PURPOSES: In this study, a numerical parametric study was performed to evaluate the effect of angular velocity and weight of wheel, and density of road-bed particles on corrugation development. METHODS : Discrete element method coupled with rigid body dynamics was applied to simulate a wheel-running circular table with variations in independent parameters, such as wheel angular velocity, wheel weight, and particle density. The position profiles for travel distance from origin were compared and analyzed to confirm if the trend from numerical analysis agrees with the analytical solution. RESULTS: The angular velocity of the wheel exhibits a clear inverse relationship with the development of corrugation even though the weight of wheel does not demonstrate clear trends for both long-wave and short-wave corrugation. The density of road-bed particles is observed to have clear proportional effect on corrugation development. The movement of corrugation to the running direction, which was observed in previous research, is also observed for various conditions. CONCLUSIONS : The parametric study using discrete element method with rigid body dynamics clearly exhibits good agreement with analytical solution for initiation of corrugation. The coupled method is confirmed to supply additional information that cannot be delivered by analytical solution only.

PURPOSES : The frequency and severity of natural disasters such as torrential rain or typhoons have become increasingly significant worldwide. Events such as summer typhoons and localized torrential downpour can cause severe damages to a residential area and road networks, resulting in serious harm to the daily lives of people, especially in rural areas by isolating residents from road networks. An immediate and emergency repair technology for the collapsed road networks is urgently needed. This study introduces a new technology to repair road bases or slopes. METHODS: The development of new technology for emergency and permanent repair consists of first, packing of cement paste-coated gravel, second, combining appropriate equipment, and third, conducting a field applicability test. In this research, the compressive strength of cement pastecoated gravel, gravel-netting concrete properties, and packing efficiency were determined, and a full scale field mock-up test was carried out. RESULTS : The compressive strength of the cement paste-coated gravel concrete satisfied the required limit for road base of 5 MPa after 7 days. With appropriate netting materials and packing size, gravel-netting concrete was successful up to a slope of 1:1.5. The full scale field mockup test showed efficiency in the field and penetration resistance performance. CONCLUSIONS: The new technology of emergency and permanent repair for damaged road bases and slopes, introduced in this study, showed satisfactory performance. The technology is expected to be applied in the field when construction procedures and quality specifications are made.

PURPOSES : In this research, the initiation and development of corrugation on a gravel road with certain wheel and boundary conditions were evaluated using a coupled discrete-element method (DEM) with multibody dynamics (MBD). METHODS: In this study, 665,534 particles with a 4-mm diameter were generated and compacted to build a circular roadbed track, with a depth and width of 42 mm and 50 mm, respectively. A single wheel with a 100-mm diameter, 40-mm width, and 0.157-kg mass was considered for the track. The single wheel was set to run slowly on the track with a speed of 2.5 rad/s so that the corrugation was gradually initiated and developed without losing contact between the wheel and the roadbed. Then, the shape of the track surface was monitored, and the movement of the particles in the roadbed was tracked at certain wheel-pass numbers to evaluate the overall corrugation initiation and development mechanism. RESULTS : Two types of corrugation, long wave-length and short wave-length, were observed in the circular track. It seems that the long wave-length corrugation was developed by the longitudinal movement of surface particles in the entire track, while the short wave-length corrugation was developed by shear deformation in a local section. Properties such as particle coefficients, track bulk density, and wheel mass, have significant effects on the initiation and development of long-wave corrugation. CONCLUSIONS : It was concluded that the coupled numerical method applied in this research could be effectively used to simulate the corrugation of a gravel road and to understand the mechanism that initiates and develops corrugation. To derive a comprehensive conclusion for the corrugation development under various conditions, the driver’s acceleration and deceleration with various particle gradations and wheelconfiguration models should be considered in the simulation.

골재 도로에서의 콜루게이션은 골재 도로의 주요한 파손 형태일 뿐만 아니라 교통량이 집중되는 구간에서의 아스팔트 콘크리트 포장의 러팅(rutting) 및 시멘트 콘크리트 포장에서의 국지적 줄눈부 파손의 발생 및 진전과도 역학적 연관성이 높다. 또한 콜루게이션의 발생을 설명하는데 활용되는 차륜과 지반의 상호작용은 사막을 포함한 극한지 탐사차량의 주행성이나 견인력 문제와도 관련성이 매우 높기 때문에, 콜루게이션의 발생과 진전 원인을 역학적으로 규명하는 것은 매우 중요한 의미를 갖는다고 할 수 있다. 본 연구에서는 골재 도로에서의 콜루게이션 발생 및 진전을 설명하기 위하여 기존의 연구에서 실험적이거나 이론적으로 설정한 가설에 대하여, 이산요소법(discrete element method, DEM)과 다물체동역학(multibody dynamics, MBD)을 조합한 수치해석기법을 통하여 검증할 수 있는 지를 확인하고자 하였다. 이를 위하여 원형 트랙을 일정한 각속도로 회전하는 단일 차륜과 해당 차륜과 상호작용하는 토질 입자를 각각 MBD와 DEM으로 모사하였으며, 가장 단순한 조건에서 전형적인 콜루게이션의 발생을 기존의 가설 및 실내 실험과 유사한 방법으로 설명할 수 있는지를 확인하였다. 이에 따른 결론은 다음과 같으며, 원형 트랙에서의 프로파일과 표면 입자의 흐름은 각각 Fig. 1과 Fig. 2에 나타나 있다. ⦁주어진 원형 트랙에서 발생된 콜루게이션은 긴 파장과 짧은 파장의 콜루게이션으로 구분될 수 있다. ⦁긴 파장의 콜루게이션은 지반의 초기 밀도 조건이나 차륜의 운동 조건에 의하여 발생의 경향이 결정될 가능성이 매우 높은 것을 확인하였다. ⦁원형 트랙에서 긴 파장의 콜루게이션은 전단변형과 같이 부피가 변화하지 않는 형태의 변형이 아닌, 상부층 중심 입자의 주행방향 이동이 주요 원인인 것으로 확인되었다. ⦁또한 긴 파장의 콜루게이션은 50회 또는 100회 이하의 초기 차륜통과 조건에서 대부분 발달하며, 이후에는 느린 속력으로 주행방향을 따라 전체적으로 회전하는 경향을 나타내는 것으로 확인되었다. ⦁짧은 파장의 콜루게이션은 긴 파장의 콜루게이션에 비하여 상대적으로 느리게 발달하며, 차륜의 통과 횟수가 증가함에 따라서 선명해지는 경향을 나타내었다. ⦁모사 결과를 바탕으로 짧은 파장의 콜루게이션은 부피가 크게 변화하지 않는 국지적 지반의 밀도 변화, 즉 전단변형이 주요한 원인으로 추정될 수 있다.