MAHALAKSHMI ENGINEERING COLLEGE

Transcription

1 MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI DEPARTMENT: CIVIL QUESTION BANK SUBJECT CODE / Name: CE 04 / Surveying -I Unit 5 ENGINEERING SURVEYS PART A ( marks) SEMESTER: III 1. What are the components of a single curve? (AUC Apr/May 011) Back Tangent, Forward Tangent, Point of Intersection, Point of Curve, Point of Tangency, Intersection Angle, Deflection Angle, Deflection Angle to any Point, Tangent Distance, External Distance, Length of the Curve, Long Chord, Mid Ordinate, Normal Chord.. What are the objectives of route surveys? (AUC Apr/May 011) Route survey is applied to the surveys required to establish the horizontal and vertical alignments for transportation facilities. The transportation facilities may be highway, railway, aqueducts, canals, water pipelines, oil and gas, cable ways, sewage disposal, power telephone and transmission lines. 3. On what basis is a vertical curve designed? Name the preferable type of vertical curve. Summit Curves Sag or Valley Curves 4. Draw a neat sketch of a compound curve and mark the salient features of it. (AUC Apr/May 010) (AUC Apr/May 010) III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 1

2 5. What are transition curves? (AUC Nov/Dec 011) A transition or easement curve is a curve of a varying radius introduced between a straight and a circular curve, or between branches of a compound curve or reverse curve. 6. Draw a neat sketch showing a simple circular curve and show essential notations. (AUC Nov/Dec 011) 7. Define point of curve. (AUC Nov/Dec 010) Point of curve is the beginning of the curve (T1) where the alignment changes from a tangent to a curve. 8. What is mean by point of tangency? (AUC Nov/Dec 010) Point of tangency is the end of the curve (T) where the alignment changes from a curve to tangent. 9. What is tangent length in a simple curve? (AUC Nov/Dec 009) Tangent length is the distance between the beginning of the curve (T1) and point of intersection (PI) of two tangents (also the distance from PI to PT). 10. What is mid-ordinate in a simple curve? (AUC Nov/Dec 009) Mid ordinate is the ordinate from the mid-point of the long chord to the mid-point of the curve. It is also called the versine of the curve. 11. What are control stations in setting out works? State how they should be. (AUC May/June 01) Primary control stations and Secondary control stations. Primary control stations may be the triangulation stations. Secondary control stations are referred to these primary control stations. It may be found by traversing methods. 1. Name the different methods of setting out a simple curve. (AUC May/June 01) i) Linear methods Offsets from the long chord Successive bisection of chord Offsets from the tangents III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page

3 Offsets from the chords produced ii) Angular Methods Tape and theodolite method Two theodolite method Tachometric method Total station Method 13. What do you mean by temporary adjustment of theodolite? (AUC May/June 013) Temporary adjustments are those which are required to be undertaken at every new set up of the instrument at each survey station before starting to make any observation. Setting Levelling and Parallax removal 14. Write about well conditioned triangles. (AUC May/June 013) A well conditioned triangle is one in which no included angle is less than 30 o or greater than 10 o. An equilateral triangle is the best well conditioned triangle. 15. What is meant by stopping sight distance? (AUC Nov/Dec 01) Stopping sight distance is defined as the distance needed for drivers to see an object on the roadway ahead and bring their vehicles to safe stop before colliding with the object. 16. List out any four special instruments used in mine surveying. (AUC Nov/Dec 01) Theodolite tachometers, Mining theodolite Tachymeters with stereoscopic range finders Angle gauges PART B (16 marks) 1. Explain the procedure for setting out a circular curve by Rankine s method. RANKINE S METHOD: (AUC May/June 013) (AUC Apr/May 011) The method is known as Rankine s method of tangential angle or the deflection angle method. The method is accurate and is used in railways and highways. Let T 1 ab be a part of a circular curve with T 1, the initial tangent point. Thus, T 1 a is the first sub-chord which is normally less than one chain length (Figure). From the property of a circle C 1 = δ 1 R C1 δ 1 = radian R = C1 R degree III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 3

4 = C1 180 o X60 o R minutes δ 1 = R C 1 minutes Therefore to locate the point a with the help of a theodolite and tape, the instrument is set at T 1 and the line of sight is put at an angle of δ 1 = Δ 1 as computed above. Then with the help of a tape and ranging rod, the tape is put along the line of sight and distance C 1 is then measured to locate point a along the line of sight. Similarly, δ = R C minutes Since the theodolite remains at T 1, b is sighted from T 1 by measuring δ 1 +δ =Δ from the tangent line. The point b is located with the help of a tape and ranging rod. The tape with the ranging rod is so adjusted that the tape measures ab = C and the ranging rod lies along the line of sight T 1 b. In practice, C 1 is the first sub-chord and Cn the last sub-chord. C = C 3 =...C n-1 are full chain lengths. As a check the deflection angle Δ is the angle of intersection. n for the last point T is equal to Δ/ where III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 4

5 . Distinguish between a compound curve and a reverse curve. (AUC Apr/May 011) COMPOUND CURVE: Compound curves are used for those applications where design constraint like topography or cost of land prevents the use of simple curve. They are generally used in the design of interchange loops and ramps. Smooth driving characteristics require that the larger radius be more than 1.3 times larger than the smaller one. Solutions to compound curve problems vary, as several possibilities exist as to which of the data are known in any one given problem. All problems can be solved by use of sine law or cosine law or by the omitted measurement traverse techniques. Elements of a Compound Curve: Figure shows a two centred compound curve T 1 T 3 T, having two circular arcs T 1 T 3 and T 3 T meeting at a common point T 3 known as the point of compound curvature (PCC). T 1 is the point of commencement (PC) and T is the point of tangency (PT). The other elements such as tangent lengths, length of the curve, etc. for the smaller and larger curves, will be designated by the subscripts S and L, respectively. Thus, R S, R L = the radii of the curves, Δ S, ΔL= the deflection angles, l S, ll= the length of the curves, and t S, tl= the tangent lengths. T S, T L = the tangent lengths on the sides of smaller and larger curves, respectively, for the Compound curve. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 5

6 Tangent Lengths for the Circular Curves III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 6

7 REVERSE CURVE: Reverse curves are seldom used in highway or railway alignment. The instantaneous change in direction occurring at the point of reverse curvature or point of reversed curve(prc) would cause discomfort and safety problems for all but the slowest speed. Additionally, since the change in curvature is instantaneous, there is no room to provide super-elevation transition from cross-slope right to cross-slope left. However, reverse curves can be used to advantage where the instantaneous change in direction poses no threat to safety or comfort. Reverse curves are unavoidable in hilly roads where a loop of a curve in a valley generally immediately followed by another loop round the shoulder of the ridge. Cities where roads turn in different directions in succession or when roads approach a flyover, the reverse curves are frequently used. Elements of a Reverse Curve: As with compound curves, reverse curves have six independent parameters (R 1, T 1, Δ 1, R, Δ,T ); the solution technique depends on which parameters are unknown. Figure shows a reverse curve between two straights AT 1 and T B having a total deviation of Δ at I. Where as O 1 and O be the centres of the two circular curves of radii R 1 and R, respectively, and Δ 1 and Δ be the deflection angles or the central angles for the respective curves. 3. Discuss the various surveying to be carried out for an engineering project. i) Reconnaissance ii) Preliminary Survey iii) Final Location Surveys i) Reconnaissance: (AUC Nov/Dec 011) Reconnaissance starts with a field inspection by walking, riding on ponies (in hills) or driving in jeeps. All information of value, either in design, construction, maintenance or operation of the facility should be collected, which may include, inter alia, the following: Details of route vis-à-vis topography of the area plain, rolling or hilly. Requirements of cross-drainage works type, number and length. Gradients that are feasible, specifying the extent of deviations needed. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 7

8 Curves and hair-pin bends etc. Existing means of communication mule tracks, jeep tracks, cart tracks etc. Constraints on account of built-up areas, monuments and other structures. Road length passing through different terrains, areas subjected to inundation and flooding, areas of poor drainage conditions, unstable slopes etc. Climatic conditions temperature, rainfall, water table and its fluctuations etc. Facilities/ Resources available e.g., availability of local labour, contractors etc. Access points indicating possibility of induction of equipment. Period required for construction. Villages, hamlets and market centres connected. Economic factors population served, agricultural and economic potential of the area. Crossing with railway lines and other existing roads. Positions of ancient monuments, burial grounds, cremation grounds, religious structures, hospitals and schools etc. Ecology or environmental factors. ii) Preliminary Survey: Preliminary survey is a relatively large-scale investigation of the alternative(s) thrown up as a result of the Reconnaissance survey. The survey consists in establishing a base-line traverse. For hill roads, it may be necessary to cut a trace of m wide to enable the traverse survey to be carried out. A theodolite or compass is used for traversing and levels are taken along the traverse and across it. The distances are measured continuously along the traverse line with a metallic tape. Bench marks should be established at intervals of 50 m to 500 m and the level should be connected to the GTS datum. Physical features such as buildings, trees, burial grounds, monuments, railway lines, canals, drainage channels etc should be located by means of offsets. The width to be covered for such detailing should be about the land width proposed to be acquired. Information on highest flood level, rainfall intensity, catchment areas of streams etc should be collected. The survey enables the preparation of a map including the plan and longitudinal section. The scales generally recommended are: Built-up areas and hilly terrain: 1:1000 for horizontal scale and 1:100 for vertical scale Plain and rolling terrain: 1:500 for horizontal scale and 1:50 for vertical scale It is desirable to mark the contour intervals at an interval of 1 to 3m. The map should show all the physical features surveyed. At the end of the preliminary survey, it is useful to involve the local community in the process of deciding on the alignment since several social issues are also involved. As such the JE/AE must conduct a Transect walk along the alignment /trace together with the Panchayat Pradhan / Ward Panchayat, local revenue and forest officials. iii) Final Location Surveys: After the preliminary survey and Transect Walk, the final alignment is to be determined. The purpose of the final location survey is to fix the centre line of the selected alignment in the field and to collect additional data for the preparation of the drawings. The centre line is translated on the ground by continuous transverse survey and pegging the same. The points of transit (POT) should be clearly marked on the ground by a nail in the existing pavement or a hub in concrete on III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 8

9 a new alignment. Suitable references (at least two) should be marked permanently on the ground. The horizontal intersection points (HIP) should be similarly marked on the ground and referenced. All curve points viz beginning of transition (BS), beginning of circular curve (BC), end of circular curve (EC) and end of transition (ES) should be marked and referenced. The centre line should be staked at 50 m intervals in plain terrain and 0m intervals in hilly terrain. Bench marks should be left permanently at 50 m intervals. The cross-sections taken during the preliminary survey should be supplemented by additional cross-sections at the curve points. Generally, cross- sections should be available at intervals of m in plain terrain, 50-75m in rolling and 0 m in hilly terrain. Survey can be accomplished these days by a Total Station, with assistance from GPS (Geographic Positioning System) which determines the location of survey points by satellite. But in the absence of these instruments, an ordinary theodolite, levelling instrument and compass would be acceptable. 4. Two straight lines having an intersection angle of 5 o 1 are to be connected by a circular curve of radius 500 m. if the chainage of the intersection point is 1000 m. calculate the data for setting out the curve by i) Deflection distances method and ii) Tangential angles method. Take the normal chord as 0 m. (AUC Nov/Dec 011) Solution: i) Deflection distances method: Angle of intersection is below 90 O. So take Deflection angle, = 5 O Degree of curve, D = = = 3 O 6 16 R 500 Tangent length, BT 1 = R tan Chainage at intersection point = 1000 m = 500 x tan Chainage at tangent point, T 1 = = m R X 500X 5 Length of the curve = 0 = ' = m 1' = m Chainage at tangent point, T = T 1 + length of curve = = m Length of long chord, L = R sin Half of long chord = m Mid ordinate, Oo = R - R = L = x 500 x sin 5 0 1' = m 500 = 1.04 m III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 9

10 Ordinates at 0 m intervals are considered and calculated from Ox = R x ( R ) O o O 0 = ( ) m O 40 = ( ) m O 60 = ( ) 8. 4 m O 80 = ( ) m O 100 = ( ) m O = ( ) 0 Ordinates for the right half are similar to those for the left half. ii) Tangential angle method: Angle of intersection is below 90 O. So take Deflection angle, = 5 O Degree of curve, D = = = 3 O 6 16 R 500 Tangent length, BT 1 = R tan Chainage at intersection point = 1000 m = 500 x tan Chainage at tangent point, T 1 = = m R X 500X 5 Length of the curve = 0 = ' = m 1' = m Chainage at tangent point, T = T 1 + length of curve = = m Hence difference between two tangents = T - T 1 = = m Length of initial sub-chord = = m Number of full 0 m chord = 10 Chainage covered = (10 x 0) = 1100 m III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 10

11 Length of final sub chord = = 8.15 m Deflection angle of initial sub chord, 1719 X " 500 Deflection angle for full chord of 0 m length, 1719 X 0 to " 500 Deflection angle of final sub chord, 1719 X " 500 Δn = " + (10 x " ) " = 0 O 4 6 = 0 O 4 6 = 0 O Hence the calculated deflection angles are correct. Other data required to set out the curve are 0 5 1' i) Apex distance = R(sec 1) 500(sec 1) 1.34m ii) Versed sine of the curve = R (1 Deflection angle details: cos ) 500( ' cos ) 1.04m Point Chainage Chord length Deflection angle for chord Total deflection angle Angle to be set Remarks T Starting point of the curve F " " " F " 34 01" 34 00" F " F " F " F " F " F " F " F " F " T " " 6 113" " " " " " " " ' " " 6 1 0" " " " " " " " 0 0 Least count of verniers = 0 0 Finishing point of the curve III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 11

12 5. Two straight AB and BC intersect at a chainage of 44 m and the angle of intersection is 140 o. It is required to set out a 5 o simple circular curve to connect the straights. Calculate all the data necessary to set out the curve by the method of offsets from the chord produced with an interval of 30 m. (AUC Apr/May 010) Solution: Angle of intersection = 140 o Deflection angle, = 180 o 140 o = 40 o Radius of curve, R = Tangent length, BT 1 = R tan = = m D 5 Chainage at intersection point = 44 m = x tan 40 0 = m Chainage at tangent point, T 1 = = m R X 343.8X Length of the curve = 0 = = 40.0 m Chainage at tangent point, T = T 1 + length of curve = = m Length of long chord, L = R sin Half of long chord = m Mid ordinate, Oo = R - = x x sin R = L 40 0 = m = 0.73 m Ordinates at 30 m intervals are considered and calculated from Ox = R x ( R ) O o O 30 = ( ) m III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 1

13 O 60 = ( ) m O 90 = ( ) 8. 74m O = ( ) 0 Ordinates for the right half are similar to those for the left half. 6. Explain the methods of transferring reduced levels from surface to underground in a tunnel setting out work. (AUC Apr/May 010) i) Setting out central line of tunnel ii) Setting out inside tunnels iii) Transferring of alignment through shafts i) Setting out central line of tunnel: The centre-line of tunnels are fixed on the surface along with shaft locations. Generally the surface control points of the tunnels are not visible from each other. However, by the method of reciprocal ranging points on the summit can be established which can be joined to get the central line. The measurements should be made accurately. Linear measurements are made using invar substance bars with an accuracy of 1 in Angular measurements are made using 1 second theodolite with an accuracy 0f 15 N where N is the number of angles. In case of tunnels in hilly regions it is neither feasible to align the tunnel ends by direct ranging or reciprocal ranging. In such cases precise triangulation has to be used. The figure shows a scheme of triangulation network with QR as base line for a tunnel project. Here all the angles are measured accurately by one second theodolite. Usual corrections for length, temperature, terrain, sag and reduction of levels with respect to sea level are all followed in arriving at the values of the coordinates. The traverse is adjusted for angles and coordinates. The proposed tunnel axis is shown in figure as HR. ii) Setting out Inside Tunnels: After the coordinates of portals and shafts are finalized, setting out is started. Centre line of tunnel is done as shown in figure from various portals and shafts. Back sighting on the pillar, aligned and constructed as far as practicable on the extended centre line such as pillar C and then by transiting. Reference points are constructed on the roof of tunnels or slightly below the invert for every 300 m. iii) Transferring of alignment through shafts: Transfer of alignment is done through shafts by adopting any one of the following methods: i) By hanging two or more plumb lines down the shaft. ii) By lighting directly from edge of shaft where shaft diameter to depth ratio is high. Co-planning is done by hanging two or more plumb lines down the shaft and determining the bearing of the plumb planes so formed which are connected to the surface. The plumb lines should be well apart as for as possible. The plumb lines are of special type. The line shall be of fine steel wire and carrying a symmetrical weight of 35 kg or more. The wire should be well stretched to keep it tight. In order to keep the wires vertical, the bob should be contained in a canister with a hood. This arrangement will shield the bob and will reduce oscillations set up by air currents or by water dropping down the shafts. The canister can be filled with water or oil to reduce the vibrations. The bearing of the plumb plane underground is assumed same as at the surface. This forms the starting direction for the underground survey work. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 13

14 The following procedure is adopted for transferring the centerline from top. A theodolite is set up on top of the hill at a suitable position to maintain the centre line of the shaft. The RLs of both the ends of the shaft are determined by a level. Knowing the bottom RLs of the ends the depth of the shaft is found. Excavation of the shaft is started and verticality is maintained with the help of the plumb-bob which is suspended from wires from top through pulleys. The excavation is continued until the required bottom level is reached. The depth of the shaft is measured by measuring the length of suspended wire. The centre line inside the tunnel is maintained by a precise theodolite. This type of theodolites are provided with an artificial illumination system to enable work at night and in the darkness of the tunnel. It should be properly taken care to see that the centre line is maintained from both ends and one transferred from top coincide. 7. List out the linear methods of setting out a circular arc. Explain any one method. (AUC Apr/May 010) Linear methods of setting out a circular arc: Offsets from the long chord Successive bisection of chord Offsets from the tangents Offsets from the chords produced i) Offsets from the long chord: The method is suitable for setting out circular curves of small radius, such as those at road intersections in a city or in boundary walls. In Figure 5, the offset O xa to the point a on the curve is the perpendicular distance of point a from the long chord T 1 T, at a distance xa from D along the long chord. Considering the origin at D, O xa is the y-coordinate of point a. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 14

15 The long chord is divided into equal parts of suitable length. The offset O xa corresponding to the distances xa from D are calculated for different points on the long chord. These offsets are measured perpendicular to the long chord with the help of an optical square and points are located. Joining these points will produce the desired curve. The points on the right side of CD are set out by symmetry. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 15

16 8. Two tangents intersect at chainage 150 m and the angle of intersection is 150 o. Calculate all data necessary for setting out a curve of radius 50 m by the deflection angle method. The peg intervals may be taken as 0 m. prepare a setting out table when the least count of the vernier is 0. Calculate the data for the field checking. (AUC May/June 01) (AUC Nov/Dec 01) Angle of intersection = 150 o Deflection angle, = 180 o 150 o = 30 o Degree of curve, D = Tangent length, BT 1 = R tan = = 6 O 5 R 50 Chainage at intersection point = 150 m = 50 x tan 30 0 = m Chainage at tangent point, T 1 = = m R X 50X 30 Length of the curve = 0 = = m Chainage at tangent point, T = T 1 + length of curve = = m Hence difference between two tangents = T - T 1 = = m Length of initial sub-chord = = 6.98 m Number of full 0 m chord = 6 Chainage covered = (6 x 0) = 1310 m Length of final sub chord = = 3.91 m Deflection angle of initial sub chord, 1719 X " 50 Deflection angle for full chord of 0 m length, 1719 X 0 to 7 481" 50 Deflection angle of final sub chord, 1719 X " 50 Δn = " + (6 x 481" ) " = 18 O = 18 O = 18 O Hence the calculated deflection angles are correct. Other data required to set out the curve are 0 30 i) Apex distance = R(sec 1) 50(sec 1) 8.8m ii) Versed sine of the curve = R (1 cos ) 50(1 30 cos 0 ) 8.5m III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 16

17 Deflection angle details: Point Chainage Chord length Deflection angle for chord Total deflection angle Angle to be set Remarks T Starting point of the curve F O O O F O O O 36 0 F O O O 4 0 F O O O 1 40 Least count of verniers = 0 F O O O F O O O F O O O 37 0 T O O O Finishing point of the curve 9. Explain the setting out of a simple curve by two theodolite method. (AUC Nov/Dec 009) Two theodolite method: This method is employed for setting out a curve by making angular measurements. Therefore, the instrument required is only a theodolite. The method is quite accurate. It is specially preferred when the ground is rough, and accurate chaining is not possible. Since, in this method each point is fixed independently the error in setting out is not carried forward. The method is based on the property of a circle that the angle between the tangent and the chord is equal to the angle which that chord subtends in the opposite segment. Thus, for the chords in Figure 1. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 17

18 IT 1 a T 1 T a 1 IT 1 b T 1 T b The method requires setting up two theodolites, one at T 1 and the other at T. The theodolite at T 1 should read zero for the point I and the theodolite at T should read zero for the point T 1. Set the first deflection angle δ 1 on both theodolites. Thus, their telescopes are in the direction T 1 a and T a, respectively. Now the attendant is asked to move with a ranging rod in the line of sight of one of the theodolites. The observer of the other theodolite finds the point where the ranging rod is intersected by the vertical hair of his theodolite. This point is the required location on the curve. The second point is located by setting the second deflection angle δ on the two theodolites and the location of the point on curve is determined by the procedure given above. The process is continued for locating the other points on the curve till all the points are located on the ground. 10. Describe the different surveys to be carried out for the highway projects. (AUC Nov/Dec 01) (AUC May/June 01) i) Reconnaissance ii) Preliminary Survey iii) Location Survey i) Reconnaissance: During the reconnaissance survey the following factors have to be taken into consideration. Obstructions along the route. Gradients and length of curves. Cross drainage works. Soil type along the route. Sources of construction materials and Type of terrain. ii) Preliminary Survey: The preliminary survey in a highway project is done with the main objectives Various alternate arrangements Estimate the quantity of earth work materials and other construction aspects Compare different proposals. The following surveys are constructed Primary transverse Topographical surveys Levelling work Hydrological data Soil surveys. iii) Location Survey: The final alignment decided after the preliminary survey is to be first located on the field by establishing the centre line. Next the detailed survey should be carried out. The detailed survey involves: Fixing temporary bench marks along the route for every 300 m. The cross sectional details are taken for 30 m on either side of the central line. All details of cross drainage works are taken. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 18

19 Topographical details are taken. Detailed soil survey is carried out. 11. Explain the concepts of route survey for highways, railways and waterways. Route surveys are performed with two objects: To determine the best general route between the terminals and To fix the alignment grades and other details along the selected route. The route survey has to be done by i) Reconnaissance survey ii) Preliminary surveys iii) Location survey iv) Construction survey. i) Reconnaissance survey: (AUC May/June 013) Reconnaissance survey of a route survey comprises of a rapid and thorough examination of a strip of an area between the terminal points. During the survey several possible routes worth trying under detailed survey are explored. The reconnaissance work of a route survey should be given to a very experienced group of engineers so as to save time and unnecessary expenses. During the first step of reconnaissance is to collect all details from the topographic maps available from survey of India. If data available is inadequate, a photogrammetric survey between the proposed points may be done to get the adequate data. Following informations have to be collected during reconnaissance for a route surveying: Based on the topography and other data, the terrain of the route between the two points may be classified as level, rolling or mountainous. The natural gradient has to be noted to fit in the required alignment of proposed project. Cross drainages, high water elevations, flood conditions, bank conditions, width of stream, etc, so as to plan proper cross drainage works such as culverts, bridges, etc. Information about other route crossings such as highways, railroads, pipelines, etc, have to be noted down. Geological and soil conditions to have a stable foundation for bridges, better subgrade for road and railways, etc. Availability of construction materials their quality and quantity all along the route. Availability of labour along the route for the construction work. Value of land along the alternate routes tobe acquired. ii) Preliminary survey: It is a detailed survey which is taken along the decided location of the route. During the preliminary survey an accurate topographic map of the strip of the area along the selected route are done so as to get a fairly close estimate of the project. They are performed by three parties under the general supervision of the location engineer: a) Transit party, b) level party and c) topography or cross section party. a) Transit party: It consisting of four to seven persons conducts open traversing. During the traverse the azimuths of the first and the last line of traverse are taken. The party also records topographical details, property lines, drainage structures, pipe lines, roads and railways, etc. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 19

20 b) Level party: It consisting of three persons undertakes two important jobs Establishes bench marks along the selected route at regular and convenient places. Conducts a longitudinal section of the traverse lines. c) Topography: It consisting of three to four persons conducts a detailed topographic survey. Also cross sections details at every 30 m intervals perpendiculars to traverse line on either side of it are taken. iii) Location survey: Transferring of paper location to the ground under the field condition is called the location survey. The main purpose of location survey is to make minor improvements on the line keeping in view the terrain reality and to fix the final grades. The final alignment and location made in the ground is called the field location. After this profile levels are run over the centre line, bench marks are established. All relevant surveys keeping the central line are performed so as to identify cross drainage works, cross sections to compute earth work, horizontal and vertical curve locations etc are done. iv) Construction survey: The purpose of construction survey is to re-establish points, line and grades on the ground at the time of construction. Remarking the central line based on the plan and reestablishing certain points on the central line. Checking RLs of bench marks and running centre line levels over the retraced line. Computing RLs to find the elevations of all stations, at points where cross sections are to be taken for earth work volume computations. Setting up slope stakes and grade stakes. Setting stakes for the complete layout of culverts and bridges. Setting out horizontal and vertical curves. Making minor adjustments with respect to drainage structure, lines or grades, etc. To submit a program report. To submit the final estimate. 1. Explain some mine survey instruments. (AUC May/June 013) The mine transit is usually of a smaller size than the ordinary instrument. Special provisions are made for steep or vertical sights. Due to very steep sights the horizontal circle of the ordinary transit will obstruct the pointings of the telescope of an ordinary transit. To overcome this difficulty an auxiliary telescope is attached either at one end of the horizontal axis or above the main telescope and at a distance more than one half of the diameter of the horizontal plate. The two mountings are arranged in such a way that the auxiliary telescope is interchangeable between the top and side positions. In each position a counterpoise is attached to keep the telescopes in balance. In either position, the line of sight of the auxiliary telescope is parallel to that of the main telescope. For steep sights upward, a prismatic eye piece is attached to the main telescope. The instrument is generally mounted on an extension leg tripod. For ease in reading the vertical angles by the transitman, the vertical circle is sometimes graduated on the edge instead of the side. The centre point of the transit is definitely marked on the top of the telescope. In places where a tripod cannot be used, suspension type mine transit is employed. The instrument is supported on a bracket being screwed horizontally into adjacent mine timbers. The III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 0

21 horizontal circles along with its verniers are on the top of the telescope and the vertical circle and hence the use of auxiliary telescope is obtained. The horizontal circle is 9cm in diameter, the vertical circle 7cm in diameter and the whole instrument weighs only 5.5 lb. if required, the instrument can also be supported on tripod and for this purpose of the vertical circle and the telescope are provided with sensitive reversion spirit levels. 13. Write short notes on sight distances and Shafts. (AUC Apr/May 011) Sight Distance: The minimum sight distance available on a highway should be sufficient length to stop a vehicle without collision. The absolute minimum sight distance is therefore equal to the stopping sight distance, which is also sometimes called as non-passing sight distance. The sight distance available on a road to a driver at any instance depends on i) Features of the road ahead ii) Height of the driver s eye above the road surface iii) Height of the object above the road surface. Design speed Stopping sight distance 30 mph (48 km/hr) 00 ft (61m) 40 mph (64 km/hr) 75 ft (84m) 50 mph (80 km/hr) 350 ft (107m) 60 mph (96 km/hr) 475 ft (145m) 70 mph (113 km/hr) 600 ft (184m) The expressions for sight distance (S) on vertical curves will now be derived for two cases: i) when the sight distance S is entirely on the curve (S < L) and ii) when the sight distance overlaps the curve and extends on to the tangent (S > L) let h 1 = height of drivers eye above the roadway. h = height of object or hazard on the travelled road. Case 1: S < L: L = L = Case : S > L: Where, g g S = 1 S S 1 L h ( g g ) ft ( g1 g ) metres 97 1 h 1 h h h h h g 1 1 XA XA h g III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 1

22 Shafts: S = 1 L = S L 100( h1 h ) A 00( h h 1 ) A Shafts are vertical holes excavated thought the soil or rock or other materials for different purposes. Shafts are also drives for installation of drilled piers. Shafts are also made for transfer of centre line inside tunnel by suspending plumb bobs. After fixed the centre line on the surface the setting out of underground line can be done by transferring surface line down the shafts wherever they are vertical. A theodolite is then set over one of these points on the surface and the line of sight is directed towards the other point. A theodolite is then transferred underground and set exactly in line with the two suspended wires. The line joining these wires and hence the line of sight of that theodolite gives the direction of the centre line of the tunnel underground. The line is then set with the instrument on nails driven into convenient byates of timber from which plumb bobs or lamps may be suspended. The exact center line is marked bt steel punch or a file mark. The plumb wires are fine wire stretched tight by attaching weight at their lower ends. The wires must be so suspended that they do not touch the sides of the shaft. to avoid this, there should be some arrangement for removing them and again placing them if required. The arrangement with the help of which the wire can be lifted up or lowered down. 14. List out the linear methods of setting out a circular arc. Linear methods of setting out a circular arc: Offsets from the long chord Successive bisection of chord Offsets from the tangents Offsets from the chords produced Successive bisection of chord: The method being approximate is suitable for small curves. It involves the location of points on the curve by bisecting the chords and erecting perpendiculars at the midpoint of the chords. In Figure 6, T 1 T is the long chord and D is its midpoint. C is the point of intersection of the perpendicular line at D, with the curve. DC is the mid-ordinate, which is equal to At D, a perpendicular offset equal to M is erected and the position C is located. Now consider the chords T 1 C and T C, locate their midpoints d 1 and d respectively. Erect two perpendiculars at d 1 and d and measure the offsets equal to d 1 c 1 and d c, respectively. The offsets d 1 c 1 and d c are computed from the following formula: Now, by the successive bisection of these chords, more points can be located in a similar manner. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page

23 After locating T 1 and T, the midpoint D of T 1 T is obtained, by measuring T 1 T. The perpendicular offset DC is set out at D with an optical square and point C is located. Measure T 1 C, and T C, and locate their midpoints d 1 and d. The perpendicular offsets d 1 c 1 and d c are set out at d 1 and d, and the points c 1 and c are established on the curve. The process is continued till sufficient numbers of points on the curve are fixed. Offsets from the Tangents: This method is used when the deflection angle and the radius of curvature both are comparatively small. In this method, the curve is set out by measuring offsets from the tangent. The offsets from the tangent can be either perpendicular or radial to the tangent. a) Perpendicular Offsets Method: Let the point a be on the curve and the perpendicular offset from the tangent T 1 to it at P be Oxa. Let the distance of P from T 1 be xa. Draw a line Qa perpendicular to T 1 O, intersecting OT 1 at Q. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 3

24 Before setting out a curve, a table of offsets for different values of x (e.g., 10 m, 0 m, 30 m, etc.) is made. Then from T1 the distances x 1, x, x 3 etc., are measured along the tangent and the corresponding offsets are measured on the perpendiculars to the tangent with the help of an optical square. Since the offsets of points equidistant from T 1 and T, are equal, the same table is used for offsets from both the tangents. b) Radial Offsets Method: Let the radial offset to the point a on the curve be O xa from the point P at a distance of xa from T 1. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 4

25 A table of offsets for different values of x is made. Then from T 1 the distances x 1, x, x 3 etc., are measured along the tangent and the corresponding radial offsets are measured such that point a etc. on the curve lie on the line joining the point and the centre of the curve. It should be noted that if the curve is set out by the approximate expression, the points on the curve will lie on a parabola and not on the arc of a circle. However, if the versed sine of the curve is less than one-eight of its chord, the curve approximates very closely to a circle. c) Offsets from the Chord Produced: The method has the advantage that not all the land between the tangents points T 1 and T need be accessible. However to have reasonable accuracy the length of the chord chosen should not exceed R/0. The method has a drawback that error in locating is carried forward to other points. This method is based on the premise that for small chords, the chord length is small and approximately equal to the arc length. For setting out the curve, it is divided into a number of chords normally 0 to 30 m in length. For the continuous chainage required along the curve, the two sub-chords are taken, one at the beginning and the other at the end of the curve. The first sub-chord length is such that a full number of chainage is obtained on the curve near T 1 and the second sub-chord length near T. From the property of a circle, if the angle FT 1 a = δ 1 (Figure 9) III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 5

26 The first chord C 1 is called the sub-chord. The length of the sub-chord is so adjusted that the chord length when added to the chainage of T 1 makes the chainage of point a as full chain. Subsequent chord lengths C, C 3, C 4... are full chains. T 1 a is then produced to b such that ab =C, full chain. The second offset O = C (δ 1 +δ ) O = C R where C n-1 is a full chain and C n is the last sub-chord which is normally less than one chain length. III Semester Civil CE04 SURVEYING-I by M.Dinagar AP / Civil Page 6