GEOGRAPHY FORM 5 – CHAIN AND TAPE MEASURE SURVEY
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GEOGRAPHY FORM 5 – CHAIN AND TAPE MEASURE SURVEY
CHAIN AND TAPE MEASURE SURVEY
Chain and tape survey is a science of measuring series of straight lines on the ground with the use of a chain or tape measure. It is the simplest and commonest method of making linear or horizontal measurements on land particularly for the smaller distances.
Significant uses of chain survey
· • Chain survey is conducted to develop details which can be used for mapping areas.
· •Chain survey is conducted to develop details for construction purposes.
· •Chain survey is conducted to collect data to be added to the existing data.
· •Chain survey is conducted to supplement other topographical survey techniques like plane table survey and prismatic compass survey.
Tools used in the conducting chain survey
The main tools used into the conducting chain survey include the following:-
The chain:-
It is a tempered steel wire with length of about 20m or 30 m. It has links connected by small rings in such a way it can be easily folded and carried in the field. The length from ring centre to another is of about 200 mm. It is used to measure distance on the ground along the line of tracery.
Tapes
(a) Those which made up of steel and available in varied length up to 100m
(b) Those make up of fiberglass and they are available in lengths of 10m, 15m, 20m, and 30m Tapes like chain, are also used for liner measurements particularly of short distances.
Cross staff
They are made of metal or wood with eye slits at right angles. They are used to measure right angles of the off sets from the line of traverse.
Ranging rods /poles
They are poles of woods or light metal 2m, 2.5 or 3m long. They are painted alternatively in red and white bans each 500 mm long so that they can be easily seen from a distance. They have pointed metal ends for driving into ground. They are used to mark points required to be seen in linear measurement
Arrows
These are steel skewers of about 0.4m long. They are used for marking points an ground when chaining a long (line) distance, They are potentially used when the chain has to be laid down several times and the positions of the end of chain are marked with the arrows.
pegs
They are wooden station marks with 40mm square and 50 cm long. They are driven into the ground to mark positions permanently during survey.
Optical square
It is optical instrument of camera like for setting out angles. It is commonly used for marking off sets at right angles from the line of traverse.
Prismatic compass
It is a compass box with needle in the magnetic liquid to enable the needle to swing freely at the centre. There is a card which is graduated in the degrees to enable the reader or the viewer to read the given bearing or observed bearing
Field sheet/Note book
They are writing sheets They are used for recording or booking all necessary field work information
FIELD WORK OF A CHAIN SURVEY
(METHOD OF CHAIN SURVEYING)
The conduct of chain survey in the field area
1. Preliminary inspection of the field area
The site whose details to be taken by conducting chain survey should be pre visited. This is commonly known as reconnaissance survey. During the pre visit, the surveyor work all over the site to obtain a picture in his or her mind of the whole area. More over, the surveyor should do the following beside walking all over the site.
· Making a sketch plan of the site in the field to be surveyed.
· Choose the surveying stations.
· Marking of the surveying stations with leader.
2. Organization of chain survey team
It should have three people including the leader, follower and booker
· The leader has a role of reading measurements taken in the field with the use of chain. He also pulls the chain forwards and insert the arrows at every point or station
· The booker has a work of recording data as given from eh leader
· The follower has a role of organizing the instruments during the field work. He also directs the leader where to insert the arrow and collect them.
3. The main chain survey work has to start as follows
(a) The chain is thrown and extended from one position to another and disentangle knots
(b) Leader takes arrows and ranging road, and follower takes ranging rod
(c) Follower erects road at first base point places brass handle of the chain against rod. In this leader ex tends the chain follower by the follower
(d) Leader straightens the chain and inserts arrow at end of brass handle. Offsets, liner distances and the point can be taken
(e) The leader drags chain so that follower is on a leader is arrow. Then follower moves to the leader arrow and places pole behind arrow.
Note:
The process of dragging the chain, signing and aligning is repeated until the line is completed the same process is also repeated with another lines until the whole area is surveyed.
correct signals as seen by surveyor leader. (a) Move chain to left (b) Move chain to left (c) Chain correct
Point fixation in chain survey.
Fixation of points as chain survey conducted is by following methods.
1.Trilaterization method.
it is by two measured distances. Where the equal measure distances from the baseline meet, the point is fixed.
i.e The AP=BP
2 Radiation method
it is also known as bearing and distance method or polar method. it is by taking both bearing and distance of position point from the line traverse.
The method is illustrated as follows:
3 intersection or triangulation method.
The position of point is given by the intersection of two rays of bearing and distance.’
4. Off set from baseline.
It is by measuring right angle and distance of the off-set from the line of traverse.
NOTE
1 Chain survey can be accurately conducted if the following are adhered to:
· -The use of few lines as possible.
· -Avoid steep slopes and major obstacles.
· -Select one major line.
· -Keep chain lines short and measure them accurately.
2.Chain errors can be avoided by doing the following
· -It should be checked that all chain lines are included.
· – Read markers on chain carefully.
· -Call measurements to booker clearly and ask him to repeat.
· -Ensure correct position of arrows as they must touch edge of handle or measuring tape and perfectly upright.
OBTACLES IN CHAIN SURVEY
Those are the features (object) lying with in the area to be surveyed along the survey line which may hinder or prevent chaining or ranging.
Types of obstruction
There are three types of obstruction in chain survey
(a) Those which do not allow crossing from side to side, river, a lake, pond preventing chaining.
(b) Those which will prevent vision but not chaining e.g a hill
(c) Those which prevent both chaining and vision e.g building.
GEOGRAPHY FORM 5 – CHAIN AND TAPE MEASURE SURVEY
TECHNIQUES (WAYS) TO OVERCOME THE OBSTACLES
There are seven ways on how to overcome the obstacles. The methods depend on the nature of obstacles as follow
HILL
Hill is a rounded upland it is a considerable obstacle if lies on the path of the chain line. The obstacle of hill can be avoided by the following consideration techniques.
(a) Simple system of offsets
This technique, a surveyor sets out equal perpendicular far long enough distances to clear the obstacle as follow
In the above application BD distance= AC distance This it obvious, as BD= AC the measured DC distance is equal to BA distance
(b)The method of similar triangle
(b It is applied as follows
(c AOC = BOD
Them
As Aoc=Bod The measured DC distance is equal to AB distance
(c)The method of equal triangle
With the technique of equal triangle a applied above C is the mid point of AO and D is the mid point of BO it thus AB=2Xcd
Trigonometric method
(d From point A measure the length of random line chosen to avoid the hill to C. Then chain a line at right angle from AB to C Calculate the length of AB by Pythagoras theorem
2. POND
The obstacle of pond can be avoided by the following application.
Measure the perpendicular the same length from AB (AX and BY) Measure the length of XY. Then AB = AY
3. RIVER
Make chain line from one side to the opposite side i.e from B to D
Set up ranging pole at A and develop chain line along the river to C and it should be assured that AO=Oc from C develop chain line of right angle to D
Then
AO = OC
BO=OD
CD=AB
4. BUILDING
· Set up ranging pole at A and B along the line traverse
· Measure an equal distance along the line of traverse AQ and BR check corner of the rectangles so farmed are right angles
· Extend the line of traverse through C and D
GEOGRAPHY FORM 5 – CHAIN AND TAPE MEASURE SURVEY
BOOKING AND PLOTTING CHAIN SURVEY
(A) BOOKING
Booking is a process where by the measurements done in a field are entered in a field note book for recording. Or is the process of entering the measurements take on the ground into the field note book. This is normally done by surveyor and not by assistant so as to avoid unnecessary errors
In booking the details the following should be taken into consideration
· All linear measurement should appear at the centre of the column and it has to start from the botton upwards
· Feature at the right hand side must be recorded on the right hand side while those at left hand side must be recorded on the left hand site of the column.
· All offsets and ties must be shown on the relevant side as appear along the survey line.
· The forward and back ward bearings must be known and they should be circled.
Methods of booking
There are two main methods of booking details in a field note book after they have been taken from the field by the conduct of chain survey
(i) Single line booking
By the single line booking the details on linear measurements are entered along the single line at the centre as illustrated below.
(ii) Double line booking
By the single line booking the details on linear measurements are entered inside along the double lines at the centre as illustrated below.
In book of the chain survey detail involves the following significant steps:
– Plot your survey booking north so that the top, bottom, left and right respectively represent top bottom left and right respectively represent north, south west and east
– Always keep you paper perfectly flat, do not remove from the drawing table
– Measure every line to away features from the survey line on right and left hand sides
-Mark out around with small circle and dot inside to represent station
Example 1.
According to the booking into field note book develops the following interpretation
· The claim survey covers two stations A to B
· The survey line has a total distance of 6.5 m
· At a distance of 1.5m observer seen the edge of the bush at off set distance of 2.4m
· At distance of 6.5 observer seen also the edge of the bush at a distance of 2.3
The figure to the last immediate page shown as follows
1. The chain survey line covers four stations A to D with total distance of about 225m
2. At point A (Station A) the survey line runs through the bearing of 326 to B
3. At station A one observe assembly hall at bearing 43 of the right side of the survey line
4. Along the survey line at a distance of 60m the surveyor observed assembly hall at 51 right side of the survey line
5. At station B, 100m from A, surveyor observed pavilion at the bearing of 331 at left of the survey line.
7. The surveyor also observed an assembly hall at 40 to the right hand side of the surveyor line
8. From point B the surveyor changed direction and surveys through direction 7
9. At a distance o f160m away from B towards C the surveyor observed line) and also at right angle at the same distance point observed a swimming pool (right hand side of the survey line
10. At point C 315 from B surveyor observed BB of 187º from C to B
11. At station C the surveyor observed a science block at a bearing 50º left side of the surrey line to the left side of the survey line a bearing of 275º be observed assort pavilion.
12. From point C surveyor changed direction and took 96º
13.The last station D was at distance of 225m. He observed the BB of 27º to C. He observed science book (left side of survey line).
(b) PLOTTING
Plotting is a process of putting or transferring the information or details obtained in the field into a piece of paper to develop conventional visual appearance of the surveyed area. The plotting date mostly from what have been bake in the field at book.
In plotting the surveyor should have the following equipment.
• A Scale ruler
• A pair of compass
• Drawing paper
• Protector
• Square ruler
• Pencil and rubber
• T square
• Drawing table
• Drawing pins
GEOGRAPHY FORM 5 – CHAIN AND TAPE MEASURE SURVEY
Plotting procedure
1. Choose suitable scale like that of 1cm to represent 10m
2. Select the starting point on the nature of data booked in the field note book
3. Establish the north direction
4. By considering the north direction the elected starting point as well as the booked data established the survey lines, off sets and ties, and respective features
A FIELD NOTE BOOK
Errors in Chaining
The operation of the chain survey may get subjected into errors. The errors result due to the following:
-Incorrect ranging length of the chain
-Chain not being too tight and not properly aligned
– Sag in the chain
– Expansion and contrition due to differential temperature conditions.
– Incorrect booking made during data collection or actual surveying.
-Arrows being not properly insured.
– Presence of sleeps on the way.
Advantages and disadvantages of chain survey
Advantages
· It is useful method for surveying small areas.
· It is useful method of taking linear measurement over smaller distances.
· Chain survey is much applied in other surveying techniques like prismatic compass survey.
Disadvantage
· Sometimes it becomes time consuming method as it is so much slow in the conduct of it
· It is heavy and tiresome to work.
· It is subjected to the problem of errors accumulation.
· It is required to the problem of errors accumulation.
· It requires more than two people to run survey effectively.
· It requires extra time for office work particularly in making of plotting of the data