Showing posts with label highway design. Show all posts
Showing posts with label highway design. Show all posts
Pavement Types
The selection of base course and the surface course depends upon the following factors:
1. Type and intensity of traffic
2. Funds available for the construction project and for the subsequent maintenance.
3. Subgrade soil and drainage conditions.
4. Availability of construction materials at site
5. Climatic condition
6. Plants and equipment available
7. Time available for completing the project.
8. Altitude at which construction has to be done.
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The selection of the pavement type therefore is governed by one or more factors listed above. However the fundamental factors is the traffic volume or intensity. It is suggested that the low cost roads could successfully function with the traffic intensity of 30 tonnes to 200 tonnes per day. The water bound macadam may cater up to 500 tonnes per day. The bituminous pavement may easily cacy up to 1500 tonnes per day. The cement concrete roads are considered suitable for traffic intensity of over 2000 tonnes per day. This however would depend upon the thickness of pavement section, the type of soil subgrade and the desired service life of the road. Each type of pavement has different periods of life after which it starts deteriorating.
2. Funds available for the construction project and for the subsequent maintenance.
3. Subgrade soil and drainage conditions.
4. Availability of construction materials at site
5. Climatic condition
6. Plants and equipment available
7. Time available for completing the project.
8. Altitude at which construction has to be done.
www.vejdirektoratet.dk
The selection of the pavement type therefore is governed by one or more factors listed above. However the fundamental factors is the traffic volume or intensity. It is suggested that the low cost roads could successfully function with the traffic intensity of 30 tonnes to 200 tonnes per day. The water bound macadam may cater up to 500 tonnes per day. The bituminous pavement may easily cacy up to 1500 tonnes per day. The cement concrete roads are considered suitable for traffic intensity of over 2000 tonnes per day. This however would depend upon the thickness of pavement section, the type of soil subgrade and the desired service life of the road. Each type of pavement has different periods of life after which it starts deteriorating.
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
General Consideration
Engineers have been always with open mind to adopt any material available to them for its use for the construction purposes. Research facilities at hand help them to judge the suitability of the materials. It is logical to see that the purpose of highway construction is to provide a firm and even surface for the carriageway or the pavement which could stand the distress caused due to number of load applications. Hence the pavement is prepared using broken stones, or soil (for stabilized soil) and binder material to bind the aggregates to form a homogeneous pavement section.
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picture from : www.nelsonconstruction.net
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
picture from : media-2.web.britannica.com
picture from : www.nelsonconstruction.net
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Climatic Variations
The climatic variations cause the following maor effects
1. Variation in moisture condition
2. Frost action
3. Variation in temperature
The pavement performance is very much affected by the variation in moisture and the forst. This is mainly because of the variation in stability, and volume of the subgrade soil due to these two effects. Variation in temperature generally affects the pavement materials like bituminous mixes and cement concrete.
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Strength Characteristics of Pavement Materials
For design purposes, it is required that the various pavement materials are assigned strength parameters suitable to the design method employed for the purpose. The general strength values evaluated are:
1. California Bearing Ratio (CBR) value
The strength values so obtained for the materials tested are of relative significance and do not provide an absolute measure. There are design methods which employ the CBR strength values of materials used in diffeerent pavement layers
2. Elastic modulii
Depending upon the design methods, the elastic modlii of different pavement materials are evaluated. Mainly, plate bearing test is employed for this purpose. Further modulus of elasticity or modulus of deformation of highway materials may be determined from triaxial compression test.
The elastic modulii of the following are determined by plate bearing tests:
1. Subgrade modulus
2. Elastic modulii of base course and sub base course materials
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
The elastic modulii of the following are determined by plate bearing tests:
1. Subgrade modulus
2. Elastic modulii of base course and sub base course materials
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Design Wheel Load
The various wheel load factors to be considered in pavement design are :
1. Maximum wheel load
2. Contact pressure
3. Dual or multiple wheel loads and equivalent single wheel load
4. Repetition of loads
Highway and Transport Engineering
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Design Factors
Pavement design chiefly consists of two aspects - the structural design and design of paving mixture. Following are the factors which affect the pavement thickness requirements
- Design wheel load
- Strength characteristics of pavement materials and subgrade supporting capacity
- Climatic variation
Highway and Transport Engineering
and this section is about Highway Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Highway Geometric Design
The geometrics of highway should be designed to provide optimum efficiency in traffic operation with maximum safety at resonable cost. The designer may be exposed to either planning of new highway net work or improvement of existing highways to meet the requirements of the existing and the anticipated traffic.
Geometric design of highways deals witj the following elements:
(i) Cross section elements
(ii) Sight distance considerations
(iii) Horizontal and vertical alignment details
(iv) Intersection elements
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Under cross section elements, the consideration for the width of pavement, formation and land, the surface characteristics and cross slope of pavement are included. The sight distance or clear distance visible ahead of a driver at horizontal and vertical curves and at intersections govern the safe movements of vehicles.
The change in the road directions are made possible by introducing horizontal curves. Superelevation is provided by raising the outer edge of pavement to counteract the centrifugal force developed on a vehicle traversing a horizontal curve; extra pavement width is also provided on horizontal curves. In order to introduce the centrifugal force and the superelevation gradually, transition curves are introduced between the straight annd circular curves. The gradients and vertical alignment of a highway.
Highway geometrics are greatly influenced by the topography, locality and traffic characteristics and the requirements. The factors which conrol the geometric design requirements are speed, road user and vehicular characteristics, design traffic, traffic capacity and benefit cost considerations.
Highway and Transport Engineering
and this section is about Highway Geometric Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Under cross section elements, the consideration for the width of pavement, formation and land, the surface characteristics and cross slope of pavement are included. The sight distance or clear distance visible ahead of a driver at horizontal and vertical curves and at intersections govern the safe movements of vehicles.
The change in the road directions are made possible by introducing horizontal curves. Superelevation is provided by raising the outer edge of pavement to counteract the centrifugal force developed on a vehicle traversing a horizontal curve; extra pavement width is also provided on horizontal curves. In order to introduce the centrifugal force and the superelevation gradually, transition curves are introduced between the straight annd circular curves. The gradients and vertical alignment of a highway.
Highway geometrics are greatly influenced by the topography, locality and traffic characteristics and the requirements. The factors which conrol the geometric design requirements are speed, road user and vehicular characteristics, design traffic, traffic capacity and benefit cost considerations.
Highway and Transport Engineering
and this section is about Highway Geometric Design
(refference : Khanna, S.K., Justo, C.E.G., Highway Engineering, 3th edition, Nem Chand & Bros Roorkee (U.P.), 1976.)
Design of Highway
This article is about highway and transport engineering, this time we talk about the Design of Highway
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pict source: www.athulabuilders.com
Each state highway agency typically develops its own versions of specifications standard drawings, and plan preparation procedures based on the national guide lines adopted by American Association of State Highway and transportation Officials (AASHTO). The establishment and distribution of requirements for the design of highway facilities serves to ensure that uniform roadways are designed and constructed on a statewide basis. This statewide uniformity facilitates the understanding of engineering designs by road building contractors an significantly contributes to the implementation of consistent construction methods.
The elements of design are influenced by a wide variety of design controls, engineering criteria, and project specific objectives. Such factors include the following:
(source: Wright, P.H, with contributions by James S. Lai, Peter S.Parsonson, Michael Meyer., Highway Engineering, 6th edition ,John Wiley & Sons, Inc.New York, 1996.)
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pict source: www.athulabuilders.com
Each state highway agency typically develops its own versions of specifications standard drawings, and plan preparation procedures based on the national guide lines adopted by American Association of State Highway and transportation Officials (AASHTO). The establishment and distribution of requirements for the design of highway facilities serves to ensure that uniform roadways are designed and constructed on a statewide basis. This statewide uniformity facilitates the understanding of engineering designs by road building contractors an significantly contributes to the implementation of consistent construction methods.
The elements of design are influenced by a wide variety of design controls, engineering criteria, and project specific objectives. Such factors include the following:
- functional classification of the roadway
- projected traffic volume and composition
- required design speed
- topography of the surrounding land
- capital costs for construction
- agency funding mechanisms
- human sensory capacities of roadway users
- vehicle size and performance characteristics
- traffic safety considerations
- public involvement, review, and comment
- environtmental considerations
- right of way impacts and costs
(source: Wright, P.H, with contributions by James S. Lai, Peter S.Parsonson, Michael Meyer., Highway Engineering, 6th edition ,John Wiley & Sons, Inc.New York, 1996.)
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