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1 Aging stormwater facilities can be replaced using open-cut or trenchless replacement, or the service life of the existing stormwater facilities can be extended using trenchless renewal. This synthesis focuses primarily on the trenchless renewal of culverts typically ranging in diameter from 12 in. to over 12 ft with both circular and noncircular cross-sections. While most aging culverts consist of either corrugated metal or concrete pipe, some of the renewal methods discussed in this synthesis are also applicable to other pipe types. Both trenchless replacement and trenchless renewal methods can reduce negative impacts associated with surface disruption by moving the work area outside of the travel lanes and concentrating the construction impacts off the roadway. Trenchless renewal can extend the service life of existing stormwater facilities by addressing decay such as corrosion, abrasion, and erosion; reducing or eliminating infiltration and exfiltration; and providing a structural repair or improving the structural capacity of culverts, pipelines, manholes, and related stormwater structures. In some situations, trenchless renewal can even improve the hydraulic capacity of the stormwater system. The purpose of NCHRP Synthesis 519 is to summarize trenchless technologies used for the renewal of stormwater systems. The six trenchless renewal methods described in this synthesis include (1) cured-in-place pipe (CIPP), (2) sliplining (SL), (3) modified sliplining (MSL), (4) in-line replacement (ILR), (5) spray-in-place pipe (SIPP), and (6) close-fit pipe (CFP). The use of manhole renewal and invert paving are also briefly discussed. The information in this synthesis was gathered through a literature review, a screening survey of state departments of transportation (DOTs), and interviews. The information gathered was focused on the methods used, decision criteria used to select a renewal method, limiting factors on the applicability of specific trenchless renewal methods, successful practices, emergent or underutilized methods, and methods from other industries. The survey was sent to the 50 state DOTs and 43 responses were received from 40 state DOTs. Survey results indicate that while 88% of the DOT respondents have experience with trenchless renewal, the majority (60%) only have experience with one or two methods. Only 8% of the DOT respondents have experience with all six primary methods. Survey results indicate that SL and CIPP are the two most commonly used methods for stormwater system renewal. The need to maintain the existing hydraulic capacity of the stormwater system was identified both by experienced and non-experienced DOTs as a primary reason for not using trenchless renewal. Based solely on this criterion, SIPP, MSL, ILR, and CFP appear to be underutilized. These four methods do not generally result in a significant reduction in hydraulic capacity, and ILR can be used to increase the pipe size and in some cases SIPP liners, MSL, and CFP can improve the hydraulic capacity of some pipes. S u m m a r y The Renewal of Stormwater Systems Using Trenchless Technologies
2 The renewal of Stormwater Systems using Trenchless Technologies Questionnaire results indicate that the primary means of selecting the trenchless renewal method is experience-based, followed closely by in-house expert/in-house consultation. This may be part of the reason that most DOTs only have experience with one or two meth- ods and that SL and CIPP pipe are the two most commonly used methods. Over 90% of the DOTs that use one or two methods use SL, and about 60% of DOTs that use two methods use both SL and CIPP. The DOTs are satisfied with the commonly used SL and CIPP. They are also generally satisfied or very satisfied with the ability of trenchless renewal to address defects, such as corrosion; leaks or infiltration; loose or open joints; and cracks, breaks, or splits. Common causes of cost overruns and claims were identified as changed or differing conditions associated with the existing pipe or subsurface conditions. Of the respondents, 64% indicated that cost overruns were generally less than 10%. DOTs can benefit from future research and synthesis of structural testing and analysis of SIPP and CIPP liners, additional published information on less commonly used ILR methods, detailed cost data, and standardized trenchless replacement and renewal selection guidelines. Some future research on these topics has already been planned. For example, a study entitled âStructural Design Methodology for Spray Applied Pipe Liners in Gravity Storm Water Conveyance Conduitsâ has been funded by the Transportation Pooled Fund Program.