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Hydraulic Loss Coefficients for Culverts (2012)

Chapter: Chapter 3 - Slip-Lined Culverts

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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
×
Page 23
Page 24
Suggested Citation:"Chapter 3 - Slip-Lined Culverts." National Academies of Sciences, Engineering, and Medicine. 2012. Hydraulic Loss Coefficients for Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22673.
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Page 24

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18 3.1 Summary Culvert rehabilitation, in many cases, represents a cost- effective alternative to culvert replacement. Slip lining old culverts with new liner pipe represents a culvert rehabilitation practice that is becoming more and more common. A relined culvert must be able to pass the design flood while meeting the necessary embankment freeboard condition. The discharge capacity of a slip-lined culvert is influenced by the geometry of the inlet end treatment. For inlet control, the culvert head- discharge relationship is a unique function of the culvert inlet geometry and driving head, which must be determined exper- imentally. For outlet control, the head-discharge relationship is determined by balancing the energy loss through the culvert (entrance, friction, exit, and other minor losses) and the avail- able driving head, with the coefficient for entrance loss being determined experimentally. A number of factors, including reduced inlet flow area, the liner pipe wall roughness, and the inlet end treatment, influence the relined culvert discharge capacity relative to the original culvert. Four different slip-lined culvert inlet end treatments asso- ciated with a thin-wall projecting host pipe were evaluated experimentally. Inlet control head-discharge relationship and outlet control entrance loss coefficient trends were evaluated as a function of liner projection distance and liner-to-host pipe transition detail (sudden or tapered). The test results showed that the entrance loss coefficient (ke) for the projecting slip liner was independent of the projection distance for projection distances of 0.17D and 0.34D; ke values for the projecting slip- lined culvert were slightly smaller (more efficient) than the traditional thin-wall projecting ke values published in design manuals. The inlet control head-discharge relationships were independent of projection distance and were consistent with the performance of traditional thin-wall projecting culverts operating under inlet control. Tapered grout transitions between the host and liner pipe were found to reduce ke due to a reduction in entrance flow contraction. 3.2 Introduction Many existing culverts have reached or will soon reach the end of their useful service life. When a culvert is in need of repair, replacement methods can be very costly and may not be feasible due to budgetary or environmental constraints (Maine DOT, 2004). Culvert rehabilitation, when applicable, can become a significant resource and time saving tool. Slip lining is a common rehabilitation technique where a new culvert, often a smooth-walled pipe, is placed inside an exist- ing or host culvert (Plastics Pipe Institute, 1993). An example of a slip-lined culvert is illustrated in Figure 3-1. In order to minimize the reduction in cross-sectional area, the slip liner typically matches the host culvert shape and has the largest available diameter that can be slipped inside the existing culvert (Ballinger and Drake, 1995b). The invert of the slip liner is placed directly on top of the invert of the exist- ing culvert, and the space between the slip liner and the host culvert is grouted. Typically, the slip liner is extended a short distance (≥ 6 in.) beyond the existing culvert at each end to allow for expansion and contraction, as well as for installation purposes. A review of publications related to the hydraulics of slip- lined culverts produced very little information regarding the effects that slip lining may have on the hydraulic parameters of a culvert inlet (i.e., entrance loss coefficients and inlet con- trol head-discharge relationships). The Plastics Pipe Institute (1993) showed how the hydraulic capacity of a slip-lined culvert may be affected because of a difference in pipe wall roughness between the existing culvert and the slip liner; however, no information was given regarding the impact of the inlet geometry on the hydraulic capacity of slip-lined culverts. Ballinger and Drake (1995a) recognized that the hydraulic capacity of a culvert may be influenced by the inlet geometry and that the flow capacity (for a given upstream head) can either increase or decrease as a result of the slip- lining procedure, but they did not produce any experimental C h a p t e r 3 Slip-Lined Culverts

19 data to show how the change in inlet geometry might affect the hydraulic capacity of a slip-lined culvert. Following the literature review, it was apparent that there is a need to quantify the hydraulic parameters (i.e., entrance loss coefficients and inlet control head-discharge relationships) of slip-lined culvert inlets since the hydraulic capacity of such culverts is typically approximated with traditional culvert design data such as the data published in FHWA’s Hydraulic Design of Highway Culverts (Normann et al., 2001), referred to here and in practice as HDS-5. The generation of data spe- cific to slip-lined culvert inlet geometries is important in the derivation of the abovementioned design parameters so that design engineers can accurately predict the hydraulic capacity of slip-lined culvert configurations. 3.3 Research Objectives The objective of this research was to determine the effect of several projecting end-treatment geometries specific to segmental-pipe slip lining on ke and on the inlet control head-discharge relationship. Two typical end treatments were constructed, and the slip liner was extended two distances from the existing culvert end for each end treatment. The first type of slip-lined culvert end treatment was cre- ated by installing a projecting liner inside a larger host pipe and grouting the annular space between the two pipes with a verti- cal grout face at the end of the host pipe (see Figure 3-2). The second type of slip-lined culvert end treatment also featured a projecting slip liner upstream of the host culvert; however, the grout was tapered and extended from the end of the host culvert to the end of the slip liner (see Figure 3-2). The projecting distance between the outside culvert and the slip liner was tested at 2 and 4 in. (0.17D and 0.34 D, respec- tively) to investigate the influence of projection distance on Figure 3-1. Example of a slip-lined culvert. Figure 3-2. Slip-lined culvert inlet end treatments.

20 inlet performance. For the tapered end treatment, the angle of the tapered grout at the crown of the pipe ranged from 34° to 53° depending on the projecting distance of the slip liner from the outside culvert. The culvert used as the slip liner was also tested alone (no host culvert) as a traditional projecting inlet in order to investigate the difference between traditional projecting end treatments and slip-lined project- ing end treatments. Examples of the end treatments tested are demonstrated in Figure 3-2. Each end treatment was tested with a ponded approach flow condition. The ponded approach represented a reservoir con- dition with negligible velocities everywhere except near the cul- vert inlet. Figure 3-3 illustrates a ponded approach condition. With velocity head equal to zero, the piezometric head equals the total head. Consequently, the flow depth, or piezometric head term (Hwi), in Equations 1-2 through 1-4 was replaced with total head (Hw) for analysis of the inlet control flow data. Hw represents a more appropriate upstream head parameter, particularly when the approach velocity head is significant (i.e., a channelized approach flow condition). Each end treatment was tested over a range of headwater depths for both submerged and unsubmerged inlet conditions. Corresponding values of ke (outlet control) and K, M, c, and Y (inlet control) were determined. The upstream energy or head- water levels were measured in terms of the dimensionless head- water over diameter (Hw/D), where D is the total vertical rise of the slip-liner culvert inlet. The submerged case was created when the upstream headwater fully inundated the culvert inlet, typically at an Hw/D value of 1.2 or greater. 3.4 Experimental Method—Outlet Control Testing A detailed discussion of the testing procedures associ- ated with the determination of ke for outlet control and the empirical constants associated with the head-discharge rela- tionships (Equations 1-2 through 1-4) for inlet control is presented in Chapter 1. A 20-ft long, 12-in. diameter, com- mercially available PVC pipe with an 11.75-in. inside diam- eter (I.D.) and a 0.25-in. wall thickness was used as the slip liner for all slip-lined culvert testing. The host culvert had an I.D. of approximately 14 in. and a wall thickness of 0.625 in. This test setup represented an inside diameter reduction of approximately 20%. Water was supplied to the test culverts via a head box, which measured 24 ft long by 22 ft wide by 5 ft deep. Water was sup- plied to the head box via a 20-in. supply line and/or 8-in. sup- ply line, both containing calibrated orifice plate flow meters. A schematic of the culvert test facility is shown in Figure 3-4, and a photo of the culvert test setup is shown in Figure 3-5. To determine entrance loss coefficients, the culvert must be flowing under outlet control, which corresponds to subcriti- cal flow conditions in the culvert. Outlet control is achieved by installing the test culvert at a slope less than the critical slope for a given discharge. For all outlet control culvert tests, the test culvert was installed in as horizontal a position as possible (i.e., So = 0) to ensure subcritical culvert flow and outlet control conditions. The culvert entrance head loss (He) is the difference between the total head in the head box and the representative one- dimensional total head value in the culvert at the inlet and was evaluated for each test condition as follows. The total head in the head box was determined by measuring the piezometric head in the head box, relative to the invert of Figure 3-3. Ponded approach flow condition. Figure 3-4. Testing facility at the Utah Water Research Laboratory.

21 the culvert inlet, at a location where the velocity head was negligible. The head box pressure tap location is shown in Figure 3-4. The total head inside the culvert inlet was found by projecting the total head determined at pressure tap locations distributed along the length of the culvert invert back to the culvert inlet by either adding back the calculated friction loss (full-pipe flow) or by using gradu- ally varied flow computational techniques (open channel culvert flow). The resulting calculated culvert inlet total head values for each of the pressure taps were averaged to give an average total head at the inlet. After determining He, the ke was calculated using Equation 1-1. Using slip liners with a smooth pipe wall made it possible to determine friction losses for full-culvert flows by applying standard closed-conduit friction loss relationships and fric- tion factors and to calculate gradually varied flow profiles for free-surface culvert flows. It was assumed that culvert entrance loss is primarily a function of the inlet geometry of the culvert, not the roughness of the culvert material. With a smooth wall boundary, the pressure taps were oriented nor- mal to the streamlines in the culvert, which facilitated accurate piezometric head measurements inside the pipe. There were no localized turbulence regions generated by a boundary pro- file as would exist with a corrugated pipe wall, for example. The Froude number was monitored for free-surface culvert flow conditions to verify that subcritical flow (Fr < 1.0) existed in the culvert barrel, an indicator of outlet control. The material roughness height for the PVC test culvert was assumed to be 0.00006 in. (Flammer et al., 1986). 3.5 Experimental Results Outlet Control The ke test results for the slip-lined circular culverts are shown in Figure 3-6, where ke is plotted as a function of Hw/D and classified by end treatment and inlet submergence condition. From the end treatment specific data plotted in Figure 3-6 (thin-wall 2-in. projecting, thin-wall 4-in. project- ing, 2-in. projecting with taper, 4-in. projecting with taper), Figure 3-5. Overview photo of the culvert test setup. Figure 3-6. Slip-lined culvert entrance loss coefficients.

22 it was discovered that at Hw/D > 1.0, ke tends to decrease in value with increasing Hw/D until the coefficient eventually levels off to a constant value. This trend may be a phenom- enon associated with the projecting end treatment. For Hw/D values less than 1.0, the entrance loss coefficients varied sig- nificantly with headwater elevation. The average ke for the traditional thin-wall projecting end treatment (without slip-lining) was 0.80 (see Figure 3-6), which is consistent with values reported by Tullis (1989). In comparison, the slip-lined end treatments were only slightly more efficient hydraulically. The slight increase in efficiency is due to the suppression of flow contraction at the inlet, espe- cially in the case of the projecting end treatment with tapered grout. Also, it can be noted that, relative to the two projecting distances tested [2 in. (0.17D) and 4 in. (0.34D)], the project- ing distance of the slip liner from the existing culvert had lit- tle influence on ke. For example, ke equals 0.71 for the tapered mortar end treatment projecting 2 in.; ke equals 0.70 for the tapered mortar end treatment projecting 4 in. The thin-wall projecting inlet slip-liner condition (no tapered mortar) yielded an average ke of 0.77, which was only slightly more efficient than the traditional projecting inlet, suggesting that slip lining a culvert without tapering the grout has little effect on ke. Table 3-1 summarizes the average slip-lined culvert ke values obtained for each end treatment tested. The average experimental uncertainty associated with the slip-lined cul- vert data was 1.5%. Inlet Control Inlet control head-discharge relationships were created for unsubmerged and submerged inlet conditions (i.e., 0.3 < Hw/D < 4.0) for each of the four end treatments. Figure 3-7 presents inlet control data for each slip-lined culvert end treat- ment plotted as a function of the Form 2 quasi-dimensionless relationship. Under inlet control conditions, the traditional thin-wall projecting end treatment and the slip-lined projecting end treatment [2 in. (0.17D) and 4 in. (0.3D)] produced nearly identical results at the same flow rates. The slip-lined project- ing with taper end treatment did, however, exhibit an increase in efficiency compared to the traditional thin-wall projecting end treatment due to the reduction of flow contraction. A regression of the inlet control data was performed to produce design coefficients for use in Equations 1-2 through 1-4; the results are presented in Table 3-2. Tabular support data for the Chapter 3 experimental results are included in Appendices C and D. 3.6 Conclusions Based on the experimental determination of entrance loss coefficients and inlet control head-discharge relationships for slip-lined culverts, the following conclusions were made: 1. Relative to the two projecting distances tested [2 in. (.017D) and 4 in. (0.34D)] for slip-lined culverts, there are no sig- nificant effects associated with the inlet hydraulics of the culvert unless the grout is tapered down from the existing culvert inlet to the inlet of the projecting slip liner. The increase in inlet efficiency that is observed over the range of tapered projections tested is due to the reduction of flow contraction at the inlet. The fact that the inlet hydraulics of the liner were independent of the projecting distance from the host culvert is not necessarily a general conclusion. As the projection distance increases, ke should approach the value of the traditional projecting inlet ke value (~0.8). There was approximately a 2.5% difference in ke between the slip-lined 2- and 4-in. thin-wall projecting end treatments. 2. For the tapered projecting end treatment, the projection length and the corresponding angle of the taper at the pipe crown, which ranged from 34° to 53°, did not influence Test culvert inlet end treatment Unsubmerged Submerged ke mean ke Hw/D ± extreme deviation from mean Traditional projecting see Figure 3-6 0.80 >1.0 ± 3.7% Slip-lined, 2-in. projecting see Figure 3-6 0.76 >1.0 ± 2.6% Slip-lined, 4-in. projecting see Figure 3-6 0.78 >1.0 ± 3.0% Slip-lined, 2-in. projecting, tapered see Figure 3-6 0.71 >1.0 ± 3.2% Slip-lined, 2-in. projecting, tapered see Figure 3-6 0.70 >1.0 ± 3.4% Table 3-1. Slip-lined culvert entrance loss coefficients.

23 the degree of flow contraction significantly enough to increase the inlet efficiency under inlet control testing, or significantly affect ke under outlet control testing. 3. The slip-lined projecting end treatment with tapered grout was more efficient than the slip-lined thin-wall projecting inlet. Under outlet control testing, the tapered projecting inlet produced values of ke on average 9% lower than those for the slip-lined thin-wall projecting inlet, and 13% lower than the traditional thin-wall projecting inlet. 4. Under inlet control, there is no appreciable difference between the head-discharge relationships for the tradi- tional thin-wall projecting inlet and the slip-lined thin- wall projecting inlet. When the inlet control data for the traditional thin-wall projecting inlet and the slip-lined Figure 3-7. Traditional and slip-lined culvert inlet control quasi-dimensionless (Form 2) performance. Test Culvert Inlet End Treatment Unsubmerged Submerged Form 1 Form 2 c Y K M K M Traditional projecting 0.0946 0.60 0.5812 0.58 0.0513 0.69 Slip-lined, 2-in. projecting 0.0971 0.55 0.5830 0.57 0.0520 0.64 Slip-lined, 4-in. projecting 0.0945 0.54 0.5808 0.57 0.0520 0.66 Slip-lined, 2-in. projecting, tapered 0.0908 0.54 0.5772 0.57 0.0467 0.69 Slip-lined, 2-in. projecting, tapered 0.0841 0.52 0.5697 0.56 0.0473 0.65 Table 3-2. Slip-lined culvert inlet control regression constants.

24 thin-wall projecting inlet [2 in. (.017D) and 4 in. (0.34D)] are combined for regression analysis, an R2 value of 0.999 is obtained for both the unsubmerged Form 2 data fit (Equation 1-3) and the submerged data fit (Equation 1-4). 5. For a long slip-lined culvert (outlet control), where the energy loss is dominated by friction, the hydraulic benefit gained by using a mortar-tapered projecting end treatment over a thin-wall projecting end treatment would likely be minimal. For shorter outlet control cul- verts or inlet control culverts, however, enhancing the inlet geometry may have a measurable influence on the hydraulic capacity of the culvert, and therefore tapering the grout is recommended. The durability of the tapered grout with respect to thermal expansion/contraction of liner pipe and/or freeze/thaw effects was not evaluated in this study. Based on the research completed, the effects of slip lin- ing on the inlet capacity of a projecting culvert are minimal when flowing under both outlet control and inlet control conditions. Although the inlet geometry may be improved to increase the inlet efficiency, more significant factors related to the hydraulic capacity of a slip-lined culvert are the diameter and hydraulic roughness of the slip liner.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 734: Hydraulic Loss Coefficients for Culverts explores culvert designs that maintain natural velocities and minimize turbulence to allow migratory species to pass through the culvert barrel.

The report describes the refinement of existing hydraulic relationships and the development of new ones for analysis and design of culverts for conventional and nontraditional, environmentally sensitive installations.

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