cve 325 levelling report

8/10/2019 Cve 325 Levelling Report

1/25

Page | 1

LEVELLING

CVE 325

GROUP 3

SUBMITTED BY

OMOLEWA JOSHUA OLUMIDE

MATRIC NO: 11CI012282

SUPERVISED BY

SURVEYOR OJO

FEBUARY 2014


2/25

Page | 2

ABSTRACT

This project is a detailed explanation of levelling. We took the

level of Electronic and Electrical Engineering Department

building in order to determine various elevations of differentstations round the building.


3/25

Page | 3

ACKNOWLEDGEMENT

I have taken efforts in this project. However, it would not have been

possible without the kind support and help of my group members. I

would like to extend my sincere thanks to all of them.

I am highly indebted to Surveyor Ojo for his guidance and constant

supervision as well as for providing necessary information regarding

the project & also for his support in completing the project.

I would like to express my gratitude towards my friends for their kind

co-operation and encouragement which helped me in completion of this

project.

My thanks and appreciations also go to my colleague in developing the

project and people who have willingly helped me out with their

abilities.


4/25

Page | 4

TABLE OF CONTENTSPage No.

Introduction 5

Methodology 6

Terms used in levelling 7

Equipment used 8

Procedure carried during the levelling 10

Personnel 12

Theory on leveling 13

Observation 23

Computation & reduction of level 24

Recommendation/ Conclusion 25


5/25

Page | 5

INTRODUCTION

Accurate levelling is thus a particularly important part of siteestablishment, installation and quality assurance. All persons

shall be thoroughly familiar with its theory andpractice.

Levelling and surveying methods are also used for

measurements of river channel and lake configurations. Often,

less accurate methods can be used for this work than for water-

level recording stations, although the techniques are common.

Levelling operation is done by the surveyor using a level,

tripod stand, staff, ranging pole, a measuring tape.

Levelling is the process used to determine a difference in

elevation between two points


6/25

Page | 6

METHODOLOGY

The method best suited for our levelling operation was the riseand fall method due to the flexibility.

There are other methods like height of collimation method


7/25

Page | 7

TERMS USED IN LEVELLING

Datum line ( M.S.L. ) :- Is the level (line), which are attributed to it points levels on the

surface of the Earth. This is the average sea level.

Reduced level ( R.L) :- Is the high point from datum line.

Benchmark (B .M ) :- Are fixed points information site and attributed placed in different

places until you start racing them when conducting settlement .

Back sight ( B.S.) :- Is the first reading taken after placing the device in any position so

that we see the greatest possible number of points required to find the elevation .

Fore sight (F.S) :- Is the last reading taken before the transfer device

Intermediate sight ( I.S.) :- Is reading taken between the back sight and fore sight

reading .

Elevation of line of sight ( H.I) :- Is the imaginary vertical level determined by the lineof sight to the amount of increase or decrease for sea level.


8/25

Page | 8

EQUIPMENTS USED

1.

LEVEL:

is an instrument with a telescope that can be leveled with a spirit

bubble. The optical line of sight forms a horizontal plane, which is at the same

elevation as the telescope crosshair. By reading a graduated rod held vertically on

a point of known elevation (Bench Mark) a difference in elevation can be

measured and a height of instrument (H.I.) calculated by adding the rod reading

to the elevation of the bench mark. Once the height of instrument is established,

rod readings can be taken on subsequent points and their elevations calculated by

simply subtracting the readings from the height of instrument

A level is an instrument giving horizontal line of sight and magnifying the reading

at a faraway distance. It consists of the following parts:

(i) A telescope to provide a line of sight

(ii) A level tube to make the line of sight horizontal and

(iii) A leveling head to level the instrument


9/25

Page | 9

2. STAFF: Is a wooden or metal ruler one side runway to meters and centimeters.

And is a ruler of solid wood 2 , 3 , 4 , 5 meters in length and usually 4 meters The

levelling staff is a box section of aluminium or wood, which will extend to 3 or 5 m in height

by telescoping, hinging or addition of sections. One face has a graduated scale attached for

reading with the cross-hairs of the level telescope. These faces can vary in pattern andgraduation; 5mm graduations should be the maximum for accurate levelling of gauging

stations.Many staves used these days are of aluminium because of its durability. However

aluminium has a co-efficient of thermal expansion of: 0.000023m/metre of length/Cand this

can cause some potential inaccuracies. For instance, "Survey Chief" and "Brookeades" staves

are standardised at 27C, and in very cold weather these staves could be as much as 3mm too

short over their full length. For low temperature work consult the temperature table for each

staff which should be with its "instruction manual" or printed on the staff itself

3.

TRIPOD:is a portable three-legged frame, used as a platform for supporting the

weight and maintaining the stability of some other object


10/25

Page | 10

PROCEDURES CARRIED OUT.Leveling of the instrument is done to make the vertical axis of the

instrument truly vertical. It is achieved by carrying out the

following steps:

Step 1: The level tube is brought parallel to any two of the foot screws,

by rotating the upper part of the instrument.

Step 2: The bubble is brought to the center of the level tube by rotating

both the foot screws either inward or outward. (The bubble moves in

the same direction as the left thumb.)

Step 3: The level tube is then brought over the third foot screw again by

rotating the upper part of the instrument.

Step 4: The bubble is then again brought to the center of the level tube

by rotating the third foot screw either inward or outward.


11/25

Page | 11

Step 8: By rotating the upper part of the instrument through 180 , the

level tube is brought parallel to first two foot screws in reverse order.

The bubble will remain in the center if the instrument is in permanent

adjustment.


12/25

Page | 12

PersonnelMy group was the group 3, which comprised of different people that all assisted in

the carrying out of the project. We carried out our levelling practical round about

the Electrical and Electronics Engineering Building.


13/25

Page | 13

THEORY ON LEVELLING

Definitions

Differential levelling is the term applied to any method of measuring directly

with a graduated staff the difference in elevation between two or more points.

Precise levelling is a particularly accurate method of differential levelling whichuses highly accurate levels and with a more rigorous observing procedure than

general engineering levelling. It aims to achieve high orders of accuracy such as 1

mm per 1 km traverse.

A level surface is a surface which is everywhere perpendicular to the direction of

the force of gravity. An example is the surface of a completely still lake. For

ordinary levelling, level surfaces at different elevations can be considered to be

parallel.

A level datum is an arbitrary level surface to which elevations are referred. The

most common surveying datum is mean sea-level (MSL), but as hydrological work

is usually just concerned with levels in a local area, we often use:

An assumed datum, which is established by giving a benchmark an assumed value

(e.g. 100.000 m) to which all levels in the local area will be reduced. It is not

good practice to assume a level which is close to the actual MSL value, as it

creates potential for confusion.

A reduced level is the vertical distance between a survey point and the adopted level

datum.

A bench mark (BM) is the term given to a definite, permanent accessible point of

known height above a datum to which the height of other points can be referred.It is usually a stainless steel pin embedded in a substantial concrete block cast into

the ground. At hydrological stations rock bolts driven into bedrock or concrete

structures can be used, but structures should be used warily as they themselves are

subject to settlement. The locations of benchmarks shall be marked with BM

marker posts and/or paint, and recorded on the Station History Form.

A set-up refers the position of a level or other instrument at the time in which a

number of observations are made without mooring the instrument. The first


14/25

Page | 14

observation is made to the known point and is termed a backsight; the last

observation is to the final point or the next to be measured on the run, and all other

points are intermediates.


15/25

Page | 15

A run is the levelling between two or more points measured in one direction only.

The outward run is from known to unknown points and the return run is the check

levelling in the opposite

direction.

A close is the difference between the starting level of the initial point for the

outward run and that determined at the end of the return run. If the levels have been

reduced correctly this value should be the same as the difference between the sum

of the rises and falls and also the difference between the sum of the backsights and

foresights.

Height of Collimation is the elevation of the optical axis of the telescope at the

time of the setup. The line of collimation is the imaginary line at the elevation.

Orders of levelling refer to the quality of the levelling, usually being defined

by the expected maximum closing error. These are given in Table 6.1

Order Purpose Maximumclose (m)

Precision order Deformation surveys 0.001 x km

First order Major levelling control 0.003 x km

Second order Minor levelling control 0.007 x km

Third order Levelling for construction 0.012 x km

Table 1 Levelling

closes

The accuracy requirements for water-level stations relate to the standards; forfurther information refer to section 6.1.5.

Change points are points of measurement which are used to carry the

measurements forward in a run. Each one will be read first as a foresight, the

instrument position is changed, and then it will be read as a backsight.

Staff bubbles

These are generally a small circular bubble on an angle plate which is held against

one corner of the staff to ensure that the staff is held in a vertical position. If the

staff is not held vertical, the reading will be too large and may be significantly inerror.

A staff bubble shall be used at all times. If one is not available, the "chainman"

(staff operator) shall rock the staff slowly back and forth about the vertical in a

line towards the instrument. The observer notes the smallest reading which will

occur when the staff is vertical.


16/25

Page | 16

Figure 1 The three main types of levels.

3.4 Care of

equipment

ensure that tripod screws and hinges are kept tight.

always transport the level in a padded box.

when removing from the box lift it by the centre and not by the eyepiece

or objective end of the telescope.

screw it firmly onto the tripod, whilst holding it in one hand (make certain that

it is not cross-threaded and that threads are compatible).


17/25

Page | 17

when carrying the level tripod assembly in the field, support it over the

shoulder or, in bush, crooked over an arm with the telescope unclamped (i.e.

free to rotate).

automatic levels should not be carried in a vertical or near-vertical position,

as the compensator will swing about and be prone to damage.


18/25

Page | 18

staves are too much of a precision item of equipment to be used in place of a

slasher, vaulting pole, etc.

staves shall be transported in their protective cases to protect the face from

damage.

wooden staves which become wet should be dismantled and dried out before

storing away. any moisture which is evident in an instrument must be allowed to disperse by

storing the level out of its case in a warm room. Should it persist after several

days the instrument may require specialist servicing.

3.5 Checking the levelsaccuracy

Levels can move out of adjustment so that their line of sight (line of collimation) is

not truly horizontal. This will cause errors in readings which become greater as the

viewing distance increases. However if a backsight and a foresight are exactly equi-distant from the instrument, the error in each sighting will cancel each other out.

This feature can be used to check the accuracy of a level by the following simple

method which is depicted in figure 6.2 (from MWD, 1981):

install three pegs or marks firmly in the ground at distances of 30 m apart in a

straight line; the centrepeg is only to mark the distance, but the outside two

shall be firm enough for reliable changepoints

set up the level over the centre peg and read the staff on each of the outside

pegs in turn. Book these values and calculate the height difference. This will

be a true height difference, as the distances areequal and any errors will be self-compensating

set up the level about 4 m to the far side of one of the outside pegs. Read the

staff on the peg 4 m away and then on the one 64 m away. Book these values

and calculate the apparent height difference

compare the two height differences; if the instrument is in adjustment (i.e. its

collimation is true) they will be within 5 mm.


19/25

Page | 19

Figure 2 A method for checking the level accuracy

If the instrument's collimation appears to be out, recheck by repeating the

process. Then, whilst setup at one of the outside locations, adjust the instrument

(according to the manufacturer's


20/25

Page | 20

instructions) so that it reads the correct value on the far staff, checking it against the

near one. Two staves are useful for this.

This type of level check shall be carried out at least once per year, preferably just

prior to carrying out a round of station inspections. The details and results of the

checks shall be recorded in a numbered level book and be readily retrievable as a

quality record, and the date of this calibration check shall also be recorded in the

instrument inventory.

3.6 Levelling procedures

(a) Setting up

Backsight and foresight distances should be approximately equal to avoid any

errors due to collimation, refraction or earth curvature.

Distances must not be so great as to not be able to read the graduations

accurately.

The points to be observed must be below the level of the instrument, but not

lower than the height of the staff.

(b) El imination of paral lax

Parallax is the apparent movement of the image produced by movement of the

observer's eye at the eyepiece.

It is eliminated by focusing the telescope on infinity and then adjusting the

eyepiece until the cross-hairs appear in sharp focus. The setting will remain

constant for a particular observer's eye.

(c) Booking

level books or loose-leaf levelling sheets shall be numbered and indexed

in a register.

details of the site, work, date, observer, chainman, booker, weather,

wind, instrument and any other relevant items shall be entered.

enter the first observation (which is on a known point) in the Backsight

column, and sufficient detail in the Remarks column to identify it. Enterthe point's R.L. zero from the site register orplate on the BM, etc.

enter all other points on subsequent lines as intermediates except the

point chosen as the foresight. Identify them in the Remarks column as

above. Enter the foresight on a further line in the Foresight column.

change the instrument to the next setup. Enter the following backsight

on the same line as theprevious foresight but in the Backsight column.


21/25

Page | 21

repeat the above procedure at each setup on the outward run then

reverse it to work back to the starting point on the return run. The

furthest point out is treated as for all other change points.

3.7 Reducing the levels

Two methods are in general use; the "rise and fall" method and the "height of

collimation" method. The latter reduces levels relative to the instrument height. As it

has inferior in-built checks it

should not be used and will not be covered here.

The "rise and fall" methods shall be used for reduction of all site levelling.

Reduction shall be carried out on site before packing up to ensure that the

levelling has been done correctly.


22/25

[22]

calculate the rises and fall between successive points and book them in the

appropriate column (one can determine whether each shot is a rise or fall by the

following rule of thumb: a higher value on top denotes a rise; a higher value on

the bottom denotes a fall)

add up the backsight and foresight columns for the entire traverse and note

the difference between them; this is the close

add up the rises and falls for the entire traverse, and compare the difference

between them with the difference between the backsights and foresights;

they should be the same

carry the reduced levels in the R.L. column down the page by adding or

subtracting the appropriate rise and fall values to the successive values of R.L.

The final value of the original starting point will differ from the original value

by the amount of the close.

If the levelling has been done correctly and all arithmetic reductions are correct,

the differences between total backsights and foresights, total rises and falls, andstarting and finishing R.L.'s should be the same. This difference is the close; and

for site inspection purposes it should bewithin 2mm or 6mm, depending upon which water-level standard is beingfollowed, 3mm or 10mm.

3.8 Level books

All levelling shall be booked in either level books or levelling sheets which shall

be retained as permanent records.Level books shall be numbered so that they can be referenced on station history and

inspection forms. They should be stored in fire-proof storage as for original record.

They should also include an index.

Levelling sheets shall be filed in time-sequential order in site files, and also

need to be in fire-proof storage as for level books.


23/25

[23]

Observation

o We started our work at a station which was our benchmark 1 with a reduced level of

50.00m.

o Before starting the work, we ensured that we checked the adjustments of the instruments

and should ensure that it is in good order. The observations were taken on the levelling

staff corresponding to the horizontal hair.

o

The levelling was done in a quiet and less busy area, so it was possible for theinstrument man to give oral instructions to the surveyor holding the staff.

o I observed that there was a change in height at different points of leveling.

o I also observed that the terrain was undulating

o I also observed that at each leveling point the spirit level had to be adjusted because all

the points where not the same.

o I also observed that during the calculation of data obtain during the practical that the B.S

F.S was equal to the last R.Lfirst R.L


24/25

[24]

Computation and Reduction of Level:

S/N B.S I.S F.S Rise Fall R.L Remark

1 1.24 50.00 BM1

2 1.67 2.14 0.90 49.10 CP1

3 1.27 0.40 49.50

4 0.96 0.31 49.81

5 0.72 0.24 50.05

6 1.59 0.59 0.13 50.18 CP2

7 1.99 1.26 0.33 50.57 CP3

8 1.14 0.85 51.369 1.18 0.44 0.70 52.06 CP4

10 1.47 0.29 51.77

11 1.17 0.30 52.07

12 1.93 0.76 51.31

13 1.19 2.08 0.15 51.16 CP5

14 1.03 1.62 0.43 50.73 CP6

1.77 0.74 49.99 BM2

Check: B.S. - F.S. = rise - fall= last R.L First R.L

Where B.S= 1.24 + 1.67 + 1.59 + 1.99 + 1.18 + 1.19 + 1.03 = 9.89

F.S.= 2.14 + 0.59 + 1.26 + 0.44 + 2.08 + 1.62 + 1.77= 9.90

B.S. - F.S.= 9.89 - 9.90 = - 0.01

rise= 0.40 + 0.31 + 0.24 + 0.13 + 0.33 + 0.85 + 0.70 + 0.30 = 3.26

fall= 0.90 + 0.29 + 0.76 + 0.15 + 0.43 + 0.74 = 3.27

rise - fall = 3.26 3.27 = -0.01

last R.L=49.99

First R.L=50.00

Last R.LFirst R.L = 49.9950.00 = -0.01


25/25

[25]

Recommendation/Conclusion

1. I recommend that if the values are much the rise and fall method should be used to

compute the reading because it saves considerable amount of time and labor.

2. Chain surveys are suited to planimetric surveys on low slopes. They rely upon

trilateration.

3. Levelling is used where terrain is more uneven. Levelling surveys often use

tacheometry to fix station positions.

4. A theodolite survey permits levelling, tacheometry or triangulation as required.

cve 325 levelling report

Documents