Which of the following Soil provisions is NOT considered expansive?

Which of the following Soil provisions is NOT considered expansive?

• A. More than 10% of soil particles pass a #200 sieve
• B. A plasticity index of 15 or greater
• C. At least 9% of soil particles are less than 5 micrometers in size
• D. An expansion index greater than 20

Answer: (C)

The reasoning that makes the selected answer correct lies in understanding the characteristics of expansive soils. Expansive soils, often referred to as shrink-swell soils, are typically clay-rich and exhibit significant volume changes with moisture variation. A defining feature of expansive soils is their plasticity index, which indicates how much the soil can expand when wet and contract when dry. An index of 15 or greater signals potential expansiveness, as does an expansion index greater than 20. The presence of a significant percentage of soil particles passing a #200 sieve indicates a finer grain size that can retain water, which is commonly found in expansive soils. In contrast, the characteristic of having at least 9% of soil particles less than 5 micrometers in size does not directly correlate with expansiveness. This particular size of soil particles suggests fine clay content but does not alone dictate whether the soil is expansive. The identification of expansive soil relies more on the plasticity index and the expansion index rather than just particle size. Thus, option C is correct because the presence of fine particles alone does not confirm expansive behavior in soils, making it the item that does not fit with the other provisions related to soil expansiveness.

The reasoning that makes the selected answer correct lies in understanding the characteristics of expansive soils. Expansive soils, often referred to as shrink-swell soils, are typically clay-rich and exhibit significant volume changes with moisture variation.

A defining feature of expansive soils is their plasticity index, which indicates how much the soil can expand when wet and contract when dry. An index of 15 or greater signals potential expansiveness, as does an expansion index greater than 20. The presence of a significant percentage of soil particles passing a #200 sieve indicates a finer grain size that can retain water, which is commonly found in expansive soils.

In contrast, the characteristic of having at least 9% of soil particles less than 5 micrometers in size does not directly correlate with expansiveness. This particular size of soil particles suggests fine clay content but does not alone dictate whether the soil is expansive. The identification of expansive soil relies more on the plasticity index and the expansion index rather than just particle size.

Thus, option C is correct because the presence of fine particles alone does not confirm expansive behavior in soils, making it the item that does not fit with the other provisions related to soil expansiveness.