Royal University of Bhutan · 2019. 8. 22. · Prepared By: Phurba Tamang, Associate Lecturer Page...

Jigme Namgyel Engineering College

Department of Civil Engineering & Surveying

SURVEYING

LABORATORY INSTRUCTION MANUAL

SEMESTER- II

Compiled By: Department of Civil Engineering & Surveying

Royal University of Bhutan

Prepared By: Phurba Tamang, Associate Lecturer Page 1 of 5

INTRODUCTION TO LAB PROCEDURES

Field book: Example of field book is given in the next page

All the practical assigned for this module will be carried out in the field. A record of each field practical

shall be kept in your respective field book. Your field book shall be kept neat and orderly as it will be

collected and graded periodically throughout the semester. Your field book shall include your name

and group information on the first single page.

Pencil only, preferably 2H drafting pencil

Essential guidelines:

1. The left page is used for recording data, while the right page is used for sketches.

2. Erasure should never be made in the field book. If a measured value is recorded incorrectly, it

should be cut by a horizontal line and the correct value should be recorded above the cut value.

3. At the end of the day’s work, the notes should be verified and signed by the tutor or lab in charge.

Practical Report:

After the verification of field data by the tutor, every students should produce an individual practical

report. The guidelines of the report shall be as per the practical manual circulated by the tutor.

Note:

Left page should be solely used for sketches and calculations or data representation written with

pencil. Any theoretical aspects/backgrounds or results can be written on the right page

Field Crews:

Each student will be assigned to a 7 or 8 people crew. A crew chief should be appointed for each

practical session. The Crew Chief will be responsible for checking out and returning the equipment at

the end of the lab session.

Survey Equipment:

Equipment for each lab assignment will be checked out at the beginning of the lab and checked

back in when the assignment is finished. Some important things to remember about the use and

care of the equipment are as follows:

• Much of the equipment used are very expensive and quite sensitive whereby great care should be

exercised to protect the equipment from damage.

• Instruments should be transported in their cases when taken to and from the field. These

instruments may be carried on the tripod from station to station as long as they are held

vertically at all times.

• Steel tapes should be straightened out prior to being wound onto their reels. Care should

be taken so that the tapes do not kink, bend or snap.

• Malfunctioning equipment should be reported to the lab in charge or tutor

Page 2

Lab. 1: Title of the experiment

Equipment: Eg. Ranging rods, measuring tapes

Weather: Eg. Sunny

Ground Cover: Eg. Grass

Scale:

Date: Group No: Example, A-1 Group No: Example, A-1 Date:

All the data recording has to be done on this page (left page). If additional information are not sufficient on this page, you may use the next left

page.

Note: Use only pencil

Use this section for sketching purpose and result inter-

pretation

(Use only pencil)

Show direction of meridian





Soil Mechanics & Foundation Laboratory

LAB-1: MEASUREMENT OF DISTANCE BY PACING AND DIRECT RANGING

Aim:

• To determine the average length of your own pace.

• To measure the direct distance between two end stations by direct ranging.

• To familiarize with using a steel tape to measure approximate horizontal distances.

• To become familiar with keeping notes in a field book.

Theory:

Pacing consists of counting the number of steps or paces in a required distance. Distances obtained by

pacing are sufficiently accurate for many purposes in surveying. Pacing is also used to validate survey

work and eliminate any taping blunders. Measuring your pace length requires a measured 100-foot

distance. You then walk this distance and count the number of steps. It is best to repeat the process

four times and average the results.

By the various methods of determining distance the most accurate and common method is the method

of measuring distance with a chain or tape commonly known by the term chaining. For work of

ordinary precision a chain is used. But where great accuracy is required a steel tape is invariably used.

The term chaining was originally applied to measure distance with a chain. The term chaining is used

to denote measuring distance with either chain or tape, in the process of chaining, The survey crew

consists of a leader (the surveyor at the forward end of the chain) and a follower (the surveyor at the

rare end of the chain and an assistant to establish intermediate points).

Ranging helps in establishing intermediate point between two points. Direct ranging is usually

employed when two end stations are inter visible.

Figure. 1. Pacing


Figure. 2. Method of Direct Ranging

Equipment:

1. Ranging rods

2. Measuring tape

Instructions:

1. The location for this lab shall be determined by the instructor.

2. Identify two inter-visible points ‘A’ and ‘B’ and fix the ranging rods at points ‘A’ and ‘B’.

3. Stand about 2 m behind the ranging rod fixed at point ‘A’.

4. Direct the person at ‘C’ to move the rod to right or left until the three ranging rods appear exactly

in the straight line ‘AB’.

5. Sight only the lower portion of rod in order to avoid error in non-vertically.

6. After ascertaining that three rods are in a straight line, direct the person at ‘C’ to fix to fix

the road to establish the intermediate point ‘C’.

7. Measure the chainage distance between ‘AC’ and ‘AB’. Add the distance to calculate the total

distance ‘AB’.

8. Use your normal walk to pace of each distance ( i.e.: 0 to 20 m ) for three consecutive trials.

9. Record the number of paces for each trial in your field book.

10. Calculate the average number of paces for each trial distance ( Refer the example given in Table. 1.)

11. Count the number of paces between point ‘A’ and ‘B’ and calculate the total distance.

12. Draw a detailed sketch of the measurement to a reduced scale in the field book.

13. Replicate all the data and sketches in your respective practical notebooks.


Table 1. Sample calculation for determining Average Pace

Trial 1 2 3

Distance 0-20 m 0-20 m 0-20 m

No. of paces 30 30 31

Average no. of paces 30.33

Average pace = 20/30.33 = 0.66 m/pace

Observation and Calculation Sheet:

Determination of Average Pace

S. No.

Trial

1

2

3

1

Distance

0-20 m

0-20 m

0-20 m

2

No. of paces

3

Average no of paces

Average pace = ________

Measurement of Distance by Direct Ranging

S. No. Chainage Line No. of paces Distance measured by

Pace (m) Distance measured by

Tape (m)

1 AC

2 CB

3 AB

Result:

By ranging and chaining the total distance between station ‘A’ and station ‘B’ is ____________

By pacing the distance between station ‘A’ and Statin ‘B’ is ____________

Precautions:

• The ranging rod should be established correctly at all points.

• The judgment of line should be taking correctly during the establishment of intermediate points.

• Distance between surveyor’s eye and ranging rods (e.g. A, B and C) should be kept at minimum

distance of 1 m.





LAB-2: MEASUREMENT OF DISTANCE BY RECIPROCAL RANGING

Aim: To measure the direct distance between two end stations by indirect or reciprocal ranging.

Theory:

When the end stations are not inter visible due to rising ground between them, or due to long distances

between the end stations, ranging is carried out in indirect manner. Indirect ranging is generally used

to lay out a line with inaccessible points or across a mountain.

Figure. 1. Reciprocal Ranging

Equipment:

1. Ranging rods

2. Measuring tape

A

C D

B

A B C D

C1 D1

C2

D2

D3 C3


Instructions:

1. The location for this lab shall be determined by the instructor.

2. Identify two non-visible points ‘A’ and ‘B’ and fix the ranging rods at points ‘A’ and ‘B’.

3. Choose two temporary intermediate points ‘C1’ and ‘D1’ between ‘A’ and ‘B’, such that the person

standing at ‘C1’ can see both the ranging rods at ‘D1’ and ‘B’. Similarly, the person standing at ‘D1’

can see the both the ranging rods at ‘C1’ and ‘A’.

4. Stand about 2 m behind the ranging rod fixed at point ‘D1’ to direct the person standing at ‘C1’

5. Direct the person at ‘C1’ to move the rod to ‘C2’ so as to be line with ‘A’.

6. Now the person standing at ‘C2‘ directs the person at ‘D1’ to move to new position ‘D2’ so as to be

line with ‘B’.

7. Continue the direction until the points are in line with ‘AB’. Fix the ranging rods to establish the

intermediate points ‘C’ and ‘D’.

8. Measure the chainage distance between ‘AC’ ,‘CD’ and ‘DB’. Add the distances to calculate the total

distance ‘AB’.

9. Draw a detailed sketch of the measurement to a reduced scale in the field book.

10. Replicate all the data and sketches from the filed book into your respective practical notebooks.

Observation and Calculation Sheet:

Measurement of distance by Reciprocal Ranging

S. No.

Chainage Line

Distance Measured by Tape (m)

1 AC

2 CD

3 DB

4 AB

Result:

By ranging and chaining the total distance between station ‘A’ and station ‘B’ is ____________

Precautions:



• Distance between surveyor’s eye and ranging rods (eg. A, B and C) should be kept at minimum

distance of 1 m.





LAB-3: CHAINING ACROSS OBSTACLES

Aim: To perform chaining across obstacles and to calculate the obstructed length using different

methods.

Theory:

The measurement of distances consist of chaining and making offsets. During measurements, it is

practically impossible to set out all the chain lines in a straight forward method because of a variety of

obstructions to chaining and raining in the field. The difficulties can be overcome by running

perpendicular and parallel lines or by running a few additional lines and measuring angles by some

instrument. The obstacles may be divided into two classes. Those which do not obstruct ranging (view)

but obstructs chaining (measurement) fall in the category of ‘ obstacles to measurement ’, e.g. ponds,

rivers, etc. The others are those which cannot be seen across i.e. both the chaining and ranging are

obstructed, e.g. houses, stacks, etc., and are know as ‘ obstacles to alignment ’.

Equipment:

1. Ranging rods

2. Measuring tape

3. Pegs and

4. Plumb bob

Procedure:

1. Obstacles to Measurement ( Obstacles to chaining but not ranging)

A) First Method: When an obstacle interrupts the chain line yet chaining is possible around the

obstacle. Such obstacles are chained using a Rectangular or a Triangular Method. E.g. Chaining

across a pond.

A.1. Chaining by Rectangular Method

Figure. 1. Chaining by Rectangular Method


Procedure:

1. Assuming a pond. Where vision is free but chaining is obstructed.

2. On both side of pond, place the ranging rods at a certain distance, marking point A and B.

3. From both the station A and B, fix another two ranging rods at certain distance away from it by

proper ranging and marking point as C and D.

4. From point C and D, draw perpendicular line with base line AB by using 3- 4 - 5 method.

5. Take equal offset distance from point C and D and mark the point as E and F respectively.

6. Connect the points E and F.

7. Distance EF is equal to CD.

8. Measure distance AC, EF and DB and add the distance AC, EF and DB

9. Draw the diagram of measured distances in reduced scale.

A.2. Chaining by Triangular Method

Figure. 2. Chaining by Triangular Method

Procedure:

1. Assuming a pond. Where vision is free but chaining is obstructed.

2. On both side of pond, place the ranging rods at a certain distance, marking point A and B.

3. From both the station A and B, fix another two ranging rods at certain distance away from it by

proper ranging and marking point as C and D.

4. From point C, draw perpendicular line with base line AB by using 3- 4 - 5 method.

5. Take certain offset distance from point C and mark the point as E.

6. Connect the points E and D.

7. Measure the distance ED.

8. By using Pythagoras theorem we get distance CD, giving length of the pond.


9. Measure distance CE and ED.


B) Second Method: When an obstacle interrupts the chain line but chaining is not possible around

the obstacle. E.g. Chaining across a river.

B.1. Chaining across a small width river

Figure. 3. Chaining across small width river

Procedure:

1. Assume a small width of river, where vision is free and chaining is obstructed.

2. On both sides of river, take two points as A and B.

3. Take another two points C and D along the base line A and B by performing proper ranging.

4. From point C, erect perpendicular line and locate a point E.

5. Determine the mid-point of line CE and name this point as F.

6. From point E, erect perpendicular line and locate a point G in such a way that by moving the rod

in EG direction, until line DFG comes in straight line.

7. Measure distance EG which is equal to CD.


E F


B.1. Chaining across a large width river

Figure 4. Chaining across a large width river

Procedure:

1. Assume a large width of river, where vision is free and chaining is obstructed.

2. On both sides of river, take two points as P and Q.

3. Take another three points A,C and R along the base line P and Q by performing proper ranging.

4. From point C and A, erect perpendicular line and locate a points D and F. Distance AD = CF.

5. Connect point FD.

6. Extend line FE in such a way that line EDR comes in straight line.

7. Determine the mid-point of line CE and name this point as F.

8. We get two similar triangle i.e. ∆ ADR and ∆EFD . By using similar triangle rule, we can determine

the distance AR.

9. Calculate the distance AR using the relation, FE/AD = FD/AR



2. Obstacles to Alignment ( Obstacles to both Chaining and Ranging)

Such a problem arises when a building comes across the chain line. Following is one of the methods

used when chain line is obstructed in which both ranging and chainage are obstructed.

A. First Method:

Procedure:

1. Let AB be the obstructed length across the building.

2. A point C is assumed arbitrarily.

3. B and C are joined such that BC = CD.

4. Now A and C are also joined such that AC = CE.

5. Connect the points D and E.

6. Triangles CAB and CDE are similar triangles. Therefore, obstructed length DE = AB



B. Second Method:

1. Assume AB is the chain line.

2. Two points C and D are selected on it at one side of the building.

3. Erect two equal perpendiculars CC1 and DD1 from C and D.

4. Extend the line C1D1 until the building is crossed.

5. On the extended line, select two points E1 and F1.

6. Erect the perpendiculars E1E and F2E such that E1E=F1E=D1D=C1C.

7. The points C, D, E and F will lie on the same straight line AB.

8. Measure the distance D1E1 to get the required chainage of DE.


Observation and Calculation:

Note:

Scaled drawings and calculations of obstructed length for all methods should be shown here.

Students are required to draw all the diagrams of all methods to scale with all dimensions on the left

pages of lab record


Result:

1. Obstacle to Measurement

• Obstructed length from First Method (Rectangular Method): _________ m

• Obstructed length from First Method (Triangulation Method): _________ m

• Obstructed length from Second Method (For small width river): _________ m

• Obstructed length from Second Method (For large width river): _________ m

2. Obstacles to Alignment ( Obstacle to both Chaining and Ranging)

• Obstructed length from First Method: _________ m

• Obstructed length from Second Method: ______ m

Precautions:



• Perpendicular offsets should be erected accurately.





LAB-4: DIFFERNTIAL LEVELLING

Reducing Levels by Rise and Fall Method and Height of Instrument Method

Aim: To determine the elevation of various points with Dumpy Level by Rise and Fall method and

Height of Instrument (Collimation) method.

Theory:

The art of determining and representing the relative height or elevation of different object/points on

the surface of earth is called leveling. It deals with measurement in vertical plane. By leveling operation,

the relative position of two points is known whether the points are near or far off. Similarly, the point

at different elevation with respect to a given datum can be established by levelling.

Dumpy level is the most widely used direct instrument. It consists of a telescope which is rigidly fixed

to its support. It can be neither be rotated about its longitudinal axis nor can it be removed from its

support. It is very advantages when several observations are to be made with one set up of instrument.

Rise and Fall method: While in rise and fall method, the difference of level between consecutives point

is determined by comparing the reading of each point after the first with immediately preceding. The

difference between their staff readings indicates a rise or fall according to the staff reading at the point

is smaller or greater than that at the preceding point. The reduced level of each point is then calculated

by adding the rise or subtracting the fall from the reduced level of the preceding point.

Arithmetic check in Rise and Fall method: B.S. - F.S. = Rise - Fall = Last R.L. - First R.L.

Height of Instrument (Collimation) method: The reduced level of the points from the staff reading

taken in the field are also calculated by using collimation method (HI). In collimation method, the height

of the instrument is found. For every set up of the instrument, height of the instrument is obtained by

adding the back sight to the reduced level of the bench mark. The RL of the intermediate points and the

first change point are then obtained by subtracting the staff reading taken on those points (I.S and F.S)

from the elevation of plane of collimation.

Arithmetic check in Height of Instrument method: B.S. - F.S. = Last R.L. - First R.L.

Equipment:

1. Dumpy Level

2. Levelling Staff

3. Tripod stand

4. Plumb bob


Procedure:

The following adjustments are made to the level before the commencement of the survey

A) Setting up the Dumpy Level

Procedure:

• Release the clamp screw of the instrument

• Hold the instrument in the right hand and fix it on the tripod by turning round only the lower part

with the left hand.

• Screw the instrument firmly and bring all the foot screws to the center of its run.

• Spread the tripod legs well apart and fix any two legs firmly into the ground by pressing them

with the hand.

• Move the third leg to up or down until the main bubble is approximately in the center.

Objective Focus

Horizontal fine

motion knob

Bottom plate Levelling screw

Eye piece lens

Optical Sight

Circular Level

Figure. 1. Dumpy Level

Figure. 2. Measuring Tape

Figure. 3. Levelling Staff


• Then move the third leg in or out until the bubbles of the cross-level is approximately in the

center.

• Fix the third leg firmly when the bubbles are approximately in the centers of their run

B) Levelling up

Procedure:

• Place the telescope parallel to a pair of foot screws.

• Bring the bubble to the center of its run by turning the foot screws equally either both inwards

and both outwards.

• Turn the telescope through 90º, so that it lies over the third foot screw.

• Turn this third foot screw so that the bubble comes to the center of its run.

• Turn the telescope through and check whether the bubble remains central

C) Elimination of Parallax:

Procedure:

• Remove the lid from the object glass.

• Hold a sheet of white paper in front of the object glass.

• Move the eyepiece right or left until the cross hairs are distinctly visible.

• Direct the telescope towards the staff.

• Turn the focusing screw until a clear and sharp image is formed in the plane of the cross hairs.

Procedure for Rise and Fall Method:

• Select a suitable area to conduct levelling.

• Fix the tripod on the level ground by moderately spreading its legs. Try to level the tripod head

approximately at suitable height.

• Fix the dumpy level on the tripod and level its base with help of foot screw and air bubble.

• To make the object clear and distinct, the eye piece is made to focus on cross hair by pointing the

telescope towards the sky and moving the eye piece in or out till the cross hair seen sharp and

distinct.

• Place the staff over a bench mark (B.M), whose reduced level is known, and set up the instrument

in convenient and safe location where the B.M (point A) is visible. Take a sight on the staff, that

reading is called Back Sight (B.S).

• Direct the telescope towards the levelling staff and take readings at position B, C, D etc. which will

be the Intermediate Sights (I.S) and Fore Sights (F.S) for the Change Points.

• Set up the instrument in new position and continue taking the readings.

• The last sighting will be the Fore Sight (F.S) after which the data would be tabulated.

• Staff stations are established at the uniform distances. Taking approximately 5 to 10 m of interval.

• Note down readings of back sights, intermediate sights and fore sights for tabulation.


Tabulation for Rise and Fall method

Staff Station

Chainage

READINGS

Rise Fall Reduced Level Remarks B.S I.S F.S

A B.M

B

C

D

E

F

G

H

I

J

K F.S

Arithmetical Check:

B.S. - F.S. = Rise - Fall = Last R.L. - First R.L.

Procedure for Height of Instrument Method:

The field procedure and booking of staff reading is done in the same way as explained in the

Rise and Fall method. However the data booking is performed as shown in the Table below.

Tabulation for Height of Instrument (Collimation Method)

Staff Station

Chainage READINGS Height of

Instrument Reduced Level Remarks

B.S I.S F.S

A B.M

B

C

D

E

F

G

H

I

J

K F.S


Arithmetical Check:

B.S. - F.S. = Last R.L. - First R.L.

Result:

1. Rise and Fall method

• B.S - F.S =

• Rise - Fall =

• Last R.L. – First R.L. =

2. Height of Collimation method

• B.S - F.S =

• Last R.L. – First R.L. =

Precautions:

• The staff should be held vertical while taking the reading;

• The bubble in the level tube is to be brought to central before taking any reading;

• Readings should be taken in the proper direction depending on the type of staff;

• Balancing of sight is to be maintained as far as possible;

• Reading and recording of observation correctly.





LAB-5: PROFILE LEVELLING & CROSS SECTIONAL LEVELLING

Aim: To determine the configuration of ground surface by conducting Profile and Cross

Sectional levelling

Theory:

Profile Levelling: The process of determining elevations at points at short measured intervals along

a fixed line is called Longitudinal or profile leveling. Profile leveling is one of the most common

applications of running levels and vertical distance measurement for the surveyor. The results are

plotted in the form of a profile, which is a drawing that shows a vertical cross section. Profiles are

required for the design and construction of roads, curbs, sidewalks, pipelines etc. In short, profile

leveling refers to the process of determining the elevation of points on the ground at mostly uniform

intervals along continuous line.

Figure. 1. Profile Levelling

Cross Sectional Levelling: The term cross-section generally refers to a relatively short profile view of

the ground, which is drawn perpendicular to the route centerline of a highway or other types of linear

projects. Cross-sectional drawings are particularly important for estimating the earthwork volumes

needed to construct a roadway; they show the existing ground elevations, the proposed cut

or fill side slopes, and the grade elevation for the road base.

Figure. 2. Cross Sectional Levelling


Any of the following checks are opted based on the method chosen for reducing the Levels.

• Arithmetic check in Rise and Fall method:


• Arithmetic check in Height of Instrument method:

B.S. - F.S. = Last R.L. - First R.L.

Equipment:

1. Dumpy Level

2. Levelling Staff

3. Tripod stand

4. Plumb bob

5. Measuring Tape

6. Pegs

Instructions for Profile Levelling:

1. Suppose AB is the direction chosen for the construction of road, drain, etc.

2. After reconnaissance survey establish several staff stations between A and B at regular interval.

3. The levelling instruments is placed at suitable position (say L1, L2, L3 …) and after temporary

adjustments, the readings are taken from staff stations.

4. The first staff reading of any set up is taken from bench mark and entered in the back sight

column, and the last reading in the foresight column.

5. The other readings are entered in the intermediate sighting column.

6. Similarly, change points are also established measuring its foresight and back sight

7. At the end of the day, a temporary bench mark must be placed at suitable points for future

reference. This temporary benchmark can also be used to continue the levelling and align the

direction of levelling work with the previous alignment. 8.

9. All the recordings are entered into the level book and the profile is being plotted.

A) Plotting the Profile and Cross Sections ( Refer Fig. 3 and Fig. 4 )

• The profile drawing is basically a graph of elevations, plotted on the vertical axis, as a

function of stations, plotted on horizontal axis.

• A gridded sheet called profile paper is used to plot the profile data from the field book.

• All profile drawings must have a proper title block, and both axes must be fully labeled with

stations and elevations.

• The elevation or elevation scale is typically exaggerated; that is, it is ' stretched ' in comparison

to the horizontal scale. For example the vertical scale might be 10 times larger. The horizontal

line at the bottom of the profile does not necessary have to start at zero elevation


Tabulation for Profile Levelling

All the readings are recorded in meters.

Staff Station

Chainage

READINGS

Rise Fall Reduced Level Remarks B.S I.S F.S

A B.M

B

C

D

E

F

G

H

I

J

K F.S

Arithmetical Check:


Figure. 34. Longitudinal Cross Section

0

50

100

150

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

R.L

. in

Me

ters

Distance in Meters

Profile Levelling

Datum 100 m

A

B


Instructions for Cross Sectional Levelling:

1. Let ABC be line of section set out on the ground and mark with pegs at equal interval (say 10 to 20

m).

2. Set up the level at side of profile to avoid too short sight on the point near instruments and care

must be taken to set up level approximately midway between two change point.

3. Start levelling from bench mark of known value.

4. From each set up, staff reading are taken on pegs already fixed at desired interval and also at

significant points.

5. All readings are recorded as intermediate sight against the respective chainages along the line is in

level book.

6. When the length of sight is beyond the power of telescope, the foresight on change point is taken.

The level is then shifted and back sight is taken on change point.

7. Continue chaining and reading as before, till whole line of section is completed.

8. The fore bearing and back bearing of section line should be taken and recorded.

Tabulation for Cross Sectional Levelling

All the readings recorded in meters.

Staff Station

Chainage READINGS

Rise Fall R.L Remarks Left Center Right B.S I.S F.S

1.415 105.405 B.M

A 0 1.875 0.460 104.945 C.S.-1

5 1.795 0.080 105.025

10 1.625 0.170 105.195

15 1.540 0.085 105.280

5 1.535 0.005 105.285

10 1.685 0.150 105.135

15 1.805 0.120 105.015

B C.S.-2

Arithmetical Check:



Figure. 4. Transverse Cross Section

Result:

Plot the Longitudinal and Transverse cross sections of the survey area.

Precautions:

• The staff should be held vertical while taking the reading;

• The bubble in the level tube is to be brought to central before taking any reading;

• Readings should be taken in the proper direction depending on the type of staff;


• Reading and recording of observation correctly.

0

50

100

150

200

-15 -10 -5 0 5 10 15

R.L

. in

Me

ters

Distance in Meters

Cross Sectional Levelling

Point of Center Line

Left Side Right Side

10 L 5 L 5 R 10 R 15 R15 R

Datum 100 m




Surveying Laboratory

LAB-6: THEODOLITE TRAVERSING

Aim: To adjust and balance a closed traverse using Gale’s Traverse Table.

Theory:

Traversing is that type of survey in which member of connected survey line from the frame work and

the direction and lengths of the survey lines are measured with help of an angle measuring instrument.

Theodolite traversing is a method of establishing control points and their position being determined

by measuring distance between the traverse station and angle subtended at the various station by their

adjacent stations. After measuring angle, length and direction, Gales table is prepared to calculate final

traversing. Gales table helps in calculating errors and getting accurate bearings, angles and lengths.

Equipment:

1. Theodolite

2. Ranging rod

3. Tripod stand

4. Plumb bob

5. Measuring Tape

6. Pegs

Objective Lens

Handle

LCD Display

Tri-pod Base Plate

Focusing Ring

Optical Plummet

Telescope clamp

Telescope fine motion

Horizontal Clamp Horizontal fine motion

Targeting Sight

Operating Keys


Instructions:

The following adjustments are made to the theodolite before traversing.

A) Setting, Levelling and Centering Theodolite

• Release the clamp screw of the instrument

• Hold the instrument in the right hand and fix it on the tripod by turning round only the lower

part with the left hand.

• Screw the instrument firmly and bring all the foot screws to the center of its run.

• Spread the tripod legs well apart and fix any two legs firmly into the ground by pressing them

with the hand.

• Move the third leg to up or down until the main bubble is approximately in the center.

• Then move the third leg in or out until the bubbles of the cross-level is approximately in the

center.

• Fix the third leg firmly when the bubbles are approximately in the centers of their run.

• Place the telescope parallel to a pair of foot screws.

• Bring the bubble to the center of its run by turning the foot screws equally either both inwards

and both outwards.

• Turn the telescope through 900 , so that it lies over the third foot screw.

• Turn this third foot screw so that the bubble comes to the center of its run.

• Turn the telescope through and check whether the bubble remains central

• Looking through the optical plummet, focus the centering index mark. Slide the theodolite on

the tripod head until the reference mark is centered in the optical plummet.

• Fully tighten the centering screw. Look through the optical plummet again and adjust the

theodolite foot screws for alignment with the reference mark.

B) Instructions for Theodolite Traversing

• The area to be surveyed is first thoroughly examined to decide the best possible way of starting

the work.


• Consider a closed traverse with stations namely ABCDEFA. The traverse stations are marked

on the ground by wooden pegs with nails on top.

• Set up the instrument at A. Complete the adjustments (levelling and centering) before sighting

the station B.

• Once levelling and centering have been achieved, turn on the theodolite by pressing the power

key.

• Place the compass over the theodolite and rotate to find the direction of meridian (North).

• Once the direction has be set, press the HOLD key twice to lock the reference direction.

• Press the L/R key for horizontal angle options. R mode is used when the traversing is carried

out in clockwise direction and L mode in counter-clockwise direction.

• Press V/% key to see the inclination angle of optical telescope. The angle has to be in 000’0’’

(zero inclination) to maintain the line of collimation throughout the process of traversing.

• After zero-inclination has been maintained, use the vertical clamp screw to restrict the rotation

of telescope.

• Now, sight the levelling staff or ranging rod placed at B and record the fore bearing.

• Station the instrument at Station B and sight at Station A and record its back bearing.

• Similarly, complete the process for entire traverse stations.

• Find the included angles ∠A, ∠B, ∠C, ∠D, ∠E, and ∠F. Measure the length of traverse legs

connecting all the stations.

• Plot the traverse and find the closing error graphically ( Draft in AutoCAD )

• Check the adjustment of interior angles using the condition, i.e. the sum of the included angles

should be (2n±4) x 900 , where n is the number of sides of closed traverse.

• Perform all essential checks using the Gale’s Traverse Table.

• Re-plot the corrected traverse.

1. Tabulation for Traversing

Station Line Fore

Bearing (DMS)

Line Back

Bearing (DMS)

Traverse Line Traverse

Length (m) Included

Angles (DMS)

A 78085’20’

AB 6000’0’’ BA 24000’0’’ AB 10

B 78085’20’

BC 6000’0’’ CB 24000’0’’ BC 12

C 78085’20’

CD 6000’0’’ DC 24000’0’’ CD 9

D 78085’20’

DE 6000’0’’ ED 24000’0’’ DE 11

E 78085’20’

EF 6000’0’’ FE 24000’0’’ EF 12

F 78085’20’

FA 6000’0’’ AF 24000’0’’ FA 9

Instruction: Plot the traverse to check the closing error. ( Draft in AutoCAD)


2. Tabulation for Gale’s Traverse Table

Instruction: Find the closing error using, CE = 2 2( ) ( )Latitude Departure +

Sta

tio

n

Lin

e

Le

ng

th

Inte

rio

r a

ng

les

Co

rre

ctio

ns

Co

rre

cte

d A

ng

les

WC

B

RB

Qu

ad

ran

ts

Consecutive coordinates

Correction (Bowditch Rule

Corrected Consecutive Coordinates

Independent Coordinates

Lat. Dep. Lat. Dep. Lat. Dep. N (+) S (-) E (+) W (-)

N (+)

S (-)

E (+)

W (-)

N (+)

S (-)

E (+)

W (-)

N (+) S (-) E (+) W (-)

A

AB

B

BC

C

CD

D

DE

E

EF

F

FA

A

Ʃ


Result:

• The graphical closing error of the traverse was found to be ……………..

• Plot the traverse ABCDEFA before and after correction

Precautions:

• The staff should be held vertical while taking the reading.

• The bubble in the level tube is to be brought to central before taking any reading.

• Readings should be taken in the proper direction depending on the type of staff.


• Reading and recording of observations should be done correctly.




Surveying Laboratory

Aim: To determine the tacheometric constant and elevation difference between two given points

using the principle of tacheometry.

Theory:

Tacheometeric surveying is a method of angular surveying in which the horizontal distance from the

instrument to the staff station and the elevation of the staff station concerning the line of collimation

of the instrument are determined from instrument observation only. Thus, chaining operation are

eliminated. There are two method in tacheometric surveying. These are stadia system and tangential

system. In this method stadia system is used to determine the difference in elevation between two

given points.

The principle of tacheometry is based on the property of isosceles triangles, where the ratio of the

distance of the base from the apex and length of the base is always constant.

∆ O1a1a2, ∆ O1b1b2 and ∆ O1c1c2 are isosceles triangles. D1, D2 and D3 are the distances of the bases from

the apices and S1, S2 and S3 are the lengths of the bases. According to this principle

31 2

1 2 3

(constant)DD D f

S S S i= = =

sin 2( )sin

2

f SV f d

i

= + +

is known as multiplying constant, D S ( )f

f de

= + +

is the focal

length of the objective lens and i is the stadia intercept.

LAB-7: TACHEOMETRIC SURVEYING


From the theory of stadia tacheometry, the following equation is used to relate the distance, stadia

intercept and the constants i.e.

D S ( )f

f di

= + +

Where, ( )f d+ is the additive constant

S is the stadia intercept and d is the distance between the vertical axis and centre of objective.

Equipment:

1. Theodolite

2. Levelling staff

3. Tripod stand

4. Plumb bob

5. Measuring Tape

Instructions:

A) Determination of Tacheometric constant

• Choose a fairly level ground. Set up the theodolite at O and fix the pegs at A1, A2 and A3

• The staff intercepts (stadia hair readings) are noted at each of the pegs. The intercepts are taken

as S1, S2 and S3

• The horizontal distances of the pegs from O are accurately measured. The distances are

recorded as D1, D2 and D3

• The values of stadia intercepts and distances are substituted in the general equation.

• The equations are then solved to obtain several values of multiplying constant (f

i) and

additive constant ( )f d+ .

• The mean of these values are taken for the required constant.


B) Instructions for Theodolite Traversing

• Select the site, which has got certain differences in elevation between two points.

• Fix the tripod on the level ground by moderately spreading its legs. Try to level the tripod head

approximately at suitable height.

• Fix the tacheometer on the tripod and level its base with help of foot screw and air bubble.

• To make the object clear and distinct, the eye piece is made to focus on cross hair by pointing

the telescope towards the sky and moving the eye piece in or out till the cross hair seen sharp

and distinct.

• Direct the telescope towards the staff and the images are made to appear clear and sharp by

adjusting the focusing screw.

• Hold the staff on the bench mark and take the bearing. Take all the readings like top, bottom

and central.

• After measuring the bench mark reading, rotate the instrument and take the forward reading

on chosen points.

• If the given point is at higher elevation, the following case is considered.

Figure. 1. Considering the angle of elevation

2cos ( )cosf

D S f di

= + +

sin 2( )sin

2

f SV f d

i

= + +

R.L of the staff station = Height of Instrument + V- h

Where, h = central hair reading

S = Staff Intercept (stadia interval)

D = Horizontal distance between instrument and staff

V = Vertical distance between instrument axis and central hair

Θ = angle of elevation


Figure. 2. Considering the angle of depression

2cos ( )cosf

D S f di

= + +

sin 2( )sin

2

f SV f d

i

= + +

R.L of the staff station = Height of Instrument - V- h

Where, h = central hair reading

S = Staff Intercept (stadia interval)

D = Horizontal distance between instrument and staff

V = Vertical distance between instrument axis and central hair

Θ = angle of depression

1. Tabulation for Tacheometric Constants

Instrument Station

Staff Station

Distance (m)

Stadia Readings f

i

( )f d+

Lower Upper

O

A

B

C

Average


2. Tabulation for Tacheometric Data Entry

Instrument Station

Staff Station HI Vertical

Angle (θ)

Staff Reading in meters

Upper Stadia Cross Hair

Lower Stadia

O

A

B

Instrument Station

Staff Station

Distance (m)

Vertical Distance (m)

Stadia Intercept

(m)

Central Hair

Reading (m)

R.L (m) Remark

O

A Point O is assumed to be

a B.M (R.L.=100 m) B

Result:

• The R.L. of points A is …………. and that of B is …………

• The multiplying and additive constants are ………….. and ……………

Precautions:

• The staff should be held vertical while taking the reading.

• The bubble in the level tube is to be brought to central before taking any reading.

• Readings should be taken in the proper direction depending on the type of staff.

• Reading and recording of observations should be done correctly.

Manual for Soil Mechanics & Foundation Engineering for DAAPractical_1Introduction to lab procedures with practial no.1Publication1Introduction to lab procedures with practial no. 1Jigme Namgyel Engineering CollegeDepartment of Civil Engineering & SurveyingSoil Mechanics & Foundation Laboratory

Introduction to lab procedures with practial no. 1Jigme Namgyel Engineering CollegeDepartment of Civil Engineering & SurveyingSoil Mechanics & Foundation Laboratory

Practical_2Jigme Namgyel Engineering CollegeDepartment of Civil Engineering & SurveyingSoil Mechanics & Foundation Laboratory




Practical_6Jigme Namgyel Engineering CollegeDepartment of Civil Engineering & SurveyingSurveying Laboratory

Practical_7Jigme Namgyel Engineering CollegeDepartment of Civil Engineering & SurveyingSurveying Laboratory

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