|EMBANKMENT OR FILL||Application Description|
An embankment refers to a volume of earthen material that is placed and compacted for the purpose of raising the grade of a roadway (or railway) above the level of the existing surrounding ground surface. A fill refers to a volume of earthen material that is placed and compacted for the purpose of filling in a hole or depression. Embankments or fills are constructed of materials that usually consist of soil, but may also include aggregate, rock, or crushed paving material.
Normally, the coarser fill materials are placed at or near the bottom or base of the embankment in order to provide a firm foundation for the embankment and also to facilitate drainage and prevent saturation. The top portion of an embankment usually is constructed of relatively high-quality, well-compacted subgrade material that is capable of supporting the overlying pavement layers and imposed wheel loadings without deflection or undesirable movement. The fill material used throughout the remainder of the embankment must be capable of meeting applicable specification quality requirements and be capable of being placed and compacted at or close to its maximum achievable density. The material is spread in relatively thin layers of 150 mm (6 in) to 200 mm (8 in) and each layer is compacted by rolling over it with heavy compaction equipment.
Many different types of soils may be suitable for use in the construction of an embankment or fill, ranging from granular soils (sand and gravel), which are highly desirable, to the more finely sized soils (silt and clay), which are usually somewhat less desirable. Certain types of soils (such as saturated clays and highly organic soils) are considered unsuitable for use as materials in embankment or fill construction. Regardless of the type(s) of soil(s) used to construct embankments or fills, the material should be well graded, capable of being well compacted, be within a proper range of moisture to optimize compaction, and be free of unsuitable or deleterious materials, such as tree roots, branches, stumps, sludge, metal, or trash.
Some oversize materials (over 100 mm (4 in) in size), such as rocks, large stones, reclaimed paving materials, or air-cooled slags, can be used for the construction of embankment bases. Although the use of oversize materials can result in a stable embankment base, the oversize materials should have strong particles that do not readily break down under the action of construction machinery, but which have a range of sizes so that void spaces are at least partially filled.
MATERIAL PROPERTIES AND TESTING METHODS
Some of the more important properties of materials that are used for the construction of embankments or fills include:
Table 24-9 provides a list of the standard test methods usually used to assess the suitability of conventional earthen fill materials for use in embankment or fill construction.
|Gradation||Particle Size Analysis of Soils||ASTM D422|
|Sieve Analysis of Fine and Coarse Aggregate||ASTM D136|
|Unit Weight and Specific Gravity||Unit Weight and Voids in Aggregate||ASTM D29|
|Specific Gravity of Soils||ASTM D854|
|Relative Density of Cohesionless Soils||ASTM D2049|
|Maximum Index Density of Soils Using a Vibratory Table||ASTM D4253|
|Minimum Index Density of Soils and Calculation of Relative Density||ASTM D4254|
|Moisture Densiity Characteristics||Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 5.5 lb (2.49 kg) Rammer and 12 in. (305 mm) Drop||ASTM D698|
|Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 10 lb (4.54 kg) Rammer and 18 in. (457 mm) Drop||ASTM D1557|
|Density of Soil in Place by the Sand-Cone Method||ASTM D1556|
|Density and Unit Weight of Soil in Place by the Rubber Balloon Method||ASTM D2167|
|Density of Soil and Soil-Aggregate in Place by Nuclear Methods (Shallow-Depth)||ASTM D2922|
|Density of Soil in Place by the Sleeve Method||ASTM D4564|
|Shear Strength||Unconsolidated Undrained Compressive Strength of Cohesive Soils in Triaxial Compression||ASTM D2850|
|Direct Shear Test of Soils Under Consolidated Drained Conditions||ASTM D3080|
|Consolidated-Undrained Triaxial Compression Test on Cohesive Soils||ASTM D4767|
|Compressibility||One-Dimensional Consolidation Properties of Soils||ASTM D2435|
|One-Dimensional Consolidation Properties of Soils Using Controlled-Strain Loading||ASTM D4186|
|One-Dimensional Swell or Settlement Potential of Cohesive Soils||ASTM D4546|
|Bearing Capacity||California Bearing Ratio (CBR) of Laboratory-Compacted Soils||ASTM D1883|
|Bearing Ratio of Soils in Place||ASTM D4429|
|Permeability||Permeability of Granular Soils by Constant Head||ASTM D2434|
|Corrosion Resistance||pH of Soil For Use in Corrosion Testing||ASTM G51|
|Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method||ASTM G57|
|Pore Water Extraction and Determination of the Soluble Salt Content of Soils by Refractometer||ASTM D4542|
REFERENCES FOR ADDITIONAL INFORMATION
Nichols, Herbert L. Moving the Earth. McGraw-Hill Publishing Company, New York, New York, 1976.
U.S. Bureau of Reclamation. Earth Manual. Washington, DC, 1991.