ACKNOWLEDGEMENTS We, students of IOE, Central Campus, studying in third year/ first part (Civil Engineering) were taken to a Survey Camp...
ACKNOWLEDGEMENTS
We, students of IOE, Central Campus, studying in third year/ first part (Civil Engineering) were taken to a Survey Camp in Tribhuvan University Campus as part of our course. We got experience working in the field. It was good revision of theoretical knowledge of Surveying and a prefect practical practice. We would heartily like to acknowledge Department Of Civil Engineering for including such program in the syllabus. We must recognize the effort of all the staffs who directly or indirectly helped us during the camp.
We are very grateful to Professor .... (HOD), Instructor ..., Instructor ... for their sincere help and appreciation. We would like to express our gratitude to all the non-teaching staffs who helped in managing the camp and guiding us. It would be unfair to forget the immense support from HCOE. We would like to show our appreciation to the Tribhuvan University administration for providing us with the working space for the Survey Camp. Lastly, working together with our colleagues helped us cope with the difficulties in the field easily, we are thankful to all our colleagues.
B.E SURVEY CAMP 2070
Group No.XX
TABLE OF CONTENTS
SECTION I: MAIN REPORT
1. INTRODUCTION
1.1 Objectives of survey camp
1.2 Project area
1.3 Location and accessibility
1.4 Topography and geology
1.5 Rainfall , climate and vegetation
1.6 Others
2. TOPOGRAPHICAL SURVEY
2.1 Objectives
2.2 Brief description of the area
2.3 Norms (Technical specifications)
2.4 Equipment and accessories
2.5 Methodology
2.5.1 Reconnaissance(recce)
2.5.2 Major traverse
2.5.3 Minor traverse
2.5.4 Leveling
2.5.5 Detailing
2.5.6 Resection
2.5.7 Intersection
2.5.8 Computation and plotting
2.5.9 Comments and conclusions
3. BRIDGE SITE SURVEY
3.1 Objectives
3.2 Brief description of the area
3.3 Hydrology, geology and soil
3.4 Norms (Technical specifications)
3.5 Equipment and accessories
3.6 Methodology
3.6.1 Site selection
3.6.2 Topographic survey
3.6.3 Longitudinal section
3.6.4 Cross section
3.6.5 Leveling
3.6.6 Detailing
3.6.7 Computation and plotting
3.6.8 Comments and conclusions
4. ROAD ALIGNMENT AND GEOMETRIC DESIGN
4.1 Brief description of the project area
4.2 Hydrology and geology
4.3 Soil
4.4 Norms (Technical specifications)
4.5 Equipment and accessories
4.6 Methodology
4.6.1 Horizontal alignment
4.6.2 Vertical alignment
4.6.3 Leveling
4.6.4 Longitudinal section
4.6.5 Cross section
4.6.6 Topographical survey of road corridor
4.6.7 Structures
4.6.8 Comments and conclusions
5. CONCLUDING RERMARKS
6. LIST OF TABLES
7. LIST OF DRAWINGS
SECTION II: DRAWINGS
1. INDEX MAP
2. LOCATION MAP
3. WORK SCHEDULE
4. TOPOGRAPHIC MAP
4.1 Drawings of major and minor traverses
4.2 Topographic map of TU ,Kirtipur
5. DRAWINGS OF ROAD AND BRIDGE SITES
5.1 Topographical map of road corridor
5.2 Longitudinal profile of road corridor
5.3 Cross section of road
5.4 Topographical map of bridge site
5.5 Longitudinal profile of river/stream
5.6 Cross section of river/stream
5.7 Drawings of typical structures
6. Bibliography
1. INTRODUCTION
Surveying is the branch of engineering that deals with the art and science of determining the relative positions of distinctive features on or beneath the surface of the earth, by measurements of distances, directions and elevations. The application of surveying requires the knowledge of mathematics, physics, and to some extent, astronomy. It comes first before and during all Engineering works such as designing and construction of highways, water supply systems, irrigation projects, buildings etc.
The B.E. Survey Camp 2070, organized by the Survey Instruction Committee, I.O.E, Pulchowk Campus is a part of the four-year Bachelor's degree in Civil Engineering course, third year first semester, carrying a total of 100 marks. The total duration of the survey camp was 10 days, from 22nd Baisakh to 31st Baisakh, 2071.
Surveying is the main roots for the execution of any civil engineering projects. The science of surveying has been developing since the initial stage of human civilization according to their requirements. The art of surveying preparation of maps has been practiced from the ancient times and the further advanced until present. In the absence of the map, it is impossible to layout the alignments of road, canals tunnels, transmission power line and microwave or television relaying towers and so on. Detailed map of the sites of engineering projects are necessary for the precision establishment of sophisticated instruments. Surveying is the first step for the execution of any project. As the success of any engineering is based upon the accurate and complete survey work, an engineer must therefore be thoroughly familiar with the principle and different methods of surveying and mapping.
For the purpose of water supply-sanitary system, irrigation system, highway designing, the relative altitudes are required, which is ascertained by the process of leveling. The details of the enclosed area and the ground nature can also be portrayed in the combined form of a topographic map. Not only this, the whole land can be surveyed as different areas and can be plotted into a single map, the main thing is not to violate the basic survey principles viz. working from whole to part, consistency in work, accuracy required according to scale and independent check. As a basic part of these principles, horizontal and vertical controls are fixed prior to the work of detailing, while surveying large areas. These necessities are also fulfilled while fixing intersection points for the primary survey on road. For the survey on river, especially for bridge site, the triangulation method is carried over for horizontal control and fixing control station for further references. In addition, for vertical control fly leveling is run to form closed circuit. These all are done very precisely and accurately to achieve the good result. Hence, the work done during the camp duration can be categorized into three main projects:
1. Topographical survey
2. Bridge site survey
3. Road alignment survey
1.1 Objectives of survey camp
The main objective of this survey camp allocated for civil engineering students is to consolidate and update their basic knowledge of different surveying techniques relevant to civil engineering works. Working in actual field conditions enhances their theoretical and practical knowledge and increases their confidence that is beneficial to their professional practice in the near future. The duration of this survey camp enabled a single group of students to perform and prepare reports on:
* Detailed survey of the given area
*Road alignment survey
*Bridge site survey.
Besides, the main objective mentioned above some other objectives can be listed as:
* To familiarize individuals with the concept of team work as surveying is not a one-man game.
* To familiarize students with the parts, functions and handling of surveying instruments and their use in surveying.
* To familiarize students with the problems that are likely to arise during the fieldwork. For e.g. Weather, ground features etc.
* To complete the given project in scheduled time and thus gives students a feel of facing and completing deadlines.
* To collect required data in the field in systematic ways.
* To compute and manipulate the observed data in the required accuracy and present it in diagrammatic and tabular form in such a way that it is understood other engineers easily and gives the layman an idea of what has been done.
Thus, this Survey Camp was organized to give the students an opportunity to feel the difference between theoretical knowledge and practical work and hence develop a quality in them by virtue of which they will be able to make a link between the two different aspects of engineering education.
1.2 Project area
Located only a few kilometers away from the center of Kathmandu, Kirtipur is a place of diverse landforms. Kirtipur meaning the city of glory is a small town in the valley, about five kilometers south-east of the capital, Kathmandu. Kirtipur, also known as Kyapoo is one of the oldest settlements in the valley. Its location is very different from the other main towns of the valley. Kathmandu and Patan are both located in plain areas while Bhaktapur is laid out on gently sloping ground. Kirtipur unlike the others is located on a hilltop and covers almost the whole hill. Tribhuvan University owns the major portions of the area of Kirtipur. The area consists of varying topography ranging from very steep slopes and deep ravines to vast, almost flat grounds.
1.3 Location and accessibility
The major part of our survey camp work was done in the compound of Tribhuwan University. Tribhuvan University (TU), founded in 1959, is Nepal’s first university. Situated in Kirtipur, five kilometers away from Kathmandu, the University offers a wide range of academic programs, including 300 courses at certificate level, 1,079 courses at Bachelor’s level and more than 1,000 courses at Master’s level.
With the rapid development of Katmandu and proximity of the capital to Kirtipur, the town has come under increasing pressure for modern development. It is a farming town. During the 1960’s, the paddy fields to the north east of the town were chosen as the site for Tribhuvan University, and were compulsorily purchased from their owners. With the university, came a new-pitched road and bus transport to the edge of the town. Naya Bazaar, which developed without any planning two decades ago to the south east of the town, at the foot of the hill is now the main commercial center. It is of course unrealistic to stop the development of new areas around Kirtipur but if the growth of Naya Bazaar is not supervised, it may develop to a large unplanned township without appropriate infrastructures. With the development of Naya Bazaar and because of the students commuting to T.U transportation facility in and around Kirtipur is quite developed. There are regular buses running to and from Kirtipur. Thus, our project area was quite suitable and easily accessible.
1.4 Topography and geology
Kirtipur has gently steep topography. It is said that the city is standing on a huge hard rock. Especially the low land below the town is found to be good for the agricultural product. The area contains ground features ranging from step slopes to almost flat grounds. These features were shown by contours. The area also shows a variation in the elevation.
The latitude and longitude of Nepal is as following:
Latitude 26°22¢N to 30°27¢N
Longitude 80°4¢E to 88°12¢E
The latitude and longitude of Kirtipur is as follow:
Latitude 29°53'06”
Longitude 84°55'
1.5 Rainfall, climate and vegetation
The weather condition of Kirtipur was not favourable as it was held in the summer during our survey camp 2070. The day temperature during the camp for most of the days was +30°C.
The climatic conditions during our camp were fine. It was hot during the days and cold in the mornings. The vegetation in Kirtipur is lush and ranges from huge trees to weeds. The main agricultural crop of Kirtipur is paddy. They also grow wheat. The plants that flourish in Kirtipur are the plants and trees that need a lot of water and sun. The trees that are found are pipal, bamboo, sirish. Long grasses also flourish in Kirtipur during this season. Large hedges of neelkanda are also found here. We also saw large patches of touch-me-not or “mimosa pudica” and shrubs of burrs. There were also large trees of camphor and pines. There were also a few Australian pines.
1.6 Others
Kirtipur is one of the oldest settlements in the Kathmandu valley and its history goes back to ancient times. According to the bamsawali of Nepalmandal, Kirtipur was the hometown of the earliest Gopalbamshi kings of the valley. In the Malla period, the people of Kirtipur were known for their skill in building. Kirtipur stone carvers and wood carvers were employed in constructing the monumental structures of the valley. In 1743, King Prithivi Narayan Shah made an attack on Kirtipur with the intention of taking over the valley. At that time, Kirtipur was the gateway to the valley from which gurkhas should enter it and would allow them to occupy the three cities. Hence, Malla kings assisted Kirtipur with all forces. In the battle, which took place near the reservoir at the south west of the town, the gurkhas were defeated. Prithivi Narayan himself had a narrow escape. His famous army commander Kalu Pandey was killed. His sword and shield and the weapons of gurkhas were then hung in the BaghBhairav temple of Kirtipur.
Umamaheswor and BaghBhairav temples are the historic and religious places of Kirtipur. Panga and Chovar are the neighboring villages. The newly constructed Buddhist monasteries at Naya Bazaar can attract everybody. From there, a beautiful view of Lalitpur can be seen.
2. TOPOGRAPHICAL SURVEY
Topographical surveying is the determining of the positions of natural and artificial features on both plan and elevation. In other words determining the configuration (relief) of the earth’s surface and to locate natural and cultural features on it is topographical survey. From the survey data, topographic maps that depict these natural and cultural features are produced using various types of lines and conventional symbols. Topographic is simply the graphical representation of positions of the earth’s surface
2.1 Objectives
The map is on sufficiently large scale to enable the individual features shown on the map to be identified on the ground by their shapes and positions is known as topographic map.
The main Objective of topographical survey is to prepare the topographic map of the given area with horizontal control and vertical control on required accuracy.
2.2 Brief description of the area
The area, where topographic survey was performed, is situated at Tribhuwan University, Kirtipur. The major traverse ran around the university area. Our job was to prepare a topographic map of the whole university. Our group i.e. group #32 had to complete the topographic survey of plot no.1 and minor plot no.5, on which we had to do detailing. Plot no.1, actually was the most attractive and important area of the university. Gandhi Bhawan, Department of Physics, Chemistry, Geology, Hydrology, Arts, Fine arts, management and Central library were near our plot area. Our plot also included a steep terrain and woody lands.
2.3 Norms (Technical specifications)
1. Conduct reconnaissance survey of the given area. Form a close traverse (major and minor) around the perimeter of the area by making traverse stations. In the selection of the traverse station, make sure that the stations are inter visible and maintain the ratio of maximum traverse leg to minimum traverse leg 3:1 for minor traverse and 1:2 in the case of major traverse.
2. Measure the traverse legs in the forward and reverse directions by means of a tape calibrated against the standard length provided in the field, note that discrepancy between forward and backward measurements should be greater than 1:2000.
3. In case of distance measurement by total station in both forward and backward direction the precision of 1:5000 in case of major traverse and 1:3000 in case of minor traverse should be maintained.
4. Measure traverse angle on two sets of reading by total station. Note the difference between the mean angles of two sets reading should be within 20 seconds.
5. Determine the R.L. of traverse stations by fly leveling from the given arbitrary T.B.M. 2 to T.B.M. 3 Perform two-peg test before the start of fly leveling. Note that collimation error should be less than 1:10000. Maintain equal fore sight and back sight distances to eliminate collimation error. Permissible error for fly leveling is ±25√k mm, where k is the distance in kilometer.
6. R.L. of TBM2 =1291.851
7. R.L. of TBM3 = 1312.924
8. Balance the traverse. The permissible angular error for the sum of interior angles of the traverse should be less than ±30"√n and ±1°√n for major and minor traverse respectively. For major and minor traverse, the relative closing error should be less than 1:5000 and 1:3000 respectively.
9. Plot the major and minor traverse stations by coordinate method in appropriate scale (1:1000, 1:500 respectively).
10. Carry out the detail survey of the given sub area by total station and tacheometric surveying with reference to the major and minor traverse, which have been already plotted. Use conventional symbols for plotting.
2.4 Equipment and accessories
1. Total station 2. Reflector, prism & prism pole 3. Auto level
4. Plumb bob 5. Staffs and ranging rods 6. Hammer 7. Tapes 8. Nails and pegs
2.5 Methodology
The methodology of surveying is based on the principle of surveying that is work should be done from whole to part with independent checks. The work done should be accurate and consistent.
2.5.1 Reconnaissance [recce]
Recce means the exploration or scouting of an area. In survey, it involves walking around the survey area and roughly planning the number of stations and the position of the traverse stations. Recce is primarily done to get an overall idea of the site. This helps to make the necessary observations regarding the total area, type of land, topography, vegetation, climate, geology and inter visibility conditions that help in detailed planning. The following points have to be taken into consideration for fixing traverse stations:
* The adjacent stations should be clearly inter visible
* The whole area should include the least number of stations possible.
* The traverse station should maintain the ratio of maximum traverse leg to minimum traverse leg less than 2:1.
* The steep slopes and badly broken ground should be avoided as far as possible, which may cause inaccuracy in tapping.
* The stations should provide minimum level surface required for setting up the instrument.
* The traverse line of sight should not be near the ground level to avoid the refraction.
Taking the above given points into consideration, the traverse stations were fixed. Then two way taping was done for each traverse leg. Thus, permanent fixing of the control points completes recce.
2.5.2 Major Traverse
Traversing is a type of survey in which a number of connected survey lines form a framework enclosing the area to be surveyed. Working from whole to part is the principle. So, the whole area is enclosed by number of control points of which details are necessary. The skeleton of lines joining those control points, which covers the whole entire area, is called Major Traverse. Work on Major traverse must be precise. So two-set of reading should be taken for Major Traverse. For convenience, the readings are taken by setting the theodolite at 0°0’0” for one set and 90°00’00” for the second set.
In the Kirtipur Survey Camp, two traverses - major and minor had to be established. The major traverse had 17 control stations including two given control points. The control stations were named as CP1 and CP2. The leg ratio of maximum traverse leg to minimum traverse leg was maintained within 1:2. The discrepancy in length between the forward measurements and the backward measurements of all the traverse legs was within 1:5000. Two sets of theodolite readings were taken for measuring the horizontal traverse angles. The difference between the mean angles of two sets of readings was within a minute for all the angles. The angular error for the sum of interior angles of thetraverse was less than ±30"√17. The relative closing error for the major traverse was 1:15637.282 i.e. greater than 1:5000. Finally, the major traverse was plotted by the coordinate method in a scale of 1:1000 on an A1 size drawing paper with grid lines provided by the survey instruction committee.
2.5.3 Minor Traverse
It is not sufficient to detail the area by enclosing with the help of major traverse. Minor traverse is that one which runs through the area to make detailing easy. Minor Traverse covers only small area. Less precise work than that of major traverse is acceptable so that single set reading is sufficient for minor traverse. The minor traverse had 3 major stations and 11 minor stations. The control stations were named as 32m1, 32m2 and so on. The leg ratio of maximum traverse leg to minimum traverse leg was maintained within 1:3. The discrepancy in length between the forward measurements and the backward measurements of all the traverse legs was within 1:3000. One set of total station readings was taken for measuring the horizontal traverse angles. The relative closing error for the minor traverse was 1: 9212.367 & 1:11226.333 in two loop of minor traverse, which was nearly equal to or more than 1:3000. Finally, the minor traverse was plotted by the coordinate method in a scale of 1:500 on an A1 size drawing paper with grid lines.
2.5.4 Leveling
Leveling is a branch of surveying the objective of which is to
(i) Find the elevations of given points with respect to a given or assumed datum and
(ii) Establish points at a given elevation or at different elevations with respect to a given or assumed datum.
The first operation is required to enable the works to be designed while the second operation is required in the setting out of all kinds of engineering works. Leveling deals with measurements in a vertical plane. To provide vertical control in topographic map, the elevations of the relevant points must be known so that complete topography of the area can be explored. Leveling was performed to determine the elevation (relative height from a given datum)
Two types of leveling were performed at the site, namely direct leveling (spirit leveling) and indirect leveling (trigonometric leveling).
1. Direct leveling: It is the branch of leveling in which the vertical distances with respect to a horizontal line (perpendicular to the direction of gravity) may be used to determine the relative difference in elevation between two adjacent points. A level provides horizontal line of sight, i.e. a line tangential to a level surface at the point where the instrument stands. The difference in elevation between two points is the vertical distance between two level lines. With a level set up at any place, the difference in elevation between any two points within proper lengths of sight is given by the difference between the rod readings taken on these points. By a succession of instrument stations and related readings, the difference in elevation between widely separated points is thus obtained.
Following are some special methods of direct (spirit) leveling:
1.1. Differential leveling: It is the method of direct leveling the object of which is solely to determine the difference in elevation of two points regardless of the horizontal positions of the points with respect of each other. This type of leveling is also known as fly leveling.
1.2. Profile leveling: It is the method of direct leveling the object of which is to determine the elevations of points at measured intervals along a given line in order to obtain a profile of the surface along that line.
1.3. Cross-sectioning: Cross-sectioning or cross leveling is the process of taking levels on each side of main line at right angles to that line, in order to determine a vertical cross-section of the surface of the ground, or of underlying strata, or of both.
1.4. Reciprocal leveling: It is the method of leveling in which the difference in elevation between two points is accurately determined by two sets of reciprocal observations when it is not possible to set up the level between the two points.
2. Indirect leveling: Indirect method or trigonometric leveling is the process of leveling in which the elevations of points are computed from the vertical angles and horizontal distances measured in the field, just as the length of any side in any triangle can be computed from proper trigonometric relations.
Temporary adjustments of Level
The temporary adjustment for a level consists of the following:
1. Setting up the level: The operation of setting up includes fixing the instrument on the stand and leveling the instrument approximately.
2. Leveling up: Accurate leveling is done with the help of foot screws and with reference to the plate levels. The purpose of leveling is to make the vertical axis truly vertical. It can be done by adjusting the screws.
3. Removal of parallax: Parallax is a condition when the image formed by the objective is not in the plane of the cross hairs. Parallax is eliminated by focusing the eyepiece for distinct vision of the cross hairs and by focusing the objective to bring the image of the object in the plane of cross hairs.
Permanent adjustments of Level
To check for the permanent adjustments of level two-peg test method should be performed.
Two staffs were placed at A and B of known length (about 50 m). First, the instrument was setup at the middle point C and both staff readings were taken. Then the machine was held near A and both staff readings (Top, Middle, and Bottom) were taken.
The precision obtained in both sets were greater than that of required precision of 1 in 10000. Therefore, the permanent adjustment was not required.
There are two methods of booking and reducing the elevation of points from the observed staff reading:
1. Height of the Instrument method
Arithmetic Check:
SBS – SF.S. = Last R.L. – First R.L.
Rise and Fall method
Arithmetic Check:
SBS – SF.S. = SRise –SFall = Last R.L. – First R.L.
Among the two Methods Height of instrument, method is widely used. After checking the accuracy of the level by two-peg test, fly leveling was performed between temporary benchmark 2 (TBM2) and temporary benchmark3(TBM3). The closing error was found to be 2 mm which was within the permissible error of ±25Ök = 21.064 mm.
The R. L of TBM3 was then transferred to the control stations of the minor traverse. The closing error was found within the permissible limits. Then the linear and angular adjustments were made in each leg.
All the necessary data and calculations are presented in the following pages in this report.
2.5.5 Detailing
Detailing means locating and plotting relief in a topographic map. Detailing can be done by either plane table surveying or tachometric surveying. Plane tabling needs less office work than tachometric survey. Nevertheless, during our camp, we used the tacheometric method, tangential method and total station method.
* Detailing by total station
On the process of detailing by total station we used reflector prism and hence total station gave the horizontal angle and hor. Dist and vert. distance directly.
* Tachometry
Tachometry is a branch of angular surveying in which the horizontal and vertical distances of points are obtained by optical means. Though it only has accuracy about 1/300 to 1/500, it is faster and convenient than the measurements by tape or chain. It is very suitable for steep or broken ground, deep ravines, and stretches of water or swamp where taping is impossible and unreliable.
The objective of the tachometric survey is to prepare contour maps or plans with both horizontal and verticalcontrols. For the survey of high accuracy, it provides a check on the distances measured by tape.
The formula for the horizontal distance is
H=100 x S x Cos2q
The formula for the vertical distance is
V = 100 x S x (Sin2q)/2
Where, S = staff intercept; q = Vertical Angle
If the angle used is zenithal angle then
H=100 x S x sin2q
V = 100 x S x (Sin2q)/2
Where, q=zenithal angle
* Detailing by tangential method
In this method we have to take two middle staff reading, with 2 different vertical angle along with horizontal angle with any traverse leg. We use the formula :
S=difference in staff reading
H=S/(tan(90-θ1)-tan(90-θ2))
V=Htan(90-θ2) ;where,θ1 is smaller zenithal angle and
θ2 is bigger zenithal angle.
Contouring
A contour is an imaginary line, which passes through the points of equal elevation. It is a line in which the surface of ground is intersected by a level surface. A contour line is a line on the map representing a contour. It represents the elevation and is one of the ways of representing relief. While drawing the contour lines, the characteristics of the contours should be considered. The characteristics are as follows:
¤ Two contours of different elevations do not cross each other except in the case of an overhanging cliff.
¤ Contours of different elevations do not unite to form one contour except in the case of a vertical cliff.
¤ Contours drawn closer depict a steep slope and if drawn apart, represent a gentle slope.
¤ Contours equally spaced depict a uniform slope. When contours are parallel, equidistant and straight, these represent an inclined plane surface.
¤ Contour at any point is perpendicular to the line of the steepest slope at the point.
¤ A contour line must close itself but need not be necessarily within the limits of the map itself.
¤ A set ring contours with higher values inside depict a hill whereas a set of ring contours with lower values inside depict a pond or a depression without an outlet.
¤ When contours cross a ridge or V-shaped valley, they form sharp V-shapes across them. Contours represent a ridge line, if the concavity of higher value contour lies towards the next lower value contour and on the other hand these represent a valley if the concavity of the lower value contour, lies towards the higher value contours.
¤ The same contour must appear on both the sides of a ridge or a valley.
¤ Contours do not have sharp turnings.
Taking the reading at the change point on the ground is the indirect method of locating contours. The interpolation method is used to draw the contour lines. Interpolation of contours is done by estimation, by arithmetic calculations or by graphical method. The eye estimation method is extremely rough and is used for small-scale work only. Generally, arithmetic calculation method of interpolation is used to draw the contour lines and it is performed as follows:
Distance of contour point from the lower elevation point = (H/V) x v
where,
H=Horizontal distance between two guide points
V=vertical distance between two guide points
v=vertical distance between lower elevation point and the point to be located
The following steps were followed in tachometric survey:
The instrument was set up over the station and centering/leveling was done accurately.
The vertical distance from the top of the station peg to the center of trunion axis of tachometer was measured.
The instrument was oriented with reference to a fixed station whose distance and bearing was predetermined.
The staff was held vertically at the nearest available benchmark and it was sighted by the tachometer to determine the reduced level of the starting point.
The staff was held at point of feature to be detailed.
Horizontal angle between the reference station and the object point was measured.
The vertical angle to the central horizontal wire was observed.
The staff readings of the stadia hair were observed.
Same procedures were repeated for all the stations.
2.5.6 Resection :
Resection is the determination of the observer’s position by means of observations taken to previously fixed points. There are several methods of resection and they include:
1. Observing horizontal angles from the unknown point to three known points.
2. Observing horizontal angles from two unknown points to two known points.
3. Observing horizontal angles from one unknown point to two known points when the Azimuth of one of them is known.
In the camp we had adopt first method i.e. resection by observing horizontal angles from the unknown point to three known points.
2.5.7 Intersection
A minimum of two control stations is required for this operation, with the unknown point visible from each of them. It is not essential that the control stations are inter-visible, but it makes it easier if they are. Clearly, the co-ordinates of the control stations will be known (otherwise they would not be control stations!) so that the distance between them can be calculated. The position is illustrated in the following diagram:
b
unknown P
point
Figure 1. Sightings and angles measured for intersection.
The theodolite is set up at each of the stations (control points) A and B in turn. At station A, the telescope is first sighted on B and then transited round to P, measuring the angle a. Similarly, at B the angle b between line BA and line BP. Note that the theodolite is not set up at the unknown point P. For this reason, intersection is used for the positioning of points over which it is difficult or impossible to set up the theodolite, for example,
· surveying points high up on buildings, perhaps for later use as reference objects,
· measurement of the deflection of large structures (e.g. dams, bridges)
· setting out of curves.
Because we know the co-ordinates of stations A and B, and because we know that the sum of the internal angles in the triangle must equal 180°, we can calculate the following:
Bearing of line AB = tan-1 (DE / DN)
Angle p = 180° - a – b
Further calculation allows us to find the length and bearing of each of the lines AP and BP:
Sine Rule: AB = AP = BP
and
bearing AP = bearing AB + a
bearing BP = bearing BA – b
Note that angle b is anticlockwise from BA to BP, hence the negative sign in the above equation.
Once we have the bearing and length of lines AP and BP then the co-ordinates of P can be calculated from each line. These two sets of co-ordinates should correspond within the expected degree of accuracy.
2.5.8 Computations and Plotting
For the calculations as well as plotting, we applied the coordinate method (latitude and departure method). In this method, two terms latitude and departure are used for calculation. Latitude of a survey line may be defined as its coordinate lengths measured parallel to an assumed meridian direction. The latitude (L) of a line is positive when measured towards north, and termed Northing and it is negative when measured towards south, and termed Southing. The departure (D) of a line is positive when measured towards east, and termed Easting and it is negative when measured towards west, and termed Westing. The latitude and departures of each control station can be calculated using the relation:
Latitude = l Cosq
Departure = l Sinq
Where, l=distance of the traverse legs
q=Whole circle bearing
If a closed traverse is plotted according to the field measurements, the end of the traverse will not coincide exactly with the starting point. Such and error is known as closing error.
Mathematically,
Closing error (e) = √ {(SL)2 + (SD)2 } and
Direction, tan θ = S D/SL
The sign of SL and SD will thus define the quadrant in which the closing error lies. The relative error of closure = Error of Closure / Perimeter of the traverse
= e / p
= 1 / (p / e)
In a closed traverse, by geometry, the sum of the interior angles should be equal to (2n-4) x 90˚ where n is the number of traverse sides. If the angles are measured with the same degree of precision, the error in the sum of the angles may be distributed equally among each angle of the traverse.
The Bowditch’s method or the compass rule is mostly used to balance a traverse where linear and angular measurements are of equal precision. The total error in latitude and in the departure is distributed in proportion to the lengths of the sides.
Mathematically,
a) Correction in departure of a side of traverse
= (Total departure misclosure / traverse perimeter) x length of that side
b) Correction in latitude of a side of traverse
= (Total latitude misclosure / traverse perimeter) x length of that side
In order to measure the lengths of the sides of the traverse, two way taping (forward and backward) was done. The difference in values obtained by forward and backward taping is called discrepancy. In addition, the reciprocal of the discrepancy divided by the mean of the two measurements is called precision. Both the discrepancy and the precision for each traverse leg should be within the given limits.
Mathematically,
Discrepancy = | Forward length - Backward length |
and, Linear precision = 1 / (Mean length / Discrepancy)
The coordinates of traverse stations were found out by resection.
2.5.9 COMMENTS AND CONCLUSION
COMMENTS:
The site for the survey camping was the campus area of TU, Kirtipur. The site was very much suitable for performing various type of surveying.
The arrangements of the survey instruments was not satisfactory as there were many faulty instruments which hampered us from running our survey works smoothly and correctly in less time. Due to limited number of subtense bar we had to wait for our turn. The lodging and fooding facilities were not up to the task.
We hope that above mentioned problems will be solved and the up coming camps will run smoothly without any problems.
CONCLUSION:
The work of the survey camp was finished within the allotted period of 10 days. Surveying is a subject which is based on not only theory but a lot of practical. Thus this camp helped us a lot in understanding the principles and techniques of surveying. The camp also helped us to work in group. This camp will help us in our future.
The whole area of TU was divided into two number of plots. A group had to complete a single plot following the routine provided. The topographic maps of several plots such prepared can be then mosaics to form a single map of the whole area.
Thus we completed our project by following given norms and technical specifications within the time allocated.
3. BRIDGE SITE SURVEY
Bridges are the structures that are constructed with the purpose of connecting two places separated by deep valleys or gorges or rivers and streams. Bridges are usually a part of road; making them shorter and hence economical. In countries like Nepal, where the land is undulated and where there are plenty of rivers, bridges are the most economic and efficient way to join two places. It is a very convenient way. That is why the task of bridge site surveying has been included in the curriculum of Bachelor's degree in Civil Engineering at Pulchowk Campus, IOE.
This part of the Survey Camp dealt with the bridge site survey done at Kirtipur. It was done at a place where a small stream flowed. It was located in the woods where two hill slopes formed a deep ravine. The duration of the survey was 2 days.
3.1 Objectives
Bridge construction is an important aspect in the development of transportation network. For the construction of bridge, surveying is required for topographical mapping; while the knowledge of longitudinal section of the river and cross- sections at both the upstream and downstream is essential. The river flow level in different seasons should also be taken into consideration before designing a bridge.
Bridge surveying is necessary to locate a site, obtain information for design, and furnish lines and grades for construction. A reconnaissance survey is made at all possible sites. A preliminary survey is made at the best site to establish horizontal and vertical control and to obtain information for the bridge design and construction planning.
The main objective of the bridge site survey is to give the students the preliminary knowledge on selection and planning of possible bridge site for the future construction of bridge. The purpose of the bridge site survey was not only to prepare plan and layout of the bridge site but also to collect the preliminary data about the site. The data should include normal water flow, high flood level, and geological features of the ground for planning and designing of the bridge from the details taken during the surveying. The details must be taken from an engineering point of view.
The other objectives of Bridge site survey are:
* To find the best location for a bridge over the river considering factors like convenience, economic and geological stability.
* To use triangulation method for the calculation of the bridge axis length.
* To take sufficient data of the details including the spot heights, around the bridge in order to prepare a topographical map of the area, cross section of the river at certain intervals and longitudinal section of the river.
* To determine the physical properties of the river like its discharge, velocity of water, bed slope, etc.
3.2 Brief Description of the area
Bridge site survey was conducted over a small rain stream on the T.U campus area. The stream flows through a ravine formed by two hill slopes. Our site was near the basketball court. The site was mossy and swampy. No huge boulders are to be found near the site. It was damp and hilly.
3.3 Hydrology, Geology and Soil
The site was surrounded by trees and bushes. There were no rocks. The ground was damp and swampy. The soil was soft and clayey. It was brown in colour. The hill slopes on both sides are not very steep and are thus geologically stable. There is not much water to be found on the bridge site. The only water is collected from rain and other sources.
3.4 Norms (Technical Specifications)
The following norms were followed while performing the bridge site survey:
* Control point fixing as well as determining the length of the bridge axis had to be done by the method of triangulation. While forming triangles, proper care had to be taken such that the triangles were well conditioned, i.e. none of the angles of the triangle were greater than 120° or less than 30°.
* The triangulation angle had to be measured on two sets of readings by theodolite and the difference between the mean angles of two sets of readings had to be within a minute.
* Transferring the level from one bank to another bank had to be done by the method of reciprocal leveling.
* The scale for plotting the topographical map was given to be 1:500
* In order to plot the longitudinal section of the river, data had to be taken along the riverbed 150 m upstream and at least 50 m downstream. The plot for the longitudinal section along the flow line had to be done in a scale of 1:100 for vertical and 1:500 for horizontal.
* For the cross section profile, data had to be taken at 25 m intervals both upstream and downstream, and one at the bridge axis. Observation had to cover about 20 m beyond the bank of river on either side. The scale being 1:100 for both vertical and horizontal directions.
3.5 Equipment and accessories
1. Theodolite or total station 2. Staffs, reflector prism and pole 3. Ranging rods 4. Tapes 5. Plumb bob 6. Level 7. Compass 8. Hammer
9. Sickle 10.Nails and pegs 11.Abney level
3.6 Methodology
The various methods performed during the bridge site survey were triangulation, Leveling, tachometry, cross section, and L-section. The brief descriptions of these methodologies are given below:
3.6.1 Site Selection
Tentative bridge sites are selected by reconnaissance and the more promising ones are reconnoitered in detail. The selection of a bridge site is governed by both tactical and technical considerations. Tactical requirements fix the general area for the bridge site. Technical requirements fix the exact location and may sometimes eliminate sites that have been tactically acceptable. For permanent construction, technical considerations govern the bridge location.
There were various factors for the selection of bridge site such as geological condition, economical aspect etc. Therefore, the site was chosen such that it should be formed on very stable hill slope. The bridge should be located at the straight path of river and at the same time, the river width should not be narrow from the economical point of view. In our case, it was assumed that the approximate alignment of bridge axis has already been established with regard to geo-technical site investigation. For the purpose of the shortest span the stations were set perpendicular to the river flows direction. The riverbanks are not eroded and are suitable for bridge construction. The site for the proposed bridge was selected at a location where a bend in the road continued smoothly into the bridge. The location of the bridge was selected in such a way that the heights of the roads joined by the proposed bridge were almost the same. This prevented a lot of cutting and filling to maintain a gentle gradient.
3.6.2 Topographic Survey
For the topographic survey of bridge site, triangulation was done. The main purpose of the triangulation was to determine the length of the bridge axis. The triangulation also serves the control points for detailing. First, the bridge axis was set and horizontal control stations were fixed on either side. Distances between stations on the same sides of river i.e. b`ase lines were measured with tape precisely. Then the interconnecting triangles were formed and angles were measured with a theodolite with two sets. The bridge axis length or span was calculated by solving the triangles using the sine rule. Thus, the horizontal control was set out.
For vertical control, the level was transferred from the arbitrary benchmark and RL was transferred to the stations on the next bank by reciprocal leveling while direct level transfer method was used for the same bank.
3.6.3 Longitudinal Section
The L-Section of the river is required to give an idea about the bed slope, nature of the riverbed, and the variation in the elevations of the different points along the length of the river. Keeping the instrument at the control (traverse) stations on the river banks, the staff readings were taken at different points along the center line of the river at an interval of about 25 m up to a 100 meters upstream and 50 m downstream. The R.Ls of the traverse stations being known previously, the levels of the different points on the river were calculated. Then the L-Section of the riverbed was plotted on a graph paper on scale for vertical and horizontal.
3.6.4 Cross Section
Cross-section of a river at a particular point is the profile of the lateral sides from the centerline of the river cut transverse to the L-Section at that point. The cross section can be used to calculate the volume and discharge of water at the particular section if the velocity at the cross section is known. Cross sections were taken at an interval of about 25 m extending 100 m upstream and 50 m downstream of the river. Staff readings of points along a line perpendicular to the flow of river were taken from the stations points and the elevations of the points were calculated using tachometric methods. At some places where tachometric methods were not suitable or feasible, the "danda" method was also applied. With all the calculations done and the required data in hand, the cross section was plotted on a graph paper on required scale.
3.6.5 Leveling
Level transfer was done in two steps - firstly to transfer the R.L. from the given B.M. to any traverse station, and secondly to transfer the R.L. from that traverse station to all other stations as well as all the detailed objects (detailing). The R.L. of TBM3= 1312.924 m. The R.L. was transferred by fly leveling from the B.M. to a station using a level, forming a closed loop and making the necessary adjustments. Then fly leveling was done in order to transfer the level from that station to all the other stations of the traverse.
The principal of differential leveling is when the instrument is kept equidistant from the back and forward staff stations, the difference in elevation of the two stations is equal to the difference of the staff readings. In addition, it can be achieved by placing the machine midway of the staffs. When it is not possible to set up the level midway between two points as in the case of leveling across large water bodies, the reciprocal leveling is employed to carry forward the level on the other side of the obstruction.
When it is necessary to carry leveling across a river, ravine or any obstacle requiring a long sight between two points so situated that no place for the level can be found from which the lengths of foresight and back sight will be even approximately equal, reciprocal leveling is done. Reciprocal leveling helps to eliminate errors such as error in instrument adjustment, combined effect of earth's curvature and the refraction of the atmosphere and variations in the average refraction.
Fig.: Reciprocal Leveling
Where,
When theodolite is kept near staff held at A
ha= staff reading at station A
hb= staff reading at station B
When theodolite is kept near staff held at B
ha'= staff reading at station A
hb'= staff reading at station B
Then, the true difference in elevation between the two stations A and B is given by
H=½ x [(ha - hb) + (ha'- hb')]
3.6.6 Detailing
Detailing of the entire bridge site was done by tachometric method, the readings being taken with a theodolite stationed at the different traverse stations. The detailing was done with respect to the skeleton formed by triangulation. The vertices of triangles serve as a control point. With the help of tachometer, the details were booked, up to 100m upstream and 50m downstream. The important details not included in the cross-section data, were taken. Trigonometric Leveling was also done to find out the RL of the inaccessible points. Abney level was used to find out the slope of cliff. The data and the calculations have been tabulated in a systematic way.
3.6.7 Computation and Plotting
The following tachometric formulas were used for the calculation of the horizontal distance and R.L. of different points:
Horizontal distance of any point from the traverse station,
H = 100 x S x Cos2θ
Where, S = Staff intercept = Top - Bottom stadia reading
θ = Vertical Angle
The topographic map, the longitudinal section and the cross section were plotted on the respective scales after the completion of calculations. Control stations were plotted accurately in the grid paper. Then all hard details as well as contours were plotted with reference to the control stations by the method of angle and distances.
3.6.8 Comments and Conclusions
The bridge site survey was performed to gain idea for selecting the bridge axis. Triangulation was performed to get the length of the proposed bridge. For triangulation, we chose two stations in one bank and two stations on the next bank. The distance between the two stations was calculated by taping. Similarly, the cross-section and longitudinal section were performed. The X-section was performed at the interval of 25m.The longitudinal section was about 100m upstream and 50m downstream. In addition, details were taken from the respective stations. The details of existing structures like walls, cliff, bridge, boulders etc were taken. The cross-section was taken at the banks of river and at the middle of the river to get the profile of the flowing river. In addition, we marked the high flood level and low flood level. Similarly, we transferred the reduced levels of the stations from the known benchmark.
4. Road Alignment and Geometric Design
Roads are specially prepared ways connecting different places for the transportation of vehicles, people and animals. In countries like Nepal, where there are less chances of airways and almost negligible chances of waterway, roads form a major part of the transportation system. Therefore, it would not be an exaggeration in saying that the roads have an utmost importance.
This part of the Survey Camp dealt with the road alignment survey done at Kirtipur in T.U facility. The duration of the survey was three days, bridge site alignment being done simultaneously.
4.1 Brief Description of the Project area
Road alignment is an important aspect in the development of the transportation network of the country. Road alignment is important part of the survey. Road alignment and bridge site survey goes side by side to run a road between two terminals and to carry a survey for the bridge construction along the route. This specific job is essential for an engineer combating with the mountainous topography of Nepal.
The place where we complete this project had no road so we made an imaginary road branching starting from the bridge to the tower about 1000m away in the North West, through the area dense with trees, sloppy terrain, terrace and a culvert.
4.2 Hydrology and Geology
The road had to go along a damp route that was much undulated. The place was damp. There were no large boulders or rocks of any kind along the proposed site.
4.3 Soil
When the soil surface is inclined, there is a component of gravity that tends to move the soil downward. If along the potential slip surface in the soil the stress produced by gravity exceeds the shear strength of the soil along the potential failure surface, the slope will become unstable. Obviously, the shear strength of soil is largely depends upon the type of soil. Cohesive soil has more shear strength than others do. The hard and dense soil is best for slopes.
We found soft clayey soil that was very damp. Other kinds of soils were not found along our proposed route.
4.4 Norms (Technical Specifications)
Recce alignment selection was carried out of the road corridor considering permissible gradient (12%), obligatory points, bridge site and geometry of tentative horizontal and vertical curves.
The road setting horizontal curve, cross sectional detail in 15m interval and longitudinal profile were prepared.
The topographic map (scale 1:1000) of road corridor was prepared. Geometric curves, road formation width, right of way, crossings and other details were shown in the map.
While performing the road alignment survey, the following norms were strictly followed:
* The road had to be designed starting at base point of the bridge and ending at the electrical tower(middle one) located in the North West.
* If the external deflection angle at the I.P. of the road is less than 3°, curves need not be fitted.
* Simple horizontal curves had to be laid out where the road changed its direction, determining and pegging three points on the curve - the beginning of the curve, the middle point of the curve and the end of the curve along the centerline of the road.
* The radius of the curve had to be chosen such that it was convenient and safe.
* The gradient of the road had to be maintained below 12 %.
* Cross sections had to be taken at 15 m intervals and at the beginning, middle and ends of the curve, along the centerline of the road - observations being taken for at least 10 m on either side of the centerline.
* Plan of the road had to be prepared on a scale of 1:1000
* L-Section of the road had to be plotted on a scale of 1:1000 horizontally and 1:100 vertically.
* The cross section of the road had to be plotted on a scale of 1:100 (both vertical and horizontal).
* The amount of cutting and filling required for the road construction had to be determined from the L-Section and the cross sections. However, the volume of cutting had to be roughly equal to the volume of filling.
4.5 Equipments and accessories
1. Theodolite 2.staff 3. Ranging rods 4.Abney level
5. Tapes 6.Plumb bob 7. Level 8.Compass
9. Hammer 10.Sickle 11.Nails and pegs
4.6 Methodology
4.6.1 Horizontal Alignment
Horizontal alignment is done for fixing the road direction in horizontal plane. For this, the bearing of initial line connecting two initial stations was measured using compass. The interior angles were observed using 6’' Theodolite at each IP and then deflection angles were calculated.
Deflection angle, D = 180 - interior angle
If +ve, the survey line deflects right (clockwise) with the prolongation of preceding line and deflects left if –ve (anti-clockwise). The radius was assumed according to the deflection angle. Then the tangent length, EC, BC, apex distance along with their chainage were found by using following formulae,
Tangent length (T L) = R x tan(D/2 )
Length of curve (L.C) = 3.142 x R x D/180
Apex distance = R x 1/(Cos(D/2)-1)
Chainage of BC = Chainage of IP – TL
Chainage of MC = Chainage of BC +LC/2
Chainage of EC = Chainage of MC + LC/2
The BC and EC points were located along the line by measuring the tangent length from the apex and the points were marked distinctly. The radius was chosen such that the tangent does not overlap. The apex was fixed at the length of apex distance from IP along the line bisecting the interior angle.
4.6.2 Vertical Alignment
Vertical profile of the Road alignment is known by the vertical alignment. In the L-section of the Road alignment, vertical alignment was plotted with maximum gradient of 12 %. According to Nepal Road Standard, Gradient of the Road cannot be taken more than 12 %. In the vertical alignment, we set the vertical curve with proper design. Vertical curve may be either summit curve or valley curve. While setting the vertical alignment, it should keep in mind whether cutting and filling were balanced or not.
4.6.3 Leveling
The R.L. of the T.B.M.3 was given to be 1312.924 m. The method of fly leveling was applied in transferring the level from the given B.M. to all the I.Ps, beginnings, mid points and ends of the curves as well as to the points along the center line of the road where the cross sections were taken. After completing the work of one way leveling on the entire length of the road, fly leveling was continued back to the B.M. making a closed loop for check and adjustment. The difference in the R.L. of the B.M. before and after forming the loops should be less than 25√ k mm, where k is the total distance in km. In our case, the value of k was within the permissible limit.
4.6.4 Longitudinal Section
The L-Section of the road is required to give the road engineer an idea about the nature of the ground and the variation in the elevations of the different points along the length of the road and also to determine the amount of cutting and filling required at the road site for maintaining a gentle slope. In order to obtain the data for L-Section, staff readings were taken at points at 15m intervals along the centerline of the road with the help of a level by the method of fly leveling. Thus after performing the necessary calculations, the level was transferred to all those points with respect to the R.L. of the given B.M. Then finally the L-Section of the road was plotted on a graph paper on a vertical scale of 1:100 and a horizontal scale of 1:1000. The staff readings at BC, EC and apex were also taken. The RL of each point were calculated.
4.6.5 Cross Section
Cross sections at different points are drawn perpendicular to the longitudinal section of the road on either side of its centerline in order to present the lateral outline of the ground. Cross sections are also equally useful in determining the amount of cut and fill required for the road construction. Cross sections were taken at 15m intervals along the centerline of the road and at points where there was a sharp change in the elevation. While doing so, the horizontal distances of the different points from the centerline were measured with the help of a tape and the vertical heights with a measuring staff. The R.L. was transferred to all the points by performing the necessary calculations and finally, the cross sections at different sections were plotted on a graph paper on a scale of 1:100 - both vertical and horizontal.
Cross section was run at right angles to the longitudinal profile on either side up to 10m distances and the change in the slope was directly measured using the staff. The method is locally named as Danda method.
4.6.6 Topographic survey of road corridor
Topographic survey of road corridor was done by taking the deflection angle at each point where two straight roads meet. The chainage of intersection point, tangent point and middle points were also taken by taping and applying formula. The staff readings of each of these points were also taken. The R.L was also transferred to find out the elevation and plot it in a map.
4.6.7 Structures
The main structures provided for road constructions are retaining structures, cross drain, side drain, bio-engineering structures etc. retaining structures are provided where the slope is critical. Gabion structure, dry masonry structures are the example. The cross drainage is provided at the interval of 150 to 200m of road mostly at the valley and where ever necessary. Causeways, culverts and bridges are the example of cross drainage. The side drain is the channel by which the pavement can be protected from the surface water. It is usually constructed along the road just below the cut slope. The collected water is drained off by the means of cross drainage.
4.6.8 Comments and Conclusions
In spite of the different kinds of obstacles in the field, our group was successful in completing the fieldwork as well as the office work in time. In the field, we had spent quite some time discussing the route of the road and in designing the curves, which led to good results. The road had to be designed on a sloping ground, so our group members felt the restrictions during the cutting and filling and for the construction of different retaining structures.
Moreover, after performing this road alignment survey, we were able to gain confidence in designing roads at difficult terrain taking factors like economy, convenience and its use into consideration.
5. Concluding Remarks
Hence, we completed the three projects assigned to us in time although we faced minor difficulties. All results we obtained were within the limits given to us. This camp really helped us with the practical parts of survey fieldwork as we were working in conditions we will surely have to face in the future. It increased our confidence in handling instruments as well as completing projects within given deadlines. This trip also offered us relief from the monotony of performing all survey practical within the college compound. It was also a chance to get to know our friends from other sections, work closely, and interact with them. This trip is a good experience in dealing with locals and other people who were interested in our work. We also learned to explain what we were doing to laymen in simple terms. We think I.O.E should organize such trips frequently and for all possible subjects, as practical knowledge is better. In these trips, we gain first hand concept of the subject matter that makes it easier for us to grasp the concept. All in this entire trip was very informative, effective and enjoyable.
B.E SURVEY CAMP 2074
