Where the bedding for piping installed in a trench consists of backfill, _____ is an approved material.

The correct answer identifies fine gravel as an approved material for bedding in trenches where the bedding for piping consists of backfill. Fine gravel is preferred because it provides excellent drainage and support for the piping. It helps to mitigate potential shifting or settling of the pipe due to soil movement, ensuring a more stable installation.

Fine gravel can also contribute to reducing the potential for pipe damage caused by freeze-thaw cycles, as it allows for better water drainage, preventing the pooling of water around the pipes. Additionally, it possesses a good balance of stability and flexibility, which is essential in maintaining the integrity of the piping system over time, especially in variable soil conditions.

In comparison, other materials like loose soil free from rocks or frozen material may not offer the same level of support and can shift easily, leading to possible misalignment or damage of the pipes. Similarly, sandy clay and organic silty clay can retain moisture, which can be problematic as they expand or contract with moisture changes, creating an unstable bedding environment for the pipes. Thus, fine gravel stands out as the best choice in this scenario.