DEVELOPMENT OF SIMPLE SAND BYPASS SYSTEM USING A SELF-SINKING SUCTION PIPE WITH HOLES

摘要

Many coastal areas in Japan are in a distressed condition due to beach erosion. Sand bypass systems offer one countermeasure for beach erosion. In the conventional sand bypass method, heavy equipment such as a backhoe is used to collect sand when the location is above sea level, and a dredger is used when the sand source is below sea level. Sand is collected by moving the sand-collecting device. This means that some mechanism for movement of the sand-collecting device and mobile equipment such as a truck or dredger are indispensable, and considerable manpower is necessary, including dump truck drivers and others.This paper proposes a new sand bypass system with a simple composition comprising a suction pipe with holes, on which a slurry pump is mounted, and a water jet holes arranged on the underside of the suction pipe. The pump inlet is connected to the suction pipe, and the outlet is connected to a sand discharge pipe.In operation, the device is placed on an area of accumulated sand and water is jetted from the water jet holes, fluidizing the surrounding sand, which is drawn into the suction pipe together with seawater. As the sand is fluidized, the suction pipe/pump assembly sinks into the sand under its own weight, enabling continuous collection/transportation of sand. The effectiveness of the system was demonstrated in field experiments in seabed sand collection and beach sand collection. 1) In the seabed experiment, where sand collection was affected by wave action, continuous collection and transportation of sand for half a day was possible at the same place.2) In the beach experiment, where sand collection was not supported by wave action, continuous collection and transportation was possible, requiring only horizontal pulling of the sand collection device by constant power of equal with its own weight.3) The cost of the proposed method was approximately half that of the "Backhoe loading and dump truck transportation on land" method.