Soil Classification for Inorganic Soils with Low Compressibility

The question asks to identify the classification symbol for inorganic soils with low compressibility. This falls under the realm of soil classification systems, specifically the Unified Soil Classification System (USCS), which is widely used in geotechnical engineering.

Understanding Unified Soil Classification System (USCS)

The USCS classifies soils based on their particle size distribution and plasticity characteristics. Soils are broadly divided into coarse-grained soils (gravels and sands) and fine-grained soils (silts and clays). Each soil type is assigned a symbol, usually two letters, to denote its primary characteristics.

• The first letter often indicates the main soil type (e.g., 'S' for Sand, 'M' for Silt, 'C' for Clay).
• The second letter often indicates a characteristic like grading (e.g., 'W' for well-graded, 'P' for poorly-graded) for coarse-grained soils, or compressibility/plasticity (e.g., 'L' for low plasticity/compressibility, 'H' for high plasticity/compressibility) for fine-grained soils.

Analyzing the Options for Soil Compressibility

Let's examine the given options in the context of the USCS:

• MH: This symbol represents inorganic silts with high compressibility. The 'M' stands for silt (M = "M" from Swedish for "mo" which means silt), and 'H' stands for high compressibility or high plasticity. These soils are often elastic silts or diatomaceous silts, meaning they undergo significant volume change under load.
• SL: This is not a standard USCS classification symbol. In some informal contexts, "SL" might refer to sandy loam, which is an agricultural soil classification, but it is not used in geotechnical engineering for soil strength or compressibility characteristics within the USCS.
• ML: This symbol represents inorganic silts with low compressibility or low plasticity. The 'M' stands for silt, and 'L' stands for low compressibility or low plasticity. These soils generally have a liquid limit less than 50% and exhibit relatively less volume change compared to high compressibility soils. This perfectly matches the description in the question.
• CH: This symbol represents inorganic clays with high compressibility or high plasticity. The 'C' stands for clay, and 'H' stands for high compressibility or high plasticity. These clays have a liquid limit greater than 50% and are known for significant volume changes due to swelling and shrinkage.

Detailed Comparison of Fine-Grained Soils (Silts and Clays)

The USCS differentiates fine-grained soils (silts and clays) primarily based on their plasticity, which is directly related to their compressibility. This is usually determined using the Atterberg limits (Liquid Limit, Plastic Limit, and Plasticity Index).

Based on this classification, ML specifically identifies inorganic silts that exhibit low compressibility. Therefore, it is the correct representation for the given description.