BY: Rakesh Kumar Verma A s s i s t a n t P r o f e s s o r , ( P . I . E . T )

P a r u l U n i v e r s i t y , V a d o d a r a

SURVEYING: Linear

Measurements

LINEAR MEASUREMENTS

measurement of distances between points on the surface of the earth

In Horizontal (Assumed) plane

p2 p1

Methods of

LINEAR SURVEYING

Direct measurement Distances are actually measured on the surface of the earth using Chain or Tape measurements 0r Ranging

Indirect Measurements

Measurement by optical means Observations are taken through a telescope and distances are determined by calculation as in tachometer or triangulation

Electronic methods Distances are measured with instruments that rely on propagation, reflection and subsequent reception of either radio or light waves

Direct

Measurements

Directly Measure Distance on Ground

Using:

1. Chain or

2. Tape

3. Arrow

4. Ranging Rod

5. Cross Staff

CHAIN

ARROW

TAPE

Length:10cm to 60cm Sides:15mm to 25mm

In general use L=15cm or 20cm

20mm

50mm Dia. 4mm Dia.

400mm±5mm

1m to 3m

Red Band

White Band

@20cm

Types of Chain

Metric chains 20m and 30m Tallies @every five-meter length brass rings @ every meter length

Gunter's chain or surveyors chain Length = 66 ft (22 yards), No of links = 100, Each link = .66’ Used for measuring distances in miles or furlongs (220 yards), acres (Area).

Engineers chain Length = 100 ft , No of links = 100, Each link = 1’ Used in all Engineering Surveys.

Revenue chain Length = 33ft, No of links = 16 Commonly used for measuring fields in cadastral Survey

5m

15m 1o m

20cm

20cm

1st Link

2nd Link

Tallies

13cm 13cm

D-13cm D-13cm

Brass Handle

Ring

Ring

Measuring Tapes

1. Cloth or linen tape Used for subsidiary measurements Very light, easy to handle May effect by moisture 2. Metric steel tape Made of steel Outer end is provided with a ring for holding 3. Invar tape Used for high precision work Made of alloy steel 4. Synthetic tape Made of glass fiber with PVC coating These are used for short measurements

Chain Survey

Simplest method of surveying.

In chain survey only measurements are taken in the field, and the rest work, such as plotting calculation etc. are done in the office.

Only linear measurements

No angular measurements

Most suitable adapted to small plane areas with very few details.

If carefully done, it gives quite accurate results.

When we can use Chain?? What are Survey Station??

For comparatively small Areas

Fairly level Ground

For open areas and

For simple detailing and less information.

Main Stations

Subsidiary or tie

Chain Surveying

Main Stations Subsidiary or tie stations

Main stations are the end of the lines, which command the boundaries of the survey, and the lines joining the main stations re called the main survey line or the chain lines.

Subsidiary or the tie stations are the point selected on the main survey lines, where it is necessary to locate the interior detail such as fences, hedges, building etc.

Stations

Lines

Base Lines It is main and longest line, which passes approximately

through the center of the field. Detailing work carryout with respect of this line.

Check Line Or Proof line is a line joining the apex of a triangle to

some fixed points on any two sides of a triangle. To check the accuracy of the framework.

The length of a check line, as measured on the ground should agree with its length on the plan.

A B

C

D

E

F

G

H

Tie Point

Check Line

Offsets

Lateral measurements from the base line

To fix the positions of the different objects

May be taken by using a tape.

Types of offsets:

Perpendicular offsets

Oblique offsets.

Perpendicular Offset

The measurements are taken at right angle to the survey line called perpendicular or right angled offsets. For setting perpendicular offsets any one of the following methods are used:

Swinging

Using cross staffs

Using optical or prism square

Oblique Offset

Offset at some angle

Well conditioned triangle must be maintained

A B

φ≠90ᵒ Φ=90ᵒ

FIELD BOOK

For record all observations and measurements size 200 mm × 120 mm (Size of Pocket) There are two forms of the book (i) single line and (ii) double line Single book :red line along in middle of width represent main survey line. Space on either side of the line :used for sketching the object and for noting offset distances. Double line book: two blue lines with a space of 15 to 20 mm is the middle of each book. Space between the two lines: used for noting the chain-ages.

Procedure in chain survey

Reconnaissance: preliminary inspection Marking Station: fixes up the required no stations at places

with maximum visibility Methods used for marking are: 1. Fixing ranging poles 2. Driving pegs 3. Marking a cross if ground is hard 4. Digging and fixing a stone. Selects main survey line Fix ranging roads on the stations Start chaining and Make ranging if required Field book Entry

A

B

Oblique Offset

Perpendicular Offset

D1

D2

Field Work

Earth

Water Tank

Home B1

B 3

A B 1

2

3 5

6 8

9

10 11

12 13

4 7

d2 d4 d7 h8 h10

d12 d13

d1 d6 d11

d9 d5 d3

wt1

wt2

B 2

B21

B11

B12 T

B31

Here; 1,2,3,………….,12,13 are the chain-edge( Where offset meets perpendicular to chain) d1,d2,d3,……….,d12,d13 are the offset distances wt1, wt2, B11, B12, B31 and B21 are the references/ oblique offset from permanent structure i.e. Water Tank, Buildings, electric towers T refers to offset taken at tree( shouldn’t consider reference, however it is oblique offset)

B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home

t1

p1

t6

t5

t4 t3 t2

t9 t8 t7

p2

p3 p4

Field Work

A B

1

2

3 5

6 8

9

10 11

12 13

4 7

d2 d4 d7 h8 h10

d12 d13

d1 d6 d11 d9 d5 d3

wt1

wt2

B21

B11 B12

T

B31

Legends or Coding 1,2,3,………….,12,13 are the chain-edge( Where offset meets perpendicular to chain) d1,d2,d3,……….,d12,d13 are the offset distances wt1, wt2, B11, B12, B31 and B21 are the references/ oblique offset from permanent structure i.e. Water Tank, Buildings, electric towers T refers to offset taken at tree( shouldn’t consider reference, however it is oblique offset)

B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home

Office Work

Legends: Pole Tree Building/Home Water Tank

A B 1

2

3 5

6 8

9

10 11

12 13

4 7

d2 d4 d7 h8 h10

d12 d13

d1 d6 d11 d9 d5 d3

Area calculation: approximate estimation of surveyed land

B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home

Office Work

A B

Area calculation: approximate estimation of surveyed land

B1, B2 & B3: Buildings, t1,t2…… used for tree, p1,p2,p3……..used for poles h8 h11 offsets for home

Office Work

Calculated Area in meter square

Ranging in Surveying

To align intermediate points on chain line so that the measurements are along the line

Process of locating intermediate points on survey line is known as ranging

Methods of ranging

1. Direct Ranging

2. Reciprocal Ranging

Direct Ranging

Used when the stations are intervisible

Done by eye-judgement

Ranging rods are erected vertically beyond each end of survey line

The surveyor stands 2m beyond the ranging rod while the assistant folds the ranging rod vertically in the intermediate stations.

The surveyor directs the assistant to move the rod to the left or right until the three ranging rods appear to be in a straight line.

Ranging at small Distance & station are visible

Station-A Station-B

Direction of Survey line

Distance to be measured

Ranging Rod-1 Ranging Rod-2

A

B

C

Ranging at Long Distance & station are visible

Station-A Station-B

Direction of Survey line

Distance to be measured

Chain Length -1 Chain Length -1 Chain Length -1

Rod-1 Rod-4 Rod-3 Rod-2

All Rods must be in the same line

Ranging at Long Distance & station are visible

Indirect Ranging/ Reciprocal Ranging

when ends of a line are not inter-visible due hill ground or stations are not clearly inter-visible

needs two assistants one at point M and another at point N, where from those points both station A and station B are visible

A

B

M1 N1

M3

M2 N2

N3

N4

M4

N M

Reciprocal Ranging: stations are not visible directly

A B D E F G H C

Reciprocal Ranging: stations are not visible directly

A

B

Master Reset: Both survey lines readjusted to bring themselves in a straight line