Joints & Joining
Plastic Pipes Conference Association # 2001 Munich
Sadler, Burn, Whittle
Root intrusion into sewer pipelines is a major concern, especially in areas with a combination of dry climate and vigorous vegetation growth. For elastomeric pipe joints to resist root intrusion, some national standards specify a minimum interfacial pressure that must be maintained between the elastomeric ring and the spigot. The appropriate interfacial pressure has been under discussion for some time and different values have been stated in different standards. This matter has been the subject of considerable controversy, as decisions on the interfacial pressure used will affect both the performance and the ease of insertion of an elastomeric ring joint. If interfacial pressure is low, root intrusion may occur, resulting in infiltration or exfiltration through the pipe joints. High interfacial pressure can make installation difficult and increase the risk of ring dislodgment. A study has been undertaken to assess the effects of interfacial pressure and spigot deformation upon root intrusion into PVC pipelines. This follows previous work investigating the role of socket geometry and controlled flaws. Root intrusion occurred in many joints with deformation and average interfacial pressures of 0.04, 0.10, 0.11 and 0.20 MPa. However, no intrusion occurred in joints with interfacial pressures of 0.37 MPa, even with socket deflection, despite these joints having small contact widths of less that 0.5 mm where the interfacial pressure exceeded 0.3 MPa. In light of these findings, the current Australian Standards requirement for an interfacial pressure of 0.4 MPa to be exceeded over a minimum contact width of 4 mm is considered more than adequate to prevent root intrusion. The interfacial pressure requirement is considered conservative, but satisfactory. The contact width requirement is also considered conservative, but necessary to account for the possibility of damaged pipes or rings.
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