Nine-hole grid pipe has the following characteristics:

1. The segment length of communication plastic pipes should be determined based on the location of manholes. On straight routes, the segment length should not exceed 200m; on high-grade highways, it should not exceed 300m, and the lengths of each segment should not be equal.

2. Each segment of the nine-hole grid pipe should be laid in a straight line. When encountering road curves or the need to bypass other pipes, the segment length of curved pipes should be less than the allowable segment length for straight pipes.

3. The bending radius of curved pipes should not be less than 10m, and the central angle of the curved section should be large. A single pipe segment should not have reverse bends (i.e., "S" bends) or curved sections with a central angle less than 90° (i.e., "U" bends).