GB/T 18477.3-2009 Unplasticized polyvinyl chloride (PVC-U) structure wall pipeline system for underground soil waste and drainage—Part 3:Bilayer and hollow-wall construction with axial hollow pipes
Unplasticized polyvinyl chloride (PVC-U) structure wall pipeline system for underground soil waste and drainage—Part 3:Bilayer and hollow-wall construction with axial hollow pipes