Visualization of Sewer Pipeline Deterioration Using Statistical Models and Spatial Mapping

A research group led by Professor Kiyoyuki Kaito (Graduate School of Engineering, The University of Osaka) has developed a new method to predict the deterioration of sewer pipelines^*1 and support the formulation of efficient rehabilitation and renewal plans.

Using multiple statistical models and spatial mapping techniques, the research team successfully estimated the deterioration rate of the entire pipeline network from partial inspection data. Furthermore, they visualized areas where pipelines are estimated to have low structural integrity and are densely concentrated, enabling the efficient identification of regions requiring rehabilitation and renewal.

*1 Sewer pipelines
The formal term for sewer pipes

Challenges in Managing Aging Sewer Pipelines

In Japan, the aging of sewer pipelines has become a serious issue. As of 2019, approximately 5% of sewer pipelines have exceeded the standard service life of 50 years. However, this proportion is projected to increase rapidly to approximately 15% in 10 years and approximately 35% in 20 years.

Because pipelines are buried underground, it is difficult to inspect all the pipelines across an entire management area. Taking Osaka City as an example, the goal is to conduct the first CCTV inspection around the benchmark of a 50-year service life. While the inspection rate for pipelines installed before 1964 has reached approximately 90%, the inspection rate for pipelines installed after 1970 remains very low.

Under these circumstances, there is a growing need to develop methods that, even when only inspection data from a subset of sewer pipelines are available, combine such data with information on soil conditions and pipeline structure to predict the deterioration status of the entire management area, including uninspected pipelines, and formulate efficient maintenance and management plans.

Development of a High-Precision Sewer Pipeline Deterioration Simulation Method

Development of a New Simulation Method

In this study, a new methodology was developed that enables the prediction of deterioration for all concrete sewer pipelines in Osaka City based on partial inspection data.

The research group first applied a statistical model that probabilistically represents the stepwise deterioration process of pipeline structural integrity to inspection data from 49,243 spans*2 of sewer pipelines that had already been surveyed, and estimated the deterioration rate of each pipeline. This model has the advantage of accounting for differences in deterioration rates among individual pipelines. The result showed that the average service life of sewer pipelines is approximately 115.5 years, while individual pipelines exhibit substantial variation, ranging from less than 50 years to more than 200 years. It was also found that nearby pipelines tend to have similar deterioration rates because their environmental conditions, such as soil conditions and distance from the coast, are similar.

Next, a predictive model was constructed by combining the tendency for similar deterioration rates among nearby pipelines with pipeline attribute information, including diameter, soil conditions, and distance from the coast. Using this model, the structural integrity of all 115,050 pipeline spans across Osaka City was predicted, including 65,807 pipeline spans that had not yet been inspected. By applying density analysis methods to these results, areas where pipelines with advanced deterioration are densely concentrated were visualized on a map, making it possible to identify regions that should be prioritized for rehabilitation and renewal.

*2 Span
A unit of pipeline section between manholes. One span corresponds to the section between two adjacent manholes.

Enabling Simulation of Sewer Pipeline Structural Integrity Through 2070

Based on the simulation results, deterioration is predicted to progress between 2020 and 2040 in sewer pipelines located near coastal areas and in the northern Yodo River region. Thereafter, deterioration is expected to expand across the entire Osaka City area by 2070, as shown in Fig. 1.

In addition, verification of the deterioration rate estimation accuracy of the proposed method demonstrated the highest accuracy compared to conventional methods, confirming its effectiveness. Because areas where sewer pipelines with advanced deterioration are densely concentrated can be appropriately identified on a map, this method is considered useful for selecting priority regions for rehabilitation and renewal projects.

As a result, even when inspection data are only partially available, it becomes possible to predict deterioration across all sewer pipelines and to formulate efficient maintenance and management plans.

Toward Sustainable Infrastructure Management

The results of this research enable the formulation of efficient maintenance and management plans for sewer pipelines. By identifying areas where pipelines with low structural integrity are densely concentrated, it becomes possible to consolidate rehabilitation and renewal work, thereby reducing construction costs and minimizing road restrictions associated with such projects. Furthermore, this method is applicable not only to sewer pipelines but also to the maintenance and management of other underground utilities and infrastructure assets.

With further research, improvements are expected in the accuracy of deterioration rate estimation for uninspected pipelines, as well as in the application of the model to other types of infrastructure facilities.