EnggPedia - The Engineering Encyclopedia


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The scale of a map is the ratio between distances on the map and corresponding distances in the real world, e. g., if a map has a scale of 1:50,000, then 1 cm on the map equals 50,000 cm or 0.5 km on the Earth's surface.

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Statistics refers to numerical facts, systematically arranged, and used to draw conclusions
It is defined as a discipline that includes procedures and techniques used to collect, process and analyze numerical data to make inferences and to reach decisions in the face of uncertainty.

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A projection is a method by which the curved surface of the earth is represented on a flat surface.

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The collection of facts and figures needed to help us make more informed decisions in different situations.
Types of data
Data is classified as:
1. Quantitatively
2. Qualitatively

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GIS can be considered as a map information system for management, analysis, presentation and distribution. A GIS stores information about the world as a collection of layers that can be linked together by geography.

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A map is a graphic form, normally to scale, of spatial abstraction of features on, or in relation to, the surface of the Earth.

Types of maps

  1. Topographic maps
  2. Thematic maps
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Pavement Requirements and Types

An ideal pavement should meet the following requirements:

  • Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil,
  • Structurally strong to withstand all types of stresses imposed upon it,
  • Adequate coefficient of friction to prevent skidding of vehicles,
  • Smooth surface to provide comfort to road users even at high speed,
  • Produce least noise from moving vehicles,
  • Dust proof surface so that traffic safety is not impaired by reducing visibility,
  • Impervious surface, so that sub-grade soil is well protected, and
  • Long design life with low maintenance cost.

Pavement Requirements and types of pavement

Types of pavements

The pavement may be defined as relatively stable layer or crust constructed over the natural soil. The main function of the pavement is to support and distribute the heavy wheel loads of vehicles over a wide area of the underlying sub grade soil and permitting the deformations with in elastic or allowable range and provide an adequate surface.

For the design purposes, the pavements may be divided into the following categories depending upon their structural action.

  1. Flexible Pavements

  2. Rigid Pavements

The main difference between these two types of pavements is the manner in which they distribute the load over their sub grade.

Flexible pavements

Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the points of contact in the granular structure (see Figure).

Deflection on flexible pavement

The wheel load acting on the pavement will be distributed to a wider area, and the stress decreases with the depth. Taking advantage of these stress distribution characteristic, flexible pavements normally has many layers. Hence, the design of flexible pavement uses the concept of layered system. Based on this, flexible pavement may be constructed in a number of layers and the top layer has to be of best quality to sustain maximum compressive stress, in addition to wear and tear.

The lower layers will experience lesser magnitude of stress and low quality material can be used. Flexible pavements are constructed using bituminous materials. These can be either in the form of surface treatments (such as bituminous surface treatments generally found on low volume roads) or, asphalt concrete surface courses (generally used on high volume roads such as national highways). Flexible pavement layers reflect the deformation of the lower layers on to the surface layer (e. g., if there is any undulation in sub-grade then it will be transferred to the surface layer). In the case of flexible pavement, the design is based on overall performance of flexible pavement, and the stresses produced should be kept well below the allowable stresses of each pavement layer.

Rigid pavements

Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below. A typical cross section of the rigid pavement is shown in Figure1. Compared to flexible pavement, rigid pavements are placed either directly on the prepared sub-grade or on a single layer of granular or stabilized material. Since there is only one layer of material between the concrete and the sub-grade, this layer can be called as base or sub-base course.

In rigid pavement, load is distributed by the slab action, and the pavement behaves like an elastic plate resting on a viscous medium. Rigid pavements are constructed by Portland cement concrete (PCC) and should be analyzed by plate theory instead of layer theory, assuming an elastic plate resting on viscous foundation. Plate theory is a simplified version of layer theory that assumes the concrete slab as a medium thick plate which is plane before loading and to remain plane after loading. Bending of the slab due to wheel load and temperature variation and the resulting tensile and flexural stress.


Insecticides are chemical compounds that are used for the control of insects either through death of the insect or through interference with the reproductive cycle of the insect.

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At the site, the drainage should cross the canal alignment at right angles. Such a site provides good flow conditions and also the cost of the structure is usually a minimum.

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The channel is the same thing that is used for the water carriage or distribution purpose, however in case of hydropower projects the channel that takes water from the intake (Diversion Structure) is usually called connecting channel.

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