Soil Classification MCQ with answer and solution

Concept

Effective Particle Size

Formula

No direct formula exists; D10 is determined graphically from the grain size distribution curve as the particle diameter corresponding to 10% finer by weight.

Step-by-step solution

1. Plot the grain size distribution curve with percentage finer on the y-axis and particle size (diameter) on the x-axis. 2. Find 10% on the y-axis (percentage finer) and move horizontally to intersect the curve. 3. Read the corresponding particle diameter on the x-axis, which is defined as D10 (the effective particle size).

Explanation

The effective particle size of soil is defined as D10, which is the particle diameter where 10% of the soil particles by weight are smaller and 90% are larger. It is considered the effective size because these smaller particles fill the voids between larger grains, significantly influencing soil properties like permeability, water movement, and drainage capacity.

Shortcut

To remember this, think of E10—Effective size corresponds to 10% finer ($D₁₀$).

Common mistake

Many students confuse effective particle size with the median or average particle size and select D 50 instead of D 10, or confuse it with D 60 which is used alongside D 10 to calculate the coefficient of uniformity.