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Services | Soil Amendment
Soil Amendment and Fly Ash
Soil Amendment is the chemical and/or mechanical modification of soil properties to improve the engineering performance of soils. The properties that are most often modified are strength, plasticity, density, and water content. Improvements to soil properties expedite construction activities which contribute to savings in time and money. Typically, fly ash is used in conjunction with other materials such as lime, cement, or lime kiln dust to achieve the desired effect.
Applications:
- Enhanced soil strength properties
- Embankment stabilization
- Improved control of shrink/swell properties of expansive soils
- Drying agent as a means to improve compaction
Benefits:
- Eliminates the need for expensive borrow materials
- Expedites construction by improving excessively wet or unstable sub-grade
- Improves sub-grade conditions allowing for reduced pavement thickness
- Reduces the need for expensive aggregates in pavement cross sections
Soil Amendment and Soil Strength
Fly ash is used to improve the compressive and shearing strength of soils. Fly ash can be used to effectively improve sub-grades, base courses and backfill which reduce lateral earth pressures and improve slope stability on embankments.
Several factors should be considered including the in-place soil properties, moisture content at time of compaction, fly ash blend ratio with lime, cement, etc.
Soil Amendment and Shrink Swell
Various soils undergo extensive volumetric changes when subjected to fluctuating moisture contents. If not controlled, these volumetric changes can impose loads that cause movement to structures that lead to premature failure.
Fly ash reduces the potential of a plastic soil to undergo volumetric expansion by bonding the soil grains which restrict or reduce soil particle movement.
Soil Amendment and Water Content
Moisture content of soil must be controlled due to the effect it has on soil density. Soil must be compacted to the maximum practical density to achieve a firm base for overlying structures. Fly ash serves as a drying agent for soils that are too wet to achieve the required density. The drying affect of fly ash in wet soil occurs rapidly which allows the contractor to quickly proceed with construction activities. Fly Ash also makes the soil more resistant to water infiltration.
Caution: Important considerations include:
- The rate of hydration reaction upon exposure to water
- Soil moisture content at the time of compaction
- Sulfate content of fly ash – greater than ten percent may cause soil to expand
- Leaching tests may be required by state agencies
The use of fly ash in soil amendment may be subject to local environmental requirements pertaining to leaching and interaction with ground water which should be considered.
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