FACULTY OF CIVIL ENGINEERING & EARTH RESOURCES ENGINEERING SURVEY FIELDWORK. CURVE RANGING COMPUTATION & SETTING-OUT (Standard Of Procedure)

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1 FACULTY OF CIVIL ENGINEERING & EARTH RESOURCES ENGINEERING SURVEY FIELDWORK CURVE RANGING COMPUTATION & SETTING-OUT (Standard Of Procedure) Subject Code Date Group Number Student Name & ID Number Group Member Name & ID Number 1 2 Lecturer Marks Remarks Endorsement

2 Objective: 1. To make necessary computation for setting-out the ranging of simple curve. 2. To make setting-out the ranging of simple curve on site. Scope of works: 1. Each group shall be carried out field survey works necessary to accurately determine the locations centerline of the curve 2. Each group shall be prepared a table of computation for setting-out. 3. Each group shall be prepared a report of had been done (Appendix III). The report shall be submitted one week after completed the fieldwork. List of Devices: 1. 1 set of Built-in EDM or Theodolite completed with accessories set of Reflector completed with accessories. Procedure of works: Conducting a survey (Appendix II).

3 Appendix I CURVE RANGING COMPUTATION & SETTING-OUT Introduction: In the design of roads and railways, straight sections of road or track are connected by curves of constant or varying radius. The purpose of the curves is to deflect the road through the angle between the two straights, θ. For these reason, θ is known as the deflection angle. In construction surveying, curves have to be set out on the ground for a variety of purposes. A curve may form the major part of route, it may form a kerb line at a junction or may be the shape of an ornamental rose bed in a town centre. Types of Horizontal Curve: i. Simple curves circular curves of constant radius ii. Compound curves two or more consecutive simple curves of different radius iii. Reverse curves two or more consecutive simple curves of the same of different radius with their centres on opposite sides of the common tangent. iv. Transition curves curves with gradually varying radius (often referred to as spiral ) v. Combined or composite curves consisting of consecutive transition and simple circular curves. This is the usual manner in which transition curves are used in road and railway practice, to link a straight and a circular curve, or two branches of a compound or reverse curve. Curve Elements: In figure, the centre lines AI and BI of two straight roadways, called simply the straights, meet at a point I called the intersection points. The two straights deviate (deflect) by the angle θ. The roadways may actually exist on the ground or may simply be proposals on a roadway development plan. Clearly it is desirable to avoid having a junction at I, so the straights are joined by a circular curve of radius R. The straights are tangential to the curve at the tangent points T1 and T2 and lengths IT1 and IT2, known as the tangent lengths, are equal. Before setting the curve on the ground, the exact location of the tangent points must be known. If the two straights are existing roadways, then, in order to locate the tangent points, a theodolite is set at point I and the deviation (deflection) angle θ is measured together with the lengths of lines AI and IB. If the roadway scheme exists only on a development plan, the angle θ and the distances AI and IB must be measured by protractor and scale rule or by calculation from the coordinates of A, I and B.

Useful lengths From the geometry of figure; Tangent length (IT1 and IT2) = R tan θ/2 External distance IV = R [sec (θ/2) -1] Mid-ordinate VC = R(1-cos θ/2) Length of curve T1VT2 = [(θ/360)2πr] m = [R

4 Useful lengths From the geometry of figure; Tangent length (IT1 and IT2) = R tan θ/2 External distance IV = R [sec (θ/2) -1] Mid-ordinate VC = R(1-cos θ/2) Length of curve T1VT2 = [(θ/360)2πr] m = [R x θ radians] m = (100 θ/d)m, θ and D are same unit Long chord (T1CT2) = 2R sin θ/2 Curve Composition: In setting out large radius curves, or in some cases small radius curves, pegs are set at regular intervals around the curve. The interval is commonly 10 or 20 m and is measured as a running chainage, from the zero chainage point of the road system. Consequently, it would be very unlikely that either tangent point of the curve would coincide with a chainage which is at an exact tape length. In figure below, straights AI and IB deviate by 13 o at intersection point I, where the chainage is m. Tangent lengths IT1 and IT2 = 400tan 6.5 o = m Therefore chainage T1 = = m Curve length = 13/360 x 2πR = m Therefore chainage T2 = = m The last peg on the straight, measured at 20m interval from A, occurs at chainage 120m; therefore the first peg on the curve, at chainage 140m, lies at a distance of ( )m = 14m from tangent point T1. This short chord is called the initial subchord. Thereafter, pegs placed at standard chord intervals of 20 m occur at chainage 160, 180 and 200m. The final tangent point T2 is reached at m; therefore the final chord is ( )m = m. This short chord is called the final sub-chord. Summarizing, the chord composition is derived as follows: Chainage T1 = m Chainage of first peg on curve = m Therefore initial sub-chord = ( ) = m

5 Chainage of last peg on curve = m Therefore number of standard chords = ( )/20 = 3 Chainage T2 = m Therefore final sub-chord = ( ) = m Setting-out by tangential angles: Give Bearing T1-I = Chord Number Length Chainage Deflection Angle c/r x Tangential Angle Bearing Distance (2RSin ) T T Appendix II 1. Setting up the Theodolite on TI Setting the tripod The tripod legs are spread out and rested lightly on the ground around the survey point. Judging by eye, the legs are moved to bring the tripod head over the point, keeping the tripod head as level as possible. Mounting the instrument The theodolite is carefully removed from the box and screwed to the tripod. Centring A sight is taken through the optical plummet to view the survey peg. The footscrews are turned to bring the instrument exactly over the peg. The theodolite is now centred but, not level. Levelling Levelling is accompolished by raising or lowering the legs of the tripod, using the sliding leg arrangement, until the circular spirit level is centred. Refinements to the centring and leveling of the instrument must now be made; (a) Set the plate spirit level over two screws and centralize the bubble, (b) Turn the instrument through 90 o and recentralize the bubble (c) Repeat operations (a) and (b) until the bubble remains central for both positions. Parallax elimination A piece of paper is held in front of the telescope and the observer, sighting the paper through the telescope, turns the eyepiece carefully until the cross-wires of the reticule are sharply defined.

6 2. Setting up bearing to I (Topcon GTS220) Released Horizontal and vertical plate, and the theodolite in face left position. Switch On Theodolite Display Panel. Make sure horizontal bearing in the mode Horizontal Right (HR). Rotate the theodolite horizontally, till the required horizontal bearing had been display in panel. Refinements to the required horizontal bearing, using horizontal tangent screw. Press the (F2)(HOLD) key. Collimate the target at RO. Press the [F3](YES) key to finish holding the horizontal angle. 3. Setting-out points of curve ranging using Built-EDM Theodolite. Released Horizontal and vertical plate. Rotate the theodolite horizontally, till HR in display panel shows TI-1 bearing. Clamp horizontal plate. o Refinements to the required horizontal bearing, using horizontal tangent screw. Instruct front man hold the reflector pole vertically approximately on the line (i.e. reflector have been seen through telescope). Press the [ ]key. Distance measurement starts. Display panel shows HR (Horizontal angle), HD (horizontal distance) and VD (Vertical distance). Press F1 (Meas). New distance display. Obtained HD. If HD is still less than actual length, instruct front man to prolong the line. Instead, if HD more than actual length. Drive in peg. Repeat operation, till whole peg for the curve have been marked on the ground. Appendix III Report: Each group shall submit the report one week after completed the fieldwork. The report shall be consisted hereundera) Introduction b) Objective c) Devices d) Procedure e) Product Computation form f) Analysis g) Conclusion

TOPOGRAPHICAL AND SITE SURVEY (Standard Of Procedure)

FACULTY OF CIVIL ENGINEERING & EARTH RESOURCES ENGINEERING SURVEY FIELDWORK TOPOGRAPHICAL AND SITE SURVEY (Standard Of Procedure) Subject Code Date Group Number Student Name & ID Number Group Member Name