What characteristic does granular material like sand or gravel provide for sewer lines?

Granular materials such as sand and gravel are often used in sewer line applications primarily because of their excellent drainage properties and ability to achieve good compaction. When installed around sewer lines, these materials create a well-draining environment that allows excess water to flow away easily, preventing the accumulation of standing water that could exert pressure on the sewer pipes.

Good compaction is also important as it minimizes settling and reduces the chances of the pipe becoming misaligned or damaged over time. The interlocking nature of granular materials allows for high stability while still permitting movement of water, thereby ensuring proper functionality of the sewer system.

The other characteristics do not align with the typical properties of granular materials used in this context. For example, granular material does not provide poor drainage; rather, it excels in this area. Additionally, insulation is generally not a primary feature of sand or gravel, and while these materials can have a considerable bulk density, that characteristic is not unique to them and does not serve the same functional purpose in sewer applications.