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 (ID and the extrados face (12). The ashlar (1) comprises at least one auxiliary injection pipe (25) having 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] In light of the above , an obj ect of the invention is to provide a prefabricated ashlar for constructing 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 .

[0016] 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 .

[0017] These obj ects are achieved by a prefabricated ashlar for a tunnel lining having the features set out in the independent claim 1 appended .

[0018] 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 .

[0019] 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 .

[0020] By means of auxiliary inj ection pipes which are configured and arranged in this manner, it is possible to inj ect sealing or filler material towards the extrados surface of a lining formed by prefabricated ashlars according to the invention near the j oints between adj acent ashlars 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 the provision of these pipes , it is therefore advantageously possible to intervene in a tunnel lining which is formed by prefabricated ashlars in order to eliminate any introductions in the region of the j oints between the ashlars in an easier, faster and more controlled manner with respect to the conventional intervention methods previously mentioned . This has positive repercussions on the quality of the repair and the intervention times required .

[0021] Preferably, the ashlar comprises non-return valve means which are arranged along the at least one auxiliary inj ection pipe .

[0022] Preferably, the valve means comprise or are constituted by a duckbill valve .

[0023] Preferably, the ashlar comprises a plurality of auxiliary inj ection pipes for each side forming the peripheral edge .

[0024] 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 of the peripheral edge .

[0025] Preferably, the at least one auxiliary inj ection pipe has a rectilinear development .

[0026] Preferably, at least the second end opening of the at least one auxiliary inj ection pipe is arranged at a distance from the corresponding side of the peripheral edge between 10 mm and 100 mm . Preferably, the at least one auxiliary inj ection pipe has a circular cross-section with a diameter between 4 and 20 mm .

[0027] DESCRIPTION OF THE FIGURES

[0028] 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 :

[0029] - Figure 1 and Figure 2 are schematic, perspective views , from di f ferent points of observation, of a prefabricated ashlar according to the invention;

[0030] - Figure 3 is a schematic, perspective view of a portion of a tunnel lining which is formed by prefabricated ashlars according to the invention;

[0031] - Figure 4 is a schematic, sectioned view of two axially adj acent ashlars which are installed in a tunnel , and

[0032] - Figure 5 is an enlarged view of the detail V in Figure 4 .

[0033] The same reference numerals and the same reference letters in the Figures identi fy the same elements or components .

[0034] DETAILED DESCRIPTION

[0035] Figures 1 and 2 show a preferred embodiment of a prefabricated ashlar according to the present invention which is generally designated 1 .

[0036] In a manner known per se , the ashlar 1 is configured as a ring segment and is installed in a tunnel lining 110 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 tunnel . Figure 4 shows two rings 111 of the lining 110 which are formed by ashlars 1 according to the invention . 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 1 ) which, in the installed condition of the ashlar 1 , is directed towards the interior of the tunnel , an extrados face 12 (visible in Figure 2 ) 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 .

[0037] The ashlar 1 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 .

[0038] The auxiliary inj ection pipes 25 mainly serve to allow the inj ection of 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 a functional degeneration of the fluid-tight seals 2 themselves and / or of incorrect positioning of the ashlars 1 . 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 .

[0039] In any case , it is not excluded to use auxiliary inj ection pipes 25 for additional or alternative purposes during the construction of a tunnel 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 in order to integrate a backfilling of the lining 110 itsel f , particularly in the case in which it is obtained by alternative methods to the conventional front inj ection of filler material , for example , by means of the expansion of expandable bags which are associated with the ashlars in the region of the respective extrados face and which can expand when filler material is inj ected therein . Furthermore , at least some of the auxiliary inj ection pipes 25 could be used to inj ect , even in the absence of introductions , sealing or water-proofing material in order to increase the hydraulic tightness of the fluid- tight seals 2 , before carrying out the backfilling .

[0040] Each auxiliary inj ection pipe 25 passes through the thickness of the ashlar 1 , that is to say it develops between the intrados face 11 and the extrados face 12 thereof ( see Figure 4 ) . Each auxiliary inj ection pipe 25 therefore comprises 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 sealing material or the filler material is inj ected into each auxiliary inj ection pipe 25 through the respective first end opening 25A and is discharged therefrom through the respective second end opening 25B . Preferably, the auxiliary inj ection pipes 25 develop along a rectilinear axis X ( indicated in Figure 5 ) and have a crosssection ( that is to say orthogonal to the axis X ) with a circular shape , the diameter of which may vary in a range preferably between 4 mm and 20 mm .

[0041] Preferably, for each side 131 , 132 forming the peripheral edge 13 of the ashlar 1 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 the ashlar 1 shown in the Figures , for example , there are provided three auxiliary inj ection pipes 25 in a position adj acent to each long side 131 and two auxiliary inj ection pipes 25 in a position adj acent to each short side 132 .

[0042] Each auxiliary inj ection pipe 25 or at least the respective second end opening 25B is arranged at a distance d ( indicated in Figure 2 ) which is preferably between 10 mm and 100 mm from the corresponding side 131 , 132 of the peripheral edge 13 , where the distance d is evaluated between the axis X of each auxiliary inj ection pipe 25 and the corresponding side 131 , 132 of the peripheral edge 13 .

[0043] As can be seen in Figures 4 and 5 , each auxiliary inj ection pipe 25 is preferably provided with a non-return valve means 26 which is configured so as to avoid, during and after the inj ection of sealing or filler material , a potential return flow as a result of counter-pressure .

[0044] The non-return valve means 26 is preferably of the passive type and can be advantageously configured as a so-called "duckbill" valve . In particular, as can better be seen in Figure 5 , the nonreturn valve means 26 comprises an annular shell 261 for connection to the auxiliary inj ection pipe 25 and at least one pair of closure edges 262 which are suitably shaped and made from resilient material and which extend from the internal surface of the annular shell 261 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 26 in the permitted flow direction brings about a temporary opening of the closure edges 262 and therefore the passage of the fluid itsel f . When the pressure is eliminated, the closure edges 262 autonomously close again, preventing a return flow .

[0045] Advantageously, the non-return valve means 26 is constructed separately and assembled with one or more tubular elements so as to obtain an auxiliary inj ection pipe 25 with a desired length . In the exemplary embodiment shown in the Figures , the non-return valve means 26 is arranged in an intermediate position of the auxiliary inj ection pipe 25 and it is formed by the non-return valve means 26 and by two di f ferent tubular elements 25 ' , 25 ' ' ( indicated in Figure 5 ) which are applied, for example bonded or thermally welded, to the opposite ends of the non-return valve means 26 itsel f . Alternatively, the non-return valve means 26 could be arranged in the region of one of the ends of the auxiliary inj ection pipe 25 and it could be formed by the non-return valve means 26 and by a single tubular element which is applied to one of the ends thereof . The auxiliary inj ection pipe 25 obtained in this manner is then suitably surrounded in the ashlar 1 during the casting thereof .

[0046] Figure 4 shows a portion of a tunnel comprising a lining 110 which is formed by ashlars 1 according to the present invention . In particular, the Figure refers by way of example to a tunnel constructed using "conventional" techniques , wherein, in a widely known manner, there is provided a primary lining 500 which is applied to an excavation wall 400 and formed by reinforcement ribs 510 and proj ected concrete 520 . The lining 110 formed by the ashlars 1 which constitutes in this case the definitive lining of the tunnel is arranged in a radially internal position with respect to the primary lining 500 . There is present between the extrados face 12 of each ashlar 1 and the intrados surface of the primary lining 500 a layer of backfilling 300 which ensures the structural continuity in the radial direction between the primary lining 500 and the definitive lining 110 .

Claims

1. 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) , wherein the ashlar (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) according to claim 1, wherein the ashlar (1) comprises non-return valve means (26) which are arranged along the at least one auxiliary injection pipe (25) .

3. A prefabricated ashlar (1) according to claim 2, wherein the valve means (26) comprise or are constituted by a duckbill valve.

4. A prefabricated ashlar (1) according to any one of the preceding claims, wherein the ashlar (1) comprises a plurality of auxiliary injection pipes (25) for each side (131, 132) forming the peripheral edge (13) .

5. A prefabricated ashlar (1) according to claim 4, 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) .

6. A prefabricated ashlar (1) according to any one of the preceding claims, wherein the at least one auxiliary injection pipe (25) has a rectilinear development. . A prefabricated ashlar (1) according to any one of the preceding claims, wherein at least the second end opening (25B) is arranged at a distance (d) from the side (131, 132) forming the peripheral edge (13) between 10 mm and 100 mm.

8. A prefabricated ashlar (1) according to any one of the preceding claims, wherein the at least one auxiliary injection pipe (25) has a circular cross-section with a diameter between 4 and 20 mm.

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