To the civil engineer, soils serve as foundation material and as construction material. For soil to be efficiently used for either of these purposes, it must pass some minimum specification limits to ensure that its engineering properties are suitable for the intended purposes.
Some soils known as problem soils are often encountered in the process of construction. These soils have the potential to expand, collapse, disperse, undergo excessive settlement, or even fail under relatively low stress conditions and they are not usually suitable for engineering applications in their natural state. Considering economy and use, these soils may be either removed and replaced with better soil or treated with some stabilizing agents to improve their strength and other desirable engineering properties.
This article shows suitable measures to treat some problems soils outlined below:
A. Low strength soils (CBRsoaked < 3% (or 2% in dry climatic zones)
1. Treatment with lime or any other cementitious material (2 – 5% by dry weight of soil).
2. Treatment with bitumen emulsion (1 – 1.8%) and cement (1 – 1.5%).
3. Raising vertical alignment to increase soil cover and therefore redefine the design depth.
4. Remove and replace the soil.
B. Cohesionless materials such as sand
1. Treatment with bitumen or foamed bitumen.
C. Dense Clays or Expansive Materials
1. Remove and replace the expansive soil up to 0.6 – 1.2 m and backfill with better materials.
2. Treat with lime to increase the plastic limit and make the material more friable and stable.
3. Provide horizontal and vertical cut-off membranes above and next to expansive soils to stabilize moisture variation.
D. Collapsible Sand and Soils
1. Induce collapse before placing the embankment by compacting the in situ material by wetting, rolling, and observing the result.
2. Compaction of the upper 0.5 m of the roadbed to 90% of Modified AASHTO and of the next 0.5 m to 85% of Modified AASHTO.
E. Dispersive Soils
1. Pay particular attention to erosion protection of cut slopes and drainage channels.
2. Modified the soil with 2 – 3% of lime if they must be used.
F. Black Cotton Soils
1. Protect the soil from moisture variations.
2. Provide thicker pavement to counteract the effect of upward swell from the soil.
3. Replace the soil with better soil.
4. Treat the soil with lime, lime + cement, or mechanical stabilisation.
G. Problem Laterites
1. Remove and replace.
2. Treat with lime, lime + cement.
3. Mechanically stabilize the soil.