Question

Question 1) You are given the following results of an ASTM D4318 (i.e. Atterberg Limits) soils test: plasticity index = 40, plastic limit= 10. Is this a low or high plasticity fine grained soil?

Answer 1

Given Data:

Plasticity Index (PI) = 40

Plastic Limit = 10

Before moving to the answer, let's have a clear idea on the basics of "SOIL CONSISTENCY".

Soil Consistency:

Consistency of the soil usually changes with the amount of water present in the soil sample. These variations in the consistency of the soil can be accurately measured in the laboratory by determining "Atterberg Limits".

Atterberg Limits corresponds to the moisture content at which soil sample changes its consistency from one to another. Two major Atterberg Limits are,

1. The Liquid Limit (LL) - Soil changes its consistency from liquid to a plastic state.
2. The Plastic Limit (PL) - Soil changes its consistency from plastic to a semi-solid state.

Plasticity Index:

Plasticity Index is defined as the numerical difference between Liquid Limit (LL) and Plasti Limit (PL)

PI = LL - PL

Based on the plasticity index, we can determine the degree of plasticity of the soil sample. If the Plasticity Index (PI) value is greater than 35, it is considered "Highly Plastic" soil, whereas, for the plasticity index value of 0, the soil sample is "Non-Plastic". The degree changes from no plastic to high plastic for the in-between ranges.

So, from the given data, PI = 40: We conclude that the soil sample is "HIGHLY PLASTIC FINE GRAINED SOIL".