Hand Excavation

The technique used to remove the material (rock, dirt, sand, etc.) by hand held tools (pick, shovel, etc.) from the tunnel face or open ditch.

HDPE

High Density PolyethyleneA plastic resin made by the copolymerization of ethylene and a small amount of another hydrocarbon. The resulting base resin density, before additives or pigments, is greater than 0.941 gins/cc.; see Polyethylene.

Head (Static)

The height of water above any plane or point of references (The energy possessed by each unit of weight of a liquid, expressed as the vertical height through which a unit of weight would have to fall to release the average energy posed.) Standard unit of measure shall be the foot. Head in feet for water at 68?/font> F is 1 psi = 2.310 ft.

Headwall

A wall (of any material) at the end of a culvert or, drain to serve one or more of the following purposes: protect fill from scour or undermining, increase hydraulic efficiency, divert direction of flow, and serve as a retaining wall.

Heave

Measurable upward movement of the ground or structure as the result of the excavation process.