Abstract
Based on the many pioneer works on earth pressure on buried pipes, it is confirmed that arching around the culvert increases the vertical pressures on the top of a culvert and reduces the horizontal pressures on the sides of a culvert. Because of the practitioners' interest in a more rational structural design of buried conduits, much attention has been paid to the vertical load imposed on the top of a conduit than on the sides. In cases of culverts constructed under fill dams, however, the present authors infer that the conditions (of reduced stresses) adjacent to the sides of a conduit are critical to the danger of hydraulic fracturing at a stage when the horizontal stresses exerting on both sides of a culvert become lower than the reservoir water pressure. Based on this inference, the authors further postulate that hydraulic fracturing is the most likely cause of leakage (mostly concentrated leakage) and of failure of many low dams along the outlet conduit especially after heavy rain. Two case studies supplemented by FEM analysis are presented and the results clearly confirm the authors' inference. Some countermeasures to cope with this situation are also recommended.
