Soil Types and Conditions for Highway Structural Design
Learn about the classification of soil types based on particle sizes, including cohesive and granular soils, and their characteristics in relation to compaction for highway structural design and pavement construction.
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Structural Design of Highway Soil Types and Conditions Highway and Transportation Engineering Al-Mustansiriyah University 2019-2020 Dr. Rana Amir Yousif & Dr. Abeer K. Jameel Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
References Nicholas J. Garber and Lester A. Hoel. Traffic and Highway Engineering , Fourth Edition. Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975. Yaug H. Huang, Pavement Analysis and Design , Prentic Hall Inc., U.S.A., 1993. AASHTO Guide for Design of Pavement Structures 1993 , AASHTO, American Association of State Highway and Transportation Officials, U.S.A., 1993. Oglesby Clarkson H., HighwayEngineering , John Wiley & Sons Inc., U.S.A., 1975. Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
SOIL Types & Conditions Every soil type behaves differently with respect to maximum density and optimum moisture. Therefore, each soil type has its own unique requirements and controls both in the field and for testing purposes. Soil types are commonly classified by grain size, determined by passing the soil through a series of sieves to screen or separate the different grain sizes. Soil classification is categorized into 15 groups, a system set up by AASHTO (American Association of State Highway and Transportation Officials). Soils found in nature are almost always a combination of soil types. A well-graded soil consists of a wide range of particle sizes with the smaller particles filling voids between larger particles. The result is a dense structure that lends itself well to compaction. A soil s makeup determines the best compaction method to use. There are three basic soil groups: Cohesive Granular Organic (this soil is not suitable for compaction and will not be discussed here) Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
1. Cohesive soils: Cohesive soils have the smallest particles. Clay has a particle size range of .00004" to .002". Silt ranges from .0002" to .003". Clay is used in embankment fills and retaining pond beds. Characteristics Cohesive soils are dense and tightly bound together by molecular attraction. They are plastic when wet and can be molded, but become very hard when dry. Proper water content, evenly distributed, is critical for proper compaction. Cohesive soils usually require a force such as impact or pressure. Silt has a noticeably lower cohesion than clay. However, silt is still heavily reliant on water content. Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
2. Granular soils: Granular soils range in particle size from .003" to .08" (sand) and .08" to 1.0" (fine to medium gravel). Granular soils are known for their water-draining properties. Characteristics Sand and gravel obtain maximum density in either a fully dry or saturated state. Testing curves are relatively flat so density can be obtained regardless of water content. The tables on the following pages give a basic indication of soils used in particular construction applications. Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
COMPACTION EQUIPMENT The desired level of compaction is best achieved by matching the soil type with its proper compaction method. Other factors must be considered as well, such as compaction specs and job site conditions. Cohesive soils clay is cohesive; its particles stick together.* Therefore, a machine with a high impact force is required to ram the soil and force the air out, arranging the particles. A rammer is the best choice or a pad-foot vibratory roller if higher production is needed. *The particles must be sheared to compact. Granular soils since granular soils are not cohesive and the particles require a shaking or vibratory action to move them; vibratory plates (forward travel) are the best choice. Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
COHESIVE SOILS MTX70 Rammer P33/24 HHMR ROLLER Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
COHESIVE SOILS RX15010CI ROLLER Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
GRANULAR SOILS MVC-88 Vibratory Plate MVH-306 Reversible Plate Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
GRANULAR SOILS AR-13H Ride-on Vibratory Roller Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
Field Compaction Equipment Compaction equipment used in the field can be divided to the following types: Rollers are used for field compaction and apply either a vibrating force or an impact force on the soil. The type of roller used for any particular job depends on the type of soil to be compacted. A smooth wheel or drum roller applies contact pressure of up to 55 lb/in.2 over 100 percent of the soil area in contact with the wheel. This type of roller is generally used for finish rolling of sub-grade material and can be used for all types of soil material except rocky soils. Smooth Wheel or Drum Roller Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
Field Compaction Equipment The rubber-tired roller is another type of contact roller, consisting of a heavily loaded wagon with rows of 3 to 6 tires placed close to each other. The pressure in the tires may be up to 100 lb/in2. They are used for both granular and cohesive materials. Rubber-Tired Roller Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
Field Compaction Equipment Tamping foot rollers are similar to sheep foot rollers in that they also have protrusions that are used to obtain high contact pressures, ranging from 200 to 1200 lb/in.2. The feet of the tamping foot rollers are specially hinged to obtain a kneading action while compacting the soil. As with sheep foot rollers, tamping foot rollers compact from the bottom of the soil layer. Tamping Foot Rollers Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
Structural Design of Highway Dr. Rana Amir Yousif & Dr. Abeer K. Jameel Yoder; E. J. and M. W. Witczak, Principles of Pavement Design , A Wiley- Interscience Publication, John Wiley & Sons Inc., U.S.A., 1975.
