LESSON NOTE ON TYPES OF LEVELLING

TYPES OF LEVELLING

1. Continuous leveling

2. Reciprocal leveling

METHODS USED IN CONTINUOUS LEVELLING

• Collimation method or height of instrument

• Rise and fall method.

In collimation method height of instrument

HI = BS + RL

And reduced level

RL = HI – FS

At the end computation, the difference of the sum of BS and FS must be equal to the difference of first RL and last RL data recorded. Meanwhile in Rise and Fall method, a rise will occur when the staff reading is less than the reading on the proceeding station. The data recorded are also checked for correctness as above, but this time, rise and fall are used instead of BS and FS.

TRAVERSE DURING LEVELLING:

Definition:

A traverse is a continuous frame work of line connecting a number of points, the lengths of the lines and their angular relationship to each other being measured. The lines are known as legs and the points as stations.

USE

Traverse surveys are used where site conditions make the chain triangulation method impossible e.g where the survey is of as large area and details are not required.

TYPES:

1) Closed traverse – when the frame work form a closed figure (or when the traverse connects two stations whose position are known). This type of traverse is used for surveying lakes or other areas across which known check line can be run. Such traverse is easily checked, as the survey starts and finishes at the fixed points.

2) Open traverse – a traverse whose starting and finishing stations do not coined or are not both fixed or known points. This type of traverse is used to survey rivers e.t.c. To enable the work to be checked, sights are taken on to some reference objects, such as well defined landmarks

Note:

a) Chain traverse √

b) Compass traverse √

c) Theodolite traverse √

Terms:

a) Bearing – the term bearing refers to the angle between the line and the north -south line or median.

b) Whole - circle bearing - the bearing from north to the leg is measured in a clockwise direction and the angle from the north line right round to the leg is known as a whole – circle bearing ( as W.C.B)

A N

N N

A

WCB

O Of

WCB OA

O Of WCB

OA O of OA

A

Forward and Back Bearing: with A as the starting station of traverse and the direction of the survey being forward B, the angle between north and AB at A is known as the forward bearing of AB. The angle between north and AB at station B is known as the back bearing of AB, this should differ from the forward bearing by exactly 1800.

The forward and back bearings of a leg will differ by 1800 except there is local attraction. The presence of metal, metallic ores or electric currents will divert the compass needle from the north– south line, and thus cause the readings taken to be inaccurate. Stations should therefore be chosen so that they are beyond the influence of this attraction.

Correction for Effects of Local Attraction:

Line Bearing Diff of FB and BB

AB 600 1800

BA 2400

BC 1200 1800

CB 3000

CD 2100 1780 (-20)

DC 320

DA 3170 1820 (-20)

AD 135

LESSON NOTE ON TACHEOMETRY

TACHEOMETRY

This is the operation of measuring distances by means of stadia hairs.

Measuring the distances using stadia hairs involves setting the instruments at one end of the line being measured and a leveling staff is held vertically at the other end. The points where the stadia hairs cut the staff are read. The difference between the readings is the staff intercept, S. Assuming H is the horizontal distance between the instrument and staff, then

H = KS + (f + C)

Where K = constant multiplier (f +c) = additive constant

Note that K = f/i

Where f = focal length of the objective lens.

i= interval between stadia hairs

The equation above is applied to external focusing telescope, but when an anallactic lens is fitted is the telescope to bring the focal point on the vertical axis and therefore remove the need for additive constant.

H = KS.

But when the ends of the line being measured are on different levels such that the telescope has to be elevated of depressed through an angle of Ө0, the formulae above changes to:

H =KS Cos 2θ`and reduced level:

V = KS Cos Ө sin Ө+ HI – H

HI = height of instrument

h = staff reading

Occasionally, if θ exceeds 45⁰, it is better to tilt the staff so that it is perpendicular to the line of sight. Short sight is therefore attached to the staff to enable this to be done accurately. The method is called normal staffing then the formulae becomes:

H = KS Cos θ+ h sin θ

V = KS sin θ+ HI –– h cos θ

Lesson Note On TYPES OF PLANE SURVEYING

TYPES OF PLANE SURVEYING

Base on the nature of work to be done, we have the following types of the plane survey.

1) Cadastral survey: Involves measuring, delivery, recording the boundaries of precipitate, supplies map plan beyond a parcel of land described in land register. This is kind of plane surveying used in committed areas of land mostly private properties it is mainly used to establish boundary of the precipitate.

2)Engineering surveying: This embraces the survey work require before, during and after a engineering work, it is done for the construction and design of new roads and rails roads.

The type of scale of engineering surveying of archtechtural work drawing are 1 – 50 or

1:50, 1:100, 1:200 for sight plane and civil engineering work, scale of 1:500, 1:1000,

1:2000, 1:2500 for town survey or highway survey, we have scale of 1:2000, 1:2500,

1:5000,

1:10000 etc.

3)Mining surveying: This is a plane surveying used in determining the position and dimension of underground passage of the mine and also the natural and artificial feature of the mine, the data include both horizontal and vertical parts, length direction and slope of the turning and geological and topographic characteristics in a particular vicinity.

We can have open cast mine survey and underground mine survey.

It generally involves establishment of mineral boundaries and fixation of reverence monuments such as locating bore hole, rail roads and constructing geological map.

4)Road surveying: It is a plane surveying carried out for the purpose of locating and constructing cones of transportation and communication such as highways, rail roads, canal pipeline etc. here primary work usually involve topographic survey.

5)Hydrographic surveying: This is the type of plane surveying carried out in relation to considerable body of water such as lakes, rivers, ponds, etc.

The survey aims at determining channel depth for the purposes of navigation, water supply or sub-aquatic construction. In the case of river hydrographic surveying is made for flood control, water storage and apply, navigation and power supply some of the process in hydrographic surveying include (i) topographic survey of shore and bank, leveling to determine underground profile.

Plotting of such profile taking cross section, calculating volume of networks measuring drawings areas and laying out culvert and bridges.

Topographic surveying: This is a plane surveying used in purchasing map’s and plans of natural and mammals features such as relief, elevation, unequal land surfaces. There is no clear differences between a plan and a map of this nature, it is generally accepted that open details are rail drawn to a chosen scale while in map many textile has to be represented in symbol.

Topographic plan survey are used for engineering or design and administrative purpose only whereas topographic map are found useful in navigation, constructional activities.

The second characteristics of plane survey base or equipment are

1)Chain surveying or linear surveying which include the use of chain or tape to measure distances.

2)Compass surveying: Which involves the use of compass I getting bearing.

3)Theoclatide surveying: Which measure angles of elevation and depression

4)Leveling: Which make use of abnormal level, land standard pole; leveling is defined as the process of finding the differences

between in height of any 2 points on the ground.

For the purpose of

a)Tracing contour line

b)Plotting vertical section

c)Establishing point at given any elevation in constructional project.

Lesson Note On How to establish controls in Hydrographic Surveying

How to establish controls in Hydrographic Surveying
	The first step in making a hydrographic survey is to control both horizontal and vertical. Horizontal Controls: In an extensive survey, the primary horizontal control is established primarily by running theodolite and tape traverse before the triangulation station. Tthe traverse lines being run to following the shore lines approximately. In survey of less extent the primary horizontal control only is required and is established by running a theodolite and tape traverse sufficiently close to shore line. For rough work, the control may be established by running a theodolite and staid traverse or plane table trader. Stadia Surveying: The distances are determined by angles there are stadia hairs from which angles and all calculations are determined without change. Vertical Controls: These are based upon a series of bench marks established near the shore line by spirit leveling and these serve for setting and checking tide gages etc to which the sounding are referred.
Shore Line Surveying: Purpose: To determine the shore lines. To locate the shore details, promise topographical feature, light house, pointt of reference etc. To determine the high and lower water lines for average spring. Both in please and elevations in the case of tidal waters. All irregularities in the shore line as well as the shore details are located by means of offsets measured with a tape form the traverse lines, by staid or plane table. The points of reference should be dearly risible form the water and should be near enough such wing mills, flag poles etc. buoys anchored off the shore and light houses are used reference points. The position of the high water line may be judged roughly form deposits an marks on rocks however to locate it accurately the elev of mean high water is determined and point are located on the shore at that elevation. The line connecting these points represent high water level.

RECIPROCAL LEVELING

RECIPROCAL LEVELING

Reciprocal leveling is employed to determine the difference in elevation between two points when it is difficult or impossible to keep backsights and foresights short and equal

In this method, two sets of rod readings are observed, (1) one set is taken with the instrument set up close to one point, and (2) another with the instrument set up close to the other point.

Considering the Figure 1 below, the equations to obtain the difference in elevation are the following

DE_A = (a – b) and DE_B = (a’ – b’)

TDE = (DE_A + DE_B)/2 = [(a - b) + (a’ – b’)]/2

Elev. BM2 = Elev. BM1 ± TDE

where:

   DE_A = the mean difference in elevation between A and B with level at left

   DE_B = the mean difference in elevation between A and B with level at right

   TDE = the true mean difference in elevation between A and B

 

Procedure:

1. Set two hubs either on the 2^nd or 3^rd floors of the Velasco and La Salle Buildings and call these the BM1 and BM2, respectively. The elevation of BM2 is to be determined while the elevation of BM1 is known or assumed to be 10.000 meters above see level. Also, imagine that the football field between the Velasco and La Salle Buildings is an intervening deep ravine or wide river.
2. Set up and level very carefully the instrument at point A at Velasco Building (3^rd floor) near BM1.
3. Take and record a series of three consecutive backsight rod readings on BM1 and six consecutive foresight rod readings on BM2.
4. Move the instrument to point B at La Salle Building (3^rd floor) which is on the opposite side of the imaginary ravine and near BM2, set up, and level the instrument carefully.
5. From the new set up, take and record three consecutive foresight rod readings on BM2 and six consecutive backsight rod readings on BM1.
6. Tabulate observed and computed values accordingly. Refer to the accompanying sample format for the tabulation of field data.

Instrument Set Up Near BM1			Instrument Set Up Near BM2
Station	B.S.	F.S.	Station	F.S.	B.S.
BM1 (a)			BM2 (b’)
BM2 (b)			BM1 (a’)
Sum			Sum
Mean			Mean

How To Avoid Sexual Temptation

How To Avoid Sexual Temptation: Guard Yourself

What’s Keeping me From Finding My Dream Job?

What’s Keeping me From Finding My Dream Job?: Thinking through God’s Calling and Your Opportunity