Penetration test module

Abstract

To realize an improved approach achieving cost-effectiveness, reliability, versatility (reliability under all conditions), and a deeper measurement of an original position.SOLUTION: A penetration test module includes: a casing having an opening part; a heat insulation material stored in the casing; a metal bar arranged in the opening part and thermally insulated from the casing by the heat insulation material; a heating device configured to heat the metal bar; and a heat sensor configured to measure the temperature of the bar.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of soil analysis, and in particular to modules used in penetration testing methods. In one non-limiting embodiment, the present invention relates to a cone penetration testing method. [Background technology]

[0002] Characterization of soil and soil-like geomaterials is of great importance in the fields of geotechnical engineering and geoenvironmental field investigation. Accurate and efficient characterization of such materials requires a combination of in situ testing and sampling approaches. Laboratory tests and cone penetration tests (CPT) are commonly employed methods for soil characterization.

[0003] Laboratory testing allows for the measurement of various soil properties, including thermal conductivity. Laboratory testing typically requires specialized excavation and sampling equipment and personnel, increasing costs and complexity in the field. Transporting samples also increases costs, logistical constraints (traceability), and greenhouse gas emissions. Laboratory work is time-consuming, and results vary depending on the method chosen and the expertise of the personnel. These limitations highlight the need for improved techniques that can overcome these challenges and provide more reliable and rapid soil characterization.

[0004] A cone penetration test (CPT) is a direct push probe test commonly used for geotechnical site investigations. A cone penetration test is performed by pushing a probe equipped with various sensors and other instrumentation into the soil / tailings. The CPT is called a CPT when cone resistance and sleeve friction are measured. The "CPTu" probe is equipped with sensors to measure tip resistance, sleeve friction, dynamic pore water pressure, slope, and temperature, and continuously records these at depth. The CPTu can be directly driven into a variety of soil types, including dykes, beaches, sludge, and flowing tailings. To further enhance the CPTu data, the CPTu can be equipped with additional modules and sensors, allowing it to collect a variety of other in-situ data.

[0005] One parameter of particular relevance is the thermal conductivity of soil, which has been measured using various methods.

[0006] The British company Datem has developed the so-called "Datem Thermal Conductivity Probe", a thermal conductivity probe that is remotely mounted on the side of the main CPT thrust shaft. This device is intended to be thrust into soft soil up to a limited distance below the seafloor. The geometry of the device makes it unsuitable for deep soil analysis.

[0007] Vardon et al. (TU Delft, DOI:10.1680 / jgeot.17.P.214, Interpreting and validating the Thermal Cone Penetration Test (T-CPT), 2018) use a thermal sensor to measure the thermal conductivity of soil. The sensor is heated by friction created when the CPT probe is pressed into the soil, and then measures the temperature as it cools. This method is not suitable for low-friction soils, because the lack of friction does not result in a sufficient temperature increase. Also, this method does not distinguish between the probe's and the soil's contribution to thermal conductivity. Therefore, this method is not suitable for all situations.

[0008] Liu et al. (Development and validation of a method to predict the soil thermal conductivity using thermal piezocone penetration testing (T-CPTU), Canadian Geotechnical Journal, Vol. 59, Number 4, April 2022, DOI 10.1139 / cgj-2021-0034) use a cylindrical metal shell in a CPT system to analyze the thermal conductivity of soil. The metal shell is heated and the temperature response is measured. However, the metal shell is very large, which makes the experiment time-consuming. In addition, the heat generated propagates through the cone-tube, reducing the accuracy of the measurement. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] Vardon et al., TU Delft, DOI:10.1680 / jgeot.17.P.214, Interpreting and validating the Thermal Cone Penetration Test (T-CPT), 2018 [Non-patent document 2] Liu et al., Development and validation of a method to predict the soil thermal conductivity using thermal piezocone penetration testing (T-CPTU), Canadian Geotechnical Journal, Vol. 59, Number 4, April 2022, DOI 10.1139 / cgj-2021-0034 Summary of the Invention [Problem to be solved by the invention]

[0010] These limitations highlight the need for improved approaches that are cost-effective, reliable, versatile (reliable under all conditions), and achieve deeper in situ measurements. [Means for solving the problem]

[0011] The present disclosure addresses such needs with a penetration testing module that includes a casing having an opening, insulation housed within the casing, a metal rod disposed within the opening and insulated from the casing by the insulation, a heating device configured to heat the metal rod, and a thermal sensor configured to measure the temperature of the rod.

[0012] Such a penetration testing module does not operate based on the friction of the soil resting on the casing and is not limited to soft soil, making it possible to provide reliable results in all types of soil. Heat transfer to the casing is prevented, so the results are not affected by the thermal conductivity of the casing. Also, the heated rod is smaller than known cylindrical sleeves (having the size of the casing), so measurements can be made faster. Overall, this makes it possible for the module herein to accurately measure the thermal conductivity of any type of soil at any depth.

[0013] Finally, the presented module is compact and can be easily integrated into standard CPT equipment and deployed behind a cone penetrometer. The portability of the tool allows for efficient and flexible deployment in various field environments, facilitating on-site data collection and analysis. Therefore, in a preferred, but non-limiting, embodiment, the penetration test module is integrated into a cone penetration test (CPT). Thus, thermal data and CPT conventional data (tip resistance, sleeve friction, dynamic pore water pressure, and tilt) can be measured simultaneously.

[0014] In some instances, the casing has a longitudinal direction and the opening has a length extending parallel to the longitudinal direction, a design that allows for a fast thermal response of the rod without compromising the mechanical balance of the casing.

[0015] In some cases, the insulation is made from a plastic material. A plastic material with very low thermal conductivity and high friction resistance can be selected. For example, polycarbonate or polyoxymethylene (Delrin®) may be used.

[0016] In some instances, the heating device is an electrical resistor delivering between 1 and 5 watts of power. A further advantage of using a rod rather than a sleeve is that less power is required to heat the rod.

[0017] In some examples, the thermal sensor is a resistive temperature device.

[0018] In some examples, the rods are made from copper. In alternative designs, the rods may be made from another metal alloy with high thermal conductivity.

[0019] In some examples, the penetration module includes a cable that passes through a penetration opening in the casing, the cable connecting the heat sensor and the heating device to a remote control unit.

[0020] In some instances, the casing has a longitudinal direction and the opening extends longitudinally for a length between 4 inches and 15 inches. The opening must be long enough to obtain a sufficient thermal response from the soil. The opening cannot be too long as this may compromise the rigidity of the module.

[0021] In some instances, the rod has a length between 2 inches and 10 inches and a diameter between 1 / 16 inch and 1 / 4 inch.

[0022] The present invention further relates to a cone penetration testing system comprising a cone, a casing connected to the cone and having an opening, insulation housed within the casing, a metal rod positioned within the opening and insulated from the casing by the insulation, a heating device configured to heat the metal rod, a thermal sensor configured to measure the temperature of the rod, and at least one sensor for measuring at least one of cone tip resistance, sleeve friction, dynamic pore pressure, and tilt.

[0023] The cone penetration testing system may include various aspects described above with respect to the penetration testing module.

[0024] The present invention further relates to a method of operating a penetration testing module, comprising: equipping the penetration testing module with a casing having an opening, insulation housed within the casing, a metal rod disposed within the opening and insulated from the casing by the insulation, a heating device, and a temperature sensor; forcing the penetration testing module into soil; heating the rod with the heating device; measuring the temperature of the rod with the thermal sensor as the rod is heated; and calculating the thermal conductivity of the soil based on the measured temperature.

[0025] In some examples, the method further includes interrupting the step of heating the rod and measuring the temperature of the rod with a thermal sensor as the rod cools. Monitoring the temperature of the rod as it cools allows for checking the accuracy of measurements made when the rod was heated.

[0026] In some examples, heating the rod includes increasing the temperature of the rod by between 1° C. and 5° C. for a duration between 1 minute and 10 minutes.

[0027] In some examples, the method further includes waiting for the temperature of the rod to stabilize after pushing and before heating. The temperature of the rod stabilizes when its temperature matches the soil temperature, which may be detected by a thermal sensor when the measured temperature fluctuates by less than a predetermined amount (e.g., 0.1°C) over a predetermined duration (e.g., 10 seconds).

[0028] In some examples, measuring the temperature is performed at a sampling rate between 0.1 seconds and 1 second and with a resolution of 0.01° C. A preferred rate is about one measurement every 0.5 seconds. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a side view of a penetration test module. [Figure 2] FIG. 2 is a cross-sectional view of the module of FIG. 1. [Figure 3] FIG. 1 illustrates a CPT test module. [Figure 4] 1 is a flowchart illustrating a method. DETAILED DESCRIPTION OF THE INVENTION

[0030] FIG. 1 shows a side view of a penetration testing module 1. The module 1 includes a casing 2 extending in a longitudinal direction A. The casing 2 is generally tubular and may be substantially cylindrical. One end of the casing 2 may be provided with a cone 4 to facilitate penetration into the soil. In use, the longitudinal direction A is vertical, and the penetration testing module 1 is forced into the soil. The casing 2 may have a cylindrical outer surface 6 that contacts or is adjacent to the soil or tailings when the casing 2 is forced down. The diameter D of the outer surface 6 may be between 1 inch and 5 inches. The casing 2 may be partially hollow to accommodate various components, as will be described later.

[0031] The casing 2 includes an opening 8. The opening 8 is a recess in the outer surface 6 of the casing 2. In this example, the opening 8 is substantially rectangular, although other shapes may be selected. The opening 8 is substantially filled with an insulating material 10, which may be made of a plastic material. The insulating material 10 has an outer surface 12 that is flush with the outer surface 6 of the casing 2. A rod 14, which may be made of copper, is housed within the insulating material. The rod 14 is flush with the outer surface 12 of the insulating material 10. When the module is pushed into the soil, the rod 12 is therefore in direct proximity to the soil. The rod 14 is completely insulated from the casing 2 by the insulating material 10. In one non-exemplary embodiment, the rod 14 is not flush with the outer surface 12 of the insulating material 10. The rod 14 may protrude beyond the outer surface 12 by, for example, less than one-third of the diameter of the rod 14.

[0032] The rods 14 may extend parallel to direction A, but need not extend parallel to direction A; the rods 14 shown in FIG. 1 are straight, but other configurations are possible for the rods; the rods 14 may be curved and may extend circumferentially, i.e., as an arc (or complete ring) around the longitudinal axis A of the casing 2.

[0033] The length L of the opening 8 can be between 4 inches and 15 inches. The length l of the rod 14 can be between 2 inches and 10 inches. The rod can have a diameter between 1 / 16 inch and 1 / 4 inch.

[0034] The width W of the opening 8 may be at least three times the diameter of the rod 14 .

[0035] At the end of the casing facing the cone 4, a connector 16 (thread) may be arranged. The connector 16 is adapted to be connected to the tubular module when the casing is pushed into the soil.

[0036] Figure 2 shows a cross-sectional view of the module 1 of Figure 1. The casing 2 is hollow and may include a lumen 18.

[0037] The module 1 includes a heating device 20, represented diagrammatically in Figure 2, below the rod 14. The heating device 20 may be an electrical resistor having a power rating of between 1 and 5 watts. The heating device 20 may be positioned at one end of the rod 14 or may extend substantially below the entire rod 14.

[0038] The module 1 further comprises a thermal sensor 22, which may be a resistive temperature sensor. The thermal sensor 22 may be positioned at the end of the rod 14 facing the heating device 20.

[0039] Both the heating device 20 and the thermal sensor 22 may be embedded in the insulation material 10. An electrical connector may provide electrical current to the heating device 20 and extract a signal from the thermal sensor 22. The electrical connector may be embedded in the insulation material 10.

[0040] The local controller 24 may be connected to the heating device 20 and the thermal sensor 22. A cable 26 connects the local controller 24 and the remote control unit 30. The cable 26 may pass through a through opening 28 in the module 1. The cable 26 may be shielded or reinforced. The cable may have a sheath that encloses multiple connectors. Any suitable type of cable may be used (e.g., coaxial, RJ45, HDMI, VDI, etc.).

[0041] 3 illustrates a CPT system 100 in which module 1 is incorporated. CPT system 100 extends along a longitudinal axis A and includes at one end a cone 4 for penetrating soil. One or more modules 102, 104 may be sequentially arranged between cone 4 and penetration test module 1. Modules 102, 104 may be equipped with various sensors typically used in CPT systems, such as sensors for measuring tip resistance, sleeve friction, dynamic pore water pressure, slope, or temperature.

[0042] 2 can transmit data from these sensors as well, which may run through multiple tubular elements 102, 104, 106 of the CPT system to the remote control unit 30. Bidirectional control of heating / cooling operation can be performed through this cable.

[0043] FIG. 4 illustrates a method 1000 of operating the penetration testing module 1 of FIGS.

[0044] The method may include a calibration step 1100. Indeed, it may be appropriate to calibrate the thermal sensors, in particular to correct the data to account for non-zero thermal conductivities of insulating materials. Calibration may be performed by sequentially placing various materials with known thermal conductivities around the penetration test module, heating the rod and measuring the temperature of the rod during heating.

[0045] In step 1200, the penetration test module is pushed to a desired depth.

[0046] To improve the accuracy of the measurement, it may be appropriate to wait in step 1300 until the temperature of the rod has stabilized, ie, matched the temperature of the surrounding soil.

[0047] After stabilization 1300, the rod is heated 1400 using a heating device. For example, the rod may be heated to a few degrees Celsius (e.g., 1 to 5 degrees Celsius). This may be done over a period of time ranging from a few seconds to a few minutes, e.g., 1 to 10 minutes, preferably about 5 minutes. The heating step may be interrupted when it is detected that the change in temperature is no longer linear with respect to the logarithm of time.

[0048] During heating 1400, the temperature is measured by a thermal sensor. The general principle for obtaining the thermal conductivity of the soil from the change in temperature during heating is as follows.

[0049] Regarding heat conduction of a line conductor in a solid medium,

[0050]

number

[0051] It may be shown that where θ is the temperature difference variable (increase or decrease), q is the amount of heat per unit length, and k is the thermal conductivity.

[0052] As can be seen from this equation, to obtain independence from b, at least two sets of measurements are required to calculate k given the temperature dissipation data. In practice, a linear regression between the series of measurements is used to fit the temperature data collected over time.

[0053] The heating operation involves three stages: in the first stage, the temperature rises very slowly as the rod warms up; in the second stage, the temperature changes linearly with the logarithm of time; and in the third stage, the temperature gradient is significantly lower than in the second stage due to boundary / edge effects (such as metal casings) becoming more pronounced. The gradient of temperature change in the second stage is inversely proportional to the thermal conductivity of the soil. Therefore, it is possible to accurately define the thermal conductivity of the soil by identifying the gradient of the second stage during heating.

[0054] During heating 1400, the temperature may be measured at a rate between 0.1 and 1 second, for example, at a rate of 0.5 seconds. The resolution of the thermal sensor may be 0.01°C.

[0055] In step 1500, the heating device is turned off and the rod is allowed to cool. As the rod cools, it may be advantageous to measure the temperature. This may help to increase the accuracy of the measurement.

[0056] The duration of the cooling step 1500 may be substantially equal to the duration of the heating step.

[0057] After the rod has cooled, the process can be repeated, i.e., the module is pushed further down for additional thermal conductivity analysis. The distance between two consecutive thermal conductivity measurements can be between 1 foot and 10 feet.

[0058] The cumulative results obtained over several cycles make it possible to form a complete map of the thermal conductivity of the soil as a function of depth. [Explanation of symbols]

[0059] A Longitudinal direction 1 module 2 Casing 4 Corn 6. External Surface 8 Openings 10. Insulation 12 External Surface 14 bars 16 connectors 18 lumen 20 Heating device 22 Thermal Sensor 24 Local Controller 26 Cable 28 Through opening 30 Remote Control Unit 100 CPT System 102, 104 modules

Claims

1. a casing (2) having an exterior surface (6) and an opening (8), the opening being a recess in the exterior surface of the casing; a heat insulating material (10) housed in the casing; a metal rod (14) disposed within the opening and insulated from the casing by the insulating material; a heating device (20) configured to heat the metal rod; a thermal sensor (22) configured to measure the temperature of the rod.

2. 2. A penetration test module (1) as claimed in claim 1, wherein the casing has a longitudinal direction and the opening has a length extending parallel to the longitudinal direction.

3. 2. The penetration test module (1) according to claim 1, wherein the insulation is made from a plastic material.

4. 2. The penetration test module (1) according to claim 1, wherein the heating device is an electrical resistor delivering a power of between 1 watt and 5 watts.

5. 2. The penetration test module (1) according to claim 1, wherein the thermal sensor is a resistive temperature device.

6. 2. The penetration test module (1) according to claim 1, wherein the rod is made of copper.

7. 2. The penetration testing module (1) of claim 1, further comprising a cable passing through a through opening in the casing, the cable connecting the thermal sensor and the heating device to a remote control unit.

8. 2. The penetration test module (1) of claim 1, wherein the casing has a longitudinal direction and the opening extends in the longitudinal direction over a length of between 4 inches and 15 inches.

9. 2. The penetration test module (1) of claim 1, wherein the rod has a length between 2 inches and 10 inches and a diameter between 1 / 16 inch and 1 / 4 inch.

10. Cone (4) and a casing (2) connected to the cone and having an exterior surface and an opening, the opening being a recess in the exterior surface of the casing; a heat insulating material (10) housed in the casing; a metal rod (14) disposed within the opening and insulated from the casing by the insulating material; a heating device (20) configured to heat the metal rod; a thermal sensor (22) configured to measure the temperature of the rod; and at least one sensor for measuring at least one of cone tip resistance, sleeve friction, dynamic pore pressure, and tilt.

11. 1. A method (1000) for operating a penetration testing module, comprising: The penetration testing module includes: a casing having an exterior surface and an opening, the opening being a recess in the exterior surface of the casing; a heat insulating material housed within the casing; a metal rod disposed within the opening and insulated from the casing by the insulating material; A heating device; a thermal sensor; forcing (1200) the penetration testing module into soil; heating (1400) the rod with the heating device; measuring the temperature of the rod with the thermal sensor as the rod is heated; and calculating the thermal conductivity of the soil based on the measured temperature.

12. interrupting the step of heating the rod; and measuring the temperature of the rod with the thermal sensor as the rod cools.

13. 12. The method of claim 11, wherein heating the rod comprises increasing the temperature of the rod by between 1°C and 5°C for a duration between 1 minute and 10 minutes.

14. After pressing and before heating, The method of claim 11 further comprising waiting for the temperature of the rod to stabilize.

15. 12. The method of claim 11, wherein the step of measuring the temperature is performed at a sampling rate between 0.1 seconds and 1 second and with a resolution of 0.01°C.

Images