Geotechnical penetrometer

Abstract

The described cone penetrometer system is a geotechnical testing apparatus designed for accurate soil assessment comprising a drive shaft with an attached cone at its distal end, a load cell connected to the shaft for precise measurement of applied force, and a depth transducer to accurately gauge the penetration depth of the cone. This system distinguishes itself from traditional methods by directly converting force to bearing capacity based on the cone's surface area, eliminating the reliance on less accurate blow conversion tables. The inclusion of a reliable depth transducer ensures precise depth measurements, facilitating accurate plotting of bearing capacity against depth. While delivering enhanced accuracy, the system retains the advantages of lightweight, cost-effectiveness, and manual operation, aligning with the simplicity and efficiency characteristic of traditional methods like the Dynamic Cone Penetrometer (DCP) compared to more intricate and expensive Cone Penetration Test (CPT) systems.

Description

Geotechnical PenetrometerField of the Invention

[0001] This invention relates generally to geotechnical penetrometers. More particularly, this invention relates to geotechnical testing apparatus that accurately assesses soil properties by directly converting force to bearing capacity based on the cone's surface area, comprising a drive shaft, a load cell for precise force measurement, and a depth transducer for accurate penetration depth readings.Background of the Invention

[0002] A Cone Penetration Test (CPT) is a geotechnical engineering method used to determine the geotechnical properties of soils and assess subsurface conditions. It involves pushing a cone-shaped probe into the ground at a constant rate and measuring the resistance to penetration as a function of depth.

[0003] The typical CPT setup consists of a conical tip which is driven (pushed) into ground by a set of rods using specialised heavy machinery. The conical tip can vary in shape and includes pore pressure sensors. The rods are pushed into the ground using hydraulic or mechanical means, and measurements are recorded continuously as the conical tip penetrates the ground.

[0004] The key parameters obtained from a Cone Penetration Test include: a. Cone Resistance, which is the force, required to penetrate the soil with the cone. It is measured in units of force per unit area (e.g., kPa). b. Sleeve Friction, which is the frictional resistance between the sleeve (located above the cone) and the soil. Like cone resistance, it is measured in units of force per unit area. c. Pore Water Pressure, which is the pressure of water within the soil, and it can be measured using the pore sensors in the cone. Pore water pressure data can be crucial for assessing the soil's drainage characteristics.

[0005] CPT provides a continuous profile of soil properties, allowing engineers and geologists to evaluate the subsurface conditions at a site. It is commonly used in geotechnical investigations for various purposes, including: a. Site Characterisation: Understanding the soil profile and stratigraphy. b. Foundation Design: Assessing soil bearing capacity and settlement characteristics. c. Landslide and Slope Stability Studies: Evaluating the stability of slopes and embankments. d. Groundwater Flow Studies: Examining permeability and drainage properties of soils.

[0006] Whereas CPT is a more efficient and cost-effective method compared to traditional methods like drilling and sampling it is still expensive and specialised equipment. Not only are these specialised cone tips including inbuilt sensors expensive, but also difficult to maintain and calibrate. Moreover, CTP apparatus invariably involves sophisticated software packages. As such, CTP apparatus is normally only used for deep exploration and / or high-end commercial use.

[0007] As such, a cheaper alternative for activities like residential development, road construction, and related domains, involves the use of lightweight and manual Dynamic Cone Penetrometer (DCP).

[0008] The DCP is a portable and manual testing device which involves dropping a cone into the ground and measuring the penetration depth for each blow or impact with a slide hammer of calibrated weight from a fixed height. It is often used for in- situ assessment of soil strength and compaction.

[0009] Furthermore, DCP equipment is generally lightweight and portable, making it suitable for field applications and is manually operated and suitable for quick assessments of soil strength. Also, DCP is suitable for shallow explorations, typically up to a few meters deep.

[0010] As such, DCP is commonly used for rapid assessment of in-situ soil strength, compaction, and subgrade evaluation such as construction projects, especially those involving roads, pavements and residential construction sites. Conversely, CPT isused for detailed geotechnical investigations to provide continuous and real-time data on cone resistance, sleeve friction, and pore water pressure, making it more applicable for site characterisation, foundation design, and environmental studies.

[0011] As such, while both DCP and CPT are used to assess soil properties, DCP is more manual and suitable for quick on-site evaluations, especially in construction settings. CPT is a more advanced and automated method that provides detailed information for comprehensive geotechnical investigations.

[0012] One notable drawback associated with the DCP lies in its method of converting hammer blow count into soil bearing capacity using conversion tables, a process that introduces a level of inaccuracy. The DCP operates by measuring the depth of penetration for each hammer blow, and while it provides a quick assessment of in - situ soil strength and compaction, the conversion of this information to soil bearing capacity is a simplified approximation.

[0013] In contrast to more advanced methods like the CPT, which provides continuous and real-time measurements of cone resistance and other parameters, the DCP's reliance on blow count conversion makes it more susceptible to limitations in accuracy, especially in situations where soil conditions vary widely or exhibit complex behaviour. DCP also presents operator risk with hammer crush injuries and RSI related injuries common.

[0014] Therefore, while the DCP serves as a practical tool for rapid on-site assessments, particularly in construction projects, it has inherent limitations in its ability to precisely quantify soil bearing capacity due to its reliance on a simplified conversion process.

[0015] The present invention seeks to provide a way to overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.

[0016] It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.Summary of the Disclosure

[0017] The described cone penetrometer system is a geotechnical testing apparatus designed for accurate soil assessment comprising a drive shaft with an attached cone at its distal end, a load cell connected to the shaft for precise measurement of applied force, and a depth transducer to accurately gauge the penetration depth of the cone.

[0018] Notably, this system distinguishes itself from traditional methods by directly converting force to bearing capacity based on the cone's surface area, eliminating the reliance on less accurate blow conversion tables and operator error.

[0019] The inclusion of a reliable depth transducer ensures precise depth measurements, facilitating accurate plotting of bearing capacity against depth.

[0020] While delivering enhanced accuracy, the system retains the advantages of lightweight, cost-effectiveness, and manual operation, aligning with the simplicity and efficiency characteristic of traditional methods like the Dynamic Cone Penetrometer (DCP) compared to more intricate and expensive Cone Penetration Test (CPT) systems.

[0021] According to one aspect, there is provided a penetrometer system comprising a drive shaft, a cone attached to a distal end of the shaft, a load cell operably coupled to the shaft to measure force applied to the shaft, a depth transducer operably coupled to the shaft to measure shaft penetration depth, and an acquisition unit operably interfacing the load cell and the depth transducer to acquire the force and the penetration depth.

[0022] In one embodiment, the depth transducer is a rotary transducer, such as a rotary encoder rotatably interfacing the shaft.

[0023] The system may convert the force to bearing capacity based on the surface area of the cone and may further plot the bearing capacity in relation to the penetration depth.

[0024] The system may comprise a digital display configured to display data, including plots of force or bearing capacity in relation to penetration depth, in real time.

[0025] The system may accommodate a plurality of cones of various sizes attachable to the drive shaft, with respective surface areas configurable via software calibration.

[0026] The system may include software calibration features, such as load cell force calibration and cone type calibration, including cone surface area calibration.

[0027] The system may comprise an electronic device operably communicating with the acquisition unit, the electronic device being configured to receive and display data from the acquisition unit. In embodiments, the electronic device may communicate wirelessly with the acquisition unit and execute a software application configured for data interaction and calibration.

[0028] The system may provide recording controls, including start, pause, and end recording options, for managing data acquisition during use.

[0029] The rotary transducer may comprise a rotary encoder held against the shaft by a sprung arm.

[0030] The system may include a ram for applying constant force to the drive shaft, ensuring steady penetration of the cone into the ground.

[0031] A method of using the penetrometer system is also provided, comprising attaching a cone to the drive shaft, applying force to drive the cone into the ground, acquiring force and penetration depth data, converting force to bearing capacity, and optionally plotting the bearing capacity in relation to the penetration depth.

[0032] Other aspects of the invention are also disclosed.Brief Description of the Drawings

[0033] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0034] Figure 1 shows a cone penetrometer system in accordance with an embodiment.Description of Embodiments

[0035] Figure 1 shows a cone penetrometer system 100 comprising a rigid drive shaft 101 and a cone 102 attach to a distal end of the shaft 101. The cone 102 has a diameter larger than the driveshaft 101. Force is applied to the shaft 101 to drive the cone 102 into ground 104.

[0036] The system 100 further comprises a load cell 103 operably coupled to the shaft 101 to measure force applied along the shaft 101 as the cone 102 is driven into the ground 104. Preferably, the system 100 comprises a ram (not shown) to apply constant force to the shaft 101 , as opposed to repeated hammer blows. The ram may be a vertically orientated hydraulic ram acting on a distal end of the shaft 101.

[0037] The system 100 further comprises a depth transducer 105 operably coupled to the shaft 101 to measure shaft penetration depth. According to the preferred embodiment, the depth transducer 105 is a rotary transducer which comprises a rotary encoder 107 rotatably engaged against the shaft 101. The rotary encoder 107 may be held against the shaft 101 by a sprung arm 108 and may oppose a roller bearing 109 located at an opposite side of the shaft 101. In alternative embodiments, the depth transducer optically reads markings along the shaft 101 .

[0038] The system 100 further comprises an acquisition unit 106 operably interfacing the load cell 103 and the depth transducer 105 and which is configured to acquire the force and the penetration depth from the load cell 103 and the rotary transducer 105.

[0039] The acquisition unit 106 may comprise a PCB based microcontroller executing firmware and / or software to acquire the force and penetration depth.

[0040] The system 100 may be configured to convert the force to bearing capacity according to the surface area of the cone 102. The system 100 may use a constant ratio to convert the force to the bearing capacity according to the surface area of the cone 102 or alternatively use a conversion table relating force to surface area residing within a memory device of the system 100.

[0041] The system 100 may be configured to plot the force or the bearing capacity in relation to the penetration depth. Such plotting may comprise depth along an X axis and the force or the bearing capacity thereof along the Y axis.

[0042] According to the embodiment shown, the system 100 has an electronic device 1 10 in operable communication with the acquisition unit 106 to receive data therefrom. The electronic device 1 10 may be in wireless communication with the acquisition unit 106 as shown.

[0043] In embodiments, the electronic device 1 10 comprises a mobile communication device executing a software application thereon which is configured to interact with the acquisition unit 106. In alternative embodiments, the electronic device 1 10 is a personal computer device, such as a laptop device executing an application, such as a Windows™ application.

[0044] In a specific embodiment, the mobile communication device 1 10 executes the Android™ operating system having the software application installed thereon and which interfaces with the acquisition unit 106 via Bluetooth wireless protocol.

[0045] The electronic device 1 10 may comprise a digital display. The system 100 may be configured to display the plot relating the force or the bearing capacity against penetration depth on the digital display of the electronic device 1 10.

[0046] In embodiments, the system 100 has software calibration. The software calibration may be used to calibrate force measurement readings obtained from the load cell 103.

[0047] In this regard, the acquisition unit 106 may comprise a weighbridge operably interfacing the load cell 103. The software application 1 10 executing on the electronic device 1 10 may display a user interface on the digital display thereof which may be used to calibrate the minimum and maximum force readings of the weighbridge or load cell 103.

[0048] The software calibration may include a cone type calibration. Specifically, the system 100 may comprise a plurality of cones of various sizes attachable to the distal end of the driveshaft 101 and wherein the user interface of the electronic device 1 10 may be used to calibrate the surface area thereof. In embodiments, the type of cone of a standardised size may be input wherein the system 100 looks up the surface area from a lookup table residing within memory. In alternative embodiments, the surface area of the cone 102 may be input directly.

[0049] User interface may comprise recording controls to at least one of start, pause and end recording.

[0050] A method of using the system 100 for assessing subsurface conditions according to the preferred embodiment shown in Figure 1 may comprise attaching acone 102 into a distal end of the driveshaft 101. The electronic device 110 may be paired to the acquisition unit 106.

[0051] The user interface of the electronic device 101 may be configured according to the type of cone or the surface area thereof. If necessary, the load cell 103 may also be calibrated using the user interface of the electronic device 1 10.

[0052] The proximal end of the shaft 101 may be operably coupled to the vertically- orientated hydraulic ram and the tip of the cone 102 placed against the ground 104.

[0053] The depth transducer 105 may be connected to the shaft 101 , such as by placing the rotary encoder 107 against the side of the shaft 101 in opposition to the bearing 109 against an opposite side of the shaft 101.

[0054] Recording may be initiated using the start recording control of the user interface of the electronic device 110 and the hydraulic ram operated to apply force to the proximal end of the shaft 1 10.

[0055] As the cone 102 to penetrates the ground 104, the load cell 103 measures the force applied to the drive shaft 101 and the depth transducer 105 measures the penetration depth of the cone 102. This data is acquired by the acquisition unit 106 and which may be transmitted to the electronic device 110 in real-time.

[0056] The electronic device 110 may display a plot of the force or a conversion thereof against the penetration depth on the digital display.

[0057] The acquisition unit 106 or the electronic device 110 may convert the force to bearing capacity according to the surface area of the cone 102.

[0058] At any time, recording may be paused using the pause recording control of the user interface of the electronic device 1 10.

[0059] At the end of recording, the end recording control may be used to cease recording. The electronic device 1 10 may transmit the recorded data to cloud storage via a GSM network.

[0060] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practise the invention. Thus, the foregoing descriptions of specific embodiments ofthe invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

Claims1 . A penetrometer system comprising: a drive shaft; a cone attached to a distal end of the shaft; a load cell operably coupled to the shaft to measure force applied to the shaft; a depth transducer operably coupled to the shaft to measure shaft penetration depth; and an acquisition unit operably interfacing the load cell and the depth transducer to acquire the force and the penetration depth.

2. The system as claimed in claim 1 , wherein the depth transducer is a rotary transducer.

3. The system as claimed in claim 1 , wherein the system is configured to convert the force to bearing capacity according to a surface area of the cone.

4. The system as claimed in claim 3, wherein the system is configured to plot the bearing capacity in relation to the penetration depth.

6. The system as claimed in claim 4, wherein the system comprises a digital display configured to plot the force or the thereof in relation to the penetration depth.

7. The system as claimed in claim 1 , wherein the system comprises a plurality of cones of various sizes attachable to the shaft and wherein the system is configurable with respective surface areas thereof.

8. The system as claimed in claim 1 , wherein the system executes software calibration.

9. The system as claimed in claim 8, wherein the software calibration includes load cell force calibration.

10. The system as claimed in claim 8, wherein the software calibration includes cone type calibration.1 1 . The system as claimed in claim 8, wherein the cone type calibration includes cone surface area calibration.

12. The system as claimed in claim 1 , further comprising an electronic device in operable communication with the acquisition unit and wherein the electronic device is configured to receive data from the acquisition unit.

13. The system as claimed in claim 12, wherein the electronic device comprises a digital display configured to display the data.

14. The system as claimed in claim 13, wherein the system is configured for realtime display of the data using the electronic device.

15. The system as claimed in claim 12, wherein the electronic device is in wireless communication with the acquisition unit.

16. The system as claimed in claim 15, wherein the electronic device comprises a mobile communication device executing a software application thereon, the software application comprising computer program code instruction controllers configured for interacting with the acquisition unit.

17. The system as claimed in claim 1 , wherein the system comprises recording controls including at least one of start, pause and end recording control inputs.

18. The system as claimed in claim 2, wherein the rotary transducer comprises a rotary encoder rotatably interfacing the shaft.

19. The system as claimed in claim 18, wherein the rotary encoder is held against the shaft by a sprung arm.

20. The system as claimed in claim 1 , wherein the system further comprises a ram applying constant force to the shaft.

21. A method of assessing subsurface soil conditions using the penetrometer system of claim 1 , the method comprising: attaching the cone to a distal end of the drive shaft; placing the cone in contact with the ground; applying force to the drive shaft to drive the cone into the ground; measuring the force applied to the drive shaft using the load cell; measuring the penetration depth of the cone using the depth transducer; acquiring the force and penetration depth measurements with the acquisition unit; andconverting the force measurements to soil bearing capacity based on the surface area of the cone.

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