EP0102340A2 - Method of making reinforced concrete constructions such as subways, road tunnels and the like; prefabricated concrete elements for making such constructions - Google Patents

Abstract

1. Method of constructing reinforced concrete works such as road tunnels, underground galleries, tunnels for underground railways, according to which an open trench is first excavated, in which there are then placed, consecutively and contiguously, prefabricated hollow concrete elements (4) each consisting of a frame, and a filling is finally executed, characterised in that there is used for each prefabricated element a frame, the external faces of which comprise reinforcements (5), that a filler concrete (18) is poured covering the joints between elements and cooperating with the reinforced concrete of the elements (4) and with the reinforcements (5) so as to construct by consecutive stages, and rapidly, a monolithic work, the strength of which is appreciably greater than the respective strengths of the prefabricated elements (4) initially placed and of the filler concrete (18).

Description

The present invention relates to the production of reinforced concrete structures, such as underground galleries, road tunnels, subway tunnels, etc., using prefabricated elements.

The execution of these works using prefabricated elements gives rise to a difficulty given that in general, on the one hand, the weight of the elements is very important, and that on the other hand, the the size of these elements makes it difficult, if not impossible, to transport by road convoy.

A first object of the present invention is to remedy this difficulty, to lighten as much as possible and to reduce the external dimensions of these prefabricated elements while retaining an internal finish as close as possible to the final finish and thus allow the execution of the process under particularly economical conditions.

A second object of the invention consists in achieving continuity of the structure by a second phase concreting carried out on site, straddling the joints between the prefabricated elements. This continuity is fundamental both from the point of view of mechanical strength and differential settlement under the action of traffic and from the point of view of sealing. With a view to achieving these aims, the process which is the subject of the invention is essentially characterized in that an open excavation is first excavated, which is then successively and successively deposited in the prefabricated hollow elements in concrete, each consisting of a frame, the external faces of which include reinforcements, in that poured concrete covering the joints between elements and collaborating with the reinforced concrete of the elements and with the reinforcements so as to be produced in phases successive and quickly, a monolithic structure whose resistance is significantly higher than the respective elements prefabricated initially installed and filler concrete; and that it finally makes a rem _- blayage.

In the practice of the method, the external reinforcements are made integral with the prefabricated element ("pre-frame") before the installation of the prefabricated element.
An essential feature of the invention is the precast reinforced concrete element, in itself, called "pre-frame", comprising the characteristics described above.

In the case of a tunnel made of very large prefabricated elements, the pre-frames have congestion which exceeds the authorized dimensions in height for road transport.

In this case, the pre-frames are made of two or more complementary elements which will then be assembled on site.

The implementation of the elements is done either in an open excavation dry excavated, or in successive transverse excavations carried out under thixotropic mud, in particular when the work must be carried out in dense urban site in streets or arteries near the existing buildings.

Hereinafter, these prefabricated elements will be described in more detail with reference to the accompanying drawings, as well as the methods of carrying out the process, dry and under thixotropic mud.

• les fig. 1, 2 sont des vues en perspective montrant différentes réalisations de l'élément dit précadre;
• les fig. 3, 4 et 5 sont des détails de construction et d'assemblage des précadres;
• les fig. 6, 7 et 8 concernent les précadres réalisés en deux ou plusieurs éléments complémentaires;
• les fig. 9 et 10 sont des vues illustrant la mise en place des éléments dans une fouille exécutée à sec;
• les fig. 11 à 15 concernent la mise en oeuvre des éléments préfabriqués dans une fouille exécutée sous boue thixotropique.
• La fig. 11 est une vue horizontale du chantier de mise en oeuvre à proximité d'immeubles.
• La fig. 12 montre une coupe verticale transversale dans laquelle sont montrées les caractéristiques essentielles du procédé de mise en oeuvre.
• La fig. 13 montre une coupe verticale longitudinale relative au même procédé lors de la mise en oeuvre d'un élément de précadre.
• La fig. 14 montre une autre coupe verticale concernant ce même procédé lors du creusement d'une nouvelle fouille transversale contre l'élément préfabriqué qui vient d'être mis en place.
• La figure 15 montre une coupe horizontale dans les piédroits de deux éléments adjacents.

On the attached drawings:

• fig. 1, 2 are perspective views showing different embodiments of the so-called pre-frame element;
• fig. 3, 4 and 5 are details of construction and assembly of the pre-frames;
• fig. 6, 7 and 8 relate to the pre-frames produced in two or more complementary elements;
• fig. 9 and 10 are views illustrating the placement of the elements in a dry excavation;
• fig. 11 to 15 relate to the implementation of the prefabricated elements in an excavation carried out under thixotropic mud.
• Fig. 11 is a horizontal view of the implementation site near buildings.
• Fig. 12 shows a vertical cross section in which the essential characteristics of the implementation process are shown.
• Fig. 13 shows a vertical longitudinal section relating to the same process during the implementation of a preadframe element.
• Fig. 14 shows another vertical section concerning this same process when digging a new transverse excavation against the prefabricated element which has just been put in place.
• Figure 15 shows a horizontal section through the sides of two adjacent elements.

The pre-frame element is a hollow block 4 produced with the thinnest reinforced concrete walls possible, that is to say in practice from 5 to 15 cm thick (fig. 1).

The inner face 2 of the pre-frame 4 is cast generally smooth around a mold having an appearance as close as possible to the desired finished appearance.

On the other hand, the external face is made either of rough concrete 53 without external formwork, or with a formwork comprising irregularities or indentations 120 resulting in creating by molding a surface comprising asperities (fig. 2).

In addition, the external face comprises (FIG. 4) waiting reinforcements 54 and / or anchor sockets 55 with threaded rods 59 and / or metal plates 56 with doguets 57 and jumpers 60 which makes it possible to set up, after the concrete has hardened and the precast concrete has been removed, peripheral reinforcements 5 which will be fixed on the waiting reinforcements 54, on the threaded rods 59 or on the jumpers 60 .

This last operation is carried out in the prefabrication plant or on the site, before the elements are implemented.

Since these elements are intended to be placed on the leveled ground 61, on the surface of the ground or in an excavation 62 (fig. 9), the future slab 13 of the precadre can be made in its final thickness while the other walls are made in thin thickness as explained above (fig. 2).

The raft 13 then has protuberances 14 outside the vertical walls with vertical reinforcements 15 anchored in these same protrusions (fig. 2).

This makes it possible to avoid concreting. Between the lower horizontal part 16 of the pre-frame (fig. 10) and the level 61 of the ground, concreting which can possibly be made quite difficult if the additional thickness to be concreted is small.

On the other hand, a pre-frame 4 produced as shown in FIG. 2 will weigh heavier and be more bulky than a similar element according to FIG. 1.

It is ultimately considerations of weight, ease of concreting and implementation that will guide the choice between the two types of "pre-frames".

When the span of the roof or of the frames of the pre-frame becomes too large to be crossed by a slab 5 to 15 cm thick for example, temporary vertical or horizontal stays may be provided to reduce this span (fig. 1-2-9-12).

These props 30 will be held in place during the execution of the external filler concrete 18 (fig. 3-9-10) and will only be removed after hardening of the same concrete until it has reached a resistance. sufficient.

Fig. 2 shows a pre-frame 4 comprising interior finishing elements 19, in this case platform elements for a metro station, the safety railings and the finishing coatings on them. floors, walls and ceilings.

Fig. 2 also shows a pre-frame comprising a stiffening rib 8 whose thickness corresponds to the total thickness of the walls after execution of the filler concrete. This rib 8 is essential in the case of implementation under thixotropic mud.

In the case of a tunnel to be made with large pre-frames, generally the clearance height allowed for road transport is exceeded.

In this case, the pre-frames include two or more complementary partial elements 99, 100 and 101 (fig. 6) which will then be assembled on site.

In the case of two complementary partial elements 100 and 101, they fit into each other, thereby reducing their height 108 during transport (fig. 7).

The joint 102 between two half-pre-frames is located approximately halfway up each pedestal. The advantage of such a position of the joint lies in the fact that the final moments which will stress the tunnel in its final phase generate pulls outside the filler concrete, and therefore in the additional reinforcements which are added around the pre-frame.

The right part of FIG. 6 shows a pre-frame 4 consisting of two half-pre-frames 100 and 101. The height 110 of this pre-frame exceeds the authorized road gauge. The lower half-frame 100 may include a raft 13 prefabricated in advance, as already explained previously (FIG. 2).

The two half-frames 100 and 101 have a rib 8 of stiffening at mid-width.

Fig. 7 shows a lowered trailer 104 pulled by a tractor 105. The half-frame 101 is placed on the trailer astride the half-frame 100 by interposing a setting 106.

The overall height in the lowered trailer thus remains less than the gauge 108 authorized in height for road transport.

Fig. 8 shows a horizontal section AA in the upper half-frame. The width 109 of the pre-frame is also less than the authorized road gauge. The assembly on site of the two half-frames 100 and 101 can also be done by a steel rod 140 comprising a nut at each end and which is placed in a tubular housing 141 reserved in the ribs 8 of the legs (fig. 6) .

After assembly on site, it will suffice to tighten the bolts with a torque wrench to perform a vertical post-stress in the corners. This post-stress can be calculated to prevent the opening of the joints 102 inside the pre-frame under the effect of lateral thrusts on the pedestals due to the terrain, water and overloads above the tunnel.

Optionally, an injection of cement grout may be provided in the joint 102 in order to seal on the one hand and the continuity of the concrete on the other to take up the compression forces. resulting from external stresses. In the calculation of the dimensioning of the total thicknesses of concrete for the side walls, the roof and the slab of the pre-frame 4 with its filler concrete, we will preferably choose values such that the stresses do not generate tensile forces on the internal face of the pedestal at the location of the joint 102 between the two half-pre-frames 100 and 101. This will make it possible to avoid having to apply a post-stress as explained above.

In the case where the pre-frame is made up of more than two partial elements, the assembly principles set out above are also used. (see left part of fig. 6).

Fig. 10 shows how a pre-frame 4 can be put into place in a dry excavated excavation 62, comprising a vertical wall reinforced by sheet piles 71 for example, and another wall 72 in a fairly steep slope taking into account the cohesion of the ground.

In such an embodiment, using a crane with a lifter 73, the pre-frame 4 is placed at the bottom 61 of the excavation 62. It is adjusted on four jacks 74 placed on the bottom of the excavation which allow d '' ensure the installation of the pre-frame with all the required precision.

As soon as the pre-frame is correctly adjusted, wooden, concrete or steel wedges are put in place and wedged between the pre-frame and the seat level on the ground, thus allowing the adjustment cylinders to be removed and recovered.

The second phase concreting 18 (fig. 10) is then undertaken by submerging these wedging elements in the mass of concrete.

Temporary cylinders 74 can be replaced by lost bag cylinders which are injected a cement grout to ensure the correct setting of the pre-frame; these cylinders no longer require wedging devices and are embedded in the mass of concrete, poured on the site outside the precadre.

The provisional cylinders 74 can also be replaced by precast concrete slabs 74 which are adjusted in advance to the required level.

If the raft 13 is prefabricated in advance (fig. 9), the space 121 between the slabs 74 is leveled off at the laying level by stabilized sand fresh at the time of laying or subsequently filled with very thin concrete fluid.

According to fig. 10, the second phase concrete 18 is poured below the pre-frame, on either side of it and above it.

Fig. 9 shows a pre-frame 4 in accordance with FIG. 2 placed at the bottom of an excavation 62 comprising a fairly steep slope 72 and another slope 75 with a slight slope.

When the slope 72 is stiff, or even vertical (69), the second phase concrete 18 will be used between this slope and the pre-frame 4.

On the side of the gently sloping embankment 75, to avoid using excessive amounts of concrete, a vertical formwork 76 (fig. 9) is put in place with supports 71, if any, on the embankment. This formwork 76 can also be bolted into the ribs 8 (fig. 2) when they are provided. This formwork 76 is recoverable after hardening of the concrete. It can also be replaced by a formwork lost in profiled steel sheet for example.

Figures 1, 2, 9, 10 and 12 show rectangular frames. It is understood, however, that these precadres can be of an embarrassed form. generally any including rounded parts.

The various pre-frames are implemented on the ground 61 previously leveled and are juxtaposed so as to produce the structure as a whole.

To achieve the possible tightness and continuity between the elements, according to the invention, provision is made for concreting 18 of the second phase straddling the joint 88 between two pre-frames with a covering frame 89 in accordance with what is shown in the figure. 3.

The possible sealing required between these elements is achieved by peripheral seals 160 of compressible material placed between the pre-frames (fig. 2 and 3). In general, this type of compressible seal only withstands lateral water pressure if the seal is compressed along the longitudinal axis of the tunnel. Before the concreting of the second phase 18, the assembly and the compression in the joint between the juxtaposed elements are then carried out by bolts 94 connecting metal angles 95 anchored in each of the juxtaposed elements, generally inside these. (fig. 3)

After hardening of the concrete 18, the bolts 94 and the angles 95 can be dismantled and recovered for the assembly of other pre-frames.

Filler concrete is a conventional concrete composed of sand, gravel, cement and water but it can also include fibers, tensile resistant, in steel, glass, asbestos or other material.

When the underground gallery must be carried out on an urban site, in streets or arteries for example, and therefore near existing buildings, it is generally not possible to carry out an excavation with a slope, because the width of the artery does not allow it.

It is rarely possible to carry out an armored excavation with sheet piles for example, because the threshing of these sheet piles constitutes a nuisance for the population living in this district. On the other hand, this threshing generally generates significant and unacceptable settlement of the buildings immediately adjacent to the excavation carried out.

The currently known technique consists of carrying out armored excavations or longitudinal walls of concrete molded into the ground under thixotropic mud. These two techniques require the successive execution of the walls then of the roof and the raft which come to connect the longitudinal walls. The execution of such works lasts a long time and therefore considerably annoys the neighboring population for a long period which is hardly acceptable to them.

The present invention provides an original method of rapid implementation of prefabricated elements of the future gallery without causing the aforementioned drawbacks.

The method is essentially characterized in that, transversely to the longitudinal axis of the future tunnel, successive excavations are carried out which are substantially rectangular and contiguous; one descends in each excavation successively at least one pre-frame as defined in FIG. 2, by positioning it so that it is juxtaposed with the gallery element previously produced; then concreting on the outside between the ribs of the two half-pre-frames and backfilling the remaining space of the excavation with a filling material such as gravel, sand or earth.

A description will be given hereinafter by way of nonlimiting example with reference to FIGS. 11 to 15. The process of implementing the pre-frames under mud thixotropique comprises a certain number of very specific execution phases which will be set out below without limitation and which respond in a simple and original way to the aims pursued.

A particular advantage is that the proposed technique makes it possible to remove the sheet from the longitudinal walls.

From the initial level of the ground 211, a guide wall 201 in reinforced concrete is first made on either side of the excavation to be excavated to a depth of one to two meters approximately. This guide wall is generally completed by a reinforced concrete slab 202 intended to serve as a raceway for the gantry 203 which will be installed subsequently. Depending on requirements, this guide wall 201 will incorporate a channel 235 (fig. 12) for urban pipes.

As shown in fig. 11, the site progresses in the direction of arrow 78.

The pre-frames 4 are prefabricated in the factory in accordance with the above indications. They are then transported to the implementation site where they are stored in sufficient numbers (fig. 11).

In accordance with the aforementioned indications, additional reinforcements 5 are fixed to this pre-frame in the factory or on site. These reinforcements 5 are arranged on the upstream side of the pre-frame 4 with respect to a shoulder 8 (fig. 2) so as to cover an upstream pre-frame element already in place up to its own shoulder 8 (fig. 13).

These additional reinforcements 5 will therefore cover the joints between the elements 4 used, thus ensuring continuity of the future gallery after the additional concreting.

The thickness of the raft is possibly increased by adding concrete incorporating the reinforcements additional 5 and thus achieving an additional slab 206 of reinforced concrete poured on the site. The raft 13 (fig. 2) can also be entirely prefabricated at the factory as explained above.

To reduce the consumption of bentonite and avoid subsequent cleaning of the interior of the gallery, the pre-frames 4 also have two flexible closing walls 207 fixed on the periphery of the pre-frame upstream and downstream. These walls 207 are made of a material which is essentially permeable to water but impermeable to materials suspended in water. For example, a non-woven polyester material may be used. This flexible wall 207 can be held in place between two sufficiently rigid metal trellises 31 which are fixed to the periphery of the pre-frame 4 and on the provisional stays 30 and / or include internal reinforcements made of tensile-resistant fibers.

Certain pre-frame elements 32 additionally comprise a rigid waterproof wall 33 generally made of concrete. This will later isolate a section of several elements 4 upstream from another element 32.

The pre-frame 4 generally comprises two shoulders 8 of reinforced concrete towards the outside and in the middle of the two vertical walls as well as on the roof of the element (fig. 2).

These reinforced concrete shoulders 8 are either prefabricated in the factory at the same time as the frame 4, or are executed on site at the same time as the possible addition of slab 206, in particular if the size authorized for road transport does not allow their prefabrication. in the factory.

These shoulders 8 also allow lateral fixing of rigid lines 9 made of steel. killed either from a metal beam, or preferably from a U-shaped steel element intended for the execution of steel foundation piles. Inside the U, a tubular element 225 of flexible and permeable fabric is fixed over the entire height. This flange 225 is closed at its lower part (fig, 15).

The lines 9 are fixed to the frame and have a sufficient length to be able to be hung and suspended from the gantry 203 of implementation. This hanger 9 with its assembly plate 45 can create a connection between a half-frame 100 and a half-frame 101 by means of a series of anchor sockets or anchor bolts 103 (fig. . 6 and 8).

As shown in Figures 13 and 14, the shoulders 8 of the roof of each frame 4 have rectangular notches which will deposit the base of a cofferdam 80 which will be discussed later.

Sheets 210 (figs. 12 and 15) perforated with round holes of small diameter, are fixed to the reinforcements 5 with spacing devices to constitute the future lost formwork wall of the sides of the tunnel to be executed, thus avoiding pollution of the concrete. contribution by possible landslides. This sheet 210 can optionally be profiled and collaborating.

These sheets 210 have a length sufficient to reach at least the upper level 22 of the elements 4 used.

The pre-frames thus prepared are ready to be used in the excavation carried out under thixotropic mud.

An important characteristic of the invention is that this digging under thixotropic mud is carried out by perpendicular transverse trenches 87 (fig. 11 and 14) at the axis of the tunnel to be made, using a crane 79 fitted with a hydraulic grab or a special bucket 70 such as those used for the execution of concrete walls molded into the ground under thixotropic mud.

In the present process, this bucket 70 will generally have dimensions significantly larger than those of the buckets currently used, and this as a result of the size of each successive excavation.

It is also possible to carry out the excavation using an excavator working in reverse, following successive passes 122 (fig. 14).

If the special bucket 70 is used, a removable transverse guide wall 85, generally made of steel, is placed in notches 86 provided in the guide walls 201.

Indeed, the excavations or trenches have a width corresponding to the distance between two guide walls 201 parallel to the longitudinal axis of the future tunnel. In practice, this width will vary from approximately five to fifteen meters.

On the other hand, the length of these successive excavations along the axis of the future tunnel to be produced will be fairly reduced. In practice, this length will be about two to three meters. This reduced length must make it possible to carry out the transverse excavation without the risk of settling for the neighboring buildings 214, the foundations 215 of which may be very close to the excavation thus carried out (FIGS. 11 and 12).

To avoid this compaction and the risks of collapse of the ground 216 in place, the excavation is permanently filled with thixotropic mud generally made up of bentonite mud and this up to level 25, higher than level 36 of the water table.

A chassis 40 for positioning and adjustment is then placed above the excavation excavated under thixotropic mud and bearing on the guide walls 201 (fig. 12 and 13).

This chassis 40, generally made of steel, essentially comprises two beams 41 spaced apart from one another by a horizontal distance greater than the longitudinal dimensions 42 of the pre-frame 4 with the reinforcements 5.

Double crosspieces 43 are provided so as to frame an extension 44 bolted to the hanger 9 by means of connection plates 45 welded respectively at the head of the hanger 9 and at the bottom of the extension 44.

The carriage 46 or a horizontal positioning device can move horizontally on the double crosspieces 43 after the pre-frame 4 has been suspended, suspended by two lines 9 on either side of the excavation.

Cylinders 47 make it possible to assume the precise adjustment in altitude of the pre-frame 4 according to the directives which will be given by a surveyor before or during the implementation of each element 4.

The chassis 40 can be replaced by a carriage 126 (fig. 12) comprising at least four steel wheels 125 of the railroad or grooved type which run on two longitudinal rails 123 bearing on the guide walls 201.

These rails are adjusted in exact position laterally and in altitude according to the indications of the surveyor by placing shims 124 under the rails so that the pre-frame 4 (fig. 13) during installation comes to be placed with precision and adequate location against the previously placed frame 32.

A transverse excavation being completed up to level 24 and the positioning frame 40 or the chain riot 126 being prepared, a pre-frame 4 with all its packaging already described is lifted by the gantry 203 and brought above the excavation still filled with thixotropic mud.

The pre-frame 4 is lowered until it partially penetrates into the thixotropic mud.

To balance the momentary pressure between the mud and the flexible and permeable wall 207 of the pre-frame 4, the latter is partially filled with water. The descent of the pre-frame 4 can then continue to a new depth less than the height of the pre-frame 4 which is again filled with water to balance the momentary pressures on either side of the flexible and permeable wall 207. This process continues until frame 4 is completely filled with water. The pre-frame 4 can then be lowered to the level provided but at a certain horizontal distance from the element 32 already placed upstream (FIG. 13).

By means of the carriage 126 or of the positioning device 46, the two lines 9 provided with their respective extensions 44 are then supported by the carriage 126 or the positioning chassis 40.

The two hooks 48 of the gantry 203 can then be disconnected from the suspension orifices 49 integral with the two extensions 44.

If necessary, the pre-frame 4 is further adjusted in altitude by the jacks 47 and then moved horizontally towards. the element 32 already installed using the carriage 126 or positioning device 46. This precise work is carried out according to the directives of a surveyor.

The juxtaposition of the new pre-frame 4 against the element 32 or 4 already implemented implies a precise and predetermined horizontal adjustment in order to be able to correct the manufacturing and implementation tolerances. see elements 4 and 32.

Fig. 5 shows the device generally provided at three points of the pre-frame 4 of the element 4 or 32 used.

The pre-frame 4 of the element 32 or 4 already in place includes this device on its edge, in three places, generally in the middle of the raft and at the two upper angles between the roof and the uprights of the element. This device consists of a steel plate 50 anchored securely in the concrete by doguets 51 or other anchoring devices. At the same corresponding locations in the section of the pre-frame 4 of the new element 4 or 32 to be put in place, this device consists of an adjustment screw 52 which can rotate in a threaded sleeve 63 secured to doguets or other anchoring device 64.

A similar device 66 allows precise vertical adjustment and recovery of the pressure due to filling under the raft.

A generally cylindrical bowl 65 is provided to completely house the head of the screw 52 when it is fully screwed. The three adjustment screws 52 of each new pre-frame 4 or 32 implemented are adjusted as indicated by the surveyor as a function of the actual position of the element 32 or 4 immediately adjacent upstream.

The new pre-frame 4 or 32 being thus correctly adjusted at the bottom (fig. 14) of the excavation against the preceding element 32 or 4, a vertical cofferdam 23 made of sheet piling or beams with precast concrete panels, or by any other system, is then implemented downstream of the pre-frame 4 which has just been installed and against it (figs. 14 and 15). This cofferdam 23 has a height which goes from the bottom of the excavation 24 to a little above the natural level of terrain 211, and in any case above the level of bentonite mud 25.

The space between the cofferdam 23 and the vertical wall of the ground 218 is then filled with gravel 224 submerged under the bentonite mud. This gravel filling is carried out at least up to level 22 corresponding to the upper level of the element 4 or 32 in place.

This gravel 224 exerts a significant horizontal thrust on the cofferdam 23 and on the element 4 which has just been placed, thus pressing it strongly against the preceding element 32 upstream (fig. 14) and crushing the seal. 160 in compressible material (fig. 3).

In practice, however, it is difficult to correctly assess the value of this horizontal thrust of the gravel, while the seal 160 must be compressed in a precise manner to be effective.

The cofferdam 23 (fig. 14) will generally comprise jacks 110 (fig. 15) which will make it possible to exert a constant, exact and adequate horizontal force to correctly crush the seal 160.

The tube 225 is then filled with concrete 26 so as to close off the space between the lines 9 and the ground 216 (fig. 15).

A material 275 such as thin fluid concrete is then poured under the raft 206 of the element 4 (fig. 14). This material 275 is poured under the thixotropic mud via concreting tubes 27 which can optionally be housed in the thickness of the cofferdam 23 (fig. 15).

Immediately after hardening of this material 275, concrete 20 is poured by a concreting tube between the vertical walls of the two adjoining pre-frames 4 and the sheets 210 of perforated lost formwork. At as this fresh concrete rises, it partially overflows through the holes in the formwork, thus filling the space between the terrain 216, the lost formwork, formed by the sheets 210, and the rod 225 filled with concrete 26. The concrete 20 incorporates the reinforcements 5 fixed to the elements 4.

This concreting continues to pour concrete 77 (figs. 13 and 14) covering the roofs of the two adjoining pre-frames 4 and 32.

A second cofferdam 80 comprising a beam 81 at its top is deposited in the notch 34 located in the shoulder 8 of the element 32 previously installed.

Gravel 83 (fig. 14) is then poured upstream of this cofferdam 80 while gradually removing an identical cofferdam 84 which was placed above the antepenultimate element.

At this point, the operating cycle can start again.

The bucket 70 excavates the next excavation 87 under thixotropic mud between the cofferdam 23 and a removable guide wall 85. This bucket will evacuate the gravel 224 at the same time as the ground 218 in place. The operating cycle then resumes as described above.

The same would apply if the special bucket 70 was replaced by a hydraulic grab or a backhoe, but in these cases, the removable guide wall 85 is not used.

Fig. 12 also shows an original and efficient device in the case of elements 4 or 32 of large range.

Oblique metal lines 90 are fixed to metal plates 91 anchored in the roof of the frame 4.

This device makes it possible to considerably reduce the thickness 93 of the concrete and the corresponding reinforcements of the roof of the element 4 by creating intermediate supports which shorten the span.

These oblique lines 90 can either be fixed to the two vertical lines 9 by means of assembly plates 45 or anchored in the future embankment.

The upper part of the excavation can be backfilled with concrete injected gravel or lean concrete 92 which completely drowns the metal lines 9 and 90.

Claims (24)

1. Method for making reinforced concrete structures such as road tunnels, underground galleries, underground tunnels, characterized in that an open excavation is first excavated, which is then successively and consecutively deposited prefabricated hollow concrete elements (4) each consisting of a frame, the outer faces of which include reinforcements (5), in that poured concrete (18) covering the joints between elements and collaborating with the reinforced concrete elements (4) and with the reinforcements (S) so as to achieve in successive phases and quickly a monolithic structure whose resistance is significantly greater than those of the prefabricated elements (4) initially. put in place and filler concrete (18); and in that ultimately backfilling is carried out. 2. Prefabricated element in reinforced concrete for the practice of the method according to claim 1, characterized in that it is constituted by a frame, the outer faces of which comprise external reinforcements (5) chosen so as to generate collaboration with a filler concrete which is subsequently applied around the elements. 3. Prefabricated element according to claim 2, characterized in that the external faces of the element comprise roughness (53) and / or imprints (120) 4. Prefabricated element according to claim 2, characterized in that the inner surface (2) of the element is substantially smooth or as close as possible to the intended state of completion. 5. Prefabricated element according to claim 2, characterized in that the walls of the element are as thin as possible, for example from 5 to 15 cm. 6. Prefabricated element according to claim 2, characterized in that the slab (13) of the element is made in its final thickness while .. the other walls are executed in small thickness, this raft then giving rise to the outside of the vertical parts to protuberances (14) in which are anchored vertical frames (15). 7. Prefabricated element according to any one of claims 2-6, characterized in that the external face of the element comprises waiting reinforcements (54) and / or anchoring sleeves (55) with threaded rods ( 59) and / or metal plates (56) with doguets (57) and jumpers (60), which makes it possible to set up, after hardening and formwork of the precast concrete, the peripheral reinforcements (5) which will be fixed on the waiting frames (54), on the threaded rods (59) or on the jumpers (60), this latter operation being able to be carried out in the prefabrication factory or on the site before the elements are implemented. 8. Prefabricated element according to any one of claims 2-7, characterized in that it is constituted by two or more partial elements (100-101) assembled on site whose joints (102) are injected with cement grout or other material. 9. Prefabricated element according to claim 8, characterized in that two half-elements (100,101) are fitted during transport on a trailer (104) thus allowing to respect the road gauge (108) authorized in height. 10. Prefabricated element according to claim 8, characterized in that the partial elements (99-100-101) are assembled together by a post-stress produced by bars or steel wires provided with anchors. 11. Prefabricated element according to claim 8, characterized in that the dimensioning of the total thicknesses of the walls, of the roof and of the write off the element is carried out by choosing values such that the stresses do not generate tensile forces on the inner face of the pie- right at the location of the joint (102) between the two half-elements (100, 101). 12. Prefabricated element according to any one of claims 2 to 11, characterized in that it is completed by temporary vertical props (30), when its width is too large and / or horizontal props when its height is too high . 13. Prefabricated element according to any one of claims 2 to 12, characterized in that the pre-frame element may include interior finishing elements (19) such as, for example, elements of platforms in a metro station, security bodies, finishing coverings on platforms, walls and ceilings, etc. 14. Prefabricated element according to any one of claims 2-13, characterized in that a shoulder (8) of reinforced concrete is provided in the middle and outside of each of or some of the walls and in that this shoulder has a total thickness identical to that of the cumulative walls of the element and the filler concrete (18). 15. The method of claim 1, characterized in that the excavation (62) in the open is carried out in successive transverse sections so as to allow each time the establishment of a prefabricated element and the implementation of concrete contribution and backfilling by covering the joint between two successive elements. 16. Method according to claim 1, characterized in that, to avoid compaction and the risk of collapse of the site in place, the excavation is permanently filled with thixotropic mud, in general consisting of bentonite mud, and this up to a level (25) higher than the level (36) of the water table. 17. Method according to claim 16, characterized in that complementary reinforcements (5) are fixed to the prefabricated element on the upstream side with respect to the shoulder (8) provided according to claim 14 so as to be able to cover the element prefabricated already in place up to its own shoulder, thus covering the joints between the elements and ensuring continuity of the future gallery after additional concreting. 18. A method according to any of claims 1, 15-17, characterized in that one or the other of the successive steps below is carried out: a) two rigid metallic lines (9) generally in the shape of a U and having a sufficient length to be able to be hung on a gantry (126-40) of implementation provided at the level (211) of the ground, are fixed to the shoulders ( 8). b) Inside the two U-shaped lines (9), a tubular element (225) made of a flexible and permeable fabric closed at its lower end is put in place substantially over the entire height. c) After completion of a transverse excavation, a chassis (40) or a carriage (126) for positioning and adjustment is placed above the excavated excavation, generally bearing on guide walls (201). d) Precise adjustment of the submerged element is carried out against the element previously placed by means of the adjustment frame (40) or the carriage (126). e) A vertical cofferdam (23) made for example of sheet piling, is put in place downstream of the element (4) which has just been put in place and against it, this cofferdam having a height extending from the bottom of the excavation to above the level of the bentonite mud. f) The space between the cofferdam (23) and the downstream wall of the land is partially filled with gravel (22) immersed in thixotropic mud, this gravel (22) pushing on the cofferdam (23) and on the precadre ( 4) which has just been placed by applying it against the preceding element (4) upstream. g) The tubular element (225) is filled with concrete in order to close off the space between the lines (9) and the ground (216). h) A material (275) such as concrete is used under the slab (206) of the prefabricated element. i) After hardening of this material, concrete is poured between the external vertical walls and the respective shoulders (8) of the two adjoining elements on the one hand and the vertical faces of the ground in place supported by thixotropic mud on the other hand. j) Concreting continues in order to pour the concrete (77) over the roofs of the two prefabricated elements joined between their respective shoulders. k) A second cofferdam (80) is placed against the shoulder (8) of the roof of the element having been previously installed. 1) Gravel or other fill material is poured upstream of this cofferdam while the identical cofferdam above the antepenultimate element is removed. m) The cycle of operations then begins again by the excavation of the next transverse section sheltered from the downstream cofferdam. 19. Process according to any one of claims 1, 15-18, characterized in that the elements (4) comprise two flexible closing walls (207) fixed on the periphery of the element upstream and downstream, these walls being made of a material permeable to water but impermeable to matters suspended in water and each wall being able to be held in place between two sufficiently rigid metallic trellises (31) fixed to the periphery of the element or on the temporary props (30), the material being able for example to be a non-woven polyester material. 20. The method of claim 19, characterized in that to balance the momentary pressure between the mud and the flexible and permeable wall (207) of the element (4), the latter is gradually filled with water during the descent of the precadre in thixotropic mud. 21. Method according to any one of claims 16-20, characterized in that prior to the installation of the elements (4), vertical profiled steel sheets (210) serving as lost formwork are fixed laterally to the pre-frame (4 ) in order to avoid pollution of the filler concrete and to resist possible landslides. 22. Method according to any one of claims 16-21, characterized in that the profiled sheets (210) comprise numerous perforations allowing the fresh concrete, poured between these sheets (210) and the vertical walls of the element (4 ) to also flow between these same sheets (210) and the vertical walls of the ground (216) supported by the thixotropic mud. 23. Method according to any one of claims 16-22, characterized in that certain elements (4, 32) comprise a rigid rigid wall (33), generally made of concrete, intended to allow subsequent isolation of a section of several elements. upstream of a element (32) in the frame. 24. Method according to any one of claims 16-23, characterized in that oblique lines (90) are anchored to metal plates (91) fixed to the roof of the pre-frame (4) to reduce the total thickness of the concrete (93) from the roof of the tunnel.

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