Non-destructive integrity evaluation of reinforced earth structures
저자
발행사항
Seoul : Graduate School, Korea University, 2016
학위논문사항
학위논문(박사)-- 고려대학교 대학원: 건축·사회환경공학과 2016. 8
발행연도
2016
작성언어
영어
주제어
발행국(도시)
서울
형태사항
xvii, 227장 : 삽화, 도표 ; 26 cm
일반주기명
지도교수: 이종섭
참고문헌: 장 219-226
DOI식별코드
소장기관
This study suggests the non-destructive technique for evaluating integrity of the reinforced earth structures. The group velocity and frequency response of the guided wave are used to evaluate the grouted ratio of the pipe roof system. The experiments and numerical simulation are conducted to evaluate the grouted ratio of the rock bolt using the group velocity of the guided wave. The propagation velocity of the low frequency elastic wave and electromagnetic wave are used to evaluate the length of the soil nail.
The pipe roof system is widely used in the New Austrian Tunnelling method (NATM) as the main support system. Thus, the integrity of the pipe roof system influences the tunnel stability. The purpose of this study is to evaluate the grouted ratio of a pipe roof system using a non-destructive method in the laboratory and in the field. In the laboratory tests, four specimens embedded in soils and five non-embedded specimens are prepared with different grouted ratios of 0%, 25%, 50%, 75%, and 100%. The steel pipes are 6 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. Field tests are conducted with two fully grouted pipes with dimensions of 12 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. The reflection method of guided waves, which are generated by a hammer impact and are measured using an acoustic emission sensor, is used for the non-destructive testing. Experimental studies demonstrate that the group velocities and the main frequencies of the guided waves decrease as the grouted ratio increases for embedded and non-embedded specimen in soils. The variation of the main frequency, however, is more significant than the variation of the group velocity. In addition, the group velocities and main frequencies of the field specimens are lower than those of the embedded specimens. This study demonstrates that the variations of the group velocity and main frequency may be used effectively to estimate the grout ratio of a pipe roof system in tunnelling.
Rock bolts have been widely used in underground structures to reinforce rock mass. Thus, the grout integrity of rock bolts should be monitored to ensure a stability of underground structures. The objective of this study is to monitor the health of rock bolts with experimental and numerical analyses using guided waves. In experiments, non-embedded and embedded rock bolts are prepared with different grouted ratios. The piezo disc element and the hammer are used to generate the guided waves. The guided waves are measured and analyzed using acoustic emission sensor and wavelet transforms, respectively. As the results, group velocities of guided waves decrease as the grouted ratios increase. The numerical simulations are conducted using the finite element method and compared with experimental results. The simulation results show the same trends to experimental results. These studies demonstrate that the group velocities of guided waves may be useful tool for the health monitoring of rock bolts.
Soil-nailed structures have been used as a permanent or temporary support system for reinforcing the tunnel surface and the soil slope using soil nails, which are grouted tension-resisting steel bars. The length of soil nails is a critical design factor because soil nails are installed into the soil slope considering the potential slip surface. As soil nails, however, are often installed with different length to designed length, the installed length of soil nails should be evaluated to prevent construction disasters and landslides. A health monitoring system of the installed length of soil nails, hence, has been required to ensure the structural integrity of soil-nailed structures. The objective of this study is the development and application of an elastic wave and electromagnetic wave for evaluating the lengths of installed soil nails. The experiments are conducted with steel bars, grouted steel bar, and soil nails of the length of 1 m ~ 10 m. The electromagnetic wave is generated and detected by the time domain reflectometer. The elastic wave is generated and detected by the hammer and accelerometer, respectively. The lengths of the soil nails are evaluated using the round-trip travel time of the electromagnetic wave and elastic wave propagating along the soil nails. The experimental results show that the round-trip travel time increases as the length of the soil nails increases. The round-trip travel times are the shortest and longest for the steel bar and the soil nails installed into soils, respectively. These studies demonstrate that the electromagnetic wave and elastic wave may be effectively applied for evaluating the lengths of soil nails in the field to prevent construction disasters and landslides.
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