Browsing by Author "Lin, C. P."

Now showing 1 - 5 of 5

Accuracy of bulk electrical conductivity measurements with time domain reflectometry
(2008-05-01)
Huisman, J. A.
;
Lin, C. P.
;
Weihermueller, L.
;
Vereecken, H.
;
交大名義發表
Accurate determination of bulk electrical conductivity with time domain reflectometry (TDR) requires calibration or direct measurement of the probe constant and the cable resistance. The aims of this study were threefold. First, the accuracy of an analytical expression for the direct determination of the probe constant was evaluated for three TDR probe designs by comparing the analytical result with the probe constant obtained by calibration to TDR measurements in solutions with varying electrical conductivity. Second, the accuracy of direct measurement of cable resistance was compared with the accuracy that can be achieved by calibrating this resistance. The uncertainty in directly measured and calibrated probe and cable properties was determined in a Monte Carlo analysis. The results showed that the analytical expression for the probe constant and calibration of the probe constant do not provide significantly different estimates when the uncertainty in both approaches is considered; however, the uncertainty in the calibrated probe constants was lower than or similar to the uncertainty in the direct measurements. Directly measured and calibrated cable resistance differed, which was attributed to recording time issues. It was concluded that calibration of probe and cable parameters should be preferred over direct measurements to achieve accurate bulk electrical conductivity measurements. The final aim of this study was to quantify how the various sources of uncertainty identified in this study affect the accuracy of TDR bulk conductivity measurements. This uncertainty analysis showed that the accuracy of TDR ranges between 0.6 and 1.2% of the bulk electrical conductivity if the reflection coefficient varies between -0.75 and 0.75. Outside this range, the accuracy of the bulk electrical conductivity measurements made with TDR is lower.
Development of TDR penetrometer through theoretical and laboratory investigations: 1. Measurement of soil dielectric permittivity
(2006-07-01)
Lin, C. P.
;
Tang, S. H.
;
Chung, C. C.
;
交大名義發表
;
National Chiao Tung University
To better characterize a bulk soil electrically, both the electrical conductivity and dielectric permittivity should be measured. This study developed a time domain reflectometry (TDR) penetrometer to allow simultaneous measurements of dielectric permittivity and electrical conductivity during cone penetration. A TDR penetrometer is formed by placing a multiple-conductor waveguide around a nonconducting shaft. Probe design considerations and calibration methods for measuring dielectric constant were first theoretically discussed and then evaluated through laboratory investigations. A prototype TDR penetrometer was fabricated and used to perform simulated penetration tests in a calibration chamber. The effect of penetration disturbance on dielectric constant is quantitatively reported and explained. The implications of the data that can be measured by the TDR penetrometer are also discussed.
Development of TDR penetrometer through theoretical and laboratory investigations: 2. Measurement of soil electrical conductivity
(2006-07-01)
Lin, C. P.
;
Chung, C. C.
;
Tang, S. H.
;
交大名義發表
;
National Chiao Tung University
A TDR penetrometer was introduced to allow simultaneous measurements of dielectric permittivity and electrical conductivity during cone penetration. This study focused on the theoretical development and experimental evaluation of electrical conductivity measurement using the TDR penetrometer. Theoretical development takes into account the cable resistance and nonconducting cone shaft, leading to a new data reduction equation and calibration procedure. Measurement sensitivity and spatial sampling bias were experimentally evaluated for various probe configurations. The results show that the measurement sensitivity of interest may be controlled by the geometric factor of the probe. The complication and implications of the spatial weighting bias are discussed. A prototype TDR penetrometer was calibrated and used to perform simulated penetration tests in a soil. Experimental results do not show significant errors in electrical conductivity due to the penetration disturbance, verifying the effectiveness of the TDR penetrometer for electrical conductivity measurement.
Non-invasive time domain reflectometry probe for transient measurement of water retention curves in structured soils
(2020-01-01)
Mu, Q. Y.
;
Zhan, L. T.
;
Lin, C. P.
;
Chen, Y. M.
;
土木工程學系
Transient evaporation method is promising for rapid measurement of soil water retention curve (WRC). Existing apparatuses of transient evaporation method are not ideal for measuring the WRC of structured soils because of the sample disturbance induced by invasive water content probes used. In this study, non-invasive TDR probes with different waveguide layouts (i.e., different number of conductors and waveguide length) were developed to measure the WRC of loess during transient evaporation, while the soil suction is recorded through a tensiometer. Results show that the WRCs of undisturbed and remolded loess measured by a three-conductor non-invasive TDR probe are in good agreement with the results of pressure plate tests. The differences in the air entry value (AEV) and desorption rate between the WRCs measured by the transient evaporation method and the pressure plate measurement are less than 10 %. On the other hand, the WRCs measured by a two-conductor non-invasive TDR probe underestimate the water content for a given suction. The AEV of undisturbed and remolded loess determined by the transient evaporation method is 66.7 % and 112.9 % smaller than the results of pressure plate measurements, respectively. The underestimation of the two-conductor non-invasive TDR probe in measuring the WRC of loess can be attributed to the fact that the vertical sampling range of two-conductor non-invasive TDR probe is two times greater than that of the tensiometer. The results in this study show the effectiveness of using the non-invasive TDR probe along with a tensiometer for measuring the WRC. More importantly, great caution should be taken on compliant sampling volume of the non-invasive TDR probe and tensiometer to obtain accurate WRC measurements.
Site characterization for the investigation of tunnel 8 collapse
(2004)
Huang, A. -B.
;
Lin, C. P.
;
Liao, J. J.
;
Pan, Y. W.
;
Tinkler, J.
A section of the high speed rail tunnel collapsed before the installation of permanent lining. The section designated as Tunnel 8 was located in Miaoli County in Northern Taiwan. The resulting spoil blocked approximately 50 in of the tunnel. A crater of 28 in in diameter, with a maximum depth of 12.1 in was formed at the ground surface, at approximately 60 in above the crown level of the tunnel. A site characterization program was carried out to define the boundaries of the collapsed zone, provide ground water information and stress and stiffitess parameters for the outer and final concrete lining design. Six 100 in deep, rotary cored holes were drilled vertically from the ground surface, within the collapsed zone and penetrated through the tunnel level. SPT, pressuremeter and suspension P-S logging tests were performed in these boreholes. Seven open boreholes, approximately 60 in deep, were drilled laterally from the concrete barricade at north and south end of the collapse zone within the tunnel at various angles. Geophysical tests which included seismic refraction tomography and resistivity tests were conducted from the ground surface. The data collected from the site characterization coupled with the geological background were analyzed and an image of the possible disturbance zone was created. The paper describes details of the site characterization, their interpretation and results of the analysis.