Identify the curve that represents 'gap - graded soil' in the figure given below.

Concept:

Particle Size Distribution Curve:

It is also known as the gradation curve and represents the distribution of particles of different sizes in the soil sample. It is a graph of the results obtained from sieve analysis, on a semi-log paper with percentage finer on the arithmetic scale as ordinate and the particle size as abscissa on a log scale.

In the above graph

Soil A: Indicate fine-grained soils,

Soil B: Indicate coarse-grained soils,

Soil C: Indicate poorly graded soils,

Soil D: Indicate well-graded soils

Soil E:  Indicate gap graded soils

​Explanation:

From the given Graph:

Curve b: Indicate poorly graded soils

Curve c: Indicate coarse-grained soils

Curve f: Indicate fine-grained soils

Curve e: Indicate gap graded soils

Curve a: Indicate well-graded soils

Important Points
Coefficient of uniformity(Cu) = D60/ D10

coefficient of curvature(Cc)= (D30)2/(D10×D60)

Where,

D10: Particle diameter at which 10% of the soil mass is finer than this size

D30: Particle diameter at which 30% of the soil mass is finer than

D60: Particle diameter at which 60% of the soil mass is finer than this size.

Well-graded soils have high Cu values and poorly graded soils have low Cu, values. If all the particles of soil mass are of the same size Cu is unity.

Cc lies between 1 to 3 for well-graded soil.

The gradation of soil is determined by the following criteria:

1. Uniform soil: Cu = 1
2. Poorly graded soil: 1< Cu<4
3. Well graded soil: Cu>4