Soil-Cement Liners for Wastewater Management
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Stabilization
of Sludge Basins
by Rich Haro
Removal of sludge at wastewater treatment facilities has traditionally
been a major operational concern. Most large sludge basins require
removal of processed sludge by large heavy equipment, causing the
basin subgrade elevation to become unstable under equipment loads.
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| Compaction of soil-cement as a liner. |
A proven method to reduce the amount of maintenance required is to
modify the existing subgrade soil. This method of soil improvement
consists of treating the native soils with additives such as portland
cement. Soil treatment increases the strength and reduces the
compressibility of the existing subsurface strata to maintain ground
stability and to control ground movement under loads induced by
heavy construction equipment. An added benefit to treating with
Portland cement is the reduction of the soil’s permeability.
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| Flooded soil-cement lined drying bed. |
Portland cement is mixed into the native soil with water creating
a material called soil-cement. This method of stabilization is conducted
under a controlled environment to provide a consistent and uniform
mat structure. This stabilized mat creates a hardened surface that
allows for many years of maintenance access for sludge removal.
Design Consideration and Quality Control
In order to structurally evaluate the stabilized soil, laboratory
tests can establish such properties as: 1) unconfined compressive
strength, 2) flexural and tensile strength, 3) R-value 4) fatigue
behavior, etc. Probably the single most important strength parameter
is the unconfined compressive strength as other strength parameters
can often be estimated from unconfined compressive strength as a
result of regression analysis.
The test samples can include laboratory and field wet samples prepared
before, during, and after construction, respectively. The results
can be used for design, construction quality control and quality
assurance.
Features/Benefits of Soil Stabilization in Sludge
Drying Beds
• Directly supports end loaders allowing them to drive
directly on the sludge drying bed without destroying the subgrade.
• Loading and cleaning time is significantly reduced.
• Reduces the permeability of the native subgrade soil.
• Establishes a clear distinction between the sludge removal
and subgrade.
• Reduction in the amount of grading required at the site,
due to enhancement of the strength of the existing soil.
• Increases the service life of the sludge bed from five
years using an untreated aggregate base to over 20 years using
a treated subgrade base.
Installation
of Soil-Cement Liner |
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| Cement spread onto soil. |
Use of "Road Reclaimer" to mix cement into soil. |
Compacted soil-cement. |
Rich Haro is with Griffin Soils in Pleasanton, California
www.griffinsoil.com
925.485.5544
All photos courtesy of Griffin Soils.
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