Differential Leveling
FIELD WORK NO. 5
DIFFERENTIAL LEVELING
I. OBJECTIVES: To determine the elevation of points relative to a reference point by differential leveling
II. INSTRUMENTS: Engineer’s level, Leveling Rods, Marking Pins
III. DISCUSSION: Direct leveling is the 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. This method of leveling is also referred to, as spirit leveling since the device used is a spirit level. Differential leveling, double – rodded leveling, and three – wire leveling are forms of direct leveling. In direct leveling, vertical distances are measured above or below a level line and these values are used to compute the elevation of points or their differences in elevation. Being the most precise method of leveling, it is used when a high degree of accuracy is required. The basic equipment used in differential leveling include a graduated leveling rod, and a leveling instrument such as a dumpy level, automatic level, or an engineer’s transit. These leveling instruments are used to establish a horizontal line of sight and to measure the vertical distance between the line if sight and the point on which the rod is held.
IV. PROCEDURES: 1. Designate a level route along the ground and mark the initial point as BM–1 and the terminal point as BM–2. 2. Set up turning points in between BM–1 and BM–2 and mark these points by means of pegs or hubs. 3. Set up and level the instrument between BM–1 and TP–1 at a point that is halfway of the distance between the two points in order to cover up the error initiated by the refraction of the sun. 4. Direct the rodmen to position the leveling rods at BM–1 and TP–1. 5. Take the backsight reading at BM-1 and record. 6. Rotate the instrument about its vertical axis until the leveling rod at TP-1 is sighted on the telescope. Take the reading on the rod and
DIFFERENTIAL LEVELING
I. OBJECTIVES: To determine the elevation of points relative to a reference point by differential leveling
II. INSTRUMENTS: Engineer’s level, Leveling Rods, Marking Pins
III. DISCUSSION: Direct leveling is the 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. This method of leveling is also referred to, as spirit leveling since the device used is a spirit level. Differential leveling, double – rodded leveling, and three – wire leveling are forms of direct leveling. In direct leveling, vertical distances are measured above or below a level line and these values are used to compute the elevation of points or their differences in elevation. Being the most precise method of leveling, it is used when a high degree of accuracy is required. The basic equipment used in differential leveling include a graduated leveling rod, and a leveling instrument such as a dumpy level, automatic level, or an engineer’s transit. These leveling instruments are used to establish a horizontal line of sight and to measure the vertical distance between the line if sight and the point on which the rod is held.
IV. PROCEDURES: 1. Designate a level route along the ground and mark the initial point as BM–1 and the terminal point as BM–2. 2. Set up turning points in between BM–1 and BM–2 and mark these points by means of pegs or hubs. 3. Set up and level the instrument between BM–1 and TP–1 at a point that is halfway of the distance between the two points in order to cover up the error initiated by the refraction of the sun. 4. Direct the rodmen to position the leveling rods at BM–1 and TP–1. 5. Take the backsight reading at BM-1 and record. 6. Rotate the instrument about its vertical axis until the leveling rod at TP-1 is sighted on the telescope. Take the reading on the rod and