The anticipated design flows determine the size of pipe or ... culverts or storm
sewers, design flows are normally ... loads on these buried pipes comes from.
Pipe Design, Testing, & Specifications
Jim Goddard JimGoddard3, LLC.
[email protected]
Design & Selection What’s Important: 1. Hydraulic Capacity 2. Structural Design 3. Durability 4. Installation 5. Quality
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Hydraulic Capacity The anticipated design flows determine the size of pipe or structure required. For culverts or storm sewers, design flows are normally determined from rainfall intensity information available from the USGS, NOAA, or BuRec. For sanitary sewer designs, the number and type/size of connections and length of the collectors. 3
Hydraulic Design For most culvert installations, inlet control determines the capacity of the pipe. Manning’s “n” value has no impact. The flow capacity of the pipe seen here is the same regardless of pipe type. 4
Hydraulic Capacity Flow capacity of storm sewers, sanitary sewers, and longer, relatively flat culverts is determined by outlet control, and Manning's “n” determines capacity. Manning's “n” IS NOT constant for any pipe type, but varies with the velocity and diameter of the pipe.
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Manning's "n" VS. Liner Roughness 0.015 y = 0.0145x + 0.01 R2 = 0.7016
3 FPS 0.014
10 FPS 15 FPS Linear (3 FPS)
0.013
Linear (10 FPS)
Manning's "n"
Linear (15 FPS)
0.012 y = 0.0108x + 0.0087 R2 = 0.7796 0.011 y = 0.008x + 0.0088 R2 = 0.8766
0.01
0.009
0.008 0
0.05
0.1
0.15 Liner Roughness (inches)
0.2
0.25
0.3
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Hydraulic Design All pipe industry tests are done in the lab with near perfect alignment, tight joints, clean water, and new, clean pipe. In the real world, none of this is true. Have you ever seen a 2 year old pipe that did not have some debris or build-up in it? Thus, for “smooth interior” pipe the “design “n” should be a minimum of 0.013 to 0.015! 7
Hydraulic Design Available diameters of available pipe types varies: 1. Depending on local capabilities, concrete pipe is available up to 10’ diameter or more. 2. Corrugated steel pipe is generally available from 6” up to small bridges (40’ or more) 3. Thermoplastic pipe is generally available from very small diameters (2”) through 10’ or greater depending on pipe type. Available diameters may determine the pipe type or types specified. 8
Structural Design AASHTO LRFD Section 12 provides current structural design methodologies for reinforce concrete pipe, corrugated metal pipe, and thermoplastic pipe (both PVC and HDPE). The determination of the loads on these buried pipes comes from LRFD Section 3. Both dead loads and live loads must be considered. 9
Live Loads
Live Loads
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Cooper E80 Live Loads
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29 Years of Highway Loads
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Dead Loads - Testing
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Pennsylvania Deep Burial Study – 23 Years of Data – 100 Feet Deep
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Utah DOT Legacy Parkway
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Utah DOT Legacy Parkway
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FEMA P-675 – Plastic Pipe in Dams
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Structural Design Every pipe type has different load or structural limits. Site loading conditions; depth of fill, magnitude of live loads; may determine pipe types to be considered. 18
Durability Every pipe type has different durability limits. Generally, the environmental conditions effecting pipe durability are: 1. pH 2. Salts 3. Soil chemistry (sulfides, chlorides, etc.) 4. Water chemistry 5. Abrasion 6. Soil resistivity 7. Stray currents 19
Supporting Durability Information Information on material selection criteria is available in: “AASHTO Highway Drainage Guidelines, Volume 14, Culvert Inspection, Material Selection and Rehabilitation Guideline” and/or
“NCHRP Project 20-5, Topic 25-21, Service Life of Drainage Pipes.” 20
Quoted Permissible pH Range for Various Pipe Materials
CMP 6 - 9.5
RCP 4 - 10
HDPE 1.5 - 14
0
2
4
6 8 pH Levels
10
12
14 21
CALTRANS HIGHWAY DESIGN MANUAL Section 850 50 Year Min. Maintenance-Free Life Pipe Material
pH Range
GALV STEEL ALUM. STEEL ALUMINUM CONCRETE HDPE
Resistivity Range
6-8 5.5-8 5.5-8.5 5.5-9 No Limits
>3000 >1500 >1500 No Limits 22
PennDOT I-99 – pH
