EP0356311A1 - Process and apparatus for working a ground surface, especially for covering a road - Google Patents

Abstract

The table (23) for extruding the covering (39) is placed behind the tracks (2) and thus can have a greater width than the overall width at right angles to the tracks. <??>The table is carried by a bridge chassis (27) articulated on the frame (1), carried by the tracks, along a transverse axis (XX). At the rear, the bridge chassis (27) rests on the fresh covering (39) by means of air cushions (32). A dragged blade (58) emits a ray (63) parallel to the surface (39) as detected by the blade. A detector (64) carried by the table (23) and receiving the ray (63) detects the height position of the table (23) relative to the surface (39). Jacks (38) correct the height position of the tool as a function of this detection . A ballast (42) is displaced automatically along the bridge chassis (27) in order to adjust the pressure in the air cushions (32). <IMAGE>

Description

The present invention relates to a method for opening a floor surface, in particular for lining a roadway with a concrete coating of bitumen or cement.

The present invention also relates to a machine designed for this purpose.

Sliding formwork machines are known, such as those described for example by RAY and CHARONNAT on pages 98 to 132 of the Liaison Bulletin of the Laboratory of Bridges and Roads n ° 95 - May, June 1968 reference 2231. These machines are intended for coating a pavement with a concrete, bitumen or cement coating. They include a frame which rests and advances on the unpaved ground by means of two or four tracks. The support members on the ground reserve between them a transverse space in which the chassis carries a sliding formwork, that is to say two lateral forms forming with a top extrusion table a tunnel through which the coating is extruded .

On the site, there are two sides of the path provided for the machine, two wires defining a reference surface to which the surface of the finished covering must be parallel. The frame carries wire followers, each of which detects the position of a point of the frame relative to the reference surface. Depending on this detection, the height position of different points of the frame relative to the support means on the ground is adjusted by jacks in a direction such that the lower surface of the extrusion table, the trajectory of which defines the profile of the pavement carried out, ie parallel to the reference surface and at a determined distance from the latter.

It is essential that the pavement produced has as smooth a profile as possible. It is therefore important to minimize the influence on the extrusion table of the movements of the frame when it is adjusted in height relative to the reference surface. This is why, in known machines, the extrusion tunnel is located between the support means on the ground, in the vicinity of the center of gravity of the machine. Under these conditions, the coating produced necessarily has a width less than the free width between the support members on the ground, generally tracks.

Known in particular from CH - A - 498 981 is a machine of the type indicated above, of the four-track type, the structure being articulated around a horizontal transverse axis positioned between the front tracks and the rear tracks. An anterior frame rests on the rough ground by the front tracks. A chassis-bridge is articulated to the frame around the horizontal transverse axis and rests on the rough ground by the rear tracks. Tools are mounted transversely under the axle chassis between the front tracks and the rear tracks. Various adjustment means 7, 26 are used to correctly position the tools in height despite the unevenness of the raw soil. The rear support means are supported on either side of the worked surface produced. The working width of the machine is therefore less than its overall width. Finally, although comprising an articulated bridge chassis, this machine differs little in principle from a rigid chassis machine. Parasitic movements can come from the front frame, which rests on the rough ground, as well as from the rear tracks, which also rest against the rough ground.

Also known from DE-B-1 049 413 a machine for depositing a constant coating layer and which is therefore devoid of means for directly or indirectly adjusting the position of the tool relative to a reference surface. The machine comprises (FIGS. 3 and 4) a front frame resting on the rough ground, a chassis-bridge supporting a tool and the rear end of which rests by rollers on the worked surface, the width of which can thus be greater than the width of support on the floor of the machine.

DE-B- 1 049 413 stresses the drawbacks of such a machine, which is only described under the state of the art. As the document rightly explains, any defect on the worked surface will produce a second similar defect when the rear support roller, when crossing the defect, will cause parasitic movement of the tool. This second defect produced by the tool will in turn be crossed by the roller, which will cause the formation of a third defect and so on.

To remedy this drawback, DE -B- 1 049 413 proposes to produce the worked surface in three parallel strips, the central strip being produced by a tool substantially located in the axis of pitch of the frame before the machine, so to minimize the impact of the machine pitch on the position of this tool in the vertical plane. It is further provided that the rear support roller of the bridge chassis rolls on the central strip of the worked surface, that is to say the strip having the least risk of defect. Two lateral tools are also provided in an offset position towards the rear to produce two lateral covering strips, on either side of the central strip. The chassis-bridge therefore positions the two lateral tools independently of the defects that the two lateral bands may have, and consequently, these two lateral bands 13 themselves have fewer defects.

This solution is unsatisfactory because it requires three tools, because it does not exclude the presence of defects on the lateral strips of worked surface and also because it necessarily results in the presence of longitudinal joints between the three strips.

We also imagined machines in which the extrusion tunnel has a width greater than the free width between the tracks and is arranged cantilevered beyond the rear of the tracks. However, this solution does not make it possible to produce pavements of excellent quality, each movement of self-positioning of the frame being transmitted with amplification to the extrusion table.

The aim of the present invention is thus to propose a method and a device for producing a very good quality worked ground surface over a width which can be significantly greater than the free width between the support means, such as tracks, on unworked soil.

According to a first aspect of the invention, the method for opening a ground surface, in which a machine carrying a tool which is in contact with said surface is moved along the surface to be worked, while adjusting the height of the means supporting at least indirectly the tool so that it follows a trajectory substantially independent of the irregularities of an unworked region of the ground on which evolve support means on raw ground located upstream of a posterior transverse end of the tool, the tool taking support, during work, under a chassis-bridge, one front end of which is supported by the support means on rough ground by means of an articulation of axis transverse to the median longitudinal plane of the machine, is characterized in that one rests a rear end of the bridge chassis on the worked surface under a sufficiently low pressure to avoid any significant alteration of the worked surface .

Given that, according to the invention, the height is adjusted at least indirectly to make its trajectory substantially independent of the unworked ground, the risk of seeing defects appear on the worked surface such as those mentioned in DE-B - 1,049,413 east greatly reduced, and above all the probable magnitude of such a defect is also very small. The level regulation filters the faults and lets pass at most only very attenuated balances. Thanks to the chassis-bridge, these disturbances occurring at the level of the front frame reach the tool only with an amplitude substantially divided by two (lever effect around an axis passing through the support means distributed over the worked surface). The risks that such a defect creates successive echoes due to the crossing by the support means distributed over the worked floor themselves become negligible, taking into account in particular the very small possible amplitude of these defects, and the fact that the support is distributed.

The result obtained thanks to the invention is better than that obtained with DE-B- 1 049 413 because it eliminates both the risk of successive echoes of a defect and the longitudinal joints between three strips of worked soil.

The result obtained thanks to the invention is also better than that obtained by the technique according to CH-A- 498 981 since, according to the invention, the rear end of the chassis-bridge rests on the very even, worked ground. , and not on rough ground, which improves the stability of the tool's trajectory, and also because the working width allowed by the invention is significantly greater. In addition, the invention does not require having a suitable unworked strip of soil on either side of the roadway to be produced.

In addition, it must be taken into account that DE-B- 1 049 413 strongly dissuaded the person skilled in the art from providing a tool formed in one piece under a bridge chassis approximately halfway along it. ci between on the one hand a frame supporting the front end of the chassis-bridge and on the other hand distributed support means on the ground supporting the rear end of the chassis-bridge.

According to a second aspect of the invention, the machine for opening a ground surface, in particular for the implementation of the method according to the first aspect comprising a frame resting movably on a region of the ground not worked by the 'intermediate support means on bare ground, a chassis-bridge, one front end of which is supported by the frame via an articulation with an axis transverse to the median longitudinal plane of the machine, and one rear end of which is provided with movable support means on the ground, a tool mounted under the chassis-bridge and comprising a posterior transverse end situated behind the support means on bare ground, and means for adjusting the height of the means supporting at least indirectly the tool so that it follows a path substantially independent of the irregularities of said region of the unworked ground, is characterized in that the support means of the rear end of the chassis-po nt are mobile support means distributed over the worked surface.

Other features and advantages of the invention will emerge from the description below.

• - la figure 1 est une vue d'un engin selon l'invention, en élévation latérale et partiellement en coupe selon la ligne I-I de la figure 2 ;
• - la figure 2 est une vue schématique de dessus de l'engin de la figure 1 ;
• - la figure 3 est une vue de face de l'engin de la figure 1 ;
• - les figures 4 à 8 sont des vues schématiques en coupe selon les plans IV-IV, V-V, VI-VI, VII-VII, VIII-­VIII de la figure 1 respectivement ;
• - la figure 9 est une vue de face à échelle agrandie, d'une plage réceptrice de rayonnement montée sur la face arrière de l'outil ; et
• - la figure 10 est un schéma bloc des moyens de commande de la position de l'outil en fonction du signal de détection de la position de l'outil.

In the appended drawings, given by way of nonlimiting examples:

• - Figure 1 is a view of a machine according to the invention, in side elevation and partially in section along line II of Figure 2;
• - Figure 2 is a schematic top view of the machine of Figure 1;
• - Figure 3 is a front view of the machine of Figure 1;
• - Figures 4 to 8 are schematic sectional views along the planes IV-IV, VV, VI-VI, VII-VII, VIII-VIII of Figure 1 respectively;
• - Figure 9 is a front view on an enlarged scale, of a radiation receiving surface mounted on the rear face of the tool; and
• FIG. 10 is a block diagram of the means for controlling the position of the tool as a function of the signal for detecting the position of the tool.

In the example shown in FIGS. 1 to 3, the machine for coating a roadway with bitumen concrete or cement comprises a frame 1 resting on the unpaved ground 5 by means of two lateral drive tracks 2. The frame 1 is connected to the tracks 2 by four jacks 3 provided for adjusting the height position of the frame 1 relative to the tracks 2 to compensate for the inequalities encountered by the tracks 2 during their progression on the rough ground 5.

By raw soil is meant the soil not coated or not yet coated by the machine.

Before the machine was put into operation, two wires 4, called "stretched wires", were stretched longitudinally on either side of the surface which it must cover, which together define a reference surface to which the surface of the coating to be produced must be parallel. Each cylinder 3 is associated with a probe 6 which follows the wire 4 located on the same side of the machine as the cylinder 3 considered and which transmits to control means of the cylinder 3 information relating to the height position of the frame 1 to the right of the jack 3 with respect to said wire 4. These means known in themselves for providing the frame 1 with a path as independent as possible of the irregularities of the raw soil are known in themselves and will therefore not be described in more detail.

The two tracks define between them a free transverse distance in which the frame 1 carries, substantially in contact with the raw ground, two anterior lateral forms 7 (Figures 2 and 3) intended to receive between them, in front of the frame 1, the share of supply means such as trucks or conveyor belts, the concrete 8 intended to form the coating. Each of the front side forms 7 is adjacent to one of the tracks 2. Between the front lateral forms 7 is rotatably mounted a distribution screw 9 (Figure 2) of transverse horizontal axis driven by a motor 11 via a transmission means 12. In known manner , the rotation of the screw 9 around its axis causes an approximate equalization of the level of concrete 8 over the free width between the anterior forms 7.

Behind the tracks 2, each front formwork 7 is connected to a rear side formwork 13 by means of a transverse formwork 14. The free distance between the rear side formworks 13 is greater than the free distance between the tracks 2, and even greater than the overall width of the machine in line with the tracks 2, probes 6 not included. Between the rear lateral forms 13 extends, just behind the transverse forms 14, a rear distribution device 16 comprising two transverse screws 17 rotating in opposite directions, aligned with each other. Each of the screws 17 is driven by a respective motor 18 fixed to the respective side formwork 13.

Downstream of the screws 17, relative to the direction of movement of the concrete through the machine, there is provided a transverse pre-equalization bar 19, followed downstream by a vibrating device 21. As shown in FIG. 1, the bar pre-equalization 19 is adjustable in height by means of a jack 22. FIG. 1 also shows that the screws 17, the bar 19 and the vibrator device 21 are supported directly by the frame 1.

Downstream of the vibrator 21, therefore even further back than the vibrator 21 with respect to the support means on rough ground 2 (tracks), an extrusion table 23 extends transversely between the rear lateral formworks 13. Thus, the active lower surface 24 of the extrusion table 23, and in particular its rear transverse edge 26 are located behind the tracks 2 and extend over a width much greater than the free width transversely between the tracks 2.

The structure of the machine comprises, in addition to the frame 1, a chassis-bridge 27 essentially comprising two longitudinal beams 28 placed at equal distance on either side of the median longitudinal plane P of the machine, and one connected to the 'other, near their rear end, by a spacer 29 articulated at each end.

At their front end, the two beams 28 are articulated to the frame 1 along a common axis XX, by means of two yokes 31. The axis XX is perpendicular to the plane P. The yokes 31 are located on the top of the frame 1, and the beams 28 extend, in their anterior region, above the frame 1.

From its articulation by means of the yokes 31, the chassis-bridge 27 extends towards the rear and it is supported at its rear end by two air cushions 32 each mounted at a lower end of a welded leg 33 under the rear end of one of the beams 28. The air cushions 32 are supplied with compressed air by means not shown.

The length of each beam 27 is such that the cushions 32 are located behind the extrusion table 23. In addition, the distance between each cushion 32 and the median longitudinal plane P of the machine (FIG. 2) is less than the half-width of the extrusion table 23 so that, in service, the two air cushions 32 bear on the upper surface 39 of the covering produced by the machine.

The extrusion table 23 is supported by the chassis-bridge 27, without any other mechanical connection with the frame 1. For this purpose, each beam 28 carries on its side opposite to the other beam 28 a tubular guide of vertical axis 34 in which is slidably engaged a column 36 whose base is fixed rigidly to the upper face of the extrusion table 23. At its upper end, each column 36 is coupled to the end of the movable rod 37 of a jack 38 for adjusting the height of the extrusion table 23.

As shown schematically in FIG. 1, the table 23 is substantially located at equal distance D from a vertical plane passing through the axis X-X and from a vertical plane passing through the air cushions 32.

It is important that the air cushions 32 do not exert on the worked surface 39 a pressure capable of reaching or exceeding the minimum pressure from which the worked surface 39 would be deformed. But it is also important that this pressure is not zero. A zero pressure would mean that the reaction undergone by the extrusion table 23, reaction directed vertically upwards, exceeds the forces of gravity exerted on the table 23. In other words, the table 23 would be lifted under the pressure concrete under it. In view of these two imperatives, it has been determined according to the invention that the pressure exerted by the air cushions 32 on the surface 39 should remain between approximately 100 and 500 g / cm₂.

The pressure exerted by the air cushions 32 on the surface 39 does not depend solely on the constructive features of the machine. In fact, the vertical reaction directed upwards undergone by the extrusion table 23 depends in particular on the quality of concrete which is used. Moreover, on this quality also depends the pressure that can be supported by the concrete on the part of the air cushions 32. This is why means are provided for permanently regulating the pressure exerted on the surface 39 by the air cushions. air 32. As such, each air cushion 32 is equipped with a pressure detector 41. In an air cushion, the pressure is a function of the load supported by the air cushion. For example, when the load increases, the air cushion gets closer to the ground, which reduces its peripheral leakage rate and increases the pressure drop caused by this leak. As a result, the pressure increases until it balances the new load. The air cushion then stabilizes at this new altitude for which the pressure exerted by the compressed air inside its chamber balances the load to be supported.

In view of the above, we understand another advantage of regulating the pressure of the air cushions in the device described: if the pressure in the air cushions is substantially constant, the altitude of the air cushions increases above the surface 39 is substantially constant, and the parasitic movements transmitted by the air cushions to the extrusion table 23 are minimized.

From the above explanations relating to air cushions in general, it is also understood that to regulate the pressure in the air cushions 32, it is necessary to act not on the supply pressure of the air cushions, but on the load they bear.

For this purpose, a movable ballast 42 is mounted in a movable manner along each of the beams 28. In practice, each ballast 42 is constituted by a carriage rolling on the upper surface of the beam by means of rollers 43. In addition, the ballast 42 carries on each side of the beam 27 associated with a lateral guide lug 44, which in turn carries an anti-detachment wheel 46 bearing under the upper wing of the beam 27, which in the example is a beam I. A belt 47 bypassing an output pulley 48 of a servo motor 49 and a return pulley 51 is hooked by its two ends 52 to two opposite faces of the ballast 42. The strand of the belt 47 which is continuous between the pulleys 49 and 51 (the upper strand in FIG. 1) passes through a conduit 53 formed through the ballast 42. The signals supplied by the detector 41 of each air cushion 32 is sent to the motor 49 carried by the same beam 27 so that the latter controls the movement of the corresponding ballast 42 in the direction tending to reduce the pressure in the cushion 32 to a predetermined set value.

The device according to the invention further comprises means for detecting the position of the tool with respect to at least one reference surface.

In the example shown, these means comprise feelers 54 (FIG. 2) each cooperating with one of the wires 4, the reference surface therefore being that defined by the wires 4, which on either side of the road to be produced, are arranged at equal height above the theoretical plane of the surface 39.

The surface 39 of the pavement produced is also used as a reference surface, and more particularly two regions of this surface located in the vicinity of the lateral edges 56 of the surface 39 and at a certain distance behind the extrusion table 23, by example three meters behind table 23.

To carry out this detection, the machine according to the invention comprises two devices 57 known as "drag rules" comprising a rule 58, one front end of which is connected to the rear face of the extrusion table by a traction cable 59 (FIG. 1 ) parallel to the surface 39. Each end of the rule 58 rests on the surface 39 by a pad 61. Each rule 58 carries an emitter 62 of electromagnetic ray 63 which may be a UV, X or laser ray. The position of each detector 62 is precisely adjusted so that the ray 63 is emitted parallel to the surface 39 as detected by the two associated pads 61, and at a well-determined height above the surface 39 thus detected.

The rear face of the extrusion table 23 carries, opposite each emitter 62, a detector 64 close to one of the lateral ends of the table. As shown in FIG. 9, the sensitive surface 66 of the detector 64 is subdivided into vertically staggered zones. These are for example photoelectric cells staggered vertically. Each detector 64 emits an output signal constituted for example by a current whose intensity is a function of the altitude of the photoelectric cell which is struck by the radius 63.

On each side of the plane P, the signals emitted by the detector 64 and by the probe 54, which also provides a current whose intensity is a function of the relative height of the corresponding end of the table 23 relative to the wire 4 neighbor, are used to adjust the height position of said end of the table 23, thanks to the jack 38 located on the same side of the plane P.

In practice, as shown in Figure 10, the signal from the output 67 associated with the probe 54 and the sigal from the output 68 of the detector 64 located on the same side of the plane P, are added with a weighting if necessary. , in an adder circuit 69. The outgoing signal is amplified by means of an amplifier 71. The output 72 of the amplifier 71 is used to control a proportional solenoid valve 73 in turn controlling the supply of the jack 38 located in the same side of plane P.

The signals present on outputs 67 and 68 are added algebraically by circuit 69.

This means that:
- if the probe 54 detects for the corresponding end of the table 23 an insufficient height compared to the wire 4 and if the detector 64 also detects an insufficient height compared to the rule 58, the two signals are added to control a significant flow to the corresponding cylinder 38, in the direction of the rise of the table 23;
- the same applies if the probe 54 and the detector 64 detect an excessive height of the table 23 relative to the wires 4 and relative to the rule 58 respectively ; however, the jack 38 is then controlled in the direction of descent;
- if the detections of the probe 54 and of the detector 64 are contrary, (for example if the detector 64 detects an excessive height of the tool 23 relative to the rule 58 while the probe 54 detects an insufficient height relative to the wire 4 ), the signal supplied by the detector 64 is subtracted from that supplied by the probe 54, in order to limit the flow rate sent to the jack 38 in the direction determined by the probe 54.

In practice, the detection carried out by reference to the surface 39 acts as a damper with regard to the corrections controlled by reference to the wires 4. For example, if a section of roadway has been made slightly below the theoretical dimension, the movement of the tool 23 to correct its position will very quickly cause a height signal from the detectors 64, which refer to the section too low, a signal which will slow the subsequent rise of the tool 23 under the control of the probes 54.

The chassis-bridge 27 is designed to allow its two beams 27 to pivot independently of one another around the axis XX in a certain relative angular movement of the order, for example of about 2 cm at the right of the extrusion table 23. This is made possible in particular by the articulated mounting of the spacer 29. For the same purpose, the columns 36 have a slight lateral clearance in the guides 34. This limited independence of the beams 27 relative to one another the other allows the pressure in each cushion 32 and the height of each end of the tool 23 to be adjusted independently.

The machine further comprises, behind the hinge axis XX, two jacks 74 each interposed between the frame 1 and a respective one of the beams 28. The jacks 74 are provided to support the chassis-bridge 27 without it takes support on its air cushions 32. This can be necessary at the start of construction, when there is not yet an adequate surface behind the machine. This may still be necessary when, for example following an incident, the pressure in the air cushions 32 is insufficient to support the bridge chassis 27. In this case, the actuation of the jacks 74 is automatic to avoid deterioration the surface 39. Finally, the jacks 74 are used during transport of the machine.

In operation, the concrete collected between the front side forms 7 (Figure 4) is distributed by the screw 9 (Figure 5), then by the distributors 16 to the rear side forms 13 (Figure 6), pre-equalized by the bar 19, vibrated (FIG. 7) then leveled definitively by the extrusion table 23 (FIG. 8) which forms, with the side forms 13, a mobile extrusion tunnel.

For this extrusion to take place, a motor 76 of the machine, mounted on the frame 1, drives the tracks 2. At the same time, the frame 1 is self-positioning in height thanks to the feelers 6 and to the jacks 3.

The extrusion table 23 is located halfway between the axis XX and the air cushions 32. The axis XX, being carried by the frame 1 stabilized in height, only undergoes from the frame 1 the weak vertical movements which could not be filtered by the self-positioning device 3, 4, 6. The pitching movements of the frame 1 are filtered by the joint XX and are therefore not transmitted in the form of amplified vertical oscillations with tool 23.

At its rear end, the chassis 27 rests on the worked surface 39. The only oscillations to which this end of the bridge chassis can be subjected are due to possible defects in the surface 39 and to possible vertical movements of the air cushions 32 relative to on the surface 39. These two types of disturbances are of very small amplitude. The tool 23 is therefore suspended midway between two support lines (joint XX and air cushion 32) none of which is exposed to significant disturbances. In addition, each disturbance is only transmitted with an amplitude divided by two to the tool 23.

In addition, any error in the position of the tool 23 is detected by the probes 54 and / or by the detectors 64 and the position of the tool is corrected by means of the jacks 38. The quality of uniformity of the worked surface 39 this is further improved, which in turn improves the quality of the support provided to the bridge chassis 27 by the air cushions 32.

Of course, the invention is not limited to the examples described and shown.

The invention could be applied to other types of tool, for example surface cutters.

It is not essential to detect the position of the tool and to remedy residual defects in its positioning. An already satisfactory quality of solid is obtained if the tool is, during work, fixed to the chassis-bridge, the tool being able however to be adjustable in height to allow the realization of coatings of different thicknesses.

The height adjustment of the tool could be carried out by adjusting the height of the chassis-bridge 27 with respect to the air cushions 32 or with respect to the frame 1 (height adjustment of the axis X-X).

It is also conceivable that the frame rests on the tracks 2 without means of self-positioning in height, the only position detection being made on the tool, the tool self-positioning by reference to marks constituted by the wires 4 and / or by spokes 63.

It would also be possible that only the frame 1 includes detectors such as the probes 6, but that the frame 1 is not self-positioned in height relative to the tracks 2, the information coming from the probes being used to auto-position the tool, for example using the jacks 38.

For the support of the chassis-bridge on the worked surface, one can provide, instead of air cushions, pads, one or more running gear with large contact area (low pressure tires) etc ...

Claims (25)

1. Method for opening a ground surface, in which a machine carrying a tool (23) which is in contact with said surface is moved along the surface to be opened, while means (3, 38) are adjusted in height ) supporting at least indirectly the tool (23) so that it follows a trajectory substantially independent of the irregularities of an unworked region (5) of the ground on which support means on rough ground (2) located upstream of a rear transverse end (26) of the tool (23), the tool taking support, during work, under a chassis-bridge, one front end of which is supported by the support means on bare ground ( 2) by means of an articulation (31) of axis (XX) transverse to the median longitudinal plane (P) of the machine, characterized in that one rests a rear end of the bridge chassis (27) on the worked surface (39) under a sufficiently low pressure to avoid any significant alteration of e the worked surface (39). 2. Method according to claim 1, characterized in that said pressure is adjusted by displacement of a ballast (42) along the chassis-bridge (27). 3. Method according to claim 2, characterized in that said pressure is detected and the ballast position is adjusted continuously (42) so as to maintain said pressure constant. 4. Method according to claim 3, characterized in that the rear end of the bridge chassis rests on the worked surface (39) by means of at least one air cushion (32), and to detect said pressure, a pressure prevailing in the air cushion (32) is detected. 5. Method according to one of claims 1 to 4, characterized in that an extrusion table (23) is used as a tool, forming part of a movable formwork in form of tunnel (23, 13) which is supplied with a covering material of the cement or bitumen concrete type (8). 6. Method according to one of claims 1 to 5, characterized in that a tool (23) is used, the useful width of which is greater than a free width between the bearing means on rough ground (2). 7. Method according to one of claims 1 to 6, characterized in that the pressure exerted on the ground by the mobile and distributed support means (32) is adjusted to about 100 to 500 g / cm₂. 8. Method according to one of claims 1 to 7, characterized in that by reference to an ideal surface which the surface of the worked floor must follow in parallel (39), the height position of a frame is adjusted on the one hand (1) carrying the articulation (31) and to which the support means on bare ground (2) are connected, and on the other hand the height position of the tool (23). 9. Method according to claim 8, characterized in that the height position of the tool (23) is adjusted relative to the chassis-bridge (27). 10. Method according to claim 8 or 9, characterized in that the reference surface is defined by means of wires (4) arranged at a fixed station longitudinally on either side of the path of the machine, and in that is made to cooperate with these son (4) of the probes (54) connected to the tool (23). 11. Machine for opening a ground surface, in particular for implementing the method according to one of claims 1 to 10, comprising a frame (1), which is movably supported on an unworked region of the ground ( 5) by means of support on bare ground (2), a chassis-bridge (27), one front end of which is supported by the frame (1) by means of an articulation (31) of axis (XX) transverse to the median longitudinal plane (P) of the machine, and one rear end of which is provided with movable bearing means (32) on the ground, a tool (23) mounted under the chassis-bridge (27) and comprising a rear transverse end (26) situated behind the support means on rough ground, means (3, 38) for adjusting the height of the means (1 , 26) supporting at least indirectly the tool (23) so that it follows a trajectory substantially independent of the irregularities of said region of the unworked ground (5), characterized in that the support means (32) of the rear end of the bridge chassis are movable support means distributed over the worked surface (39). 12. Machine according to claim 11, characterized in that the rear transverse end (26) of the tool (23) has a useful width greater than a free transverse distance between the bearing means on rough ground (2) . 13. Machine according to one of claims 11 or 12, characterized by means (54, 64) for detecting the position of the tool (23) relative to a reference surface, the detection means providing a signal control of at least some (38) means for adjusting the height of the tool (23). 14. Machine according to claim 13, characterized in that the detection means comprise feelers (54) intended to follow marks (4) located at a fixed position longitudinally on either side of the surface to be worked. 15. Machine according to claim 13 or 14, characterized in that the detection means comprise means (57, 64) for detecting the position of the tool (23) relative to a region of the worked surface (39) located at a distance behind the tool (23). 16. Machine according to claim 15, characterized in that the means for detecting the position of the tool (23) relative to a region of the worked surface (39), comprise means (57) dragged by the machine in contact with said region of the worked surface (39), and means (62, 64) for detecting the relative position of the tool (23) relative to the trailed means (57). 17. Machine according to claim 16, characterized in that the means for detecting the relative position comprise a radiation emitter (62) (63) carried by the trailed means (57), and a detector surface (66) carried by the tool (23) and sensitive to the height position where the radiation (63) strikes it. 18. Machine according to one of claims 13 to 17, characterized in that the means for adjusting the height of the tool comprise means (3) for adjusting the height of the frame (1) relative to the support means on rough ground (2) and means (38) modifying the geometry of the machine between the articulation (XX) and the distributed mobile support means (32), the means (54, 64) for detecting the position of the tool (23) providing a control signal from said means (38) modifying the geometry. 19. Machine according to claim 18, characterized in that the means modifying the geometry of the machine are means for adjusting the position of the tool (23) relative to the chassis-bridge (27). 20. Machine according to one of claims 11 to 17, characterized in that the tool is an extrusion table (23) forming with two side forms (13) an extrusion tunnel mounted downstream of means supply and distribution (7, 9, 16, 19) of a covering material (8) such as cement or bitumen concrete, the side forms (13) and the supply and distribution means (7, 9, 16, 19) being carried by the frame (1). 21. Machine according to one of claims 11 to 17, characterized in that the machine comprises means (74) for supporting the chassis-bridge (27) relative to the frame (1) in the absence of support of the chassis-bridge (27) on the worked surface (39), in particular at the start of a structure. 22. Machine to open a ground surface according to one of claims 11 to 21, characterized in that the distributed mobile support means (32) comprise at least one air cushion. 23. Machine for opening a ground surface according to one of claims 11 to 22, characterized by means (42 to 44, 46 to 49) for adjusting the pressure exerted on the worked surface (39) by the means of distributed mobile support (32). 24. Machine for opening a ground surface, according to claim 23, characterized in that the means for adjusting the pressure comprise a ballast (42) movable along the chassis-bridge (27). 25. Machine for opening a ground surface according to one of claims 11 to 24, characterized in that the chassis-bridge (27) comprises two longitudinal elements (28) having a limited angular independence around the axis of articulation (XX) and each supporting the tool (23) on a respective side of a median longitudinal plane (P) of the machine.

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