1 SHREE VENKATESHWARA HI –TECH ENGINEERING COLLEGE GOBI –638 455 DEPARTMENT OF CIVIL ENGINEERINGMANUAL CE 2259 –SURVEYING PRACTICAL II ANNA UNIVERSITY CHENNAI –600 025 (Regulation 2008) II –Year IV –Semester Prepared by Mr.J.Saravanakumar, ME Assistant professor / Civil Staff HOD Principal
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It is used as seat for altitude bubble and also provides vernier reading for vertical
angle measurement.
8. Telescope:
The telescope of a theodolite is identical in structure and uses, as in case of a dumpylevel. But, in theodolite, the telescope is mounted on a horizontal spindle called the
horizontal axis or the trunnion axis to rotate it also in vertical plane.
9. Vertical Circle:
The vertical circle is attached with the trunnion axis. It is engraved with a scale
reading vertical angle in degrees and minutes. The vertical circle is divided into four
quadrants each reading 0° to 90° with 0° - 0° either along vertical or in horizontal. It
provides the main scale reading for vertical angle.
10. Altitude Bubble:
A sensitive level tube placed on vernier frame is called altitude bubble. It is used to
make horizontal axis truly horizontal.
11. Screws:
A theodolite instrument has number of screws as its component parts. These are
classified into different types depending on their functions.
a) Levelling Screws
b) Clamp Screws
c) Tangent Screws
a) Levelling Screws:
These are present in the leveling head of a theodolite in between trivet and tribrach.
These work in threaded holes in the tribrach arms and their lower ends rest in recesses in
the trivet. These screws are used for leveling the instrument i.e., to make plate level axis
These are used to fix the parts of a theodolite with which these are attached.
i. Lowerplate Clamp Screw
ii. Upperplate Clamp Screw
iii. Vertical plate Clamp Screw
i. Lowerplate Clamp Screw:
The clamp screw attached to the lower plate of a theodolite is called lower plate
clamp screw. When it is tightened, the outer spindle gets fixed with the tribrach, and, thus,the lower plate gets fixed in position.
ii. Upperplate Clamp Screw:
The clamp screw attached with the upper plate of a theodolite is called upper plate
clamp screw. When it is tightened, the inner spindle gets fixed with the outer spindle and,
thus, the upper plate gets fixed in position.
The manipulation of the upper plate and lower plate clamp screws provide three
conditions:
When both the upper plate clamp screw and the lower plate clamp screw are
tightened, the instrument gets fully fixed.
When the upper plate clamp screw is tightened and the lower plate clamp
screw is opened, the instrument rotates on its outeraxis, There is no relative
motion between the two plate and the readings in the horizontal vernier
scales do not change.
When the lower plate clamp screw is tightened, and the upper plate is
opened, the instrument rotates on the inner axis with outer axis fixed. The
readings in the horizontal vernier scales change.
iii. Vertical plate Clamp Screw:
It is present on a frame fixed with standard and above the shaft of trunnion axis. It is
used to clamp the telescope in any plane and hence at any desired vertical angle.
c) Tangent Screws:
With each clamping screw, there is a tangent screw present in the instrument to
provide fine movement. The tangent screws work only after its clamping screws get
tightened. Thus when the upper clamp screw has been tightened, small movement of the
upper plate can be made by the upper tangent screw; when the lower clamp screw has
been tightened, small movement of the lower plate can be made by the lower tangent screw
and similarly for vertical clamp screw.
12. Tripod:
The theodolite is mounted on a strong tripod when being used in the field. The legs of thetripod are solid or framed. At the lower ends of the legs, pointed steel shoes are provided to get
them pushed into ground. The tripod head has male screws on which the trivet of the leveling
3) Vernier scale readings are taken by this method.
a) Determine the least count of the vernier. ( 20seconds)
b) Note the main scale graduation beyond which the index lies. ( inVernier A & B ). This is
the approximate reading ( say 127° right & 232° left ) in vernier A.
c) Observe which division of the vernier coincides exactly with any divisions on the main
scale. ( i.e, 14’ right & 46’ left )
d) Multiply the number of the coinciding Vernier divisions by the least count. This is the
value of fractional part. Add this to the approximate reading taken to get the exactreading on the main scale. ( i.e,127°+ 14’ = 127°14’ right & 232°+ 46’ = 232°46’ left )
RESULT:
Temporary adjustment of a theodolite has been practiced and reading horizontal angles in
MEASUREMENT OF HORIZONTAL ANGLES BY REPETITION METHOD
AIM:
To measure the horizontal angle at a particular given instrument station by Repetition
method.
INSTRUMENTS REQUIRED:
1. Theodolite
2. Tripod
3. Two Ranging Rods
4. Arrows
PROCEDURE:
The method of repetition is used to measure the horizontal angle to a finer degree ofaccuracy than that obtainable with the least count of the vernier. By this method an angle is
measured two (or) more time by allowed the vernier to remain clamped each time at the end of
each measurement of the previous station. Thus an angle reading is mechanically repetitions. The
average horizontal angle is then obtained by dividing the final reading by number of repetitions.
To measure the angle of horizontal AOB, the following Procedure:
1. Set the instrument at station ‘O’ and level it with the help of alidade bubble and foot screw.
Set zero reading (or) vernierA note the reading at vernier B.
2. Loose the lower clamp and direct the telescope towards the point ‘P’ accurately by lowertangential screw.
3.
Then unclamp the upper clamp and turn the instrument clockwise about inner axistowards ‘Q’ accurately with the upper tangential axis.
4. Unclamped the lower clamp and turn the telescope and sight P. Again bisect ‘P’ accuratelyby using the lower tangential screw. It should be noted that the vernier reading will not be
changed in this operation. Since the upper plate is clamped to the lower.
5. Unclamp the upper clamp, turn the telescope clockwise and Sight ‘Q’ accurately by uppertangent screw.
6. Repeat the process until the angle i.e. for repeated no. of times say three times. The average
angle with face left will be equal to the final reading divided by number of repetition (3).
To find the Reduced level of a point Q and the distance between two given points P and
Q.
APPARATUS REQUIRED:
1. Theodolite
2. Levelling staff
PROCEDURE:
1. Setup the instrument at point ‘P’ and center the instrument. Level the instrument with
the help of foot screws and the bubble tubes.
2. Keep the staff at the Bench mark and note down the axial hair reading. Let it be ‘h’. 3. Direct the theodolite towards point Q. Keep the leveling staff at point ‘Q’. Mark the two
readings on the leveling staff such that the distance between the two readings is 1m andlet it be ‘S’.
4. Sight the top reading marked in the leveling staff and note down the vertical angle, with
reference to horizontal. Let it be ‘1’.
5. Similarly sight the bottom reading marked in the staff and note down the vertical angle
with reference to the horizontal and let it be ‘2’.
6. Calculate the distance ‘D’ and vertical distance‘V’ using the formula,
if 1 and 2 are angles of elevation,
D = S/ (tan 1- tan 2) and V = D tan 2
If α1 and α2 are angles of depression,
D = S/ (tan α2 – α1) and V = D tan α2
If one is angle of depression and the other is angle of elevation,
D = S/ (tanα1 + tanα2) and V = D tan α2
Reduced level of point Q = R.L of P + h + V – r.
Where,
r is the axial hair reading noted down at point ‘Q’.
DETERMINATION OF CONSTANT K AND CThe values of the multiplying constant k and the additive constant C can be computed
by the following methods:
1st METHOD:
In this method ,the additive constant C=(f +d) is measured from the instruments while
the multiplying constant k is computed from field observations
1) Focus the instruments to a distant object and measure along the telescope the
distance between the objective and crosshair.
Since f1 is very large in this case ,f is approximately equal to f2 i.e , equal to the
distance of the diaphragm from the objective.
2) The distance d between the instrument axis and the objective is variable in case of
external focusing telescope, being greater for short sights and smaller for long sights. It should,
therefore, be measured for average sight. Thus, the additive constant (f +d) is known.
3) To calculate the multiplying constant k, measure a known distance and take the S1 on
the staff kept at that point , the line of sight being horizontal. Using equation
For the average value, staff intercepts, s2, s3 etc., can be measured corresponding
to distance d2, d3 etc., and mean value can be calculated.
2nd METHOD:
In this method, both the constants are determined by field observations as under:
1) Measure a line, about 200 m long on fairly level ground and drive pegs at some
intervals, say 50 meters.
2) Keep the staff on the pegs and observe the corresponding staff intercepts with
horizontal sight.
3) Knowing the values of d and s for different points, a number of simultaneousequations can be formed by substituting the values of d and s in equation (1.1). the
simultaneous solution of successive pairs of equations will give the values of k and c, and the
average of these can be found. If s1 is the staff intercept corresponding to distance D1 and s2
To set out the centerlines for the Foundation walls of the buildings and mark the
lines for excavation.
APPARATUS REQUIRED:1. Tape or chain.
2. Cross staff.
3. Ranging rod.
4. Arrows.
5. String.
PROCEDURE:
1. Prepare a centre line sketch of the building (indicate the centre of cross walls also).
2. Remove any vegetation in the construction site.
3. Set out the baseline with reference to given any reference points.4. Mark the ends of the cent re line of the walls, point s A and B from the base line.
5. As the end marks A, B, C, et c. disturbed during excavat ion, stakes (or masonry pillars) are
fixed at L, M, N,etc., a little away (about 2 to 3 m) for end mark and tie a string accurat ely.
6. Mark the centre line for all other walls AD, BC, etc. by dropping perpendicular. For small
buildings the perpendiculars may be setout by using a chain or a tape by'3-4-5' method.
For aimportant and big building when sides are long a theodolite may be employed t o
accurat ely set out the perpendiculars and to range t he lines.
7. For every wall drive the pegs a lit t le away f or end mark and tie a string accurately.
8. Measure the diagonals and check with t heir corresponding calculated lengt hs.
9. Mark the width of foundation from t he centre line and fix up the corners 1,2,3,4,5, etc.,
pegs are driven at t hese corners, the chord is stretched and lime is spread along t hechords.
10. Now the trench plan being marked on the ground, excavation may be started.
RESULT:
The centerline and foundation mark to be excavated has been set out.
Let OP be a line whose azimuth ( fore bearing) is to be determined by taking
extrameridian observation on the sun.
APPARATUS REQUIRED:
1) Theodolite
2) Ranging rod
PROCEDURE:
1. Set up the instrument at O, and make all temporary adjustment.
2. Keep the vernier A at 0º.
3. Sight the ranging rod P for bisecting the rod using lower tangent screw for
necessary.
4. Release the upper clamp and direct the telescope to the sun and note down linevertical angle , the sun first quadrant by upper tangential screw and Vertical
tangent screw.
5. Next being to image of the sun III quadrant the down, the time for vertical angle 2
.Note down the horizontal angle θ2also.
a) Indian standard time observation t n = t 1 + t 2 / 2.
b) Altitude of the sun of the time of observation, = 1 + 2 / 2
c) GMT of observation = t – 5 h 30 min
d) Declination of the sun of the GMT = sqrtSin (S-Z)x sin (S-C)
Sin (S-P) x sin S
S = (Z + C + P)/2
e) Average horizontal angle between OP and OS is θ = (θ1 + θ2)/2
f) Azimuth of line OP = True bearing of DA = θ -
PRINCIPLE AND SIGNIFICANCE:
The required altitude and the horizontal angles are those to the sun centre. Hence
the hairs should be set tangential to the two limbs simultaneously. The opposite limbs are
1. Setup the subtense bar at one of the given points. Level the instrument with the help of
the bubble tube and foot screws. Let the length of the subtense bar be‘s’. 2. Keep a telescope in between the two arms of the subtense bar and locate a line which is
perpendicular to the subtense bar.
3. Along the perpendicular line, set up the theodolite at the other given point.
4. Center the instrument over that point and do the initial levelling adjustments.
5. Direct the telescope towards the marking in any one arm of the subtense bar and set the
horizontal circle in the theodolite at 0-0.
6. Rotate the theodolite in the horizontal direction till the vertical cross hair coincides
with the marking in the other arm of the subtense bar.
7. Note down the horizontal angle in the horizontal circle of the theodolite. Let it be β.8. The distance between the two points can be calculated using the formula,