Soil Stability Test and Pit Lining Guide

The soil stability test is a simple method used to classify soil types based on their composition. The test involves adding soil to a jar until it is ½ full, then adding water and shaking the jar for 3 minutes. The jar is then left to settle for 1 minute, 1 hour, and 24 hours, with lines drawn to mark the sand, silt, and clay layers. The distance between the lines is measured in millimeters and recorded for each layer. The total distance is then calculated by adding the values for sand, silt, and clay. The percentage of each layer is calculated by dividing the amount of each layer by the total distance and multiplying by 100. The resulting percentages are then plotted on a soil triangle to determine the soil type. The soil triangle is a graphical representation of the soil composition, with the x-axis representing the percentage of sand, the y-axis representing the percentage of silt, and the z-axis representing the percentage of clay. The intersection of the lines on the soil triangle indicates the soil type. The soil types are classified as follows: sand, loamy sand, sandy loam, clay, silty clay, clay loam, loam, silt loam, and sandy loam. The soil stability test is used to determine the need for lining a latrine pit. Soils that require lining include soft sands and gravels, unconsolidated soils, filled land, compressed mudstones and shales, soils with a significant clay content, and soils with a high proportion of iron oxides. Soils that do not require lining include most consolidated sedimentary rocks and soils with a high proportion of sand. When in doubt, it is recommended to line the whole pit. The characteristics of the soil can change with soil moisture, and the soil stability can be affected by periodic wetting and drying. Layered soils can also be a concern, as the "weakest link" can give way and cause a pit to collapse. Previously excavated soils are also rarely as strong as undisturbed soils, and exercise caution should be taken if the soil has been excavated before.