EP0705941A1 - Membrane apparatus with inclined piezometer - Google Patents

Abstract

The equipment for measuring the mechanical characteristics of the ground includes dropping a membrane tube into a bore hole in the ground. A liquid is introduced under pressure into the tube, and the increase in volume of the tube is then measured as a function of the pressure exerted. A pressure sensor is dropped into the ground into a position just above the maximum deformations of the membrane tube in order to determine the interstitial pressure in the region of the probe. The pressure sensor is a piezoelectric device, and there is also a piston and hydraulic element to prevent the collapse of the tube.

Description

INTRODUCTION

• 1. essai de pénétration statique
• 2. essai pressiométrique

Various in-situ tests are used to study the mechanical characteristics of the soil, as well as the bearing capacity and compaction of the soil, including:

• 1. static penetration test
• 2. pressuremeter test

STATIC PENETRATION TEST

• Faire pénétrer le tube vertical dans le sol avec une vitesse connue.
• Au cours de la pénétration et à chaque 20 cms de profondeur, on enregistre la mesure de resistance du sol contre la pénétration du tube et ainsi, la mesure de la pression interstitielle.

This type of experiment consists in using a vertical tube, the end of which contains a force sensor and another of the pore pressure.
The implementation method is carried out as follows:

• Make the vertical tube penetrate the ground with a known speed.
• During penetration and at every 20 cm depth, the measurement of resistance of the soil against the penetration of the tube is recorded and thus, the measurement of pore pressure.

So in this type of experiment, all the measurements are a function of the penetration, and the speed of penetration is a factor of the implementation method.

• 1 apparait le problème de colmatage qui empeche de mesurer la pression interstitielle.
• 2 il s'est avéré que :
  • a. toute modification de la vitesse de pénétration provoque un effet important sur la valeur de la pression interstitielle.
  • b. si on fait des essais avec deux appareils differents de meme type dans le meme endroit du meme site. Alors, les mesures obtenues sont différentes les unes des autres.

The disadvantage of this type of experience is that it:

• 1 appears the clogging problem which prevents measuring the pore pressure.
• 2 it turned out that:
  • at. any change in the penetration speed has a significant effect on the value of pore pressure.
  • b. if we test with two different devices of the same type in the same place on the same site. So the measurements obtained are different from each other.

Consequently, the measurement of pore pressure during penetration experiments lacks precision and comes up against the problem of clogging. However, it is not possible to accept measurements of the pore pressure as a function of the resistance of the soil during penetration to determine the bearing capacity and the compaction of the soil.

2. PRESSIOMETRIC TEST

• 2.1 pressiomètre avec foravage préalable (PFP)
• 2.2 pressiomètre à enfoncé (PMF)
• 2.3 pressiomètre auto-foreur (PAF)

There are three categories of pressuremeter based on their method of implementation:

• 2.1 pressuremeter with preliminary foravage (PFP)
• 2.2 depressed pressuremeter (PMF)
• 2.3 self-drilling pressure gauge (PAF)

2.1 pressuremeter with prior drilling (PFP)

It is a three cell probe installed in a cavity. The probe is supplied by a pressurized liquid. The increase in the pressure of this liquid causes the probe to swell. For each meter of depth, the bearing capacity and the compaction of the soil are determined by the relationship between the measurements of change of the previous pressure and the change of the volume of the central measurement cell.

• a) L'inexistance des mesures de la pression interstitielle,
• b) La détermination de la capacité portante et le tassement dépendent des expériences et des déductions,
• c) Ce genre d'essai nécissite un temps assez long sur le site.

The disadvantage of this type of device:

• a) The non-existence of the pore pressure measurements,
• b) The determination of the bearing capacity and the compaction depend on experiences and deductions,
• c) This kind of test requires a fairly long time on the site.

2.2 PRESSURE GAUGE PRESSED (P MF)

Penetration into the soil by means of a vertical tube terminated by a single cell membrane probe supplied with a pressurized liquid.

For each meter of depth, the penetration of the system is stopped to determine the bearing capacity and the settlement followed by the same steps of the previous procedure.

This device has the same advantages and the same defects as that described (2.1) but the rework in this case is the result of the backflow.

2.3 SELF-DRILLING PRESSIOMETER (PAF)

The device consists of a single cell probe preceded by a thin-walled corer carrying the measuring membrane cell.

• l'appareil français:
  pressiomètre auto-foreur (PAF) du LCPC avec sa membrane soutenue par un liquide.
• l'appareil anglais:
  pressiomètre auto-foreur de Cambridge.

There are two kinds of devices:

• the French apparatus:
  LCPC self-drilling pressiometer (PAF) with its membrane supported by a liquid.
• the English apparatus:
  Cambridge self-drilling pressuremeter.

The two devices agree on the principle, but the English device also includes a pore pressure sensor in the middle of the membrane cell, this membrane cell is equipped with springs with strain gauges.

These two types of apparatus make it possible to eliminate the drawbacks of the reworking of the soil in contact with the probe by prior drilling or by pumping back the depression.

• a) Dans l'appareil anglais Le pressiomètre de Cambridge (PAF), étant donné que le capteur de la pression interstitielle est fixé dans la cellule de mesure, celui-ci mesure la pression interstitielle en fonction de la pression horizontale exercée par la sonde sur le sol dans l'anneau plastique constitué directement autour de la cavité; surtout dans le cas des sols cohérants . et par rapport aux sols non-cohérants les liens entre les contraintes crées just autour la cavité et la consolidation du sol deviennent trop complex. Mais, pour déterminer la capacité portante et le tassement du sol, l'intérêt est de relever les mesures dans l'anneau élastique en son extérieur.
• b) Mesurer les déformations d'une cavité s'exprime ni les déformations plastiques ni élastiques étant donné que l'anneau élastique empêche l'anneau plastique qu'il déforme librement plastique.

The disadvantage of this type of device:

• a) In the English device The Cambridge pressuremeter (PAF), since the pore pressure sensor is fixed in the measuring cell, this measures the pore pressure as a function of the horizontal pressure exerted by the probe on the soil in the plastic ring formed directly around the cavity; especially in the case of cohesive soils. and compared to non-coherent soils the links between the stresses created just around the cavity and the consolidation of the soil become too complex. But, to determine the bearing capacity and the compaction of the soil, the interest is to take the measurements in the elastic ring outside.
• b) Measuring the deformations of a cavity is expressed neither plastic nor elastic deformations since the elastic ring prevents the plastic ring that it freely deforms plastic.

• La pression du fluide alimentant la cellule à membrane.
• Le volume de la cellule à membrane.
• La pression interstitielle d'un élément, sa place est précis avec certaines conditions pour que le mesures s'accomodent avec la concept de la méthode scientifique concernant l'appareil objet de la présente invention. Ces conditions du placement du capteur de la pression interstitielle ( piezomètre ) sont :
  • a. au niveau des déformations maximales de la cellule à membrane.
  • b. au voisinage de la cellule à membrane et en deça d'une distance de 10 cms.

C'est porquoi L'appareil l'objet de la présente invention est constitué de deux parties principales, ne peut pas séparer l'un de l'autre. Les deux parties sont:

• a. appareil à membrane: l'origine(la ressource) de la charge. La pression du fluide alimentant la cellule à membrane, exerce une pression horizontale sur la cavité du sol. Cette pression conduit a une expansion de la cavité resultant du gonflement de la cellule à membrane.
• b. piezomètre (capteur de la pression interstitielle ): au voisinage de l'appareil à membrane dans un emplcement précis avec ses certaines conditions .

I would like to say that:
It is impossible to determine the bearing capacity and the compaction of the soil by the sole measurement of pore pressure. However, it is necessary to measure the relationships of each of the changes in pore pressure and the resistance of the soil as a function of a load exerted.
Thus, the object of the apparatus which is the subject of the present invention is to construct and record the measurements of the relationships between the following three parameters:

• The pressure of the fluid supplying the membrane cell.
• The volume of the membrane cell.
• The pore pressure of an element, its place is precise with certain conditions so that the measurements can be accommodated with the concept of the scientific method relating to the apparatus which is the subject of the present invention. These conditions for placing the pore pressure sensor (piezometer) are:
  • at. at the level of the maximum deformations of the membrane cell.
  • b. in the vicinity of the membrane cell and within a distance of 10 cms.

This is why the apparatus which is the subject of the present invention consists of two main parts, cannot separate from one another. The two parts are:

• at. membrane device: the origin (resource) of the charge. The pressure of the fluid supplying the membrane cell exerts horizontal pressure on the soil cavity. This pressure leads to an expansion of the cavity resulting from the swelling of the membrane cell.
• b. piezometer (pore pressure sensor): in the vicinity of the diaphragm device in a precise location with certain conditions.

• 1. piezomètre à enfoncé.
• 2. piezomètre pour forage.

on se heurte à l'inconvenient qui suit :

• 1. Etant donné que; la distance requise entre l'axe de l'appareil à membrane et celui du piezomètre, doit etre loin d'une courte distance. Alors, l'installation de deux apparerils en parallel conduit à des remaniements trop élèvés, non-acceptable quel que soit la méthode d'installation de chacun des deux appareils:
  • a. dans le cas d'un ensemble, soit de deux appareils pour forage ou soit un appareil à enfoncé et l'autre pour forage; l'installation conduit à détruire la partie du sol entre les deux appareils.
  • b. dans le cas d'installation d'un ensemble de deux appareils à enfoncé en parallel il resulte un refoulement trop élèvé.
• 2. Les piezomètres qui sont actuellement utilisés ne sont pas adaptés à mesurer la pression interstitielle à chaque mètre de profondeur.

So, if we compose the invention of a set of one of the diaphragm devices in parallel with one of the existing piezometers, And given that, the existing piezometers can be classified in two categories:

• 1. piezometer pressed.
• 2. piezometer for drilling.

we come up against the following disadvantage:

• 1. Given that; the distance required between the axis of the membrane apparatus and that of the piezometer must be far from a short distance. So, the installation of two devices in parallel leads to too high modifications, not acceptable whatever the method of installation of each of the two devices:
  • at. in the case of a set, either of two apparatuses for drilling or either a recessed apparatus and the other for drilling; the installation leads to destroying the part of the ground between the two devices.
  • b. in the case of installation of a set of two devices pushed in parallel it results in too high a backflow.
• 2. The piezometers which are currently used are not suitable for measuring the pore pressure at each meter of depth.

• 1. Montage d'un capteur de la pression interstitielle (piezomètre) a l'extrémité de tube de manoeuvre d'un piston incliné directement juste au dessus d'une cellule à membrane (d'un appareil à membrane) qui exerce une pression horizontale sur la cavité du sol.
  Le but du piston incliné est d'amener le capteur de la pression interstitielle (piezomètre) au voisinage de la cellule à membrane pour que le piezomètre soit au niveau des déformations maximales de la cellule et sur une distance supérieure ou égale au maximum au rayon de l'anneau plastique crée autour de la cavité.
• 2. L'introduction du piezomètre (capteur de la pression interstitielle ) s'effectue par pénétration au moyen du tube de manoeuvre du piston incliné; Pour éviter le problème du colmatage qui gene la mesure de la pression interstitielle -ce qui est le cas dans l'essai de pénétration - on procéde de la manière suivante:
  • 2.1 Maintenir en permanence le piezomètre dans un fourreau dans le tube d'intermediaire de l'appareil, quel que soit la méthode de mise en place de l'appareil l'objet de la présente invention.
  • 2.2 Le piezomètre, au bout du tube de manoeuvre du piston incliné, est emboité dans un cylindre qui sert à éviter le colmatage pendant la pénétration du tube de manoeuvre du piston incliné. Lors du mouvement où le piezomètre approche du niveau de mesure, il se dégage du cylindre qui reste sur place tout en étant relié à celui-ci par des liens souples attachés a l'extrémité profonde de la chambre d'huile du piston incliné. le tube de manoeuvre contenant le piezomètre continue sa course jusqu'au niveau des mesures .
  • 2.3 Le tube de manoeuvre du piston incliné contenant le piezomètre a son embout, contient un élément hydraulique assurant le decolmatage pendant sa pénétration .

It is confirmed that the essential in the design of the present invention can be summarized as follows:

• 1. Installation of a pore pressure sensor (piezometer) at the end of the operating tube of a piston inclined directly just above a membrane cell (of a membrane device) which exerts a horizontal pressure on the soil cavity.
  The purpose of the inclined piston is to bring the pore pressure sensor (piezometer) in the vicinity of the membrane cell so that the piezometer is at the level of the maximum deformations of the cell and over a distance greater than or equal to the maximum of the radius of the plastic ring created around the cavity.
• 2. The introduction of the piezometer (pore pressure sensor ) is effected by penetration by means of the operating tube of the inclined piston; To avoid the problem of clogging which hinders the measurement of the pore pressure - which is the case in the penetration test - we proceed as follows:
  • 2.1 Maintain the piezometer permanently in a sheath in the intermediate tube of the apparatus, whatever the method of positioning the apparatus which is the subject of the present invention.
  • 2.2 The piezometer, at the end of the inclined piston operating tube, is fitted into a cylinder which serves to prevent clogging during penetration of the inclined piston operating tube. During the movement where the piezometer approaches the measurement level, it emerges from the cylinder which remains in place while being connected to the latter by flexible links attached to the deep end of the oil chamber of the inclined piston. the maneuvering tube containing the piezometer continues its course up to the level of the measurements.
  • 2.3 The operating tube of the inclined piston containing the piezometer at its tip, contains a hydraulic element ensuring the unclogging during its penetration.

• Le piston incliné est une partie indivisible de l'appareil objet de la présente invention (appareil à membrane à piezo - incliné ) et son role est une partie de la méthode de mise en oeuvre .
     Le piston incliné est dimenssioné sous le condition suivante :
     Le déplacement du piston incliné ( double track ) est suffisement long pour permettre au tube de manoeuvre du piston incliné d'amener le piezomètre, qui est fixé à son extrémité, jusau'à l'endroit précis.
• On n'enregistre jamais les mesures de la pression interstitielle au cours de la pénétration ni du tube de manoeuvre du piston incliné ni de l'appareil objet de la présente invention .

Following the above explanations, it should be noted that:

• The inclined piston is an indivisible part of the device which is the subject of the present invention (piezo diaphragm device - inclined) and its role is a part of the implementation method.
  The inclined piston is dimensioned under the following condition:
  The displacement of the inclined piston (double track) is long enough to allow the operating tube of the inclined piston to bring the piezometer, which is fixed at its end, to the precise location.
• One never records the measurements of the pore pressure during the penetration neither of the maneuvering tube of the inclined piston nor of the apparatus object of the present invention.

DESCRIPTION OF THE DEVICE

• Type I : Appareil à membrane à enfoncer à piezoincliné
     La sonde (l'ensemble de l'appareil à membrane et du piezomètre) est enfoncée dans le sol par l'intermédiaire d'une tige verticale d'un diamètre d'au moins 4.0 cm. Toutes les canalisations qui alimentent la sonde, passent dans la tige verticale et dans le corps du piston incliné dehors de sa chambre d'huile.
• Type II :Appareil à membrane pour forage à piezoincliné
     Soit par forage (d'un diamètre d'au moins 6.00cm) préalable ou soit par autoforeur, car toutes les canalasations qui alimentent la sonde passent dans la cavité et autour du piston incliné.
  Le tube de manoeuvre du piston incliné est en forme télésopique.

   Détails explicatifs des dessins de l'appareil objet de la présente invention de type I : de page 1.4 à 4.4

• fig 1 : montre l'assemblage global du système de l'appareil de l'invention du type I pour l'étude de mécanique des sols.

  (7)

  : cellule à membrane.

  (18)

  : L'appareil objet de la présente invention à enfoncer de type I (appareil à membrane à enfoncé à piezo-incliné)

  (6)

  : Niveau de mesure . Ce niveau de mesure se répète tous les mètres par rapport à la surface du sol.

  (5)

  : Le piezomètre (pierre poreuse contient le capteur de la pression interstitielle)

  (8)

  : Piston à l'extrémité de son tube de manoeuvre (12) est le piezomètre (5)

  (15)

  : Ordinateur raccordé au piezomètre (5) pour enregistrer la pression interstitielle au niveau (6) au voisinage de la cellule à membrane (7) .

• Coupe verticale suivant S-S, montre:
  • l'emplacement des coupes suivant A-A, B-B, C-C et D-D, voir page page 3 / 4
  • l'emplacement du détail (F), voir page 4.4

    (8)

    : piston incliné par rapport à l'axe vertical du système

    canalisations (1), (3)

    : ressources de pression pour faire sortir et rentrer du tube de manoeuvre (12) du piston (8).

    canalisation (2)

    :

    comprend deux voies

    :

    • une pour raccorder le capteur dans le piezométre (5) à l'ordinateur (15) (fig (1)).
    • l'autre voie pour fournir du fluide sous pression qui nettoie la pierre poreuse du piezométre (5)

    (20)

    : espace autour du piezométre (5)

    (13)

    : la chambre d'huile du piston (8)

    (12)

    : le tube de manoeuvre du piston (8) qui glisse autour d'un tube fixe (17).

• page 3/4 : coupe suivant A-A , B-B, C-C, D-D.

  detail (F)

  : detail au bout du tube de manoeuvre (12) du piston (8) et le systéme de la protection du piezométre (5) ( pierre poreuse et le capteur ) du colmatage pendant la pénétration dans le sol

  (16)

  : piéces d'etanchéietés.

  (10)

  : cylindre qui emboite la pierre poreuse du piezométre(5).

  (14)

  : lien qui relie le cylindre (10) au systéme et est en longueur de 5 cm moins long que la longueur du tube de manoeuvre (12) du piston (8).

• 4. L'appareil objet de l'invention de type (I), ( appareil à membrane à enfoncé à piezo - incliné ), contient quatre canalisations numérotées de (1) à (4) :

  (1)

  : Dans la canalisation (1) l'huile sous pression fait sotir le tube (12) de manoeuvre du piston (8) de sa place à une distance suffisante pour arriver au niveau (6); niveau de déformation maximale de la sonde pressiométrique (7).

  (2)

  : La canalisation (2) comprend deux voies :

  • L'une pour contient un cable électrique qui joint le capteur du piezomètre (5) à un ordinateur (15) de l'enregistrement de la pression interstitielle.
  • Dans l'autre voie passe un fluide sous pression qui assure le nettoyage de la pierre poreuse du piezomètre (5).

  (3)

  : La canalisation (3) contient l'huile sous pression permettant la retour du tube de manoeuvre (12) du piston (8) à sa position initiale.

  (4)

  : La canalisation (4) alimente la sonde pressiométrique (7) par ses ressources des chargements ( fluide sous pression ).

The device object of the invention can be in two categories based on the method of positioning the probe.

• Type I: Piezoinclined diaphragm device
  The probe (all of the membrane apparatus and the piezometer) is driven into the ground by means of a vertical rod with a diameter of at least 4.0 cm. All the pipes supplying the probe pass through the vertical rod and into the body of the inclined piston outside its oil chamber.
• Type II: Membrane apparatus for piezoinclined drilling
  Either by drilling (with a diameter of at least 6.00 cm) beforehand or by self-drilling, because all the canalizations which feed the probe pass into the cavity and around the inclined piston.
  The operating tube of the inclined piston is in telesopic shape.

Explanatory details of the drawings of the device which is the subject of the present invention, type I: from pages 1.4 to 4.4

• fig 1: shows the overall assembly of the system of the apparatus of the invention of type I for the study of soil mechanics.

  (7)

  : membrane cell.

  (18)

  : The device which is the subject of the present invention for type I driving (piezo-inclined driving diaphragm device)

  (6)

  : Measurement level. This level of measurement is repeated every meter from the ground surface.

  (5)

  : The piezometer (porous stone contains the pore pressure sensor)

  (8)

  : Piston at the end of its operating tube (12) is the piezometer (5)

  (15)

  : Computer connected to the piezometer (5) to record the pore pressure at level (6) in the vicinity of the membrane cell (7).

• Vertical section following SS, shows:
  • the location of the cuts according to AA, BB, CC and DD, see page page 3/4
  • the location of the detail (F), see page 4.4

    (8)

    : piston inclined to the vertical axis of the system

    pipes (1), (3)

    : pressure resources for removing and returning from the operating tube (12) of the piston (8).

    pipeline (2)

    :

    includes two tracks

    :

    • one to connect the sensor in the piezometer (5) to the computer (15) (fig (1)).
    • the other way to provide pressurized fluid which cleans the porous stone of the piezometer (5)

    (20)

    : space around the piezometer (5)

    (13)

    : the piston oil chamber (8)

    (12)

    : the piston operating tube (8) which slides around a fixed tube (17).

• page 3/4: section along AA, BB, CC, DD.

  detail (F)

  : detail at the end of the operating tube (12) of the piston (8) and the piezometer protection system (5) (porous stone and the sensor) from clogging during penetration into the ground

  (16)

  : sealing parts.

  (10)

  : cylinder which fits the porous stone of the piezometer (5).

  (14)

  : link which connects the cylinder (10) to the system and is 5 cm shorter in length than the length of the operating tube (12) of the piston (8).

• 4. The device which is the subject of the invention of type (I), (device with a piezo-depressed membrane - inclined), contains four pipes numbered from (1) to (4):

  (1)

  : In the pipeline (1) the oil under pressure causes the piston operating tube (12) to come out of its place at a sufficient distance to reach the level (6); maximum deformation level of the pressuremeter probe (7).

  (2)

  : The pipeline (2) has two channels:

  • One for contains an electric cable which joins the piezometer sensor (5) to a computer (15) for recording the pore pressure.
  • In the other way passes a fluid under pressure which ensures the cleaning of the porous stone of the piezometer (5).

  (3)

  : The line (3) contains the pressurized oil allowing the return of the operating tube (12) of the piston (8) to its initial position.

  (4)

  : The pipe (4) supplies the pressuremeter probe (7) with its loading resources (fluid under pressure).

The porous stone of the piezometer (5) is fitted by a cylinder (10) which serves to avoid clogging during the penetration of the system as well as to prevent the re-entry of small grains of soil in the oil chamber (13) of the piston (8).

The space (20) allows the establishment of links (14).

The pressurized fluid circulating in the pipe (2) prevents the cylinder (10) from moving relative to the porous stone of the piezometer (5). During the movement where the piezometer (5) approaches level (6), it emerges from the cylinder (10) which remains in place by the effect of the link (14).

The maneuvering tube (12) containing the piezometer (5) continues its stroke up to level (6). The fluid in the pipe (2) is evacuated through the porous stone of the piezometer (5).
In its movement back to its initial position, the operating tube (12) of the piston (8) fits into the cylinder (10) and drives it in its movement.

Claims (5)

Method for measuring the mechanical properties of soils of the type consisting in driving a membrane cell (7) into which a liquid is introduced under pressure vertically or by drilling, in measuring the increase in volume of the membrane cell as a function of the pressure exerted, characterized in that it consists in introducing into the soil in an inclined direction from the just upper part of the membrane cell (7) a pressure sensor to a position opposite from the level (6) of the maximum deformations of the membrane cell (7) and to measure the change in the measurements of the pressure sensor at level (6) as a function of the pressure in the membrane cell (7) so as to measure the pore pressure in the vicinity of the membrane cell (7). Device for measuring mechanical characteristics of soils for the implementation of the method according to claim 1 of the type comprising a vertical intermediate tube comprising a membrane cell (7), characterized in that it consists of a sheath provided with '' a piston inclined (8) relative to the axis of the vertical tube, the intermediate and at the end of the operating tube (12) of the piston (8), a piezometer (5) provided with the pore pressure sensor and hydraulic element to avoid clogging. Device according to Claim 2, characterized in that this membrane cell (7) is supplied with pressure by an intermediate tube, and in that it additionally comprises three pipes; the pipes (1) & (3) under pressure intended to bring out and re-enter the maneuvering tube (12) of the piston (8), and the pipe (2) comprising two channels, one for connecting the pore pressure sensor to a recording computer (15) and the other for supplying pressurized fluid ensuring the unclogging of the piezometer (5). Device according to claim 2 or 3 characterized in that the pipe (2) is fitted into a fixed tube (17) to protect it from the effect of the oil pressure in the oil chamber (13) of the inclined piston (8). Device according to any one of Claims 2 to 4, characterized in that the piezometer (5) is provided with a protective cylinder (10) and is retained by links (14).

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