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Thursday, July 12, 2018

How soil cement is used in earthfill dams & embankments

Now-a-days soil cement as a facing material for earthfill dams is considered very cost-effective where proper riprap is unavailable near the site.

A fairly rigid foundation is suitable in order that deformation after disposition of soil-cement is not vital; however, no uncommon design features should be integrated into the embankment.

Normal embankment construction methods are followed, with perhaps proper precaution to make sure a minimum of embankment consolidation and foundation settlement once the construction is completed.

The soil-cement is normally arranged and compacted in stair-step horizontal layers. It provides greater construction efficiency and operational potency. With standard embankment slopes of 2:1 and 4:1, a horizontal layer with 8 feet width will set least protective thicknesses of about 2 and 3l/2 feet correspondingly, measured normal to the slope.

It starts at the lowest layer of soil-cement, each subsequent layer is stepped back a distance equivalent to the product of the compacted layer thickness in feet times the embankment slope.

As for instance, if the compacted thickness is 6 inches and the slope is 2:1, the step back is = 0.5(2) = 1 foot. The normal compacted layer thickness is 6 inches. Soil-cement layers of this dimension is positioned efficiently and compressed with standard highway equipment.

A plating system that develops a single soil-cement layer parallel to the slope is often applied in less critical areas for slope protection. If the soil-cement facing does not start at natural ground level, the lower part of the embankment should remain on a flatter slope than the part safeguarded by the soil-cement; or a beam is arranged at the lowest elevation of the facing. It is necessary that the soil-cement expand underneath the minimum water level and over the maximum water level.

The top of the facing should contain a freeboard allowance of minimum 1.2 times the projected maximum wave height, or 5 feet, whichever is higher. The edges of the finished soil-cement layers should not be cropped since the rounded starstep effect allows retard wave runup. Soil-cement is produced with different types of soils.

The main standard for finding out the soil type is gradation. Coarse sandy or gravelly soils having about 10 to 25 percent material passing the No.200 sieve are perfect (American Society for Testing and Materials Standard Sieve Series). These soils are sufficiently stabilized with from 3 to 5 sacks of cement per cubic yard of compacted soil cement.

Standard compaction and placement control for soil-cement is recommended. If the amount of material smaller than the No.200 sieve surpasses 35 percent, some effort to determine a coarse material is appropriate from a processing cost standpoint. Soils with 50 percent or more material passing the No.200 sieve are not suggested for being applied in their natural state.

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How soil cement is used in earthfill dams & embankments

Published By
Rajib Dey

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