Treatment Profiles
»Sludge Drying Beds
 Stabilization of Drying Beds
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.
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 quicklime or 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 these reagents is the reduction of the
soil permeability.
Additives such as quicklime or cements are
mixed into the native soil with water. This method of stabilization is
conducted under a control environment to provide a consistent and
uniform mat structure. This stabilized mat creates a harden 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
samples, field wet samples, and core samples prepared before, during,
and after construction, respectively. The results can be used for
design, construction quality control and quality assurance.
Soil
type is the most dominant factor that influences the strength of
treated soils. The same treatment used in different soils produces
results with a wide variation. The effect is attributed to the
adsorption and pozzolanic reaction in the various soils as well as the
reaction of the hardening reagent itself.
Features/Benefits of Soil Stabilization Drying Beds
- Directly supports end loaders allowing them to drive directly on the sludge drying bed without destroying the subgrade.
- Loading, cleaning, and grading time is significantly reduced.
- Reduces the permeability of the native subgrade soils.
- 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.
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