Development of simple sand bypass system using a self-sinking suction pipe with holes

Because many coastal areas in Japan are in a distressed condition due to beach erosion, beach preservation and restoration have become important problems. Sand bypass systems offer one counter-measure for beach erosion. A typical example of conventional sand bypassing is collection of sand with an excavator and transportation by dump truck. However, with this method, some mechanism is required to move the shovel which is used to collect the sand, and considerable manpower is necessary, including dump truck drivers and others. Moreover, truck transportation also causes air pollution, noise, and other environmental problems. 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 pipe attached to 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 pipe, 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. A prototype experimental device was test-manufactured and used in field experiments. In continuous operation for approximately 1 hour, it was possible to collect/transport 200-500 1/m³ of sand, which is roughly equivalent to 50,000 m³ in a 3-month period.