Rehabilitation of Culverts and Buried Storm Drain Pipes (2022)

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1   State departments of transportation (DOTs) make management plans to extend the service life of their aging assets, including culverts and buried storm drain pipes. Considering safety, functional performance, and economics, state DOTs make critical decisions about mainte- nance, repair, rehabilitation, or replacement of deteriorating culvert structures. This synthesis report presents currently available and emerging repair and rehabilitation practices used by state DOTs and investigates the factors affecting the selection and implementation of these methods. The synthesis methodology included collection and analysis of information from (1) a literature review of relevant standards, best practices, and guidance documents; (2) a web- based questionnaire that was completed by state DOTs; and (3) interviews with four state DOTs to develop case examples demonstrating their practices and field applications. As part of the literature review, ASTM standards and state DOT repair and rehabilitation design specifications and guidance documents were reviewed. The survey was sent to DOT agencies in 50 states and the District of Columbia, for a total of 51 agencies. The response rate was 82% (i.e., 42 state DOTs responded to the survey). It was found that corrugated metal pipe (CMP) culverts are rehabilitated more frequently than concrete culverts (50% of the responding state DOTs frequently rehabilitated CMP, compared with the 17%, 19%, and 2% of state DOTs that frequently rehabilitated concrete box, concrete pipe, and plastic pipes, respectively). Concrete invert pavement and sliplining are the most commonly used methods to rehabilitate CMP culverts (68% and 84% of the responding state DOTs sometimes or frequently rehabilitated culverts using invert pave- ment and sliplining methods). According to the state DOTs responding to the survey, the expected service life is estimated to be approximately 20–50 years for CMP and ≥50 years for concrete culverts. Installation of thermoplastic pipes has been more recent. They are the least-rehabilitated culverts, mainly due to a lower number of older plastic pipe installations. Impacts on the users of the roadway and on hydraulic performance are found to be the two most critical factors affecting the selection of rehabilitation method. As a result, the majority of the responding state DOTs use trenchless methods, such as invert concrete pave- ment, sliplining, and cured-in-place pipe (CIPP). Aquatic organism or fish passage was mentioned by several DOTs as another important factor affecting the rehabilitation design. The synthesis revealed areas for new research that could help accelerate the adoption and successful implementation of current and emerging rehabilitation methods. More specifi- cally, development of design criteria, best practices, and design guidance documents could support broader application of spray-applied structural lining, CIPP, sliplining, invert con- crete paving, stabilization of surrounding backfill soil, end treatment, and trenchless replace- ment methods. Some state DOTs develop their own requirements or design criteria if they S U M M A R Y Rehabilitation of Culverts and Buried Storm Drain Pipes

2 Rehabilitation of Culverts and Buried Storm Drain Pipes frequently use certain rehabilitation methods. State DOTs could benefit from research addressing questions that could be used to further develop design guidance, such as: Can the invert concrete paving/lining be unreinforced or reinforced with welded steel mesh, shear studs, or steel rebar? What are the material, thickness, and other design and installa- tion requirements and the limitations of the invert paving, spray-applied structural lining, sliplining (grouting), and other rehabilitation methods? New research data and guidance would be helpful for wider use of emerging methods or less commonly used methods, such as rehabilitation of noncircular culverts using slip- lining, fiber-reinforced polymer (FRP) materials, methods to increase hydraulic capacity, and rehabilitation designs to address fish passage requirements. In addition, half of the state DOTs responding to the survey do not consider the existing structural capacity of the host pipe in their rehabilitation designs. New research could help DOTs quantify the remaining capacity of the deteriorated soil–pipe system when the backfill soil is lost (e.g., through joints or perforations in the culvert walls), so that the required additional struc- tural capacity can be determined for the rehabilitation design.