SURVEYING (REVIEWER CHAP 4)

LEVELING

• Process of directly or indirectly measuring vertical distances to determine the elevation of points or difference in elevation

• Leveling ensures accurate measurements of elevations helping in the design and construction of roads, buildings, and drainage systems.

DIRECT OR SPIRIT LEVELING

The most commonly employed method of determining the elevation of points some distance apart by a series of set ups of a leveling instrument along a selected route

 RECIPROCAL LEVELING

• The process of accurately determining the difference in elevation between two intervisible points located at a considerable distance apart

PROFILE LEVELING

Used to determine differences in elevation between points at designated short measured intervals along an established line to provide data from which a vertical section of the ground surface can be plotted.

TRIGONOMETRIC LEVELING

Used to determine the difference in elevation between two points by trigonometric computations from measurements of its horizontal or slope distance and vertical angle between the points

STADIA LEVELING

• Combines features of direct leveling with those of trigonometric leveling.

• Differences in elevation between points are computed from observed vertical angles and the three intercepts on a rod held at each point backsighted or foresighted.

BAROMETRIC LEVELING

Determination of differences in elevation between points by measuring the variation in atmospheric pressure at each point by means of a barometer.

CROSS-SECTION LEVELING

Used to obtain a representation of the ground surface on either side of the centerline.

BORROW-PIT LEVELING

Method of determining the relative elevations of points in borrow-pit excavations for the purpose of calculating volumes of earthwork.

DUMPY LEVEL

(TYPES OF LEVELS)

• Has a long telescope attached to the level bar

• The telescope, which can be rotated 360°, fixes the direction of the line of sight

• Attached to the level bar is the level vial which always remain in the same vertical plane as the telescope

• Leveling Head- supports the telescope and permits the bubble in the tube to be centered by means of the leveling screws

WYE LEVEL

(TYPES OF LEVELS)

• Has a detachable telescope which rests in supports called wyes.

• Curved clips- used to fasten the telescope in place

BUILDER’S LEVEL

(TYPES OF LEVELS)

• Also called a construction level or architect’s level

• Used primarily in building construction where a high degree of precision is not a primary requisite

• Horizontal Circle- used when measuring or laying out horizontal angles.

AUTOMATIC LEVEL

(TYPES OF LEVELS)

• Does not use a level vial and its stability to level itself depends upon the action of a complex pendulum- and –prism device

• Equipped with a prismatic device called a compensator which is suspended on fine, non-magnetic wires

TILTING LEVEL

(TYPES OF LEVELS)

• Can be tilted or rotated about its horizontal axis

• Tilting knob- Used to rotate the telescope into a correct horizontal position

• Employed for very precise leveling operations and is equipped with a horizontal circle which makes it suitable for layout and construction surveys.

GEODETIC LEVEL

(TYPES OF LEVELS)

• A level instrument where most of its metal parts are made of invar to reduce the effects of temperature

• Employed in first-order leveling work where extreme precision is an important requirement

• Equipped with stadia hairs and vertical and horizontal cross hairs which makes it suitable for three-wire leveling.

TRANSIT AS A LEVEL

(TYPES OF LEVELS)

• Engineer’s Transit- Universal surveying instrument.

LASER LEVEL

(TYPES OF LEVELS)

Usually attached to conventional surveying instruments and uses laser light for leveling work

HAND LEVEL

(TYPES OF LEVELS)

• Hand held instrument used on surveys involving short sights

• Consists of a brass tube about 15 cm long having a plain glass objective and a peep sight eye-piece

LEVELING ROD

A graduated rod used for measuring the vertical distance between the line of sight through a leveling instrument and the point whose elevation is either required or known.

SELF-READING ROD

It can be read directly by the instrument man through the telescope by noting the apparent intersection

TARGET ROD

Has a sliding target which is set and read by a rodman at the position selected by the instrument man (used when longer distances are involved)

ROD RIBBONS

• An improvised type of rod used in leveling work.

• The graduations on this rod are marked either on canvass or metal strips which are attached to a long piece of selected lumber by staples

• Can be easily removed from the wood to which it is attached, rolled, and put into one’s pocket after usage

PRECISE ROD

A form of rod ribbon which uses a graduated invar strip permanently fastened to a 4-meter long wooden or metal frame

GEODETIC ROD

• A form of rod ribbon which uses a graduated invar metal strip.

• The graduations on this rod are painted upside down for use with inverting telescopes

TAPE ROD

• Also known as the automatic rod

• Used when numerous elevations are to be determined from a single set-up of the leveling instrument

• A 3-meter long graduated metal tape is looped around the frame of the rod by means of rollers located at both ends of the frame

ROD LEVEL

• A device used for fast and correct plumbing of a rod

• L-shape in design

• Consists of a small circular spirit level fastened to the rod or to a small bracket held against the side of the rod

TARGET

A small device attached to a rod when extremely long sights make direct reading of the rod difficult or impossible

1. INSTRUMENTAL ERRORS

2. PERSONAL ERRORS

3. NATURAL ERRORS

SOURCES OF ERROR IN LEVELING

• Instrument out of adjustment

• Rod not of standard length

• Defective tripod

INSTRUMENTAL ERRORS

• Bubble not centered

• Parallax

• Faulty rod readings

• Rod not held plumb

• Incorrect setting of target

• Unequal backsight and foresight distances

PERSONAL ERRORS

• Curvature of the earth

• Atmospheric refraction

• Temperature variations

• Wind

• Settlement of the instrument

• Faulty turning points

NATURAL ERRORS

• Misreading the rod

• Incorrect recording

• Erroneous computations

• Rod not fully extended

• Moving turning points

COMMON MISTAKES IN LEVELING

Leveling Head

• supports the telescope and permits the bubble in the tube to be centered by means of the leveling screws

Curved clips

• used to fasten the telescope in place

Horizontal Circle

• used when measuring or laying out horizontal angles.

Tilting knob

Engineer’s Transit

• Universal surveying instrument.