Flexible And Rigid Pavement Design PdfBy Clemencia G. In and pdf 22.05.2021 at 22:06 8 min read
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- Flexible Pavement Empirical Design Example
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- Pavement Design and Analysis for Overlaying of Flexible to Rigid Pavement
Flexible Pavement Empirical Design Example
Design is the process of developing the most economical combination of pavement layers in relation to both thickness and type of wheel load to suit to the soil foundation and the cumulative traffic to be carried during the design life.
Design of Highway Pavements Types of pavements 1 Flexible pavements. Design factors for pavements. Flexible pavement design methods 1 Group Index G. I method. For design purposes 1 design traffic in terms of cumulative number of standard axles kg ;and. Is required. For estimating design traffic following information is needed: 1 initial traffic after construction in terms of CVPD. For the purpose of structural design ,only the number of commercial vehicles of gross weight of 3 tonnes or more and their axle loading is considered.
To obtain a realistic estimate of design traffic,due consideration should be given to to the existing traffic or that anticipated based on possible changes in the road network and land use of the area served,the probable growth of traffic and design life.
Estimate of the initial daily average traffic flow for any road should normally based on atleast 7 days 24 hour classified traffic counts. Traffic estimate can be made on the basis of potential land use and the traffic on the existing routes in the area. Traffic growth rate may be estimated by 1 by studying the past trends of traffic growth.
If adequate data is not available it is recommended that an average annual growth rate of 7. Design life. Design life is defined in terms of the cumulative number of standard axles that can be carried before strengthening of the pavement is necessary.
It is recommended that pavements for national highways and state highways should be designed for a life of 15 years. Expressways and urban roads may be designed for a longer life of 20 years. For other categories of roads, a design life of 10 to 15 years may be adopted. It is a multiplier to convert the no. It is defined as equivalent number of standard axles per commercial vehicle. The VDF varies with the vehicle axle configuration,axle loading,terrain,type of road and from region to region.
These are used to convert different axle load repetitions into equivalent axle load repetitions. It is recommended that designer should take the realistic values of VDF after conducting the axle load survey. Where sufficient information on axle loads is not available and the project size does not warrant conducting an axle load survey, the indicative value of VDF are as :.
Distribution of commercial traffic over the carriageway A realistic assessment of distribution of commercial traffic by direction and by lane is necessary as it directly affects the total equivalent standard axle load applications used in design. In the absence of adequate and conclusive data following distribution may be assumed. Where significant difference between the two streams can occur,condition in the more heavily trafficked lane should be considered for design.
Computation of design traffic. The design traffic is considered in terms of the cumulative number of standard axles in the lane carrying maximum traffic to be carried during the design life.
Subgrade Subgrade in cut or fill should be well compacted. IRC Recommended practice for the construction of earth embankment for road works.
Material used as subgrade in expressways,national highways,state highways should have the dry density not less than 1. CBR gives the strength of subgrade soil in cut and fill at most critical moisture condition likely to occur in situ. CBR can be determined as per IS part 16 in lab. In-situ CBR is not recommended for design purposes. Soaking for 4 days may be unrealistically severe moisture condition,in certain cases were the climate is arid throughout the year ie the annual rainfall is less than mm is less and the water table is too deep,CBR value may be prepared at the natural moisture content of soil at subgrade depth immediately after recession of the monsoon.
Use of expansive soil is not allowed for subgrade construction particularly for heavily trafficked roads. When expansive soils are unavoidable compaction requirement as per Annexure-4 of this code should be followed.
Expansive soils swells very little when compacted at low densities and high moisture but swells greatly when compacted at high densities and low moisture.
For the design of pavement to carry traffic in the range of msa and traffic in the range of msa the pavement thickness design chart is given in fig. Based on the recommended designs minimum thickness and compositions of pavement layers for new constructions are given in the pavement design catalogue, plates 1 and 2. The material passing micron sieve when tested in accordance with IS pt 5 should have liquid limit and plasticity index of not more than 25 and 6 respectively.
From drainage consideration the granular sub base should be extended over the entire formation width in case the subgrade soil is of relatively low permeability. The thickness of sub base should not be less than mm for design traffic less than 10msa and mm for design traffic of 10msa and above.
The recommended minimum thickness of granular base is mm for traffic upto 2msa and mm for traffic exceeding 2msa. In case the granular material is manually laid or if recommended by engineer, the DBM may be preceded by a 75 mm thick BM layer. Choice of appropriate type of bituminous wearing course will depend upon several factors like design traffic, sub grade conditions, rainfall etc.
For wearing course ref. Where the wearing surface adopted is open graded premix carpet of thickness upto 25 mm, the thickness of the surfacing should not be counted towards the total thickness. Refere plate 1 and 2. In some cases the total pavement thickness given in the recommended designs is slightly more than the thickness obtained from the design chart this is in order to : A provide the minimum thickness of sub base.
B adapt the design to stage construction which need some adjustment. DBM shall be constructed in 2 layers when prescribed thickness is more than mm. For intermediate traffic ranges, the pavement layer thickness will be interpolated linearly. For traffic exceeding msa, the pavement design appropriate to msa may be chosen further strengthening to extend the life based on pavement deflection measurements as per IRC Drainage Measures The performance of a pavement can be seriously affected if adequate drainage measures to prevent accumulation of moisture in the pavement structure are not taken.
Some of the measures to guard against poor drainage conditions are: 1 Maintenance of transverse section in good shape. Drainage of the pavement structural section can be greatly improved by providing a high permeability drainage layer satisfying the following criteria Non woven geosynthetic can be provided to act as filter. Tension and Compression The intensity of normal force per unit area is expressed as normal stress, and is expressed in units of force per unit area.
If the forces applied to the ends of the bar are such that the bar is in tension, then tensile stresses are set up in the bar. If the bar is in compression we have compressive stresses.
Normal Strain :- The elongation per unit length or can be defined as change in length by original length. For any material having a stress strain curve it is evident that the relation between stress and strain is linear for comparatively small volumes of strain. This linear relation between elongation and the axial force causing it was first noticed by Sir Robert Hook in and is called Hooks law.
Poissons ratio :- When a bar is subjected to a simple tensile loading there is an increase in the length of the bar in the direction of load, but a decrease in the lateral dimensions perpendicular to load. The ratio of the strain in the lateral direction to that in axial direction is defined as Poissons ratio. For most metals it lies between 0. Rigid pavement where and why? Vehicles, like, agricultural tractor trailers, light goods vehicles, buses, animal drawn vehicles, motorized 2 wheelers and cycles.
Light and medium trucks carrying sugarcane timber, quarry material etc. Neglected maintenance. Concrete pavements offer an alternative to flexible pavement where the soil strength is poor, the aggregates are costly and drainage conditions are bad, waterlogged area.
Tyre Pressure 0. Design Period The design methodology is based on wheel load stresses. Design life of not less than 20 years. Characteristics of the subgrade Modulus of subgrade reaction, k, which is determined by carrying out a plate bearing test, using mm dia. Plate according to IS Subgrade strength is desirable to determine during or soon after the rainy season.
An idea of the k value of a homogeneous soil subgrade may be obtained from its soaked CBR value using table 1. Sub-Base The Provision of a sub-base below the concrete pavements has many advantages such as: It Provides a uniform and reasonably firm support It Prevents mud-pumping on subgrade of clays and silts It acts as a leveling course on distorted, non-uniform and undulation sub-grade It acts as a capillary cut-off.
Concrete Strength Since concrete pavements fail due to bending stresses, it is necessary that their design is based on the flexural strength of concrete. It is suggested that the day strength be used for design instead of the day strength as the traffic develops only after the lapse of a period of time.
The 90 day flexural strength may be taken as 1. For rural roads, it is recommended that the characteristic day compressive strength should be at least 30 MPa. The characteristic day flexural strength shall be at least 3.
The factors commonly considered for design of pavement thickness are traffic loads and temperature variation, as the two are additive. The effects of moisture changes and shrinkage are not normally considered critical to thickness design.
Three different regions slab-corner, edge and interior-which react differently from one another to the effect of temperature differentials, as well as load application.
The concrete pavements undergo a daily cyclic change of temperature differentials, the top being hotter than the bottom during day and cooler during night.
The consequent tendency of the pavement slabs to warp upwards top convex during the day and downwards top concave during the night, and restraint offered to this warping tendency by selfweight of the pavement induces stresses in the pavement, referred to commonly as temperature stresses.
These are flexural in nature, being tensile at bottom during the day and at top during night. As the restraint offered to warping at any section of the slab would be a function of weight of the slab upto the section, it is obvious that corners have very little of such restraint.
The restraint is maximum in the slab interior, and somewhat less at the edge. Consequently, the temperature stresses induced in the pavement are negligible in the corner region, and maximum at the interior.
Under the action of load application, maximum stress is induced in the corner region, as the corner is discontinuous in two directions especially when load transfer steel dowels are not provided in rural roads. The edge being discontinuous in one direction only has lower stress, while the least stress is induced in the interior where the slab is continuous in all directions.
The maximum combined tensile stresses in the three regions of the slab will thus be caused when effects of temperature differentials are additive to the load effects.
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Normally, overlays of existing pavements are used to increase the load-carrying capacity of an existing pavement or to correct a defective surface condition on the existing pavement. Of these reasons, the first requires a structural design procedure for determining the thickness of overlay, whereas the second requires only a thickness of overlay sufficient to correct the surface condition and no increase in load-carrying capacity is considered. The design method for overlays included in this chapter determines the thickness required to increase load- carrying capacity. The study section is a part of the National Highway No. The long-term objective of the project is to construct a highway link, which is an integral part of a National Highway System, which can serve the countrys transportation needs in the future, before any actual construction can begin many factors affecting the population near by the proposed project and future road users have to be examined. A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to distribute the applied vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. National Research Council, S. Hanna, A.
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Pavement Design and Analysis for Overlaying of Flexible to Rigid Pavement
This represents a typical range of reliability levels encountered for Interstate highways. By looking at several different design periods and reliability levels this example gives an idea of the relative influence of these inputs. This step involves converting the daily traffic volume into an annual ESAL amount.
Guide to Pavement Technology Part 2: Pavement Structural Design provides advice for the structural design of sealed road pavements. The advice has been generally developed from the approaches followed by the Austroads member agencies.
Однажды вечером на университетском представлении Щелкунчика Сьюзан предложила Дэвиду вскрыть шифр, который можно было отнести к числу базовых. Весь антракт он просидел с ручкой в руке, ломая голову над посланием из одиннадцати букв: HL FKZC VD LDS В конце концов, когда уже гасли огни перед началом второго акта, его осенило. Шифруя послание, Сьюзан просто заменила в нем каждую букву на предшествующую ей алфавите. Для расшифровки Беккеру нужно было всего лишь подставить вместо имеющихся букв те, что следовали непосредственно за ними: А превращалось в В, В - в С и так далее.
И все же Сьюзан понимала, что остановить Хейла могут только его представления о чести и честности. Она вспомнила об алгоритме Попрыгунчик. Один раз Грег Хейл уже разрушил планы АНБ.