TRAVERSE SURVEY - Civil Engineering psc short notes

A traverse survey is the frame work consists of a series of connected lines, the lengths and directions of which are measured with chain or a tape and with an angular measuring instrument respectively. 

I. Closed traverse : A traverse is said to be closed when it returns to the starting point forming a closed polygon. E.g. plot 

II. unclosed or open traverse : A traverse is said to be an open traverse when it does not return to the starting point. E.g.. Road, river, railway

METHODS OF TRAVERSING 

1. BY THE CHAIN ANGLES: - 

• Linear measurements are taken 

• Angles fixed by the lateral measurements are known as chain angles. 

2. COMPASS TRAVERSING /FREE NEEDLE/ LOOSE NEEDLE METHOD 

• Angles are measured by compass and length measured by chain

• In this method an angular measuring instrument, is set up at each of the successive stations and the bearing of each line is taken with reference to the magnetic meridian. 

• In this system the errors are not cumulative, but compensating. 

• This system less accurate than Fast needle and measurement of angles methods

3.PLANE TABLE TRAVERSING 

a. Fast needle method / bearing method 

• In this system a theodolite is used to determine the magnetic bearing of 1st line 

• Bearing of successive lines are formed by measuring direct or deflection angle 

b. Methods of measurement of angles : 

• In this method, the angles measured directly by using theodolite. 

• Angles can be deflection angles or direct angles 

i. Traversing by direct angles
• Angles are measured clockwise from presiding line to following line
• For CW traverse angle should be exterior angle
• For ACW traverse angle should be interior angle
• ACW traversing is commonly used 

ii. Traversing by deflection angles
• Angles can be measured clockwise or anti clockwise from prolongation of preceding station to the following
• Commonly used in railway, road, pipeline

Errors in traversing 

1. LINEAR ERROR 

• Checked by chaining a second time in reverse direction 

2. ANGULAR ERRORS 

i. For direct angles 

• Sum of interior angles = (2n-4)90* 

• Sum of exterior angles = (2n+4)90* 

ii. For deflection angle : sum of deflection angles = 360* 

iii. For bearing : FB = BB ± 180* 

COORDINATE SYSTEM 

1. DEPENDENT / CONSECUTIVE COORDINATE SYSTEM 

• Traversing are plotted taking preceding station as origin 

• Error in plotting a point can affect all other following points 

2. INDEPENDENT COORDINATE SYSTEM 

• All traverse points are plotted wrto a common origin 

• Better method as Error in plotting a point will not affect all other following points

BALANCING OF TRAVERSE 

• Process of applying correction to satisfy the condition ( ΣL = 0 ΣD = 0 ) is called balancing of traversing 

LATITUDE : Coordinate length measured parallel to the assumed meridian direction 

DEPARTURE : Coordinate length measured perpendicular to the assumed meridian direction

For a closed traverse ΣL = 0 ΣD = 0

METHODS OF BALANCING TRAVERSE 

1. BOWDITCH RULE / COMPASS RULE 

• Both linear and angular measurements are equally precise 

2. TRANSIT RULE 

• Angular measurements are more precise than linear measurements 

3. THIRD RULE 

• If corrections applied separately

PREVIOUS YEAR QUESTIONS BASED ON TRAVERSING BELOW