DESIGN REQUIREMENTS FOR THE CULVERTS AND ARRANGEMENTS FOR THE HEAD WALLS AND THE WING WALLS.

Culvert is a small type of bridge structure, less than six metres of span between the faces of abutments and doesn't generally has two spans. It must be large enough to carry the flow without any heading up at the entrance. To provide for this, culverts should be assumed as flowing only half full when the approach channel is wide and shallow;If the banks are steep and the channel narrow 3/4 th full may be taken. Where masonry abutments supporting arches or slabs are designed for culvert functioning under head bed pavement must be provided and in all cases including pipe and the box culverts, adequate provision must be made at the exit against erosion by proving the curtain walls. It is best advantage of the capacity of a culvert for which the shape of the entrance should be such as to cause the least amount of restriction to the free flow of the water, for which pitched aprons at both ends must be provided. In the case of culverts or cause way on black soils or soft stata, a complete raft of concrete should be laid as per design requirements at the full width and the length and curtain wall is also provided at the downstream edge of the wing walls. It is not generally convenient to design a culvert smaller than 90×90 CM or 90 cm dia and it is then called a vent way. In the case of pipe culverts or other small culverts which should extend across the whole formation width, wing walls can be omitted, especially where there is good amount of earth filling over the culvert and a straight wall is provided. The length of such a wall should be little more than sufficient to keep the earth of the embankment spilling around its end and from reaching the opening. There should be sufficient earth cushion over the top of the pipe laid. Where a defined channel don't exist and the natural velocity of flow is very low, it is economical to design a culvert as consisting of a pipe or a number of pipes of circular or rectangular section (box) functioning with the inlet submerged.