Surveying BEC102 4 - Longitudinal and Cross Sections

Longitudinal and Cross Sections

Sr SITI NUR NUR ALIAA ROSLAN KLIUC

Outline of Lecture 

Introduction

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Definitions

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Methodology

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Calculation

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Output / Products

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 Applications

Introduction Two other major uses of levelling are: 

Longitudinal sections

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Cross--sections Cross -sections

Definition Longitudinal sections 

The existing ground profile along a particular line (normally the centre line of existing proposed work)

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Centre line of railway, road, canal etc

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Staff reading to 0.01m is adequate

Definition Cross--sections Cross -sections 

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 Are lines of levels or short profiles profiles perpendicular to the centre line of a project Provide info needed for estimating the quantities of earthwork

Methodology 

The process of determining a series of elevations along a fixed line is referred to as Profile Levelling

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Data are taken at regular intervals after the setting out of Centre Line (CL)

Methodology The levels for the defining of the sections may be obtained by one of the following methods: 

Conventional levelling

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Tacheometric methods

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Interpretation from digital terrain models

Methodology 

The fixed direction is usually of significance such as the centreline of a road or river 

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Cross section may be taken at right angles to this direction at a constant interval

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 Along the cross section levels are measured at points, usually separated by a fixed distance

Methodology 

Similar to the usual process of levelling except that more readings to the Intermediate Sight (IS)

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In order to get more info about the land profile FS1

ISQ ISP

BS A 

Q P

 A 

1

Output / Products 

Longitudinal section plan

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Cross section plan

Horizontal/vertical scale 

It is common to use a vertical scale larger than the horizontal one (usually 10:1) in order to make the elevetion differences clear 

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For eg: Horizontal scale = 1:20 Vertical scale = 1:20

Cross--section Cross -section plan

Uniform Unif orm slope slope – 3 readings readings sufficient sufficient

Some changes changes in in slope – e.g. 5 readings readings

Significant changes in slope – e.g. 9 readings

The typical cross sections

EXISTING GROUND PROFILE

FORMATION LEVEL

WATER WA TER LEVEL LEV EL

Calculations 

Construction levelling: often involves relatively short distances yet a large number ( n) of instrument stations

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In this case, an alternative criterion for E can be used: Max. acceptable misclosure

E

(in mm):

E = ±D √n mm 5mm & 8mm: commonly adopted values for D

Plotting the plans - Longitudinal Long Lo ngit itud udin inal al section secti sec tion on 

Define the horizontal and vertical scale (e.g. vert – – 1:20 ; horz  – –  1:500)

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Can use the engine ering ruler to do the plotting

RL of CLs

Datum = 40.000m

Ground Level (m)

Chainage (m)

        8         5         8   .         0         4         0         0   .         0

        8         9         9   .         0         4

        3         7         7   .         0         4

        8         5         7   .         0         4

        2         0         9   .         0         4

        7         0         9   .         0         4

        1         0         0   .         1         4

        0         0   .         0         1

        0         0   .         0         2

        0         0   .         0         3

        0         0   .         0         4

        0         0   .         0         5

        0         0   .         0         6

Plotting the plans - Cross Cro ross ss s section ect ctiion 

Define the horizontal and vertical scale (e.g. vert – – 1:20 ; horz – – 1:20)

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To highlight both components

Exercise: 

Draw both the longitudinal and crosscrosssection plans in accordance to exact scale

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Use the data provided in the lecture slide

 Advanced source of data 

LIDAR (Light Detection and Ranging)

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It is rapidly emerging technology for determining the shape of the ground surface plus natural and man--made man -made features

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LIDAR is combined with Geographic Information System (GIS) data and other surveying information to generate complex data

 Application of Long and CrossCross sections 

In the construction and design of roads, highways, railways, pipelines and drainage systems

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Earthwork operations

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Cut and fill volume calculations

Height of Collimation Method 

 An alternative to the Rise Rise and Fall method

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Normally used when a large number if Intermediate Sights are observed

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The height of the telescope axis or height of collimation (HC) is measured

Example BS BS

IS

2.027 2.027 2.109 2.109

FS

HC

RL

Remarks Remarks

73.105 73.105 + 2.027 2.027 = 75.132

73.105 73.105

BH1 BH1

75.132

75.132 75.132 – – 2.109 =

(73.105m) 73.023

2.543 2.543

75.132

75.132 75.132 – – 2.543 = 72.589

4.681 4.681

75.132

75.132 75.132 – – 4.681 = 70.451

Example (Cont’d) BS BS

IS

2.133 2.133

FS

HC

RL

Remarks Remarks

4.427

70.705 70.705 + 2.133 2.133 = 72.838

70.451 – – (4.681 (4.681-4.427) = 70.705

D (CP)

72.838

72.838 72.838 – – 3.246 =

E

3.246 3.246

69.592 1.957 1.957 3.159 3.159

72.838

72.838 72.838 – – 1.957 = 70.881

F

0.681

72.157 72.157 + 3.159 3.159 = 75.316

72.157 72.157

G (CP) (CP)

2.988 2.988

75.316

75.316 75.316 – – 2.988 = 72.328

BH2 (72.328m)

 Arithmetic checks 

Sum of BS – – FS = Last RL – – First RL

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Sum RLs – – First RL = [Sum (HCi) x ni] –  –  Sum IS – – Sum FS

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Where: HCi is the i th height of collimation and n i is the no. of times the i th height of collimation was used to compute RLs

 Applications of HC method 

Longitudinal and Cross Cross--sections -sections

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Contouring using grid and levelling

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In general, it is applied when large no. of IS are taken – – e.g. in Earthwork Earthwork levelling levell ing

Contouring by Grid and Levelling

Contour  

 A contour is is a line drawn on a plan plan joining all points of the same height above or below a datum

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Contours cannot cross, split or join other contours, except in the case of an overhang. e.g. a cliff 

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The height between successive contours is called the vertical interval or the contour interval

Contour  

Contour interval value depends on the variation in height of the area being contoured - the contour contour interval interval is kept constant for a plan or map

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The plan spacing between contour line indicates the steepness of slopes - Closely spaced spaced lines lines indicates indicates a steep steep gradient gradient gradient - Widely spaced spaced lines indicate indicate a flatter flatter gradient gradient

Example

5

25 20 15 10 5

10

15

20

25

Productions of contours 

Direct method 

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Finding points on the ground with the value of the required contour 

Indirect method 

Random spot heights

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Grid of spot heights

Productions of contours (indirect method)

From random spot heights

From a grid of spot heights

For next practical 

Determine the cross cross--section -section and long long-section for a road, with distance of 100m

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Contouring using the Grid and Levelling method

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Use the rise/fall or HC method for data calculation