WO2014147349A1

WO2014147349A1 - Method for consolidating the ground encasing a tunnel

Info

Publication number: WO2014147349A1
Application number: PCT/FR2014/050649
Authority: WO
Inventors: Jean-Pierre Hamelin; Nicolas UTTER; Sara CASCARINO
Original assignee: Soletanche Freyssinet
Priority date: 2013-03-21
Filing date: 2014-03-20
Publication date: 2014-09-25
Also published as: FR3003583B1; EP2976465B1; FR3003583A1; EP2976465A1

Abstract

The invention relates to a method for consolidating the ground (S) encasing a tunnel (10) excavated in sections (R₁,...RN), a pre-supporting beam (V₁,..., VN) being mounted over each section (R₁,...RN) of the tunnel (10), said beam consisting of a plurality of tubes (12) arrangement substantially parallel to each other and to the axial direction of the tunnel (10) and sealed to the ground (S) by means of a sealing grout. Once the sealing grout has hardened, the method comprises a novel step of injecting a consolidation grout into the ground (S) via at least one tube (12) of the pre-supporting beam (V₁,..., V_N).

Description

METHOD FOR CONSOLIDATING A SOIL COVERING A TUNNEL

TECHNICAL AREA

The present invention relates to the realization of buried structures and in particular tunnels.

It relates, in particular, the improvement by consolidation of the soil located in the vicinity of such a buried work. Even more especially, the invention relates to a method for consolidating the soil during the construction of the structure, as and when slaughter (process also called "progress").

BACKGROUND OF THE INVENTION

In the construction of underground structures, it is common to implement pre-retaining systems intended to reinforce the soil in front of and behind the face of the face, before the installation of the retaining wall and the final coating of the tunnel.

These pre-retaining systems consist of reinforcing the soil by inclusions including steel set up in boreholes and linked to the surrounding soil by a grout.

For example, the technique of presutment vaults, better known under the name of "umbrella vaults" (or "pipe umbrella" or "piperoof"), which consists in introducing into the ground a plurality of hollow tubes arranged in parallel and relatively tight to each other, usually metal, and inject into these tubes a sealing grout to seal them to the surrounding soil. The assembly of these tubes forms an arch below which the ground can be excavated without risk of collapse, before the realization of the walls of the tunnel.

The action of pre-support inclusions occurs at different levels. The soil resistance to traction and shear can be improved, as well as the stiffness of the surrounding soil mass, but the known pre-retaining methods do not sufficiently prevent damage to the massif, especially the soil decompression problems and subsidence on the surface. OBJECT AND SUMMARY OF THE INVENTION

The object of the invention is to provide a method for easily consolidating the soil located in the vicinity of a tunnel and, in particular, to avoid the phenomenon of settlements related to the excavation work.

This object is achieved with a method of consolidating a soil encasing a tunnel excavated in sections, wherein each section of said tunnel is surmounted by a pre-retaining vault consisting of a plurality of tubes sealed to the ground with a grout. sealing, and comprising the following steps:

a) a plurality of tubes are introduced into the ground so as to form the pre-supporting profile vault corresponding to that desired for the tunnel, each tube having an open proximal end and at least a first outlet orifice on its distal portion; buried in the ground, and

b) introducing a sealing grout into the soil, through said first outlet of said tube, so that the grout sealing the tube to the surrounding ground,

the method being characterized in that it further comprises the following step:

c) after the grout has hardened, a consolidation grout is injected into the soil through said first outlet of said tube or by at least a second outlet formed on its distal portion.

The method according to the invention makes it possible to improve the mechanical characteristics of the soil located in the vicinity of the tunnel, quickly and simply. The consolidation grout is injected directly by the tubes constituting the pre-retaining vault (or umbrella vault), so that it is not necessary to perform additional drilling specific to the injection. The injection treated soil is hardened. The structure of the injected soil is modified to increase its apparent rigidity, which will be mobilized during the subsequent excavation phases.

Conventionally, the soil located at the right of an excavated zone is weakened. In these places, the soil has undergone settlements. Such settlements also occur in front of the excavated area, on a short portion of soil indirectly undergoing the effects of adjacent excavation. The tubes of the pre-retaining vault extend from the excavated zone but their distal end opens into a soil zone located in front of the face, ie in a zone not yet excavated. According to an advantageous arrangement of the invention, the drilling reaches a zone of non-embrittled ground and the injection is thus carried out in a potentially intact soil zone of any settlement. The consolidation method thus makes it possible to anticipate future settlements, by modifying the characteristics of the ground in the right of a future section of tunnel, before said section is excavated. In other words, the injection of the consolidation slurry is intended, at least to a certain extent, to prestress the soil, that is to say to modify the state of stress before it undergoes the disorders (settlements , especially decompression) related to the excavation of the tunnel.

In the present application, the terms front and rear are used with reference to the axis of the tunnel, the excavated area being located behind the face of the face and the unexcavated area being located in front of the face of size.

Sealing grout should be understood as a hardenable product. Generally used for cementing the tubes, a grout of cement.

Consolidation grout should be understood as a curable product, suitable for being pumped into the soil. The consolidation grout may be the same or different from the grout. Depending on the nature of the ground, it will be possible to use a liquid slurry (mixture of water and a binder, in particular cement, possibly with added bentonite) or a more rigid mortar (grout added with aggregates, in particular sand).

Advantageously, the setting parameters of the consolidation grout, in particular the injected volume and / or the injection pressure, are controlled so as to cause a displacement of the ground, in particular a compression or a deformation of said ground, in the purpose of modifying its state of stress so that its apparent rigidity is increased.

According to one mode of implementation, the consolidation grout is injected at a low pressure and a low flow rate. The total volume is optionally injected in several steps separated by a rest period. The total injected volume is chosen so that the apparent stiffness of the soil located around the point (s) of injection is increased.

According to another embodiment, which is particularly advantageous in the clay-type soils, the injection of the consolidation slurry is a fracturing injection (also called "breakdown" injection) in which the grouting injection pressure is chosen. greater than the soil confining pressure resulting from the state of the constraints existing in the field. The consolidation grout used is usually a fluid slurry, and the objective is to create a fracture in the soil that may contain a grout lens.

According to another embodiment, which is particularly advantageous in rather sandy soils, the injection of the consolidation slurry is a solid injection in which the grout (for example a mortar) is viscous, and in which said grout remains immediate proximity to the borehole and generates compressive stress on the surrounding soil.

Depending on the needs, the injection can be done in all the tubes of the vault of pre-support, or in only some of these tubes. For example, consolidation grout may be injected into only one out of every two or three tubes, or only into the tubes at the upper end of the vault or at its lateral ends.

Preferably, however, a consolidation injection will be performed in at least 50%, preferably at least 75% of the tubes of the pre-retaining vault.

To facilitate and accelerate the installation, the tubes forming the pre-retaining vault can serve both as a drilling member and as a drilling fluid injection tube, as a sealing slurry and, where appropriate, as consolidation grout.

Conventionally, the umbrella vault comprises a single layer of tubes arranged next to each other. In some cases, however, the tubes will be arranged in two superimposed layers.

The tubes of a pre-retaining vault are substantially parallel to each other and to the axis of the tunnel. Generally, the tubes of a pre-retaining vault have a slight inclination with respect to the axis of the tunnel, allowing the tubes of an umbrella vault of a section of rank N to overlap partially, that is to say over a certain length, the tubes of the vaults at least Nl and N + 1 tunnel sections of tunnel. It is said that the successive vaults of the tunnel are partially nested within each other.

According to an implementation example, before step c), the interior of the at least one tube of the pre-support vault in which it is desired to perform the injection of the consolidation grout is cleaned.

Each tube of a pre-retaining vault has at least one opening at each of its ends. The cleaning step consists in disengaging the tube from the sealing grout contained therein, for example with water, so as to make the two openings of the tube communicate and allow the reuse of said tube for the injection of the consolidation grout.

According to an exemplary implementation, the method according to the invention further comprises the following steps:

d) in the space delimited by the tubes of the vault, a section of soil less than the length of the vault is excavated, and

e) the wall of the tunnel section is made.

The tubes constitute, on the length excavated, a temporary protection structure, which prevents the landslide behind the face of the face.

The realization of the wall of the tunnel section may include the laying of temporary or permanent hangers and / or the realization of the final coating of the section, for example but not exclusively by the technique of shotcrete.

According to an exemplary implementation, steps a) to e) are repeated until the tunnel is excavated along its length. If the steps a) to e) correspond to the realization of a section of the tunnel of rank N, these same steps are repeated for the realization of at least one section of rank N + 1, and possibly a plurality of rows of rank N + n, n varying according to the length of the tunnel. In the process according to the invention, preferably, an injection step is carried out in the tubes of the vault of a N-rank tunnel section, before the excavation of said section of rank N.

In one example, the step d) of excavation can be carried out once the injection of consolidation grout has been stopped.

According to another example, the step of injection of consolidation slurry can continue during step d) of excavation and, possibly, during subsequent steps of tunneling.

As indicated previously, the zone injected by the tubes of the vault of the section of rank N, before the beginning of the excavation of said section, is advantageously a zone of ground which theoretically would not have been damaged because of the excavation work sections of rank N, N-1, etc., in particular by decompression phenomena, settlements, etc.

The soil can be treated before disturbances occur due to excavation. The injection made in the ground located at the right of a section of rank N + 2 comes to prevent settlements which would have been generated, otherwise, by the excavation of the section of rank N. The injection carried out in the ground located at the right a section of rank N + 3 comes to prevent settlements which would have been generated by the excavation of the section of rank N + 1. And so on. One can thus speak of injection of prestressing of the ground.

For this purpose, it is possible to choose the length of the tubes of the presutment vault of a section of rank N so that the zone of soil injected by said tubes is situated in front of the tunnel section of rank N + 1, in particular at the right of the N + 2 rank tunnel section.

Generally, the different sections of the same tunnel will have a length (hereinafter length excavated, measured along the main axis A of the tunnel) identical. In this case, preferably, each tube of the pre-retaining vault has a length at least 2.5 times greater than this excavated length.

In a particularly advantageous manner, the method may comprise a step of predictive modeling of settlements of the soil at the progress of the excavation. This predictive modeling can to be obtained either by finite element numerical models or by empirical models (in particular, the Peck model - In a particularly advantageous way, these models can be regularly updated according to the observations made on them. previous phases of work.

Advantageously, the injection pressure and / or the volume of consolidation grout injected are determined according to the predicted settlements.

Advantageously, the unit settlement of the ground situated in line with an N + 2 section generated by the excavation of the N-rank tunnel section is evaluated, and the parameters of the injection (pressure, volume of grout, phasing of the injection operations) carried out by at least one tube of the retaining vault of the rank N segment in the ground zone located at the right of the N + 2 rank section so that the consolidation grout is applied to the injected soil constraints for neutralizing said unitary settlement.

According to an example of implementation, the movements of the soil are continuously monitored during the injection. The control can for example be done at the level of the ground surface (i.e. the upper surface of the excavated massif), for example by means of a laser level. It can also be done by means of an extensometer inserted directly into the soil volume by means of a borehole, for example executed from the face of size.

Detecting an amplitude of displacement of the ground greater than a predetermined value, for example by the displacement tolerances imposed for the project, can for example determine the moment of the stop of the injection. The control of the movements of the ground makes it possible, for example, to avoid damage, because of the uprisings, the dwellings founded on the mass of excavated ground.

According to an implementation example, after step d) of excavation of the N-rank tunnel section, at least one tube of the pre-retaining vault of a section of rank Nn is cleaned, n being between 1 and N1, and a further injection of consolidation slurry into the soil, through said cleaned tube. More generally, a consolidation grout may be injected into one or several tubes of a N-shaped pre-support vault at any moment during tunneling, in order to correct excessive deformations in front of or behind the face of size. surface. In this case, care must be taken to maintain access to the open ends of the injection tubes, even after bending and / or laying of coating operations on the tunnel walls.

Apart from the prestressing injection carried out in the tubes of the rank N segment before the excavation of said section, it is possible to proceed to new injections, in the same tubes, during the excavation of the section N (injection controlled according to the coefficient pre-calculated volume loss), and / or during the installation of tubes of the N + 1 section (to compensate for the volume losses related to the drilling), and / or during the different phases of laying the hangers and / or the final coating, and / or after the laying of the final coating.

The tubes used for the realization of the vault and for the injection can be perforated tubes. A perforated tube makes it possible to accurately produce localized injections in several zones to be treated which are distant from each other.

By perforated tube means a tube provided with openings of any shape, for example a sleeve tube, well known elsewhere. Traditionally, in a sleeve tube, the openings are closed by rubber sleeves which open when the pressure in the sleeve tube is greater than the pressure outside the tube.

Advantageously, the perforated tube is a sleeve tube and, for the injection of consolidation grout in particular, is introduced into the sleeve tube a shutter tube, preferably a double shutter tube, to perform the injection through some of openings.

According to one aspect of the invention, a consolidation grout injection can also be performed in the face of size.

Thus, according to an exemplary implementation, at least one borehole is drilled into the face of the borehole, an injection tube is placed in said borehole and sealed to the ground with a grout. sealing, said injection tube having an open proximal end and at least one outlet orifice on its distal portion sunk into the ground, and a consolidation slurry is injected into the soil through said tube.

Preferably, the injection tube is sealed to the ground with a sealing slurry before the consolidation slurry is injected.

Preferably, the length of the injection tube introduced into the cutting face of a section of rank N is chosen so that the soil zone injected by said tube is situated axially in front of the tunnel segment of rank N + 2. .

In addition to the umbrella vaults reinforcing the upper section of the excavated areas, it is common practice to reinforce the face to limit the deformations, by the so-called nailing technique of the front, which consists in sealing in the ground reinforcing frames passive reinforcement. These frames are sealed and injected to ensure good transmission of tensile forces and shear between the frame and the ground. These reinforcements being then excavated, it is generally used friable elements, including fiberglass: crenellated bars, tubes, or blades.

According to an advantageous arrangement of the invention, the nailing of the forehead is completed by a treatment of the soil by injection. In this case, the drilling carried out for the nailing can be used also for the realization of the injection operations.

Thus, according to one example, an armature, in particular a fiberglass bolt, is introduced into the borehole drilled into the face and intended to receive the injection tube, and the armature is sealed to the ground at using a grout.

According to an implementation example, after injection of the consolidation slurry into the soil through the injection tube inserted into the cutting face, the reinforcement is inserted inside the injection tube, it is removed. the tube, and the reinforcement is sealed to the ground by means of a grout.

According to another example of implementation, the injection tube and the reinforcement are introduced into the borehole, side by side in the radial direction of the borehole, a sealing grout is injected into the ground for sealing said injection tube and the frame on the ground, and the consolidation grout is injected into the ground through the injection tube.

Several embodiments and implementations are described in this disclosure. However, unless otherwise specified, the features described in connection with any embodiment or implementation may be applied to another embodiment or implementation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the following description of an embodiment of the invention given by way of non-limiting example, with reference to the appended drawings, in which:

Figure 1 is a transverse view of a tunnel being excavated, just before the beginning of the realization of the rank N segment;

Figures 2 to 7 illustrate the steps of making the N-rank tunnel section and the soil consolidation method according to an embodiment of the invention;

Figures 8 to 12 illustrate a variant of the consolidation method according to the invention;

Figure 13 shows the face of Figure 12;

FIG. 14 shows the soil zone consolidated by the process according to the invention and the predicted curve of settlements after excavation of the rank section N-1, in the absence of consolidation of the soil;

FIG. 15 illustrates a second variant of implementation of the consolidation method according to the invention.

Figure 1 illustrates a tunnel 10 during excavation. In this figure, several sections of the tunnel, of the same length L _T , have already been excavated and coated.

In the remainder of the description, each section R of the tunnel is designated according to its rank, the first excavated section being of rank one, the second, of rank two, and the Nth, of rank N, and so on. The realization of a tunnel segment R _N of rank N will be described in detail with reference to FIGS. 2 to 7. This method being reiterated for each section of the tunnel in a systematic way, it is only described once.

As can be seen from FIG. 1, each tunnel section Ri,... _Fn 10 is surmounted by a portion of an umbrella vault Vi,..., _N of conventional type, consisting of an assembly of tubes 12 introduced into the ground from the previous section, the assembly having, in section, an arcuate profile of main axis A, corresponding to the desired profile for the tunnel. The general profile of the umbrella vault is visible in particular in Figure 13.

In the present description, an axial direction is a direction parallel to the main axis A of the tunnel 10. In addition, a radial direction is a direction perpendicular to the axis A.

Unless stated otherwise, the adjectives and adverbs axial, radial, axially and radially are used with reference to the aforementioned axial and radial directions. In the same way, an axial plane is a plane parallel to the axis of the tunnel and a radial plane is a plane perpendicular to this axis.

In the present description, it is considered that the umbrella vault V _N of rank N is constituted by the tubes located at the periphery of the N-rank tunnel section being the closest to the axis A of the tunnel 10 in the radial direction.

Furthermore, in the following, the face of size F _N of the segment of rank N designates the slice of ground marking the end of the excavation of the section of rank N. The face of size F _N forms a defined terrain wall. in a substantially radial plane, and marking the limit with the following section R _{N +} i.

In a first step of realization of the tunnel section R _N N rank illustrated in Figure 2, the soil is drilled and the tubes 12 are introduced into the soil, one after the other, so as to form the vault V _N of section R _N of rank N.

In the example, each tube 12 comprises an open proximal end 14 and an open distal end 16 having an annular peripheral edge which is provided with cutting teeth 24. By teeth cutting means drilling tools in general, such as pimples, knobs, tungsten carbide pellets, etc. to excavate the soil S during the drilling. The cutting teeth 24 are sized to excavate the ground, so that the tube 12 is also used as a drilling tool, before being left in place in the ground. The steps of drilling and introduction of the tube into the soil are therefore carried out concomitantly (it is commonly spoken cased bore tool lost).

According to an implementation variant, the soil is first drilled with an independent drilling tool, not intended to remain in place in the soil (in this case it is referred to as uncased drilling), and then, after the Drill tool was removed, the tube is introduced into the well drilled borehole.

In the example, the tubes 12 are, more particularly, cuffed tubes. Conventionally, a sleeve tube 12 is provided with openings 20 which are formed at different heights of the tube, as well as flexible sleeves 22 which surround the sleeve tube 12 so as to seal the openings 20 when the pressure at inside of the sleeve tube is less than or equal to the pressure outside the sleeve tube. These flexible sleeves 22 are arranged to deform outwardly to allow flow through the openings 20 when the pressure inside the sleeve tube is substantially greater than the pressure outside the sleeve tube.

In the illustrated example, the openings 20 covered with flexible sleeves 22 are distributed over the distal portion of the tube, in particular on the last third of the tube 12.

For its introduction into the ground, each tube 12 is connected, by its proximal end 14, to means 18 for driving in rotation, which here comprise a hydraulic motor 19.

As illustrated in FIG. 2, each tube 12 is introduced into the ground via its distal end 16, being rotated by the drive means 18. Each tube 12 is inserted on the crown (ie at the periphery) of the forehead of size of the section R _N-1 of rank Nl, substantially skirting the upper part of this section R _N- i. Once in place, the tube 12 extends in a direction defined in a substantially axial plane and slightly inclined relative to the main axis A, for example an angle β between 5 ° and 10 °. The inclination of the tubes 12 relative to the axis A of the tunnel 10 allows the overlap of the V umbrella vaults successive tunnel. As illustrated in FIG. 1, each new umbrella vault V _N formed is, as it were, embedded or partially fitted into the umbrella vault V _N- i of the preceding section.

During drilling, a drilling fluid, for example water, is injected from the inside of each tube 12 and leaves in the bore through the distal end of the tube 12. The debris excavated by the cutting teeth 24, mixed with the drilling fluid, are discharged from outside the tube 12 through a narrow space, usually a few millimeters thick, defined all around the tube (hereinafter annular space).

The drilling is carried out so as to bring the distal end 16 of each tube 12 to a predetermined depth at which the soil zone to be consolidated Z is located.

When each tube 12 is in place, a sealing grout, in particular a grout, referred to herein as CS, is introduced into said tube 12 of the umbrella vault V _N , in particular by means of a single obturator tube 25 inserted into each tube 12 as illustrated in Figure 3. Escaping at low pressure by the open distal end 16 and optionally the side openings 20 of the tube 12, the sealing grout CS impregnates the soil around the tube 12, fill the annular space, and thus seal the tube 12 on the ground and adjacent tubes 12.

If necessary, particularly if the grout has soiled the inside of the tube, each tube 12 is cleaned in a second step (not shown), for example with water, so that at least some of the openings 20 to the periphery of the tube 12 and at its distal end 16 communicate with the opening of the tube at its proximal end 14.

The tubes 12 of the umbrella vault V _N form, once cleaned, injection tubes through which a consolidation grout, referenced here CC, will be injected into the soil zone to be activated (hereinafter consolidation injection).

The aim of the consolidation injection according to the invention is to bring the soil of the zone to be activated into a state of constraints different from its initial state. In particular, the injection is intended to prestress this area of soil before it undergoes the disorders (settlements, decompression in particular) related to the excavation of previous sections. In FIG. 14, for example, the predicted soil settlement curve has been illustrated at the surface of the massif at the end of the excavation of the sections up to the row N1 and in the absence of any consolidation of the soil. We observe, on this curve, that the largest settlements T are measured at the right of the excavated areas and that the settlement amplitude decreases progressively until becoming almost zero at a distance D from the face of size F _N- i, in front of the latter.

The length L _A of the tubes 12 is chosen so that at least one injection orifice of each tube 12, provided on its distal portion, is located in the zone to be activated Z in which the settlements related to the excavation work of the section N are theoretically evaluated as being less than a limit value (low value characterizing a quasi-absence of settlements) in the absence of prior consolidation of the soil. In the example, the distance D is approximately twice the length L _T of a section. The length L _A of the tubes is therefore greater than two and a half times the length L _T of a section, here about three times this length.

Each construction project is subject to technical specifications upstream. In the case of a tunnel, a maximum volume loss coefficient is usually set by contract globally, for the tunnel or for a tunnel area. This coefficient of volume loss, which corresponds to the ratio between the volume of the settlement basin on the surface of the massif and the theoretical volume of ground excavated for the tunnel, characterizes the maximum of settlement admissible over the length of the tunnel or the zone. considered.

By calculation, it is possible to determine the contribution of the excavation of each tunnel section to the overall settlement, and thus to define the volume loss coefficient corresponding to each particular section of the tunnel.

The objective of the injection is to compensate, as and when tunneling, the settlements induced by the excavation of each section. Injection treatment is all the more effective when applied to the source of settlements, and includes a preventive component (soil prestressing). From the volume loss coefficient corresponding to a section of the tunnel, it is possible to deduce an injection program at this section, and especially a volume and pressure set point, for the injection around this section. Each injection pass can be modeled by a lift. It is thus possible to determine, generally automatically, an optimum distribution of injection points and amounts of substance to be injected so that the theoretical uprisings related to the injection neutralize the theoretical settlements related to the excavation.

In certain cases, it may be provided that the injection set point for a section of rank N + 2, especially in volume, is reached in a single injection phase in the tubes of the vault of a section of rank N, upstream of the excavation of said rank section N. In other cases, it may be expected that the setpoint is reached in several successive injection phases, carried out in the tubes of the row vault N, at different times during excavation of the tunnel.

As illustrated in FIG. 5, the consolidation grout CC is thus injected into each tube 12 via a double obturator tube 26 which is introduced into the tube 12 in order to isolate one or more openings 20.

As shown in FIG. 5, when pumping the consolidation grout into the sleeve tube 12, increasing the pressure of the grout CC in the sleeve tube 12 has the effect of opening the sleeve which allows the CC consolidation grout from flowing into the soil S to treat the Z zone.

In a new step illustrated in Figure 7, the soil is excavated under the umbrella vault V _N , a length L _T less than the length L _v of the vault measured in the axial direction.

After excavation of a tunnel section, the difference between the actual settlement of the mass of land to the excavated section and the tolerance imposed by the technical specifications of the project is generally measured and the volume loss coefficient of the section is adjusted. those of the following sections to take account of this difference in the determination injection instructions. If necessary, the injection is completed on the section concerned.

After the excavation step, and as shown in FIG. 7, hangers 60 are placed on the side walls of the tunnel section and the section is coated with concrete 62, for example by the shotcrete technique.

As can be seen in FIG. 7, there is a continuity between the different zones injected along the tubes 12 of the successive presutment vaults. The treatment of the ground is thus continuous along the route of the tunnel.

Prior to the realization of the umbrella vault V _N for reinforcing the upper section of the section R _N , it is common to reinforce the face size F _N -i of the section RN-I to limit deformation.

A first mode of implementation according to the invention, allowing such a reinforcement, is illustrated in FIGS. 8 to 12.

As illustrated in FIG. 8, tubes, for example cuff tubes 42, of the same type as those described above are introduced into the face-piece F _N and then sealed to the ground by means of a CS grout (grout seal filling the annular space surrounding the injection tube).

The injection tubes 42 have a length advantageously greater than 2.5 times the length of a section. In this way, the tubes 42 make it possible to consolidate the face of size but also, to a certain extent, the zone of soil to be activated Z located at the right of the tunnel section of rank N + 2.

The inside of the tubes 42 is then cleaned, for example by means of a water injection lance 41, and then, as illustrated in FIG. 9, a consolidation grout CC is injected into the ground by the tubes 42, possibly by means of a double shutter tube 26.

As illustrated in FIG. 10, the tubes 42 are cleaned again and a fiberglass reinforcement 44 is introduced into each of them.

The tubes 42 are then removed (Figure 11), and the frame 44 is sealed to the ground by means of a sealing grout CS, introduced around the frame 44 (Figure 12). A second mode of implementation according to the invention, allowing the reinforcement of the front of size F _N -i of the section of rank Nl, is illustrated in FIG.

According to this embodiment, a borehole 50 is firstly made in the face of size F _N , said borehole being sufficiently wide to receive one next to the other, an armature 44 such as A fiberglass bolt and an injection tube 70. In the illustrated example, the borehole 50 is a cased bore to the lost tool. In other words, the drill member is a drill pipe 52 which is kept in the ground when, during a second step, the frame 44 and, next to it, the injection tube 70 are introduced into the borehole 50. In the illustrated example, the diameter of the injection tube 42 is obviously smaller than the diameter of the borehole 50 and the drill pipe 52 and the length of the injection tube 70 is Moreover, in this embodiment, the injection tube 70 is advantageously made of a plastic material, allowing its easy destruction during the excavation of the section of rank N.

In a third step, the drill pipe 52 is withdrawn from the borehole 50.

In a fourth step, a sealing grout CS is injected through the injection tube 70 to seal said injection tube 70 and the frame 44 to the ground.

The injection tube 70 is then cleaned in a fifth step.

Finally, in a sixth step, a consolidation grout CS is injected into the ground, through the injection tube 70.

According to an alternative embodiment adapted to the case of a coherent ground, the borehole 50 is made using a drill bit removed before the introduction, into the borehole 50, of the reinforcement. 44 and the injection tube 70. Because it is consistent, the soil is held without casing.

Claims

1. A method of consolidating a soil (S) surrounding a tunnel (10) excavated in sections (R 1, R _N RN + I, RN + 2, ■■■), wherein each section (Ri, R _N , RN + I, RN + 2, ...) of said tunnel

(10) is surmounted by a pre-retaining vault (Vi, V _N , V _{N +} 1, V _N + 2, ■■■) consisting of a plurality of tubes (12) sealed to the ground by a grout (CS), and comprising the following steps:

a) is introduced into the soil (S) a plurality of tubes (12) so as to form the pre-retaining vault (Vi, V _N , VN + I, V _{n + 2} , ...) of profile corresponding to the one desired for the tunnel (10), each tube (12) having an open proximal end (14) and at least one first outlet on its distal portion sunk into the ground (S), and b) introducing a slurry of sealing (CS) in the ground, by said first outlet of said tube (12), so that the sealing grout (CS) is sealing the tube (12) to the surrounding ground,

the method being characterized in that it further comprises the following step:

c) after the sealing grout (CS) has hardened, a consolidation grout (CC) is injected into the soil (S) through said first outlet of said tube (12) or by at least a second outlet formed on its distal portion.

2. Consolidation method according to claim 1, wherein before step c), the inside of the tube (12) of the pre-support vault (Vi, V _N , V _{N +} i, V _N +) is cleaned. 2, ■ · ■) to inject consolidation grout (CC).

The method of claim 1 or 2, wherein:

d) in the space delimited by the tubes of the pre-retaining vault (Vi, V _N , V _{N + 1} , V _N + 2, ■■■), a section is excavated (R1, RN, RN + I, RN + 2, ■ · ■) of soil length (L _T ) less than the length (L _v ) of the vault (Vi, V _{N /} V _{N +} 1, V _N + 2 (■■■) tubes (12) constituting, on the excavated length (L _T ), a temporary protective structure, and

e) the wall of the tunnel section (RN) is made.

4. The method of claim 3, wherein the steps a) to e) are repeated until the tunnel (10) is excavated along its entire length.

5. Method according to claim 3 or 4, wherein, after step d) excavation of the tunnel section (R _N ) of rank N, is cleaned at least one tube (12) of the vault of the vault (V _Nn ) of a section of rank Nn, n being between 1 and Nl, and a new injection of consolidation slurry (CC) into the soil (S) is carried out through said cleaned tube (12).

6. A method according to any one of claims 3 to 5, wherein the injection of consolidation slurry is carried out continuously during at least step d) of excavation.

7. Method according to any one of claims 1 to 6, comprising a step of predictive modeling of settlements (T) of the soil at the progress of the excavation.

8. Method according to claim 7, wherein the injection pressure and / or the volume of consolidation grout (CC) injected is determined as a function of the predicted settlements (T).

9. A method according to claim 7 or 8, wherein the unit settlement of the ground located at the right of a section (RN + 2) of rank N + 2 generated by the excavation of the tunnel section (R _N ) of rank N, and the parameters of the injection made by at least one tube (12) of the pre-support vault (V _N ) of the section (R _N ) of rank N in the ground zone located at the right of the section (R _N + 2) of rank N + 2 so that the consolidation grout (CC) applies on the injected soil constraints to neutralize said unit settlement.

The method according to any of claims 1 to 9, wherein the movement of the soil (S) during the injection step is continuously monitored, and the detection of a soil displacement amplitude greater than a value predetermined determines the timing of the injection stop.

11. A method according to any one of claims 1 to 10, wherein the at least one tube (12) is a perforated tube, including a sleeve tube.

12. Method according to any one of claims 1 to 11, wherein each tube (12) has a length greater than 2.5 times the length (L _T ) of a section (Ri, ... R _N , RN + I, RN + 2, ■■■) tunnel.

13. A method according to any one of claims 1 to 12, wherein the length (LA) of the tubes (12) of the pre-retaining vault (V _N ) of a section (R _N ) of rank N is chosen. so that the soil zone injected by said tubes is situated axially in front of the section (RN + I) of tunnel N + 1.

14. A method according to any one of claims 1 to 13, wherein at least one borehole (50) is drilled in the face (Fi, F _N , F _N + 1, F _N + 2, ■), an injection tube (42) is disposed in said borehole (50), said injection tube (42) having an open proximal end and at least one outlet orifice on its distal portion sunk into the ground, and a consolidation slurry (CC) is injected into the soil through said tube (42).

15. The method of claim 14, wherein the length of the injection tube (42) introduced into the face (F _N ) of a section of rank N is chosen so that the soil zone injected by said tube (42) is located axially in front of the tunnel segment (RN + 2) of rank N + 2.

16. The method of claim 14 or 15, wherein a reinforcement (44), in particular a fiberglass bolt, is introduced into the borehole (50) drilled in the face of the face and the reinforcement is sealed (44). ) on the ground with a grout (CS).

The method of claim 16, wherein after injecting the consolidation slurry (CC) into the soil through the injection tube (42) inserted into the face

(Fi, F, FN + 1, FN + 2, ■■■),

the armature (44) is inserted inside the injection tube (42),

the tube (42) is removed, and

the reinforcement (44) is sealed to the ground by means of a grout (CS).

18. The method of claim 16, wherein

the injection tube (42) and the armature (44) are introduced into the borehole (50), side by side in the radial direction of the borehole (50),

a grout (CS) is injected into the ground to seal said injection tube (42) and the armature (44) to the ground, and

the consolidation grout (CC) is injected into the soil through the injection tube (42).