Q1: A plane inclined at an angle φ to the horizontal at which the soil is expected to stay in the absence of any lateral support, is known as

ANS:D - all the above.

1. Natural slope line: This term is not commonly used in geotechnical engineering or soil mechanics to describe the plane inclined at the angle of repose. While natural slopes do exist in geology, the term "natural slope line" is not typically used to describe the specific angle of repose.
2. Repose line: The repose line refers to the plane or surface along which soil or granular material naturally comes to rest when no external forces are applied. It represents the angle of repose, which is the maximum angle at which a pile of unconsolidated granular material can remain stable without collapsing or sliding. The angle of repose varies depending on the properties of the material but is a key consideration in slope stability analysis and geotechnical engineering.
3. The φ line: The symbol φ commonly represents the angle of internal friction in soil mechanics and geotechnical engineering. The φ line, therefore, could refer to the line or plane along which the soil exhibits the angle of internal friction, which is related to the angle of repose. While the term "φ line" is not as commonly used as "repose line" or "angle of repose," it can describe the same concept in certain contexts.