The chain surveying is the most commonly used surveying for quick and short measurements. Chain (Tape) surveying is the simplest form of detail surveying. In this method, the lengths of lines marked on the field are measured, while the details are measured by offsets and ties from these lines. So, this fieldwork aimed to train the student on the following process:
1. Selection of a framework (chain or baselines) and control points.
2. Direct method of linear measurements (horizontal distance measurement).
3. Setting out right angles (offsets).
4. Determining the direction of any line in the field with respect to magnetic north
5. Booking Method.
6. Plotting Method.
Equipment used for chain surveying:
Tapes, Ranging rods, Arrows/Marker paint, Prism Square, Prismatic Compass Booking
The procedure of chain surveying
1. Make a reconnaissance of the area and select a suitable framework (chain lines) and stations
based on the criterion given in Note 1.
2. Measure all the chain (based) lines once in each direction using the direct measurement
3. Measure the offsets/or ties from every necessary point on the details to the corresponding
baseline. Use the procedure explained in Note 2.
4. You may need some measurements on the details (on the building sides…).
5. Measure the bearing of one of the chain lines by using the prismatic compass. See Note 3.
6. Record all the information and measurements properly in the booking papers as explained in
7. Make the necessary calculations and corrections.
8. Draw the details in a suitable scale to produce a detailed map of the area. See Note 5
Note 1: CHAIN LINES & STATIONS SELECTION
To locate suitable stations and chain lines, a reconnaissance of the area should be undertaken by walking around the area required to be surveyed. Any obstacles should be noticed. The selected stations should produce well formed linked triangles or braced quadrilaterals.
The principles to be considered are:
1. Few long lines should be used.
2. Avoid any obstacles to ranging or chaining.
3. Angles should be > 30o & <120o .
4. Make check lines when possible to detect errors when plotting.
5. The lines should be closed to the details (Avoid long offsets (>10m) and ties. After selection of the framework you should draw sketch of the area and mark the stations by wooden pegs or marker paints, and give a number for each station.
Note 2: SETTING THE OFFSET
Any point on the details can be related to the chain line by offset or ties:
The pair of ties method depends on taking the measurement of two distances from the point
to be surveyed to a traverse line (base line).
The offset method is based on taking a perpendicular distance from the point to the survey
line (base line).
To set out offsets, a prism square can be used. To locate the point at which a perpendicular from
any point on the feature would meet the chain line (say AB) you can follow the following steps:
1. One man should hold the ranging pole at the given point, while the other pole is placed at
any point on the chain line AB.
2. The observer holds the instrument and walk along the line AB until he sees both poles
coincide in each other. Then the distance to this point along the chain line can be measured
beside the length of the perpendicular.
Another method can be used by holding the zero point of the tape at the given point and swinging
tape over the chain line and mark the point on the chain line at minimum reading.
NOTE 3: MEASURING THE BEARING OF A LINE
To measure the angle that any line (say AB) makes with the magnetic direction, you can use a
prismatic compass. The procedure is as follow:
1. Place the ranging pole vertically at point B.
2. Place the prismatic compass over its tripod at point A and level it using the bubble and
3. Rotate the compass until it is directed to the pole and read the angle.
4. Repeat the whole procedure for point B.
NOTE 4: BOOKING
The field book should be neat and consistent:
1. Each chain line is represented by double line drawn through the corner of the page.
2. Entries start at the bottom of the page.
3. Detail that is on the right-hand side of the line is booked on the right-hand side of the page
and vice versa.
4. The lengths from the beginning of the line are written inside the double lines while the offset
NOTE 5: PLOTTING
A. Plot the framework of chain lines by:
1. Draw the longest line according to its bearing.
2. Build up the other chain lines by using beam compasses.
3. Draw the check lines, and if there are any errors, check the drawn lines in the incorrect
triangles. (You may need to measure them in the field).
B. Draw the details for each chain line based on offsets and ties information. Then connect these
points to get the details.
I hope you like this post, chain surveying. If you want more, please go through this website.