JNTU B.Tech IV SOIL MECHANICS Previous Question Paper (October/November - 2020 - R16)

The Indian Standard Soil Classification System (ISSCS) classifies soils based on grain size distribution and plasticity characteristics. The engineering properties of the primary soil groups are as follows:

1. Coarse-Grained Soils (Gravels G and Sands S): These soils contain less than 50% fines. They exhibit high permeability, high shear strength, and excellent drainage characteristics. They are generally stable and undergo minimal settlement under load. Well-graded soils (W) are superior for construction as they have a wide range of particle sizes, leading to high density upon compaction, whereas poorly graded soils (P) have uniform particle sizes and are more susceptible to erosion.

2. Fine-Grained Soils (Silts M and Clays C): These soils contain more than 50% fines. Their behavior is governed by plasticity and moisture content.

• Silts (M): These exhibit low to medium plasticity. They have low permeability, are highly susceptible to frost action, and can lose significant strength when saturated. They are difficult to compact and prone to liquefaction under dynamic loads.
• Clays (C): These are characterized by high plasticity and cohesion. They exhibit low permeability and high compressibility. Clays are prone to long-term consolidation settlement and may undergo significant volume changes (swelling and shrinkage) depending on the mineralogy (e.g., Montmorillonite).

3. Organic Soils (O): These contain organic matter, which significantly reduces their engineering suitability. They possess high compressibility, low shear strength, and are generally unsuitable for use as foundation material or structural fill due to their tendency to decompose and settle excessively.

The classification also uses plasticity charts to differentiate between low (L), medium (I), and high (H) compressibility, which directly correlates to the soil's potential for volume change and its suitability for subgrade or foundation construction.

Given data:

Natural moisture content (w) = 0.15

Bulk density (ρ) = 1.9 g/cc

Specific gravity of solids (G) = 2.7

Density of water (ρw) = 1.0 g/cc

First, calculate the dry density (ρd):

Calculate the void ratio (e) using the relation ρd = (G × ρw) / (1 + e):

Calculate the degree of saturation (Sr) using the relation Se = wG:

Calculate the saturated unit weight (γsat) using the formula γsat = [(G + e) / (1 + e)] × γw:

Alternatively, in terms of density: ρsat = (G + e) / (1 + e) × ρw = 2.040 g/cc.