Sand Flow

A method of sand bedding whereby the sand-water mix is transported through a pipe system with fixed outlets in the soffit of the element. The mix is usually discharged through one outlet at a time. As the velocity of the mix decreases after leaving the outlet, sand is deposited by gravity to form a firm pancake-shaped mound almost touching the underside of the tunnel, with a small depression beneath the outlet. While pancake dimensions vary, an area of 100 square metres would not be unusual. The sand-water mix may be supplied either externally though inlets in the roof or walls, or from inside through non-return valves.