FR2669259A1 - Process for the manufacture of prefabricated arch units - Google Patents

Abstract

The subject of the invention is a method for manufacturing a precast concrete segment comprising two cylindrical curved faces (11, 12), and at least four lateral faces (13, 14, 15, 16). According to the invention, the segment is cast upright on one of its side faces (15) which corresponds to the bottom (35) of the mold, so that the two sides of the upper surface (11) and lower surface (12) of the segment (1) are directly shuttered on two side walls (31) (32) of the mold to which a corresponding curvature is given and, at the end of the casting, at least one is placed in the casting opening (30) plate (5) which is maintained, during casting, in a determined position relative to the mold, so that said plate (5) thus sealed forms, after demoulding, a distribution sole materializing a reference bearing plane respecting the geometry to be given to the segment (1). The invention applies especially to the production of large tunnels.

Description

The subject of the invention is a process for manufacturing concrete segments.

  prefabricated for the realization of a tunnel lining and also covers the segments thus produced as well as the molds and

  accessories allowing their manufacture.

  For the realization of an underground gallery, it is almost always necessary, after having drilled the tunnel, to cover its wall

  a coating which, currently, is generally made of reinforced concrete.

  Such a coating can be produced by means of a sliding formwork which is put in place after having drilled the tunnel over a certain length and which delimits the internal profile of the tunnel Concrete is injected between this formwork and the wall of the excavation, after possible installation of a reinforcement, and, after the setting of the concrete, the formwork is

  taken off then advanced for the formwork of a next section.

  However, it is often preferred to make the covering in prefabricated elements bearing on one another. When the section of the tunnel is large enough, the tunnel generally has a circular section and the covering is made by successive rings made up

  each of a series of "segments" each covering an angular sector.

  When the tunnel is made in a rock of good behavior, one can dig the excavation over a certain length, make the corresponding covering in the form of one or more rings, inject concrete between the wall of the excavation and the covering which has just been asked,

  then drill a new length of tunnel.

  However, when carrying out large galleries, one must always fear landslides and water inflows and this is why drilling is generally carried out by means of a device called "tunnel boring machine" which includes a disc of section forming a front wall provided with drilling tools and driven in rotation about a substantially horizontal axis, and a metal tubular wall which ensures the maintenance of the earth between the cutting disc and the concrete covering

already done.

  When the rock shows a certain resistance and there is no fear of significant water coming in, we can consider dismantling part of the protective tubular wall to set up the segments one after another, so as to make a new coating ring. However, it is often necessary to maintain a seal between the tubular wall and the covering, for example when one is in the water table or else when, due to the risk of landslides, it is necessary to inject, between the tunnel boring machine and the wall of the excavation, a pressurized fluid, a bentonite mud or air. In this case, the rear end of the tubular part of the tunnel boring machine must remain telescopically threaded on the front part of the already constructed covering, with the interposition of a seal. In Figure 1 which shows, by way of example, such an arrangement, there is shown, inside the tunnel T, the tunnel boring machine comprising a drilling disc A rotated about the axis 10 of the tunnel by a mechanism B and associated with a tubular shielding wall C, the end Cl of which remains threaded on the concrete covering R, with the interposition of a seal D.15 The covering R consists of successive rings Ri, R 2 Rn, each ring itself being made up of contiguous segments V Concrete E is injected between the coating R already made and the wall of the excavation T. -To construct a new ring Rn + l, the tunnel boring machine T digs all of first the excavation by resting on the last ring Rn of the covering by means of jacks. The cutting disc A is thus advanced over a length at least equal to that of a ring, but taking care that the rear end Ci of the shield remains in contact with the coating already 25 Thanks to an equipment F for handling and laying, associated with the TBM, we then put in place the desired number of adjacent segments V

  to constitute the new ring Rn + 1. After setting the ring Rn + 1 thus produced, it is then possible to proceed with a new advancement of the tunnel boring machine.

  As it progresses, concrete E is injected between the coating R already made and the rock wall of the tunnel T. This type of tunnel boring machine, used for some time, is now well developed; however, when working under a large depth of water and therefore the pressure of the bentonite mud or the air pressure must be increased accordingly, significant leaks may occur. To maintain the seal, it is therefore advantageous to give the external face of the segment on which the joint slides a surface as smooth as possible, so as to reduce the risk of leaks between the joint and the segment and to reduce friction. In addition, the dimensions of the segments must strictly respect the geometry fixed so that the facing side faces apply well to each other In particular, as the tunnel boring machine is supported, for its advancement, on the coating already made , very high pressures are applied to the lateral faces transverse to the axis and surface irregularities, even slight, can cause concentrations of stresses causing cracking of the segment. The invention relates to a new method of manufacturing prefabricated segments making it possible to easily and economically meet all of these requirements. The invention therefore relates, in general, to the manufacture of precast concrete segments each comprising two curved cylindrical faces, respectively of lower and upper surfaces, centered on a longitudinal axis, and at least four lateral faces, each segment being poured into a mold comprising a bottom, at least four walls and an upper pouring opening. In accordance with the invention, the segment is poured upright on one of its lateral faces which corresponds to the bottom of the mold so that the two cylindrical faces, respectively of lower and upper surfaces of the segment, are directly shuttered on two walls of the mold to which a corresponding curvature is given and, at the end of the casting, a distribution sole is placed in the casting opening which is maintained, during the casting, in a determined position relative to the mold, so that, after demolding, said soleplate is sealed in the corresponding face30 of the segment opposite to the formwork face on the bottom and materializes a reference support plane respecting the geometry to be given

  in the evening. The invention also covers the segments thus produced and the molds for manufacturing.

  Such a mold therefore comprises two curved side walls so as to form formwork for the two cylindrical faces of the arch, the upper opening and the bottom corresponding respectively to two of the lateral faces of the arch. Preferably, at least the curved wall of the mold serving for the shuttering of the upper surface is mounted so that it can be removed after the setting of the concrete for the stripping of the segment. In a particularly advantageous manner, such a mold can be provided with positioning means, across the pouring opening and at an adjustable level, of accessory members capable of being incorporated, after setting, in the corresponding lateral face. of the segment, for example means of suspension of the segment or fixing means

  a seal. Indeed, such a segment must sometimes be provided with a peripheral seal extending along its lateral faces.

  Such a joint comprises four sections placed in the extension of one another and extending respectively along the

  four lateral faces of the segment, each section comprising an external part projecting outwards from the corresponding face of the segment and an internal fixing part on said face, in the thickness of the segment.

  In a first embodiment, the external parts of the three sections of the joint corresponding to the shuttered side faces of the segment are removably mounted, before casting, on the bottom and the corresponding side walls of the mold, so that the internal parts of the seal protrude towards the inside of the mold and the external part of the fourth section of the seal is held across the opening

  pouring and positioned so that its internal part is below the level of the corresponding face of the segment, said internal parts of the four sections of the joint being integrated, after the pouring and setting of the concrete, in the corresponding faces of the segment.

  In another embodiment, the bottom and the side walls of the mold serving for the shuttering of the side faces of the segment, are provided, before casting, each of a rule projecting towards the inside of the mold and one places in through the pouring opening, a fourth rule maintained positioned below the level of the corresponding face of the segment, said rules leaving, after setting, in the corresponding face of the segment, each an imprint capable of constituting a removable fixing groove of the external part of the

corresponding section of the seal.

  In a preferred embodiment, the external part and the internal part of the joint are made of two different materials, the external part being made of a material specially adapted to ensure sealing with sliding on the segment, and the internal part being made of a compressible material such as an elastomer and engaging in a removable manner, for example by clipping, in a groove formed along the corresponding face of the segment The external part

  of the joint can also be fixed by clipping on the internal part.

  However, the invention will be better understood from the following description

  of certain particular embodiments given by way of example and

  shown in the accompanying drawings.

  Figure 1 schematically shows the realization of a tunnel lining in the form of prefabricated segments, Figure la

  showing, in perspective, a segment.

  Figure 2 shows, in vertical section, the flow of a

element.

  Figure 3 shows, in perspective, the release of an element.

  Figure 4 is a detail view showing the establishment

accessory organs.

  Figure 5 is a detail view, in cross section, of a

seal.

  Figure 6 is a detail view showing the establishment

other accessory organs.

  Figure 7 is a perspective view of a prefabricated segment

according to the invention.

  In Figure 1, there is shown schematically, and by way of simple example, the production of the cylindrical lining of a tunnel with circular section consisting of a series of consecutive tubular sections Ri, R 2 Rn, each section being constituted itself even of a series of segments 1 each covering an angular sector Each segment 1, shown in perspective in FIG. 1 a, consists of a prefabricated element of reinforced concrete comprising six faces, that is to say two curved cylindrical faces centered on the axis 10 of the covering, respectively one upper face 11 and one lower face 12, and four flat lateral faces, respectively two rectangular faces 13, 14, located in planes parallel to the axis 10 and passing , generally, by the latter, and two circumferential faces 15, 16, located in planes

perpendicular to axis 10.

  Generally, a prefabrication mold delimits a casting cavity comprising a substantially horizontal bottom formed on a molding table and substantially perpendicular side faces.

  at the bottom, and defined by formwork walls fixed on the table.

  When, as is the case here, the prefabricated element has the form of a slab of substantially constant thickness and much less than the other dimensions, it is usual to pour this slab horizontally so as to limit the height concrete In this case, the molding table has a convex part constituting the bottom of the mold and having a curvature equal to that of the underside face 12 and a wide open upper opening through which the concrete is poured from a hopper after placing a frame in the mold cavity The upper surface 11 of the segment is then produced by smoothing

concrete with a straightedge.

  However, it has been found that, in this case, the upper surface 11 does not have a sufficient surface quality to properly maintain the seal when the TBM is working under high pressure. We therefore had the idea of modifying the usual conditions and of pouring the segments standing in their mold so that the upper surface of the segment is shuttered, during the casting, by one of the walls of the mold instead of '' be constituted, as usual, by the

  face corresponding to the pouring opening.

  Thus, an excellent surface quality is obtained of the upper surface 11 which is shuttered and vibrated along the vertical wall 31, which will make it possible to obtain a very good seal with the possibility of sliding of the seal D, placed at the tail. of the tunneling machine, along the face

coating.

  In Figure 2, which is a cross-sectional view, and in Figure 3, which is a perspective view, there is shown respectively the casting of a segment element in the mold and its formwork. The mold 3 comprises a fixed part constituting the bottom and three of the lateral faces of the casting cavity 30, and a movable part constituting the fifth lateral face and which can advantageously be constituted by an openable door 31, as seen in Figure 5. Given that in the example shown, the side walls 33, 34, 10 converge radially, it is advantageous to facilitate the formwork, that the openable door constitutes the formwork wall 31 of the convex face, that is to say the extrados 11 of the segment, the fixed part therefore comprising the formwork wall 32 of the concave face 12, the two sides 33, 34, and the bottom 35.15 To make a segment, as shown in FIG. 2, after having closed door 31, we put to first put in place a prefabricated reinforcement 17, centering it well in relation to the walls,

  then the concrete 18 is poured preferably by vibrating it. The mold 3 can, for this purpose, be associated with one or more vibrators.

  After the setting of the concrete, the door 31 can be opened and the segment Il is removed from its mold 3 by lifting it, as has been

  represented in FIG. 5, by means of slings 28 which are hooked on handling members 4 fixed on the upper face 16 of the element 1.

  Thanks to such a casting mode, it is possible to obtain a perfect surface quality of the upper surface 11 of the segment On the other hand,

  it is the lateral face 16 located at the level of the pouring opening 30 which then has to be smoothed and this results in relative uncertainty about the geometrical positioning of the face 16.

  In addition, to perform the casting of the segment in a standing mold under good conditions, it is obviously preferable for the axis of the cylindrical walls 11 and 12 to be vertical and, in this case, the two opposite lateral faces corresponding respectively to the bottom. of the mold and at the opening of the casting are constituted by the two circumferential faces35 and 16 transverse to the longitudinal axis of the segment Or, as the tunnel boring machine must bear, for its advancement, on the concrete covering already produced, thrusts very large are applied to the circumferential faces 15 and 16 which bear on one another. As a result, surface irregularities, even small enough, on the facing faces of two adjacent segments, can cause stress concentrations causing a crack in the segment. This is why, according to one of the essential characteristics of the invention, it is made so that the upper face 16 of the segment has on the one hand a perfect geometry, and on the other hand a surface quality such as the there is no need to fear a concentration of constraints. To this end, the face 16 is provided, during casting, with at least one distribution plate 5, of metal or synthetic material, which is

  fixed in concrete so as to precisely define an assembly plane of the segment with the adjacent segment along the side face 16.

  Each support plate 5 is provided, on its internal face, with anchoring members 53 and is sealed in the lateral face 16 as shown schematically in Figure 4.20 The mold 3 is provided, at its upper part, with '' a lifting device consisting of at least two arms 7, articulated around a horizontal axis and which, when lowered, straddle the mold and are fixed, by their end 72, on the upper edge of the convex wall 31.25 During most of the casting, the arms 7 are raised, as shown in Figure 2, so as to clear the casting opening 30 Furthermore, the plate or plates 5 which must be sealed in the face 16 are mounted in advance on support members 51, 52, fixed to the arms 7.30 At the end of the casting, the arms 7 are lowered and the support plate or plates 5 are placed across the casting opening 30 of the mold Then the vertical position of the a plate 5 so that its upper level corresponds exactly to the theoretical dimensions of the segment For this purpose, each support member 51, 52 advantageously comprises a fine adjustment system, by

example with screw-nut.

  In this way, the lateral face 16 of the segment can be provided with one or more distribution plates 5 which constitute zones of

  transmission of thrusts perfectly positioned and define a support reference plane5 corresponding exactly to the geometry of the segment.

  Generally, the two circumferential lateral faces 15 and

  16 are mutually parallel and perpendicular to the axis of the cylindrical faces 11 and 12, the distribution flanges 5 being horizontal.

  In this case, as shown in Figure 1, the junction planes between the different tubular sections are perpendicular to the axis.

  However, the junction planes can also be slightly inclined relative to the axis, for example for a change of direction of the tunnel. In this case, the two circumferential faces 15 and 16 are no longer parallel and, moreover, their distance can vary according to the position of the segment The arrangements according to the invention make it possible to easily resolve this problem because it is possible to adjust at will the level and the orientation of each soleplate 5 relative to the bottom 35 of the mold on which the Opposite face 15 To this end, each sole 5 can be suspended from two rods 52 whose lengths are adjusted differently, the support 51 of the sole 5 may include an articulation to adjust the orientation of the sole. The inclination of the face 16 relative to the horizontal will generally be small enough not to present any disadvantages to the

  casting In the event of a steeper inclination, one could envisage inclining the entire mold 3 so that the face 16 is horizontal.

  The arrangements which have just been described for maintaining the distribution soles 5 can advantageously be used for

  seal other accessory members at the upper face 16 of the segment.

  In particular, in many cases, it is necessary to provide, between the facing faces of the adjacent segments, a seal

  which, in the example shown, will include four sections extending respectively along the four side faces 13, 14, 15, 16, du35 voussoir.

  Such a seal 6 generally comprises an external part 60 protruding outside and an internal part 61 for fixing in the segment. In Figure 5, there is shown, by way of example, such a seal 6 made of an elastic material such as an elastomer, removably fixed in a groove 62 formed on the lateral face of the segment 1. In in this case, the seal 6 is made of two different materials, the external part 60 being made of a material specially adapted to ensure sealing with the upper surface of the segment while allowing sliding while the internal part 61 is simply provided for s 'removably and tightly engage in the groove 62. For example, the part 60 will advantageously constitute a "water-swelling" seal which swells on contact with liquids, and which is "clipped'T on the internal part 61 which constitutes a base of fixing The latter can advantageously have a trapezoidal section, the groove 62 having a corresponding dovetail section In addition, the part

  61 can be provided with recesses which facilitate its deformation.

  The seal 6 as well as the groove 62 consist of four sections corresponding, respectively, to the four lateral faces 13, 14,

, 16 of the segment.

  To make the three groove sections on the shuttering faces 13, 14, 15 of the segment, it suffices to place on the corresponding walls 33, 34, 35 of the mold 3 a rule 63 in three sections which protrude from the shuttering faces of so as to be incorporated in the segment 1 at the casting After the formwork is removed, each rule section 63 is removed, the imprint thus reserved constituting the groove 62 Of course, taking into account the dovetail profile of the groove, you must allow the removal of rule 63, for example by making it

  in several parts, but this is one of the known problems that we know how to solve in prefabrication techniques.

  To make the groove on the upper face 16 of the element, a horizontal rule 64 is used which is maintained at the desired level by supports 71 fixed on the arms 7 for supporting the plates 5 and the lengths of which can be adjusted so as to precisely position the

rule 64.

  For example, in Figure 6, there is shown another embodiment of the seal 6 The latter, which is made of a compressible elastomeric material, comprises a fixing portion 65 intended to be sealed in concrete For this purpose , the seal 6 is removably attached to the end of the support 71, the length of which can be adjusted,

  so that the upper part of the joint 6 protrudes above the level of the opening 30 During the casting of the mold, the joint 6 is sealed in the concrete by its part 65 and therefore remains fixed along the face 16 when 10 the supports 71 are removed.

  The walls 33, 34, 35 of the mold can be equipped in the same way to produce the joint sections corresponding respectively to the faces 13, 14, 15. Furthermore, the segment 1 must be provided, as we have seen, hooks 4 on which slings are hung for demolding and handling the segment and these hooks must be able to be removed at the time of installation in order to fully release the bearing face 16. This is why each handling hook 4 can advantageously have a threaded part which engages in a

  bush 41 internally threaded and sealed in the segment 1, during casting.

  As shown in FIG. 6, the sockets 41, which are provided, on their external face, with anchoring parts, are screwed onto supports 42 mounted on the arms 7 and the length of which can be adjusted. when the arms 7 are lowered, the sockets 41 are placed at the desired level and are embedded in the upper part of the element 1 during the pouring of the concrete After setting, the supports 42 are simply unscrewed, each socket 41 remaining sealed in the concrete for the removable fixing of a hook 4.30 Of course, the invention is not limited to the detail of the embodiments which have just been described and which could be the subject of other variants, each element segment 1 which can be fitted with other accessory members placed in advance on the mold. Thus, in Figure 7 which shows an example of segment produced according to the invention, the internal face 12 of the segment is provided with housings 43 into which open holes 44 serving for the passage of lag screws for fixing between them segments, the housings 43 and the orifices 44 being reserved during molding by suitable inserts placed in the mold 3. Furthermore, the invention has been described in the case of segments having a generally rectangular shape, comprising four side walls planes, respectively parallel and perpendicular to the axis, but the same provisions could apply to segments of other shapes

  having side faces which may be convex or concave.

  The reference signs, inserted after the technical characteristics mentioned in the claims, have the sole purpose of

  to facilitate the understanding of the latter and in no way limit their scope.

Claims (8)

  1 Method of manufacturing a precast concrete segment comprising two curved cylindrical faces, respectively of upper surface (11) and lower surface (12), centered on a longitudinal axis, and at least four lateral faces (13, 14, 15 , 16), by pouring the concrete into a mold (3) comprising a bottom, four side walls and an upper pouring opening, characterized in that the segment is poured upright on one of its side faces (15 ) which corresponds to the bottom (35) of the mold, so that the two cylindrical faces, respectively of upper surface 10 (11) and lower surface (12) of the segment (1), are directly shuttered on two side walls (31) ( 32) of the mold to which a corresponding curvature is given and that, at the end of the casting, there is placed in the casting opening (30), at least one plate (5) which is maintained, during the casting, in a determined position relative to the mold, so that said plate (5) is sealed in the corresponding face (16) of the segment opposite to the face (15), shuttered on the bottom (35) and forms, after demolding, a distribution sole materializing a reference support plane respecting the geometry to be given to the segment (1) 2 Method of manufacturing, according to claim 1, of a prefabricated segment for the realization of the lining of a tunnel, characterized in that the level and the orientation can be adjusted   plates (5) relative to the bottom (35) of the mold (3) so as to adjust the length of the segment (1) and the orientation of the lateral faces (15) and (16) as a function of the position of the segment ( 1) in the covering. 25 3 A method of manufacturing a segment according to one of claims 1 and 2, characterized in that each segment is   provided, during casting, with means for fixing a seal comprising four sections extending respectively along the four lateral faces (13, 14, 15, 16) of the segment and placed in the extension 1 one from the other so as to form a continuous joint, each section comprising an external part (60) projecting outside the corresponding face of the segment (1) and an internal part (61) for fixing in said face.  4 A method of manufacturing a segment according to claim 3, characterized in that the bottom (35) of the mold (3) and the side walls (33, 34) of formwork of the lateral faces (13, 14) of the segment ( 1), are provided, before casting, each of a rule (63) projecting towards the inside of the mold (3) and which is placed across the casting opening (30), a fourth rule (64) maintained positioned 5 below the corresponding lateral face (16) of the segment (1), said rules (63) (64) each leaving, after setting, in the face   corresponding (13, 14, 15, 16) of the segment (1), an imprint capable of constituting a groove (62) for removable fixing of the external part (60) of the corresponding section of the joint (6).   5 A method of manufacturing a segment according to claim 3, characterized in that the external parts (60) of the three sections of the joint (6) corresponding to the shuttered side faces (13, 14,) of the segment (1) are mounted removably, before casting, on the bottom (35) and the corresponding side walls (33, 34) of the mold (3) so that the internal parts (61) of the seal (6) protrude towards the inside of the mold and that the external part (60) of the fourth section of the seal (6) is held across the pouring opening (30) and positioned so that its internal part (61) is below the level of the corresponding face (16), said internal parts (61) of the four sections of the joint (6) being integrated, after the pouring and setting of the concrete, in the corresponding faces (13, 14, 15, 16) of the   segment (1). 6 A method of manufacturing a segment according to one of the preceding claims, characterized in that one incorporates,   during casting, in the upper face (16) of the segment (1) corresponding to the casting opening (30), members (41) for anchoring suspension means (4) allowing, after setting, the handling of the segment. 7 Precast concrete segment, capable of being combined with other adjacent segments for the lining (R) of an underground tunnel (T) and comprising two curved cylindrical faces of upper surface (11) and lower surface respectively (12), and at least four lateral faces (13, 14, 15, 16) bearing on the adjacent segments, said segment (1) being produced inside a mold (3) comprising a bottom and four side walls for the formwork of five sides of the segment, and an upper opening for pouring concrete, corresponding to the sixth face, characterized in that the two cylindrical faces of upper surface (11) and lower surface (12) constitute two faces shuttered in the mold (3) and that the upper face (16) of the segment corresponding to the casting opening (30) is provided with at least one plate (5) perfectly positioned during casting so as to form a distribution sole capable of material align a support reference plane on an adjacent segment. 10 8 Prefabricated segment according to claim 7, characterized in that the level and the orientation of the plate (5) relative to the   mold base are adjusted according to the position of the segment (1) in the covering (R) so that the support reference plane is inclined at an angle other than 900 relative to the axis of the tunnel. 15 9 Prefabricated segment according to one of claims 6 and 7, characterized in that it is provided with a continuous seal   comprising four sections extending respectively along the four lateral faces (13, 14, 15, 16) of the segment (1) and each comprising an external part (60) projecting outwards from the corresponding face 20 of the segment (1) and an internal part (61) for fixing on said face, in the thickness of the segment (1).   Prefabricated segment according to claim 9, characterized in that the external part (60) and the internal part (61) of the joint (6) are made of two different materials, the external part (60 being made of a material (65 ) specially adapted to allow sliding with maintenance of the seal and the internal part (61) consisting of a compressible material (66) such as an elastomer and having a shape adapted to engage in a sealed and removable manner in a groove (62) formed along the corresponding face of the segment (1). 30 11 Prefabricated segment according to claim 10, characterized in that the external part (60) is fixed by clipping on the internal part (61). 12 Mold for manufacturing a concrete segment comprising a bottom (35), four side walls (31, 32, 33, 34) and an upper opening (30) for pouring concrete, said segment (1) comprising two curved faces cylin bricks (11, 12), centered on an axis and at least four lateral faces (13, 14, 15, 16), characterized in that two of the lateral walls of the mold (31, 32) are curved so as to constitute formwork for the two cylindrical faces respectively of upper surface (11) and lower surface (12) of the segment (1), the bottom (35) of the mold and the upper opening (30) corresponding respectively to two opposite lateral faces (15 , 16) of the segment (1) and that the mold (3) is provided with means (51, 52) for positioning, across the casting opening (30) and at an adjustable level, at least one plate (5) provided with means (53) for sealing in the concrete and positioned so as to constitute, at the level of the lateral face (16) of the segment (1), a sole for distributing the thrust forces perfectly respecting the geometry to be given in the evening. 13 Mold according to claim 12, characterized in that the plate positioning means (5) comprise at least one rod (51, 52) of adjustable length provided at one end with a means of   removable fixing of the plate and fixed its other end on at least one arm (7) extending across the casting opening (30) and removably mounted on the mold (3) so as to be able to clear the opening of casting 20 (30).   14 Mold according to claim 13, characterized in that the means (51, 52) for positioning the plates (5) are arranged so as to allow the level and orientation of each   plate (5) relative to the bottom (35) of the mold (3).   15 mold according to one of claims 13 and 14, characterized in that the arm (7) is provided with means (71) (42) for positioning   across the pouring opening (30) and at an adjustable level, of accessory members capable of being incorporated, after setting, in the corresponding lateral face of the segment (1) .30 16 Mold according to claim 15, characterized by the fact that the arm (7) is provided with positioning means (71) supporting a rule (64) held at the level of the lateral face (16) of the segment so as to form therein an imprint capable of constituting a groove   (62) for removable fixing of a seal (6).   17 mold according to claim 15, characterized in that said positioning means (71) support a seal (6)   fixed to said means (71) by an external part (60) extended by an internal part (61) and positioned so that the external part (60) is above the level of the lateral face (16) and that the internal part5 (61) is sealed in concrete.   18 Mold according to one of claims 16 or 17, characterized in that the external part (60) of the seal (6) is constituted, at   at least partially, of a material specially adapted for making   sealing with the possibility of sliding, in particular of the type 10 hydrogonflant.   19 Mold according to claim 15, characterized in that the arm (7) is provided with positioning means (42) on which are   removably attached anchoring members (41) capable of being sealed in the segment (1) below the level of the lateral face (16) 15 and to which members (4) can be removably attached segment handling (1).   Mold according to one of claims 12 to 19, characterized in that at least the curved wall (31) of the mold (3) used for   formwork of the upper surface (11) is removably mounted so that it can be removed after setting the concrete for the formwork stripping (1).