General Contractor Practice Exam

What is one characteristic of expansive soil that prevents its use for backfill?

1. High permeability

2. Low shear strength

3. Compressibility

4. Expansiveness

The correct answer is: Expansiveness

Expansive soils are characterized by their ability to undergo significant volume changes in response to moisture fluctuations. When these soils absorb water, they expand, and when they dry out, they shrink. This trait can lead to substantial ground movement, which can compromise the structural integrity of any constructions made above them. Such volatility makes expansive soils highly unsuitable for backfill, as they can exert unpredictable pressure on foundations and other structural elements, potentially causing cracks and structural failure. While factors like compressibility, permeability, and shear strength are also important aspects of soil mechanics, they do not capture the inherent challenge posed by expansive soils. Other soil types may have compressibility, high permeability, or low shear strength without undergoing the dramatic volume changes that expansive soils do, which is why expansiveness is specifically noted as a critical characteristic preventing their use in backfill applications.