Surveying - Module I - Introduction to surveying

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  • OPTC Edavanna Page 1

    MODULE I: INTRODUCTION TO SURVEYING

    1. Define surveying?

    Art/Science of determining the relative positions of points on, above or below earths

    surface by means of direct or indirect measurement of distances, elevations or

    directions.

    2. What are the primary objects of surveying?

    a) Preparation of plans / maps

    b) To find horizontal distances b/w points

    c) To find elevation (height) b/w points

    d) To find relative and absolute directions

    3. What are the primary divisions of surveying?

    a) Plane survey

    Curvature of earth is not considered

    For small areas

    b) Geodetic survey

    Curvature of earth is considered

    For large areas

    4. Write down the cardinal principles of surveying?

    a) Working from whole to part

    Area to be surveyed is divided into large triangle and further divided into

    small triangles (Triangulation)

    A system of control points is identified and located with high precision

    To prevent accumulation of errors

    To control and localize minor errors

    b) Locating a point with reference to two fixed points

    chain survey

    Traversing

    offset method

    compass method

    5. List classification of surveying based on instrument used?

    a) Chain surveying

    b) Compass surveying

    c) Theodolite surveying

    d) Plane table surveying

    e) Tachometric surveying

    Orphanage Polytechnic College, Edavanna REVISION PACKAGE

    Surveying - I ( Revision 2015)

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    6. Name instruments required for chain survey?

    a) Chain or tape

    b) Arrows

    c) Ranging rods

    d) Cross staff

    e) Offset rods

    f) Pegs

    g) Plumb bob

    7. What is reconnaissance? What is its importance in chain surveying?

    Before starting the actual survey, surveyor walks around the area to prepare a

    reference sketch of the ground to fix best positions of survey lines and stations.

    Objectives:

    To check the possibility of a building / constructing road through that area

    To choose best route and mark on maps

    To prepare estimate and draft report

    This gives the surveyor an overall idea of the land and the important features.

    8. What is mean by ranging? What is direct and indirect ranging? or Write the

    basic methods of ranging out survey lines?

    The process of establishing intermediate points on a straight line between the end

    stations is called ranging. Intermediate ranging rods are placed to maintain correct

    direction. There are two methods of ranging on slopping grounds.

    a) Direct ranging

    b) Indirect ranging

    Direct Ranging:

    When the starting, ending points and intermediate stations are intervisible along a

    straight line. It can be done by eye, line ranger or theodolite.

    Line Ranger: The line Ranger is a small reflecting instrument used for fixing

    intermediate points on the chain lines. Without going to either end, we can fix the

    intermediate points.

    (i) To range a point P, two ranging rods are fixed at ends A and B

    (ii) Surveyor hold the line ranger near AB

    (iii) The reflected rays forms imag, but may not be in same vertical line.

    (iv) Surveyor moves the line ranger sideways till both images are in same

    vertical line as in figure.

    (v) Point P is transferred to ground with help of plumb bob

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    Indirect Ranging:

    If the end stations are not intervisible due to hill/other land features.

    Also known as reciprocal ranging

    9. What is mean by reciprocal ranging? Write the condition under which the

    reciprocal ranging is resorted to. Explain the procedure for indirect ranging?

    It is the method of fixing intermediate station points b/w two terminal points, when

    they are not intervisible. This method is adopted under following situations or

    conditions.

    A raising ground b/w the two end points

    A hill (Steeply raising ground) b/w the end points

    A deep valley b/w the end points

    Procedure:

    1. The ranging rods are drawn vertically at A and B

    2. The person carrying ranging rods C and D should be sent to the positions

    that they are to be visible from A and B.

    3. The initial positions of C and D are marked on the ground as C1 and D1

    4. The surveyor at A will now direct the man at C1 to put his rod at C2 in line with

    A and D1

    5. The surveyor at B will next direct the man at D1 to put his rod at D2 in line with

    B and D2

    6. This process is repeated several times till the points C and D are found out in

    the line AB

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    10. Briefly explain the direct and indirect method of measuring distances, if the

    ground is slopping?

    There are two methods of chaining on sloping grounds,

    Direct method

    Indirect method

    Direct method (Method of stepping or stepping method):

    The horizontal distance between A and B is measured in small horizontal steps

    Total horizontal distance = l1 + l2 + l3 + l4

    The follower holds the zero end of the tape at A while the leader selects any

    suitable length of tape and moves forward.

    In case of irregular slopes, this is the only suitable method

    Indirect method: Three types

    a) By using clinometer

    b) By applying hypotenusal allowance

    Correction is applied in the field at every chain length and at every point

    where the slope changes

    BC Hypotenusal allowance

    c) By knowing the difference of level between the points

    D =

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    11. What is well conditional triangle and ill conditional triangles?

    well conditional triangle ill conditional triangle

    Error is minimized due to equal

    distribution

    Error gets accumulated in one

    angle or one length only

    All angles are nearly equal to 600 Angles are 120

    0

    12. Explain reference sketch, Index sketch?

    Index sketch Reference sketch

    It is a rough sketch of the

    entire area to be surveyed

    It is a rough sketch showing

    location/reference of a

    survey station

    All lines, stations,

    topographical features are

    shown approximately

    minimum two distances are

    shown w.r.t. permanent

    object like building

    Useful for proper selection of

    stations

    Used for locating a station

    correctly

    13. Explain the principle on which chain survey is based? Mention the different

    methods generally adopted to find the areas from previously plotted plan?

    Basic principle used in chain survey is triangulation. The plotted framework is

    divided into number of connected triangles.

    14. Explain the terms: Main line, Base line, Check line, Tie line?

    Main Line: Lines joining main stations Base line : Biggest line that divides the total area almost into two parts

    Check line: Lines drawn to check accuracy of survey

    Tie line : Lines drawn to collect more details of object 15. Describe different types of chain used for linear measurements?

    Following are the various types of chain in common use

    1) Metric chains

    2) Gunter` s chain or surveyors chain

    3) Engineers chain

    4) Revenue chain

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    Metric chain:

    Metric chains are made in lengths 20 m and 30 m.

    Tallies are fixed at every 5 m length

    Brass rings are provided at every one meter length except where tallies are

    attached.

    20 m chain has 100 links and 30 m chain has 150 links.

    Length of one link is 20 cm.

    Gunters or Surveyors Chain

    It is 66 feet long

    It is divided into 100 links

    Each link is 0.66 feet long

    Engineers Chain

    It is 100 feet long

    It is divided into 100 links

    Each link is 1 feet long

    Revenue Chain

    It is 33 feet long

    It is divided into 16 links

    Each link is 2.06 feet long

    16. Mention the three different operations in chain surveying?

    (i) Ranging: The process of locating intermediate points on a straight line between two end points in a straight line

    (ii) Chaining: The process of measuring the distance with a chain or tape. (iii) Offsetting: The process of measuring the lateral distance of the object from the

    survey line to the left or right according to their positions.

    17. Explain the process of setting plane table over a station?

    It involves

    (i) Fixing: Fixing the table on the tripod

    (ii) Setting : (a) Levelling the table (b) Centering (c) Orientation

    (iii) Sighting the points

    18. How levelling is done in plane table survey?

    For small work, levelling is done by estimation. For accurate works, spirit level is used

    19. What is meant by centering?

    The process of making the point correctly on paper by placing the table exactly over

    the ground station point is called centering.

    20. What is orientation?What are the different methods of orientation of plane table?

    Orientation is the process of putting the plane table into some fixed direction so that

    the line representing a certain direction on the plan is parallel to the direction on the

    ground.

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    The methods of orientation are

    (i) Orientation by means of trough compass

    (ii) Orientation by means of back sighting

    21. Describe the method of orienting the plane table by magnetic needle (trough

    compass). What are the limitations of this method?

    In this method, the magnetic north is drawn on paper at a particular station.

    At the next station, the trough compass is placed along the line of magnetic

    north and then the table is turned in such a way that the ends of magnetic needle

    are opposite to the zeros of the scale.

    The board is then fixed in position by clamps.

    This method is inaccurate in the sense that the results are likely to be affected

    by the local attraction.

    22. Describe the method of orientation of plane table by back sighting?

    In this method, the orientation is carried out by the back sighting of a particular

    line. Suppose a line is drawn from station A on paper representing line AB on

    ground. The table is centered and leveled at station B and then the alidade is

    placed along the line ba. The table is turned till the line of sight bisects the

    ranging rod at A. The board is then clamped in this position. This method is

    better than the previous one and it gives perfect orientation. 23. Difference between plane surveying and geodetic surveying?

    Plane Survey Geodetic survey

    Curvature of earth is not

    considered

    Curvature of earth is

    considered

    For small areas For large areas

    24. List the various methods of plane table surveying? Under what field conditions

    each method is used?

    a) Radiation method

    b) Intersection method

    c) Traverse method

    d) Resection method

    25. Explain resection method of plane tabling?

    Resection is the process of determining the plotted position of the station occupied by

    the plane table, by means of sights taken towards known points, locations of which

    have been plotted. Depending on how the table is orienting, resection is of four types

    1. Resection after orientation by compass

    2. Resection after orientation by back sighting

    3. Resection after orientation by back sighting

    4. Resection after orientation by two point problem.

    26. What are survey stations in chain surveying? What are the points to be

    considered in selection of survey stations and survey lines?

    Survey stations are the beginning point or end points of a chain line. The points to be

    considered are

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    1. Survey stations must be mutually visible

    2. Survey lines must be as few as possible

    3. The frame work must have one or two baselines.

    4. The lines must run through levelled ground as possible

    5. The main lines should form well-conditioned triangles

    6. The main survey lines should not pass through obstacles as far as possible

    27. Draw a typical page of a chain survey field book? Explain?

    The book in which chain or tape measurements are entered is called a field book. It is

    an oblong book of size 20 cm X 12 cm and opens length wise. Chain line is

    represented by single or double lines and land features are marked in either direction.

    Good quality paper

    well bounded and pocket size

    Date, Name of surveyor, details of survey lines, page index, location sketches

    should be added

    28. Describe the advantages and disadvantages of plane table survey?

    Advantages:

    It is simple and cheaper

    No great skill required

    It is rapid

    It is suitable for small scale maps

    less possibility of mistakes

    easy to compare plotted figure with field features

    Disadvantages:

    Less accurate

    Difficult to transport from one location to another

    Not suitable for rainy season or wet climate

    It is essentially a tropical instrument

    There are several accessories to carried and chances of missing is high

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    29. List the types of obstacles in chaining

    Obstacles prevent us from direct measurement b/w two points

    They are of three kinds

    (i) Obstacle in ranging

    (ii) Obstacles in chaining

    (iii) Obstacles to both chaining and ranging

    Obstacle in Ranging: Obstacles which obstruct ranging but not chaining

    (Chaining free-vision obstructed). When the ends are not intervisible due to hill or

    other land features, ranging is not possible directly.

    Obstacle in chaining: When the end points are inter-visible but chaining is

    obstructed due to river, pond, other land features. i.e, Obstacles which obstruct

    chaining but not ranging (Vision free chaining obstructed).

    Obstacle in both chaining and ranging: When the end points are not intervisible

    and chaining is not possible. Obstacles which obstruct both chaining and ranging

    30. Describe briefly the various accessories of plane table.

    Plane table with tripod:

    The drawing board made of well-seasoned wood such as teak or pine which is used for

    the purpose of plotting is called plane table. The top surface of board is perfectly plane and to bottom is fitted with a levelling head or ball and socket arrangement.

    Spirit level:

    A small sprit level circular or rectangular is required for seeing if the table is properly

    level or not. The level must have flat base so that it can be placed on the table.

    Trough compass:

    The compass which is used to mark the direction of the magnetic meridian on the

    plane table is called trough compass.

    U-frame with plumb bob:

    A plumbing fork or U-Frame with a plumb bob is used for centering the point and to

    transfer that point on ground to sheet.

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    Alidade:

    A plane table alidade is a straight edge with some form of sighting device. They are of two types, Plain alidade and telescopic alidade. The bevelled graduated edge in an alidade is known as the fiducial edge. It consists of sighting vane and object vane.

    31. Explain with neat sketch intersection method of plane table survey?

    Intersection method is used when the distance b/w the point and instrument station are

    too large.

    Principle: The location of an object is determined by sighting at the object from two

    plane table stations (previously plotted) and drawing the rays. The intersection of these

    rays gives the position of that object.

    * Draw step by step figures given in notebook

    Procedure

    1. Set, level and transfer A to sheet, mark north direction.

    2. Pivoting the alidade about A, sight to B. Measure AB and plot ab

    along B

    3. Sight to all boundary points and draw rays

    4. Shift the instrument to B

    5. Orient the compass by back sighting to A

    6. Draw rays towards all boundary points

    7. The intersection of two rays gives the position of the object.

    32. Prepare a survey plan and determine the area of the field from the following

    observations?

    E

    625 D 65 520

    500 45 F C 73 420

    310 61 G

    B 58 160 0

    A

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    Ans:

    33. What are offsets? Classify them.

    An offset is the lateral distance of an object or ground feature measured from a survey

    line. There are two types of offsets.

    (i) Perpendicular offset: The angle of offset from a point on a chain line is 900

    (ii) Oblique offset : When the angle of offset is other than 900 .

    34. What is a cross staff ? What are different types of offset?

    It is a kind of instrument used for setting out right angles from a point on the chain and

    finding the foot of perpendicular from a given point to the chain line. Three types,

    (a) Open cross staff

    (b) French cross staff

    (c) Adjustable cross staff

    35. What is the basic principleof plane table survey?

    Lines drawn during plotting always lies parallel to the corresponding lines actually

    present on the ground.

    36. Explain with neat sketch the radiation method in plane tabling?

    37. Explain the procedure for solving two point problems in plane table surveying?

    SL

    NO Fig Chainage

    (m) Base

    (m) Offset

    (m) Mean

    (m) Area

    (m2)

    1

    0,160 160 0,58 29 4640

    2

    3

    4

    5

    6

    7