| Time domain reflectometry (TDR) has been successfully used to monitor shear deformations in rock and soil masses in the field. It remains a challenge to apply TDR measuring in small physical soil models, mainly because commercial coaxial cables, commonly used in the field, are not sensitive enough for lab applications. There is also a limitation to the existing system in monitoring soil settlement, due to coaxial cable's low sensitivity to tension. The study presented in this thesis targets the above two points.; Several prototype cables had been developed in the earlier studies, and one of them with better signal quality was chosen for the experimental program in this research. A series of soil model tests, including direct shear, clay beam, and slope model tests were conducted to examine the sensitivity of the selected prototype cable for detecting shear deformation in small to mid-size soil models at 1-g condition. The selected prototype cable was found to be able to detect small shear deformations in medium to stiff clays, yet less responsive in soft clays. The sensitivity of the prototype cable varied with the soil stiffness. The TDR-based measuring systems were also employed in a centrifuge test and a shaking table test. It was found higher g-levels and seismic vibration had no adverse effect on the functions of the TDR instruments, which suggests the TDR measuring systems can be adopted in centrifuge and shaking table testings.; A looped TDR sensor that is highly sensitive to tension was developed. A soil tank test was conducted to examine the performance of the looped cable in monitoring soil settlements. It was found that the looped cable was capable of locating a subsidence zone in sand. To help to quantify the TDR readings, a correlation procedure was proposed to convert the TDR reflections to the actual soil settlement.; In addition, a soil-cable interaction study was conducted using the soil nailing analysis method. The key factors affecting the response of a soil-cable system with regard to TDR performance were identified. They were used to re-examine the prototype cable which was tested earlier in the experimental program. The analysis showed the prototype cable can be sufficiently sheared in medium to stiff clays with undrained shear strength over 50KPa. |
