TDR과 suction probe에 의한 흙-수분 곡선

TDR과 suction probe에 의한 흙-수분 곡선

 

영신컨설턴트 (02) 529 8803 ystcha@naver.com 2020.8

 

종래의 흙수분 곡선 시험은 공기압조절 배수량 측정 장치가 필요하고 TDR 센서와 부간극수압 센서로 시료의 증발 시 흙-수분 곡선

 

불포화토 unsaturated soil

모세관현상과 불포화토

 

모세관 수두

수두 Uwm는 모세관 직경 d에 반비례한다.

d is the diameter of the capillary and Ua is the air pressure

 

 

모세관 직경과 수두

 

종래의 수분 곡선 시험

공기압Ua 수압Uw 조절 장치 (Ua-Uw)

Transient Release and Imbibition Method (TRIM) for automated measurement of soil hydrologic properties.

 

(a) Tempe pressure and flow cell

 

(b) pressure plate apparatus used to desaturatesoil samples to specified matric potentials.

 

 

Some common SWC measurement methods and their corresponding matric potential ranges

 

 

 

TDR

a measurement device for soil moisture on the base of Time Domain Reflectometry technique, and electrical conductivity (salinity)

- 현장용 field probe for moisture, temperature and salinity of soil

- 시험실용 Laboratory miniProbe for soil moisture and salinity

 

Range of readings volumetric moisture. : 0 - 100 %,

temperature : -20 - +50°C,

electrical conductivity : 0.000 - 1 S/m

Accuracy moisture absolute error : displayed water content ±2 % or less

Resolution of readings volumetric moisture : 0.1 %,

temperature : 0.1°C,

electrical conductivity : 1 mS/m

Battery Type. : Li-Polymer, 2500 mAh, 3.7VDC (possible factory replacement)

Battery Life : 3000 measurements or 182 days of stand-by Charging

 

 

TDR에 의한 체적함수비

TDR 교정 공기

TDR 교정 물

 

 

 

v the travel time of the reflected pulse can be measured and its propagation velocity is known, The obtained reflections indicate discontinuities, impedance changes or damages of cables under test

ε dielectric permittivity

c : the velocity of light in vacuum (300,000 km/s),

L : the length of the transmission line of the sensor

Δt : the time between the reflections from the beginning and the end of the open transmission line

 

volumetric water content θ of porous materialsion line.

ε = f (v)

θ = f (ε)

 

 

시험실용 suctin and TDR probe

a 2.75 mm thick wall of a sampling steel cylinder, height of 100 mm and 55 mm inner diameter.

 

 

 

 

시험실용 suction probe

probes:

pressure diaphragm: a 15 mm long ceramic cup, 3 mm in diameter,

pressure transducer: an integrated, fully active Wheatstone bridge

with four piezoresistive strain gauge resistors diffused into a silicon diaphragm,

air entry pressure: about 900 mbar,

offset drift: ± 20 mbar/month, relative error: ± 15 %, resolution: 1 mbar,

delay: 0 to 800 mbar in about 120 s, 800 to 0 mbar in about 3 s, cable length: 2 m, installation hole: 8 mm diameter, tapped with 8x1 mm thread.