Inadequate soil compaction leads to structural failure because it leaves physical gaps in the ground that cannot support the weight of a building. According to the provided content, this process involves the following mechanisms:

• Creation of Voids: When fill or backfill soil is placed loosely without proper mechanical densification, it leaves hidden voids within the soil matrix.
• Differential Settlement: Over time, the heavy weight of the foundation and the building loads compress these voids. This causes the structure to sink unevenly, a process known as differential settlement.
• Structural Damage: This uneven movement triggers visible damage, including cracked walls, uneven floors, and doors that stick or fail to close properly.
• Amplified Soil Pressures: In environments with expansive clay soil, poor compaction worsens moisture-related movement. Saturated loose fill can also accelerate settlement caused by hydrostatic pressure against basements and retaining walls.

To prevent these issues, proper construction requires placing soil in thin "lifts," controlling moisture levels, and verifying soil density through standardized tests.