WO2010064193A1

WO2010064193A1 - Modular lining for tunnels

Info

Publication number: WO2010064193A1
Application number: PCT/IB2009/055443
Authority: WO
Inventors: Giampaolo Capaldini
Original assignee: Giampaolo Capaldini
Priority date: 2008-12-04
Filing date: 2009-12-01
Publication date: 2010-06-10
Also published as: ITRM20080650A1; IT1392239B1; SI2364399T1; PL2364399T3; EP2364399A1; HRP20130592T1; EP2364399B1; DK2364399T3; PT2364399E; ES2410367T3

Abstract

The present invention refers to a modular lining for tunnels excavated with traditional methods, comprised of prefabricated reinforced-concrete modules, and to a method for manufacturing said lining. The modular lining subject-matter of the present invention, executed by the method it also subject-matter of the present invention, has the evident advantage of being manufactured by the laying of prefabricated modules, thereby evidently increasing structure efficiency and drastically decreasing execution times, in the last analysis also influencing realization costs.

Description

MODULAR LINING FOR TUNNELS

DESCRIPTION

The present invention refers to a modular lining for tunnels excavated with traditional methods, comprised of prefabricated reinforced-concrete modules, and to a method for manufacturing said lining. History of technology

The present invention finds application in the tunnel-making field, for tunnels excavated by conventional systems like, e.g., explosive or arm-mounted tool such as bucket, pizza wheel, single-tooth ripper, road header, etc... From a construction standpoint, the various grounds involved in tunnel-making are usually grouped under different categories depending on the degree of stability of the tunnel breast or face:

1) stable face: when the wall under excavation and the entire back-lying ground core yet to be excavated self-supports (due to the ground ability to enact the known "arch effect"), keeping the surface of the hollow in static balance in the long term, and when no significant material releases occur at the profile of the excavated section;

2) face stable in the medium term: when the static conditions of which at 1) above hold only for a time period beyond which, both due to the varying of the chemico-physical conditions of the ground, and to its mere loosening owing to the excavation, ground geomechanical conditions undergo decay and alteration such as to make unstable the face, along with a more or less significant portion of the back- lying core, with the entailed loss of the ground ability to enact the arch effect;

3) unstable face: when, immediately after excavating, the face and the back-lying core lose their static stability generating actual ground extrusions and releases of consistent amounts of material inside the hollow. Modern excavation techniques (always full-section) allow to operate safely even in case of an unstable face, or of a face stable over short periods, by performing a varied array of pre-consolidations and retainings of the face (or breast) core which improve the geomechanical characteristics of the ground until letting it attain a behavior similar or close to that characterizing stable faces. Description of the prior art

Currently, the near-totality of tunnels excavated with traditional systems are lined (after having made a first, so-called "first-phase" provisional lining) with a final lining of reinforced or plain concrete, manufactured on-site and comprised of a bottom portion performing the structural function of base "inverted arch", a function well-known to a person skilled in the art, side portions thereof referred to as "low side walls" and a top portion referred to as "calotte".

In extremely rare cases, such as hydraulic tunnels with a reduced and strictly circular section, reduced-size modules are used, prefabricated off-site and subsequently mounted with special equipment alike those utilized for the making of an excavation with TBM (Tunnel Boring Machines) technique. Drawbacks of the prior art

Known-art linings as substantially described above suffer from several evident drawbacks. Concerning a lining manufactured on-site by concrete casting, it will be appreciated that such a methodology entails evident difficulties, as the lining is completely manufactured on-site and makes use of no prefabricated members. On the other hand, the excessive intricacy of a laying of prefabricated modules having standard sections, usually comprised between 50 and 150 m², has always relegated said methodology to an extremely marginal role, it surely having never been taken into account in the standard execution of road, highway or railway tunnels. Objects of the Invention

Object of the present invention is to solve the abovementioned drawbacks by providing a prefabricated module as substantially described in claim 1 , a modular lining as substantially described in claim 20, and finally a method for manufacturing such a modular lining as substantially described in claim 21. Further features of the process are defined in the corresponding dependent claims. Advantages of the Invention

The present invention, by overcoming the mentioned problems of the known art, entails several evident advantages.

The modular lining subject-matter of the present invention, executed by the method it also subject-matter of the present invention, has the evident advantage of being manufactured by the laying of prefabricated modules, thereby evidently increasing structure efficiency and drastically decreasing execution times, in the last analysis also influencing realization costs. Brief description of the drawings

Still further advantages, as well as the features and the operation steps of the present invention will be made evident in the following detailed description of a preferred embodiment thereof, given by way of example and not for limitative purposes. Reference will be made to the figures of the annexed drawings, wherein: Fig. 1 depicts a front view of a prefabricated module according to the present invention;

Fig. 2 depicts a sectional view of a first detail of the prefabricated module according to the present invention; Fig. 3 depicts a sectional view of a second detail of the prefabricated module according to the present invention;

Figs. 4 - 21 illustrate the steps of a method for manufacturing a modular lining according to the present invention.

Detailed description of the drawings Referring to Fig. 1 , a front section 11 of a tunnel 2 is shown by way of example. Referring to section 11 , associated to a respective drive breast (advance face) of the excavation, the tunnel 2 has a respective portion of walls, denoted by number reference 40 in the Figure, comprising a bottom base 41 and a top vault 5.

The section 11 of the tunnel 2 has, by way of example and not for limitative purposes, a substantially half-circumference shape, and defines a vertical axis 10 of symmetry.

A prefabricated module 3 subject-matter of the present invention is set to support said tunnel 2, at the breast relevant to the section 11 shown.

The prefabricated module 3 is apt to be set consecutively with respect to the adjacent module (not visible in Fig. 1) in a structurally independent manner with respect to the latter, along an axial drive direction that is orthogonal to the plane defined by section 11.

Always referring to Fig. 1 , the prefabricated module 3 comprises a base member 6, performing the structural function of an "inverted arch", and a top retaining portion 7 which in turn performs the structural function of a "top calotte". The base member 6 is apt to be connected to the top retaining portion 7 by connecting means 15 arranged in correspondence of an interface thereof. Said connecting means, by way of example and not for limitative purposes, is of groove-and-tongue joint type.

As is clearly visible in the figure, the base member 6 has a shape having a substantially C-shaped section, whereas the top retaining portion 7 has a section - A - having a substantially circular half-crown shape. Therefore, base member 6 and top portion 7 are such as to give to the prefabricated module 3 a substantially annular shape when connected therebetween.

The base member 6 in turn comprises a pair of base ashlars 8 and 9, preferably made of reinforced concrete, and arranged on a bottom base 41 of the respective portion of wall 40, at which the module 3 is just set to support. The ashlars 8 and 9 are arranged on the bottom base 41 symmetrically with respect to the vertical axis 10 of symmetry of the section 11. They are connected therebetween by first connecting means 12, which comprises a hinge 12, positioned just along the vertical axis 10 of symmetry. The hinge 12 is preferably blocked by concrete casting, in order to prevent any relative shifting between the two ashlars 8 and 9. In an entirely analogous way, the top retaining portion 7 comprises a pair of top ashlars 18 and 19, them also preferably made of reinforced concrete, apt to be arranged along the top vault 5 of the respective portion 40 of the walls of the tunnel, said ashlars 18 and 19 being them also arranged symmetrically with respect to the vertical axis 10 of symmetry of the section 11. The ashlars 18 and 19 are connected therebetween by second connecting means 17, comprising a hinge 17 arranged along the vertical axis 10.

Referring now to next Fig. 1a, there are shown by way of example sections of the ashlars 9 and 18 along the respective section lines B-B and A-A.

Making reference to the section of the base ashlar 9, denoted in figure by reference number 31 , it comprises two side faces 32 and 33, each having a region defining a respective recess 34 and 35. Moreover, the section 31 has a third region defining a third bottom recess 36. Always referring to Fig. 1a, the top ashlar 18 has a section 37 in all analogous to section 31 , therefore it will not be further described herein.

Referring to Fig. 1b, sections 31' and 37' are shown having a shape alternative to that of the above-described sections 31 and 37. In particular, they have no third bottom recess. Should it be opted, on the basis of the specific applicative scenario, to make the ashlars at provisional factories set near the yard (instead of carrying them, sometimes even from considerable distances) making the ashlar with stiffening ribs, in other words having the third bottom recess, might be not advantageous; rather, it might be advantageous to complete casting at the factory until having the sections 31' and 37' assume the substantially rectangular shape shown just in Fig. 1b. Referring now to next Fig. 2, the ashlar 9 of the base member 6 (related to the prefabricated module 3) is shown in a side view. In particular, in Fig. 2 there can be seen an ashlar 9' belonging to the adjacent prefabricated module, denoted in Figure by reference number 3'. The ashlars shown here are, by way of example and not for limitative purposes, those having a substantially rectangular section without the main ribs. The ashlar 9' in turn has a region defining a respective recess 34', faced to the recess 34 of the ashlar 9.

The ashlar 9 is apt to form a transversal duct 50 by juxtaposition the two recesses 34 and 34'. In said duct 50 it is set a hose of waterproofed canvas expanded by binder material, preferably comprising cement grout.

As an alternative to the above-mentioned expansible hoses, analogous tubing of rubber or silicone materials. In such a case, they have to be juxtaposed in the duct prior to setting side-by-side and compressing the ashlar subjected to launching to the preceding one laid-down. As a further alternative expanding resins or other cement- or polymer-based foams may be used in order to tamp an air gap created between two adjacent ashlars. Always referring to Fig. 2, binder material, preferably comprising cement grout, is arranged at the interface between the base member 6 of the module 3 and the bottom base 41. Finally, the ashlar 9 is preferably coated with a waterproofing external coating made of PVC.

It will be appreciated that what has been described for the ashlars 9 and 9' is analogously valid for all ashlars of each base member, set to support the respective portions of tunnel wall for each excavation drive breast (advance face).

Referring to Fig. 3, the ashlar 18 of the top retaining portion 7 related to the prefabricated module 3 is depicted in a sectional view and by way of example. Always by way of example, the section of the ashlar 18 offers main ribs, as it has a third recess, according to what has already been described in the foregoing. In this case as well, the recesses faced therebetween, belonging to two ashlars adjacent therebetween, are such as to form ducts, in each of which it is set a waterproofed hose having thereinside binder material, preferably comprising cement grout. Like in the preceding case, as an alternative, alike tubing of rubber or of silicone materials may be used. In that case, said tubing has to be juxtaposed in the duct prior to juxtaposing (setting side-by-side) and compressing the ashlar subjected to launching to the preceding one laid-down. As a further alternative, expanding resins or other cement- or polymer-based foams may be used in order to tamp an air gap created between two adjacent ashlars.

Moreover, analogously to the preceding case, the interface between the retaining portion 7 and the top vault 5 is tamped with binder material. In particular, said binder material comprises a primary injection of concrete and a secondary injection of cement grout. Finally, each ashlar of each top retaining portion is coated with a waterproofing coating made of PVC.

Therefore, by juxtaposing (setting side-by-side) in sequence as many prefabricated modules as above-described as needed, depending on the excavation length required for the tunnel-making, a modular lining subject-matter of the present invention is obtained.

The modular lining is obtained according to a method, it also subject-matter of the present invention, described hereinafter.

The method for manufacturing the modular lining comprises a step of positioning, for each drive breast (advance face) of the tunnel, one or more prefabricated modules as described in detail above.

Referring to Fig. 4, said positioning step comprises a step of arranging the base member 6 in correspondence of a respective bottom base 41. The step of arranging the base member 6 comprises a step of placing said member 6 in a folded position, so that the hinge 12 lies along the axis 10 of symmetry of the section 11. It will be appreciated that the base member 6 is placed near the breast of the tunnel by gripping equipment, preferably mounted on cars, like self-moving cranes or other types of self-moving cars, well known in the current state of the art and therefore within the reach of a person skilled in the art.

Then, said arranging step comprises a step of laying the base member 6 so as to arrange it in support of the bottom base 41 , as illustrated in Fig. 5. Then, referring to Fig. 6, the hinge 12 is blocked by concrete casting, in order to prevent relative shifting between the base ashlars, as already highlighted hereto.

Alternatively, referring to Fig. 7, in case the base ashlars 8, 9 are disjoined therebetween and similarly specular, the step of arranging the base member comprises a step of coupling said ashlars in correspondence of the vertical axis 10 of symmetry, arranging them in support of the bottom base 41. The ashlars are coupled on-site, preferably by solidarization with a supplementary casting, or by dowelling for hinge joint. As an alternative, in case the specific geometry of the tunnel section allows it, the entire base member could be carried and laid on-site even in a single ashlar (e.g., in the end portions of artificial tunnels). Referring to next Fig. 8, to the step of arranging the base member 6 (for which in Figure the ashlar 9 is depicted in a plan view) there follows a step of performing a correct altimetric and planimetric positioning thereof. More specifically, said altimetric and planimetric positioning is performed on each ashlar (for brevity's sake, only ashlar 9 is depicted in the figure) by 4 hydraulic jacks, each one denoted by number reference 90, placed substantially at the vertexes of a base thereof. In Fig. 8 the case of a firm ground is depicted, capable of safely bearing at least a unitary load estimated to be equal to about 2.5/5 kg/cm². The hydraulic jacks 90 are apt to actuate metal plates directly laid on the ground, upon leveling off of a thin layer of sand, preferably of 5/10 cm, suitably hardened and solidarized with the underlying ground by dusting with cement or alike materials.

Instead, in next Fig. 9, the case of a relatively yielding and/or wet ground is depicted. In this case as well, correct altimetric and planimetric positioning of the base member 6 is performed with the aid of hydraulic jacks 90' (only one of which is visible in figure) placed as in the preceding case. They are apt to actuate metal plates laid on respective caissons 91 driven into the ground. Preferably, should the ground be particularly yielding, it will be possible to further be assisted by metal rods 92 provided with self-drilling points such as to drive into the ground for some meters until acquiring the required load-bearing capacity in connection to the loads assigned thereto. Accordingly, it is advisable to test on-site the load-bearing capacity of the rods with suitable load tests.

In both cases, for yielding ground as well as for a nonyielding ground, upon having carried out a firm resting of the metal plates, the four jacks with which each ashlar is provided will be actuated to bring in position the entire base member. It will be appreciated that the selection of jacks is given herein by way of example and not for limitative purposes, as they might be replaced also by devices based on screw- nut screw systems, well-known in the current state of the art, driven directly by the ashlar intrados: such a selection would be more economical, though to the detriment of operation simplicity and rapidity. Referring to Fig. 10, it is still depicted, always by way of example, the ashlar

9 in a side view. The method subject-matter of the present invention further comprises a step of applying a coating of PVC-reinforced canvas, denoted in figure by reference 60, shielded from possible damage by a layer of non-woven fabric, which is positioned on the ashlar 9 so as to exhibit a remainder portion 61 , apt to be heat-sealed with a remainder portion 61' of an ashlar 9" consecutive thereto. The heat-sealed remainder portions 61 and 61' are subsequently reintroduced inside a hollow 63 present between two consecutive base members. It will be appreciated that said procedure will be performed for each one ashlar of the base member, and more generally for each one base member of each prefabricated module set to support of the tunnel, for each drive breast (advance face) thereof.

Then, the method subject-matter of the present invention comprises a step of fixing the base member 6 in correspondence of the bottom base 41. Such a fixing is obtained by injection of binder material, preferably comprising concrete made suitably fluid by fluidifying agents, within an air gap 70 present between the base member 6 and the bottom base 41 , as indicated in the figure. Preferably, suitable accelerators will further be added to said concrete, so as to accelerate its setting time and achieve, over the shortest possible time, the firmness of a good ground (approximately equal to 2.5/5 kg/cm²). The concrete, having no real structural function but merely that of thickening, might exhibit compression strength comparable to that of a surrounding mass, and therefore might also be replaced by chemical foams or cement mortars lightened with aerants or foam-generating agents.

In case the present ashlar be manufactured at provisional factories set near the yard, and therefore having no stiffening ribs, concrete casting is preferably replaced, owing to the reduced volumes and thicknesses involved, by injections of fluid grouts (primary injection) always suitably added with accelerants; in both of the above cases, however, subsequently to concrete or grout setting, and optionally even after calotte mounting, a secondary injection of cement grout at a medium pressure (preferably in the neighborhood of 10/20 bars) should be performed so as to achieve perfect occlusion of any residual gap between ashlar and ground; the above casting and injections will be performed over the entire interface surface between structure and ground, for all the development of the base member. The step of tamping the air gap is preferably performed subsequently to the heat- sealing and the reintroducing of the remainder portions inside the hollow. Finally, the ashlar 9 will be sealed to an ashlar adjacent thereto by injection of grout inside the expansible hose located internally to the above-described duct 50.

Upon fixing the base member on the respective bottom base, the method subject-matter of the present invention envisages, referring to Fig. 11 , a step of arranging the top retaining portion 7 in contact with the base member, so as to give a substantially annular shape to the prefabricated module. Always referring to Fig. 11 , said arranging step is carried out by carrying the top portion in correspondence of the respective top vault 5 in a semi-open position on cars mounted on side rails and subsequently hoisted in place by hydraulic jacks 80, 81. Alternatively, referring to next Figs. 12 - 12g, said step of arranging the top retaining portion is carried out by installing in a semi-open position by a self-moving or towed car 90. The car 90, thanks to a drive system based on hydraulic pistons, performs the moving of the retaining portion 7, and its positioning on the base member, thanks to the relative mobility of the two ashlars 18 and 19 obtained by the connecting by the hinge 17.

As a further alternative, the positioning of the top retaining portion could be carried out according to still different modes. By way of a non-limiting example, the top ashlars forming the top retaining portion could be:

• carried in correspondence of the drive breast (advance face) and directly laid on-site by mechanical arms or suitable cars (Fig. 13)

• carried to the breast, joined topwise by hinge and directly laid on-site by mechanical arms mounted on self-moving cars or overhung to cars (Fig. 14);

• carried to the breast while joined by hinges to the piece-formed base member, and laid on-site by suitable hydraulic equipment for opening the same ashlars; and moreover carried to the breast by suitable cars (Figs. 15a

- 15c);

• carried to the drive breast (advance face) while joined by hinges to the base member formed of two pieces, and laid on-site (installed) with methodologies analogous to those highlighted above (Figs. 16a - 16c); • base ashlars member carried to the breast while joined by hinges to the piece-formed calotte ashlar (Figs. 17a - 17c); and, finally,

• in the last Figs. 18 and 19 there two hypotheses of car for the moving (carrying and laying) of the above ashlars are depicted.

Upon arranging the top retaining portion in correspondence of the respective top vault, the method subject-matter of the present invention envisages, referring now to next Fig. 20, a step of waterproofing each ashlar of the top retaining portion by a PVC-reinforced canvas 100, exhibiting it also a remainder portion apt to be heat- sealed with a remainder portion related to a canvas of an ashlar adjacent thereto. In a manner entirely analogous to the preceding case, said heat-sealed portions will be reintroduced inside a hollow present between two ashlars adjacent therebetween. Always in a manner analogous to the above-described case related to the base member, the method subject-matter of the present invention subsequently comprises a step of fixing said top retaining portion by injection of binder material, preferably comprising concrete, within an air gap located in correspondence of the interface between the top retaining portion and the respective top vault, and in particular within the sleeve 101 of the ashlar located between two main ribs. Such a sleeve, by increasing in volume owing to the pressure-injecting of concrete or other suitable mortars, foam-generating substances or aerants mentioned above, will adhere to the surface 5 of the top vault generating a coaction between the prefabricated module and the tunnel wall.

The ashlar 18 will then be sealed to an ashlar 18' adjacent thereto by injection of mortar (preferably of the "bull flex" type) into an expansible hose 110 positioned inside the duct. Finally, a secondary injection of cement grout 111 will be performed in order to attain complete adherence between top retaining portion 7 and respective top vault 5.

In case of a rectangular section, in the presence of a reduced tamping volume, it is possible to operate the ashlar-ground solidarization, analogously to what has been described for the base member, with a single injection of grout or lightened mortars, beside the waterproofing canvas.

Preferably, prior to passing to the next excavation phase for the breast drive (face advance), it will be advisable to apply to most of the extrados surface of the base member one or more reinforcement members comprising, e.g., resilient materials or steel plates, to protect it from wear and damage entailed in demolition and truck loading of demolition materials.

In case of an unstable breast, and therefore in the hypothesis of having to carry out breast consolidation/retaining prior to the excavation phase, once consolidation has taken place it will be possible to carry out the excavation of the first section (about 1.5 m) and the laying of the two pre-assembled ashlars of the base member with methodologies analogous to the above-described ones; subsequently, in case the situation does not allow to operate safely, the temporary or first-phase lining might be carried out with the traditional system (shot-concrete and metal ribs) laterally positioned above the base member in a backward position to allow for subsequent mounting of the top ashlars. Once the entire field (9-12 m) has been consolidated, it will be possible to carry out in total safety the mounting of the final lining of the top vault and the solidarization thereof with the first-phase lining lying behind it, always operating in the above-described way.

As an alternative, the provisional lining might be executed even before excavating the volume that has to house the base member and, in the traditional manner, carry out the first-phase lining (shot-concrete and metal ribs) for all the field, and only subsequently execute the laying of the base ashlars and top ashlars according to the above-described modes; already this methodology, in fact, would constitute a great saving, both in terms of time and costs, in the execution of the final lining, as the activity stop at the breast, consequent to the time required for manufacturing the base member, would be greatly reduced; moreover, the duration of execution of the final lining of the top vault would be greatly reduced, by virtue of the fact that the operations of positioning the metal reinforcements (where envisaged), shuttering, casting, deshuttering of the entire vault are not necessary anymore. Under stable breast conditions, as an alternative to the mode described in the foregoing it might be possible to operate as follows: once excavation has taken place, a provisional mounting of the two top ashlars is carried out, even before the positioning of the base ashlars; referring to last Figure 21 , this is possible by placing top ashlars overhanging by nailings 150 placed on top of the excavation; once breast drive (face advance) has taken place, in due time, the base ashlars will be positioned and only thereafter, when this latter operation will be concluded, the final positioning of the top ashlars may be executed, by lowering them until resting on the base member; finally, said ashlars will be solidarized with the wall of the excavation in a manner analogous to the above-described one. At the ends of a natural tunnel, beyond the bulkheads of the entrance works, it is sometimes necessary to execute a section of artificial tunnel by preventive overburden removal and subsequent backfilling.

In these cases the same operations as above are possible, yet with some simplifications:

• if ashlar prefabrication occurs on-site, or on premises not far from the yard, it is possible to piece-form both the entire base member and the top retaining portion; the ashlars can be laid simply by a self-moving crane;

• in case of monolithic ashlars, rib forming could be omitted in order to attain an ashlar cross section, both for base member and top retaining portion, of rectangular type and, for the latter, lacking the PVC hose; in that case, always for the top portion, it will be possible to execute in correspondence of the extrados an additional reinforced-concrete slab for connecting between ashlars, slab that shall subsequently be waterproofed and adequately protected, according to methodologies commonly utilized in the current state of the art; at that point, the structure is ready for the subsequent final lining. The present invention has been hereto described with reference to a preferred embodiment thereof. It is understood that other embodiments might exist, all falling within the concept of the same invention, and all comprised within the protective scope of the claims hereinafter.

Claims

1. A prefabricated module (3) for a modular lining for retaining internal walls of a tunnel (2) having a section (11), apt to be set to support a respective portion of said walls (40) of the tunnel (2) consecutively with respect to a module (3¹) adjacent

S thereto along an axial drive direction, and in a structurally independent manner with respect to the latter.

2. The prefabricated module (3, 3') according to the preceding claim, wherein each module (3, 3') comprises:

• a base member (6); 0 • a top retaining portion (7), connectible with said base member (6);

• connecting means (15) between said base member (6) and said top retaining portion (7); said base member (6) and top retaining portion (7) being such as to give to said prefabricated module (3, 3') a substantially annular shape when connected5 therebetween.

3. The prefabricated module (3, 3') according to the preceding claim, wherein said base member (6) has a shape having a substantially C-shaped section.

4. The prefabricated module (3, 3') according to claim 2 or 3, wherein said top retaining portion (7) has a shape having a substantially circular half crown-shaped0 section.

5. The prefabricated module (3, 3') according to one of the claims 2 to 5, wherein said base member (6) comprises a pair of base ashlars (8, 9) apt to be arranged on a bottom base (41) of said respective portion of internal wall (40) of the tunnel (2), symmetrically with respect to a vertical axis (10) of symmetry of said section (11).5

6. The prefabricated module (3, 3') according to the preceding claim, wherein said base ashlars (8, 9) are connected therebetween by first connecting means (12) positioned in correspondence of said vertical axis (10).

7. The prefabricated module (3, 3') according to the preceding claim, wherein said first connecting means (12) comprises a first hinge (12). 0

8. The prefabricated module (3, 3') according to one of the claims 2 to 7, wherein said top retaining portion (7) comprises a pair of top ashlars (18, 19) apt to be arranged on a top vault (5) of said respective portion of internal wall of the tunnel (2) symmetrically with respect to a vertical axis (10) of symmetry of said section (11).

9. The prefabricated module (3, 3') according to the preceding claim, wherein said5 top ashlars (18, 19) are connected therebetween by second connecting means (17) positioned in correspondence of said vertical axis (10).

10. The prefabricated module (3, 3') according to the preceding claim, wherein said second connecting means (17) comprises a second hinge (17).

11. The prefabricated module (3, 3¹) according to one of the claims 5 to 7 and 8 to 10, wherein each ashlar (8, 9, 18, 19) has a section (31 , 37) comprising two side faces (32, 33) opposite therebetween, each having a region defining a respective recess (34, 35).

12. The prefabricated module (3, 3') according to the preceding claim, wherein each ashlar (9) is apt to form a transversal duct (50) with an ashlar (9') of a prefabricated module (3¹) consecutive thereto, by juxtaposition of the respective recesses (34, 34') faced therebetween.

13. The prefabricated module (3, 3') according to the preceding claim, wherein inside each duct (50) it is set a hose of waterproofed canvas expanded by injection of binder material.

14. The prefabricated module (3, 3') according to the preceding claim, wherein said binder material comprises cement grout.

15. The prefabricated module (3, 3") according to claims 11 to 14, wherein said section (31) has a third region defining a third bottom recess (36).

16. The prefabricated module (3, 3') according to one of the preceding claims, comprising binder material interposed at the interface between each module (3, 3') and the respective walls (40) of the tunnel (2).

17. The prefabricated module (3, 3') according to the preceding claim, wherein said binder material comprises cement grout.

18. The prefabricated module (3, 3") according to one of the claims 5 to 17, wherein each ashlar (8, 9, 18, 19) has a waterproofing external coating of PVC.

19. The prefabricated module (3, 3¹) according to one of the claims 2 to 18, wherein said connecting means (15) between said base member (6) and said top retaining portion (7) is of groove-and-tongue joint type.

20. A retaining modular lining of the internal walls of a tunnel, said modular lining comprising a plurality of prefabricated modules (3, 3¹) according to any one of the claims 1 to 19.

21. A method for a retaining modular lining of the internal walls of a tunnel (2), said method comprising a step of positioning, for each breast of said tunnel (2), one or more prefabricated modules (3, 3') according to one of the claims 1 to 19.

22. The method for a retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, said tunnel (2) having, for each breast, a section (11) having a bottom base (41) and a top vault (5), wherein said positioning step comprises the steps of:

• arranging a substantially C-shaped base member (6) in correspondence of a respective bottom base (41) of said tunnel (2);

• fixing said base member (6) on said bottom base (41);

• arranging a top retaining portion (7) along the respective top vault (5) and into contact with said base member (6) so as to give to said prefabricated module (3, 3') a substantially annular shape; • fixing said top retaining portion (7) in correspondence of said top vault (5).

23. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein said base member (6) comprises a pair of specular ashlars (8, 9) connected by a hinge (12), said step of arranging a base member (6) comprising a step of placing said base member (6) in a folded position so that said hinge (12) lies substantially along a vertical axis (10) of symmetry of said section (11), and a subsequent step of laying said base member (6) in so as to arrange it in support of the respective bottom base (41) of said tunnel (2).

24. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein to the step of laying said base member (6) there follows a step of blocking said hinge (12) by concrete casting.

25. The method for the retaining modular lining of the internal walls of a tunnel (2) according to claim 22, wherein said base member (6) comprises a pair of ashlars (8, 9) disjoined and specular therebetween, said step of arranging said base member (6) comprising a step of coupling said ashlars (8, 9) in correspondence of a vertical axis of symmetry (10) of said section (11), arranging them in support of a bottom portion of the bottom base (41) of the walls of said tunnel (2).

26. The method for the retaining modular lining of the internal walls of a tunnel (2) according to one of the claims 22 to 25, wherein to said step of arranging said base member (6) there follows a step of performing a correct altimetric and planimetric positioning of said ashlars (8, 9) with the aid of hydraulic jacks (90) placed at their bottom.

27. The method for the retaining modular lining of the internal walls of a tunnel (2) according to any one of the claims 22 to 26, further comprising a step of waterproofing said base member (6) by coating with a PVC-reinforced canvas protected by a layer of non-woven fabric, said waterproofing step being subsequent to said step of arranging said base member (6) in correspondence of the respective bottom base (41) and preceding to said step of fixing said base member (6) on said bottom base (41).

28. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein said PVC canvas is positioned on said base member (6) so as to have a remainder portion (61), apt to be heat-sealed con a remainder portion (61 ') of a base member (6¹) consecutive thereto.

29. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein said consecutive remainder portions (61 , 61") heat-sealed therebetween are subsequently reintroduced inside a hollow (63) present between said base members (6, 6') consecutive therebetween.

30. The method for the retaining modular lining of the internal walls of a tunnel (2) according to any one of the claims 22 to 29, wherein said step of fixing said base member (6) to the respective bottom base (41) comprises a step of tamping with binder material an air gap (70) located in correspondence of the interface present between said base member (6) and the respective bottom base (41) of the tunnel (2).

31. The method for the retaining modular lining of the internal walls of a tunnel (2) according to claims 29 and 30, wherein said tamping step is subsequent to the heat-sealing of the two remainder portions (61 , 61') of PVC canvas consecutive therebetween.

32. The method for the retaining modular lining of the internal walls of a tunnel (2) according to any one of the claims 22 to 31 , wherein said step of arranging said top retaining portion (7) comprises a step of carrying said top portion (7) in correspondence of said respective top vault (5), and a subsequent step of positioning said top retaining portion (7) along said top vault (5) by hoisting operated by hydraulic jacks.

33. The method for the retaining modular lining of the internal walls of a tunnel (2) according to one of the claims 22 to 31 , wherein said step of arranging said top retaining portion (7) comprises a step of installing said top retaining portion (7) in correspondence of the respective top vault (5), by a self-moving car equipped with a hydraulic drive system for the moving and positioning of said top retaining portion

(7).

34. The method for the retaining modular lining of the internal walls of a tunnel (2) according to one of the claims 22 to 33, further comprising a step of waterproofing said top retaining portion (7) by coating with a PVC-reinforced canvas, said waterproofing step being subsequent to said step of arranging said top retaining portion (7) in correspondence of the respective top vault (5) and preceding to said step of fixing said top retaining portion (7) on said top vault (5).

35. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein said PVC canvas is positioned on said top retaining portion (7) so as to have a remainder portion, apt to be heat-sealed con a remainder portion of a top retaining portion (7') consecutive thereto.

36. The method for the retaining modular lining of the internal walls of a tunnel (2) according to the preceding claim, wherein said remainder portions consecutive heat-sealed therebetween are subsequently reintroduced inside a hollow present between said top retaining portions (7, 7') consecutive therebetween.

37. The method for the internal lining of the walls () of an excavation (2) according to one of the claims 22 to 36, wherein said step of fixing said top retaining portion (7) comprises a step of sealing said retaining portion (7) with a retaining portion (7¹) consecutive thereto, by pressure injection of binder material inside a transversal duct present between said retaining portions (7, 7').

38. The method for the retaining modular lining of the internal walls of a tunnel (2) according to one of the claims 22 to 37, wherein said step of fixing said top retaining portion (7) on said respective top vault (5) comprises a step of pressure-injecting binder material within an air gap located in correspondence of the interface present between said top retaining portion (7) and the respective top vault (5) of said tunnel (2).

39. The method for the retaining modular lining of the internal walls of a tunnel (2) according to one of the claims 22 to 38, further comprising a step of applying one or more reinforcement members on at least one portion of an extrados surface of said base member (6).