Testing and Analysis of No-Dig Structural Manhole Rehabilitation Materials

This paper presents the testing part of a research project for the Water Environment Research Foundation (WERF) to investigate the structural capabilities of no-dig manhole rehabilitation materials to develop a decision-support tool. The project tasks included literature search; industry expert workshop with participating utilities, manufacturers, and other consultants; experiments on structural properties of select manhole rehabilitation materials; and computational analysis with the finite element method. Gravity flow wastewater collection systems essentially comprise sewer pipes and manholes. Failure of a manhole may have catastrophic consequences such as developing a sinkhole in the street and roadway, and at the minimum, wastewater flow will be blocked and upstream of the manhole will backup causing a sanitary sewer overflow (SSO). Improving structural conditions of a manhole is critical to minimize these types of failures. This research considers the impact of several lining materials including cement mortar, epoxy, polyurethane, cured-in-place composites, and a multilayer material on increasing the structural capabilities of deteriorated manholes. Several preliminary tests according to ASTM C-39 on coated concrete cylinders and ASTM C-293 on coated concrete beams were performed at UT Arlington's Center for Underground Infrastructure and Research and Education (CUIRE) Laboratory. These test results showed significant increase in the performance of concrete samples under compression and flexure. A second round of testing was performed on 4-ft long, 24-in. diameter concrete pipe sections with 3-in. thick wall manufactured according to ASTM C-76. These pipe sections were lined internally with the same materials as the preliminary tests and tested according to ASTM C-497 under standard three-edge-bearing test. Using computer data acquisition system, strain gauges, and extensometers, strains and deflections were measured and stresses calculated. The results show that lining materials tested in this study can significantly improve structural performance of deteriorated manholes.