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The Renewal of Stormwater Systems Using Trenchless Technologies (2018)

Chapter: Chapter 3 - Current Practice and Experience

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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
×
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Suggested Citation:"Chapter 3 - Current Practice and Experience." National Academies of Sciences, Engineering, and Medicine. 2018. The Renewal of Stormwater Systems Using Trenchless Technologies. Washington, DC: The National Academies Press. doi: 10.17226/25167.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

22 Introduction This chapter synthesizes the literature search, questionnaire responses, and interviews to provide a summary of the relative frequency of use, how decisions are made to perform trench- less renewal, how methods are selected, the relative use and satisfaction with the methods, and costs and the degree to which costs are tracked. The questionnaire was sent to all 50 DOTs. A total of 43 responses were received from 40 DOTs. The following sections summarize the results and include related supplementary information obtained from interviews and collected during the literature search. Experience Of the respondents, 88% have experience with using at least one method of trenchless storm- water system renewal (Figure 10). Appendix B contains the list of the questionnaire respondents. This appendix can be found on the TRB website (www.trb.org) by searching for “NCHRP Synthesis 519.” The number of different trenchless renewal methods used by respondents is included in Table 5. As shown in Table 5, most DOTs have experience with either one or two methods. Methods and Frequency Used The selection of a trenchless method requires an assessment of the current condition of the stormwater facility. While assessment is beyond the scope of this synthesis, in general, the assess- ment needs to identify the underlying cause of the problems that resulted in the system being selected for renewal. At a minimum, the selection of the appropriate trenchless renewal method for a project requires an assessment of the geometry and condition of the existing structure, an understanding of the current and projected functionality and performance of the structure, and general site conditions including site access. Other information, such as anticipated soil and groundwater conditions, the presence of contamination, and adjacent utilities might also be required if access pits are required, if ILR methods will be considered, or if external spot repair is required to facilitate the trenchless renewal. Some additional information on assessment is included in NCHRP Synthesis 303: Assessment and Rehabilitation of Existing Culverts (Wyant 2002). The questionnaire identified the relative use of trenchless renewal by experienced agencies. The results indicate that on stormwater system projects open-cut is used 75% of the time, trenchless renewal is used 16% of the time, and trenchless installation is used 9% of the time (Figure 11). C H A P T E R 3 Current Practice and Experience

Current Practice and Experience 23 Figure 10. Experience with trenchless stormwater system renewal (40 state DOT respondents). Number of Methods Count Percentage of All Respondents Percentage of Experienced DOTs 0 4 10% — 1 10 24% 26% 2 13 31% 34% 3 4 10% 11% 4 5 12% 13% 5 3 7% 8% 6 3 7% 8% Table 5. Number of commonly used trenchless renewal methods (37 respondents). Figure 11. Frequency various construction methods are used on stormwater projects (36 respondents). The respondents were asked to identify the approximate frequency with which they per- formed trenchless renewal of manholes and vaults. Based on the responses, trenchless renewal of manholes and vaults is only performed about 11% of the time (Figure 12). The questionnaire asked which trenchless renewal methods respondents have used on their projects. The ability to select “Other” and a corresponding write-in field was provided to try and identify new methods. The results, which are summarized in Table 6, identified three respon- dents who considered invert paving to be trenchless renewal. Masada (2017) provides a summary

24 The Renewal of Stormwater Systems Using Trenchless Technologies of a study on the structural benefits of concrete paving of steel culvert inverts. One respondent identified the use of internal bands and joint repair as trenchless renewal. Because each DOT could potentially use more than one method and because some DOTs provided responses at the district level, the questionnaire asked for an approximate percentage of projects completed using the various trenchless methods. The results are provided in Figure 13 and represent the weighted average frequency with which the various methods are used. Note that because the number of projects completed by each respondent are not the same, these responses do not necessarily represent the frequency they are used on a project level. Additional information on the use of trenchless methods was obtained from follow-up inter- views with respondents and from interviews with selected municipalities and special districts. Two questionnaire respondents stated that they do not currently consider either CIPP or SIPP for structural renewal. Three questionnaire respondents stated that their in-house crews perform the renewal using SL. Interviews with municipalities and special districts did not reveal any significant differences in the methods used or the application of the methods. Satisfaction with Methods Used The questionnaire also asked respondents to characterize their relative success or satisfac- tion with the various methods as a percentage (Table 7). The satisfaction percentages range from 100%, always satisfied, to 0%, never satisfied. The number of responses (count) should Figure 12. Frequency trenchless renewal of manholes and vaults is performed on stormwater projects (36 respondents). Methods Used Method Count Percentage SL 33 89% CIPP 23 62% SIPP 14 38% MSL 9 24% ILR 8 22% CFP 5 14% Other (Paved invert) 3 8% Other (Internal bands or joint repair) 1 3% Table 6. Percentage of DOTs that have used the various renewal methods (37 respondents).

Current Practice and Experience 25 be considered when reviewing the results. The results may not be representative for the less fre- quently used methods. One respondent experienced with both CIPP and SL reported a lower satisfaction with CIPP than with SL. Based on a follow-up interview, the relative dissatisfaction with CIPP was clarified as being a function of a smaller sample size (i.e., they perform much more SL than CIPP) and a result of larger-than-anticipated site disturbance during construction, and not the functionality or performance of the liner. One respondent reported a lower satisfaction with SIPP as opposed to the other methods they used. Based on a follow-up interview, the respondent noted that the SIPP liners generally exhibit more leaking than the other methods they use. The leakage was noted as a concern due to the potential for spalling and cracking of the SIPP liner because of freeze-thaw. One respondent noted that where mountainous terrain would make SL difficult, they use CIPP. They also use CIPP at some locations because they anticipate that the CIPP liner will hold up better to fires associated with crop burning than the SL pipe. One respondent noted that their dissatisfaction with some of their SL projects is associated with the perceived lower value of the renewed culvert compared with a replacement concrete box culvert. Figure 13. Relative frequency, on the respondent level, with which the various trenchless renewal methods are used (37 respondents). Satisfaction with Renewal Method Method Count Satisfaction Percentages MSL 7 91% CIPP 22 90% SL 32 88% ILR 7 87% SIPP 12 77% Other (Paved invert) 2 75% CFP 5 68% Table 7. Relative satisfaction, where 100% is always satisfied and 0% is never satisfied, with the renewal method used (36 respondents).

26 The Renewal of Stormwater Systems Using Trenchless Technologies DOT respondents did not have shareable case studies of unsuccessful application of trench- less renewal methods. Interviews with municipalities and special districts did identify several failures associated with CIPP. The failures were reported as rare and appeared to be associated with project specific issues. The hypotheses offered for the failures included insufficient original resin saturation, insufficient preparation of the existing pipe, incomplete curing, and damage to the liner prior to installation. Increasing Trenchless Renewal Use The questionnaire asked what information would be useful for experienced agencies when considering using trenchless renewal more frequently. The results provided in Table 8 indicate that the top three types of additional information are case studies, typical costs, and examples of decision criteria used by other agencies. The questionnaire asked respondents to identify reasons trenchless renewal was not used even when it was technically feasible. Table 9 provides the frequency of the reasons for not perform- ing trenchless renewal when it is technically feasible. One respondent noted that for shallow cover and low-volume roads, they prefer open-cut replacement. Another respondent noted that they do not currently perform much SL since they do have a standard specification to perform the work. Additional Information Count Percentage Typical cost information 33 89% Agency experience with the applicable methods (case studies) 30 81% Decision criteria used by facility owners 28 76% Limiting factors to the applicability of specific methods 27 73% Emergent technologies 27 73% Sources of claims and mitigation methods 19 51% Settlement, heave, and vibration impacts and mitigation methods 19 51% None of the above 1 3% Other (Durability of trenchless repairs) 1 3% Table 8. Information that would be useful for experienced agencies when considering using trenchless renewal more frequently (37 respondents). Reason Percentage Condition of existing pipe (e.g., offset joints, collapse) 78% Reduction in hydraulic capacity not acceptable 61% Economics/costs 56% Limited organizational experience 39% Uncertainty regarding design life/performance of trenchless methods 36% Preference for new construction 36% Site access limitations (e.g., limited staging area) 28% Faster to open-cut 19% Environmental considerations (e.g., pH, existing fish/wildlife, and required habitat improvement [fish passage]) 19% Lack of local experienced contractors 11% Flow bypass difficulties 11% Presence of laterals 8% Potential damage to existing, adjacent facilities or pavement 6% Prior unfavorable experience 3% Table 9. Reasons experienced agencies elect not to use trenchless renewal when technically feasible (37 respondents).

Current Practice and Experience 27 For respondents that do not have experience with trenchless renewal, the questionnaire asked for the top five reasons for not using it. Table 10 provides an overall rank, where 1 is the highest and 10 is the lowest, for the reasons provided. The four respondents without trenchless experience were also asked what information would be useful when considering using trenchless renewal. Table 11 provides the results as a “count” rather than a percentage because of the small sample size. Method Selection The survey results indicate that approximately 11% of the 38 respondents have standard- ized decision criteria to assist with deciding whether to perform trenchless renewal and which method to use. The criteria provided by the respondents or identified during interviews are summarized below. The Florida DOT has a pipe repair matrix that is available on the internet (Florida DOT 2017). The matrix was developed for repair of new construction damaged during installation and identified during final pipe inspection. The potential use of three trenchless renewal methods (CIPP, SL, and SIPP) are identified in the matrix for cracks or leaks of metal or concrete pipes. The matrix also references a pipe liner standard specification, which includes additional references to MSL and the ILR (pipe bursting). Neither the matrix nor the specification provide guidance for selecting a particular method. The preface for the matrix states that it does not replace engi- neering judgment and “encourages the review and use of emerging repair technologies provided they are based on sound scientific principles and defendable engineering analysis.” Reason Overall Rank Reduction in hydraulic capacity not acceptable 1 Limited organizational experience 2 Preference for new construction 3 Uncertainty regarding design life/performance of trenchless methods 4 Condition of existing pipe 5 Economics/costs 6 Faster to open-cut 7 Lack of local experienced contractors 8 Presence of laterals 9 Flow bypass difficulties 10 Table 10. Reasons why DOTs that do not have experience with trenchless renewal do not use it (4 respondents). Additional Information Count Decision criteria used by facility owners 4 Agency experience with the applicable methods (case studies) 3 Typical cost information 3 Limiting factors to the applicability of specific methods 2 Emergent technologies 2 Sources of claims and mitigation methods 1 Settlement, heave, and vibration impacts and mitigation methods 1 Table 11. Information that would be useful for non-experienced agencies when considering using trenchless renewal (4 respondents).

28 The Renewal of Stormwater Systems Using Trenchless Technologies The Minnesota DOT’s HydInfra Inventory and Inspection program, which includes data from inspections such as size, shape, material, and condition descriptor, in combination with a related flow chart, can provide a planning-level suggested repair (Wagener and Leagjeld 2014). Trenchless renewal methods included in the flow chart are limited to SL and CIPP. Additional site-specific data such as access, laydown area, flow diversion feasibility, and hydraulic capacity need to be considered before the suggested repair is selected as the recommended repair. The Virginia DOT (2017) provides another example of guidelines for selecting a trenchless renewal method based on the deficiency (defect) and site access considerations. Virginia DOT identifies three methods of pipe rehabilitation. These three methods are corrugated steel pipe liner, flexible pipe liner, and smooth wall steel pipe liner. The flexible pipe liner, referred to as “Method D,” covers CIPP, SL, SIPP for pipes 36 in. or larger, and the F&F variant of CFP. The California Department of Transportation (Caltrans) has a design bulletin that supple- ments the 1995 FHWA publication Culvert Repair Practices Manual—Volumes 1 and 2. The bulletin includes a discussion of trenchless renewal and trenchless replacement methods (Caltrans 2013). The bulletin provides a summary of approaches to identifying possible replace- ment and renewal methods based on the culvert size, traffic, and culvert condition. The Ohio DOT has designer guidelines for trenchless culvert repair and rehabilitation (Ohio DOT 2016). The guidelines are provided for existing structurally and non-structurally sound RCP, and metal (steel and aluminum) pipe as well as structurally sound plastic pipe. The guidelines include trenchless renewal with SL, SIPP, and CIPP. For agencies that do not have a standardized process, Figure 14 summarizes the selection pro- cess used. “Own equipment/crews” in Figure 14 means that the selection of the method is based on the ability of in-house personnel to perform the work. “All the above” in Figure 14 refers to “Experienced-based,” “in-house expert/consultation,” “own equipment/crews,” and “input from outside consultants” as all being methods used by the respondents. The literature review identified publications providing decision criteria for selecting trenchless renewal methods published by non-state DOTs. These include a publication by the Federal Lands Highway and a publication by the United States Forest Service. A manual entitled Culvert Assessment and Decision-Making Procedures Manual for Federal Lands Highway (Hunt et al. 2010) provides guidance for selecting replacement or rehabilitation of culverts. The manual includes an assessment tool with proposed rating codes with reference photographs and flow charts for identifying potential renewal, replacement, or repair alternatives. Figure 14. Decision criteria used by DOTs without a standardized process (34 respondents).

Current Practice and Experience 29 The assessment form illustrates the types of information that is commonly required to identify the potentially applicable trenchless renewal methods. For SL, CFP, spiral-wound liner, CIPP, and SIPP, the Federal Lands Highway manual provides a liner selection matrix with some of the typical applications and advantages and disadvantages, as well as rough comparative costs. The United States Forest Service developed a guide for rehabilitating and replacing CMP culverts using trenchless methods (Matthews et al. 2012). The guidelines contain a flow chart for selecting from SIPP, CIPP, MSL, SL, and invert paving, depending on the condition of the CMP. Reasons for Using Trenchless Renewal The questionnaire asked for the top five reasons for using trenchless renewal. The two “Other” reasons were related to minimize traffic disruption and the smaller staging requirements. The responses highlight the usual assumed reasons related to cost and schedule. The top five reasons include the height of fill over the existing pipe, the desire to limit surface disturbance, perceived economic/cost benefit, the anticipation it will be faster than open-cut, and temporary deferral of constructing a larger replacement pipe. Table 12 provides an overall rank, where 1 is the highest and 13 is the lowest, and weighted score for the reasons provided. The number of rankings indicates the frequency with which it was selected as one of the top five reasons. The survey asked for the approximate percentage of trenchless renewal projects that were per- formed to temporarily defer replacement. Based on the results, about 30% of trenchless renewal projects are performed for temporary renewal. This value was calculated using a weighted average of the results of the survey provided in Table 13. Note that because the number of projects Reason Overall Rank No. of Rankings Height of fill (cover) over structure 1 23 Limit surface disturbance 2 25 Perceived economic/cost benefit 3 22 Faster than open-cut 4 23 Temporary or permanent deferral of constructing a larger replacement pipe 5 14 Environmental considerations (e.g., existing fish/ wildlife, wetland impact) 6 13 Favorable past experience 7 13 Commonly used/standard practice 8 7 Own the equipment and have in-house crews that perform the work 9 8 Lots of local experienced contractors 10 5 Other 11 2 Outcome from formalized cost benefit analysis 12 3 Outcome from formalized decision process 13 2 Table 12. Reasons for using trenchless renewal (34 respondents). Trenchless Renewal Performed for Temporary Mitigation Never 10% 20% 30% 40% 50% 60% 70% 80% 90% Always 10 10 3 1 0 3 0 1 1 3 3 Table 13. Frequency with which trenchless renewal is performed for temporary mitigation (35 respondents).

30 The Renewal of Stormwater Systems Using Trenchless Technologies completed by each respondent is not the same, these responses do not necessarily represent the frequency that the renewal is considered temporary on a project level. The questionnaire asked for a relative percentage of projects where the renewal was considered to be for non-structural reasons. Based on the results, about 26% of trenchless renewal projects are performed for non-structural reasons (Figure 15). This value was calculated using a weighted average of the results of the survey provided in Table 14. Note that because the number of projects completed by each respondent are not the same, these responses do not necessarily represent the frequency that the renewal is performed for non-structural reasons on a project level. Defects Commonly Mitigated and Satisfaction The survey results indicate that trenchless renewal is most commonly used to mitigate cor- rosion; leaks or infiltration; loose or open joints; and cracks, breaks, or splits. The experience of respondents mitigating defects is summarized in Table 15. Because each DOT could potentially attempt to mitigate more than one defect, respondents were asked for an approximation of the relative frequency with which the defects were mitigated. Figure 15. Frequency trenchless renewal is performed for structural versus non-structural renewal (36 respondents). Trenchless Renewal Performed for Non-Structural Reasons Never 10% 20% 30% 40% 50% 60% 70% 80% 90% Always 19 3 2 1 2 2 0 1 0 2 4 Table 14. Frequency trenchless renewal is performed for non-structural reasons (36 respondents). Defect Count Percentage Corrosion 34 90% Leaks or infiltration 30 79% Loose or open joints 29 76% Cracks, breaks, or splits 27 71% Cavitation or erosion 14 37% Flattened or oval pipes 10 26% Sags 5 14% Alignment offsets 5 13% Table 15. Experience with mitigating defects using trenchless renewal (36 respondents).

Current Practice and Experience 31 The questionnaire asked for one of six frequency categories shown in Table 16 to be selected based on the answers to the proceeding question on which defects were commonly mitigated. Table 16 provides a count of the responses for each category. The data shows the same trend: corrosion is the most frequent defect mitigated, followed by attempting to mitigate leaks or infiltration; loose or open joints; and cracks, breaks, or splits. The questionnaire asked for a qualitative response opinion on the ability of trenchless renewal to mitigate the previously defined defects. With the exception of the responses indicating dis- satisfaction with mitigating flattened or oval pipes, sags, and the eight “neutral” responses, the DOTs overall indicated they were satisfied or very satisfied with the ability of trenchless renewal to mitigate most defects. Table 17 provides a summary of the responses. Costs Of the 38 respondents, 24% indicated that they had shareable trenchless renewal costs. The costs were not obtained as part of the survey. The questionnaire asked for the frequency that cost overruns occurred in four categories. The magnitudes in these categories were 0% to 10%, 10% to 20%, 20% to 30%, and greater than 30%. To characterize the relative frequency with which cost overrun occur, the data from the survey are summarized in Figure 16. The respondents were asked to identify the most common reason for cost overruns. A total of nine respondents provided answers. The following answers were provided: • Changed conditions. • Limited number of contracts. • Overruns are typically low because the work is paid for by the linear foot of existing pipe and the quantity is usually fairly accurate. Defect Relative Frequency Mitigation Attempted Never <10% 10% to 40% 40% to 60% 60% to 90% Always Alignment offsets 31 3 1 1 0 0 Loose or open joints 9 2 10 6 7 2 Flattened or oval pipes 26 4 1 2 2 1 Sags 31 1 3 1 0 0 Cracks, breaks, or splits 11 2 8 8 7 0 Cavitation or erosion 23 4 2 4 2 1 Corrosion 3 4 8 11 8 2 Leaks or infiltration 8 3 12 10 2 1 Table 16. Relative frequency with which mitigation is attempted (38 respondents). Defect Relative Satisfaction with Mitigation Attempted Very Dissatisfied Dissatisfied Neutral Satisfied Very Satisfied Alignment offsets 0 0 0 5 0 Loose or open joints 0 0 1 18 8 Flattened or oval pipes 1 0 0 6 3 Sags 0 1 1 3 0 Cracks, breaks, or splits 0 0 0 20 5 Cavitation or erosion 0 0 2 9 2 Corrosion 0 0 2 22 9 Leaks or infiltration 0 0 2 19 7 Table 17. Relative satisfaction with mitigation attempted (36 respondents).

32 The Renewal of Stormwater Systems Using Trenchless Technologies • Rare due to mostly bid items. • Building the pit. One respondent uses master agreements with fixed costs that are determined before the project begins so that they do not have overruns. The questionnaire asked respondents to select the common reasons for construction claims on trenchless renewal projects. The most common reason identified by the 29 respondents was a difference in the existing pipe condition (59%), followed by differing groundwater/soils condi- tions (40%). Comments regarding the most common reason for construction claims provided by respondents are summarized below: • Existing pipe condition and/or size different than anticipated (three comments). • Differing site conditions (two comments). • Additional liner thickness required. • Wrong method selected for conditions. • Difficulty with the annular void filling. Six respondents noted that they have not had any construction claims on trenchless renewal projects. Underutilized Methods Both experienced and non-experienced DOTs identified concerns about the ability to main- tain the existing hydraulic capacity as one of the main reasons for not using trenchless renewal. Therefore, CFP, MSL, ILR, and SIPP, which typically do not result in a significant reduction in hydraulic capacity and could potentially improve the hydraulic capacity of existing stormwater systems, appear to be underutilized. Chapter Summary The following list contains a summary based on the synthesis of the literature search, questionnaire responses, and interviews: • Of the respondents, 88% have experience with some form of trenchless renewal of stormwater systems. • SL is the most commonly used trenchless renewal method. • The respondents are generally satisfied with the SL (88%). Figure 16. Weighted average frequency with which cost overruns occur (32 respondents).

Current Practice and Experience 33 • Of the DOTs, 24% use only one trenchless renewal method. • Of the DOTs, 55% have experience with two methods. • About 88% of the respondents do not use a standardized decision criterion to assist with selecting the trenchless renewal method; the decision is most commonly made based on past experience. • The most common reason for using trenchless renewal is the height of cover over the exist- ing pipe. • The most common reason for experienced DOTs not to use trenchless renewal is the condition of the existing pipe. • The most common reason for non-experienced DOTs to not use trenchless renewal is the condition of the unacceptable reduction in hydraulic capacity. • The respondents are generally satisfied or very satisfied with the ability of trenchless renewal to mitigate the common defects, such as corrosion; leaks or infiltration; loose or open joints; and cracks, breaks, or splits. • The most common cause of cost overruns and claims is changed or differing conditions associated with the existing pipe (59%). • Of the respondents, 64% indicated that cost overruns were generally less than 10% of the original project cost. • CFP, MSL, ILR, and SIPP may be underutilized relative to the other SL and CIPP. A more detailed summary is provided in Chapter 4.

Next: Chapter 4 - Conclusions »
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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 519: The Renewal of Stormwater Systems Using Trenchless Technologies summarizes technologies used for the renewal of stormwater systems, including new, emerging, and underutilized trenchless methods, and identifies future research needs.

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.

Appendix A and Appendix B are available to download in separate documents.

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