SUBGRADEThe soil prepared to support a
structure or a pavement system. It is the
foundation for the pavement structure. The
subgrade soil is sometimes called basement soil
or foundation soil.
SYSTEMATIC ERRORSErrors that, as long
as conditions are unchanged, will always have the
same magnitude and the same algebraic sign.
TANGENTThe ratio between the side opposite
and the side adjacent an angle in a right triangle:
tan = opp/ad.
TANGENT LINEA line that touches the
circumference of a circle at one point and is
perpendicular to the radius at the point of
TARGETAny object to which the instrument
is pointed. A target may be a plumb bob or plumb
bob cord, a nail in the top of a stake, a taping
arrow, a ranging pole, a pencil, or any other
object that will provide a sharply defined,
stationary point or line. A target is usually placed
vertically over an unoccupied transit station.
TECHNICAL ENGINEERING CHARTS
Charts based on a series of measurements of
laboratory experiments or work activities.
TEMPLATESTimesaving devices used to draw
various shapes and symbols. Templates are
available for all types of drawings.
projection commonly used in the United States.
The top view projects above the front view, and
the sides and bottom automatically project into
their proper positions.
TITLE BLOCKBlock drawn in the lower right
corner of a drawing; it should contain all the
information necessary to identify the drawing.
TRACING PAPERHigh-grade, white, trans-
parent paper that takes pencil well; used when
reproductions are to be made of drawings; also
known as tracing vellum.
TRACING VELLUMSee TRACING PAPER.
TRANSIT STATIONA marked point over
which the instrument is, has been, or will be,
accurately positioned for use.
TRANSPORTED SOILA soil that has been
moved by natural forces to a location other than
TRAVERSE THE INSTRUMENTRotate the
instrument about its vertical axis; that is, turn the
instrument in azimuth.
TRIANGLEA polygon of three sides.
TRIANGULAR PRISMA solid figure whose
base is a triangle.
TRIGONOMETRYThat branch of mathematics
that deals with certain constant relationships that
exist in triangles and with methods of applying
these relationships to compute unknown values
from known values.
TRAPEZOIDA quadrilateral with only one
pair of opposite sides parallel, the other pair being
TRAPEZIUMA quadrilateral with no sides
TRIM LINESLightly drawn lines used as guides
to trim a drawing to standard size.
VERTICAL ANGLEAn angle between two
intersecting lines in a vertical plane. It should be
understood that one line lies on the horizontal
plane, and the angle originates from the
intersection of the two planes.
VERTICAL CONTROLEstablished bench
VERTICAL LINEA line that lies in the vertical
plane and is perpendicular to the plane of the
horizon, such as the direction of a plumb line.
V E R T I C A L P L A N E A p l a n e t h a t is
perpendicular to the horizontal plane.
VIEWING PLANE LINESThick, heavy lines
used to indicate the plane or planes from which
a surface or several surfaces are viewed.
VISIBLE LINESSolid, thick lines indicating the
edges of the object being drawn.
WATER-CEMENT RATIOThe ratio of the
amount of water, exclusive only of that absorbed
by the aggregates, to the amount of cement in a
concrete mixture. This ratio is variously stated as
follows: (1) by bulk volume of cement (assuming
cement to weigh 94 lb per cu ft); (2) by absolute
volume of cement; (3) by weight; and (4) in terms
of gallons of water per 94-lb sack of cement.