EP1229172B1 - Method and apparatus for making drilled piles in hard ground - Google Patents

Abstract

The drilling machine is fitted with detectors which measure dynamic characteristics of the drill tool. The measurements at different successive depths are stored and used to calculate a succession of variable representative of terrain quality at each depth. When a succession of values which correspond to a acceptable terrain quality is encountered, drilling is stopped.

Description

The present invention relates to a method and a machine for producing piles bored in hard ground and in particular in granite soils.

When it is necessary to carry out a set of bored piles to serve in particular as a basis for carrying out subsequent constructions, it is well known that, initially, a drilling is carried out with the required diameter and depth, then it is poured into the drilling thus carried out of possibly reinforced concrete to constitute the pile, the drilling constituting the mold in which the pile is manufactured.

One of the problems which arise in ensuring the proper construction of bored piles is to ensure that the bottom of the borehole is well located over a sufficient depth in a soil of suitable physical properties to serve as anchoring to the piles. The soil with suitable physical properties will be for example a hard rock and in particular granite. In the case of this last rock, it is necessary to ensure that the granite zone is sufficiently healthy, that is to say that the granite is non-friable and that it has little or no cracks which would be susceptible alter the mechanical resistance of the granite zone or, more generally, of the zone with high mechanical resistance.

To solve this problem, the solution currently used consists in carrying out, in the ground where the piles are to be made, cores of relatively reduced diameter of the order of 20 to 30 cm used to take rock samples from the depth. coring.

It is understood, however, that in certain cases, these cores, owing to their relatively small diameter and the fact that they are necessarily relatively spaced from one another, do not make it possible to ensure that the bored piles actually produced will have an anchoring in a layer of hard ground with the required physical properties.

A first object of the invention is to provide a method which makes it possible to ensure that the bored pile produced actually has an anchoring in a layer of ground having the required physical properties.

• on équipe la machine de forage de capteurs pour mesurer des caractéristiques dynamiques de l'outil de forage comprenant au moins certaines des caractéristiques suivantes : couple de l'outil, vitesse de pénétration de l'outil, vitesse de rotation de l'outil, poussée exercée sur l'outil ;
• on mémorise, au fur et à mesure de leur acquisition, les mesures faites par lesdits capteurs pour des profondeurs successives correspondant à un pas prédéterminé ;
• pour chaque profondeur, on calcule au moins une première variable représentative de la qualité du terrain rencontré à partir des mesures mémorisées, et on mémorise les valeurs successives de la première variable pour les profondeurs successives au fur et à mesure de leur calcul ;
• on traite les valeurs successives de ladite variable pour rechercher dans les valeurs successives de ladite variable une succession sensiblement continue de valeurs de la variable correspondant à une qualité de terrain acceptable, pour des profondeurs successives correspondant à une différence de profondeurs prédéterminée ; et
• on interrompt le forage lorsqu'on a détecté ladite succession sensiblement continue de valeurs acceptables pour ladite différence de profondeur prédéterminée.

To achieve this object according to the invention, the method of producing a pile drilled in hard ground using a drilling machine is characterized in that it comprises the following steps:

• the drilling machine is equipped with sensors to measure dynamic characteristics of the drilling tool comprising at least some of the following characteristics: tool torque, tool penetration speed, tool rotation speed, thrust exerted on the tool;
• the measurements made by said sensors are stored, as they are acquired, for successive depths corresponding to a predetermined pitch;
• for each depth, at least a first variable representative of the quality of the terrain encountered is calculated from the stored measurements, and the successive values of the first variable are stored for the successive depths as they are calculated;
• the successive values of said variable are processed to search in the successive values of said variable for a substantially continuous succession of values of the variable corresponding to an acceptable quality of terrain, for successive depths corresponding to a predetermined difference in depths; and
• the drilling is interrupted when said substantially continuous succession of acceptable values for said predetermined depth difference has been detected.

It will be understood that, in the method according to the invention, at least one variable representative of the quality of the subsoil is measured in real time, for successive predetermined depths, from measurements carried out using sensors mounted on the machine. The calculated successive values of the variable are processed to determine or detect the fact that the variable has the required value substantially continuously for a predetermined depth difference, this predetermined depth difference corresponding to the required pile anchoring height. When such a difference in depth has been detected, drilling is stopped and the pile can then be made.

It should be noted that the measurements made by the sensors, as well as the calculated values of the variable for the different depths, which will constitute evidence that the bored pile was made under the conditions laid down.

Preferably, from the parameters provided by the sensors for the different depths, two distinct variables are calculated, representative of the qualities of the soil necessary for the detection of a layer of soil having the physical properties required in order to constitute an anchorage for the pile. drilled. The detection of course relates to the values of the two variables and the drilling is interrupted when, for the two variables, there is a common predetermined depth difference.

It is understood that, in this variant, the method makes it possible to obtain a more precise evaluation of the qualities of the subsoil and therefore to ensure more precisely that the layer of suitable hard ground has actually been drilled.

A second object of the invention is to provide a machine for making bored piles for implementing a method of the type mentioned above.

• des capteurs pour mesurer des caractéristiques dynamiques de l'outil de forage comprenant au moins certaines des caractéristiques suivantes : couple de l'outil, vitesse de pénétration de l'outil, vitesse de rotation de l'outil, poussée exercée sur l'outil ;
• des moyens pour mémoriser au fur et à mesure de leur acquisition les mesures faites par lesdits capteurs pour des profondeurs successives correspondant à un pas prédéterminé ;
• des moyens pour calculer, pour chaque profondeur, au moins une première variable représentative de la qualité du terrain rencontré à partir des mesures mémorisées, et des moyens pour mémoriser les valeurs successives de la première variable pour les profondeurs successives au fur et à mesure de leur calcul ;
• des moyens pour traiter les valeurs successives de ladite variable pour rechercher parmi les valeurs successives de ladite variable une succession sensiblement continue de valeurs de la variable correspondant à une qualité de terrain acceptable, pour des profondeurs successives correspondant à une différence de profondeurs prédéterminée ; et
• des moyens pour interrompre le forage lorsque ladite succession sensiblement continue de valeurs acceptables pour ladite différence de profondeur prédéterminée a été détectée.

The machine for making piles drilled in hard ground comprising a drilling tool fixed to the lower end of a drill string and means for rotating the drill string and driving this drill string into the soil is characterized in that it further comprises:

• sensors for measuring dynamic characteristics of the drilling tool comprising at least some of the following characteristics: tool torque, tool penetration speed, tool rotation speed, thrust exerted on the tool;
• means for memorizing, as they are acquired, the measurements made by said sensors for successive depths corresponding to a predetermined pitch;
• means for calculating, for each depth, at least a first variable representative of the quality of the terrain encountered from the stored measurements, and means for storing the successive values of the first variable for the successive depths as they are calculation;
• means for processing the successive values of said variable to search among the successive values of said variable for a substantially continuous succession of values of the variable corresponding to an acceptable quality of terrain, for successive depths corresponding to a predetermined difference in depths; and
• means for interrupting drilling when said substantially continuous succession of acceptable values for said predetermined difference in depth has been detected.

• la figure 1 est une vue simplifiée en élévation d'une machine de réalisation de pieux forés conforme à l'invention ;
• la figure 2 est un bloc-diagramme montrant les principaux circuits de traitement utilisés dans la machine ;
• la figure 3 est un organigramme simplifié du traitement des mesures fournies par les capteurs ; et
• la figure 4 montre un exemple d'enregistrements effectués à partir des capteurs et l'exploitation de ces enregistrements.

Other characteristics and advantages of the invention will appear better on reading the following description of several embodiments of the invention given by way of nonlimiting examples. The description refers to the appended figures, in which:

• Figure 1 is a simplified elevational view of a machine for making bored piles according to the invention;
• Figure 2 is a block diagram showing the main processing circuits used in the machine;
• FIG. 3 is a simplified flow diagram of the processing of the measurements supplied by the sensors; and
• FIG. 4 shows an example of recordings made from the sensors and the use of these recordings.

FIG. 1 shows a drilling machine 10 comprising a platform 12 on which a guide mast 14 is articulated. On the guide mast 14 is mounted a carriage 16 which itself carries a drilling head or rotation head 18. In the drilling head 18 is engaged a drill string 20 at the lower end of which is mounted a drilling tool 22. As is well known, the drilling head 18 comprises in particular a motor 24 for rotating the drill string. The insertion of the tool 22 into the ground to carry out the drilling is controlled, for example, by a set of chains or belts 26 serving for the translational movement of the carriage 16 along the mast, the chains 26 being driven in displacement by a motor assembly 28.

According to the invention, the machine is equipped with a number of sensors which are in particular a thrust sensor 30 corresponding for example to the pressure of the hydraulic motor 26 causing the sinking of the drill string, by a sensor 32 mounted on the carriage 16 and supplying the penetration speed V _p of the tool, into the ground, and of the sensors 34, 36 also mounted on the drilling head supplying the speed of rotation of the drill string V _r , as well as the torque C applied to the drilling tool. Finally, means represented schematically by 38 make it possible to determine the depth of the drilling tool 22. These different sensors 30 to 38 are connected to a processing assembly 40 making it possible to control the execution of the drilling using the tool 22 and machine 10.

In the following description, the dynamic parameters of the drilling tool chosen are the thrust P, the torque C exerted by the tool, the speed of rotation V _r of the tool and the penetration speed V _p of the tool in the ground. It goes without saying that we would not depart from the invention if we used other dynamic parameters of the tool.

The measurements made by the sensors 30 to 36 are transmitted in real time to the processing unit 40. This processing unit essentially comprises a central unit 42 built around a microprocessor, a data memory 44, a working memory 46 and a program memory 48.

The measurements provided by the sensors and transmitted in digital (or possibly analog) form in real time to the central unit 42 are stored in the data memory 44 by being associated with the depth at which these measurements have been made. The depth is, for example, taken into account for steps of 1 cm.

To obtain significant measurements of the parameters, for steps of depth of the order of 1 cm, two techniques can be used. When the ground is not too hard, the depth step of 1 cm can be implemented by memorizing the measurements corresponding to the successive depths detected by the depth sensor 38. When the ground is harder, the time taken to drill 1 cm can be important. The determination of successive depths in relation to the measurements of the parameters is therefore random. In this case, it is possible to carry out measurements for predetermined time intervals and to assign to each predetermined depth an average value of the measurements made for the time intervals corresponding to this depth. In any case, in memory 44, measurements of the four parameters associated with a depth are stored in real time.

In FIG. 4, curves 4a to 4d show values of parameters P, C, V _r and V _p for different depths as they are recorded in real time.

According to the invention, from the measurements of the four parameters, two variables representative of the quality of the soil are calculated. These variables can be in different numbers and calculated according to different formulas. In the particular example described, the first variable C _M is the variation of the average torque which represents the average value of the couple over a certain period. It is understood that, the lower this variable C _M , the more constant the force necessary to drill the soil, that is to say the more the soil will have properties of homogeneous hardness.

The second variable chosen is known as the Sommerton coefficient. It is given by the following formula: $$\text{S = P}\sqrt{\frac{{\text{V}}_{\text{r}}}{{\text{V}}_{\text{p}}}}\text{.}$$

The higher this coefficient S, the harder the soil.

According to the method of the invention, for the successive depths in the values of the variables C _M and S, a succession of the values of these variables corresponding to acceptable qualities of ground to constitute the anchoring of the piles is detected. For example, for the variable C _M , this criterion will be that this parameter is less than a first predetermined value V ₁ . On the other hand, for the second variable S, the criterion will be that this variable is greater than a predetermined value V ₂ .

As the acquisition and storage of the parameter values in the memory 44, the variables C _M and S are calculated for each depth. The subroutines necessary for these calculations are stored in the memory 48. These variables are calculated in the memory 46 and stored again in the data memory 44. The central unit compares the values of the variables C _M and S with the predetermined values V ₁ and V ₂ . If the two values of variables conform to the criteria retained for the depth considered, a counter 50 is incremented as shown in FIG. 3 after the comparison step 52. On the other hand, if one of the two criteria retained does not is not respected in step 52, the counter 50 is reset to zero by 54.

To consider that the bottom of the borehole corresponds to the required conditions, an anchoring depth in hard ground is determined in advance, which most often depends on the diameter of the borehole itself. This anchoring depth L shown in Figure 4 can therefore be converted into a number of unit depth steps. When the counter 50 is incremented to a value corresponding to the number N of depth steps associated with the difference in depth L, which is detected in step 56, the bottom of the drilling actually carried out penetrates the required depth L into a soil hard. The drilling machine can then be stopped since the required anchoring conditions are met.

We then proceed to the introduction of concrete or grout into the borehole which has just been carried out to obtain the bored pile.

It is understood that, during the production of each pile molded by the technique described above, it is possible to keep the records of the type of those represented in FIG. 4 produced for the four parameters P, C, V _r and V _p and for the values of variables C _M and S. The contracting authority will thus be able to prove that the molded pile was actually produced under the conditions provided for in the specifications.

Claims (10)

1. A method of making a pile bored in hard ground using a boring machine, characterised in that it comprises the following steps:

   - fitting the boring machine with sensors for measuring dynamic characteristics of the boring tool and comprising at least some of the following characteristics: tool torque, speed of penetration of the tool, speed of rotation of the tool, thrust exerted on the tool;

   - acquiring the measurements made by said sensors and storing them progressively as they are being acquired for successive depths, each corresponding to a predetermined depth increment;

   - calculating, for each depth and from the stored measurements, at least a first variable representative of the quality of the ground encountered, and storing successive values of the first variable for the successive depths as they are calculated;

   - processing the successive values of said variable in order to find a substantially continuous succession of values of the variable in the successive values of said variable which succession corresponds to ground of acceptable quality at successive depths corresponding to a predetermined depth difference; and

   - interrupting boring once said substantially continuous succession of acceptable values has been detected for said predetermined depth difference.
2. A method of making a bored pile according to claim 1, characterised in that:

   - calculating, for each depth and from the stored measurements, a second variable representative of the quality of the ground encountered, and storing successive values of the second variable for the successive depths;

   - processing the successive values of said first and second variables in order to find a substantially continuous succession of values for each of said variables in the successive values of each of said variables which succession corresponds to granite of acceptable quality at successive depths corresponding to the same predetermined depth difference; and

   - interrupting boring once said substantially continuous succession of acceptable values has been detected for the said same predetermined depth difference.
3. A method according to claim 1 or claim 2, characterised in that the measured value of each parameter is calculated by measuring said parameter at predetermined time intervals and in allocating a parameter value to each determined depth, where said value is equal to the mean of the measurements performed at those ones of said time intervals which correspond to said depth.
4. A method according to claim 2, characterised in that said first variable is the mean value of the tool torque, and said second variable is a function of the thrust, the speed of penetration of the tool, and the speed of rotation of the tool.
5. A method according to claim 4, characterised in that said second variable is calculated using the following formula: $$\text{S = P}\sqrt{\frac{{\text{V}}_{\text{r}}}{{\text{V}}_{\text{p}}}}$$ where P is thrust, V_r is speed of rotation, and V_p is speed of penetration.
6. A method according to claim 5, characterised in that the value of said first variable is considered as being acceptable when it is less than a predetermined value, and the value of said second variable is considered as being acceptable when it is greater than a predetermined value.
7. A machine for making a pile bored in hard ground, the machine comprising a boring tool fixed at the bottom end of a drill string and means for causing the drill string to rotate and to be driven into the soil, the machine being characterised in that it further comprises:

   - sensors for measuring dynamic characteristics of the boring tool, said characteristics comprising at least some of the following characteristics: tool torque, speed of penetration of the tool, speed of rotation of the tool, and thrust exerted on the tool;

   - means for storing the measurements made by said sensors as they are acquired for successive depths corresponding to a predetermined depth increment;

   - means for calculating for each depth and on the basis of the stored measurements at least a first variable representative of the quality of the ground encountered, and means for storing successive values of the first variable for the successive depths as they are calculated;

   - means for processing the successive values of said variable in order to find a substantially continuous succession of values of the variable in the successive values of said variable which succession corresponds to acceptable ground quality at successive depths corresponding to a predetermined depth difference; and

   - means for interrupting boring when said substantially continuous succession of acceptable values has been detected for said predetermined depth difference.
8. A machine for making a bored pile according to claim 7, characterised in that it further comprises:

   - for each depth, means for calculating from the stored measurements a second variable representative of the quality of the ground encountered and for storing successive values of the second variable for the successive depths;

   - means for processing the successive values of said first and second variables in order to find a substantially continuous succession of values for each of said variables in the successive values of each of said variables which succession corresponds to granite of acceptable quality at successive depths corresponding to the same predetermined depth difference; and

   - means for interrupting boring when said substantially continuous succession of acceptable values has been detected for said same predetermined depth difference.
9. A machine according to claim 7 and claim 8, characterised in that the measured value of each parameter is calculated by measuring said parameter at predetermined time intervals and by allocating a value of the parameter to a determined depth where said value is equal to the mean value of the measurements performed at those ones of said time intervals which correspond to said depth.
10. A machine according to claim 8, characterised in that said first variable is the mean value of the tool torque, and said second variable is a function of the thrust, the speed of penetration of the tool, and the speed of rotation of the tool.