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34 Of the surveyed state DOTs, 88% have current experience with some form of trenchless renewal of stormwater systems. Respondents indicated it is used on about 16% of the storm water projects. The trenchless renewal of vaults and manholes is performed on only about 11% of respondentsâ projects. Trenchless renewal methods are commonly considered to be âpermanentâ (70%) rather than a temporary repair to defer replacement. Trenchless renewal is also commonly considered to be a structural repair (74%). It is uncommon for the decision to use trenchless renewal and the decision on which method to use to be made based on a standardized decision criterion. Only 11% of respondents identified they had an established procedure. The remaining respondents overwhelmingly relied on previous experience (38%), inÂhouse experts (27%), or the fact that they had their own equipment and experienced crews (15%) to decide which trenchless method to use. The four most common reasons, in order from more common to less common, for using trenchless renewal were identified as follows: ⢠Height of fill (cover) over the structure ⢠Limiting surface disturbance ⢠Perceived economic/cost benefit ⢠Faster than openÂcut The three most common reasons, in order from more common to less common, for DOTs with trenchless renewal experience for not using trenchless renewal when it is technically feasible were identified as follows: ⢠Condition of existing pipe ⢠Reduction in hydraulic capacity not acceptable ⢠Economics/costs The five most common reasons, in order from more common to less common, for DOTs without trenchless renewal experience for not using trenchless renewal were identified as follows: ⢠Reduction in hydraulic capacity not acceptable ⢠Limited organizational experience ⢠Preference for new construction ⢠Uncertainty regarding design life/performance of trenchless methods ⢠Condition of existing pipe C H A P T E R 4 Conclusions
Conclusions 35 The five most common types of information, in order from more common to less common, that DOTs identified as being helpful for increasing the use of trenchless renewal were as follows: ⢠Typical cost information ⢠Agency experience with applicable methods (case studies) ⢠Decision criteria used by facility owners ⢠Limiting factors to the applicability of specific methods ⢠Emergent technologies The same top five types of information, in a slightly different order, were identified by DOTs without trenchless renewal experience as being most helpful for considering using trenchless renewal. The surveyed DOTs have the most experience with SL (89%), CIPP (62%) and SIPP (38%). On a DOT basis, as opposed to on a project basis, SL is the most commonly used method (56%), with CIPP being used less than half as often (25%) and SIPP being used about 6% of the time. The relatively low number of responses regarding experience with MSL, CFP, and ILR make it difficult to characterize the frequency with which these methods are used. The respondents are generally satisfied with SL (88%) and CIPP (90%). The reported satisfaction rates for the other methods may not be representative because they are not fre quently used. The respondents are generally satisfied or very satisfied with the ability of trenchless renewal to mitigate common 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 condi tions associated with the existing pipe (59%) or subsurface conditions (40%). Of the respon dents, 64% indicated that cost overruns were generally less than 10%, and 6% noted experience with cost overruns exceeding 30%. These findings, combined with literature search and interviews, suggest the following research opportunities. A comprehensive review of structural testing and analysis of SIPP and CIPP liners. SIPP and CIPP do not significantly reduce the existing hydraulic capacity. However, uncertainty regarding the design and structural performance of these two methods is limiting the acceptance and use by some of the interviewed DOTs. A document providing a comprehensive review of the structural testing and analysis of these methods could further their use. Second application renewal. Researching the potential limitations on future renewal or repair resulting from the initial use of a renewal method could be considered. As a result of the relatively short timeÂinÂservice of trenchless renewal methods, the reÂapplication of renewal methods on previously renewed pipes is not well documented. Additional published information on less commonly used ILR. ILR could potentially address the top two identified reasons provided for not using trenchless renewal when it is technically feasible (deteriorated condition of the existing pipe and unacceptable reduction of hydraulic capacity). While this synthesis provides some information on ILR used for trenchless renewal of stormwater systems, a publication focused on the successful use, limitations, advances in equipment and tooling, and costs could be of value to DOTs.
36 The Renewal of Stormwater Systems Using Trenchless Technologies Detailed cost data on trenchless renewal methods. While 88% of DOTs have experience with trenchless renewal, only 24% of experienced respondents said that they had shareable cost data. The wide range of costs for the methods available in the literature, combined with the low percentage of DOTs with data to share, suggests that collecting the requisite data and the data analysis to provide cost data will be challenging. Practitionerâs guide. The process of performing an assessment and using the results to select a preferred renewal method is beyond the scope of this synthesis. While some DOTs and other agencies have guidelines, a comprehensive report or practitionerâs guide could be beneficial to those agencies without standard guidelines or sufficient organizational experience.
