Unit 2: Chain Surveying 25 November 08 Unit 2 :Chain Surveying

Topics covered Different methods for linear measurement, instruments for chaining Different types of Chains/Tapes Ranging - Direct, Indirect, chaining on sloping ground Chain surveying: survey station, survey line, locating the ground features with the help of offsets. Chain surveying, fieldwork & office work 25 November 08 Unit 2 :Chain Surveying

2.1 Linear measurement- Basics One of the basic function in surveying Always horizontal not sloping distance No way to check the error other than remeasuring A B Inclined distance AB is not correct Horizontal distance is correct Mention about the greater area of land when purchase on the sloping ground. Measurement should be made very carefully as there is no means of checking if it is accurate or not? 25 November 08 Unit 2 :Chain Surveying

2.1 Linear measurement methods Electronic methods By optical means Direct measurements 25 November 08 Unit 2 :Chain Surveying

2.1 Direct measurements Instruments such as Pacing Passometer Pedometer Odometer or Speedometer Rough methods for preliminary survey Check of large mistakes in measurement made by more precise method Unsuitable in irregular and sloping ground Precision – 1/50 to 1/200 25 November 08 Unit 2 :Chain Surveying

2.1 Taping / Chaining Chaining or taping carries same meaning Use of either chain or tape. One of the accurate method of direct measurements This method is basis for most surveying. Precision 1/1000 to 1/5000 (ordinary land survey) Use of chain or tape Chain (Early 1600s) Steel tape in use by early 2000s Tape is very common nowadays. 25 November 08 Unit 2 :Chain Surveying

2.1 Instruments for chaining/taping Chain/tape Arrows pegs Ranging rods Plumb bob Hand level 25 November 08 Unit 2 :Chain Surveying

2.1 Instruments for chaining/taping Contd…. Arrows 10 arrows Pegs Station position Terminal points of survey line 25 November 08 Unit 2 :Chain Surveying

2.1 Instruments for chaining/taping Contd…. Ranging rods Used to range intermediate points on survey line Length 2 m ( very common) or 3 m Bands of 20 cm painted alternate colour( red & white, black & white) Ranging poles Similar to ranging rod but big in size Used in case of long lines 25 November 08 Unit 2 :Chain Surveying

2.1 Instruments for chaining/taping Contd…. Plumb bob Verticality of ranging pole Transferring the points to ground Also used for centring purpose in other surveying methods. 25 November 08 Unit 2 :Chain Surveying

2.2 Different types of chain/tape Chain (Absolute equipment at present) Metric chain (available in 5,10,20 meter) Gunter’s or surveyor’s chain (66 ft of 100 links) Engineer’s chain (100 ft of 100 links) Revenue chain (33 ft of 16 links) Steel band or band chain ( 20 or 30 m) 25 November 08 Unit 2 :Chain Surveying

2.2 Different types of chain/tape Contd…. Tape Cloth or Lenin tape Metallic tape Steel tape Invar tape (Alloy of nickel 36% & steel) Steel Tape Linen Tape Metallic Tape Cloth Tape 25 November 08 Unit 2 :Chain Surveying

2.3 Ranging When the length of survey line is greater than chain or tape length Process of establishing intermediate points Methods Direct Ranging Indirect Ranging Intermediate points > one tape length B A 25 November 08 Unit 2 :Chain Surveying

2.3 Direct ranging Direct ranging When two end points are intervisible Either by eye or through optical instruments such as Line ranger Theodolite Code of signals used to direct assistant A P B Transverse movement < one tape length 25 November 08 Unit 2 :Chain Surveying

2.3 Indirect ranging Indirect ranging When two end points are not intervisible With the aid of two intermediate points very near to the line M N A B M N M3 B A N3 M2 N 2 N1 M1 25 November 08 Unit 2 :Chain Surveying

2.3 Chaining/taping over sloping ground Methods Direct method or method of stepping Indirect method With the aid of vertical angle measurement With the aid of difference in level measurement Hypotenusal allowance 25 November 08 Unit 2 :Chain Surveying

2.3 Chaining/taping over sloping ground Contd…. Direct method or stepping method Convenient to proceed down-hill Tape shall be horizontal Sufficient pull to avoid sag Lengths of steps inversely proportion to degree of slopes. A B l4 l3 l2 l1 D = (l1+l2+l3+l4) 25 November 08 Unit 2 :Chain Surveying

2.3 Chaining/taping over sloping ground Contd…. Indirect method (Vertical angle measured) Clinometer to measure vertical angle D2 Φ1 Φ2 s1 s2 C B A D1 D1 = s1×cosΦ1 The required horizontal distance (D) =∑s cosΦ Indirect method (difference in height) Level machine is used to measure h to compute D. D h s A B C D = √( s 2 - h 2 ) Indirect method (Hypotensual allowance) B A’ C A θ 1 chain BA / = BC = 1 CHAIN BA = 1 CHAIN × sec θ AA / = BA - BA / = 1 CHAIN ( sec θ – 1) 25 November 08 Unit 2 :Chain Surveying

2.4 Chain surveying What is chain surveying? Principle of chain surveying Triangulation Survey stations Main station (A, B, C,…E) Subsidiary stations (F, G, H) Marking of stations Survey lines Main survey lines Base lines Check lines Tie lines 25 November 08 Unit 2 :Chain Surveying

2.4 Survey stations & survey lines Mutually visible Survey lines Few as far as possible Must have one base line Pass through level ground Form well-conditioned triangle Sufficient check line Short offset Should not pass through obstacle Should fall within the boundaries 25 November 08 Unit 2 :Chain Surveying

2.4 Locating the ground features Offsets- lateral distance of an object from survey line. Offsets should be as small as possible Types Perpendicular – less measuring on ground Oblique Method of ties A C P B 900 B A P C ≠ 900 P Q 25 November 08 Unit 2 :Chain Surveying

2.4 Locating the ground features Contd…. Swing of the tape on chain line Shortest distance is perpendicular offset P 25 November 08 Unit 2 :Chain Surveying

2.4 Locating the ground features Contd…. Offsets are taken in the order of their chaninage. Number of offsets depends upon the shape of objects Straight wall, zigzag wall, road with constant width Boundary wall Constant width road 25 November 08 Unit 2 :Chain Surveying

2.4 Locating the ground features Contd…. 25 November 08 Unit 2 :Chain Surveying

2.5 Chain surveying (field/office work) Equipment Chain/Tape (>30 m) 10 Arrows Raging rods A tape ( 10 m or 20 m ) Cross staff or Optical square Field book, pencil Plumb bob Pegs, wooden hammer, chalks 25 November 08 Unit 2 :Chain Surveying

2.5 Field work Field work consists of three steps Reconnaissance Marking and fixing survey stations Running survey lines Reconnaissance Walkover survey with the view of principle of surveying Reference sketch Thinking of possible problem and their solution in actual survey 25 November 08 Unit 2 :Chain Surveying

2.5 Field work Contd…. Purpose is to enable to locate stations during progress of work Wooden pegs in soft ground Nails or spikes in hard surface (road) & flushed with pavement For a long time used station, a stone of standard size fixed with mortar Reference of two or three permanent object Chaupari Building Electric pole 9.65m 10.50m 9.90m 25 November 08 Unit 2 :Chain Surveying

2.5 Field work Start chaining from base line Consists of two folds Contd…. Start chaining from base line Consists of two folds Chain the survey line Locate the adjacent details Chaupari One tape length Building 25 November 08 Unit 2 :Chain Surveying

2.5 Field work Contd…. 25 November 08 Unit 2 :Chain Surveying

2.5 Office work Part of office work Computation of data Plotting work Size of paper should be standard (in mm) A0 = 840 * 1188 A1 = 594 * 840 A2 = 594 * 420 A3 = 420 * 297 A4 = 297 * 210 25 November 08 Unit 2 :Chain Surveying

2.5 Plotting work Fix the scale of survey before starting Purpose of survey Extent of survey Finance available North upward rule Nice lettering (Always in the drawing) Skeleton first then offsets Use of tracing paper for proper orientation Put the details of title and legend box in the slide 25 November 08 Unit 2 :Chain Surveying

2.5 Plotting work Start with base line Triangles are laid by intersection of arcs Verification of check lines Offsets are then plotted by Set square or Offset scale Ground features representation with symbol Title box and legend box Use of HB, 2H and 3H pencils Put the details of title and legend box in the slide 25 November 08 Unit 2 :Chain Surveying

Conventional symbols 25 November 08 Unit 2 :Chain Surveying

Conventional symbols Contd…. 25 November 08 Unit 2 :Chain Surveying

Thank you for your attention! Any questions? Querries? 25 November 08 Unit 2 :Chain Surveying