CHAPTER 1

1.0 INTRODUCTION:

An art and science of determining the relative position of point on above or beneath the surface of the earth by means of angular and linear measurements is defined as Surveying. It is the most important subject matter before and during all engineering works like civil engineering works such as designing and construction of highways, water supply systems, irrigation projects, buildings etc. The application of surveying requires the knowledge of mathematics, physics, and to some extent, astronomy. Surveying basically consists of collecting data and information about the terrain of the topography of the proposed area, land use, property and the state boundaries, the charting of coastlines and navigable streams and lakes, the location of valuable mine deposits etc. It is a framework for the conception, design and execution of any engineering work. The information about these features are gathered by measuring the horizontal and vertical distances between the objects, by measuring the angle between the lines and by establishing points by predetermined angular and linear measurements. The actual measurements are accompanied by mathematical calculations for determining distances, angles, directions, locations, elevations, areas and volumes. The information thus collected is then portrayed graphically by the construction of maps, profiles, cross-sections and other diagrams.

The main objectives of surveying courses allocated for civil engineering students is to promote them the basic knowledge of different surveying techniques relevant to civil engineering works in their professional practice. The completion of all surveying courses including 15 days survey camp work organized by the Department of Civil Engineering, Khwopa Engineering College will give better enhancement to students to use all surveying technique covered in lecture classes.

Survey Camp is a part of the third-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 12th Kartik to 26th Kartik 2069 . 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

This is a detail report of the works, which were performed by

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group no. B3, having five members, during the camp period. It briefly explains the working procedures and technique used by this group during that camp period. In addition, it also contain observations, calculations, methods of adjustment of error, main problem faced during work and their solution, results of all calculations and their assessments with some comments is presented in a concise form.

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 main objectives of the survey camp are as follows:

To become familiar with the surveying problems that are arise during the field works. To became familiar with the parts of the instruments, their functions and handling the

surveying instruments for its use in surveying. To become familiar with the spirit and importance of teamwork, as surveying is not a

single person work. To complete the given project in scheduled time and thus knows the value of time. 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 order to understand by other engineers and related personnel easily.

To tackle the mistake and incomplete data from the field while in office work. To know the complete method of report preparation.

1.2 METHODOLOGY: 

The methodology of the surveying is based on the principle of surveying, which includes:    • Working from Whole to the Parts  • Independent Check   • Accuracy Required  • Consistency in Work 

1.3 INDEX MAP/LOCATION MAP:

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1.4 PROJECT AREA:  

The description of the project area is as follows:

Nepal  Electricity Authority Training Center (NEATC),  Kharipati,Bhaktapur is about 18 km North East of Kathmandu. The area to us for survey is about 200 ropanis of land with varieties of land (i.e. jungle, vegetation, human settlement etc) .The details of the area is as  follows

                                   Country: ‐ Nepal  

                                   Region: ‐   Central Development Region  

                                   Zone: ‐      Bagmati  

                                   District: ‐   Bhaktapur    

Location: ‐ NEATC premises for Topographical Survey Nagarkot, Dolalghat of Kavre  for Bridge Site Survey

NEATC premises for Road Alignment Survey

1.5 LOCATION AND ACCESSIBILITY:

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Our Survey Camp site was located near about 27º41'16"N and 85º27'20"E, at the altitude of

1362 m and about 16 km East of Kathmandu. The area allocated to us for survey is about

292065.62 sq m. of land with variable land features and almost all the man made mentors like

road, sports ground building and pond etc.

It took about twenty minute drive to reach Kharipati from Libali, Bhaktapur. The project site

is situated in the range of about 1330 m. above mean sea level.

i) Region: Kharipati VDC and Nagarkot VDC

ii) District: Bhaktapur

iii) Zone: Bagmati

1.6 TOPOGRAPHY AND GEOLOGY

Kharipati has gentle and steep topography differing from places to places. The area contains ground features ranging from steep slopes to flat grounds. These features were shown by contours. The geological structure is in good condition, so there is no any geological disasters and eruption. Soil types are found similar to any other part of Bhaktapur i.e. soft clay, irrigated by river and well suitable for cultivation. And the bridge site, Cha Khola perennial however the flow decreases considerably during dry seasons. Different types of rock exposure are seen most of them are amphibolites, gneiss, sandstones, schists etc.

1.7 RAINFALL,CLIMATE AND VEGETATION:

The weather is moderate between autumn seasons. During the camp period temperature was fluctuating from maximum to minimum of it just similar to the annual temperature variation and rain fall around Kathmandu valley is:-

Temperature: maximum 25oC to minimum 4oC

Rainfall: - 200mm (approx. annually)

The atmosphere was cool in the morning with high value of humidity.

Most of the empty spaces of the project area were full of vegetation but without cultivated land except for some land around canteen area. Ordinary grassland covered most of the areas. Presence of few plants, trees and bushes made environment green and pleasant.

1.8 DESCRIPTION OF WORK 

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Topographic Survey: -

Objective: To make the topographic map with engineering requirements.

Location: premises of NEATC

Salient Features: Total Numbers of major traverse stations = 14

: Total numbers of minor traverse stations = 2

: Contour Interval = 1m

: Scale of map = 1:1000 in major, 1:500 in minor

: Detailing = Total Station

Check: Plane Table

Leveling: -

Objectives: Two peg test was carried out. As our auto level was within precesion no correction was needed.

Location: premises of NEATC

Silent Features:

Transfer of RL from BM to CP1

Transfer of RL from CP1 to major station

Transfer of RL from major station to minor station

Bridge Site Survey:

Objectives: To fix the bridge axis and topographic map of the existing site along with the L-section,X-section of river.

Location: Dolalghat, Kavre

Salient Features:

No. of stations used :Topographic map at 1:200

: Contour Interval 1m

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:Cross section upto 150m on upstream and 75m on downsream at 10m interval.

Road alignment:

- Objectives: to make L-section, X-section and topographic map of area of the site-

- Location: premises of NEATC

- Salient feature:Map scale = 1:1000

Profile : Cross section at every BC, EC & MC and 20m interval with minimum of 5m and 10m left and right details.

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Chapter 2

2.0 TOPOGRAPHICAL SURVEY: The survey in which the position of natural and artificial features on both plan and

elevation are determined is known as 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. In other words topographical surveying is the process of determining the positions of natural and artificial features of the locality by means of conventional signs up on a topographical map. Topographic surveys are three-dimensional; they provide the techniques of plane surveying and other special techniques to establish both horizontal and vertical control. Hence the fieldwork in a topographical surveying consists of three parts.

It establishes both horizontal and vertical control. It locates the contours. It also locates the details such as rivers, streams, lakes, roads, houses, and trees

etc.

2.1 OBJECTIVESThe main objective of topographical survey is to prepare the topographical map of the

given area with horizontal control and vertical control on required accuracy.

2.2. BRIEF DESCRIPTION OF THE AREAThe area, where surveying was performed, is situated at NEA training center,

Kharipati, Bhaktapur. The major traverse was run throughout the land area, which cover the full area of the NEA. Our objective was to prepare a topographic map of the given small area, which is a part of the NEA area. So, we were assigned to prepare the topographic map of the area including the two Dormitories, Teacher's Quarter, Guest house, and all the natural and man made features that may come in the general survey work. The two identical and symmetrical Dormitories were situated at southern side of NEA Training Center building, Teacher's Quarter is north of it, Guest house is east of the two. The rest of the area includes grassland with bushes near the walls of the site and backyard of the dormitories. The far south-west area consists closed exit gate with an guard house and a drain pond opposite to it.

2.3 NORMS (TECHNICAL SPECIFICATIONS)o Reconnaissance was conducted at first. A close traverse (major and minor) around the

perimeter of the area was formed by making traverse stations. In the selection of the traverse station, it was made sure that the stations were inter-visible and maintained the ratio of maximum traverse leg to minimum traverse leg 3:1 for minor traverse and 2:1 in the case of major traverse.

o The traverse legs were measured in the forward and reverse directions by Total station

note that discrepancy between forward and backward measurements should be greater than 1:2000.

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o Traverse angles were measured on two sets (both 0 set and 90) of reading by Total

station. Note the difference between the mean angles of two sets reading should be within 1’.

o Determined the R.L. of traverse stations by fly leveling from the given arbitrary B.M.

Perform two-peg-test before the start of fly leveling. Note the collimation error should be less than 1:10000. Maintain equal foresight and back sight distances to eliminate collimation error. Permissible error for fly leveling is 25√k mm, Where k =distance (km)

o R.L of B.M. = 1340.000 m

o Balance the traverse. The permissible angular error for the sum of interior angles of

the traverse should be less than ±√n x 1 minute for Major Traverse and ±√n x 1.5 minutes for Minor Traverse (n = no of traverse station). For major and minor traverse the relative closing error should be less than 1: 2000 and 1: 1000 respectively.

o After computing the coordinate of the control points, they are ready to be plotted. Full

size drawing sheets i.e. A1 size is divided into gridlines of 5cm square. The gridlines are made with the help of beam compass. Both the major and minor traverse is plotted to 1:1000 for major traverse and 1:500 for minor traverse. The plotted traverse is made at the centre of the sheet with the help of least coordinates and high coordinates.

o Then detail survey of the given sub area was carried out by tachometry with reference

to the major and minor traverse, which have been already plotted. Use conventional symbols for plotting.

2.4 EQUIPMENTS:

Theodolite Staffs and ranging rods Tapes Plumb bob Level Compass Plane table Alidade Compass Spirit level Marker Hammer Pegs Arrows Total Station

2.5 METHODOLOGYThe methodology of surveying is based on the principle of surveying which

are listed as below:-

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Working from whole to a part Independent check Consistency of work Precision maintained

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-visibility 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 1:2 for major and 1:3 for minor. 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. Thus, permanent fixing of the control points completes recce. So for better planning, detailed inspection of the area to be surveyed (NEA) was performed by the method known as RECONNANISSANCE (RECCE) survey.2.5.2 TRAVERSING

Traversing is a type of surveying connecting number of survey lines forming the framework. It is also a method of control surveying. This survey consists of the measurement of :

o Angles between successive lines or bearings of each line.o The length of each line.

The directions and the lengths of the survey lines are measured with the help of total station. If the co-ordinates of the first station and the bearing of the first line are known, the co-ordinates of all successive points can be computed as follows:XB = XA + L CosӨYB = YA + L SinӨWhere, L=Length of traverse legӨ=Bearing of that leg

There are two types of traverse. They are as follows:

1. CLOSE TRAVERSEIf the figure formed by the lines closes at a station i.e. if they form a polygon

or it starts and finishes at the points of known co-ordinates then the traverse is called closed traverse.

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2. OPEN TRAVERSEIf a traverse starts and finishes at points other than the starting point or point

of known co-ordinates, then the traverse is called open traverse.

(i) Closed Loop Traverse (ii )Closed (Linked) Traverse (iii) Open Traverse

Fig: Types of Traverses

BALANCING THE TRAVERSE:

During the computation of the traverse, we need to balance the traverse because of the different errors in the field measurement. There are different methods of adjusting a traverse such as:

Bowditch method Transit method Graphical method Axis method

The basis of these methods is on the assumptions that the errors in linear measurements are proportional to ‘L’ and that the errors in angular measurements are inversely proportional to ‘L’ where L is the length of a traverse leg.

The Bowditch’s Rule is commonly 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 sides. The Bowditch rule gives the correction as,

CorrectionToLat.or Dept

=Total Error inLat

.(or Dept . )∗( Lengthof That Leg

)Perimeterof that

Traverse

2.5.3 ADJUSTMENT OF ANGULAR ERROR AND BEARING:

The error (e) in a closed traverse due to bearing may be determined by comparing the two bearings of the last line as observed at the first and last stations of traverse. If the closed traverse, has N number of sides then,

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Correction for the first line = e/N

Correction for the second line = 2*(e/N)

And similarly, correction for the last line = N*(e/N) = e

In a closed traverse, by geometry, the sum of the interior angles should be equal to (2n-4)*90˚ where n is the number of traverse stations. 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.

2.5.4 DISCREPANCY AND LINEAR MISCLOSURE:

In order to measure the lengths of the sides of the traverse, two ways measurement (forward and backward) is done with the help of total station. The difference in values obtained by forward and backward measurement is called discrepancy. The reciprocal of mean of the two measurements divided by the discrepancy 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 &, Linear precision = 1 / (Mean length / Discrepancy)

2.5.5 MAJOR TRAVERSETraversing 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 0o0'0" for one set and 90o00'00" for the second.

In the KHEC Survey Camp, two traverses - major and minor had to be established. The major traverse had 14 control stations including two given control points and the ends of the given control line. The control stations were named as M1,M2… and so on CP1 and CP2 were the two given control points and 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 1:2000. Four sets of total station readings were taken for measuring the horizontal traverse angles. The difference between the mean angles of two sets of readings was within a minute 1’ or all the angles.

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2.5.6 MINOR TRAVERSEIt 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 minor traverse. The minor traverse had 2 control stations and enclosed the dormitories and its premises. The control stations were named as m1 and m2 on along with two control stations common for both the major and the minor traverses. The leg ratio of maximum traverse leg to minimum traverse leg was maintained within 1:3. The discrepancy in length between the forward measurements of all the traverse legs was within 1:1000.

Chapter 3

3.0 TOTAL STATION:

3.1 INTRODUCTION:

A total station is an optical instrument used a lot in modern surveying and archaeology and, in a minor way, as well as by police, crime scene investigators, private accident re-constructionists and insurance companies to take measurements of scenes. It is a combination of an electronic theodolite (transit), an electronic distance meter (EDM) and software running on an external computer known as a data collector

With a total station one may determine angles and distances from the instrument to points to be surveyed. With the aid of trigonometry and triangulation, the angles and distances may be used to calculate the coordinates of actual positions (X, Y, and Z or

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northing, easting and elevation) of surveyed points, or the position of the instrument from known points, in absolute terms.

Some total stations also have a GPS interface which combines these two technologies to make use of the advantages of both (GPS - line of sight not required between measured points; Traditional Total Station - high precision measurement especially in the vertical axis compared with GPS) and reduce the consequences of each technology's disadvantages (GPS - poor accuracy in the vertical axis and lower accuracy without long occupation periods; Total Station - requires line of sight observations and must be set up over a known point or within line of sight of 2 or more known points).

Most modern total station instruments measure angles by means of electro-optical scanning of extremely precise digital bar-codes etched on rotating glass cylinders or discs within the instrument. The best quality total stations are capable of measuring angles down to 0.5 arc-second. Inexpensive "construction grade" total stations can generally measure angles to 5 or 10 arc-seconds.

Measurement of distance is accomplished with a modulated microwave or infrared carrier signal, generated by a small solid-state emitter within the instrument's optical path, and bounced off of the object to be measured. The modulation pattern in the returning signal is read and interpreted by the onboard computer in the total station. The distance is determined by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency. Most total stations use a purpose-built glass Porro prism as the reflector for the EDM signal, and can measure distances out to a few kilometers, but some instruments are "reflectorless", and can measure distances to any object that is reasonably light in color, out to a few hundred meters. The typical Total Station EDM can measure distances accurate to about 3 millimeters or 1/100th of a foot.

Some modern total stations are 'robotic' allowing the operator to control the instrument from a distance via remote control. This eliminates the need for an assistant staff member to hold the reflector prism over the point to be measured. The operator holds the reflector him/herself and controls the total station instrument from the observed point.

The basic principle of Total Station is that the distance between any two points can be known once the time light takes to travel the distance and back and the velocity of light is known. Then the following relation, which is already programmed in the memory of the instrument along with other correction factors, calculates the required horizontal distance and is displayed on the LCD screen.

SETUP:

1. Place tripod approximately over a known point locking legs at a convenient height so machine will be at or lower than eye level and the legs are at equal distances from each other. Eyeball the head of the tripod so it is as close to level as possible.

Be sure the legs of the tripod are firmly planted into the ground. For smooth surfaces (such as concrete, asphalt, or tile), use folding metal

tripod footing to secure the legs.

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2. Remove instrument carefully from casing with both hands. Place on top (supporting with top handle) of tripod and tighten centering screw below platform into instrument, aligning the three corners of machine and platform. Use sight tangent screw on back side of LCD display to center the instrument over the exact known point to be surveyed.

3.2 POWER AND PREPARATION

a. Attach one of the batteries to the side of instrument with the clamp side up. Press any one of the five buttons below the display to turn on machine. It shall beep and the display should indicate the instrument is not level and must be leveled and indexed (precisely level internal components).

To switch power off, hold ESC button and press indicated button that corresponds to OFF on the display.

If the battery is at a low level, the following will be displayed, “Battery is low!”-switch batteries and charge the drained one using provided jack.

Prior to storing the instrument for its next use, check the status of both provided batteries. If either is only ENTIRELY drained, charge overnight using given equipment.

b. Locate the horizontal level bubble above the LCD display. Rotate instrument by loosening the horizontal clamp and align the display with any two of the leveling screws. Tighten or loosen the left screw so bubble is in center. Rotate instrument clockwise to the next two screws and again use the left one to center bubble. Rotate to the final two pair of screws and center bubble. Check stationary leveling bubble to see if it is center. If not, repeat previous leveling process.

If the error message “Tilt out of range” is displayed, it is indicating the instrument is off-level. Relevel the instrument.

c. To index the vertical circles, loosen the vertical clamp, and manually rotate the telescope either way twice. The beep should be heard and the zenith angle (ZA vertical angle) will appear on the LCD display.

d. Loosen the horizontal clamp and rotate the instrument clockwise twice to index the horizontal circles. The beep is heard again and the horizontal angle (HAR) is displayed.

Vertical and horizontal indexing has now been completed.e. Note the menus displayed. Each option shown on the home page (reached by pressing

ESC) opens a section which contains several (up to 3) pages. To scroll through these pages to reach other options, press button left of the yellow ESC button that reads PX.

f. Set the target and instrument height by pressing Ht. in S-O mode. Measure the target height by reading the measurement on the reflector pole at the clamp (set at any arbitrary height suitable for job). Measure the instrument height by taping the distance from the black point on side of instrument (level with center of telescope) to the known point on ground.

Be sure to note the units used (currently default set at feet and decimal fractions of feet; see manual to change to metric units) and height of instrument and target in the field book.

When using two reflecting poles, be sure to set each at same height.

3.3 ANGLE MEASUREMENT:

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1. Sight the first point (focus with eye piece and align center hairs with center of reflector) using the horizontal clamp and the fine motion screw. Set the angle to zero by pressing 0SET in THEO mode. Sight the second target and read the HAR on the display.

If you wish to read the angle by rotating the instrument to the left, press R/L in THEO mode (display will read HAL or HAR for left or right respectively).

2. For higher accuracy, the average of a number of readings can be taken using repetition. Sight the first target and press REP in THEO mode. Press BS (back sight) then sight the second target. Press FS (fore sight) and the angle between the two will be displayed. Sight the first target again, presses BS, and site the second target again and press FS. The average of the two readings will be displayed. Repeat up to 10 times for higher accuracy.

3. The slope of the line being shot can be displayed as a percentage by pressing ZA% in THEO mode. This is read as VA and gives the percentage grade of the line. Press it again to return to the ZA reading.

VA% will be displayed when the parameter is set to “Horizontal 0” instead of “Zenith 0” but performs the same function.

Fig:Total Station

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3.4 DISTANCE AND ANGLE MEASUREMENT:

This is the most useful and suggested method. The working procedure is described as follow:

1. Sight target and select for slope, horizontal, or height (SHV) measurement. Press Sdist to start the measurement and STOP to end. The distance, vertical, and horizontal angle are displayed. Press SHV to view the other measurements (Horizontal distance or Height difference).

2. To measure the horizontal distance several times and display the average, sight the target and press H-dist in THEO mode. Three measurements are taken and the average (H-A) is displayed after a few seconds.

* The most recently taken data can be recalled and displayed by pressing RCL in the EDM mode.

3.5 COORDINATE MEASUREMENT:

This is not much more useful. So co-ordinate measurement is not suggested for use.

1. In order to begin the coordinate measure, set the initial coordinates of the station. This is done by pressing the S-O button at the main menu. Then press the Stn-P button on the second page of the S-O menu. Choose the Input button, then set the initial coordinates and press ENTER.

2. Sight the target and press COORD in S-O mode, then press STOP to end the measurement. The coordinates of the target are given with respect to the initial starting position (0,0,0) and designated direction to be North.

3.6 MEASURING THE DISTANCE BETWEEN 2 POINTS:

1. Sight the first position and press either Sdist, Hdist, or Vdist in EDM mode to start the measurement. Stop the measurement by pressing the STOP and sight the next point. Press MLM on the same page to start the measurement, the press STOP to stop the measurement. The slope, horizontal, and height difference between the two points is displayed. This can be repeated as many times as necessary.

2. The slope may be read as a percentage by pressing S% in the same mode after the missing line measurement has finished. This displays the percent grade between the two points.

3.7 DISTANCE SETTING-OUT MEASUREMENT:

1. To find the direction and distance of a point set out a wanted distance from the instrument station, sight the reference direction and press 0SET in THEO mode to set the HAR at 0. Turn theodolite until the required angle is displayed and locks the horizontal movement.

2. Press ESC to go to basic mode and go to S-O mode. Go to S-O_D for the data and input the desired distance to set out. Set the reflecting prism in the sighting line and press SO_Hd to start the distance measurement. The difference between the desired distance and the measured distance is displayed on the 1st line.

3. Move the reflecting prism towards or away from the Instrument until H distance becomes 0m to determine the point at the desired distance.

* If there is negative (-) data: Move prism away from Instr.

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* If positive (+) data: Move prism towards Instr.* Press STOP to end the measurement.

3.8 COORDINATES SETTING-OUT MEASUREMENT:

a. Set the station coordinates and initial azimuth angle. Press S-O_P in S-O mode and input the desired coordinates for N and E and press YES to store the data. Press SO_HA in S-O mode to start the angle measurement. The setting-out horizontal angle, dHA is displayed. Use the horizontal clamp and fine motion screw to turn theodolite until dHA reads 0° 00’ 00” and lock the clamp.

b. Sight the reflecting prism on the sighting line and press SO_HD and move reflecting prism until H reads 0m as in part 3 of the distance setting-out measurement.

3.9 LEVELLING

Leveling is a branch of surveying, the objectives of which are:

To find the elevation of given points with respect to a given or assumed datum. To establish points at a given elevation or at different elevations with respects to a

given or assumed datum.

Two types of leveling are used in general Engineering practices, namely direct leveling (spirit leveling) and in-direct leveling (trigonometric leveling).

DIRECT LEVELLING:

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 staff 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:

DIFFERENTIAL LEVELING:

It is the method of direct leveling the objective 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.

PROFILE LEVELING:

It is the method of direct leveling the objective 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.

CROSS SECTIONING:

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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.

At every 20m chainage the readings were taken for cross sectioning. The RL were taken

where the change in slope was noticed or remarkable points were noticed or else at 5m and

10m both left and right. Autolevel was used for this purpose. Cross sectioning was plotted on

the graph.

RECIPROCAL LEVELING:

Reciprocal leveling

1For transferring the RL across the bridge reciprocal leveling was performed. This method

eliminates the error due to focusing, collimation, earth’s curvature and refraction of

atmosphere etc.

True difference in elevation between A and B = H = ha- (hb-e)

Also the true difference in elevation = H = (ha '- e)-hb’

Taking the average of the two differences we get the difference in elevation between A and

B.

.

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

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)]''()[(2

1baba hhhhH

in the field, just as the length of any side in any triangle can be computed from proper trigonometric relations.

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.

TEMPORARY ADJUSTMENT OF LEVEL: The temporary adjustment for a level consists of the following:

Setting up the level: The operation of setting up includes fixing the instrument on the stand and leveling the instrument approximately.

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 and horizontal line of sight truly horizontal.

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 60 m). First the instrument was setup on the line near B and both staff readings (Top, Middle, and Bottom) were taken. Then, the instrument was setup at the middle C on the line and again both staff readings on A and B was taken. Then computation was done in order to check whether the adjustment was within the required accuracy or not.

The error obtained was within the given permissible error. So, the permanent adjustment was not required.

BOOKING AND REDUCING LEVELS:

There are two methods of booking and reducing the elevation of points from the observed staff reading:

Height of the Instrument method

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Arithmetic Check: ∑BS – ∑F.S. = Last R.L. – First R.L. Rise and Fall method

Arithmetic Check: ∑ BS – ∑ F.S. = ∑ Rise – ∑fall = Last R.L. – First R.L.

FLY LEVELING:

The RL of Given TBM1 point was found by transferring the level from Known BM. In this method auto level was used and the level was transferred directly by taking BS and FS at every Turning Point. For transferring the RL across the bridge reciprocal leveling was performed. This method eliminates the error due to focusing, collimation, earth’s curvature and refraction of atmosphere etc.True difference in elevation between A and B = H = ha- (hb-e)Also the true difference in elevation = H = (ha '- e)-hb’

Taking the average of the two differences we get the difference in elevation between A and B.

LEVEL TRANSFER TO MAJOR AND MINOR TRAVERSE STATIONS:

The R. L of the temporary benchmark was then transferred to the control stations of the major and minor traverse. The closing error was found to be within the permissible limits. The misclosure was adjusted in each leg of the leveling path by using the following formula:

Permissible error = ±25K mm.

Where k is perimeter in Km

Actual Error (e) = ∑BS – ∑F.S. = Last R.L. – First R.L.

Correction ith leg=-(e x (L1 + L2 +….+ Li)/P

Where L1, L2… Li are Length of 1st 2nd,.. ith leg.

P is perimeter

Relative Precision= 1/(p/e)

3.10 DETAILING

3.10.1 TACHEOMETRY:

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)]''()[(2

1baba hhhhH

Tachometry is a branch of angular surveying in which the horizontal and vertical distances of points are obtained by optical means. Though it has less 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.

The objective of the tachometric survey is the preparation of the topographic map or plan with both horizontal and vertical controls. For the survey of high accuracy, it provides a check on the distances measured by tape.

The formula for the horizontal distance, for the tachometer with the additive constant 0.00 and multiplying constant 100.00 is,

H= K S Cos2Ө

The formula for the vertical distance is,

V = (K S Sin2Ө)/2 = H Tan Ө

Where, S = staff intercept =Top Reading – Bottom Reading

K = Multiplying Constant (Generally = 100)

Ө = Vertical angle on Theodolite.

Thus knowing the V value, reduced level (R. L.) of instrument station, Height of instrument (H. I.) and central wire reading (R) the R. L. of any point under observation can be calculated as:

R. L. of Point = R. L. of Instrument Station + H. I. + V- R

3.10.2 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. Every fifth contour lines must be made darken. While drawing the contour lines, the characteristics of the contours should be approached.

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.

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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 ridgeline, 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 toward 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.

3.11 METHODS OF CONTOURING:

Taking the reading at the change point on the ground does 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.

There are two method of locating contour:

i) The Direct Method:

In this method, the points of equal elevations are found directly on the field. The horizontal control of the point is found by the help of plane table.

ii) The Indirect Method:

In this method, some suitable guide points need not necessarily be on the contour. There are some of the indirect methods of location the ground points:

a) Square Method

b) Cross- Section Method

c) Tachometric Method

Interpolation is the process of spacing the contours proportionately between the slopes of the ground between the two points is uniform. The interpolation of contour cans be done on following three ways:

1) ESTIMATION:

2) ARITHMETIC CALCULATION:

Generally, arithmetic calculation method of interpolation is used to draw the contour

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lines and is performed as follows:

Dist .of ContourPo

int=( Diff .inRL

.of OnePt

. _&_Reqd .Pt .)∗( Hz .Dist .inScale)

Difference inRL.of Two

KnownPts

.

3) GRAPHICAL METHOD:

Generally, we use arithmetic method of interpolation to draw the contour line.

2.5.6. COMPUTATION 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 south, and termed Westing. The latitude and departures of each control station can be calculated using the relation:

Latitude = L Cos

Departure = L Sin

Where, L=distance of the traverse legs

=Reduced 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) = √ {(L) 2 + (D) 2}

Direction, tan θ = D/L

The sign of L and D 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)

The error (e) in a closed traverse due to bearing may be determined by comparing the two bearings of the last line as observed at the first and last stations of traverse. If the closed traverse, has N number of sides then,

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Correction for the first line = e/NCorrection for the second line = 2e/NAnd similarly, correction for the last line = Ne/N = 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,

Correction in departure of a side of traverse= (Total Dept. Misclosure / Traverse Perimeter)*(length of that side)

Correction in latitude of a side of traverse

= (Total Lat. Misclosure / Traverse Perimeter) * (length of that side)

In order to measure the lengths of the sides of the traverse, two ways taping (forward and backward) is done. In difficult areas where taping is not possible, other methods like the subtense bar is used. 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 station were found out by resection. The resection point was selected at the top of hostel building from where all the known points can be sighted. The coordinates of known points are given below.

PLOTTING OF MAJOR & MINOR TRAVERSE :

The traverse was made closed in order to check the sum of interior angles, which should be equal to (2n-4)*90 degrees, where n= number of control points. (Traverse stations or legs).

The bearing of the one of the stations with another adjacent station was found out compass. The bearing of other traverse legs were obtained from the help of bearing of preceding line and the included angle at the particular station.

After computing the co-ordinate of each of the control points, they were made ready to plot in grid paper. Both major and minor traverses were plotted to 1:1000 scales. The

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plotted traverse was made at the center of the sheet with the help of least co-ordinates and highest co-ordinates.

3.12 COMMENTS AND CONCLUSIONThe site for survey camping was NEA Training Center. The pattern was very

suitable because all the facilities for engineering work were available with the good environment of doing work. The arrangements of the survey instruments were appreciable although there were some faulty instruments that made the fieldwork time consuming. Some instruments like theodolite, levels etc. do not given the accurate reading. Some other problems during the field works were during fly leveling during transferring the R.L. from given benchmark to the CP due to the by traffics disturbances.

The given Topography survey camp work was finished within the given span of time. The subject survey needs practice as much as possible. For surveying, theory can only taken as the introduction but if there is practice, there will be much gain of knowledge about the techniques of surveying. Thus, this camp helps us by practicing the survey work to gain the much essential knowledge as far as possible. It is better to say that it provides us a confidence to perform survey and apply the techniques at any type of problem facing during the actual work in the future career. The whole area of NEA Training Center was divided in number of plots. A single group had to complete a single plot following the routine provided. Then from the control stations details were taken by tachometry. Recorded data's were established by MS-excel and the drawing was prepared. After computing the co-ordinate of each of the control points, they were plotted in grid paper. Both major and minor traverse were plotted to 1:1000 and 1:500 scale respectively. The plotted traverse was made at the center of the sheet with the help of least co-ordinates and highest co-ordinates. Contouring was done with the help of arithmetic interpolation.

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CHAPTER 4

4.0 BRIDGE SITE SURVEY

4.1 INTRODUCTION

This part of the Survey Camp deal with the bridge site survey at Dolalghat where a narrow river flowed. The structures that are constructed with the objective of connecting two places separated by deep valleys or gorges or rivers and streams are basically known as BRIDGES. The bridges are usually a part of roads making the roads shorter and hence economical. In countries like Nepal, where there are a lot of uneven lands and plenty of rivers, bridges are the most economic and efficient ways to join two places by road in a convenient way . The bridge site surveying was conducted in a Dolalghat.

4.2. OBJECTIVES : Following are the objectives of Bridge site survey:

To select the best location in terms of convenience, economy and geological stability. To calculate the length of the bridge axis via triangulation. 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.

4.3 BRIEF DESCRIPTION OF THE AREA Bridge site survey was done over cha khola river. The site is surrounded with stepped

grassy fields. Its flow direction is north to south. There is plain ground as well as highly sloping ground on some places surrounding. There is big and small stones on the river.

4.3.1 HYDROLOGY, GEOLOGY AND SOIL

In both sides of the river there was steep slope that was the main obstacle. The river was seasonal where water flow in high speed during rainy season and less at dry season.

4.4 NORMS (TECHNICAL SPECIFICATIONS) The following norms were followed while performing the bridge site survey:

Determining the length of the bridge axis and control point fixing was done by the method of triangulation. While forming triangles none of the angles of the triangle were greater than 120o or less than 30o.

The triangulation angle was measured on two sets of readings by theodolite and the difference between the mean angles of two sets of readings had to be within 1’.

Transferring the level from one bank to another bank had to be done by the method of reciprocal leveling.

The scale for plotting of our topographical map is 1:500. In order to plot the longitudinal section of the river, data had to be taken along the river

bed upto 150 m upstream and at least 75 m downstream. However it was not possible in our case.

The plot for the longitudinal section along the flow line was done in a scale of 1:50 for vertical and 1:500 for horizontal.

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For the cross section profile, data had to be taken at 10 m intervals both upstream and downstream, and one at the bridge axis.

4.5 EQUIPMENTS USED Total station Tapes Auto Level Compass Hammer Pegs Tripod

4.6 METHODOLOGY : The various methods were performed during the bridge site survey such as

triangulation, leveling, Tachometry, cross section, L-section etc. The brief descriptions of these methodologies are given below

4.6.1 RECONNAISSANCE For the purpose of the shortest span, the stations were set perpendicular to the flow

direction. The riverbanks were not eroded and were suitable for bridge construction. The chance of change of direction of river on the selected axis line was nominal.

4.6.2 SITE SELECTION:The sites was chosen such that it should be laid on the very stable rocks or hill slope

at the bed of river as far as possible and not affect the ecological balance of the flora and fauna of the site area. The bridge axis should be so located such that it should be fairly perpendicular to the flow direction and at the same time, the river width should be narrow from the economical point of view and the free board should be at least 5m. The starting point of bridge axis should not in any way lie or touch the curve of the road.

4.6.3 TRIANGULATION

For the determination of the approximate span of the bridge axis Triangulation was performed. The triangulation stations were taken as the control points for detailing. Following criteria is met in this process:

Two points on either bank of the river were fixed as control points and one of the sides of the triangle was taken as the bridge axis.

The base line was measured accurately measured by two-way tapping and interior angles were measured by taking two sets of reading by theodolite.

The accurate span of bridge was computed by applying sine rule. To minimize the plotting error well-conditioned triangles were constructed i.e. the

angles greater than 30 degree, less then 120 degrees and nearer to 60 degree. The best triangle is equilateral triangle.

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BC

Fig: Bridge Triangulation

4.7 TOPOGRAPHIC SURVEY

A total of 4 control stations were selected along the banks. Thus a traverse was formed running across the river, covering a distance of 150m upstream and 75 m downstream.

The method of triangulation was used for the determination of the bridge axis as well as the traverse legs, which also served as checks on our work.

And the triangulation angles with two sets of reading were taken using a theodolite. Details of the objects around the bridge along with their spot heights were taken from these control stations by tachometric method.

While transferring the R.L. from the given benchmark to the control stations, fly leveling was done. And for transferring the R.L. from one point to another point across the bridge axis, reciprocal leveling was done.

All the internal angles were measured using Totalstation. Then Sine Law was used to calculate the lengths of the other legs of the triangulation series along with the proposed bridge axis.

4.8 LONGITUDINAL SECTION (L-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 (triangulation) stations on the river banks, the different detailing points along the center line of the river at an interval of about 10 m up-to a 150 m upstream and 75 m downstream is taken.

The R.L.s of the traverse stations being known previously by reciprocal leveling; the levels of the different points on the river were calculated.

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A D

4.9 CROSS SECTION

Cross sectioning of river at a point extends laterally on either side of the center line of the

river at right angle to the L-section.

At every 10m chainage the readings were taken for cross sectioning. The reading were taken

where the change in slope was noticed or remarkable points were noticed or at 10m interval.

Totalstation was used for this purpose.

Cross sectioning was plotted on the graph at a scale of 1:100 vertically and 1:100 horizontally

4.10 LEVELINGTransferring R.L. from B.M. to control points:

The R.L of benchmark BM = 622.00 m was given and was transferred to the triangular stations from the B.M. by fly leveling along the road turning points by taking the back sight reading to the bench mark which should be within the given accuracy. Reciprocal leveling transferred the R.L. to the opposite bank of the river.

RECIPROCAL LEVELING:For transferring the RL across the bridge reciprocal leveling was performed. This method eliminates the error due to focusing, collimation, earth’s curvature and refraction of atmosphere etc.

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True difference in elevation between A and B = H = ha- (hb-e)

Also the true difference in elevation = H = (ha '- e)-hb'

Taking the average of the two differences we get the difference in elevation between A and B is given by H=1/2[(ha-hb) + (ha’-hb’)]

4.13 COMMENTS AND CONCLUSION :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. Similarly, the cross-section and longitudinal section were performed. The X-section was performed at the interval of 10m. The longitudinal section was about 150m upstream and 75m downstream. In addition, details were taken from the respective stations. 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.

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Chapter 5

5.0 ROAD ALIGNMENT SURVEY AND GEOMETRIC DESIGN

5.1 INTRODUCTION

Roads are specially prepared ways between different places for the use of vehicles, people and animals. It is an accepted fact that of all the mode of transportation, road transport is the nearest to the people. The passengers and the goods have to be first transported by road before reaching a railway station or a port or an airport. The road network alone could serve the remotest villages of the vast country like ours. 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 road alignment survey done at in Nepal Electricity Authority Training Center, Kharitapi. The duration of the survey was two days.

5.2 OBJECTIVES Road Alignment Survey was done to accomplish the following objectives:

To choose the best possible route for the road such that there were a minimum number of Intersection Points (I.P.) thereby decreasing the number of turns on the road.

To design smooth horizontal curves at points where the road changed its direction, in order to make the road comfortable for the passengers and the vehicles traveling on it.

To take sufficient data of the details including the spot heights, around the road segment in order to prepare a topographical map of the area, cross section of the road at certain intervals and longitudinal section of the road segment, hence making it convenient to determine the amount of cut and fill required for the construction of the road.

5.3 TOPOGRAPHY AND GEOLOGY OF THE AREA The starting point of the route was the P8 major station. The site is surrounded with

various type of ground features with grass in most of the part. The route selected by our group A3 with 9I.P. and minimum grade of 0.1% and maximum grade of 12%. There are several rise and fall along the route needing lots of cutting, and filling.

The road alignment survey was done at Nepal Electricity Authority Training Centre Bhaktapur. The area was having steep slopes as well as plane land. The area was ideal for survey for hill road. Steep slopes and drastic change in alignment made the work more challenging and more interesting. The area was full of clay and exposed rocks particularly of metamorphic type. The area having steep slopes, but few slopes were unstable and there was chance of slide, so slope protective works are necessary.

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5.3.1 HYDROLOGY AND GEOLOGY :The road had to go along a damp route that was much undulated. The place was damp

and clayey. There were no large boulders or rocks of any kind along the proposed site.

5.3.1.1 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. Other kinds of soils were not found along our proposed route.

5.4 NORMS (TECHNICAL SPECIFICATIONS) While performing the road alignment survey, the following norms were strictly

followed:

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 point of the curve along the centerline of the road.

The radius of the curve had to be greater than 12 m and The gradient of the road had to be maintained below 12% Cross sections had to be taken at 20 m intervals and also at the beginning, middle and end

of the curve, along the centerline of the road - observation being taken on either side of the centerline.

Plan of the road had to be prepared on a scale of 1:500. 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.

5.5 EQUIPMENTS USED Theodolite Staffs Ranging rods Tapes Level Compass Hammer Pegs

5.6 METHODOLOGY : 5.6.1 RECONNAISSANCE

The reconnaissance survey was carried out starting from the main road to the low elevated region along the graveled road. Pegging was done at different places and the possible I.P.s were also numbered and pegged. The condition of inter-visibility was checked at each step.

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MC

EC

O

BC

IP

5.6.2 HORIZONTAL ALIGNMENTThe locations of the simple horizontal curves were determined carefully considering factors like the stability of the area, enough space for the turning radius, etc. The I.P.s was fixed so that the gradient of the road at any place was less than 7 - 12% . After determining the I.P.s for the road, theodolite was stationed at each I.P. and the deflection angles measured. The distance between one I.P. and another was measured by two way taping.

The horizontal curves were set out by angular methods using theodolite at I.P. and tape. 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 Theodolite at each IP and then deflection angles were calculated.

Deflection angle = (360 or 180) - observed angle

Fig: Simple circular horizontal curve

where

BC: Beginning of curve

EC: End of curve

MC: Midpoint of curve

IP: Apex distance

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

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R

Tangent Length, BC1IP = R Tan /2

Apex distance, IPMC1= R(sec/2-1)

IPBC= IPEC: Tangent length

: External deflection angle

R: Radius of curve

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 (/2)

Length of curve (L.C) = 3.142 x R x /180

Apex distance = R x 1/ (Cos (/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.

After performing the necessary calculations, the points T1 and T2 were fixed at a distance equal to the tangent length from I.P. using a tape. Then the line bisecting the internal angle at the I.P. was found out with the help of a theodolite. And on this line, a peg was driven at point M at a distance equal to the apex distance (VM) from the I.P. Then the necessary calculations were done, thus giving the required numerical values of the different parameters.

5.6.3 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.

5.7 LEVELING The method of fly leveling was applied in transferring the level from the given B.M.

to all the 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 25k mm, where k is the total distance in km.

5.8 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

34

maintaining a gentle slope. In order to obtain the data for L-Section, staff readings were taken at points at 20 m intervals along the centerline of the road with the help of a level by the method of fly leveling. And 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.

5.9 CROSS SECTION Cross sections at different points are drawn perpendicular to the longitudinal section

of the road on either side of its centerline. Cross sections are also equally useful in determining the amount of cut and fill required for the road construction. Cross sections were taken at 5m intervals along the centerline of the road and also 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 as well as staff 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.

5.10 CALCULATIONS AND PLOTTING After the work of taking the data was completed, all the necessary calculations were

done and tabulated in systematic order. The calculations were done in order to compute the Chainage of the different distinct points of the road using the following relations:Chainage of beginning of curve, BC1 = Chainage of I.P. - Tangent lengthChainage of mid point of curve, MC1 = Chainage of BC1 - 1/2* Curve lengthChainage of end of curve, EC2 = Chainage of BC1 - Curve length

Similarly,Chainage of an I.P. = Chainage of previous I.P. + I.P. to I.P. distance.The R.L. of the different points was also computed using this formula.

R.L. of a point = R.L. of station + Height of Instrument + H * Tan - Mid wire reading

Where, = Vertical Angle

Hence, with the required calculated data regarding the road site in hand, the plan was plotted on a scale of 1:500, L-Section on a graph paper on a scale of 1:1000 horizontal and 1:100 vertical and the cross section at different points also on a graph paper on a scale of 1:100 (both vertical and horizontal).

All the data, calculation (in a tabulated form) and the drawings of the necessary plan, longitudinal section and the cross section of the road are attached with this report.

5.11 COMMENTS AND CONCLUSION

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 also in designing the curves, which led to

35

good results, The grade change was very sharp which created nuisance in working with the Auto Level. However, all the group members were very cautious and tried their best to get error free data and calculations. The road had to be designed on a sloping ground, so our group members felt the restrictions during the cutting and filling.

Moreover, after performing this road alignment survey, we were able to build up our confidence in designing roads at difficult terrain taking factors like economy, convenience and its use into consideration.

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