R. Bulut & E.C. Leong. International Symposium Advanced Experimental Unsaturated Soil Mechanics Trento, Italy June 27-29, 2005

Transcription

1 State-of-the-Art Report on Indirect Measurement of Soil Suction R. Bulut & E.C. Leong International Symposium Advanced Experimental Unsaturated Soil Mechanics Trento, Italy June 27-29, 2005

2 Indirect Suction Measurement Techniques Primary Methods Secondary Methods Tertiary Methods

3 Indirect Suction Measurement Techniques Primary Methods Thermocouple Psychrometers Transistor Psychrometers Chilled-Mirror Psychrometer

4 Indirect Suction Measurement Techniques Secondary Method Filter Paper Method

5 Indirect Suction Measurement Techniques Tertiary Methods Thermal Conductivity Sensors Electrical Conductivity Sensors

6 SOIL SUCTION Total Suction = Matric Suction + Osmotic Suction

7 SOIL SUCTION Primary Methods Total Suction Secondary Method Total Suction and Matric Suction Tertiary Methods Matric Suction

8 OUTLINE Working principle Calibration Measurement Range Equilibration Time Applications

9 PRIMARY METHODS Thermocouple Psychrometers (Peltier Type Psychrometer) Insulated Cable Seebeck Effect Peltier Effect Relative Humidity Chromel 200 Mesh Outer Liner Constantan Welded Junction 400 Mesh Inner Liner Stainless Steel Screen Cap Kelvin s Equation ψ = RT ln V P P o

10 PRIMARY METHODS Thermocouple Psychrometers A Typical Calibration Curve of a Single Thermocouple Psychrometer Calibration Salt Solutions (NaCl) Constant Temperature Total suction, kpa Linear micro V Osmotic Suction π = ν RTm φ

11 PRIMARY METHODS Thermocouple Psychrometers Osmotic Suction of NaCl Solutions at 25 o C Molality (m) Osmotic Coefficient (φ) Osmotic Suction (kpa) Molality (m) Osmotic Coefficient (φ) Osmotic Suction (kpa)

12 PRIMARY METHODS Thermocouple Psychrometers Dataloggers: HR-33T CR7 40 Channel Output: Microvolt and Temperature

13 PRIMARY METHODS Thermocouple Psychrometers Measurement Range: kpa Equilibration Time: One Hour

14 PRIMARY METHODS Thermocouple Psychrometers Applications Soil Diffusion Test

15 PRIMARY METHODS Transistor Psychrometer Working principle is very similar to the Peltier psychrometer Differences: Manually applied water drop Transistors Wet Transistor Water Drop Circuit Board Soil Sample Container Dry Transistor Probe

16 PRIMARY METHODS Transistor Psychrometer 12-Probe Unit 8-Probe Unit Datalogger

17 PRIMARY METHODS Transistor Psychrometer A Typical Calibration Curve of a Single Transistor Psychrometer Probe Linear Calibration Salt Solutions (NaCl) Constant Temperature Total suction, kpa mv Osmotic Suction π = ν RTm φ

18 PRIMARY METHODS Transistor Psychrometer Measurement Range: kpa Equilibration Time: One Hour

19 PRIMARY METHODS Transistor Psychrometer Applications

20 PRIMARY METHODS Chilled-Mirror Psychrometer Working Principle: Chilled Mirror WP4 Dewpoint PotentiaMeter Closed Chamber Infrared Sensor Optical Sensor Soil Fan Mirror Sliding Tray Electronic Display Dew Point Technique Decagon Devices

21 PRIMARY METHODS Chilled-Mirror Psychrometer Characteristic Curve Osmotic Suction, log kpa Theoretical (NaCl) WP4 (NaCl) Theoretical (KCl) WP4 (KCl) WP4 Characteristic Curve: Using NaCl and KCl Salt Solutions at 25 o C Salt Solution Molality, m Osmotic Suction, log kpa Theoretical (NaCl) WP4 (NaCl) Theoretical (KCl) WP4 (KCl) WP4 Characteristic Curve: Using NaCl and KCl Salt Solutions at 25 o C Salt Solution Molality, m

22 PRIMARY METHODS Chilled Mirror Psychrometer Measurement Range: kpa Equilibration Time: 10 Minutes

23 PRIMARY METHODS Chilled Mirror Psychrometer Applications

24 SECONDARY METHODS Filter Paper Method Lid Non-Contact Method Total Suction Filter Paper(s) Tape Sharp Ed Ring Sup Contact Method Matric Suction Middle Filter Paper Soil Protectiv Filter Papers Moisture (suction) equilibrium between filter papers and soil Glass Jar Container Constant Temperature In Closed Container

25 SECONDARY METHODS Filter Paper Method Two Commonly Used Filter Papers Whatman No. 42 Schleicher & Schuell No. 589-WH (Now in US called No. 989-WH)

26 SECONDARY METHODS Filter Paper Method Calibration Curves Non-Contact Method Salt Solutions (also called Total Suction Curve) Contact Method Pressure Plate Type Devices (also called Matric Suction Curve)

27 SECONDARY METHODS Filter Paper Method Calibration Curves

28 SECONDARY METHODS Filter Paper Method Calibration Curves Houston et al Total Suction Matric Suction

29 SECONDARY METHODS Filter Paper Method Recent Calibration Curves for Schleicher & Schuell No. 589-WH Suction (kpa) 1E+6 1E+5 1E+4 1E+3 1E+2 1E+1 1E+0 Total suction Matric suction test data Equations 4a Total suction test data Equations 4b Matric suction Filter paper water content (%) Suction, h, kpa 1.E+05 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 Wetting Curve h = e w R 2 = (50 < h < 43500) S&S No. 589-WH Filter Papers Equilibration Temperature: 25 o C Equilibration Period: 2 Weeks Sodium Chloride Ammonium Chloride Calcium Chloride Sodium Sulfate Distilled Water Sensitivity-Not real data Filter paper water content, w Leong et al Bulut & Wray 2005

30 SECONDARY METHODS Filter Paper Method Soil Total and Matric Suction Measurements Filter Paper(s) for Non-Contact Method Sharp Edge Ring Support Soil Sample Filter Paper(s) in Between Two Protective Papers Soil Specimens Brought Together for Contact Method Soil Sample

31 SECONDARY METHODS Filter Paper Method Measurement Range: kpa Equilibration Time: 5 to 14 days

32 SECONDARY METHODS Filter Paper Method Applications

33 TERTIARY METHODS Thermal Conductivity Sensor 4 lead wires Heater Embedded Porous Block Spaghetti and h shrinkage tube Moisture (suction) equilibrium between porous block and soil Diode Copper wire Porous block

34 TERTIARY METHODS Thermal Conductivity Sensor Calibration 8 ln(-uw)= TA R 2 = Temperature change is related to the thermal conductivity of the porous medium and the moisture content ln(-uw) (kpa ) Two drying processes Two wetting processes ln(-uw)= TA R 2 = TA ( o C ) Zhang et al Pressure Plates Tensiometers

35 TERTIARY METHODS Thermal Conductivity Sensor Measurement Range: kpa Equilibration Time: hours to days

36 TERTIARY METHODS Thermal Conductivity Sensor Applications There are both laboratory and field applications of thermal conductivity sensors

37 TERTIARY METHODS Electrical Conductivity Sensor Wires A Porous Block and Two Concentric Electrodes Embedded inside the Block Gypsum block Brass foil Polystyrene tube The Porous Block serves the same purpose as the porous block in the thermal conductivity sensor (a) Cross-section (b) Plan view Copper wire

38 TERTIARY METHODS Electrical Conductivity Sensor Calibration Manufacturer calibration curve ECS1 Electrical conductivity is related to the moisture in the porous medium Meter reading ECS Soil suction in kpa Pressure Plates From He 1999 Tensiometers

39 TERTIARY METHODS Electrical Conductivity Sensor Measurement Range: kpa Equilibration Time: 6 to 50 hours

40 SUMMARY Reliable Measurements with Thermocouple Psychrometers Transistor Psychrometers Chilled Mirror Psychrometer Non-Contact Filter Paper Method Depend on A Good Laboratory Testing Protocol Constant Temperature Environment

41 SUMMARY Reliable Measurements with Contact Filter Paper Method Thermal Conductivity Sensors Electrical Conductivity Sensors Depend on A Good Laboratory Testing Protocol Intimate Contact Between the Measuring Sensor and Soil

42 SUMMARY Category Method Suction Component Suction Range (kpa) Equilibration Time Source/ Manufacturer Primary Thermocouple Psychrometer Total Suction hour Wescor: Campbell Scientific: Transistor Psychrometer Total Suction hour Soil Mechanics Instrumentation: Chilled-Mirror Psychrometer Total Suction (or higher) 10 minutes Decagon Devices: Secondary The Filter Paper Method Total/Matric Suction (or higher) 5 to 14 days Whatman: Schleicher & Schuell: Tertiary Thermal Conductivity Sensor Matric Suction hours to days Campbell Scientific: GCTS: Electrical Conductivity Matric Suction to 50 hours Soil Moisture Equipment: