JNTU B.Tech III GEOTECHNICAL ENGINEERING Previous Question Paper (February - 2022 - R13)

Bulk density (ρ) is the total mass of a soil sample per unit of its total volume, including the mass of solids, water, and the volume of voids. It is expressed as ρ = M / V, where M is the total mass and V is the total volume.

Dry density (ρd) is the mass of soil solids per unit of total volume of the soil mass. It represents the density of the soil when it is completely oven-dried, expressed as ρd = Ms / V, where Ms is the mass of solids.

To derive the relationship, consider a soil element with total volume V, total mass M, mass of solids Ms, mass of water Mw, and volume of solids Vs and volume of voids Vv. The water content (w) is defined as w = Mw / Ms, which implies Mw = w * Ms.

The total mass is M = Ms + Mw = Ms + (w * Ms) = Ms(1 + w). Substituting this into the bulk density formula:

Since dry density is defined as ρd = Ms / V, we can substitute ρd into the equation:

Rearranging this gives the final relationship:

The Indian Standard (IS) Classification System, as per IS: 1498-1970, classifies soils based on their grain size distribution and plasticity characteristics. The system uses a two-letter symbol to represent the soil type, where the first letter denotes the primary soil component and the second letter describes its gradation or plasticity.

The classification is based on the following criteria:

• Coarse-grained soils: Soils where more than 50% of the material is retained on a 75-micron IS sieve. These are divided into Gravel (G) and Sand (S). Further sub-classification depends on gradation (W for well-graded, P for poorly graded) or fines content (M for silt, C for clay).
• Fine-grained soils: Soils where more than 50% of the material passes through a 75-micron sieve. These are classified based on their plasticity index (PI) and liquid limit (LL) using the A-line on the plasticity chart.
• Plasticity classification: Fine-grained soils are grouped as Silt (M) or Clay (C) based on the A-line, with sub-divisions for low (L), medium (I), or high (H) compressibility based on the liquid limit (LL < 35%, 35% < LL < 50%, and LL > 50% respectively).
• Highly organic soils: Soils containing significant organic matter are denoted by the symbol 'O' or 'Pt' (peat).

The classification process involves determining the percentage of gravel, sand, and fines, and then performing Atterberg limit tests (Liquid Limit and Plastic Limit) to plot the soil on the plasticity chart to identify its specific group symbol (e.g., GW, SP-SM, CH, MH).