Method and probe for measuring hydraulic conductivity of soil

• US 20050177309A1
• Filed: 05/09/2003
• Published: 08/11/2005
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: University of Manitoba
• Original Assignee: University of Manitoba
• Inventors: Petrak, Martin, Sri Ranjan, Ramanathan
• Granted Patent: US 7,059,174 B2
• Time in Patent Office: Days
• US Class Current: 73/38
• CPC Class Codes: E21B 49/008 by injection test; by analysing pressure variations in an injection or production test, e.g. for estimating the skin factor measuring pressure E21B47/06
• CPC Class Codes: G01N 1/08 involving an extracting tool, e.g. core bit
• CPC Class Codes: G01N 15/0826 and measuring fluid flow rate, i.e. permeation rate or pressure change
• CPC Class Codes: G01N 33/246 for water content for control of watering A01G25/167

Abstract

Agricultural waste lagoons are the predominant method currently utilized to contain large quantities of livestock by-products such as manure. Clay liners are the most common materials used to line the bottom of storage lagoons in order to prevent waste effluent seepage. Clay liners are an economical lining material and have a hydraulic conductivity of less than 1×10⁻⁷ cm/s. Proper containment of waste in storage lagoons is critical to avoid the implications of local groundwater contamination. A hydraulic conductivity probe was designed to alleviate the negative aspects of the current methods used to determine hydraulic conductivity. The probe includes a housing for insertion into the ground, electrical potential gradient means for generating an electrical potential gradient in the ground and pressure sensing means for measuring changes in pressure in the ground.

Claims

1. A method of measuring hydraulic conductivity in soil, said method comprising:

providing a probe having electrical potential gradient means for generating an electrical potential gradient and pressure sensing means for measuring changes in pressure;

inserting the probe into the soil;

measuring a first pressure condition within the soil using the pressure sensing means of the probe;

applying an electrical potential gradient to the soil using the electrical potential gradient means of the probe for an elapsed period of time;

measuring a second pressure condition within the soil using the pressure sensing means of the probe;

removing the application of the electrical potential gradient to the soil using the electrical potential gradient means of the probe after the elapsed period of time has expired;

measuring a measured duration for condition of the soil to return from the second pressure condition to the first pressure condition; and

calculating hydraulic conductivity based upon a prescribed relationship of hydraulic conductivity and the measured duration.

2. The method according to claim 1 including calibrating the probe to determine the prescribed relationship between hydraulic conductivity and the measured duration prior to calculating the hydraulic conductivity.

3. The method according to claim 1 including applying the electrical potential gradient until a pressure condition of the soil reaches a prescribed pressure.

4. The method according to claim 1 wherein the prescribed pressure is an adjustable set point pressure.

5. The method according to claim 1 including applying the electrical potential gradient for a prescribed duration.

6. The method according to claim 1 including wetting the soil before measuring the first and second pressure conditions.

7. The method according to claim 6 wherein the probe includes a water port for introducing water into the soil, the method including sealing the water port before measuring the first and second pressure conditions.

8. The method according to claim 6 including waiting for a pressure condition of the soil to become constant after wetting the soil before measuring the first and second pressure conditions.

9. The method according to claim 1 including bleeding air surrounding the pressure sensing means within the soil before measuring the first and second pressure conditions.

10. The method according to claim 9 wherein the probe includes an air port for removing air from the soil surrounding the pressure sensing means, the method including sealing the air port before measuring the first and second pressure conditions.

11. The method according to claim 1 wherein the probe includes two electrical potential sensors at prescribed spaced locations within the electrical gradient generated by the electrical potential gradient means, the method including measuring electrical potential at each of the sensors and calculating electrical conductivity.

12. The method according to claim 11 including wetting the soil before measuring the first and second pressure conditions if the calculated electrical conductivity indicates the soil is dry.

13. The method according to claim 1 including recording the elapsed period of time of the electrical potential gradient and calculating electro-osmotic conductivity based upon the elapsed period of time and a difference between the first and second pressure conditions.

14. The method according to claim 1 including inserting the probe into soil in situ.

16. The method according to claim 1 including:

providing a probe insertion tube for slidably receiving the probe therethrough;

inserting the probe insertion tube into the soil prior to insertion of the probe;

inserting the probe into the soil by inserting the probe through the probe insertion tool;

removing the probe from the probe insertion tube subsequent to measurement of the first and second pressure conditions;

introducing soil sealing material through the probe insertion tube to fill a cavity in the soil formed by the probe; and

removing the probe insertion tube from the soil.

17. The method according to claim 16 wherein the soil sealing material comprises bentonite pellets.

15. The method according to claim I including inserting the probe into clay soil beneath a retention pond.

18. A probe for measuring hydraulic conductivity in soils, the probe comprising:

a housing being suitably shaped for insertion into the ground;

electrical potential gradient means for generating an electrical potential gradient in the ground surrounding the housing; and

pressure sensing means for measuring changes in pressure in porewater within the ground.

19. The probe according to claim 18 wherein the housing comprises an elongate tubular member.

20. The probe according to claim 18 wherein the housing includes a pointed soil penetrating end, the electrical potential gradient means and the pressure sensing means being located adjacent the pointed soil penetrating end.

21. The probe according to claim 18 wherein the electrical potential gradient means comprises first and second electrodes insulated from one another at spaced locations on the housing and an electrical power supply coupled therebetween.

22. The probe according to claim 21 wherein the housing extends in a longitudinal direction between an exposed end and a soil penetrating end and wherein the first and second electrodes are spaced apart from one another in the longitudinal direction of the housing.

23. The probe according to claim 22 wherein the first electrode is coupled to a pointed end cap at the soil penetrating end of the housing and the second electrode is coupled to side walls of the housing, the pointed end cap being insulated with respect to the side walls of the housing.

24. The probe according to claim 18 wherein there is provided two electrical potential sensors supported on the housing at prescribed spaced locations within the electrical gradient generated by the electrical potential gradient means.

25. The probe according to claim 18 wherein there is provided a plurality of apertures in the housing for communication with an internal cavity of the housing supporting the pressure sensing means therein.

26. The probe according to claim 25 wherein the pressure sensing means comprises a pressure transducer.

27. The probe according to claim 25 wherein the housing extends in a longitudinal direction between an exposed end and a soil penetrating end and wherein there is provided an air port communicating between the exposed end of the housing and the internal cavity of the housing.

28. The probe according to claim 27 wherein the air port includes a valve for selectively sealing the air port in a closed position.

29. The probe according to claim 27 wherein there is provided a water port communicating between the exposed end of the housing and the internal cavity of the housing.

30. The probe according to claim 29 wherein the water port includes a valve for selectively sealing the water port in a closed position.

31. The probe according to claim 20 wherein there is provided an elongate probe insertion tube for receiving the housing therein, a soil penetrating end of the insertion tube being formed of resilient material permitting the pointed end of the housing to be penetrated therethrough.