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UNIT- II
SURVEYING AND CIVIL ENGINEERING MATERIALS
Surveying Surveying is the art of determining the relative position of points on above or beneath the surface of the earth by means of direct or indirect measurements of distances, direction and elevation. Objective of surveying The main objective of surveying is to create a plan or map. When survey results are drawn on paper, they form a plan, which represents the land and its features on a horizontal plane at a specific scale. Large-scale representation → called a plan (e.g., a building plan). Small-scale representation → called a map (e.g., a map of India). Location and Mapping: To determine the relative positions of natural and man-made features on or below the Earth's surface. This helps in creating accurate maps and plans. Construction Layouts: To provide precise measurements for the layout and construction of structures such as buildings, roads, bridges, and dams. Surveyors ensure that these structures are built in the correct location according to the design plans. Boundary Determination: To establish property boundaries and ensure legal and accurate property ownership. This is crucial for resolving disputes and defining land ownership. Topographic Surveys: To create detailed topographic maps that depict the contours and features of the land. These maps are essential for planning and design purposes, helping engineers understand the terrain and plan accordingly. Volume and Quantity Calculations: To calculate the volumes of earthwork, materials, and other quantities required for construction projects. This helps in budgeting and resource management. Monitoring and Maintenance: To monitor the condition and stability of existing structures and infrastructure. Regular surveys can detect any movements or deformations, allowing for timely maintenance and repairs. Infrastructure Development: To support the planning and development of infrastructure projects such as roads, railways, pipelines, and utilities. Accurate surveying ensures that these projects are efficiently and safely executed. Environmental Impact Assessment: To assess the environmental impact of construction projects by mapping and analyzing natural features and habitats. This information is used to minimize environmental disruption and comply with regulations Classification of surveying Surveying can be classified in several different ways based on various criteria. Here is an overview of the common classifications:
SYLLABUS
Surveying: Objects – classification – principles – measurements of distances – angles – leveling – determination of areas– contours – examples. Civil Engineering Materials: Bricks – stones – sand – cement – concrete – steel – timber – modern materials.
1. Based on the Nature of the Survey: Geodetic Surveying: This type of surveying takes the curvature of the Earth into account. It is used for large areas and involves precise measurements. The positions of points are considered in a global coordinate system. Plane Surveying: Here, the Earth is considered as a flat surface, assuming the curvature is negligible over small areas. This is suitable for small projects such as building layouts. 2. Based on the Purpose: Topographical Surveying: This type focuses on determining the positions of natural and man-made features on the land's surface. It helps in creating maps showing terrain and features. Cadastral Surveying: Also known as boundary surveying, it involves the demarcation of property boundaries for legal purposes. Engineering Surveying: Conducted to gather data for designing and executing engineering projects such as roads, bridges, dams, and buildings. Hydrographic Surveying: Focuses on surveying bodies of water, measuring depths, and mapping the underwater features. Astronomical Surveying: Involves determining the positions of points on Earth by making astronomical observations. 3. Based on the Instruments Used: Chain Surveying: Involves using chains or tapes to measure distances. Compass Surveying: Utilizes a compass to measure the directions of survey lines. Theodolite Surveying: Employs a theodolite to measure horizontal and vertical angles. Tachometric Surveying: Uses a tachometer for rapid measurements of distance, elevation, and direction. Electronic Distance Measurement (EDM): Involves using electronic instruments to measure distances accurately. 4. Based on the Method of Surveying: Triangulation: Involves dividing the survey area into a network of triangles. The sides of the triangles are measured or calculated. Traversing: Consists of a series of connected survey lines whose lengths and directions are measured. Levelling: Focuses on determining the elevation of points relative to a datum. It is often used to measure vertical distances. 5. Based on the Area of Survey: Land Surveying: Conducted on land to determine distances and positions of points. Marine Surveying: Takes place on or near water bodies to measure and map underwater features. Aerial Surveying: Uses aircraft or drones to capture aerial photographs or laser scans of the survey area. Principles of surveying The principles of surveying ensure accuracy and reliability in measurements and data collection for civil engineering and construction projects. The fundamental principles include: 1. Working from Whole to Part Begin with a broad control framework (whole) and then establish smaller, detailed surveys (part). Minimizes errors and ensures accuracy in the overall survey.
Arrow Ranging Rods: Ranging rods are used to mark the positions of survey stations and points. They are generally 2-3 meters long with alternate bands of black and white or red and white to make them visible at a distance. Ranging Rod Offset Rod Offset Rods These rods are also similar to ranging rods and they are 3 m long. They are made up of hard wood and are provided with iron shoe at one end. A hook or a notch is provided at other end. At height of eye, two narrow slits at right angles to each other are also provided for using it for setting right angles. Pegs Wooden pegs are used in measuring a length of a line to mark the end points of the line. The pegs are made of hard wood of 25 mm ×25 mm section, 150 mm long with one end tapered as shown in Fig. When driven in ground to mark station points they project about 40 mm.
Plumb Bob: A typical plumb bob is shown in Fig. In measuring horizontal distances along sloping ground plumb bobs are used to transfer the position to ground. They are also used to check the verticality of ranging poles. Principles and Procedures: Reconnaissance: An initial survey of the area is conducted to understand the terrain and determine the stations. This helps in planning the survey lines and avoiding obstacles. Selection of Survey Stations: Choosing suitable and visible points as survey stations is crucial. These stations are marked using ranging rods and pegs. Linear Measurement: Measuring the distance between two points using the chain. Chainmen handle the chain and ensure it is properly aligned and tensioned. Ranging: Ensuring that the chain line is straight and free from bends. Ranging rods are used to keep the chain aligned. The "ranger" stands at one end and guides the chainmen to align the chain correctly. Record: Recording the measured distances and any offsets in a field book. The surveyor notes down any irregularities, such as slopes or obstacles. Offsets: Measurements taken at right angles from the survey line to locate features such as buildings, trees, or boundaries. Offsets help in creating detailed maps and plans. Plotting: Transferring the measurements from the field book to a scale drawing. This involves plotting the distances and angles to create an accurate map of the surveyed area. Advantages of Chain Surveying: Simple and inexpensive method. Easy to conduct in open areas with clear lines of sight. Suitable for small and relatively flat areas.
2. Included Angle Method Fig. 22 shows the included angles θ 1 , θ 2 and θ 3 measured clockwise from the back line to a forward line. Instruments used for the measurement of angles are: Compass, Theodolite and Box Sextant. Compass surveying Compass Surveying: In a traverse surveying, when the direction of survey lines measured with compass and the length of survey lines measured with tape or chain, then it is said to be Compass Surveying. When the area to be surveyed is large, chain and compass surveying is preferable. A compass is used to measure the bearings of directions of survey lines. There are two types of compass available, namely, 1. Prismatic Compass and 2. Surveyor's Compass. 3. Bearing Prismatic Compass surveying is a significant part of surveying that is frequently used to locate an item using both angular and linear measurements. In this case, a compass is used to measure angles, while a chain or tape is used to measure lengths. Bearing: Bearing is the horizontal angle between the reference meridian and the survey line. The angular measurement is done indirectly from the difference between the bearings of directions of two survey lines. 1. PRISMATIC COMPASS Prismatic Compass consists of a Circular Metal Box. The box has a Pivot fixed at its center. The pivot carries a Magnetic Needle. A circular Graduated Aluminium Ring (non- magnetic) is attached to the needle. The needle can turn freely about its center. A Glass Lid is provided to view the graduations on the ring. Aluminium ring is graduated from 0° to 360° clockwise. An Eye Vane and an Object Vane are fixed diametrically opposite. The Eye Vane consists of an Eye Hole and a Triangular Reflecting Prism, which can be raised or lowered. The Line of Sight is defined by the object vane and the eye hole. A Pair of Sun Glasses are provided between the eye hole and object vane to sight luminous objects.
The prism has openings on the horizontal and vertical faces to read the angles on the ring through the eye hole. The prism has both horizontal and vertical faces convex, so that a magnified image of the ring graduation is formed. The Object Vane has Horse Hair to bisect the field objects. It is provided with an Adjustable Reflecting Mirror to bisect very nearer objects and objects in the sky. This enables bearing of very low or high objects to be taken. A Brake Pin at the base of the object vane damps the oscillations of the needle and brings it to rest before taking a reading. Lifting Lever lifts the aluminium ring with magnetic needle off its support and holds it firmly against the glass lid. In this way, undue wear of the supporting pivot point is prevented. Procedure to measure the Bearing of Station B from Station A Prismatic Compass is used as a portable instrument or fitted on a Tripod.
1. Centering: Compass is centered over the station A, where bearing has to be taken. A plumb bob is used to judge centering. 2. Levelling: Levelling is the process of making the graduated ring to swing freely without touching the glass lid. The compass is levelled by adjusting the ball and socket support till the top of the box is horizontal. 3. Focusing the Prism: The eye vane and the prism are raised or lowered, till the readings on the ring are seen sharp and clear. When an object is sighted, the eye vane will rotate with respect to the NS end of the ring through an angle which the line makes with the magnetic meridian.
- The compass must be adjusted for magnetic declination, if fail, it can lead to significant errors in the direction.
- The mechanical components of the prismatic compass (such as the needle and pivot) may wear down or become misaligned, affecting its accuracy. a) Prismatic Compass b) Surveyor’s Compass System of Graduation SURVEYOR'S COMPASS Surveyor's Compass was used in earlier days for land surveying. It is not in use now. It consists of a Graduated Ring attached to the Metal Box. The ring is not oriented in the magnetic meridian, as was the case in Prismatic Compass. The object vane is similar to that of prismatic compass. The ring is divided on to four quadrants. Each quadrant is marked with the graduation from 0° to 90°. 0° is marked with the letters N (North) and S (South). Similarly, 90° is marked with the letters E (East) and W (West). E and W are interchanged from their true positions. With this, it is possible to read only the reduced bearings. A Magnetic Needle is placed on the Pivot at the center of the metal box. One side of the needle is indicated with red mark showing the North. Graduations in this compass go from 0 to 90 degrees, with 0 representing north or south and 90 degrees representing east and west. The surveyors compass is used for measurement of quadrantal bearing. The least count of a surveyors compass is 15 minutes
(15ꞌ). An angle of 40 degrees to the north direction to the east is written as N 40 ° E and an angle of 60 degrees to east from the south is written as S 60 ° E. The reading is taken at the tip of the needle. It’s a tool for calculating horizontal angles. To determine the surveying line of sight’s bearing. It is simple to use, as well as portable and lightweight. Advantages:
- The surveyor's compass is relatively easy to use, even for beginners. Its design is simple, making it a practical tool for general surveying tasks.
- The surveyor’s compass is portable and lightweight, making it ideal for fieldwork in rugged or remote locations.
- It is more affordable compared to more advanced instruments like the theodolite or prismatic compass, making it a budget-friendly choice for basic surveying needs.
- The instrument is designed for quick and efficient measurement of bearings, which is especially useful in large-scale or preliminary surveys.
- Since it’s often used for route surveys (e.g., roads, pipelines, railways), it is suitable for surveying over long distances, where high precision is not always essential.
- The surveyor’s compass works with quadrantal bearings (0° to 90°), which is useful in boundary surveys and simpler land surveys, especially when mapping land parcels.
- Made of robust materials, the surveyor’s compass is designed to withstand the wear and tear of fieldwork. Disadvantages:
- The surveyor’s compass is less accurate. It is mainly suitable for general surveying rather than highly detailed work.
- The surveyor’s compass only measures quadrantal bearings (limited to 90° in each of the four quadrants).
- The surveyor’s compass is affected by local magnetic fields, which can lead to errors if the instrument is near metal objects, electrical equipment, or magnetic minerals.
- The compass must be calibrated for magnetic declination to ensure accurate readings. If this is not properly accounted for, measurement errors can occur.
- For complex or high-precision surveys, the surveyor’s compass is not suitable. Instruments like the theodolite or total station would be needed for better accuracy.
- The compass requires a clear line of sight between the instrument and the survey points. This can be challenging in areas with obstructions like trees, buildings, or uneven terrain.
- The surveyor’s compass measures angles in the horizontal plane only, meaning it cannot account for vertical angles or 3D measurements, which may be necessary in certain types of surveys. Compare prismatic compass and surveyor compass S. No. Category Prismatic Compass Surveyor Compass 1 Type of Bearing Whole circle bearing (360°) are calculated Quadrantal bearing (90°) are calculated. 2 Need for Adjustment More accurate with adjustments for declination Requires fewer adjustments, less precise in measurement
DESIGNATION OF BEARINGS OF SURVEY LINES
Whole Circle Bearing (W.C.B.) Whole Circle Bearing of a survey line is the horizontal angle measured in clock-wise direction from a reference meridian on a full circle. The W.C.B. of a line may have any value from 0° to 360°. It is measured from the North point of magnetic meridian. Prismatic compass is graduated on this system. Line W.C.B Quadrant Rule of conversion from W.C.B. to R.B.
RB
AB 𝟎° − 𝟗𝟎° NE 𝐑. 𝐁 = 𝐖. 𝐂. 𝐁 𝐍∅𝟏𝐄
AC 𝟗𝟎°^ −^ 𝟏𝟖𝟎°^ SE 𝐑. 𝐁. = 𝟏𝟖𝟎° − 𝐖. 𝐂. 𝐁 𝐒∅𝟐𝐄
AD 𝟏𝟖𝟎°^ −^ 𝟐𝟕𝟎°^ SW 𝐑. 𝐁. = 𝐖. 𝐂. 𝐁 − 𝟏𝟖𝟎° 𝐒∅𝟑𝐖
AF 𝟐𝟕𝟎°^ −^ 𝟑𝟔𝟎°^ NW 𝐑. 𝐁. = 𝟑𝟔𝟎° − 𝐖. 𝐂. 𝐁 N∅𝟒𝐖
Reduced Bearing (R.B.) or Quadrantal Bearing (Q.B.) Reduced Bearing of a survey line is the horizontal angle measured clockwise or anticlockwise from North end or South end of the reference meridian towards East or West whichever is nearer. Hence, to designate R.B. of a line, it is necessary to mention N or S to refer the meridian and E or W towards which the line is nearer. Thus, the plane round a station is divided into four quadrants, namely, NE, SE, SW and NW as shown in Fig. 28. Note: R.B. of a line has value from 0° to 90° with prefix N or S and suffix E or W to indicate the quadrant in which the line lies. These bearings are noted by surveyor's compass.
CONVERSION OF WHOLE CIRCLE BEARING INTO REDUCED BEARING
PROBLEM 2: Convert the following reduced bearings of survey lines to whole circle bearings: i) N 30° 30' E ii) S 45° 10' E iii) S 50° 30'W iv) N 75° 20' W Solution
- N 30° 30' E 𝐅𝐨𝐫𝐦𝐮𝐥𝐚,
2 S 45° 10' E
So, W.C.B = 30° 30' 𝐖. 𝐂. 𝐁. = 𝟏𝟖𝟎° − 𝐑. 𝐁. = 𝟏𝟖𝟎° − 𝟒𝟓°𝟏𝟎′ 𝐖. 𝐂. 𝐁. = 𝟏𝟑𝟒°𝟓𝟎′
- S 50° 30'W 4. N 75° 20' W 𝐅𝐨𝐫𝐦𝐮𝐥𝐚, 𝐅𝐨𝐫𝐦𝐮𝐥𝐚, 𝐑. 𝐁. = 𝐖. 𝐂. 𝐁 − 𝟏𝟖𝟎° 𝐑. 𝐁. = 𝟑𝟔𝟎° − 𝐖. 𝐂. 𝐁 𝐖. 𝐂. 𝐁 = 𝟏𝟖𝟎° + 𝐑. 𝐁. 𝐖. 𝐂. 𝐁 = 𝟑𝟔𝟎° − 𝟕𝟓° 𝟐𝟎′ = 𝟏𝟖𝟎° + 𝟓𝟎° 𝟑𝟎′
Levelling Levelling is a branch of surveying to be determining the relative height s of different point on or below the surface of the earth is known as levelling. Thus levelling deals with measurements taken in the vertical plane. Terminology used in levelling Level surface: Any surface parallel to the mean spheroid of the earth is called level surface and the line drawn on level surface is known as level line. Horizontal surface: Any surface tangential to level surface at a given point is called - Horizontal surface at point. Hence horizontal line is at right angles to plumb line. Vertical surface: It is the line connecting the point & centre of earth. Vertical & horizontal line is normal to each other. Datum: The point or the surface with respect to which levels of other points or planes are calculated is called ‘Datum or surface. Mean sea level (MSL): Mean sea level is the average height of sea of all stages of tides. Any particular place is derived by averaging over a long period of 19 years. In India the means sea level used is that at Karachi (Pakistan). In all important survey this is taken as datum. Reduced level: Levels of various points are taken as heights above the datum surface are known as reduced level. Bench mark: Bench mark is a relatively permanent point of reference whose Elevation w.r.t some assumed datum is known. There are four types of bench mark
- G.T.S (Great trigonometry survey)
- Permanent bench mark
- Arbitrary bench mark.
- Temporary bench mark. Great Trigonometric Survey (GTS) Benchmark: These benchmarks are established by the Survey of India at an interval of about 100 km all over the country, with the datum being taken as the mean sea level at Bombay Port. The elevations of the benchmarks are shown in the GTS Maps. Permanent Benchmark: In between the GTS benchmarks, permanent benchmarks are established by the Government departments on a clearly defined and permanent point like the top of a parapet wall, a bridge or a culvert, kilometre stone, railway platform, etc.
Arbitrary Benchmark: These are the reference points whose elevations are arbitrarily assumed generally for a small levelling purpose. It should be noted that arbitrary benchmarks do not imply any fixed datum. Temporary Benchmark: These are the reference points on which a day's work is closed and from where levelling is continued the next day. Examples of such types of benchmarks are the kilometre stones, parapets etc. METHODS OF LEVELLING Three principal methods are used for determining difference in elevation
- Barometric levelling
- Trigonometric levelling or (indirect levelling)
- Spirit levelling or (direct levelling) Barometric levelling:- Barometric levelling makes use of the phenomenon that difference in elevation between two points is proportional to the difference in atmospheric pressure at these points. A barometric, may be used and the reading observed at difference points would yield a measure of the relative elevation of those point Trigonometric levelling:- Trigonometric or indirect levelling is the process of levelling in which the elevation of points are computed from the vertical angles horizontal distance measured in the field just as the length of any side in any triangle can be computed from proper trigonometric relation. It is commonly used in mapping, both the difference in elevation and the horizontal distance between the point are directly computed from the measured vertical angle and staff reading .In a modified from called stadia levelling. Spirit levelling:- Spirit level is a branch of levelling in which the vertical distance with respect to a horizontal line may be used to determine the relative difference in elevation between two adjacent points. A horizontal plane of sight tangent to level surface at any point is readily established by mean of a spirit level or a level vial. The method is also known as direct levelling. It is the most precise method of determining elevations and the one most commonly used by engineers.
Parts of Telescope in Dumpy Level The important parts of telescope are as follows i) Eye piece ii) Objective lens iii) Diaphragm iv) Focusing screw v) Ray shade Eye piece:- Eye piece is used by the observer’s eye to view the distant object. It contains magnifying glass which magnify the observing image and also the cross hairs of diaphragm. So, accurate reading can be obtained. Erecting eyepiece is used to view the normal image which is generally inverted by objective lens. Objective lens:- Objective lens is provided at the other end of the telescope. The objective lens consists of two parts, the front part consists convex type lens and the back part consists concave lens. So, the image obtained from the objective lens is always inverted Diaphragm:- Diaphragm is provided in front of the eye piece. It contains cross hairs made of dark metal which are arranged in perfect perpendicular positions. These cross hairs are used by the eye piece to bisect the objective through objective lens. Focusing screw:- Focusing screw is used to adjust the focus if cross hairs and the image clarity. The magnification of eye piece is managed by this focusing screw.
Ray shade:- Ray shade is used to prevent the objective lens from sunlight or any other light rays which may cause disturbance to the line of sight. Bubble tubes:- Bubble tubes are provided to check the level of the instrument. Two bubble tubes are provided in a dumpy level which is arranged perpendicular to each other on the top of the telescope. One tube is called as longitudinal bubble tube and another is called as cross bubble tube. The instrument is said to be in perfect position when both the bubbles of the tubes are at center or middle of the tube. Compass:- Compass is used to determine the magnetic bearing of line. In case of dumpy level, circular compass is provided just under the telescope. The compass contains a pointer in it and readings are marked inside it. The pointer is set to zero when it faces the north line from which the magnetic bearings are measured. Vertical spindle:- Vertical spindle is located at the center of the whole instrument. The telescope can be rotated in horizontal direction with respect to vertical spindle. The instrument is connected to the tripod stand using vertical spindle. Tribrach:- Tribrach plate is parallel to the leveling head or trivet. It is connected to trivet by leveling screws or foot screws which can adjust the tribrach plate. The horizontal level of the instrument can be achieved by adjusting this tribrach plate. Foot screws:- Foot screws are provided to regulate the tribrach position and hence the instrument can be leveled which is known by observing the bubble tube. The tribrach plates can be lowered or raised using foot screws. The position of tribrach is said to be correct when the bubble in bubble tube is at centre. Levelling head:- Levelling head is also called as trivet. It contains two triangular shaped plates which are arranged parallel to each other. Three groves are provided at the three corners of the plates in which foot screws are supported.
