Skip to Main Content
 

Global Search Box

 
 
 
 

ETD Abstract Container

Abstract Header

Predicting and Preventing Hydraulic Blow-Outs during High Velocity Jet Cleaning of Sanitary Sewer Lines

Hoffman, Daniel Eugene

Abstract Details

2009, MS, University of Cincinnati, Engineering : Environmental Engineering.
High velocity water jets are utilized by many municipal wastewater collection organizations to clean sewer lines clogged with roots and debris in order to restore or maintain full capacity. In rare cases, the cleaning operation expels air and water from the sewer into private laterals, even out of drains, water closets, and other fixtures in nearby homes and businesses. These accidents, known as “blowouts”, can cause property damage, strain public relations and pose a potential health hazard. The objective of this research is to determine the circumstances under which blowouts occur in an attempt to predict and reduce their occurrence. Analysis of 418 blowout events observed over a 10-year period by the Hamilton County Metropolitan Sewer District compared against GIS shapefiles of Hamilton County's sewer system indicate that blowouts occur most often in sewers mains with low capacity. Other site factors often suspected to be important, such as lateral length to the affected residence or elevation difference between structure and sewer, were found to have no statistically significant explanatory power on the rate of blowouts. A Poisson-type predictive model was developed (R2>0.9) to estimate the probability of at least one blowout occurring given a pipe of a known flow capacity and serving a neighborhood with a specified number of lateral connections. The SWMM computer model was used to test the hypothesis that blowouts are triggered when the hydraulic head rises in the sewer main. The SWMM model found that blowouts can occur under extreme conditions, that is, with jet nozzle flows exceeding 120 gpm with mainline clogs blocking 90% or more of the total sewer flow area. However, since these conditions are inconsistent with field observations, it was concluded that sewer line blowouts do not result from surcharging due to excessive hydraulic head. A computational fluid dynamics model (Fluent) was used to test the hypothesis that blowouts are induced by dynamic air pressure gradients. The Fluent runs found that, at home locations with limited plumbing ventilation, air pressures within a residential plumbing system could exceed 1000 Pa, the minimum pressure necessary to cause a blowout of residual water from a basement drain trap. Hence, the likely mechanism responsible for causing blowouts during jetting operations is thought to be a transient air pressure surge that travels through the connecting lateral as the cleaning nozzle passes in the sewer mainline. As this numerical finding is not conclusive, further experimental and/or field research would be required to confirm this.
Steven Buchberger, PhD (Committee Chair)
James Uber, PhD (Committee Member)
Michael Flanders, PE (Committee Member)
185 p.

Recommended Citations

Citations

  • Hoffman, D. E. (2009). Predicting and Preventing Hydraulic Blow-Outs during High Velocity Jet Cleaning of Sanitary Sewer Lines [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1236010806

    APA Style (7th edition)

  • Hoffman, Daniel. Predicting and Preventing Hydraulic Blow-Outs during High Velocity Jet Cleaning of Sanitary Sewer Lines. 2009. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1236010806.

    MLA Style (8th edition)

  • Hoffman, Daniel. "Predicting and Preventing Hydraulic Blow-Outs during High Velocity Jet Cleaning of Sanitary Sewer Lines." Master's thesis, University of Cincinnati, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1236010806

    Chicago Manual of Style (17th edition)