# Soil Sample Laboratory Analysis ## Given Data - **Gravel:** 10% - **:** 35- **S:** 30- **Clay 25% **Liquid Limit ():** % - ** Limit (PL):** 28% - **Shrinkage Limit (SL):** 15% - **Specific Gravity (Gs):** 2. - **Natural Water Content (w):** 32% --- ## (a) USCS Classification and Plasticity Chart ### Step 1: Soil Type (Coarse or Fine-Grained) - **% Fines (Silt + Clay):** 30% + 25% = **55%** - >50% passes through #200 sieve ⇒ **Fine-grained soil** ### Step 2: Silt or Clay? - **LL = 55%** (LL > 50% → High plasticity: use the prefix H) - **Plasticity Index (PI) = LL - PL = 55% - 28% = 27%** - To distinguish clay (C) from silt (M), check the A-line on the plasticity chart: - **A-line equation:** \( PI = .73(LL - 20) \) - \( PI_{A-line} = .73 \times (55 - 20) = .73 \times 35 = 25.55 \) - **Measured PI = 27% > 25.55%** (Above A-line ⇒ Clay) ### USCS Symbol - **CH:** Clay of high plasticity ### Plasticity Chart - **Plot point:** (LL = 55%, PI = 27%) - It will lie above the A-line, in the "CH" (high-plasticity clay) region. **Plasticity Chart Illustration**  *Plasticity chart showing PI and LL, with sample plotted above the A-line in CH region.* --- ## (b) Calculations ### 1. Plasticity Index (PI) \[ PI = LL - PL = 55\% - 28\% = 27\% \] ### 2. Degree of Saturation (\( S_r \)) #### Step 1: Estimate Bulk and Dry Density - **Assume 1 kg dry soil for calculation** \[ w = \frac{W_{water}}{W_{dry}} \implies W_{water} = .32 \text{ kg} \] - **Total mass:** 1.32 kg \[ \text{Assume total volume} = V \] - **Specific gravity (Gs):** 2.70 - **Density of water (\( \rho_w \)):** 1.00 g/cm³ = 100 kg/m³ \[ \text{Volume of solids} = \frac{W_{dry}}{Gs \cdot \rho_w} = \frac{1}{2.70 \times 100} = .000370 \text{ m}^3 \] \[ \text{Volume of water} = \frac{.32}{100} = .00032 \text{ m}^3 \] \[ \text{Total volume} = V = \text{Volume of solids} + \text{Volume of water} + \text{Volume of air} \] #### Step 2: Void Ratio (\( e \)) \[ e = \frac{\text{Volume of voids}}{\text{Volume of solids}} \] \[ \text{Volume of voids} = \text{Volume of water} + \text{Volume of air} \] Assume **fully saturated** first, then refine using of saturation. \[ w = \frac{W_{water}}{W_{dry}} = S_r \cd e / Gs \] \[ e = w G_s / S_r \] - For fully saturated( S_r = 1 \)): \[ e_{sat} = .32 \times 27 = .864 \] #### Step 3: Degree of Saturation (\( S_r \)) [ S_r = \frac{w G_s}{e} \] Assume actual \( e \approx 86 \) (since air volume is small for fine soil at this w), so: \[ S_r = \{.32 \times 2.7}{.86} = 1.004 \] - **Result:** \( S_r \approx 1 \)i.e., nearly fully saturated) --- ### Summary Table | Property | Value | |--------------------|----------------| | Plasticity Index | 27% | | Void Ratio | .86 | | Degree of Saturation | ≈ 100% | --- ## (c) Suitability for Subgrade Construction ### Comments - **Soil Type:** High plasticity clay (CH) - **Characteristics:** - High compressibility - High shrink-swell potential - Poor drainage - Low shear strength when wet **Conclusion:** **High-plasticity clays (CH) are generally not suitable for subgrade construction** of expressways due to their tendency for large volume changes with moisture, low strength, and poor stability. Subgrade may require soil improvement or replacement in such areas. --- ## References - ASTM D2487: Standard Practice for Classification of Soils (Unified Soil Classification System) - IS 272: Methods of Test for Soils --- **Alt text for chart:** *Plasticity chart illustrating the position of the sample (LL = 55%, PI = 27%) above the A-line, within the CH region.*