PROBE FOR PRESSURE METER

Abstract

The invention relates to a probe intended to be fitted to a pressure meter and including a fluid dispenser (1), a central measuring cell (21) suitable for being inflated by a pressurized liquid, and two boundary cells (22, 23) arranged on either side of the measuring cell and suitable for being inflated by a pressurized gas. According to the invention, the cells (21-23) are made from a single resilient sleeve (2) sheathing a hollow cylindrical mandrel (3) removably and sealingly fitted onto the dispenser (1), which dispenser has to this end an external surface in the shape a cylinder.

Description

The invention concerns, in general terms, logging techniques.

More precisely, the invention concerns a probe for a pressure meter, comprising at least one fluid distributor and three inflatable annular cells, the distributor extending parallel to the axis of the probe and comprising hydraulic fluid passages and gaseous fluid passages, and the cells extending respectively over three successive adjacent longitudinal sections of the probe, surrounding the distributor, and comprising a central cell connected to at least one hydraulic fluid passage and two lateral cells, each of which is connected to at least one gaseous fluid passage.

Pressure meters have been well known to persons skilled in the art since their invention by L Ménard in 1955, and are used for evaluating mechanical parameters of soils in situ.

Once the probe has been introduced into a borehole, each inflatable cell is subjected to a pressure increasing in stages, six to fourteen in number for example, and in an arithmetic progression.

At each stage, the volume of liquid introduced into the central cell is measured at several instants after the end of the pressurisation.

These measurements are then translated into graphs from which the mechanical parameters of the terrain explored are evaluated.

In practice, the volume measurements are therefore made only with the central cell, also referred to as the “measuring cell”, the lateral cells or “guard cells” merely having the function of confining the central cell in a substantially cylindrical volume in order to guarantee that the results obtained do not depart from their field of validity.

The known probes, which constitute essential components of the existing pressure meters, suffer from several very annoying defects.

This is because these probes generally have a complex structure, so that they require long manufacturing times and high manufacturing costs.

Moreover, the intrinsic fragility of the elastic membranes used for producing the cells and the relatively high frequency of damage that results from this, now lead to significant operating delays corresponding to the time required for procuring a new probe.

In this context, the purpose of the present invention is to propose a probe free from these main defects.

To this end, the probe of the invention, also in accordance with the generic definition given by the above preamble, is essentially characterised in that the distributor has an external surface fitting within a cylinder, in that the probe also comprises a removable and sealed hollow cylindrical mandrel on the distributor and having at least three fluid orifices with a sealed separation from one another and opening out respectively in the three longitudinal sections of the probe, the orifice of the central section being connected to at least one hydraulic fluid passage and each of the other two orifices being connected to at least one gaseous fluid passage, and in that the three cells are at least partially formed by a single elastic sleeve fitted on the mandrel and divided, by means of hoops locally applying and sealing this sleeve so against the external face of the mandrel, in order to form the three longitudinal sections of the probe.

Not only can the probe thus arranged be produced easily and at less cost, but it can also easily be repaired in the event of damage by replacing the mandrel carrying the defective cells with a mandrel equipped with a new elastic sleeve.

The hoops comprise for example two end hoops, each of which consists of a metal crimp, and two intermediate hoops, each of which consist of a plurality of turns of a flexible tie coiled under tension around the sleeve.

In order to more easily achieve a seal between cells and guarantee the dimensional stability of the cells, the mandrel can have two external peripheral grooves, each intermediate hoop applying the elastic sleeve against the bottom of one of these grooves.

In a simple and effective embodiment of the probe of the invention, the turns of the flexible tie of each intermediate hoop are held with respect to one another and under tension by adhesive bonding, for example by means of a two-component adhesive.

The probe can also comprise a deformable protective mechanical sheath, for example produced from a coated textile.

In the case where such a protective sheath is used, the metal crimps are applied to this sheath.

The probe of the invention is also provided with O-ring seals applied in external peripheral grooves of the distributor and isolating from one another with a seal, the three fluid orifices formed in the mandrel.

Other characteristics and advantages of the invention will emerge clearly from the description that is given below, by way of indication and no way exhaustively, with reference to the accompanying drawings, in which:

FIG. 1 is a view in divided partial axial section of a probe according to the invention; and

FIG. 2 is a view in axial section, to an enlarged scale, of a longitudinal length of the probe illustrated in FIG. 1.

As stated previously, the invention concerns a probe intended to equip a pressure meter.

Such a probe comprises, traditionally, a fluid distributor 1 and three inflatable annular cells 21, 22 and 23.

The distributor 1 extends along the axis Z of the probe and comprises hydraulic fluid passages 11 and gaseous fluid passages 12.

The cells 21, 22 and 23 surround the distributor 1 and extend respectively over three successive adjacent longitudinal sections of the probe, denoted S1, S2 and S3.

The central measuring cell 21 is connected to a hydraulic fluid passage 11, generally consisting of water under pressure, while the guard cells 22 and 23, which are disposed on each side of the central cell 21, are each connected to a gaseous fluid passage 12, this gaseous fluid generally consisting of pressurised nitrogen.

According to the invention, the cells 21 to 23 are produced from a single elastic sleeve 2, sheathing a removable, sealed hollow cylindrical mandrel 3 on the distributor 1, this distributor for this purpose having an external surface within a cylinder.

More precisely, the mandrel 3 has three fluid orifices sealed off from one another, denoted 31, 32 and 33, and opening out respectively in the three longitudinal sections S1, S2 and S3 of the probe.

The orifice 31 of the central section S1 is connected to the hydraulic passage 11, and each of the orifices, 32 and 33, is connected to the gaseous fluid passage 12.

To define the three cells 21, 22 and 23 and form the corresponding three longitudinal sections S1, S2 and S3 of the probe, the elastic sleeve 2 is divided by means of hoops such as 4e and 4i that are locally applied and sealed off against the external face of the mandrel 3.

These hoops comprise in particular two end hoops 4e each consisting of a metal crimp.

In the case where the sleeve 2 is covered with a deformable protective mechanical sheath 5, for example produced from a coated textile, the metal crimps 4e are applied against this sheath 5.

The hoops comprise two intermediate hoops 4i intended to provide separation between the central cell 21 and the guard cells 22 and 23.

It should be stated here that, for reasons of size of representation, only the location of the hoops 4i is made visible in FIG. 1.

As shown on the other hand in FIG. 2, each of the intermediate hoops 4i is advantageously formed by a plurality of turns of a flexible tie coiled under tension around the sleeve 2, these turns preferably being held with respect to one another and under tension by adhesive bonding.

To facilitate the placing and holding of the intermediate hoops 4i, the mandrel 3 preferably has two external peripheral grooves 30, each intermediate hoop 4i thus being able to apply the elastic sleeve 2 against the bottom of one of these grooves 30.

Finally, as shown by FIG. 1, the probe of the invention is equipped with O-ring seals 6 installed in external peripheral grooves 10 of the distributor 1 and sealed off to isolate from one another the three fluid orifices 31, 32 and 33 formed in the mandrel 3.

Claims

1. Probe for a pressure meter, comprising at least one fluid distributor (1) and three inflatable annular cells (21-23), the distributor (1) extending parallel to the axis (Z) of the probe and comprising hydraulic fluid passages (11) and gaseous fluid passages (12), and the cells (21-23) extending respectively over three successive adjacent longitudinal sections (S1-S3) of the probe, surrounding the distributor (1), and comprising a central cell (21) connected to at least one hydraulic passage (11) and two lateral cells (22, 23), each of which is connected to at least one gaseous fluid passage (12), characterised in that the distributor (1) has an external surface fitting within a cylinder, in that the probe also comprise a removable and sealed hollow cylindrical mandrel (3) fitted on the distributor (1) and having at least three fluid orifices (31-33) sealed off to isolate from one another and opening out respectively in the three longitudinal sections (S1-S3) of the probe, the orifice (31) in the central section (S1) being connected to at least one hydraulic fluid passage (11) and each of the other two orifices (32, 33) being connected to at least one gaseous fluid passage (12), and in that the three cells (21-23) are at least partially formed by a single elastic sleeve (2) fitted on the mandrel (3) and divided, by means of hoops (4e, 4i) locally applying this sleeve (2) and sealed against the external face of the mandrel (3), in order to form the three longitudinal sections (S1-S3) of the probe.

2. Probe according to claim 1, characterised in that the hoops (4e, 4i) comprise two end hoops (4e), each of which consists of a metal crimp.

3. Probe according to claim 1, characterised in that the hoops (4e, 4i) comprises two intermediate hoops (4i), each of which is formed by a plurality of turns of a flexible tie coiled under tension around the sleeve (2).

4. Probe according to claim 3, characterised in that the mandrel (3) has two external peripheral grooves (30) and in that each intermediate hoop (4i) applies the elastic sleeve (2) at the bottom of one of these grooves (30).

5. Probe according to claim 3, characterised in that the turns of the flexible link of each intermediate hoop (4i) are held with respect to one another and under tension by adhesive bonding.

6. Probe according to claim 2, characterised in that it also comprises a deformable protective mechanical sheath (5), for example produced from coated textile.

7. Probe according to claim 6, characterised in that the metal crimps (4e) are applied against the protective mechanical sheath (5).

8. Probe according to claim 1, characterised in that it comprises O-ring seals (6) applied in external peripheral grooves (10) of the distributor (1) and sealed off to isolate from one another the three fluid orifices (31-33) formed in the mandrel (3).

9. Probe according to claim 2, characterised in that the hoops (4e, 4i) comprises two intermediate hoops (4i), each of which is formed by a plurality of turns of a flexible tie coiled under tension around the sleeve (2).

10. Probe according to claim 1, characterised in that it also comprises a deformable protective mechanical sheath (5), for example produced from coated textile.

11. Probe according to claim 2, characterised in that it comprises O-ring seals (6) applied in external peripheral grooves (10) of the distributor (1) and sealed off to isolate from one another the three fluid orifices (31-33) formed in the mandrel (3).