Geotechnical Terms

Angle of draw – This is the angle between a vertical line drawn upward to the surface
from the edge of the underground opening and a line drawn from the edge of the opening
to the point of zero surface subsidence.
Breach – Remove a section of a dam to prevent the dam from impounding water.
Concrete Gravity Dam – A structure designed to safely impound water entirely by its
weight and internal strength.
Extensometer – An extensometer is a device that is used to measure changes in the length
of an object. It is useful for HstressH-HstrainH measurements.
Inclinometer – An inclinometer is an instrument for measuring angles of HslopeH (or HtiltH),
HelevationH or HinclinationH of an object with respect to gravity. It is also known as a tilt
meter, tilt indicator, slope alert.
Non-overflow Section – The section of a dam adjacent to the spillway designed to safely
impound water in amounts up to the flood for which the dam was designed.
Ogee Weir or Ogee Section – A spillway designed to pass flow through a dam. In cross
section the weir is in the shape of an “S”, or ogee.
Spalling – The process by which fragments of a larger mass break away due to stress.
Spillway – The portion of the dam designed to safely pass the flow past the dam. The
structure may be a primary spillway designed to pass normal flows, an emergency
spillway designed to pass flood flows, or a combination spillway designed to pass both.