PURPOSES: The purpose of this study is to evaluate and improve the potential risk of road cave-ins due to subsurface cavities based on the deflection ratio measured with light falling weight deflectometer (LFWD) tests. METHODS : A cavity database for Seoul was developed and sorted. LFWD tests based on the database were conducted on pavement sections with and without road cavities detected by ground-penetrating radar (GPR) tests; after excavating the area, the cavity sizes were measured. The deflection ratio was applied and analyzed by cavity management grade methods of Japan and Seoul. RESULTS : The results of comparative analysis show that the deflection method can detect road cavities in areas of the narrow road (or in narrow areas of the road). The average deflection ratio of the cavity sections to the robust sections were 2.48 for high-risk cavities, 1.85 for medium-risk level cavities, and 1.49 for low-risk cavities. Risk levels in Japan and Seoul were reclassified according to the deflection ratios. CONCLUSIONS : LFWD test results can be applied to verify and improve the subsurface cavity risk level by comparing maximum deflection and deflection ratio between cavity area and non-cavity area at the loading center. LFWD devices also have more advantages compared with larger NDT(Nondestructive test) because FWD and GPR encounter difficulties in traffic control and they could not get in a narrow roads.

As the Sewer Pipe is transformed by the expansion of life cycle as a result of the technology development, flexible pipe is developed by the transformed environmental conditions. To change pipe design, three phases(compaction ration - inner deflection ratio - ring stiffness) should be considered in design conditions. The input data of pipe design were provided by compaction-inner deflection ratio-ring stiffness. M oreover, The guidelines of sewerage pipes should be considered by flexible pipes design criteria.

연약지반에서 측방 유동에 의해 주변 지반에 큰 변형을 일으키며 이로 인하여 말뚝기초에 손상을 입히게 된다. 이러한 경우 설치된 말뚝을 수동말뚝이라 하며 편재하중이 작용하게 되고 이로 인해 측방토압을 받게 되며 측방변위가 발생하여 상부구조물에 영향을 미치게 된다. 그러나 국내의 경우 이러한 말뚝과 교대 변위간의 관계에 대한 예측 및 메커니즘에 대한 연구가 부족한 실정이다. 본 연구에서는 교대이동에 대한 해석을 위해 입체, 판 및 프레임 요소를 복합적으로 해석할 수 있는 연성 3차원 유한요소해석 프로그램을 개발하였다. 개발된 연성해석 프로그램을 이용하여 연약지반상 형상비(두께-지름비, t/D비)를 변수로 한 교대강관파일의 변형특성을 명확히 하였다.