Use of toposheets in civil engineering projects

USE OF TOPOSHEETS IN CIVIL ENGINEERING PROJECTS ARJUN. K & DR.A.BALASUBRAMANIAN

DOS IN EARTH SCIENCE

UNIVERSITY OF MYSORE

Contents

• Introduction • Contour • Contour interval • Types of slope • Topographic survey • Types of Landforms • Use of Toposheets in Civil Engineering Projects • Conclusion • Reference

Introduction

• Topographic maps are detailed,accurate graphic representation of features that appear on the Earth’s surface.These features include:

1.Cultural:roads,buildings,urban development,railways,state and

international borders

2.Hydrography:lakes,rivers,streams,swamps and coastal flats

3.Relief:mountains,valleys,hills,contours,cliffs and depression

4.Vegetation:wooded and cleared areas,vineyards and orchards

Contour

• An imaginary line on the ground surface joining the points of equal elevation is known as contour.

• The lines are numbered giving the height above sea level in meters.

• The process of tracing contour lines on the surface of the earth is called Contouring.

Characteristics of Contour line

• A contour line is drawn to show places of equal heights.

• Contour lines and their shapes represent the height and slope or gradient of the landform.

• Closely spaced contours represent steep slopes while widely spaced contours represent gentle slope.

• Two contours of different elevation usually do not cross each other.

Contour Interval

• The vertical distance between any two consecutive contour lines is called contour interval.

• The contour interval depends on the nature of the ground(i.e.whether flat or steep)

Types of slope

Gentle slope:

• When the degree or angle of slope of a feature is very low,the slope will be gentle.

• The contours representing this type of slope are far apart.

Steep slope:

• When the degree or angle of slope of a feature is high,the slope will be steep.

• The contours are closely spaced,they indicate steep slope.

Gentle slope

Steep slope:

Topographic survey

• Topographic survey is a field of geoscience which deals in the study and description of surface shape and features of the earth. Topography in general is related with mapping of the local details such as relief and natural/artificial features.

Types of Landforms Conical Hill

• A conical hill with uniform uniform slope and narrow top represented by concentric contours,spaced almost at regualar intervals.

Plateau

• A widely stretched flat-topped high land with relatively steeper slopes.

V – shaped valley

• V – shaped valley occurs in mountainous areas.

• The lowermost part of this valley is shown by the innermost contour line with small contour interval.

• The contour value increases with uniform intervals for all other contour lines outward.

U-shaped Valley

• A U-shaped valley is formed by strong lateral erosion of glaciers at high altitudes.The flat wide bottom and steep sides makes it resemble the letter ‘U’.

• The lowermost part of the U-shaped valley is shown by the innermost contour line with a wide gap between its two sides.

Gradient of Terrain

• Topographic map allows the calculation of the gradient of a terrain.

• This process requires taking the difference in height between two points and dividing by distance between these points.

• One useful application of this formula is for calculating the flow of a river down a mountain

USE OF TOPOSHEETS IN CIVIL ENGINEERING PROJECTS

1. Toposheet provide valuable information about the topography of area,whether it is flat,undulating or mountainous.The nature of the ground surface of an area can be understood by studying topographic map.

2. By drawing the section in the plan,it is possible to find out profile of the ground along the line.It helps in finding out depth of cutting and filling,if formation level of road/railway is decided.

3. The routes of the railway,road,canal or sewer lines can be decided so as to minimize and balance earthworks.

4. Catchment area and hence quantity of water flow at any point of river can be found.This study is very important in locating bunds,dams and also to find out flood levels.

5. From the contours,it is possible to determine the capacity of a reservoir.

DAMS

• A narrow U- shaped valley, i.e., a narrow stream flowing between high rocky walls, would suggest a concrete flow dam.

• A low plain country, would suggest an earth fill dam with separate spillways.

• A narrow V-shaped valley indicates the choice of an Arch dam.

• After studying the topography of the site and catchment area, it is possible to fix the height of the dam and reservoir capacity . Steep shoulder hills across the rivers may be suitable site for location of the proposed dam.

ROAD ALIGNMENT

• Class and purpose

• Obligatory points

• Gradient

• Horizontal curves

• Obstructions

• Cross drainage works

• Bridges

• Railway crossing

• Agricultural land and dense forests

BRIDGE

• Local terrain and site condition

• A straight reach of river.

One cross section each cross the river at the selected sites can be taken.

• Catchment area – used mainly for the flood analysis.

BUILDING

• It is very important for the building site to avoid low-lying areas with flooding potential.

• Adequate drainage to control storm water.

• Slope analysis

• Cultural factors

• Natural features

TUNNELS

• The underground routes are called tunnels.These are provided,particularly in hilly regions,to cut down distance and save time for the traffic.

• The physiography of the area is the first thing to be investigated.It involves a knowledge of valleys,hills,slopes and other physical features.This tell about the possible locations for the alignment of tunnel.

RAILWAYS

• Adequate land

• Alignment

• Drainage

• Water supply

• Gradient

• Accessibility

CONCLUSION

• A topographic map furnishes information regarding the features of the ground,whether it is flat,undulating or mountainous.

• A civil engineer studies the contours and find out the nature of the ground to identify.Suitable site for the project works to be taken up.

• It enables an engineer to approximately select the most economical or suitable site for an engineering project such as a road, a railway, a canal or a pipeline etc.

• Catchment area and capacity of a reservoir may be determined from the contour map.

REFERENCE

• D.Venkat Reddy-Engineering Geology-Vikas publishing pvt ltd(page no:326 – 328)

• Dr.D.S.Arora-Geology For Engineers-Mohindra Capital Publishers(page no:332-347)

• K.M.Bangar-Principles of Engineering Geology-Standard Publishers(page no:362-371)

• http://geology.about.com/use of toposheets in civiengineering.htm

• http://en.wikipedia.org/wiki/toposheet