EMBANKMENT OR FILL Application Description


INTRODUCTION


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.

MATERIALS

Soils

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.

Oversize Materials

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.

Table 24-9. Embankment or fill material test procedures.

PropertyTest MethodReference
GradationParticle Size Analysis of Soils ASTM D422
Sieve Analysis of Fine and Coarse AggregateASTM D136
Unit Weight and Specific GravityUnit Weight and Voids in AggregateASTM D29
Specific Gravity of SoilsASTM D854
Relative Density of Cohesionless SoilsASTM D2049
Maximum Index Density of Soils Using a Vibratory TableASTM D4253
Minimum Index Density of Soils and Calculation of Relative DensityASTM D4254
Moisture Densiity CharacteristicsMoisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 5.5 lb (2.49 kg) Rammer and 12 in. (305 mm) DropASTM D698
(Standard)
Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 10 lb (4.54 kg) Rammer and 18 in. (457 mm) DropASTM D1557
(Modified)
Compacted Density
(In-Place Density)
Density of Soil in Place by the Sand-Cone MethodASTM D1556
Density and Unit Weight of Soil in Place by the Rubber Balloon MethodASTM D2167
Density of Soil and Soil-Aggregate in Place by Nuclear Methods (Shallow-Depth)ASTM D2922
Density of Soil in Place by the Sleeve MethodASTM D4564
Shear StrengthUnconsolidated Undrained Compressive Strength of Cohesive Soils in Triaxial CompressionASTM D2850
Direct Shear Test of Soils Under Consolidated Drained ConditionsASTM D3080
Consolidated-Undrained Triaxial Compression Test on Cohesive SoilsASTM D4767
CompressibilityOne-Dimensional Consolidation Properties of SoilsASTM D2435
One-Dimensional Consolidation Properties of Soils Using Controlled-Strain LoadingASTM D4186
One-Dimensional Swell or Settlement Potential of Cohesive SoilsASTM D4546
Bearing CapacityCalifornia Bearing Ratio (CBR) of Laboratory-Compacted SoilsASTM D1883
Bearing Ratio of Soils in PlaceASTM D4429
PermeabilityPermeability of Granular Soils by Constant HeadASTM D2434
Corrosion ResistancepH of Soil For Use in Corrosion TestingASTM G51
Field Measurement of Soil Resistivity Using the Wenner Four-Electrode MethodASTM G57
Pore Water Extraction and Determination of the Soluble Salt Content of Soils by RefractometerASTM 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.