12 are a schematic, perspective view and a schematic, sectioned view of another possible embodiment of a prefabricated ashlar according to the invention, respectively, and

[0042] - Figure 13 is an enlarged view of the detail XI I I of Figure

[0043] 8 .

[0044] The same reference numerals and the same reference letters in the Figures identi fy the same elements or components . DETAILED DESCRIPTION

[0045] With reference to Figures 1 to 10 , one possible embodiment of a prefabricated ashlar according to the present invention is generally designated 1 .

[0046] In a manner known per se , each ashlar 1 is configured as a ring segment and is put to use in a tunnel lining 110 (visible in Figure 1 ) so as to form a plurality of closed circular rings 111 which are adj acent to each other in the longitudinal development direction of the excavation of a tunnel 100 . Figure 4 shows separately two complete rings 111 of ashlars 1 which form the lining 110 .

[0047] As can better be seen in Figures 2 and 3 , each ashlar 1 is constituted by a prefabricated element made from reinforced concrete , having a rectangular or trapezoidal peripheral shape ( in the case of the so-called " key ashlar" and the two ashlars adj acent thereto in each ring 111 ) and a curvature in one of the two extent directions , in particular the greatest extent direction corresponding to the curvature of the rings 111 . Each ashlar 1 therefore comprises an intrados face 11 (visible in Figure 2 ) which, in the installed condition of the ashlar 1 , is directed towards the interior of the tunnel , an extrados face 12 (visible in Figure 3 ) opposite the intrados face 11 and a peripheral edge 13 which connects the intrados face 11 and the extrados face 12 . The peripheral edge 13 is formed by a pair of long sides or faces 131 which are mutually parallel and by a pair of short sides or faces 132 which are mutually parallel or oblique . Each ashlar 1 is further provided in known manner with a peripheral fluid- tight seal 2 which extends along the entire peripheral edge 13 , preferably near the extrados face 12 . With particular reference to Figure 3, according to an aspect of the present invention, the extrados face 12 of the ashlar 1 defines at least one seat (or recess) 30, in which an expandable bag 7 which is preferably made from woven material or another material suitable for the purpose is arranged (for clarity, shown only in Figures 5 to 8) , that is to say to allow an expansion of the bag following the injection of filler material therein. For the purposes of the present invention, the filler material may be a two-component mortar of the type normally used for the operation of backfilling.

[0048] Each ashlar 1 further comprises a bag-filling pipe 15 for injecting the filler material into the bag 7. The bag-filling pipe 15 passes through the thickness of the ashlar 1, that is to say it develops between the intrados face 11 and the extrados face 12. Therefore, the bag-filling pipe 15 comprises a first end opening 15A in the region of the intrados face 11 and a second end opening 15B in the region of the extrados face 12.

[0049] According to one possible embodiment, shown in the Figures, the bag-filling pipe 15 develops along a rectilinear axis XI which has a cross-section (that is to say orthogonal to the axis XI) with a circular shape and the diameter of which may vary, for example, in a range between 40 and 80 mm. Therefore, the two end openings 15A, 15B of the bag-filling pipe 15 also have a circular cross-section. In any case, the filler material is injected into the bag-filling pipe 15, for example, by means of an injection lance 200 (shown only partially and schematically in Figure 6) which is supplied by a pump (not shown) , through the first opening 15A and is discharged from the bag-filling pipe 15 through the second opening 15B. According to a preferred embodiment , the bag- filling pipe 15 is provided with a non-return valve means 16 (which can be seen, for example , in Figures 5 to 8 ) . Preferably, the nonreturn valve means 16 is constructed separately and assembled with one or more tubular elements so as to obtain a bagfilling pipe 15 with a desired length . In the exemplary embodiment shown in the Figures , the non-return valve means 16 is arranged in an intermediate position of the bag- filling pipe 15 and it is formed by the non-return valve means 16 and by two di f ferent tubular elements 15 ' , 15 ' ’ which are applied to the opposite ends of the non-return valve means 16 . Alternatively, the non-return valve means 16 could be arranged in the region of one of the ends of the bag- filling pipe 15 . In this case , the bag- filling pipe 15 can be formed by the non-return valve means 16 and by a single tubular element which is applied to one of the ends thereof .

[0050] In any case , the non-return valve means 16 is configured so as to avoid, during and after the operation for filling the bag 7 , a potential depletion as a result of counter-pressure . The non-return valve means 16 is preferably of the passive type and can be advantageously configured as a so-called "duckbill" valve .

[0051] In particular, according to the embodiment shown in the Figures , the non-return valve means 16 comprises an annular shell 161 ( for clarity, indicated only in Figure 13 ) for connection to the bag- filling pipe 15 and at least one pair of closure edges 162 ( for clarity, indicated only in Figure 13 ) which are suitably shaped and made from resilient material and which extend from the internal surface of the annular shell 161 and converge obliquely inwards until coming mutually into contact in the region of the respective distal free edges . A pressuri zed fluid which flows through the non- return valve means 16 in the permitted flow direction brings about a temporary opening of the closure edges 162 and therefore the passage of the fluid itsel f . When the pressure is eliminated, the closure edges 162 autonomously close again, preventing a return flow .

[0052] The bag 7 comprises an opening 7A which communicates with the bag- filling pipe 15 so that the filler material , while leaving the bag- filling pipe 15 , is distributed inside the bag 7 without being discharged from it .

[0053] Figure 13 shows in greater detail a preferred method for connection between the bag 7 and the bag- filling pipe 15 . In particular, the tubular element 15 ' ’ of the bag- filling pipe 15 is configured in this case as a bush which is provided with a collar 151 which proj ects radially in the region of a longitudinal end thereof which is intended to define the second opening 15B of the bag- filling pipe 15 . The opening 7A of the bag 7 has a diameter substantially equal to the external diameter of the tubular element 15 ' ’ and in any case less than the diameter of the collar 151 . In order to bring about the connection, the longitudinal end of the tubular element 15 ' ’ which is provided with the collar 151 is introduced into the bag 7 through the opening 7A. The collar 151 is then fixed, for example , bonded or thermally welded, to the wall of the bag 7 in the region of the internal side thereof . At this point , a ring 152 with an internal diameter substantially equal to the external diameter of the tubular element 15 ' ’ is fitted thereon, brought into abutment against the collar 151 and therefore fixed, for example , bonded or thermally welded, to the wall of the bag 7 , in the region of the external side thereof . The wall of the bag 7 remains clamped between the collar 151 and the ring 152 , thereby obtaining a stable connection which is fluid-tight between the bag 7 and the tubular element 15 ' ’ . Once the bag 7 has been fixed to the tubular element 15 ' ’ , in the region of the free end thereof there are applied, for example , bonded or thermally welded, in series the valve means 16 and the tubular element 15 ' , thereby completing the formation of the bag- filling pipe 15 . The assembly which is thereby obtained and constituted by the bag- filling pipe 15 and the respective expandable bag 7 is then suitably surrounded in the ashlar 1 during the casting thereof .

[0054] Figures 5 , 6 and 7 are sectioned views of an ashlar before , during and after the filling of the bag 7 with the filler material , respectively . With reference to Figure 5 , the bag 7 is initially received in the seat 30 , preferably so as to remain under the plane of curvature PC of the extrados face 12 . In this regard, the formation of the seat 30 and the formation of the bag 7 may vary as a function of the formation and / or thickness of the ashlar 1 . In the case of an ashlar 1 having a rectangular extrados face 12 , for example , the seat 30 may also have a substantially rectangular formation and be defined in a centred position with respect to the perimeter of the extrados face 12 . In the case of an ashlar 1 having a trapezoidal extrados face ( such as , for example , in the case of the so-called " key ashlar" ) , the seat 30 may again have a rectangular formation or also a trapezoidal formation, which does or does not conform to the formation of the extrados face . The formation of the seat 30 is in any case evaluated by considering a plan view of the extrados face 12 .

[0055] Still with reference to the seat 30 , the depth p of the seat 30 may also vary, it being able to depend on the thickness of the ashlar 1 and / or the f ormation / extension of the bag 7 . As shown in Figure 5 , before the inj ection of the filler material the bag 7 could be folded in order to remain under the plane of curvature PC of the extrados face 12 as already indicated above .

[0056] With reference to Figures 6 and 7 , following the inj ection of filler material through the bag- filling pipe 15 , the bag 7 is able to expand, that is to say it is "potentially expandable" , until reaching an extent L and a thickness D . As better set out below, the inj ection of the filler material and therefore the expansion of the bag 7 is brought about after the ashlar 1 is installed, preferably upon completion of the lining ring to which the ashlar 1 belongs . Therefore , the bag 7 expands in a gap which is radially delimited between the extrados face 12 of the ashlar 1 and a radially external wall , towards which the ashlar 1 faces and which can be defined by a primary lining in the case of a tunnel which is constructed using "conventional" techniques or directly by the excavation wall in the case of a tunnel constructed using "mechani zed" techniques . Advantageously, the bag 7 is configured so as to be able to expand by a radial thickness D which is far greater than the real thickness of the gap .

[0057] In this regard, Figure 1 which was previously mentioned shows , by way of example , a tunnel excavation which is carried out using "conventional" techniques , wherein, in a widely known manner, there is provided a primary lining 500 which is applied to the excavation wall and formed by reinforcement ribs 510 and proj ected concrete . The lining 110 , which is formed by the ashlars 1 and which in this case constitutes the definitive lining of the tunnel , is arranged in a radially internal position with respect to the primary lining 500 . The intrados surface of the primary lining is irregular while the extrados surface of the lining 110 formed by the ashlars 1 is regular, that is to say substantially linear . The filling of the gap between the extrados face 12 of each ashlar 1 and the intrados surface of the primary lining 500 is particularly performed by the expansion of the bag 7 associated with the ashlar itsel f , at locations where this expansion is brought about by the inj ection into the bag 7 of filler material which is pumped under pressure through the bag- filling pipe 15 . Each bag 7 bonds to the intrados surface of the primary lining 500 , adj usting to the formation thereof , as shown by Figure 1 . In particular, each bag 7 will expand in a manner dependent on the formation of the primary lining section which is directed towards the extrados face 12 of the respective ashlar 1 .

[0058] As shown in particular in Figures 2 , 3 and 8 to 10 , according to another aspect of the present invention the ashlar 1 also comprises one or more auxiliary inj ection pipes which are generically designated 25 and each of which is defined in a position adj acent to a side 131 , 132 of the peripheral edge 13 of the ashlar 1 . Preferably, for each side 131 , 132 there are provided a plurality of auxiliary inj ection pipes 25 which are spaced apart from each other, preferably arranged in a row parallel with the corresponding side 131 , 132 of the peripheral edge 13 . In any case , each auxiliary inj ection pipe 25 develops over the entire thickness of the ashlar 1 , therefore comprising a first opening 25A in the region of the intrados face 11 and a second opening 25B in the region of the extrados face 12 ( see Figure 8 ) .

[0059] The auxiliary inj ection pipes 25 mainly serve to inj ect sealing material towards the extrados surface of the lining 110 near the j oints between adj acent ashlars 1 at any locations where , in the course of the li fe of the tunnel , in the region of such j oints there occur introductions of water as a result of a mal function of the peripheral fluid-tight seals 2 of the ashlars 1 as a result , for example , of incorrect positioning of the ashlars 1 and / or a functional degeneration of the fluid-tight seals 2 themselves . The auxiliary inj ection pipes 25 allow an intervention in order to eliminate these introductions in an easier, faster and more controlled manner with respect to the conventional intervention methods .

[0060] In any case , it is not excluded to use auxiliary inj ection pipes 25 for additional or alternative purposes during the construction of the tunnel 100 or in the course of the service-li fe thereof . For example , at least some of the auxiliary inj ection pipes 25 could be used to inj ect filler material towards the extrados of the lining 110 externally and around the expandable bags 7 which are already filled and therefore expanded, as described above . This may be advantageous for integrating or completing the backfilling which is obtained by means of the bags 7 themselves , filling empty spaces which can remain between the bags 7 of adj acent ashlars 1 . Furthermore , at least some of the auxiliary inj ection pipes 25 could be used to inj ect , even in the absence of occurrences of introduction, sealing or waterproofing material in order to increase the hydraulic tightness of the fluid-tight seals 2 .

[0061] The Applicant considers that the provision of auxiliary inj ection pipes 25 having the features and functions described above may also be advantageous in conventional prefabricated ashlars , particularly without any expandable bags 7 and respective bag- filling pipes 15 .

[0062] Preferably, for each side 131 , 132 of the ashlar 1 , the auxiliary inj ection pipes 25 are configured so that the respective second opening 25B is defined in a position between the corresponding side 131, 132 and the recess 30 formed in the extrados face 12 of the ashlar 1.

[0063] Preferably, the auxiliary injection pipes 25 develop along a rectilinear axis X2 (indicated in Figure 10) and have a cross-section (that is to say orthogonal to the axis X2) with a circular shape, the diameter of which may vary in a range between 4 mm and 20 mm.

[0064] As can better be seen in Figure 10, according to a preferred embodiment each auxiliary injection pipe 25 is provided with a non-return valve means 26 (preferably arranged between the two openings 25A, 25B or alternatively in the region of one of them) in order to avoid discharge post-in ection. Each valve means 26 is preferably of the passive type and can be advantageously constituted by a "duckbill" valve, for example, configured as already described above with reference to the non-return valve means 16 of the bag-filling pipe 15.

[0065] Figures 11 and 12 show another possible embodiment of a prefabricated ashlar according to the present invention, which is generally designated 1' . The ashlar 1' differs from the previously described ashlar 1 as a result of the presence, in the region of the extrados face 12 thereof, of a pair of seats (or recesses) 30, 30' , in each of which a respective expandable bag 7, 7' is received (for clarity, shown only in Figure 12 in the non-expanded configuration) . The bags 7, 7' have features which are generally similar to the bag 7 of the ashlar 1 previously described and are similarly intended to expand when they are filled with a filler material. To this end, the ashlar 1' is provided with a pair of bag-filling pipes 15, 15' which are hydraulically connected to the bags 7, 7 ’ , respectively, in order to allow the injection therein of the filler material. The bag-filling pipes 15 , 15 ' also have features which are generally similar to the bag- filling pipe 15 of the ashlar 1 previously described . In particular, the bag- filling pipes 15 , 15 ' pass through the thickness of the ashlar 1 ' , that is to say they develop between the intrados face 11 and the extrados face 12 thereof , and each comprise a respective non-return valve means 16 , 16 ' .

[0066] The ashlar 1 ' also comprises a plurality of auxiliary inj ection pipes 25 having a configuration, arrangement and function similar to those of the auxiliary inj ection pipes 25 of the ashlar 1 previously described . In addition, the ashlar 1 ' may also comprise at least one additional auxiliary inj ection pipe 25 ' having a first end opening 25A' in the region of the intrados face 11 of the ashlar 1 ' and a second end opening 25B' in a region of the extrados face 12 of the ashlar 1 ' between the seats 30 .

[0067] With particular reference to Figures 1 and 4 to 7 , there is now described a method for constructing a tunnel lining 110 by means of prefabricated ashlars according to the present invention . In the following description, reference will be made particularly to a configuration of an ashlar corresponding to that of the ashlar 1 previously described, but this description also applies mutatis mutandis to ashlars which are configured similarly to the ashlar 1 ' .

[0068] The method provides for placing the ashlars 1 in a radially internal position with respect to an excavation wall ( in the case of a tunnel excavation carried out by means of "mechani zed" techniques ) or, as in the case considered here , which refers to a tunnel excavation carried out using "conventional" techniques , a wall of a primary lining 500 so as to form at least one ring 111 of ashlars 1 defining a longitudinal section of the lining 110 , in this case constituting the definitive lining of the tunnel being constructed .

[0069] Once the ring 111 is completed or also during the construction thereof , after each ashlar 1 or a speci fic number of ashlars 1 intended to form the ring 111 has / have been positioned, the method provides for inj ecting, for each ashlar 1 of the ring 111 , filler material in the respective bag- filling pipe 15 through the first end opening 15A thereof , so as to bring about , by means of the filler material itsel f , the expansion of the corresponding bag 7 in the gap between the respective extrados face 12 and the primary lining 500 of the excavation of the tunnel 100 ( see Figures 6 and 7 ) . The inj ection continues until the filler material in the bag 7 reaches a predetermined pressure .

[0070] The steps of positioning and inj ection described above are then repeated iteratively for each ring of ashlars 111 until the lining 110 is complete .

[0071] The ashlars 1 or 1 ' of the invention therefore allow a backfilling to be carried out for a tunnel lining which is formed by prefabricated ashlars and therefore allows the necessary consolidation of the excavation to be achieved in a particularly ef fective and timely manner, even in the field of construction of tunnels using "conventional" techniques .

[0072] Furthermore , i f introductions of water should occur in the region of the j oints between the ashlars as a result of a mal function of the peripheral fluid-tight seals thereof , once the construction of the lining is completed and after the tunnel has been put into service , in this case it is also possible to carry out repairs in an easy, rapid and ef fective manner by injecting sealing material towards the extrados of the lining near the introduction locations through the auxiliary injection pipes 25, 25' which are suitably provided in the ashlars 1 or 1' of the invention.

Claims

1. A prefabricated ashlar (1; 1' ) for a tunnel lining (110) comprising an intrados face (11) , an extrados face (12) opposite the intrados face (11) and a peripheral edge (13) which connects the intrados face (11) and the extrados face (12) , wherein the extrados face (12) defines at least one recess (30, 30' ) , in which an expandable bag (7, 7 ’ ) which can expand when it is filled with filler material is received, the ashlar (1; 1' ) comprising at least one bagfilling pipe (15, 15' ) in order to inject the filler material into the expandable bag (7, 7 ’ ) , wherein the bag-filling pipe (15, 15' ) comprises a first end opening (15A, 15A' ) in the region of the intrados face (11) and a second end opening (15B, 15b' ) in the region of the recess (30, 30' ) of the extrados face (12) , wherein the expandable bag (7, 7' ) is in hydraulic communication with the second end opening (15B, 15B' ) of the at least one bag-filling pipe (15, 15' ) in order to receive the filler material, and wherein the ashlar (1; 1' ) comprises at least one auxiliary injection pipe (25) comprising a first end opening (25A) in the region of the intrados face (11) and a second end opening (25B) in the region of the extrados face (12) , the at least one auxiliary injection pipe (25) being defined in a local position at a side (131, 132) which forms the peripheral edge (13) .

2. A prefabricated ashlar (1; 1' ) according to claim 1, wherein the ashlar (1; 1' ) comprises non-return valve means (16, 26) which are arranged along the at least one bagfilling pipe (15, 15' ) and / or along the at least one auxiliary injection pipe (25) .

3. A prefabricated ashlar (1; 1' ) according to claim 1 or 2, wherein the ashlar (1; 1' ) comprises a plurality of auxiliaryinjection pipes (25) for each side (131, 132) forming the peripheral edge (13) .

4. A prefabricated ashlar (1; 1' ) according to claim 3, wherein, for each side (131, 132) forming the peripheral edge (13) , the pipes of the plurality of auxiliary injection pipes (25) are spaced apart along a line parallel with the corresponding side (131, 132) forming the peripheral edge(13) .

5. A prefabricated ashlar (1; 1' ) according to any one of claims 1 to 4, wherein the second opening (25B) of the at least one auxiliary injection pipe (25) is arranged in a region of the extrados face (12) between the recess (30, 30' ) and the corresponding side (131, 132) forming the peripheral edge ( 13 ) .

6. A prefabricated ashlar (1; 1' ) according to any one of claims 1 to 5, wherein the recess (30) has a peripheral shape which geometrically conforms to the shape of the peripheral edge ( 13 ) .

7. A prefabricated ashlar (1' ) according to any one of claims 1 to 6, wherein the extrados face (12) defines a pair of recesses (30, 30' ) in each of which an expandable bag (7, 7 ’ ) which can expand when it is filled with filler material is received, and wherein for each expandable bag (7, 7' ) there is provided a bag-filling pipe (15, 15' ) which passes through the entire thickness of the ashlar (1' ) and which is hydraulically connected to the expandable bag (7, 7' ) in order to allow the expansion thereof for filling following the injection of the filler material.

8. A prefabricated ashlar (1' ) according to claim 7, wherein the ashlar comprises at least one additional auxiliary injection pipe (25' ) comprising a first end opening (25A' ) in the region of the intrados face (11) and a second end opening (25B' ) in the region of the extrados face (12) , wherein the second end opening (25B' ) of the at least one additional auxiliary injection pipe (25' ) is arranged in a region of the extrados face (12) between the recesses (30, 30' ) .

9. A prefabricated ashlar (1; 1' ) according to any one of claims 1 to 8, wherein the at least one auxiliary injection pipe (25) and, if present, the at least one additional auxiliary injection pipe (25' ) have a rectilinear development .

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