Date of Award

Summer 8-16-2018

Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

John Matthews


The dissertation research work described here has four primary objectives: (1) the development of a comprehensive wastewater pipe condition rating model that incorporates a large number of environmental, structural, and hydraulic parameters of the pipe; (2) the development of a wastewater pipe deterioration model used to predict future overall condition states of the pipe, as well as determining the probability of failure at any given age of the pipe; (3) the development of a comprehensive consequence of failure model that assesses the consequence of wastewater pipe failure using economic, social, and environmental cost factors; and (4) the development of a proposed risk-based decisionmaking framework that combines the probability of failure with the consequence of failure to determine the wastewater pipe’s risk of failure for rehabilitation and/or renewal decision-making purposes.

The industry-accepted protocol for condition rating of sewer pipes in the U.S. is the Pipeline Assessment and Certification Program (PACP) developed by the National Association of Sewer Service Companies (NASSCO, 2001). The PACP method relies exclusively on visual inspections performed by means of Closed-Circuit Television (CCTV) where existing structural and operation and maintenance (O&M) defects are observed by certified operators. A limitation of the PACP method is that it does not use pipe characteristics, depth, soil type, surface conditions, pipe criticality and capacity, nor the distribution of structural defects, or history of preventative maintenance to determine the condition rating of the sewer pipe segment. Therefore, this research work addresses this limitation and develops a condition rating model that incorporates information about pipe characteristics, environmental parameters, as well information about structural and O&M defects, and hydraulic factors. Factors such as pipe material, diameter, shape, pipe material’s age, soil type, depth of burial, type of carried waste, seismic zone, loading, groundwater, flow, inflow, and pipe surcharge are used.

As part of an asset management program, the ability to predict future sewer pipe conditions and potential failures is vital for capital improvement planning and budgeting. The deterioration model developed herein is unique in that it uses a Continuous Time Markov Chain method, as opposed to the widely used Discrete Time Markov Chain methods in the literature, to determine probabilities of transitioning from a better to a worse condition at any given age of the pipe.

To obtain a complete risk-based decision-making framework, the probability of failure is combined with the consequence of failure of the pipe to determine its risk of failure. The developed consequence of failure model incorporates a large number of economic, social, and environmental cost factors to determine the consequence of failure of the asset. Among the factors considered in the assessment of the consequence of failure are the pipe age, diameter, length, depth of burial, access to pipe, distance to critical laterals, soil type, seismic zone, distance to critical laterals, average daily traffic, proximity to other infrastructure, distance to bodies of water, and land use. Combined with the probability of failure, it results in the pipe’ risk of failure. The obtained information is useful for future capital project planning and improvement budgeting.