Road Site Survey and Building Layout

7/31/2019 Road Site Survey and Building Layout

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4. Road alignment and geometry design

4.1 Brief description of the project area

The project area for the present study is Jiri, Dolakha, district. It is located in the hilly area of the CentralDevelopment region. Jiri is rural area with diverse topography. The area consists of many valleys and

ridges. For the alignment of road and its geometry design, we selected a track located after the bridge that

we surveyed situated north-west of Pasu Bikas Chhetra. The area is locally accessible and this road is of

utmost importance for the local people because it connects the main town area with the rural areas located

a little far from there and also there is no other major road available to connect these places.

4.2 Hydrology and Geology

The area has a lot of rainfall in the season when we were there so we made a conclusion that whenever a

road is to be constructed in the area we have to consider the application of methods in the construction to

counter the effect of too much of rainfall. Also the foundation there seemed to be stable.

4.3 Soil

The soil in the area was compacted and the rock was stable.

4.4 Norms (Technical Specification)

i. Stable ground

ii. Permissible gradient (according to NRS)

iii. Geometry of road (according to NRS)

iv. Making use of existing road or track

v. Location of bridge site

vi. Indivisibility between intersection point (I.P.)

vii. Obligatory points

viii. Optimum use by public

ix. Minimum use by public

x. Minimum road length as far as possible

xi. Economic condition of Project

xii. The road has to be designed for a width of 5 meter and length of 500m.

xiii. If the external deflection on the road is less then 3 the curve need not to be

fitted.


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xiv. Simple horizontal curve has to be laid out where the road changed its direction, determining and

pegging the three points on the curves the beginning of the curve, mid of the curve and the end of the

curve along the central line of the road.

xv. The radius of the curve should be greater then 12m.

xvi. The gradient of the road has to be maintained below 7%.

xvii. Crosssection should be taken at the interval of 15 to 20m and also at the beginning, middle and end

of the curve along the central line of the road.

xviii. Plan of the road should be prepared in the scale of 1:500.

xix. L Section of the road has to be plotted on the scale of 1:500 on X axis and

1:100 vertically.

xx. The cross section of the road should be plotted on the scale of 1:100 for both

the axis.

4.5 Equipment

Digital Theodolite: It is used for measuring both horizontal and vertical angles. Leveling staffs: It is used for calculating the staff intercept and reading the central hair reading. Ranging rods: It is used for marking the position of stations while ranging a line. Plumb bob: It is used for transferring the end points of the chain onto the ground while measuring

distances in a hilly terrain.

Tape: It is primarily used for measuring the horizontal distances. Prismatic compass: It is used for determining the bearing of stations. Hammer: It is used to fix the pegs. Pegs : It is used to locate the traverse station Auto level: It is used to transfer R.L. from a known bench mark to the station.

4.6 Methodology

4.6.1 Horizontal alignment

The location of the simple horizontal curve were determined carefully considering factors like the

stability of the area, enough space for the turning radius etc. The I.P. was fixed so that the gradient of the

road at any place was less than 710%. After determining the I.P 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.


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The horizontal curve was set out by angular method using theodolite at I.P. and tape. The radius of the

curve was fixed first, assuming it to be more than 15m. Then for that radius, the tangent length and apex

distance of the curve were calculated using the following formulas:

Tangent Length =2R tan

Apex Distance =

Length of the Curve = R/180Where = External deflection angle

After performing the necessary calculation, the points T1 and T2 were fixed at a distance equal to tangent

length from the 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 mid of curve at a distance equal to the apex

distance from the I.P. Then the necessary calculation was done, thus giving the required numerical values

of different parameters.

4.6.2 Vertical alignment

Most of the works related to the vertical alignment was done in the works of leveling. We were careful

that the gradient of the road is not more than 12% as this was not a highway but a road in a simple area.

When doing the recee, there are various places on the road falling at different elevations so in order to

connect those places with a road, a gradient should be provided. While providing the gradient we should

be careful that we follow the code give by NRS. This also gives us the information about the rough

quantity of cutting or filling that might be required in the process of the construction of the road.

4.6.3 Leveling

The method of fly leveling was applied in transferring the level from the given B.M. to all the I.P.,

beginnings, mid points and end of the curve as well as to the points along the center line of the road where

the cross section 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 before and after forming the loops should be

less than 25 Kmm, where k is total loop distance in km.

4.6.4 Longitudinal Section

The Lsection of the road is required to the road engineer an idea about the nature of the ground and the

variation in the elevation of the different points along the length of the road an also to determined the

amount of cutting and filling required at the road site for maintaining a gentle slope. In order to obtain the

data for LSection, Staff reading was taken at a point at 25m intervals along the central line of the road

with the help of a level by the method of fly leveling. And thus after performing the necessary calculation

the level was transferred to all those point with respect R.L. of the given B.M. Then finally the LSection

of the road was plotted on a graph paper on a vertical scale of 1:100 and a horizontal scale of 1:500.

4.6.5 Cross Section

Cross Section at different points is drawn perpendicular to the longitudinal section of the road on either

side its center line is order to present the lateral out line of the ground. Cross Section is also equally useful

in determining the amount of cut and fill required for the road construction. The cross sections were taken

at 25m intervals along the center line of the road and also at point where there was a sharp change in the

elevation. While doing so, the horizontal distance of the different points from the center line measured

with the help of a tape and vertical height with a measuring staff. The R.L. was transferred to all the

points were performing the necessary calculation and finally the cross section at different section were

plotted on a graph paper on a scale of 1:100 both vertical and horizontal.


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4.6.6 Topographical survey of road corridor

While surveying the road the road corridor was also taken into consideration. The topographical survey of

road corridor was also done. This could give a general idea of the land that the road would be occupying.

4.6.7 Computation and plotting

4.7 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 field, we had spent quite some time discussing the route of

the road and also in designing the curves, which led to good results. However, the entire group members

were very cautious and tried their best to get error free data and calculations. Moreover, after performing

this road alignment survey, we were able to build confidence in designing roads at difficult terrain taking

factors like economy, convenience and its use into consideration. We believe that such a work will be a

lot of help for us in understanding the actual situation while undertaking actual design and constructionwork in the future and we hope that organizes such useful field trips of the entire subject frequently.

5. Layout of building

5.1Brief description of layout

The real meaning and purpose of setting out (layout) is to transfer the plan, length and width of its

foundation on the ground so that the foundation can be excavated for construction of purposed building as

per drawing.

There are also many other complex uses of a building layout which are described below. The layout

shows how to use a transit to locate a building correctly on the lot, plan proper grades with minimum

excavation, find utility lines and easements, establish correct elevations, lay out accurate foundations, and

set correct floor heights. It also explains how to plan sewer connections, level a foundation that's out of

level, use a story pole and batterboards, work on steep sites, and minimize excavation costs.

5.2 Norms

The following preliminary works should be executed before actual planning of layout for the house.

Clear the site from all grass, bushes, trees, etc. Record spot levels of the ground. Construct a permanent bench mark in construction area.


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Base Line

For setting out /layout, the most important requirement is to establish a baseline. This is marked on the

ground as per site plan requirement with the help of offsets which are taken from the existing road or

existing building.

Centre Line

Centre line divides the plan into two equal parts. This can be marked in the field with the help of baseline.

This line is very necessary and useful for layout. This line should be transferred to Burjis and be kept up

to the completion of foundation work.

'Burjis' and its' Distance

Burji or marking pillars are masonry pillars constructed with bricks and cement mortar. These are

constructed on both ends of walls /columns and center line should be marked on the top surface of the

burjis with the help of base line. Burji is also constructed for indicating the plinth level of the building.

Burjis are very useful for the layout. Accuracy of the foundation can be checked with the help of Burji atany time during construction. Burjis should be kept intact till completion of foundation work.

5.3Location and site plan

The location was situated to the north west of Pashu Bikas Chhetra, Jiri. The ground had some ups and

downs and it was a little bit uneven. However the ground was free from grasses and bushes so there was

no major difficulty in setting out the plan.

5.4EquipmentThe various equipments used in the laying of building layout procedure are as follows:

Pegs Measuring tape Hammer Thread Nails

5.5Methodology

5.5.1Site selectionThe site for the laying out of the plan of the building was selected near the site for the survey of bridgeand road. We were careful in choosing the site which had the least ups, downs and irregularities. Also the

area was chosen so that it was free from long grasses and bushes.


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5.5.2 Topographical survey

Many other points also had to be considered while setting the layout of the building on the ground. The

main gate of the building had to be in the direction of the road. Also every line of the layout connecting

the various pegs had to be straight and orthogonal to each other at the edges. All these points were taken

care of in the topographical survey of the area.

5.5.3 Determination of area

The theoretical area occupied by the building was already known from the map of the plan. Also the area

at the site was found out by measuring the actual dimensions and it was made sure that the area was equal

to the theoretical area

5.5.4 Steps of layout

The following procedure was followed in order to make the layout of the building:

i. A peg was hammered into the ground to mark one of the edges of the area.ii. The various dimensions were measured and pegs were inserted into the ground starting from the

external edges of the ground.

iii. Also nail was hammered on the top and center of the peg.iv. Thread was tied on the nail of the hammer and the pegs were tied by the same thread therebygiving the exact layout of the building.

5.5.5 Comments and conclusion

By performing the process of building layout on the ground we became accustomed to the various

techniques followed in this process. It greatly helped us in increasing our confidence about performing

this job.

6. Intersection and Resection

6.1 INTRODUCTION

In the method of intersection, either the coordinates of at least two accessible and intervisible points must

be known or the distance between them is measured directly in the field. These points are plotted on the

required convenient scale. The locations of other detail points are determined by drawing rays from each

end station after proper orientation of the table. The intersection of rays gives the location of detail point.

It is thus evident that it is very essential to have at least two points whose locations are plotted before the

survey may be started. The line joining the locations of the given stations is known as the base line. In

this method, no other linear measurement is required except that of the base line. The point of intersection

of the rays drawn from the ends of the base line forms the vertex of the triangle and two rays represent the

remaining two sides. The position of the vertex is determined by completing the triangle graphically. This

is why the method is also known as 'Graphic triangulation'. Moreover, the field work of intersection

involves the setting up of the theodolite at each existing control station, back-sighting onto another


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existing station, normally referred to as the reference object (i.e. R.O.), and is then sighted at the point to

be established. Normally, a number of sets of horizontal angle measurements made with a second-order

theodolite (i.e. capable of giving readings to the nearest second of arc) will be required to give a good fix.

The process of determining the location of the station occupied by the plane table, by means of drawing

rays from stations whose locations have already been plotted on the sheet, is called resection. This method

which is also generally known as Interpolation Method or Fixing Method consists of drawing rays from

known points whose locations are already available on the sheet. The intersection of these rays will be at

a point if the orientation of the table was correct before rays are drawn. It is seldom possible to get an

accurate orientation even with a magnetic compass. The problem therefore lies in orienting the table at the

unknown occupied station. It may be solved by one the following methods:

1. Back ray method

2. Two points method

3. Three points method

4. A box compass method

The three point problem may be defined as 'finding the location of the station occupied by a plane table

on the sheet, by to means of sighting to three well defined points whose locations have previously been

plotted on the sheet'. It is location of a single point by measuring horizontal angles from it to three visible

stations whose positions are known.

6.2 CALCULATION

6.2.1 CALCULATION OF INTERSECTION

The intersection formulae for the determination of the x and y co-ordinates of the intersected point may

be easily developed from first principle as:


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Let the existing control stations be A(Xa, Ya) and B(Xb,Yb) and from which point P(X, Y) is

intersected.

= bearing of ray AP

= bearing of ray BP.

It is assumed that P is always to the right of A and B. ( & is from 0 to 90)

tanY-YtanXX

X-X=tanY-tanY

Y-Y

X-Xtan

AA

AA

A

A

Similarly,

tanY-YtanXX

X-X=tanY-tanY

Y-Y

X-Xtan

BB

BB

B

B

)tan-(tan

tanY-YtanXX

Y

tanY-YtanXX)tan-Y(tan

tanY-YtanX=tanY-YtanX

BAB

BAB

BBAA

Similarly,

cotX-XcotYY;X-X

Y-Y=cot

AA

A

A

cotX-XcotYY;X-X

Y-Y=cot

BB

B

B

)cot-(cot

cotX-cotX+YY=X

cotX-cotX+YY=)cot-X(cotcotX-XcotY=cotX-XcotY

BAAB

BAAB

BBAA

A

B


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If the observed angles into P are used, the equation becomes:

)cot+(cot

cotY+cotY+XX=Y

)cot+(cot

cotX+cotX+YY=X

BABA

BAAB

The above equations are also used in the direct solution of triangulation. Inclusion of additional ray from

C, affords a check on the observation and computation.

6.2.3 CALCULATION OF RESECTION

The Theodolite occupies station P, and angles and are measured between stations A and B, and B and

C.

Let BAP = , then

BCP = (360 - - - ) -

= S -

is computed from co-ordinates of A, B and C

S is known

From PAB,

PB = BA sin / sin (1)

From PAB

A

B

C

P


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PB = BC sin(S - ) / sin (2)

Equating (1) and (2)

Q

sinBC

sinBA

sin

)-sin(S

Qsin

)sinScos-cosS(sin

sin S cot - cos S = Q

cot = (Q + cos S) / sin S

Knowing and (S - ), distances and bearings AP, BP and CP are solved. Co-ordinates of P can be solved

with the three values. This method fails if P lies on the circumference of a circle passing through A, B,

and C, and has an infinite number of positions.

Example of the resection is given below:

Refer to Figure,

= 4120 35

= 4853 12

Control points:

XA = 5,721.25, YA = 21,802.48

XB = 12,963.71, YB = 27,002.38,

A

B

C

P


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XC = 20,350.09, YC = 24,861.22

Calculate the coordinates of P is done through method of resection as:

Dist. BC =7690.46004

Bearing of BC = 106-09-56.8

Dist. AB =8915.8391

Bearing of AB = 54-19-21.5

= 180 - ((106-09-56.8)+(54-19-21.5))

= 128-09-24.6

S = (360 - - -)

= 141-36-48.4

Q = AB sin /BC sin =1.322286

cot = (Q + cos S) / sin S

= 49 -04-15.5

BP = AB sin /sin

= 10197.4831

BP = BC sin (S - ) / sin

= 10197.4831 (checks)

CBP = 180 - [ + (S - ) ]

= 38.5708769

Bearing BP = Bearing. BC + CBP

= 144 - 44 - 12.0

Ep = EB + BP sin (BRG BP)

= 18851.076

Np = NB + BP cos (BRG BP)

= 18676.061

Checks can be made by computing the coordinates of P using the length and bearing of AP and CP.


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6.3 PROCEDURE

6.3.1 PROCEDURE OF INTERSECTION

1. The theodolite is set up at one of the station whose coordinates and the reduce level are known say at

A.

2. The ranging rod is kept at another known station (say B) accessible from A.

3. Setting zero at the known station 'B , and viewing another unknown and inaccessible point 'C', the

angle BAC is measured .

4. The theodolite is again set up at B, and the angle ABC is taken in similar way.

5. The distance between the known points 'A' and 'B' is measured.

6. The bearing of any line AB is taken.

7. The coordinate of the unknown point is then calculated using the trigonometric relation.

6.3.2 PROCEDURE OF RESECTION

1. The Theodolite is set up at the unknown station (say A).

2. The ranging rod is kept at the three known points (Say B, C,D).

3. The angle BAC and CAD is taken.

4. The distance between the known points BC and CD is measured.

5. The bearing of any line joining known point say CD is taken.

6. The coordinate of point A and its distance from three known points B, C and D is calculated by

trigonometric relation.


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6.4 RESECTION VERSUS INTERSECTION

Resection and its related method, intersection, are used in surveying as well as in general land navigation

(including inshore marine navigation using shore-based landmarks). Both methods involve taking

azimuths or bearings to two or more objects, then drawing lines of position along those recorded bearingsor azimuths.

When intersecting lines of position are used to fix the position of an unmapped feature or point by fixing

its position relative to two (or more) mapped or known points, the method is known as intersection. At

each known point (hill, lighthouse, etc.), the navigator measures the bearing to the same unmapped target,

drawing a line on the map from each known position to the target. The target is located where the lines

intersect on the map. In earlier times, the intersection method was used by forest agencies and others

using specialized alidades to plot the (unknown) location of an observed forest fire from two or more

mapped (known) locations, such as forest fire observer towers. It is used to increase or densify control

stations in a particular survey project. It enables high and inaccessible points to be fixed. The newly-

selected point is fixed by throwing in rays from a minimum of two existing control stations. These two (ormore) rays intersect at the newly-selected point thus enabling its co-ordinates to be calculated.

The reverse of the intersection technique is appropriately termed resection. Resection simply reverses the

intersection process by using crossed back bearings, where the navigator's position is the unknown. Two

or more bearings to mapped, known points are taken; their resultant lines of position drawn from those

points to where they intersect will reveal the navigator's location. It is extremely useful technique for

quickly fixing position where it is best required for setting-out purposes. It is weaker solution than

intersection.

6.5 SUITABILITY OF INTERSECTION AND RESECTION

The method of intersection is suitable when distances between detail points are either too large or cannot

be measured accurately due to undulations. The method is generally used for surveying the detail points.

Whenever this method is used for locating other points to be used at subsequent stations, the points

should be got by way of intersection of at least three rays. It may be noted that the angle of intersect of

different rays should not be acute to obtain accurate locations of the points. Triangle s should be well

conditioned. The angle of intersections of rays, should not preferably be less than 30 and not more than

120. As no linear measurements are required in this method it can be suitably employed for surveying

mountaineous regions. As accumulation of error is limited only to the scale of plotting of the base line,graphic triangulation can be extended to cover a large area without introducing any appreciable error.

Similarly, the method of resection can be suitably employed for the survey when a prominent point such

as a temple spire, chimney, etc... is available in the centre of the area.

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Road Site Survey and Building Layout