Civil Engineering Survey Review, 3ed

# Chapter 8: Leveling

## Overview

LEVELING is a process to determine the vertical position of different points below, on, or above the ground.

BENCH MARK is a permanent point of known elevation.

VERTICAL LINE follows the direction of gravity to the center of the earth.

HORIZONTAL LINE is perpendicular to the Vertical Line.

LEVEL SURFACE is a curved surface which has every point perpendicular to the direction of gravity.

LEVEL LINE is a line in a Level Surface, hence is a curved line.

DATUM: Any level surface to which elevations are referred. Mean Sea Level is usually used for a datum.

DIFFERENTIAL LEVELING is the most commonly used leveling method.

An example for differential leveling is illustrated below.

Table 8-1: (See Figure 8-A)

LEVEL NOTES

STATION

BS (+S)

HI

FS ( ?S)

Elevation

BM1

7.25

107.34

114.59

TP1

9.66

1.07

113.52

123.18

TP2

8.09

0.48

122.70

130.79

BM2

10.70

120.09

Figure 8-A: Profile view of differential leveling

Terminology

 BM Bench Mark TP Turning Point BS BackSight (also called plus sight) FS ForeSight (also called minus sight) HI Height of the Instrument

Height of the Instruments:

• HI1 = 107.34 + 7.25 = 114.59

• HI2 = 114.59 + 9.66 ? 1.07 = 123.18

• HI3 = 123.18 ? 0.48 + 8.09 = 130.79

Bench Marks:

• BM1 = 107.34

• BM2 = 130.79 ? 10.70 = 120.09

• The difference in elevation = 120.09 ?