A MEASURING DEVICE AND METHOD OF USE THEREOF

Abstract

The present invention concerns a device and method for selectively or simultaneously measuring shear strength and pore water pressure of a soil in the field. The device includes a rod adapted to be at least partially inserted into the soil and rotated. The rod has a soil engaging portion and an opposed coupling portion configured to be coupled to a torque applying machine or device. The device further includes at least one vane blade extending at least partially along and from the soil engaging portion of the rod for shearing the soil when rotated together with the rod. At plurality of pore water pressure sensors are operatively associated with at least one of the soil engaging portion and the at least one vane blade. The sensors are configured to sense pressure indicative of the pore water pressure of the soil while the at least one vane blade shears the soil.

Claims

1. A device for selectively or simultaneously measuring shear strength and pore water pressure of a soil in the field, said device comprising: a rod adapted to be at least partially inserted into the soil and rotated, said rod having a soil engaging portion and an opposed coupling portion for coupling to a toque applying machine or device; at least one vane blade extending at least partially along and from the soil engaging portion of the rod for shearing the soil when rotated together with the rod, said at least one vane blade having a leading face, an opposed trailing face, an upper edge, an opposed lower edge and an outer side edge; and a plurality of pore water pressure sensors operatively associated with two or more of the soil engaging portion, the leading face, the trailing face and the outer side edge, said sensors configured to collectively sense pressure indicative of the pore water pressure of the soil while the at least one vane blade shears the soil.

2. The device of claim 1, wherein the at least one vane blade includes four vane blades extending along and from the soil engaging portion of the rod in an opposed arrangement.

3. The device of claim 2, wherein the plurality of pore water pressure sensors are located on the outer side edge and the leading face of the at least one vane blade.

4. The device of claim 3, wherein the plurality of pore water pressure sensors further comprise a pore water pressure sensor located on the soil engaging portion of the rod.

5. The device of claim 4, wherein the plurality of pore water pressure sensors further comprise a pore water pressure sensor located on the trailing face of at least one vane blade.

6. The device of claim 5, further comprising a plurality of casings each having at least one ground water inlet port and configured to contain one of the plurality of pore water pressure sensors, each said casing configured to enable a flow of groundwater into the inlet port and pressure indicative of the pore water pressure to be measured.

7. The device of claim 6, wherein the at least one ground water inlet port of each casing further comprises a screen or filter to prevent the passage of materials other than groundwater into the inlet port.

8. The device of claim 7, wherein the screen or filter has a pore size of between about 2 μm and about 20 μm.

9. The device of claim 7, wherein the screen or filter is removable and replaceable so that the screen or filter can be cleaned or replaced between measurements or as required.

10. The device of claim 6, wherein each said casing is filled with a fluid having a viscosity greater than water and wherein pressure indicative of the pore water pressure is measured based on the pressure of the ground water on the fluid in the casing.

11. The device of claim 10, wherein the fluid is selected from any one of glycerin, silicone oil and grease.

12. The device of claim 11, wherein the fluid is added and replaced between measurements with the device or as required.

13. The device of claim 10, further comprising a cleaning mechanism for cleaning or flushing the pore water pressure sensors.

14. The device of claim 13, wherein each said pore water pressure sensor is operatively associated with a source of the fluid for flushing the sensor following or in between measurements with the device.

15. The device of claim 14, wherein the fluid is delivered from a fluid source into the casing of each pore water pressure sensor via one or more outlets in fluid communication with the casing and the source.

16. A system for selectively or simultaneously measuring shear strength and pore water pressure of a soil in the field, said system comprising: a device in accordance with claim 1; and a torque applying machine having a controller coupled to the coupling portion of the rod of the device for rotating the rod, said controller configured to control rotation of the rod at a desired rate of rotation.

17. The system of claim 16, wherein the controller further controls an angle of rotation and an amount of torque applied to the rod.

18. The system of claim 16, wherein the desired rate of rotation ranges from about 0.05° per second to about 1.00° per second.

19. A method of selectively or simultaneously measuring shear strength and pore water pressure of a soil in the field, said method comprising: providing the device of claim 1; at least partially inserting the soil engaging portion and the at least one vane blade into the soil; applying torque to the coupling portion to rotate the rod and the at least one vane blade to cause the at least one vane blade to shear the soil; and monitoring and collecting at least data corresponding to pore water pressure from the at least one pressure sensor simultaneously with said applying.

20. The method of claim 19, wherein the monitoring and collecting occur in real time and continuously while the torque is applied to rotate the rod.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0156] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[0157] FIG. 1 is a photograph showing an upper perspective view of a device according to an embodiment of the present invention;

[0158] FIG. 2 is an upper perspective view showing the device according to another embodiment of the present invention;

[0159] FIG. 3 is an upper perspective view showing the device according to yet another embodiment of the present invention;

[0160] FIG. 4 is an upper perspective view showing the device according to a further embodiment of the present invention;

[0161] FIG. 5 is a flowchart showing steps in a method of using the device as shown in FIGS. 1 to 4 according to an embodiment of the present invention;

[0162] FIG. 6 is a graph plotting pore water pressure against time during a field vane shear test using the device as shown in FIG. 1; and

[0163] FIG. 7 is another graph plotting pore water pressure against time during a field vane shear test using the device as shown in FIG. 1.

DETAILED DESCRIPTION

[0164] FIGS. 1 to 4 show embodiments of a device (100) for simultaneously measuring shear strength and pore water pressure of a soil in the field when performing a field vane shear test.

[0165] Referring to FIG. 1, the device (100) includes a rod (110) adapted to be at least partially inserted into a soil of an earthen substrate. The rod (110) has a soil engaging portion (114) located at or near a soil engaging end (112) and an opposed coupling portion (118) located at or near a torque applying machine or device engaging end (116).

[0166] The device (100) also includes four vane blades (120) extending at least partially along and from the soil engaging portion (114) for shearing soil when rotated together with the rod (110).

[0167] The device (100) further includes a pressure sensor (130) located on the soil engaging portion (114) at least partially between the vane blades (120) for sensing pressure indicative of pore water pressure of the soil while the vane blades (120) shear the soil.

[0168] Generally, the soil may form part of an earthen substrate. For example, the earthen substrate may include a portion of land, an embankment, a levee, a transportation embankment, an embankment dam, an earthen dam wall (e.g., a tailings dam wall) or reclaimed land alongside a body of water, such as, e.g., a riverbank or beach. The soil may include any non-fissured clay, silt or other saturated fine-grained geomaterials, such as, e.g., mine tailings, organic muck, slimes, leach residues, slickens, dredge spoils and other like material and/or materials.

[0169] The rod (110) is formed of stainless steel.

[0170] As indicated, the rod (110) includes a pair of opposed ends (112, 116) and extends longitudinally between the opposed ends (112, 116) in a linear direction.

[0171] The coupling portion (118), located at or near the torque applying machine or device engaging end (116), is for coupling to a torque applying machine or device.

[0172] The coupling portion (118) can couple directly, or indirectly via a torque rod (150) as shown, with the torque applying machine or device.

[0173] Generally, the torque applying machine or device includes an actuating mechanism for rotation of the rod (110) in a clockwise or anti-clockwise direction. The actuating mechanism may typically be driven by a drive motor.

[0174] The coupling portion (118) and the torque applying machine or device may be connected together by a connecting mechanism or part of a connecting mechanism, a clamping mechanism or a socket type connection.

[0175] The vane blades (120) are also formed of stainless steel. Each blade (120) has a rectangular shape defined by a pair of opposed side surfaces (122), an upper edge (124), an opposed lower edge (126), an inner side edge (127) and an opposed outer side edge (128).

[0176] The rod (110) and the vane blades (120) are joined together using conventional welding techniques.

[0177] As shown, each vane blade (120) extends from the rod (110) in a direction perpendicular to a longitudinal axis of the rod (110).

[0178] The vane blades (120) are arranged in diametrically opposed pairs about the soil engaging portion (114) of the rod (110).

[0179] Each blade (120) typically has a height, measured as the distance that the blade (120) extends at least partially along the soil engaging portion (114) of the rod (110), that is approximately two times the diameter of a diametrically opposed pair of the blades (120).

[0180] Each blade (120) has a thickness ranging between about 1.5 mm and about 3.5 mm.

[0181] As mentioned, the device (100) includes a pressure sensor (130) located on the soil engaging portion (114) at least partially between the vane blades (120).

[0182] The pressure sensor (130) is a piezoelectric sensor and is provided in a casing including a cavity and a groundwater inlet port (132). The pressure sensor (130) measures the pressure of groundwater that passes through the groundwater inlet port (132) into the cavity, the pressure being indicative of the pore water pressure.

[0183] The groundwater inlet port (132) includes an opening of suitable size to allow the passage of groundwater and a filter to prevent the passage of soil materials other than groundwater into the cavity via the opening. The filter has a pore size of between about 2 μm and about 20 μm.

[0184] The filter is removable and/or replaceable so that the filter can be cleaned and re-fitted or replaced between field vane tests or as required.

[0185] The pressure sensor (130) is electrically connected to a data bus or like connection.

[0186] The device (100) includes a dedicated microprocessor or microcomputer, including one or more processors and a memory, operatively associated with the pressure sensor (130) for collecting data corresponding to the pressure sensed and transmitting the data to an external device, controller or processing device. The data is at least partially transmitted via at least one electrical circuit extending along and within the rod (110), or portions thereof.

[0187] In some embodiments, the device (100) further includes a communications module for wirelessly connecting the device to a remote controller in the form of an external processing device via a wireless network (e.g., Wi-Fi (WLAN) communication, Satellite communication, RF communication, infrared communication or Bluetooth™). The communications module includes a cellular or radio modem.

[0188] The external processing device can be any one of a desktop, a laptop, a smart phone, a tablet or smart watch. The external processing device includes software configured to run on the external processing device and allow an operator to control at least aspects of operation of the device (100) and display and analyse data transmitted from the device (100).

[0189] FIG. 2 shows another embodiment of the device (100). For convenience, features that are similar or correspond to features of the previous embodiment will be referenced with the same reference numerals.

[0190] Referring to FIG. 2, the device (100) again includes a rod (110) having a soil engaging portion (114) located at or near a soil engaging end (112) and four vane blades (120) extending therefrom.

[0191] However, in contrast to the previous embodiment, in this embodiment the device (100) includes a plurality of pressure sensors (130) each located on a side surface (122) of a vane blade (120).

[0192] In a variation of this embodiment, the device (100) can include pressure sensors (130) located on both opposed side surfaces (122) of each blade (120).

[0193] FIG. 3 shows another embodiment of the device (100). Again, and for convenience, features that are similar or correspond to features of the previous embodiment will be referenced with the same reference numerals.

[0194] Referring to FIG. 3, the device (100) again includes a rod (110) having a soil engaging portion (114) located at or near a soil engaging end (112) and four vane blades (120) extending therefrom.

[0195] However, in contrast to the previous embodiments, in this embodiment the device (100) includes a plurality of pressure sensors (130) each located on an outer side edge (128) of each blade (120).

[0196] In a variation of this embodiment, the device (100) can include pressure sensors (130) on only one pair of the vane blades (120).

[0197] FIG. 4 shows another embodiment of the device (100). Again, and for convenience, features that are similar or correspond to features of the previous embodiment will be referenced with the same reference numerals.

[0198] Referring to FIG. 4, the device (100) again includes a rod (110) having a soil engaging portion (114) located at or near a soil engaging end (112) and four vane blades (120) extending therefrom.

[0199] However, in contrast to the previous embodiments, in this embodiment the device (100) includes a plurality of pressure sensors (130) located on both side surfaces (122) and the outer side edge (128) of each vane blade (120) as well as on the soil engaging portion (114) at least partially between the vane blades (120).

[0200] In a variation of this embodiment, the device (100) can include pressure sensors (130) on only one pair of the vane blades (120).

[0201] A method (400) of using the device (100) as shown in any one of FIGS. 1 to 4 will now be described in detail with reference to FIG. 5.

[0202] At step 410, the soil engaging portion (114) of the rod (110) is at least partially inserted into a soil layer of interest such that the vane blades (120) fully penetrate the intact soil layer.

[0203] At step 420, torque is applied to the coupling portion (118) of the rod (110) such that the rod (110) and vane blades (120) rotate at a constant rate. The torque is increased until the vane blades (120) cause the soil to shear. The torque required to cause the vane blades (120) to shear the soil is noted and recorded.

[0204] At step 430, while applying torque, data corresponding to the pore water pressure of the groundwater in the soil layer is monitored and collected via the pressure sensor (130). The monitoring and collecting occurs in real time.

[0205] At step 440, the undrained shear strength of the soil layer is determined based on the torque reached at step 420. The undrained shear strength is adjusted to account for the effect of the pore water pressure measured at step 430. For example, the pore water pressure can be accounted for and/or subtracted from the torque determined at step 420 when determining the undrained shear strength of the soil layer to provide a more accurate measurement of the shear strength of the soil.

[0206] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

EXAMPLE

[0207] The following example is provided to demonstrate the effectiveness of the device (100) of the present invention. The example is not to be considered limiting on the scope and ambit of the present invention as hereinbefore described.

Example 1

[0208] Referring to FIGS. 6 and 7, field vane shear tests were conducted on privately owned land in May 2020.

[0209] The tests were conducted using the device (100) as shown in FIG. 1 coupled to a piezocone (CPTu). The tests were conducted on an earthen substrate consisting of mine tailing at locations approximately 100 m from one another.

[0210] Referring to FIG. 6, in this test, the pore water pressure can be seen to be stable and hydrostatic before commencement of the field vane shear test. However, once the device (100) starts to rotate and increasing amounts of torque are applied, the pore water pressure initially spikes before dropping for the remainder of the test. When the test concludes, the pore water pressure once again stabilises to a level measured before initiation of the test.

[0211] These test results suggest that the soil is dilative and the pore water is initially compressed between the soil particles when the test initiates causing the pore water pressure to initially spike before the pore water drains away from the site of the test.

[0212] The measurement of the pore water pressure during the test enables the pore water pressure to be accounted for when determining the undrained shear strength of the soil. If the pore water pressure were not measured, it is likely that the undrained shear strength of the soil would be incorrectly calculated.

[0213] Referring to FIG. 7, in this test, the pore water pressure can be seen to again be stable and hydrostatic before commencement of the field vane shear test. However, once the device (100) starts to rotate and increasing amounts of torque are applied, the pore water pressure spikes and remains elevated for the duration of the test. When the test concludes, the pore water pressure gradually stabilises to a level measured before initiation of the test.

[0214] These test results suggest that the soil has a low hydraulic conductivity with rotation of the device (100) causing the pore water between soil particles to compress and generate an artificial spike in pore water pressure for a duration of the test.

[0215] The measurement of the pore water pressure during this test again enables the pore water pressure to be accounted for when determining the undrained shear strength of the soil. If the pore water pressure were not measured, it is likely that the undrained shear strength of the soil would be incorrectly calculated.

[0216] In the present specification and claims (if any), the word ‘comprising’ and its derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0217] Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0218] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.