Indian Standard Soil Classification System

The Indian Standard Soil Classification System is based on the Unified Soil Classification System (USCS), which classifies soils based on their particle size distribution and plasticity characteristics. The classification system is widely used in India for engineering and construction purposes.

Classification of Silty Clay

The given soil sample is classified as silty clay. Silty clay is a fine-grained soil with a high percentage of silt and clay particles. It falls under Group C in the Indian Standard Soil Classification System.

Plasticity Index (PI)

The plasticity index (PI) is a measure of the range of moisture content within which a soil remains plastic. It is calculated by subtracting the liquid limit (LL) from the plastic limit (PL). The plasticity index indicates the soil's ability to change its shape without cracking or crumbling.

In this case, the plasticity index is given as 28%. A plasticity index between 15% and 30% corresponds to Group I soils.

Liquid Limit (LL)

The liquid limit (LL) is the moisture content at which a soil transitions from a plastic state to a liquid state. It is determined through a laboratory test called the Casagrande method. The liquid limit is expressed as a percentage.

In this case, the liquid limit is given as 40%. A liquid limit of less than 50% corresponds to Group C soils.

Classification of the Soil Sample

Based on the given values of liquid limit and plasticity index, the soil sample is classified as CI according to the Indian Standard Soil Classification System. The classification can be determined as follows:

- The liquid limit of 40% falls under Group C.
- The plasticity index of 28% falls under Group I.
- The soil sample is classified as CI, which indicates that it is a silty clay soil with moderate plasticity.

Therefore, the correct answer is option B, CI.