Manning s n Values History of Research

Transcription

1 10 INTRODUCTION Selectio of the proper value for the coeffi ciet of roughess of a pipe is essetial i evaluatig the fl ow through culverts ad sewers. A excessive value is uecoomical ad results i oversizig of pipe, while equally, a low value ca result i hydraulically iadequate pipe. Proper values for the coeffi ciet of roughess of commercially available pipe has bee the objective of periodic ivestigatios ad, as a result, extesive kowledge ad data are available o this ofte cotroversial subject. To the desiger, the presetly accepted values for the coeffi ciet of roughess are of great importace. Of equal importace is a uderstadig of how these values were determied. Research ofte idicates ew values for pipe materials sigifi catly differet from those previously used. DESIGN VALUES The differece betwee laboratory test values of Maig s ad accepted desig values is sigifi cat. Numerous tests by public ad other agecies have established Maig s laboratory values. These laboratory results, however, were obtaied utilizig clea water ad straight pipe sectios without beds, maholes, debris, or other obstructios. The laboratory results idicated the oly differeces were betwee smooth wall ad rough wall pipes. Rough wall, such as ulied corrugated metal pipe have relatively high values which are approximately 2.5 to 3 times those of smooth wall pipe. Smooth wall pipes were foud to have values ragig betwee ad but, historically, egieers familiar with sewers have used or This desig factor of percet takes ito accout the differece betwee laboratory testig ad actual istalled coditios. The use of such desig factors is good egieerig practice ad, to be cosistet for all pipe materials, the applicable Maig s laboratory value should be icreased a similar amout i order to arrive at comparative desig values. Recommeded desig values are show i Table 1. FLOW FORMULAS The Kutter fl ow formula was developed about 1870 Maig s Values History of Research Table 1 Pipe Material Recommeded Values of Maig s Values of Maig's Lab Values Promoted ACPA Values Recommeded Values Cocrete storm sewer saitary sewer HDPE lied storm sewer PVC solid wall storm & saitary sewer Corrugated Pipe America Cocrete Pipe Associatio s Cocrete Pipe Desig Maual Tullis ad Barfuss Study CPPA Specifi catios 4 Ui-Bell s Hadbook of PVC Pipe Uiversity of Miesota test o Culvert Pipes NCSPA S Moder Sewer Desig U.S. Departmet of Trasportatio Federal Highway Admiistratio s Hydraulic Desig of Highway Culverts ad extesively used for may years to calculate pipe fl ows. Roughess coeffi ciet values for use i the Kutter formula were derived ad are kow as Kutter values. The Kutter formula was mathematically cumbersome, eve though charts ad graphs were developed as desig aids. The simpler Maig formula, developed i 1890, has geerally replaced the Kutter formula i use. Maig s formula, i terms of fl ow, is expressed as follows: Q = AR 2/3 S 1/2 where: Q = fl ow i pipe, cubic feet per secod A = cross-sectioal area of flow, square feet R = hydraulic radius, equal to the cross-sectioal area of fl ow divided by the wetted perimeter of pipe, feet S = slope of pipe, feet per foot = coeffi ciet of roughess appropriate to the type of pipe ACPA

2 The Maig formula factors are similar to those i Kutter formula ad are expressed i the same uits. Values for the coefficiet of roughess,, were at first thought to be the same as those used i the Kutter formula but this assumptio has bee prove to be wrog. MANNING VALUE RESEARCH As the Maig formula came ito more commo use, the direct iterchage of values with Kutter s was questioed. A series of studies, prior to 1924, at the Uiversity of Iowa provided the fi rst extesive data o this disputed poit. These were cooperative studies sposored by the Bureau of Public Roads, U.S. Departmet of Agriculture, ad the Uiversity of Iowa. The test program cosisted of 1,480 hydraulic experimets o 12, 18, 24 ad 30- ich cocrete pipe, corrugated metal pipe, ad clay pipe. Results of these tests were published i 1926 by the Uiversity of Iowa i Bulleti No. 1, The Flow of Water Through Culverts, by David L. Yarell, Floyd A. Nagler ad Sherma M. Woodward. Values obtaied from the test results for Maig ad Kutter roughess coefficiets, are give i Table 2. After the Iowa test results were published, may desigers re-evaluated the values for Maig s formula ad used for smooth wall pipe ad for corrugated pipe. These values were ot uiversally accepted, however, ad other desigers used = for cocrete ad clay pipe. Metal pipe maufacturers were advocatig = for corrugated metal pipe, ad some desigers still erroeously use this comparatively low value for corrugated pipe today. HDPE PIPE Research by Tullis ad Barfuss i 1989, preseted to the America Society of Civil Egieers showed that tests o corrugated HDPE pipe with a lier has a laboratory Maig s value i the rage of to 0.015, depedig o the coditio of the liers. The bodig of the lier to the corrugatios, i may cases, made the pipe iterior wavy, explaiig the broad rage i values. This waviess causes the HDPE pipe to have hydraulic values similar to CMP. Maig s cocers regardig HDPE pipe, however, are ot widely uderstood because the pipe has ever bee tested uder a exteral load, ad further research is required. Because of the broad rage of values, a value of for HDPE pipe will ot provide a 20 to 30 % factor of safety ad is ot recogized by the FHWA ad the Army Corps of Egieers. Frequetly the ier lier of a double wall (profi le) wall HDPE pipe udergoes a pheomeo called corrugatio growth. After a short period of time, sometimes prior to istallatio, plastic deformatio occurs i the lier creatig waviess that makes the iterior of HDPE pipe appear similar to corrugated metal pipe. The ier liig is iteded to produce a smooth-walled pipe, however, a corrugated patter results whe stresses are trasferred from the outer corrugated wall to the ier lier. The smooth lier is uable to resist stresses from the outer wall ad corrugatio growth appears. Desigers of pipig systems utilizig lied HDPE pipe should size the pipe usig a Maig s value similar to that of corrugated metal pipe. COMPARATIVE TESTS FOR CONCRETE AND CORRUGATED METAL PIPE The ext sigificat ivestigatio of Maig values for pipe bega i 1946 ad cotiued over a four-year period at St. Athoy Falls Hydraulic Laboratory, Uiversity of Miesota. A primary purpose of these large-scale tests was to obtai pipe frictio coeffi ciets which would be more accurate ad depedable. A total of 181 hydraulic tests were ru o 18, 24, ad 36-ich circular cocrete pipe ad corrugated metal pipe, ad corrugated metal pipe Table 2 Uiversity of Iowa Tests o Culvert Pipe Average Values for the Coefficiet of Roughess i Cocrete, Vitrified-clay, ad Corrugated Metal, Culvert Pipe 2

3 Table 3 Uiversity of Miesota Test o Culvert Pipes Summary of Test Results arches for the full flow ad partly full flow coditios. May of the shortcomigs of previous hydraulic tests were elimiated i the Miesota tests. Culvert test legths were 193 feet, which were loger ad more represetative of actual istallatio coditios. Pipe sectio legths were closer to actual commercial legths, particularly for cocrete pipe, with six-foot sectios beig used istead of the two-foot ad three-foot legths used i the 1926 Iowa test. The test results were published i 1950 by the Uiversity of Miesota i Techical Paper No. 3, Series B, Hydraulic Data Compariso of Cocrete ad Corrugated Metal Pipes by Lorez G. Straub ad Hery M. Morris ad are as show i Table 3. These results idicate a sigifi catly lower value of Maig s for cocrete pipe tha the 1926 Iowa tests. Techical Paper No. 3 also icluded recommeded desig values for for both corrugated metal ad cocrete pipe as reproduced i Table 4. Comparig the values from Tables 2, 3 ad 4, it is readily apparet that o safety factors were applied to the laboratory values whe covertig them to desig values. The footote beeath Table 4, however, qualifi es the applicatio of the recommeded values to such a extet that they could ot be used for realistic pipe istallatio. As previously discussed, laboratory values should ot be used for desig purposes without appropriate safety factors. Durig the period , research was coducted i Caada to determie desig values of for pipe used i culvert costructio. The research was uder the auspices of the Cooperative Highway Research Program i Alberta, which icluded the provicial Departmet of Highways, the Research Coucil of Alberta, ad the Faculty of Egieerig of the Uiversity of Alberta as participatig bodies. Tests were made o field istallatios of 60-ich structural plate corrugated metal pipe culverts 70 ad 150-feet log Table 4 Uiversity of Miesota Tests o Culvert Pipe Recommeded Desig Coefficiets of Corrugated Metal ad Cocrete Culverts 3

4 with various ilet shapes ad slopes from 1 to 3 percet, ad o a 48-ich cocrete pipe culvert 78-feet log o a slope of 0.5 percet. Laboratory tests were coducted o 15-ich diameter stadard corrugated metal pipe 36 ad 724-feet log with slopes from 0 to 8 percet. Test results were published by the Research Coucil of Alberta i the 1962 Alberta Highway Research Report 62-1 titled Hydraulic Tests o Pipe Culverts by C. R. Neill. Summaries of the Maig values computed for the 60-ich structural plate pipe are quoted as follows: The values computed from 33 tests showed a ormal type of statistical scatter, with a mea of ad a stadard deviatio of Pedig further tests, the value of was adopted for structural plate corrugated metal pipe. Maig values determied for the 15-ich stadard corrugated metal pipe, are quoted as follows: Values raged from at very low velocities to at high velocities. It appeared that was probably a peak value ad that was reasoable for desig purposes. Additioal quotes as to values of Maig s for cocrete pipe are as follows: No determiatio was made of roughess coeffi - ciets, sice the pipe was too short ad smooth to show appreciable frictio losses. As oe purpose of the experimets was to determie the possible hydraulic advatages of usig cocrete pipe istead of corrugated metal pipe, the followig statemets from the test report are sigifi cat: By compariso, it ca be see that the capacity of the 48-ich cocrete culvert was approximately the same as that of the 60-ich structural plate corrugated metai oe, of approximately the same legth. At the upper ed of the test rage, the cocrete culvert showed rather better performace. The tests o cocrete pipe culvert showed that a cocrete culvert of give diameter was cosiderably more efficiet tha a corrugated metal oe i most desig situatios especially whe subjected to high headwater depths, the mai reaso beig the much smaller frictio losses i the cocrete pipe. It appeared that cocrete culverts prime readily whe their ilets are slightly submerged, ad may the be assumed to fl ow full throughout, ad also that the stadard type of grooved ilet is quite effi ciet. CONCRETE PIPE TESTS I additio to those previously discussed, other tests have bee performed o cocrete pipe. I Jue 1956, experimetal studies o 24 ad 36-ich cocrete pipe were iitiated by the State Road Departmet of Florida to determie the effect of iterior surface fi ishes ad joit irregularities o the pipe coeffi ciet of frictio. The test program was expaded i May 1957, placed uder joit sposorship of the State Road Departmet of Florida ad the Bureau of Public Roads, ad studies were performed at St. Athoy Falls Hydraulic Laboratory, Uiversity of Miesota. This series of tests is sigifi cat i that field layig coditios were simulated, a coditio desigers foud lackig i other hydraulic studies. Laboratory test istallatios were 240-feet log for the 36-ich pipe ad 192-feet for the 24-ich pipe. Tests were made o pipe istalled i two ways: (1) pipe laid with ormal costructio practices ad closely simulatig fi eld measuremets of joit irregularities, ad (2) pipe laid with extreme care to elimiate, as far as possible, all fl ow iterferece at Figure 1 Diaper Seal e o e = 0 to 1.37" o Offset Cross-Sectio of Cocrete Pipe Test Joits Groove 119 o Bead or Fillet Joist may have offset i additio to groove ad bead or fillet Exterior of Pipe e b W e = 0 to 0.72" b Wave = 5.32" Bead Fillet b = 1.54" b Groove 4

5 the joits. The fi rst coditio was referred to as average joits ad the secod as good joits. Figure 1 illustrates the irregularities oted i fi eld joits ad a cross sectio of the pipe showig the average circumferetial legth of grooves ad beads. Joit irregularities were of three basic types: offsets-due to misaligmet or variatio i diameter of pipe. grooves-formed by aular opeigs betwee togue ad groove eds of pipe. beads ad fi llets-formed by mortar smoothed over the iterior surface of the joit. Results of this series of tests were published i December 1960, by St. Athoy Falls Hydraulic Laboratory, Uiversity of Miesota, Techical Paper No. 22, Series B, titled Resistace to Flow i Two Types of Cocrete Pipe by Lorez G. Straub, Charles E. Bowers ad Meir Pilch. A compariso of the test data for pipe with good ad average fi eld irregularities idicates a differece i Maig s o the order of 1.9 percet. Numerical values of for 36-ich ad 24-ich pipe with average joits were ad , respectively ad, as a result, ASTM Specificatio C76 was writte to require, the joits shall be of such desig ad the eds of the cocrete pipe sectios so formed that whe the sectios are laid together they will make a cotiuous lie of pipe with a smooth iterior free from appreciable irregularities i the fl ow lie. I the mid-1980 s, laboratory tests of cocrete ad plastic pipe were coducted at the T. Blech Hydraulics Laboratory, Departmet of Civil Egieerig, The Uiversity of Alberta. A report by D.K. May, A.W. Peterso ad N. Rajaratam, A Study of Maig s Roughess Coefficiet for Commercial Cocrete ad Plastic Pipe, was published i Jauary, Commercially available cocrete pipe i 8, 10 ad 15-ich diameters ad PVC plastic pipe i 8, 10 ad 18-ich diameters were tested with clea water ad straight aligmet. The average Maig s values were foud to be for cocrete pipe ad for PVC pipe as preseted i Table 5. To recofirm the results of the Alberta ad previous studies, the America Cocrete Pipe Associatio commissioed additioal tests o 8, 12 ad 18-ich diameter precast cocrete pipe at the Utah Water Research Laboratory, Utah State Uiversity, Loga, Utah. Results were published i Hydraulics Report Number 157, J. Paul Tullis, October, Laboratory values of Maig s for precast cocrete pipe were recofirmed as Results are show i Table 6. CORRUGATED METAL PIPE TESTS Prior to 1950, comparatively few tests had bee made o large size corrugated metal pipe. For this reaso, U.S. Army Chief of Egieers Offi ce, i 1951, authorized tests o 3, 5, ad 7-foot diameter corrugated metal pipe Table 5 Uiversity of Alberta Summary of Test Results Table 6 Utah State Uiversity Summary of Test Results at the Boeville Hydraulic Laboratory, Boeville, Orego. Legth of the test istallatios was 350 feet for all diameters. All pipe had a corrugatio patter of 1 / 2 -ich x 2 2 / 3 -ich. The experimetal coditios, as far as size ad legth of pipe tested, exceeded ay previously used. Results of these tests were published i 1959, i the Joural of the Hydraulics Divisio, Proceedigs of the America Society of Civil Egieers, Frictio Factors i Corrugated Metal Pipe by Marvi J. Webster ad Laurece R. Metcalf. Recommeded Maig values are preseted graphically i the report. As a coclusio, the report states that for 3, 5 ad 7-foot omial diameter corrugated pipe with a 1 / 2 -ich x 2 2 / 3 -ich corrugatios ad fl owig full, a Maig s = was obtaied. I 1958, a program of hydraulic tests was iitiated by the U. S. Army Corps of Egieers, ad the Bureau of Public Roads at the U. S. Army Waterways Experimet Statio, for the purpose of determiig roughess factors for structural plate corrugated metal pipe. The results were preseted i a paper at the 44th Aual Meetig of the Highway Research Board, Jauary 1965, ad published i Highway Record No The paper is titled Frictio Factors for Hydraulic Desig of Corrugated Metal Pipe, by Joh L. Grace, Jr. A major highlight of this research report was the preparatio of graphs showig the relatioship of Maig s with pipe size for three commercially available corrugatio patters. These graphs are reproduced i Desig Data 2 (Frictio Factors for Corrugated Metal Pipe). A summary of the rage of values ad the ap- 5

6 plicable equatios relatig Maig s to pipe diameters are preseted i Table 7. Table 7 Equatio Corrugated Patter Pipe Size Rage = 2 2 / 3 " x 1 / 2 " 12" - 96" D = 3" x 1" 36" - 96" D = 6" x 2" 36" - 96" D Value Rage to to to The corrugated metal pipe idustry has formally recogized the higher laboratory values of Maig s, which research has prove for available corrugatio patters. The values of recommeded for upaved corrugated metal pipe i the May 1999 Moder Sewer Desig, published by the Natioal Corrugated Steel Pipe Associatio ad the America Iro ad Steel Istitute, are preseted i Table 8. Table 8 Corrugatios (Aular) Diameter Upaved Frictio Factors for Hydraulic Desig of Corrugated Metal Pipe Values of Coefficiet of Roughess for Corrugated Steel Pipe (Maigs Formula) 2 2 / 3 x 1 / 2 i.. 3 x 1 i. 1 to 8 ft to 8 ft *BPR Circ. 10, Mar. 1965, p. 78. Based o 108-i. diam. Structural Plate 6 x 2 i. 5 to 20 ft * To date, limited testig has bee coducted o helically corrugated metal pipe. Tests were coducted o helically corrugated metal pipe by A. R. Chamberlai ad the results were published i 1955 at Colorado State Uiversity i a report titled Effect of Boudary o Fie Sad Trasport i Twelve Ich Pipes. Charles E. Rice coducted fl ow tests at the Stillwater Outdoor Hydraulic Laboratory, Stillwater, Oklahoma, o 8-ich ad 12-ich pipe. His report titled Frictio Factors for Helical Corrugated Pipe, was published by the U. S. Departmet of Agricultural Research Service i I 1970, the Federal Highway Admiistratio, Offices of Research ad Developmet published a report Hydraulic Flow Resistace Factors for Corrugated Metal Coduits by J. M. Norma ad H. G. Bossy. The observatios by the authors were that, as the pipe diameters icreases, the helix agle also icreases, ad as the helix agle approaches 90 degrees the pipe must behave as a corrugated pipe with aular corrugatios. For a partly full fl ow coditio i a helically corrugated metal pipe i which the spiral flow caot be maitaied, it is presumed that eve a small helix agle would cause little reductio i resistace ad that the same resistace coeffi ciet as that for stadard corrugated metal pipe should be used. There is a eed to further test helically corrugated metal pipe, especially the larger sizes. At preset, the use of a reduced resistace coeffi ciet is idicated oly for small diameters, 2 feet or less, ad the oly uder full fl ow coditios... The best course for coservative desig, pedig further test results, is to use aular corrugated metal pipe resistace coeffi ciets for helically corrugated pipe. A updated Hydraulic Flow Resistace Factors for Corrugated Metal Coduits was published by the Federal Highway Admiistratio i Jauary, I 2001, the Federal Highway Admiistratio published Hydraulic Desig of Highway Culverts, Hydraulic Desig Series No. 5 by J.M. Norma, R.J. Houghtale ad W.J. Johsto. Both publicatios recommed aular fl ow resistace factors be used for helically corrugated metal pipe istallatios uless all the followig coditios are met: The coduit fl ows full. The coduit is circular i shape. There is o erosio resistat sedimet build-up i the coduit. The coduit is greater tha 20 diameters log. The coduit is upaved. There are o maholes, wyes ad tees. There are o chages i grade ad aligmet. CORRUGATED ALUMINUM PIPE TESTS I April 1971, a report was published titled Further Studies of Frictio Factors for Corrugated Alumium Pipe Flowig Full by Edward Silberma ad Warre 0. Dahli, St. Athoy Falls Hydraulic Laboratory, Uiversity of Miesota. Laboratory tests were coducted o pipe which raged i diameter from 12 iches to 66 iches ad legths from 100 feet to 220 feet usig both aular ad helical corrugated alumium pipe. The tests were coducted with a head of 20 feet so that the pipe would fl ow full. The coclusios reached by the authors are The experimets described i this report have bee coducted usig corrugated alumium pipes fl owig full. The measuremets were made followig a etry regio of 20 or more pipe diameters, ad although this distace appears 6

7 to be suffi ciet, it is ot kow whether this is a miimum distace for fully developed fl ow. Measuremets were made uder laboratory coditios with pipe carefully aliged ad joits carefully made so as to avoid itroducig additioal roughess. The water used i the tests carried a light load of sad, mostly as suspeded load, from the Mississippi River. No sigificat amout of sad was foud i the pipes after the flow was shut dow; it is ot believed that the sad affected the results. Values of Maig s raged from for 12-ich helical pipe to for 48-ich helical pipe. Use by desigers of such low values is ot recommeded as these are based o laboratory tests for full flow coditios, a 20-foot head, o appreciable bed loads, carefully aliged joits, ad a 20 diameter legth of fl ow developmet regio. Therefore, the coclusios ad recommedatios of the Federal Highway Admiistratio i the 2001 updated report Hydraulic Desig Series No. 5 regardig fl ow resistace factors for helical corrugatios are applicable whether the pipe is made of alumium or steel. PVC PIPE TESTS Tests were coducted by Lawrece C. Neale ad Robert E. Price i 1962 at Alde Laboratory, Worcester Polytechic Istitute, Worcester, Massachusetts, o 8-ich ad 12-ich PVC plastic pipe flowig both full ad partially full, usig clea water ad straight sectios. The oly other published reports o laboratory tests of PVC pipe roughess coeffi ciets are a 1985 Utah State Uiversity report o Fluid Frictioal Headloss Coeffi ciet Determiatio for Spirally Woud Ribbed PVC Sewer Pipe by Professor R.W. Jeppso ad the 1986 Uiversity of Alberta Study previously cited. Test results idicated a laboratory value of which the plastic pipe idustry recommeds as a desig value. For proper desig, plastic pipe should be classed as ay other smooth wall pipe with a desig value for Maig s as show i Table 1. Slime ad grease adhere to all commoly used sewer pipe materials. Plastics, which although presetig a smooth surface, have become accepted for use as a biological filter media for which purpose slime adherece is a prime requisite. I Jauary, 1978, the Joural of the Water Pollutio Cotrol Federatio published a study, Accumulatio of Slime i Draiage Pipes ad Their Effect o Flow Resistace, which was coducted at the Water Research Ceter, Eglad by C.E.G. Blad, R.W. Bayley ad E.V. Thomas. After passig raw domestic sewage through a pipelie cosistig of equal pipe sizes ad legths of polyviyl chloride, asbestos cemet, bitumiized fi ber, uglazed clay, ceramic glazed clay ad salt glazed clay, the study cocluded the amout of accumulated slime was idepedet of pipe materials ad surface fi ish. Slimes ad grease are ot the oly factors to cosider whe selectig a value for plastic pipe. Other factors such as debris, beds, maholes, coectios, grit, warpage due to sulight or storage, ad scourig of walls due to cleaig, must be take ito accout. The joit ASCE Maual Number 60 ad Water Eviromet Federatio Maual Number FD-5, Gravity Saitary Sewer Desig ad Costructio, makes the followig statemet about pipe materials ad Maig s : Geerally, Maig s for a give sewer, after some time i service, will approach a costat which is ot a fuctio of the pipe material but represets the grit accumulatio ad slime build -up o the pipe walls. This will be o the order of A coeffi ciet which will yield higher frictio losses should be selected for sewers where disturbig ifl ueces are kow or aticipated. Because of the empirical ature of each formula, coservative desig is prudet. CLAY PIPE From the Clay Pipe Egieerig Maual published by the Natioal Clay Pipe Istitute, the followig discussio of values is quoted: is a empirically derived coeffi ciet which is used as a measure of the iterior surface characteristics of a pipe desiged for the trasmissio of liquids. This coeffi ciet comes ito use i determiig the frictioal losses i the coduit whe trasportig a liquid fl ow. The value of is affected by size, depth of flow, velocity or slope ad quality of costructio. The actual value of i a istalled lie may be icreased appreciably by debris, grit deposits ad brach coectios ito the pipe. I cotrolled experimets, usig clea water, values of uder have cosistetly bee obtaied for vitrifi ed clay pipe. However, because of the variatios i due to variable flow coditios, it is recommeded that a coservative value of be selected. A value of is commoly used by experieced saitary egieers. Recogized authorities poit out that umerous tests have defi itely established a factor as the same for all materials commoly used i gravity fl ow saitary sewer lies. CAST IRON/DUCTILE IRON PIPE TESTS Tests were coducted by Do E. Bloodgood ad Joh M. Bell, Purdue Uiversity o 4-ich cast iro pipe ad vitrifi ed clay pipe. The tests used ew pipe ad clea water ad the value for cast iro was foud to be compared to for clay. The Ductile Iro Pipe Research Associatio, i its Hadbook, uses the Haze-Williams equatio rather tha the Maig s equatio to calculate the fl ow. I the HazeWilliams formula, a C value is used as the coeffi - ciet of roughess for the pipe walls. The Haze-Williams formula geerally is used for pressure pipe calculatios rather for gravity systems. The Ductile Iro Research Associatio recommeded Haze-Williams C values 7

8 coverted to Maig s values results i values of to I the corrosio process (tuberculatio), growths or mouds form o the walls of the iro pipe. These growths are ofte so large ad umerous that the frictioal resistace is greatly icreased ad, i additio, a serious reductio i the effective cross sectioal area of the pipe is produced. The result is a tremedous reductio i hydraulic capacity. I order to offset the destructive effects of tuberculatio, the cast iro ad ductile iro pipe maufacturers geerally supply pipe with either cemet mortar liigs or polyethylee liigs. These are relatively thi liigs, ad it is quite probable that the liigs will lose their protective capabilities withi a few years, due to leachig ad scrubbig actio, ad permit the start of tuberculatio. For cast iro or ductile iro sewers a value of should be used regardless of the type of liig. AGENCY POLICIES ON Begiig i 1953, may govermetal agecies made policy statemets relatig to the Maig values for use o work uder their jurisdictios. Policy statemets are listed i Table 9. Sice these policy statemets were so similar, the selectio of the proper value for differet pipe types appeared to be settled. I the FHWA s Hydraulic Desig Series Number 5, all values are lab values. I all other policy statemets, the fact that the values for cocrete pipe have a built i safety factor, however, was ot cosidered ad a correspodig safety factor is ot applied to the laboratory values for some other smooth wall pipe or for corrugated metal pipe. 8

9 Table 9 Policy Statemets Agecy Year Publicatio Values of Maig's Roughess Cofficiets Headquarters Departmet of the Army Office of Chief of Egieers 1978 Techical Maual TM Draiage ad Erosio-Cotrol Structures for Airfields ad Heliports Type of Pipe All smooth wall Corrugated metal pipe 2 2/3 by 1/2 ich 3 by 1 ich 6 by 2 ich 9 by 2 1/2 ich Headquarters Departmet of the Army Office of Chief of Egieers 1983 Techical Maual TM Draiage for Areas Other Tha Airfields Type of Pipe All smooth wall Corrugated metal pipe 2 2/3 by 1/2 ich 3 by 1 ich 6 by 2 ich 9 by 2 1/2 ich US Departmet of Trasportatio Federal Highway Admiistratio 1980 Hydraulic Flow Resistace Factors for Corrugated Metal Coduits Corrugatio 2 2/3" x 1/2" 3" x 1" 6" x 1" 6" x 2" struct. plate 9" x 2 1/2 struct. plate Diameter Rage (ft.) to to to to to.0318 For helically corrugated pipe - use the same values as a aular corrugated pipe US Departmet of Trasportatio Federal Highway Admiistratio 2001 Hydraulic Desig Series Number 5, Hydraulic Desig of Highway Culverts Type of Pipe Cocrete Pipe Cocrete Box Culverts Spiral Rib Metal Pipe Corrugated Metal Pipe 2 2/3" x 1/2" 6" x 1" 5" x 1" 3" x 1" 6" x 2" 9" x 2 1/2" Corrugated Metal Pipes, Helical Corrugatios, Full Circular Flow 2 2/3" x 1/ The Maig's value rages idicated i this table are laboratory values. I geeral, it is recommeded that the aular resistace factors be used for corrugated metal pipes with helical corrugatios. 9 Techical data herei is cosidered reliable, but o guaratee is made or liability assumed.