Evaluation of Pavement Design in Virginia Based on Layer Deflections, Subgrade and Its Moisture Content PDF Download
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Author: Nari K. Vaswani Publisher: ISBN: Category : Pavements Languages : en Pages : 35
Book Description
In this investigation, the optimum structural strength contributed by a material to the overall strength of the pavement was studied for cases applicable to Virginia. The variables were (a) the modulus of elasticity or the thickness equivalency of the material, (b) the thickness of the material in the layer, (c) the location of the material with respect to other layers containing stronger or weaker materials and in varying thicknesses, and (d) the effect of the total pavement thickness and the depth of the material from the top of the pavement. The investigation consisted of two parts: (a) a study of the thickness equivalencies of the materials on interstate, primary, secondary and subdivision roads in Virginia, and (b) a model study. The evaluation of the highway system was quantitative, while that of the model study was qualitative only. This investigation showed that the structural strength of a pavement is decreased when a weaker layer is placed over a stronger layer or when a weaker layer is sandwiched between two strong layers. The investigation also showed that when the bottom of the top layer does not bend, the stress distribution is bulb type; and when the bottom bends, the stress distribution is fan type. Each case would therefore need a different mathematical treatment for design.
Author: Nari K. Vaswani Publisher: ISBN: Category : Pavements Languages : en Pages : 35
Book Description
In this investigation, the optimum structural strength contributed by a material to the overall strength of the pavement was studied for cases applicable to Virginia. The variables were (a) the modulus of elasticity or the thickness equivalency of the material, (b) the thickness of the material in the layer, (c) the location of the material with respect to other layers containing stronger or weaker materials and in varying thicknesses, and (d) the effect of the total pavement thickness and the depth of the material from the top of the pavement. The investigation consisted of two parts: (a) a study of the thickness equivalencies of the materials on interstate, primary, secondary and subdivision roads in Virginia, and (b) a model study. The evaluation of the highway system was quantitative, while that of the model study was qualitative only. This investigation showed that the structural strength of a pavement is decreased when a weaker layer is placed over a stronger layer or when a weaker layer is sandwiched between two strong layers. The investigation also showed that when the bottom of the top layer does not bend, the stress distribution is bulb type; and when the bottom bends, the stress distribution is fan type. Each case would therefore need a different mathematical treatment for design.
Author: Nari K. Vaswani Publisher: ISBN: Category : Pavements Languages : en Pages : 40
Book Description
Studies were conducted to relate the deflection of flexible pavements to such environmental factors as temperature and moisture content of the pavements and their subgrade soils. Also considered were the thickness and the relative positions of the different components making up the pavement systems. Seven pavement designs were studied with respect to the above factors. The major conclusions of the study are: 1. The effect of a weak sandwiched layer in reducing pavement strength needs to be considered during pavement design and evaluation. 2. The air temperature considerably affects the pavement modulus. There is a great need for correcting dynaflect deflections for temperature in Virginia. 3. Another factor that affects the value of the pavement modulus is the rigidity of the support to the asphaltic concrete; the greater the rigidity, the, higher the pavement modulus. 4. The temperature sensitivity of the pavement modulus is directly proportional to the pavement modulus and the thickness of the asphaltic concrete layer. 5. The primary factor that affects the subgrade modulus appears to be the relative density of the subgrade soil. Low density soils cause high subgrade moisture and low subgrade modulus and high variations in both the moisture and modulus. The reverse is also true.
Author: David E. Newcomb Publisher: Transportation Research Board ISBN: 9780309068574 Category : Science Languages : en Pages : 84
Book Description
This synthesis report will be of interest to pavement and geotechnical design and research engineers, geologists and engineering geologists, and related laboratory personnel. It describes the current practice for measuring in situ mechanical properties of pavement subgrade soils. The tests conducted to measure the mechanical properties of soil strength and stiffness are the primary topics, and these are discussed in the context of design procedures, factors affecting mechanical properties, and the variability of measurements. Information for the synthesis was collected by surveying U.S., Canadian, and selected European transportation agencies and by conducting a literature search. This TRB report provides information on existing and emerging technologies for static and dynamic, and destructive and nondestructive testing for measuring in situ mechanical properties of pavement subgrade soils. Correlations between in situ and laboratory tests are presented. The effects of existing layers on the measurement of subgrade properties, and soil spatial and seasonal variability are discussed. Most importantly, the use of soil properties in pavement design and evaluation are explained. New applications or improvements to existing test methods to support the use of mechanistic/stochastic-based pavement design procedures are also explained.
Author: Nari K. Vaswani Publisher: ISBN: Category : Pavements Languages : en Pages : 31
Book Description
The use of a weak sandwich layer in a four-layer system is common in the construction of flexible pavements, but the use of a sandwich layer in a three-layer system is in the experimental stage in Virginia. Theoretical and field studies have been carried out to determine how sandwiched layers affect the design and performance of pavement systems. It has been determined that a flexible sandwiched layer can be economically used in a four-layer system by providing an optimum thickness of the sandwiched material. The optimum thickness as determined in this investigation is the minimum thickness that will: (1) act as a cushion to prevent cracking in the soil cement subbase from reflecting to the surface, and (2) permit compliance with the density specifications. For crushed stone this thickness is 4". Use of this thickness should increase pavement life .and reduce construction costs. It has also been shown that the four-layer system pavements can be evaluated through elastic layered theory. A three-layer sandwich system of economical design and based on traffic requirements is recommended for low traffic volumes. In this case it has been determined that the optimum thickness is that which will (1) prevent reflection cracking through the untreated aggregate from the 6-inch soil cement layer, and (2) satisfy the density specification. These requirements can be met with a 3" to 4" layer of crushed stone with a prime and double seal. The evaluation of the four-and three-layer systems has shown that the strains and the resulting pavement life can be predicted from dynaflect deflections.
Author: Nari K. Vaswani
Author: Nari K. Vaswani
Author: Nari K. Vaswani
Author: National Research Council (U.S.). Highway Research Board
Author: 
Author: David E. Newcomb
Author: Harry T. Craft
Author: 
Author: Nari K. Vaswani
Author: 
Author: Nari K. Vaswani