Survey Method 04- Methods of leveling

       Three pisicale method are used for determined deference in elevations. Normally barometric leveling, trinometric leveling, and sprit leveling.

1.Barometric leveling

Barometric leveling mark use of the pinerminon that deference in elevation between  2 points is proportional to the difference in atmostiric pressures at the point. A barrow meter there for heavy used and the readings observed at difference points world yield a measure of the relative elevations of those points at a given points. The atmospiaric pressures duos not reaming constant in the course of the even in the course of in hours of the even in the course of hours. There for relatively inaccurate an is little used in surveying work except on reconnaissance for expio rotator surveys.

2.Trigonometric leveling (indirect leveling)

This I s the cross of leveling In which the elevations of points are computed from the vertical angles and horizontal distance measure in the field just as the length of any side in any triangle can be computed from proper trigonometric relations in the  modified from called stadia leveling. Commonly using in mapping broth of the difference of elevations and the horizontal distance between the points are directly computed from the measure vertical angle and staff readings.

3.Sprit leveling(direct leveling )

It is that branch of leveling in witch the vertical distances witch respect to a horizontal line(perpendicular to the directions of gravity). May be used to determined the relative deference in elevations 2 between adjacent points. a horizontal plane of site tangent to level surface at  any point is reading establish by means of a sprit level and a sighting devise(telescope) are combined and vertical distance are measure by observing on graduated rods rise on the point. The method is also known as direly leveling. It is the most precise method of ditumiding elevations and the one most commonly used by engineers.

Calculations.

Methords of baking observations

1.rise staumented

eel. Of point A  = 100.00m RL

rile turn A>B     = 0.87m

eel of point B    = 100.00+0.87

                            = 100.87 m

2. Height of instrument method (line of collimation)

Elevations of point A                = 100.00m RL

Elevations of collimation line = 100.00+2.65(BS)

                                                    = 102.65m RL

Elevation of point B                  =  elevation of line (FS) 1.78 collimation

                                                    = 102.65-1.78                           

                                                    = 100.87m RL                            

BS	IS	FS	Fall	Rise	RL	Distance	Remark
2.65					100.00		Point A
0.52	1.78			0.87	100.87		Point B

Read More

Survey Method 03-Leveling

Leveling is a branch of surveying. The object of which:
I. To find the elevations of give points with respect to a given or assumed datum
II. To establish to point at a given elevations or at difference elevations  with respect to a given or assume datum

The first operation is required to enable the works to be destined wild the second operation is required in the setting out of all kinds of engineering works. Leveling deals with measurement in vertical plumes.

Level surface 

A leveling surface is define as a curved surface which at each point is perpendicular to a directions of gravity at the point the surface of a steel water is a truly level surface. any surface pararal to the mean spheroidal of the earth is there for a level surface.

Level line 

A level line is a line laying in a leveling surface. it is there for normal to the plumb line at all points.
Horizontal plane - Horizontal plane true a point is a plane tangential to the level surface at that point. It is there for perpendicular to the plumb line through the point.
Horizontal line
It is strength line tangential to the level line at a point. It is also perpendicular to the plumb line through the point

Vertical line 

It is a line normal to the level line at the point it is commonly considered to be the line deference by plumb line.

Datum 

Datum is any surface to witch elevations are reflect the mean sea level affords a convention datum world over, and elevations are commonly given as so much oblive or billow sea level. It is often more convenient, however to assume some other datum specially if only the relative elevations of points are required.

Elevations

The elevations of a point on or near the surface on a earth is it’s vertical distance above or below and arbitrarily assume level surface or datum. The deference in elevations between 2 points is a vertical distance between the 2 level surface in which the 2 points lie.

Vertical angle 

Is an angle between to intersection lines in a vertical plane. Generally on of this line is horizontal. Mean sea level M.S.L.  is a coverage height of the sea for all stagers on the tides. At any perpendicular place it is derived by averaging the hourly time height over a long period of 19 years

Bench mark 

Bench mark is a relative permanent point of reference hours elevations with respect to some assume datum is known. It is used ether as a starting points for leveling for as a point upon which to close as check.

Read More

SURVEY INSTRUMENTS 04-Staffs

A level staff, also called leveling rod, is a graduated wooden or aluminum rod, the use of which permits the determination of differences in elevation. Leveling staff may be divided into two groups. It is Self reading staff and Target staff.

Reading a rod

        In the photograph on the up , both a metric (left) and imperial (right) leveling rod are seen. This is a two-sided aluminum rod, coated white with markings in contrasting colors. The imperial side has a bright yellow background. Commonly used are metric rods.
         The metric rod has major numbered graduations in meters and tenths of meters (e.g. 18 is 1.8 m - there is a tiny decimal point between the numbers). Between the major marks are either a pattern of squares and spaces in different colors or an E shape (or its mirror image) with horizontal components and spaces between of equal size. In both parts of the pattern, the squares, lines or spaces are precisely one centimeter high. When viewed through an instrument's telescope, the observer can easily visually interpolate a 1 cm mark to a quarter of its height, yielding a reading with accuracy of 2.5 mm. On this side of the rod, the colors of the markings alternate between red and black with each meter of length.
        The imperial graduations are in feet (large red numbers), tenths of a foot (small black numbers) and hundredths of a foot (unnumbered marks or spaces between the marks). The tenths of a foot point is indicated by the top of the long mark with the upward sloped end. The point halfway between tenths of a foot marks is indicated by the bottom of a medium length black mark with a downward sloped end. Each mark or space is approximately 3mm, yielding roughly the same accuracy as the metric rod.

Read More

SURVEY METHODS 02

To drop a perpendicular to a chain line from a point out faid  it

1st  method

Select any point E on the line with C as center and CE as various show and arg to out the chain line if F by sect CD will be perpendicular to AB

2nd method

Select any point D on the chain line. Join DC and by select it at E . with E as center and DE  or EC as readies draw and arg to cut the chain line in F. FC will be perpendicular.

3rd method

Select any point E on the chain line witch a center and as radius draw and arg to cut the chain line in F measure FD and FE obtain the point C by macking FC=〖FD〗^2/2FE joint C and D. CD will be perpendicular the chain line.

Read More

SURVEY METHODS 01

To erect a perpendicular to a chain line from a point on it 

The method of establishing perpendiculars with the tape is base on familiar geometric construction. The flowing is same of the methods most commonly used.

3.4.5. method

Establish at point A at a distance of 3m from C. put zero end end of the tape (10m long) at A end the 10m end at C. the 5m and 6m mark brought together to from a loop of 1m. the tape is now stretched tight by fastening  the end A and C. the point A is thus establish the angle BCA will be 900    one person can be set out angle by this method.

2nd method

Select E and F Equidistant from C hold the zero end on the tape at E and 10 meter            end at F. pickup 5m mark, stretch the tight and establish D. joint DC .

3rd method

Select any point F outside the chain line preferably at 5m distance from C. hold 5m mark at F 20m mark at C Witch as center draw and arg to cut the line at E. join EF and produce in to D such that EF = FD = 5m. next dust point D will lie at the 10m mark of the tape head along EF with end zero at E join DC. 

Read More

SURVEY INSTRUMENTS 03- RANGINNG POLES, ARROWS AND WOODEN PEGS

Ranging poles

Ranging poles are used to mark areas and to set out straight lines on the field. They are also used to mark points which must be seen from a distance, in which case a flag may be attached to improve the visibility. Ranging poles are straight round stalks, 3 to 4 cm thick and about 2 m long. They are made of wood or metal. Ranging poles can also be home made from strong straight bamboo or tree branches. Ranging poles are usually painted with alternate red-white or black-white bands. If possible, wooden ranging poles are reinforced at the bottom end by metal points.

Arrows 

Accompanying each chain are 10 arrows. They are also called marking or chaining pins, and are used to mark the end of each chain during the process of chaining. They are made of good quality metallic wires of 4 mm (8 s. w. g.) in diameter and of a minimum tensile strength of 700N/ mm2. The wire is black enameled. The arrows are made 400 mm in length, are pointed at one end for inserting into the ground and bent into a ring at the other end for facility of carrying. They should have a piece of white or red tape tied to the ring so that they can be made easily visible at a distance. To mark the end of each chain length, the arrow is inserted in the ground, but when the ground is hard, a scratch may be made with the pointed end.

Wooden Pegs 

Wooden pegs are used to mark the positions of stations. They are made of hard timber and are tapered at one end they are usually, 2.5 cm square and 15 cm long, but in soft ground, pegs 40 to 60 cm long and 4 to 5 cm square suitable.

Read More

survey instruments 02-Dumpy level and Tripod

Dumpy level and Tripod

Invention
In 1832, English civil engineer William Gravatt, who had worked with Marc Isambard Brunel and his son Isambard on the Thames Tunnel, was commissioned by Mr. H.R. Palmer to examine a scheme for the South Eastern Railway's route from London to Dover. Forced to use the then conventional Y level, during the works Gravatt devised the more transportable and easier to use dumpy level.  

What is dumpy level
 A dumpy level is used to establish or check points in the same horizontal plane. It is used in surveying and building to transfer, measure, or set horizontal levels. But Dummy level is the most commonly used level.  The dummy level is simple compact and stable. It is cheaper, and easier to maintain in adjustment.
      The term dumpy level endures despite the evolution in design. A dumpy level is an older-style instrument that requires skilled use to set accurately. The instrument requires to be set level (see spirit level) in each quadrant, to ensure it is accurate through a full 360° traverse. Some dumpy levels will have a bubble level ensuring an accurate level.

A variation on the dumpy and one that was often used by surveyors, where greater accuracy and error checking was required, is a tilting level. This instrument allows the telescope to be effectively flipped through 180°, without rotating the head. The telescope is hinged to one side of the instrument's axis; flipping it involves lifting to the other side of the central axis (thereby inverting the telescope). This action effectively cancels out any errors introduced by poor setup procedure or errors in the instrument's adjustment. As an example, the identical effect can be had with a standard builder's level by rotating it through 180° and comparing the difference between spirit level bubble positions.

Setting the Level
The level instrument is set up on a tripod and, depending on the type, either roughly or accurately set to a leveled condition using foot screws (leveling screws). The operator looks through the eyepiece of the telescope while an assistant holds a tape measure or graduated staff vertical at the point under measurement. The instrument and staff are used to gather and/or transfer elevations (levels) during site surveys or building construction. Measurement generally starts from a benchmark with known height determined by a previous survey, or an arbitrary point with an assumed height.

Parts of dumpy level

1. Telescope
2. Eye-piece
3. Ray shade
4. Objective end
5. Longitudinal bubble
6. Transverse bulb tube
7. Bubble tube adjusting screws
8. diaphragm adjusting screws
9. diaphragm adjusting screws
10. foot screws
11. upper parallel plate
12. foot plate

Dumpy Levels can be used for
• Determining the height of a particular point.
• Determining differences in height between points.
• Drawing contours on a land.
• Providing data to calculate volumes for earthworks.
• Setting out level surfaces for construction.
• Setting out inclined surfaces for construction.

Measuring height using Dumpy Level 

• The place of which height is to be measured is called Station.
• Height is always measured with reference to sea level.
• Survey of srilanka established benchmarks (B.M) at several places.
• Ideally the distances should be taken from the benchmark.
• If it is not available then we can select point on the map whose distance from sea level is known as the reference.
• We can fix any suitable point as Temporary bench mark and all heights can be measured from that point. We can fix any temporary bench mark , but if its MSL( at temporary BM) is not sure , then before starting the surveying permanent BM reading should be clear.
                 HI= BM+BS BACKSIGHT(BS)
      In the picture Bench mark is setup at a height of 100 ft.As a first step we need to know the height of the place from where instrument is placed. In the picture, a boy is standing on a place from where survey will begin.To know the height of the instrument place a staff or level rod at bench mark location. And from the instrument take the reading on the staff. In this case reading on the staff is 5.5ft . This reading is called as backsight reading (BS).
                Height of the instrument = BM + BS = 100 + 5.5 = 105.5 ft.
Now surveyor can go ahead and determine heights of other places. Look at the following figure to take further reading. These readings are called as foresight reading (FS):
                HI+FS=ELEVATION FORESIGHT(FS)
Now staff or level rods are put on the point (D) height of which is to be measured. The reading on the staff is recorded through telescope of dumpy level. In present case the reading shows 2.3ft.This reading is called Forward site ( FS) Therefore height of point D is calculated as follows Height of point D = Height of Instrument (HI) – FS = 105.5 – 2.3 = 103.2 ft. Distance between the instrument and the station D can be measured using meter tape or from the difference between upper & lower readings on the telescope.

Read More

Traditional survey - chain survey -02

  Chain Survey

Chain survey is the simplest method of surveying. In this survey only measurements are taken in the field, and the rest work, such as plotting calculation etc. are done in the office. This is most suitable adapted to small plane areas with very few details. If carefully done, it gives quite accurate results. The necessary requirements for field work are chain, tape, ranging rod, arrows and some time cross staff.



Principles of Chain Survey
A triangle is a simple figure which can be plotted from the lengths of three sides even if the angles are not known. In chain survey, the area to be surveyed is divided into a framework consisting of triangles.
Selection of survey station and Survey lines
I. The main station should be mutually invisible so that ranging can be done easily.
II. Survey lines should be as few as possible so that framework of triangles can be plotted easily.
III. Survey lines should pass through a level open ground as far as possible so that chaining can be done easily.
IV. The frame should have at least one long baseline that runs through the middle of the area.
V. The main survey lines should form well conditioned triangles with no angles less than 30 degrees or more than 120 degrees.
VI. The survey lines should be selected such that there are no obstacles in chaining and ranging.
VII. The survey lines will be close to the details to avoid long offsets.
VIII. If required, number of subsidiary stations should be selected and subsidiary lines run to avoid long offsets.
IX. Each triangle should have a check line to detect mistakes in measurements and plotting.
X. While selecting main stations and survey lines, the basic principles of surveying of working from whole to the part should be followed.

Main Stations
Main stations are the end of the lines, which command the boundaries of the survey, and the lines joining the main stations re called the main survey line or the chain lines.

Subsidiary or the tie stations
Subsidiary or the tie stations are the point selected on the main survey lines, where it is necessary to locate the interior detail such as fences, hedges, building etc.

Tie or subsidiary lines
A tie line joints two fixed points on the main survey lines. It helps to checking the accuracy of surveying and to locate the interior details. The position of each tie line should be close to some features, such as paths, building etc.



Base Lines
It is main and longest line, which passes approximately through the centre of the field. All the other measurements to show the details of the work are taken with respect of this line.

Check Line
A check line also termed as a proof line is a line joining the apex of a triangle to some fixed points on any two sides of a triangle. A check line is measured to check the accuracy of the framework. The length of a check line, as measured on the ground should agree with its length on the plan.

Offsets
These are the lateral measurements from the base line to fix the positions of the different objects of the work with respect to base line. These are generally set at right angle offsets. It can also be drawn with the help of a tape. There are two kinds of offsets:
• The measurements are taken at right angle to the survey line called perpendicular or right angled offsets.
• The measurements which are not made at right angles to the survey line are called oblique offsets or tie line offsets.

Read More

survey instruments 01-Tapes

Tapes

Tapes are used in surveying to measure horizontal, vertical, and slope distances. They may be made of a ribbon or a band of steel, an alloy of steel, cloth reinforced with metal or synthetic materials. Tapes are issued in various lengths and widths and graduated in a variety of ways.
I. Cloth or Linen Tape
II. Metric Woven Metallic Tape
III. Metric Steel Tape
IV. Invar Tape
V. Synthetic Tape


I. Cloth or Linen Tape
It is made of varnished strip of woven linen 12 to 16 mm wide with a brass handle at zero ends, whose length is also included in the length of the tape. The tape is attached to a spindle and is wound in a leather case. It is very light and handy, but not so accurate. For very precise measurements, it is not used. The linen tape may be used for taking subsidiary measurements such as offsets. It is easily affected by damp. When the tape gets wet, it shrinks and care should be taken that it is not wound up until is cleaned and dried. It stretches easily and is likely to twist and tangle. It is therefore little used in surveying.

II. Metric Woven Metallic Tape
They are available in 2, 10, 30, and 50 meters. The tape is made of yarn and metal wire. A metal ring is attached to the outer end of tapes. The length of the tape includes the metal ring. At every centimeter a black line 8 to 10 mm in height is drown. Every 5 centimeters is marked with an arrow in black. Every decimeter and meter is marked with a back line extending over the full width of the tape the graduation marks at every decimeter and meter are numbered with black and red figures, respectively.

III. Metric Steel Tape
Tape is available in 1, 2, 10, 30, and 50 meters. The tape is of steel or stainless steel. The outer end is provided with a ring. The length of the tape includes the metal ring. The tape is marked with a line at every five millimeters, centimeters, decimeters, and meter. Every decimeter and meter shall be marked with Hindu Arabic numerals in bold. When the button release devised is pressed, the tape automatically rewind in to the case.

IV. Invar Tape
For highest precision work the invar tape in used. Invar tapes are made of an alloy of nickel (36%) and steel (64%) having very low co-efficient of thermal expansion (0.000000122 per 1 C) These are 6mm wide and are available in length of 30m, 50m and 100m, Invar taps are used mainly for high degree of prevision required for base measurements.

V. Synthetic Tape
The tapes are manufactured of glass glass fiber having PVC coating. They are graduated every 10 mm and figured every 100 mm. Meter, figures are shown in red. They are convenient for measuring shorts lengths.

Read More

Traditional survey - chain survey-01

Chain

The chain is a instrument and unit, using for surveying and measure distances. The chains used in surveying are generally of the following types.

I. Gunter’s chain

II. Engineer’s chain

III. Metric chain

IV. Steel Band Chain

V. Revenue Chain

         

I. Gunter’s chain

surveyor’s chain, also called Gunter’s chain, measuring device and arbitrary measurement unit still widely used for surveying in English-speaking countries. Invented by the English mathematician Edmund Gunter in the early 17th century, Gunter’s chain is exactly 22 yards (about 20 m) long and divided into 100 links. In the device, each link is a solid bar. Measurement of the public land systems of the United States and Canada is based on Gunter’s chain. An area of 10 square chains is equal to one acre.

II. Engineer’s chain

This steel engineers’ chain would have been used by a surveyor measuring out lands and plot sizes.  It is different from a surveyor’s chain as it is larger in length however it would have been used for the same purpose, measuring out horizontal distances.  The chain measures 100 ft and contains 100 links, each measuring 12 inches.  The links each consist of a thin round steel rod joined with an oval ring on each end.  Tags mark the chain at every ten links.  It was made by W. & L.E. Gurley of Troy, New York.  Brothers William Gurley and Lewis formed the company in 1852; they were both graduates of Rensselaer Polytechnic Institute in New York.

III. Metric chain

A metric chain is generally divided into 100 or 150 links. The links are composed of pieces of galvanized mild steel wire 4mm in diameter. The ends of each link are bent into loops and connected together by means of three oval shaped rings which afford the flexibility to the chain. The joints of the links are usually pen but in good quality chains, these are welded so that true length of the chain does not alter due to stretching. The ends of the chain are provided with brass handles with swivel joints so that the chain can be turned round without twisting. The outside of the handle is the zero point or the end point of the chain. The length of a chain is measured from the outside of one handle to the outside of the other. The length of a link is the distance between the centers of the two consecutive middle rings. The end links also include the length of the handle. Metallic tags of different patterns are fixed at various important points of c chain.

IV. Steel Band Chain

It consists of a ribbon of steel with bras handle at each end. It is 20 or 30 long and 16 mm wide. It is wound on an open steel cross or on the metal reel in a closed case. The graduations are etched as meters decimeters, centimeters on one side and 0.2 m links on the other. Brass tallies are fixed at every 5 m length of the band.

V. Revenue Chain

It is commonly used for measuring fields in cadastral survey. It is 33 ft long and divided into 16 links. Each link is 2.0625 ft long.

Read More