What must be true for soil to be considered Type A?

For soil to be classified as Type A, it is essential that it is stable and has not been subject to physical disturbance or external forces that could compromise its integrity. Type A soil is typically defined as cohesive soil with a high clay content, characterized by its ability to maintain its structure under pressure and to resist movement. Its classification is based on the physical properties that ensure safety during excavations and construction processes.

The requirement that the soil must not be subject to vibration from heavy traffic emphasizes the need for Type A soil to maintain its cohesion and stability. Vibration can lead to soil displacement or structure failure, which undermines the characteristics that define Type A soil. Therefore, ensuring that the soil remains undisturbed by external forces such as vibrations from traffic is crucial in maintaining its classification and safety in construction practices.

Options suggesting that the soil is fissured, has been previously disturbed, or is primarily sand and gravel do not align with the criteria for Type A soil, as these factors would generally indicate compromised stability or a lack of cohesiveness.