To measure the distance between two stations by using chain or tape and direct ranging.
Chain, Tape, Arrows, Ranging Rods
Chaining is a term which is used to denote measuring distances either with the help of a chain or a tape and is the more accurate method of making direct measurements. While measuring the length of a survey line or ‘chain line’, chain or tape must be stretched straight along the line joining its two terminal stations. If the length of line is less than the length of the chain, there will be no difficulty, in doing so.If, however, the length of the line exceeds the length of the chain, some intermediate points will have to be established in line with the two terminal points before chaining is started. The process of fixing or establishing such an intermediate points is known as ranging. There are two methods of ranging: i) Direct Ranging, ii) Indirect ranging
Direct ranging is done when two ends of the survey lines are intervisible .In such cases ranging can either be done by eye or through some optical instruments such as line ranger or a theodolite.
Procedure for direct ranging:
- Let A and B be two points at the ends of a survey line.
- One ranging rod is erected at the point B, while the surveyor stands with another ranging rod at point ‘A’, holding the rod at about half meter length in line with AB.
- The assistant then goes with another ranging rod and establishes the rod at a point approximately in the line with AB (by judgment) at a distance not greater than one chain length from ‘A’.
- The surveyor at ‘A’ then signals the assistant to move traverse to the chain line,till he is in line with ‘A’ & ‘B’.
- Similarly, other intermediate points can be established. The code of signal used for this purposes are given in the table below.
|Sr No||Signal by Surveyor||Action by the Assistant|
|1||Rapid sweep with right hand||Move considerably to right|
|2||Slow sweep with right hand||Move slowly to right|
|3||Right arm extended||Continue to move to right|
|4||Right arm up and moved to the right||Plumb the rod to the right|
|5||Right sweep with left hand||Move considerable to Left|
|6||Slow sweep with left hand||Move slowly to left|
|7||left arm extended||Continue to move to left|
|8||Left arm up and moved to the left.||Plumb the rod to the left|
|9||Both hands above head and then brought down||correct|
|10||Both arm extended forward horizontally and the hands depressed briskly||Fix the road|
Procedure for Accurate ranging and chaining:
- Let the length of the line ‘AB’ is to be measured, point ‘A’ being the starting point. Place a ranging rod behind the point ‘B’ so that it is on the line with respect to the starting point ‘A’
- The follower stands at the point ‘A’ holding one end of the tape while the leader moves ahead holding zero end of the tape in one hand a bundle of arrows in the other. When he reaches approximately one tape length distance from ‘A’ the follower directs him for ranging in the line. The tape is then pulled out and whipped gently to make sure that its entire length lies along the line. The leader then pushes the arrow into the ground, opposite the zero.
- The follower then releases his end of the tape and the two moves forward along the line, the leader dragging the tape. When the end of the tape reaches the arrow just placed, follower calls out of tape and lines the leader in and the procedure is repeated as in step 2.
- When the second arrow has been established by the leader, follower picks up the first arrow, and both the persons move ahead as described in step 3.The procedure is repeated until ten tape lengths have been measured. At this stage, the leader will be out of arrows, while follower will have nine arrows. The leader will then call “arrows” or “ten”. When the leader moves further after the tape length has been measured, and reaches the tape length ahead, the follower takes out the tenth arrow, erects a ranging rod or a nail in its place and then transfers 10 arrows to the leader. The surveyor records the transfer of arrows in the field book.
- At the end of the line, at ‘B’, the last measurement will generally be a partial tape length from the last arrow set to the end point of the line. The leader holds the end of the tape at ‘B’while the follower pulls the tape back till it becomes taul and then reads against the arrow.
- The ranging is done between ‘A’ and ‘B’
The total chain length =
- The accurate ranging is done between ‘A’ & ‘B’.
The total tape length =
i) Average pace value = Actual Distance/ No of steps = 30/39 =0.77 mt.
No. of steps from ‘A’ to ‘B’=
Distance by pacin’s between ‘A’ & ‘B’ = (No. of steps from ‘A’ to ‘B’) x (Avg.pace value)
ii) The actual chain length = 30 m
No. of chain lengths measured =
After the——chain, length to ‘B’ =
Total chain length between ‘A ‘& ‘B’=
iii) The actual chain length = 30 mt
No. of tape lengths measured =
After the——Tape, length to ‘B’ =
Total tape length between ‘A ‘& ‘B’ =