Hydrometer test for soil is used for 1.soil classification as per IS code 2.determination of specific gravity of soil 3.determination of percentage of silt 4.determination of Cu and Cc of fine grained soil 5.useful in determination of activity of soil Out of these statements,
- A1 and 2 are correct
- BOnly 3 is correct
- COnly 4 is correct
- D3 and 5 are correctCorrect
Solution
Concept
Hydrometer analysis is a method of sedimentation analysis based on Stokes' Law to determine the particle size distribution of soil fractions passing the 75-micron sieve.
Formula
Activity (A) = Ip / (% of clay particles finer than 2μm)
Step-by-step solution
1. Identify the purpose of Hydrometer analysis: It determines the distribution of particle sizes smaller than 75 microns (silt and clay). 2. Evaluate Statement 3: Since it provides the grain size distribution, the percentage of silt (particles between 0.075 mm and 0.002 mm) can be determined. 3. Evaluate Statement 5: Activity of soil depends on the percentage of clay-sized particles (< 0.002 mm), which is a direct output of the hydrometer test. 4. Verify other statements: Specific gravity (Statement 2) is an input for the test, not an output; Cu and Cc (Statement 4) are typically used for coarse-grained soils; IS classification (Statement 1) uses the results but the test itself is just a part of the process.
Explanation
Hydrometer analysis is used for grain size distribution of fine-grained soils (silt and clay), allowing for the determination of the percentage of silt and clay. Additionally, the 'Activity' of soil is defined as the ratio of Plasticity Index to the percentage of clay-sized particles (obtained from hydrometer analysis), making it useful for determining soil activity.
Why the other options are wrong
1: Soil classification requires both sieve analysis and Atterberg limits, not just the hydrometer test. 2: Specific gravity is determined using a Pycnometer or Density bottle, not a hydrometer. 4: Cu and Cc (Uniformity and Curvature coefficients) are parameters primarily used to describe the gradation of coarse-grained soils (sand/gravel).
Shortcut
Remember: Sedimentation analysis (Hydrometer/Pipette) = Fine-grained soil distribution = Clay % = Activity.
Common mistake
Confusing specific gravity as an output of the test, whereas it is actually a required parameter to calculate the particle diameter and percentage finer.
Correct answer: D) 3 and 5 are correct