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GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
SURVEYING FIELD WORK I LABORATORY
GUDLAVALLERU ENGINEERING COLLEGE SESHADRI RAO KNOWLEDGE VILLAGE: GUDLAVALLERU
DEPARTMENT OF CIVIL ENGINEERING
Name : ………………………………………………………
Regd. No : ……………………………………………………….
Year & Semester :………………………………………………………..
Academic Year : ……………………………………………………….
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
GUDLAVALLERU ENGINEERING COLLEGE SESHADRI RAO KNOWLEDGE VILLAGE::GUDLAVALLERU
DEPARTMENT
OF
CIVIL ENGINEERING
Surveying Field Work I- Lab Manual
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
GUDLAVALLERU ENGINEERING COLLEGE SESHADRI RAO KNOWLEDGE VILLAGE:: GUDLAVALLERU
DEPARTMENT OF CIVIL ENGINEERING
INDEX S.n
o Date
Name of the Experiment Signature
of the
faculty
1
2
3
4
5
6
7
8
9
10
11
12
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
CHAIN SURVEY OBSTACLES
AIM: To perform chain surveying across obstacles.
Equipment : 30 mts chain; Offset rod
Ranging rods; Field books
Cross staff; Arrows
Procedure and Principle:
The principle of chain survey is triangulation. Chain survey that type of surveying in
which only linear measurements are made in the field. This type of survey is most useful for
small areas or ground to take a sample details.
Procedure:
Before going to actual survey prepare enough idea in mind for locating main stations
and substations, then start actual survey by using 30 mts chain. We have an obstacle in
main survey line so we have to calculate the obstructed length. So we set out two sub help
of cosine rule calculations are done in this way. We calculate the obstructed length while
changing across of stable as pond.
Formula:
Cosine rule
PT2 = RR2 + TR2 – 2 PRTR cos θ
PQ2 = RR2 + RQ2 – 2 PR.RQ cos θ
Precautions:
1. Ranging rod should be ranged accurately.
2. Before starting the chain survey the chain length must be checked whether it is
accurate or not.
3. While changing across survey line chain must be held tightly. Loose in chain is
not permitted.
Result:
The length of A.D =
CHAIN SURVEY TRAVERSE
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
AIM: To determine the area by the chain survey.
Equipment: Ranging Rod: Chain or tape : offset rods, cross staff, arrows.
Formulas: Rectangular area A = b X h
Triangular area A = ½ X b X h
Trapezoidial area A = ½ X L [h1 + h2]
Procedure:
Set the two stations A and B. By ranging these two stations place the ranging rod or
intermediate points, Using intermediate points locate offsets for the ranging between A and
B. Measure the distance range by rotating the off set taken starting from A and B.
Join the offsets and ranging poles to get some required amount of triangles or
trapezoidal which enables to calculate given area.
Precautions:
1. It should be taken without parallax error.
2. Must and should be taken ranging offsets changing.
Result: Total area occupied =
CONTOURING
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
AIM: To plot the contours of a given area.
Apparatus: Dumpy level, chain, pegs, staff, tape etc.
Procedure:
Make the boundary of a given surface and plan divide the are a into number of
small squares or rectangles of 5 or 10 m width and mark the points. Now place the
boundary level such that all the readings can be taken. Adjust the dumpy levels having
necessary temporary adjustments such as eye piece, cross wires etc. Now place the
leveling staff at TBM and tabulates the B.S. continue the procedure of taking reading at all
the marked points.
Now change the station after few readings and continue the same process.
Calculate the R.L of all points. Draw the area of plane by making & all are using
necessary scales. Taking necessary contour intervals. Join the points which have same
R.Ls. Some R.L points can be obtained by measuring.
EX: A, B, C, D be quite points plotted on map having elevations.
Let AB = BC = CD = DA = 5 mts.
Locate the points on these using the vertical difference b/w these two points is the
difference of contours from B.
i) In this process points having some R.L s are marked.
ii) Join these points with smooth curves.
Precautions:
1. Dumpy level should have no errors.
2. Staff should be stand vertically.
FLY LEVELLING
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
AIM: To find the elevations of a given stations by rise and fall method .
Apparatus: Leveling staff, Tripod.
Theory:
The process of keeping height of instrument axis at differential levels and finding out
the reduced levels of the station is called the differential leveling.
Procedure:
Set up the level instrument at P (nearer to the temporary bench mark) as shown in
fig. and level the instrument roughly with the leveling screws. Till the circular bubbles
comes to the centre by using foot screws, till the bubble is in an exact coincidence.
Focus the eye piece through the point. The telescope towards the object and focus
the objective.
Focus the Telescope toward the temporary bench mark and bisect the staff correctly
and take the back sight as it and record the readings is leveling field book as shown in the
table.
Keep the leveling staff at the stations as intermediate sights and enter the readings
before shifting the instrument to the next station. The readings must be entered in the
foresight column in the field book. Shift the instrument to the next station and follow the
same procedure which you have done above.
` At the point F the staff is kept inverted position and at intermediate sight is taken and
enter the readings in the field book as negative. Lastly the survey is completed at the
beginning station of temporary bench mark calculation can be done by the height of the
instrument rise and fall.
Precautions:
1. The staff should held vertically when the reading is taken. The staff man should
be behind the staff.
2. While taking readings, always make sure that the bubble of the level is at the
centre.
3. Read the staff correctly, there should be no parallax error.
Result:
We obtained the R.L at required stations.
PLANE TABLE BY INTERSECTION
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
AIM: To plot the given area by methods of radiation by plane table.
Apparatus:
A plane table, alidade, plumbing fork or U. Frame and plumb bob, spirit level,
compass, drawing paper with a rain proof covers.
Theory:
A plane consists of a small drawing board mounted on a tripod thus the board can
be rotated about the vertical avis and can be clamped in any position on the table and
leveled by adjusting tripod legs.
Alidade:
A plane table alidade is a straight edge with some form of straight device. It
generally consists of a metal or wooden rule with two wanes at the ends. The two wanes
or sights are hunged to fold down on the rule when it is not in one of the wanes is provided
with a narrow slit while the other is open and carries a hair on the wire. Both the slits thus
provide a definite line of sight passes through the object to the sighted.
Plumbing fork:
The plumbing fork is used in large scale work. Its meant centering the table over a
point occupied by the plane table. It is meant for transferring the ground on the point on the
sheet. So that the plotted point on the ground station one in the same vertical line.
Spirit level:
A small spirit level may be used far ascertaining as if the table is properly level. The
table is leveled by placing the level on the board in two positions at right angles and getting
the bubble central in both positions.
Intersection:
Intersection is resolved when the distance between the point and instrument station
is either too large or can be measured accurately due to some field conditions the location
of a object is determined by sighting at the object
from the two plane table stations and drawing the rays. The intersection of rays will give
the position of the object. The distance between two instrument stations is measured and
plotted on the sheet.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
Fix the table at point A, level the table with the help of plumb-bob and V frame with
the help of trough compass mark the distance in the board. Locate the point ‘A’ on it and
place the alidade about point ‘A’ and sight the point ‘B’. Measure the distance between A
and B and plot it on the board then draw A and B in direction AB. Pivot the alidade and
sight the stations C,D,E etc. and draw the corresponding rays along the alidade to intersect
the previously drawn rays. This method is mainly used for mapping.
Precautions:
1. Centering and leveling can be done carefully.
2. Ranging rods should be ranged accurately.
3. Vertical rods hair of the alidade may not be loose.
4. Alidade readings should be done carefully.
5. Rotating the instrument and plotting errors.
6. Chaining, measuring must be done without parallax error.
Result:
The given area is plotted by plane table by inter section method.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
PLANE TABLE BY RADIATION
AIM: To plot the given area by methods of radiation by plane table.
Apparatus:
A plane table, alidade, plumbing fork or U. Frame and plumb bob, spirit level,
compass, drawing paper with a rain proof covers.
Theory:
A plane consists of a small drawing board mounted on a tripod thus the board can
be rotated about the vertical avis and can be clamped in any position on the table and
leveled by adjusting tripod legs.
Alidade:
A plane table alidade is a straight edge with some form of straight device. It
generally consists of a metal or wooden rule with two wanes at the ends. The two wanes
or sights are hunged to fold down on the rule when it is not in one of the wanes is provided
with a narrow slit while the other is open and carries a hair on the wire. Both the slits thus
provide a definite line of sight passes through the object to the sighted.
Plumbing fork:
The plumbing fork is used in large scale work. Its meant centering the table over a
point occupied by the plane table. It is meant for transferring the ground on the point on the
sheet. So that the plotted point on the ground station one in the same vertical line.
Spirit level:
A small spirit level may be used far ascertaining as if the table is properly level. The
table is leveled by placing the level on the board in two positions at right angles and getting
the bubble central in both positions.
Method of Radiation:
In the method of Radiation of plane table surveying we will draw radiating lines by
sighting the ranging rods at their respective positions on ground.
In this method, a ray is drawn from the instrument station towards the point, the
distance is measured between the instrument station and that point, and the point located
by plotting to some scale the distance so measured. Evidently, the method is more suitable
when the distances are small (within a tape length) and one single instrument can control
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
the points to be detailed. The method has a wider scope if the distances are obtained
tacheometrically with the help of telescopic alidade.
1. Set the table at T, level it and transfer the point on the sheet by, means of plumbing
fork, thus getting point t representing T. Clamp the table.
2. Keep the alidade touching t and sight to A. Draw the ray along the fiducial edge of the
alidade. Similarly, sight different points B,C,D,E etc., and draw the corresponding rays.
A pin may be kept touching the pin while sighting the points.
3. Measure TA,TB,TC, TD, TE etc., in the field and plot their distances to some scale along
the corresponding rays, thus getting a, b, c, d, e etc. Join these if needed.
Precautions:
1. Centering and leveling can be done carefully.
2. Ranging rods should be ranged accurately.
3. Vertical rods hair of the alidade may not be loose.
4. Alidade readings should be done carefully.
5. Rotating the instrument and plotting errors.
6. Chaining, measuring must be done without parallax error.
Result:
The given area is plotted by plane table by inter section method.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
PLANE TABLE TRAVERSE
AIM: To plot the given area by the method of traversing by plane table surveying.
Instruments:
A plane table, alidade, plumbing fork and plumb-bob, spirit level, compass, drawing
paper with a rain proof cover.
Theory:
A plane table consists of a small drawing board mounted on a tripod. Thus the
board can be rotated about the vertical axis and can be clamped in any position the table is
leveled by adjusting the tripod legs.
Alidade:
A plane table alidade is a straight edge with some form of sighting. It generally
consists of a metal or wooden rule with two vanes at the ends. The two vanes or sights are
hanged to fold down on the rule when it is not in use. One of the vane is provided with a
hallow slit, while the other is open and carries a hair or a thin wire. Both the slits thus
provide a definite line of sight passes through the object to the sighted.
Plumbing Fork:
It is used in large scale work. It is meant for centering the table over a point
occupied by the plane table. It is meant for transferring the ground point on to the sheet.
So that the plotted point and ground station are in the same vertical line.
Spirit level:
A small spirit level may be used for ascertaining as if the table is properly level. The
table is leveled by placing the level on the board in two positions at right angles and getting
the bubble at central in both positions.
Plane table traverse involves the same principle as a transit traverse at each
successive stations. The table is set, a fore sight is taken to the focusing station. As in the
radiation method described earlier. In plane table traverse, the
table is set at each successive stations, a fore sight is taken to the next station and its
location is plotted on the foresight, by measuring the distance directly between the two
stations. This method is widely used to lay down the survey lines between the instrument
stations of a closed or unclosed traverse.
Procedure:
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
1. Set the table at A use plumbing fork for transferring A on to the sheet. Draw the
direction of magnetic meridian with help of trough compass.
2. With the alidade pivoted about A sight to B and draw the ray, measure AB and
scale (a b) to some scale. Similarly draw a ray towards E measure AE and plot to
same scale used earlier.
3. Shift the table to B and set it to the table accurately by back sighting A clamp on
the table.
4. Pivoting the alidade about ‘b’, sight to C measure BC and plot it on the ray drawn
to the same scale. Simultaneously the table can be set at other stations and the
traverse is completed.
Precautions:
1. Centering and leveling should be done carefully.
2. Ranging rods should be ranged accurately.
3. Vertical hair of the alidade may not be loose.
4. Alidade readings should be carefully noted.
5. Rectify the instrument and plotting errors.
6. Weighing, measuring should be done with out any parallax error.
Result:
The area of traversing by plane table surveying is _________ m2.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
PROFILE AND CROSS SECTIONAL LEVELLING AIM: To plot the features of the given area by longitude section (L.S) and cross section
leveling.
Apparatus:
Ranging rods, leveling staff, tripod, chain, cross staff dumpy level, auto level etc.
Theory:
1) Longitudinal Section: To find out the elevations of the ground a long a fixed
line. The fixed line is generally to the central line of high way and railway track.
2) Cross Sectional leveling: C.S are run at right angles to the lived line, along
which longitudinal section is done. The solutions are taken on either side of the
fixed line. To obtain the lateral out line of the ground surface.
Procedure:
1. Fix the line AB along with profile. Leveling is to be done.
2. Mark of the Intermediate stations a, b,c etc on the fixed line at a interval of 6 mts.
3. The instrument is set up temporarily adjustments and positions and intermediate
points are located by chaining along the fixed line AB and noting the distances
from starting station.
4. Set the instrument at a point L so as command a large number of points on the
fixed line.
5. A,B.S is taken on the temporary B.M to determine the H.I or rail C and fall of
ground level.
6. Establish a right angle line of a station A on either side of the fixed line with the
help of cross staff.
7. By placing the leveling staff of a spacing 1 mt and 3 mts on either side of the
fixed line and the corresponding R.L.S are noted into the field book.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
Precautions:
1. The staff should be held vertically when the reading is taken and the staff should
be behind the staff.
2. While taking readings always make sure that the bubble of the tube is in central.
3. Read the staff reading without any parallax error.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
SURVEYING AN AREA BY CLOSED TRAVERSE
AIM: To survey an area by prismatic compass and plotting after adjustment.
Equipment:
30 mts chain; ranging rods; off sets; pegs prismatic compass, tripod, field
books, arrows etc.
Theory:
The principle of compass traversing is it contains a magnetic meddle and divided
into degree and half degrees. The graduations start from N=1800, S=00, E=900, W=270 Eye
wane and object wane passes through the centers of the prism. A glass cover is provided
at the top. So that dust particles cannot enter into compass box. A mirror is provided to
measure too low or too far objects.
Centering:
A tripod is placed over the station with its legs spread well apart so that it is at a
workable height. The compass is fixed on the tripod. It is then centered over the station
where the bearing is to be take (i.e) centre of the compass the pivots brought exactly below
the ground station. A plumb is bob is not provided a stone is dropped below the compass
and it should fall on the peg marking in the ground station.
Leveling:
The compass is leveled by the eye-judgment this is essential so that the graduated
ring springs freely. Some times two plate levels are at right angles and also provided to
level the instrument. The leveling is achieved by a ball and socket adjustments which is
adjusted till the bubbles concentrated in both the plate levels.
Local attraction:
The magnetic needle does not point to the magnetic north, when it is under the
influence of the external attractive forces in the presence of magnetic materials, such as
iron pipes, iron lamps, steel structures, rails cables chain, arrows, mineral deposits in the
ground etc. The needle is deflected from the
normal position hence the local attraction by the magnetic materials. Needle of the
compass the amount of deviation of the magnetic needle is the measured of the local
attraction.
Procedure:
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
1. Select the building or area to be plotted.
2. Mark the corners of the given area to the plotted.
3. Take the convenient points A1,B1,C1 and D1around the building for measuring the
corners of the building.
4. The points A1,B1,C1, D1 are selected in such away that from every point both pole
bearing FB and back bearing BB should be taken.
5. Fix the prismatic compass at a station A and measure the distance b/w A and
A1and recording the bearing at AA1.
6. From A1 right B1and record the bearing of the line A1B1 with same adjustment of
the instrument sight D1 and A1 and record B. B of line D1 A1.
7. Shift the instrument station from A1 and B1 sight C1 and record FB.
8. Eliminate local attraction.
Precautions:
1. Ranging rods should be ranged accurately.
2. Magnetic needle should be perfectly straight.
3. Vertical hair of the compass should not be loose.
4. Eye wane and object wane should be vertical.
5. Chaining, reducing, measuring, leveling and centering should be done without
any parallax error.
Result:
Surveying of an area by closed traverse is done.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
The Three – Point Problem
AIM: To plot the given point is by three point problem method by plane table surveying.
Instruments:
A plane table, alidade, plumbing fork and plumb-bob, spirit level, compass, drawing
paper with a rain proof cover.
Theory:
The three-point problem is also a problem of resection. The objective is to obtain the
position of the station occupied by the table after orientation. The three-point problem can
be stated s follows: Given three visible stations and their plotted positions, to plot the
station occupied by the plane table with the table correctly oriented with respect to the three
points already plotted.
The three – point problem can be solved using many methods. The following three
methods will be discussed here:
1. tracing paper method
2. graphical method
3. trial and error method
Tracing Paper Method:
The following procedure is adopted (refer to below figure) in this method.
1. Let P,Q, and R be the three stations whose plotted positions p, q, and r are available on
the plan. Let S be the station where the plane table is to be set up. The objective is to
orient the table with respect to P, Q and R and then plot the position of S.
2. Set up the plane table at S and level it. Fix the sheet with the plotted positions of P, Q
and R on the table. Rotate the table and approximately orient it visually so that A-B or B-C
is parallel to a-b or b-c.
3. Fix a tracing paper on the table over the sheet. Mark the position of S on the tracing
sheet as s1 using a plumbing fork. This is only approximate, as the table is not oriented.
4. With the alidade centered on s1, sight the signals at P, Q, and R and draw rays s1p1,
s1q1, and s1r1. These rays will not pass through the point p, q, and r plotted earlier, as the
orientation is only approximate.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
5. Loosen the tracing paper from the table. Rotate the tracing paper so that rays s1p1, s1q1
and s1 r1 pass through p, q, and r. Fixing the sheet in such a position, transfer the position
of s1 to the drawing sheet as s.
6. Remove the tracing paper. Place the alidade along s-p. It will not pass through the
signal at P, as the table is not oriented. Rotate the table so that the signal at P is sighted
when the alidade is kept along s-p and clamp it. The table is now oriented.
7. Check the orientation by sighting the signals at Q and R by placing the alidade along s-q
and s-r, respectively. If the orientation is correct, these signals must be seen in these
positions.
Precautions:
1. Centering and leveling can be done carefully.
2. Ranging rods should be ranged accurately.
3. Vertical rods hair of the alidade may not be loose.
4. Alidade readings should be done carefully.
5. Rotating the instrument and plotting errors.
6. Chaining, measuring must be done without parallax error.
Result:
The given point is plotted by plane table by three point problem method.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
The Two-point Problem AIM: To plot the given point by the two point problem by plane table surveying.
Instruments:
A plane table, alidade, plumbing fork and plumb-bob, spirit level, compass, drawing
paper with a rain proof cover.
Theory:
The two-point problem is a special case of resection to obtain the position of the station
occupied by the table, given the plotted position of two points. The two-point problem can
be stated follows: To determine the position, s, of the station S occupied by the plane
table, given the accurately plotted positions, p and q, of two points, P and Q, visible from
the instrument station and without occupying these two stations.
Figure below shows the problem. P and Q are two survey stations which have been
surveyed earlier and their positions plotted as p and q on the sheet. S is the instrument
station (where the plane table is to be set up) and it is required to get the position of S on
the sheet as s when the table is oriented correctly, i.e., when P-Q is parallel to p-q. The
following procedure can be adopted to solve the two-point problem.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
1. Select an auxiliary station R such that the signals at P,Q and S are clearly visible from R
and the angles formed by P,Q and S are not very acute.
2. Set up the plane table at R. Level the table. Approximately orient the table so that p-q
is nearly parallel to P-Q. Clamp the table in this position.
3. Plot the position of R on the table by sighting to P and Q. For this, keep the alidade
against p and sight the signal at P. Draw a line along the ruling edge of the alidade.
Similarly, sight the signal at Q by pivoting the alidade against q and draw a ray. The
intersection of the two rays drawn gives the position of the station occupied by the table.
Label this point r. Point r is obtained as the position of the station occupied and is
accurate to the extent the line p-q is parallel to P-Q.
4. Transfer the point r on the table to the ground as R using the plumbing fork. A peg can
be driven to locate the ground station.
5. With the alidade kept against r, sight the ranging rod or other signal at S and draw a
line. Mark the distance S by approximation or rough chaining. Point s1 is thus obtained.
6. Shift the table to S. Level and centre the table over s1. Orient the table by back sighting
at R. For this, keep the alidade against s1. and sight the signal at R by rotating the
table. Clamp the table in this position.
7. With the alidade kept against p, sight the station P and draw a ray. This ray intersects
the line r-s at s, giving the station s. Keep the alidade against s, sight the signal at Q,
and draw a ray. This ray will intersect the ray r-q not at q but at q’, as the orientation of
the table is only approximate.
8. p-q’ is the representation obtained of p-q due to the error in orientation. The angle q-p-
q’ is the angular error in orientation.
9. To remove this error, place the alidade against p-q’ and keep a ranging a rod at a large
distance M.
10. Keep the alidade against p-q and rotate the table until the signal at M is sighted and
clamp the table. This position is the correct oriented position, with P-Q parallel to p-q.
11.Obtain the position of S by sighting P and draw a ray. Keep the alidade against q and
sight the signal at Q. The intersection of the two rays gives the true position, s, of S.
The distance of M must be large enough to correct the orientation of the table.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
Precautions:
1. Centering and leveling can be done carefully.
2. Ranging rods should be ranged accurately.
3. Vertical rods hair of the alidade may not be loose.
4. Alidade readings should be done carefully.
5. Rotating the instrument and plotting errors.
6. Chaining, measuring must be done without parallax error.
Result:
The given point is plotted by plane table by two point problem method.
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
TO CALCULATE THE DISTANCE BETWEEN TWO IN ACCESSIBLE POINTS.
AIM: To determine the distance between two in accessible points with compass.
Equipments Used:
30 mts chain; ranging rod; cross staff, off sets: Prismatic compass Tripod: Field
book; arrows.
Theory:
1. The principle of compass traversing is it contains a magnetic needle and
dividing into degrees and half degree graduations starts from N=1800
= O0 E = 900 W=2700.
2. Eye wane and object wane passes through the centre of prism. A glass
cover is provided into the compass box. Incline mirror is provided to
measure too low or too tall of objects.
Centering:
A tripod is placed over the stations with its legs, spread with a part. So that it is a
workable height. The compass is firmed on the tripod. It is the centre over the station
where the bearing is to be taken (i.e) the centre of the compass pivot is brought exactly
above the ground station. A plumb bob is hung from the centre of compass. In case of
arrangement of work plumb bob is not provided as stone is should flow on the peg working
the ground station.
Leveling:
The compass is leveled by high judgment. This is essential so that the graduated
ring swings freely. Some times, in surveys compass two plate levels at right angles are
also provided to level the instrument. The leveling is achieved by a ball and socket
arrangement which is adjusted till the bubbles becomes centre in both the plane levels.
Local attraction:
The magnetic needle does not point to the north when it is under the influence of the
external attractive forces in the presence of magnetic material such as iron pipes, Iron
lamps, steel structures, Iron lamps, rails cables, chain arrows, mineral deposits in ground
etc. The needle is deflected from its (ground) normal
GUDLAVALLERU ENGINEERING COLLEGE Surveying Lab- I
Department of Civil Engineering Chain Survey Obstacles
position. Hence local attraction by the magnetic materials is disturbing influence on the
magnetic needle.
Procedure:
Let P and Q are the two points and there is an obstacle between them. Now we
have to measure the distance between P and Q by compass. Select two points A and B
such that line AB is almost perpendicular to the line PQ and the distance between A and B
is measured with a chain.
Place the compass and station a centering and levelly with centre A. Note the
readings of AP, AQ and AB then shift the compass to stations B after centering and leveling
its place the bearing of BA, BP and BQ.
Cosine rule
PQ2 = PA2 + AQ2 – 2 PA.AQ cos(PAQ)
From ∆ APB sine rule.
AB = PA from ∆ABQ AB = AQ
Sin P Sin B SinQ SinB
Precductions:
1. Ranging rod should be ranged accurately.
2. Magnetic needle should be perfectly straight.
3. Vertical hair of the compass may not be loose eye wave and direct wave should
be vertical changing, reading, measuring, leveling and centering should be done
without parallax error.
Result:
The distance between in accessible points is ___________.