Fluor Piping Design Layout Training Les08- Underground

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 1 of 25 15/30/2002 REV 0 8. UNDERGROUND 8.1 PREFACE

This lesson will cover the procedures required for underground studies. Two things to keep in mind; first, use Fluor standards as a guide, and second, the guidelines mentioned in this lesson may be different than jobs you may have worked on in the past. Some clients have their own engineering standards.

8.1.1 Lesson Objectives

Lessons provide self-directed piping layout training to designers who have basic piping design skills. Training material can be applied to manual or electronic applications. Lesson objectives are:

• To know the types of underground systems.

• To know how to make underground studies avoiding major mistakes and costly changes. • To familiarize you with Fluor standards. (Fluor standards are a guide. The standards used on

your contract may differ.) 8.1.2 Lesson Study Plan

Take the time to familiarize yourself with the lesson sections. The following information will be required to support your self-study:

• Your copy of the Reference Data Book (R.D.B.)

• Fluor Technical Practices. The following Technical Practices support this lesson: 000.210.1150 000.210.1160 000.210.1200 000.210.1210 000.210.1211 000.250.2040

If you have layout questions concerning this lesson your immediate supervisor is available to assist you. If you have general questions about the lesson contact Piping Staff Group.

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 2 of 25 15/30/2002 REV 0 8.1.3 Study Aids

Videos on Piping Design Layout Practices supplement your training. It is suggested that you view these videos prior to starting the layout training. You may check out a copy of the videos from the Knowledge Centre (Library).

8.1.4 Proficiency Testing

You will be tested on your comprehension of this lesson. Proficiency testing will be scheduled three to four times a year. Piping Staff will notify you of the upcoming testing schedule.

• Questions are manual fill-in, True-False and short essay (bring a pencil). • The test should take approximately one hour.

• You may use your layout training Reference Data Book and material from previous layout training lessons during the test.

• The test facilitator will review your test results with you at a later date. • Test results will be given to Piping Staff.

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 3 of 25 15/30/2002 REV 0

8.2 TECHNICAL DUTIES OF LAYOUT PERSON

Develops the following specifications, in accordance with contract requirements and Technical Practices 000.250.1938 and 000.250.1939.

• Gravity sewers - design, layout and testing

• Plant and unit firewater systems. Prepares fire protection system layouts and data and attends meetings pertaining to it.

• Advises general piping supervisor as to the need for any additional specifications relating to underground piping by Civil.

• Reviews piping material specifications and recommends additions, deletions or changes based on design requirements. Initiates action for the development of purchase descriptions for any

underground items that are normally not covered in the piping material specifications.

• Develops and/or directs the development of the underground piping standard details, consistent with contract and material requirements.

• Develops and/or directs the development of unit underground layouts and insures they reflect the job philosophy. Assembles data and calculations relating to the sizing of the unit sewer systems. • Maintains underground workbooks: collections of vital data relating to the design of U/G systems. • Coordinates underground piping with other groups and establishes a two-way flow of information. • Represents general piping in meetings with vendor, clients, engineering and other internal groups. 8.2.1 Underground Systems Work Book

It is the responsibility of the underground layout person to develop and maintain an underground systems work book that contains:

•

Schedules

•

Narrative underground specifications.

• Applicable sections of codes having jurisdiction. • Piping material information and specifications.

•

Process data (P&ID's, flow conditions, quantities and temperature). • Job instructions and design memos relating to underground piping. • Calculations and sketches.

•

Notes on interface meetings.

•

Questions and answers.

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8.2.2 Prerequisites to Start Underground Piping Layout and Design

ITEM SOURCE

1. Meteorological Data, Rainfall, Frost Depth Basic Jobsite Questionnaire

2. Existing Obstructions Client Via Project Manager

3. Sewer Systems, Segregation Process Engineer

4. Soil Conditions Structural Engineer

5. Paving Structural Engineer

6. Clients Design Requirements Project Manager

7. Federal, State and Local Codes Project Manager

Additional Information

8. Schedule Piping Supervisor

*9. Approved Plot Plan(s) Piping Supervisor

10.00 P&ID's Piping Supervisor

+11 Preliminary Foundation Design Sketches Structural Engineer 12. Process Drainage Rates, Temperatures

and Intermittent or Continuous

Process Engineer

13. Piping Materials Specifications Piping Materials Engineer

14. Fire System Capacity (in spec.) Process Engineer

15. Site Preparation Drawings Structural Engineer

16. Decision on Location of Cooling Water System (above or below ground)

Project

* May not be available at start of layout (use best available info). + Discuss approximate size with Structural Engineer.

8.3 UNDERGROUND PIPING MATERIALS

Purpose

The purpose of this guide material is to provide the designer with information relating to some of the more commonly used underground pipe and fittings.

Scope

The list that follows is for information only and gives the A.S.T.M. or A.W.W.A. specification reference, size range, and normal use for each type. For additional information the designer should refer to the specifications or manufacturer's catalogs that are listed. The designer needs to work with the material engineer for material selection on the project.

Selection of Pipe

Selection of pipe for underground service depends upon pressure, temperature, commodity, durability, cost, availability, and client requirements.

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8.3.1 Vitrified Clay Pipe

Vitrified clay pipe (standard and extra strength, A.S.T.M. C-700) is used for gravity piping handling surface drainage and process drainage when this piping is not under concrete paving or buildings. It is also used for sanitary sewage to within 5 feet of an outside wall of a building where there is no paving and for acid sewers with acid proof cement joints.

It is available in extra strength in the following sizes: 4"-6"-8"-10"-12"-15"-18"-21"-24"-27"-30"-33"- 36". Joint lengths vary per manufacturer, but are approx. in 2' or 3' lengths in sizes up to 12" and 3' to 5' lengths in sizes 15" through 36". (Catalogs: Cantex, Interpace)

8.3.2

Cast Iron Soil Pipe

Cast iron soil pipe (A.S.T.M. A-74) is used for gravity piping handling surface drainage, process drainage or sanitary sewage under concrete paving or buildings. It is available in 2"-3"-4"-5"-6"-8"-10" -12"-15" sizes. Joint lengths available in 5' & 10' lengths. (Catalogues: Tyler, Cal-Alabama, Rich Manufacturing).

8.3.3 Cast Iron Water or Pressure Pipe

Cast iron water pipe (A.W.W.A. C-106, 108 & 110) is used for pressure or sewer systems where long runs with few branches are required. Pipe & A.W.W.A. fittings are available in sizes 2" through 48". Joint lengths vary from 12' to 18' depending upon the manufacturer. (Catalogs: U.S. Pipe, Mead Pipe.)

8.3.4 Asbestos Cement Pipe (Transite Pipe) (Reference only no longer used)

Asbestos cement pipe (A.W.W.A. C-400) in conjunction with cast iron fittings was used for pressurized water service. It had the advantage of lower installed cost than most other piping materials, but would not be used in congested areas where it is susceptible to damage.

Available sizes were 4"-6"-8"-10"-12"-14"-16"-18"-20"-24"-30"-36" in pressure classes 100, 150 and 200. (Catalogs: Johns-Mansville, Certain-teed.)

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 6 of 25 15/30/2002 REV 0 FIGURE 8-1 FIGURE 8-2

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8.4

DESIGN CONSIDERATIONS 8.4.1 Settlement

The following list identifies problems created by differential settlement together with

recommended solutions. The degree of the problem should be determined by discussions with the Structural Engineer and a review of the soil report.

Sewer lines connected to manholes -- differential settling of the manhole and the sewer sometimes breaks the sewer pipe. A pipe joint just outside the manhole lessens this danger. If the soil conditions are unstable or a high water table could leach sand bedding out from under the pipe a second joint within three feet of the first should be provided. In these situations cast iron pipe should be used in place of vitrified clay pipe. The joints must be flexible such as a compression joint, mechanical joint, or even a lead joint is considered flexible.

Differential settlement involving cooling water branch lines between large cooling water headers, which could settle and exchangers on piled foundation which may not, could over stress the piping. This problem can be remedied by locating the headers so that the branch lines are at least 10 feet long and providing flexible connectors (Dresser, Smith-Blair, etc.) at either end of the branch for steel pipe, or by using mechanical joints for cast iron pipe.

For other types of settlement problems these methods just described should provide a remedy.

Unstable bedding -- when the bottom of the trench is not sufficiently stable or firm, to prevent vertical or lateral displacement of the pipe after installation a non-yielding foundation must be designed.

8.4.2 Crushed rock

The simplest supplementary foundation is to excavate native soil below grade of bedding material and replace with a layer of broken stone, crushed rock, or other coarse aggregate that may produce the desired stability under conditions where the instability is only slight.

8.4.3 Encasement

Under conditions where an extremely unstable area is to be crossed, and that area represents a very short length of line, it is possible to reinforce the pipe by full concrete encasement and adequate reinforcing steel to produce a rigid beam.

8.4.4 Piling

In some instances, lines must be constructed for considerable distances in areas generally subject to subsidence, and consideration should be given to constructing them on a timber platform or reinforced concrete cradle supported by piping. Supports should be adequate to sustain the weight of the full sewer and backfill.

The details and requirements for the above should be worked out in conjunction with the Structural Engineer based on the recommendations of the soil report.

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 8 of 25 15/30/2002 REV 0 8.4.5 Angle of Repose

Underground lines installed below adjacent foundations should not undermine the 45o angle of repose

of the foundation (See Figure # 8-3). Where there is no obvious solution consult with the Structural Engineer to see if the actual conditions permit a steeper angle. It may also be possible to brace the trench if equipment has been set, and to protect the pipe against loads by encasement.

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 9 of 25 15/30/2002 REV 0 8.4.6 Breakage

Precautions must be taken to prevent breakage of pipe due to construction and maintenance equipment traffic.

Depth of cover for protection against surface loads is covered in another section. Guard posts are provided to protect the above ground features of the firewater system.

Cleanouts in vitrified clay systems are subject to breakage, particularly in offsite areas. Where cleanouts are thus exposed, protective structures similar to those for the firewater system, as well as concrete cradles, must be detailed. Notes on offsite drawings should state, "INSTALLATION OF CLEANOUTS SHOULD NOT BE COMPLETED UNTIL PROTECTION SHOWN ON DETAIL DRAWING CAN BE PROVIDED".

Use Cast Iron adjacent to manhole to avoid breakage caused by differential settlement of loss of bedding in high water table (See Figure #8-4).

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 10 of 25 15/30/2002 REV 0 8.4.7 Stub-Ups

Stub-ups are used to connect underground lines carrying water, steam, air process liquids and the like with above ground facilities. Flanged and welded underground lines should terminate 18 inches above high point finish surface with a flame cut end. The above ground spool should indicate bevel end or face of flange at 12" above H.P.F.S. (See Figure #8-5). This will permit field fit-up.

Cathodic protection may be required depending on the soil conditions.

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8.5

SYSTEM SAFETY CONSIDERATIONS

8.5.1

Purpose of Seals

Seals play a vital role in maintaining safe operation of a process plant sewer system. Under normal conditions, sewers are only partially filled because flow rates are designed for storm or firewater quantities. The large vapor spaces in process plant sewers will frequently contain flammable vapors. Liquid seals form vapor barriers and prevent flame fronts or explosions from running the full length of the sewer system. Without a sealed sewer system, a fire in one area could ignite vapors in a catch basin, which could flash through the sewer to initiate a fire at some other location.

Seals also prevent the release of vapors or gases to the atmosphere at grade level where they could create a hazard or contribute fuel to a fire.

8.5.2 Location of Seals Catch Basins

Catch basins discharging to any sewers that have the possibility of containing flammable or hydrocarbon vapors are isolated from the lateral by one of the following:

(a) Providing an outlet seal at the line where it leaves the catch basin (See Figure # 8-6a). (b) Routing the outlet line to a manhole or adjacent catch basin and providing an inlet seal at

the point of entry (Figure # 8-6b). Manholes

Laterals leaving a unit are isolated from main or trunk sewers by providing manholes at junction points and routing the lateral into the manhole at a sealed inlet (Figure # 8-6b).

The plant main sewer may be sectionalized by providing sealed inlets at those manholes that would enable isolation of major process area groups, storage areas, treatment areas, marine terminals, etc. Baffle type manholes serve this purpose on larger sewer runs (Figure # 8-6c).

Drains and Funnels

Groups of drain funnels in fairly close proximity, say up to 30' apart, are connected to a single branch line which is isolated from the rest of the system by running it to a catch basin or manhole and providing an inlet seal at the point of entry.

Generally funnels serving pumps are isolated from the other funnels on the branch by providing a running trap between the pump funnels (Figure # 8-6d).

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Where a sewer system must handle toxic or extremely hazardous material, each funnel is provided with a "P" trap type seal (See Fig # 8-6e), and the branch line is connected to the lateral at an inlet sealed manhole.

Where a funnel is located close, say within 10' of the catch basin it is connected to, an inlet seal is not required, since a fire can travel above ground as easily as through the sewer.

8.5.3 Types of Seals

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 13 of 25 15/30/2002 REV 0 8.5.4 Venting

Sewers in general are designed for gravity flow. In a sealed system (i.e. without vents), a rise in water level would reduce the vapor space and cause an increase in pressure. This would reduce the design capacity of the sewer. Therefore vents are necessary to prevent vapor lock and to release vapors to a safe location.

Vents serve to prevent rapid pressure buildup in the sewer should hot commodities or water enter the sewer and vaporize any liquid hydrocarbons present.

8.5.5

Location of Vents

Vents are provided at every manhole where the inlet line is liquid sealed so as to prevent venting to the next upstream manhole.

The highest manhole in a system is provided with a vent.

Both chambers of a baffle sealed manhole are provided with vents. See the design specification for additional information.

8.6

ON-SITE UNDERGROUND LAYOUT

The purpose of this guide material is to provide the layout designer with instructions and a standardized approach to the layout of the Underground Piping Systems within a unit.

Scope

This instruction covers the step by step development of the underground systems layout and points out critical items with respect to the design.

General

Specifications covering the layout and design of sewer and firewater systems are normally prepared for each contract. These specifications must be carefully followed as they provide the basis for design.

8.6.1

Drainage Areas

In process or operating areas, the distance a liquid spill must travel across the pavement to a catch basin should be kept to a minimum. Concrete paved areas are subdivide into drainage areas, normally 3600 sq. ft. (See contract specifications.) Each drainage area is bounded by a high perimeter and drains to a catch basin located at a low point. Figure 8-7.

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 14 of 25 15/30/2002 REV 0 See Figure 8-7. 8.6.2 Drainage Area Sizing Guide

Figure #8-8 may be used as a guide to make a quick evaluation of the minimum and maximum

drainage area sizes and catch basin locations based on maintaining required paving slopes at various drops in paving from high to low point.

Drainage areas are based on two considerations: The elevation difference between high and low points, and the prevention of fire flow and process spills flowing between adjacent areas. Ideally, a drainage area should be about 50 to 60 feet square, draining to a catch basin at or near the center. Equipment requiring curbed areas shall be noted on the P&ID's or defined in the job specifications.

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FIGURE # 8-8

8.6.3 Guidelines

Locate the high point of paving: at perimeter of concrete paving or edge of road. at edge of buildings

along major access ways around heater areas, to direct spillage away from heater and other equipment.

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When locating catch basins give consideration to the following: • locate near center of drainage area if possible.

• do not locate under equipment or piping manifolds.

• do not locate at building entrances or ladder and stairway landings.

• keep at least five feet clear of equipment work areas, such as alongside of pumps.

8.6.4 Preliminary Work

In order to avoid design and construction problems resulting from interferences the following items are shown on the layout.

• Existing concrete obstructions (foundations, sumps, etc.). • Existing underground electrical ducts and piping systems.

Foundations of columns, heaters, pumps, structures and pipe supports should be indicated based on whatever information the Structural Engineer can provide (or your best guess). Foundation depths and thickness have an important bearing on the routing of underground piping (structural engineering. will advise).

8.6.5 Paving and Surface Drainage

Perimeter of concrete paving to encompass all equipment within unit area. Paving perimeter is normally five feet beyond the furthest projecting equipment. In the interest of economy this outer limit may be staggered to suit groups of equipment which do not project as far. (Keeping the jogs to a minimum.) Drainage outside the perimeter of the concrete paving is by Civil.

NOTE: Job specifications may dictate that certain equipment groups handling gases or liquids that vaporize at ambient temperatures may not require concrete paving.

Types and characteristics of paving (verify with your Civil/Structural Eng.) • Concrete, 6" thick Process liquid spills truck traffic. • Concrete, 4" thick Process liquid spills, no truck traffic.

• Asphalt, 3" thick Primary roads.

• Asphalt, 2" thick Secondary roads, general paving and parking areas. • Crushed rock - 3" deep General area cover.

• Concrete sidewalks - 4" thick 3'- 0" wide, raised 1" above adjacent finished surface.

Paving slope - Minimum 1/8"/ft. Maximum 1/2"/ft.

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8.6.6 Types of Catch Basins

Figure 8-9 illustrates four basic types of catch basins and drain boxes.

• Concrete box per job standards, precast or poured-in-place are used as area drains and seal boxes in combined sewer (storm and process water). Liquid level in box should be at or below frost line.

• Concrete pipe may be used for perimeter areas where only a single outlet is required. • Dry box type catch basins, are used as area drains for heater drainage areas in order to

remove all hydrocarbon liquids from the area promptly in event of a tube break. Do not locate dry boxes under burners. The downstream end of the dry box outlet line shall be kept

separate from other heaters or equipment areas and sealed in a catch basin or manhole. (Generally located 50' or more from the shell of the fired equip.)

• Cast Iron - [Not shown] used as area drain only generally in separate storm sewer. Not used in cold climates where they could be subject to freezing. Not used in crushed rock areas.

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8.6.7

Drawings

Process area underground layouts are normally done on a brownline of the plot plan at a scale of 1" = 20' or 1" = 10'. The initial layout is in the form of a transposition with sufficient information shown to enable a reasonably accurate material takeoff. The final layout and design is handled as a part of the development of the underground piping drawings. Figure 8-10 shows a portion of an underground plan drawing.

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8.6.8 Sewer System Piping

The unit collection headers for storm, process or combined sewers (laterals) are usually located under the pipeway area for convenience in connecting catch basins and drain funnels on both sides of

pipeway. If the electrical power duct system is also located in this area, the layout designers from both groups should work closely to establish easements. Laterals are installed below frost line.

Normally the slope of the longest path governs the inverts in the system and the depth of the sewer at the start, or high end.

Sewer laterals leaving process units are sealed at manholes on the plant sewer mains. Sealing and venting philosophy for sewers containing hydrocarbon or flammable vapors is shown on Fig. 8.6a and Fig. 8-6b, and in the section on Manholes in this document.

Sublaterals are routed from the catch basins and/or branches to the laterals. The connection at the lateral may be at a WYE branch or at a manhole. In a sewer collecting process drainage, manholes may be located along the lateral to serve as seal boxes for the incoming branches.

Pump and equipment process drains discharge into drain funnels. A 6" minimum size opening for all drain funnels is preferred. Where a 6" opening does not provide sufficient area to accommodate multiple drains a larger opening is provided.

Drain funnel requirements are indicated on the P&ID's. Approximate locations are shown on the initial layout. Exact locations are set later by the above ground piping layout. Groups of funnels in fairly close proximity, say 30' apart, are connected to a single branch line which is run to a catch basin, manhole or seal box.

Each drain, sublateral or lateral shall be accessible for rodding out by providing either a cleanout or catch basin at its upper terminus.

Limitations for the use of cleanouts are defined in the job specifications.

Indicate line class, size, and slope for laterals, sublaterals, and branches. Indicate invert elevation for start and termination of unit lateral. Use line sizing criteria provided in conjunction with Sewer Sizing Chart, or job specification.

NOTE:

It will be necessary for the Layout Designer to consult with the Process Engineer to determine the source, nature and quantity of each process waste stream discharging to the sewer. A permanent record of this information should be maintained for future reference.

To facilitate construction, maintain a constant slope over long runs, change line sizes as required, and maintain common invert elevations for adjacent parallel lines.

Sanitary sewers within buildings are designed by the Plumbing Section of the Architectural Group to a point five (5) feet outside of the building, at this point you will be given the design information, e.g., fixture units being served, gpm and velocity. Sanitary sewer minimum size is 4". Minimum slope to be 1/8" per foot.

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8.6.9 Manhole and Catchbasin Piping Elevations

Use Figure # 8-11 and the formulas that follow to calculate and set the elevations of manholes and catchbasins.

FIGURE # 8-11 Where:

x = horizontal distance from inside face of wall to intersection of invert (or B.O.P.) lines at 22½o bend. (feet)

y = difference in invert (or B.O.P.) elevations between points 2 and 3.

w = sum of:

= difference in inlet and outlet line size (D2-D1) (feet)

= minimum liquid seal = .5 feet = D1 x cos 22.5o

(W is tabulated in Table 1 & 2., for lines at 22½o only.)

s = slope of inlet line (feet/foot)

E = inside diameter or inside face to face of walls for manhole or

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Procedure

Calculate invert elevation (or B.O.P. for steel pipe fabrication) at point 1 or 1a. Deduct "W" which yields invert elevation (or B.O.P.) of seal pipe at point 2.

Calculate X and Y using equations 1 and 2 that yield invert (or BOP) and location of point 3. When seal pipe enters box at an angle other than 22.5o use the natural tangent of that angle in

place of 0.4142 in equations 1 and 2.

Dimension "W" must be calculated in the above situation using D1 x cos of the angle used, for

dimension (c).

Dimension "W" is the sum of (b), (c), and (d) when inlet line is a branch run at a higher elevation than the normal flow line of the system.

DO NOT USE THESE TABLES IF THE LINE ENTERS AT AN ANGLE OTHER THAN 22.5o.

TABLE 1

DIMENSION "W" (FEET)

BASED ON INVERT EL. FOR C.I. OR CLAY PIPE

OUTLET PIPE SIZE

4" 6" 8" 10" 12" 14" 15" 16" 18" 20" 24" 4" 0.81 0.97 1.14 1.31 1.47 1.64 1.72 1.81 1.97 2.14 2.47 6" 0.96 1.13 1.30 1.46 1.63 1.71 1.78 1.95 2.13 2.46 8" 1.12 1.28 1.45 1.61 1.70 1.78 1.95 2.12 2.45 10" 1.27 1.44 1.60 1.69 1.77 1.94 2.10 2.44 12" 1.42 1.59 1.67 1.76 1.92 2.09 2.42 14" 1.58 1.66 1.74 1.91 2.08 2.41 15" 1.65 1.74 1.90 2.07 2.40 16" 1.73 1.90 2.06 2.40 18" 1.89 2.05 2.39 20" 2.04 2.37 24" 2.35 TABLE 2 DIMENSION "W" (FEET) BASED ON B.O.P. FOR STEEL PIPE

OUTLET PIPE SIZE

4" 6" 8" 10" 12" 14" 16" 18" 20" 24" 4" 0.85 1.02 1.19 1.37 1.53 1.64 1.80 1.97 2.14 2.47 6" 1.01 1.18 1.35 1.52 1.62 1.79 1.96 2.12 2.46 8" 1.16 1.34 1.51 1.61 1.78 1.95 2.11 2.45 10" 1.33 1.49 1.60 1.76 1.93 2.10 2.43 12" 1.48 1.59 1.75 1.92 2.09 2.42 14" 1.58 1.74 1.91 2.08 2.41 16" 1.73 1.90 2.07 2.40 18" 1.89 2.05 2.39 20" 2.04 2.37 24" 2.35

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8.6.10 Sewer Sizing Guide • Purpose

The intent of this instruction is to provide the designer with an organized approach to sizing sewer lines, and to promote a better understanding of the hydraulics involved in sewer design. • Design Basis

The general requirements for the plant sewer systems are outlined in the design specification. Line sizing is based on the expected flows in the line plus a safety factor for storm water flows. The design specification should provide the following:

• Rainfall intensity (inches/hour)

• Maximum fire water flow based on pumping capacity, and fire protection facilities. (spray systems, monitors, etc.)

• Definition of waste water system.

8.6.11 Sewer Layout

The Civil Group is responsible for the sewer system layout.

• Generally inverts for the mains can be set by determining which "path" is the longest. However this must be analyzed since shorter paths at steeper slopes may govern.

• On a large plant several trial designs may be required to determine the most advantageous routing.

8.6.12 Sewer Sizing Calculation Sheet

The Sewer Sizing Calculation Sheet may be utilized to provide a permanent record of the hydraulic design of the principal sewer systems. It is used during the layout and design phase to keep track of calculations.

The intent is to use the form for unit laterals, sublaterals and branches. (See design specification for definitions)

Using the chart is actually a "step by step" automatic way to size the system. The notes that follow serve as instructions.

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SEWER SIZING CALCULATION SHEET

Line No. _________________________ Layout Dwg No. ______________________

System No. __________________________ Contract No. ______________________

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

FROM TO SQ. FT. SQ. FT. STORM STORM PROCESS FIRE DESIGN SEWER VELOSITY SLOPE LENGTH INVERT I.E. I.E. ELEV. APPROX. MK. MK. PAVED UNPAVED RUNOFF RUNOFF DRANAGE WATER FLOW DIA. (FT./SEC.) (FT./FT.) (FT.) DROP UPPER LOWER GROUND COVER

(GPM) (GPM) (GPM) (GPM) (IN.) (IN.) (12X13) (FT.) (FT.) UPPER 17-(15+10)

INCREMENT TOTAL 6+7 or 7+8

NOTES:

1. STORM RUNOFF BASED ON THE RAINFALL INTENITY OF ______"/HOUR 2. FACTOR OF IMPERVIOUSNESS FOR UNPAVED AREAS = _______ 3. FIREWATER FLOW IS BASED ON ________GPM PER CATCH BASIN

4. LINE SIZE CHANGES ALONG A RUN SHOULD BE REFLECTED - COLUMN 14 BY AN APPROXIMATE INCREASE IN THE INVERT DROP

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Using the Sewer Sizing Calculation Sheet

• On a copy of the sewer layout, assign identifying letters to each junction where flow is increased, breaking the sewer into individual segments or runs to be separately sized on the chart.

• Column 1: List the identifying letter for the upstream end of the first run. (The first line should be used for the first run in the system.)

• Column 2: List the identifying letter at the downstream end of the same run.

• Column 3: Enter the square footage of the paved area with runoff to the junction point designated in column 1 of the same line.

• Column 4: Enter the square footage of unpaved areas.

• Column 5: Calculate and list the storm runoff based on areas listed in columns 3 and 4, using appropriate formulas in the design specification.

• Column 6: List the total cumulative runoff for run by adding runoff in column 5 to that listed in column 6, in the preceding line.

• Column 7: List the total cumulative process drainage to the point listed in column 1. • Column 8: List the total cumulative firewater flow, based on requirements in the design

specification.

• Column 9: List the design flow, the total of columns 6 + 7 or 7 + 8 whichever is greater. • Column 10, 11 and 12: Select and enter the pipe size, flow velocity and line slope

respectively, using the Pipe Flow Chart in 000.210.1160, Attachment 2, in the Piping Engineering Design Guide, Vol. 2. In the larger sizes there is a range in choices for any given flow. Selections are a matter of judgement, but consider the following:

; Velocities of 3 to 4 ft. per sec. are preferred.

; Use lesser slopes where limited by elevations at the terminus of the system, or where excavation is difficult and/or excessive.

; Use steeper slopes where terrain gradient permits.

• Column 13: Enter the length of run in feet and decimals of a foot between the points designated in columns 1 and 2. (For example: 242.25').

• Column 14: Multiply col. 12 x col. 13 to calculate the invert drop in decimals of a foot, and enter the result. If there is a size change in the run, add half the difference in nom. pipe size.

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• Column 15: The highest invert elevation at the start of a system should be based on the cover requirements and length of the branches serving the junction point listed. In subsequent runs if the line size is larger than in the preceding section, the invert should drop accordingly.

• Column 16: The lowest invert elevation, at the end of the system. Calculate by deducting the value in column 14 from that in column 15.

• Column 17 and 18: Self-explanatory, used for reference only. Remember to add the required information in notes: 1, 2 & 3.

8.6.13 Utility Water Systems

Cooling water supply and return headers, if underground, are routed approximately five (5) to ten (10) feet from the exchanger channel end connections to keep branches short yet still permit for some adjustment. If there is a choice it is preferable to keep the main headers out from under concrete paved areas.

Where frost is not a factor the trench depth for the cooling water headers should be kept to a minimum. As a general rule 3'-0" cover is adequate protection for truck loading for steel lines 24" and smaller in unpaved areas. Greater cover may be required for larger sizes and/or other piping materials. Under concrete paving one (1) foot cover may be adequate. (See Civil/Structural Eng.)

Branch lines from the cooling water headers to the exchangers are taken off the bottom quadrant of the header if clearance above will not permit adequate cover. Short branch piping may be routed in the frost zone and supply and return need not be at the same B.O.P.

Provide a minimum clearance of eighteen (18) inches between cooling water supply and return headers (24" for lines 30" and larger) to prevent heat transfer.

Utility water headers are located under the pipeway area in order to keep branches to the utility stations at pipe support columns short.

Potable water piping within buildings is designed by the Plumbing Section of the Architectural Group to a point five (5) feet outside of the building.

If practical the potable water header and sewer laterals and/or mains shall not be less than ten (10) feet apart horizontally. If the requirement cannot be met, the water header shall be placed on a solid shelf and at all points shall be at least twelve (12) inches above the top of the sewer line at it's highest point. Locate unit block valves at plot limits. Protect from maintenance vehicles with guard posts.

In freezing climates all utility water headers shall have their top of pipe at or below the frost line. (Firewater shall be 1'-0" below frostline.)

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PIPING DESIGN LAYOUT TRAINING LESSON 6 UNDERGROUND Page 25 of 25 15/30/2002 REV 0 8.6.14 Firewater System

Hydrants are located along plant roads or unit perimeters, so that a fire at any location in the process unit can be approached from two directions by men handling fire hoses connected to the hydrants. The hose coverage area is based on a nozzle with a 1 1/8" tip connected to 250 feet of hose. A brownline of the plot plan should be marked-up to show monitor and hydrant locations as well as their coverage arcs. The Fire Protection Engineer, a plant Fire Marshall, and local Fire Authorities review this document. (Several onionskin circles with 250' radius positioned on the plot can assist in

determining the best hydrant locations.)

Hydrants or monitors should not be located where they will conflict with exchanger tube pull or other maintenance activities. Hydrants or monitor locations that might interfere with construction erection activities should be noted to "install after equipment has been erected."

Monitors and hose reels are located to protect specific hazards as outlined in the job specifications. Water spray systems, when required are designed in accordance with the National Fire Specification, N.F.P.A. #15. Stub and valve location is also covered by this standard.

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PURPOSE

This practice provides guidelines for overall storm drainage design for a project site and applies to projects being performed by the Civil Discipline that require storm drainage design.

Information contained herein should be used by the Civil Engineer as a guide. Many design criteria, data, charts are available in text books, handbooks, manuals, but some of them are shown here. The Design Engineer should stay up to date on materials, specifications, and design criteria.

Each project will have its own set of situations to be analyzed and addressed with the best engineering concept. Good engineering judgment and most economical solutions should be utilized.

For complicated projects, obtain appropriate reference publication and design storm drainage system as specified in the publication. For very large projects, computer programs are available where time and cost saving is justified. Even for smaller systems, simple computer programs are available which provide quick and accurate results.

SCOPE

This practice utilizes many design criteria, data, charts, textbooks, handbooks, and manuals available for storm drainage design.

This practice contains types of commonly used hydrology analysis, hydrology design criteria, the rational method to determine storm water runoff from a drainage area, hydraulic design of open channel and closed storm sewers, storage basins, and design of culverts.

APPLICATION

Each engineer or designer performing storm drainage design should utilize this guideline on each project. It is the overall responsibility of the Lead Engineer to ensure that this practice is used for storm drainage design on projects.

GENERAL

CONSIDERATIONS

Comprehensive storm drainage design includes more than determination of runoff quantities and the layout of a collection or conveyance system to dispose of the runoff. Integral to the design is the consideration of erosion control and its impact on adjacent properties. The design of the storm drainage system should be prepared in conjunction with the grading design since the grading directly influences the type and design of drainage system employed. It is necessary that the drainage philosophy be established before the grading design is prepared.

The impact of increased/decreased runoff from the project site to adjacent properties must be considered. Further development within the watershed must also be considered. Stormwater management is integral to the drainage system design. It is becoming more commonplace

Practice 670 210 1150 Publication Date 20Sep95 Page 1 of 21 FLUOR DANIEL

STORM DRAINAGE

Civil Engineering This copy is intended for use solely with

Piping Design Layout Training. For other purposes, refer to the original document

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for local/state authorities to require stormwater management programs in the form of retention/detention ponds. The rate of runoff is frequently controlled by statute.

Implementation Of Storm Drainage Practice

Implementation of storm drainage practice includes the following: Data collection

Define existing watershed

Define/develop drainage philosophy for site Develop proposed layout of system

Prepare calculations for system

Design stormwater management facilities, if required

Data Collection

Review local/state statutes.

- Erosion Control

- Stormwater Management

Establish/determine requirements for permit applications.

- Plan Requirements

- Calculations

Obtain most recent topographic plans of watershed.

- Use USGS to establish general location and define total watershed.

- Use city/county topographic plans for preliminary design in absence of more accurate data.

- Obtain topographic survey prepared at suitable accuracy for final design. Obtain rainfall data.

- Obtain latest rainfall data from appropriate governmental agency (weather bureau).

Define Existing Watershed

Delineate watersheds on topographic plans.

Calculate existing runoff (Q10, Q25, Q50, and Q100) as required.

- Onto site

- From site

Define/Develop Design Philosophy For Site

Consider method of collecting runoff.

- Sheet flow versus series of drainage inlets

- Ditches versus underground piping system

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Establish design criteria.

Develop Proposed Layout Of System

Prepare conceptual grading and drainage plan.

Delineate drainage area for each inlet or section of ditch.

Note!!! For conceptual design, space inlets based on 1 inlet per 10,000 sf. Prepare Calculations

For System

Design collection system for design storm frequency. Refine grading plans and adjust layout of storm drainage.

- Check ponding at inlets. Check capacity of grates.

- Consider special inlets with high capacity grates.

- Check ditch flow for depth and velocity. Consider need for erosion netting, sod, or rip rap/energy dissipaters. Use available charts for design of open channels.

- Check pipe flow for cleansing/scouring velocity and depth of flow.

- Determine inlet and outlet losses for manholes and culverts. Pay special attention to details for proper drainage at the following:

- Intersections of roadways

- Truck docks

- Building entrances

- Rail docks/yards

- Pedestrian crossings

- Roof drainage discharge points

- Parking lots

Design Stormwater Management Facilities

Code search

- Check state/local/federal requirements. Prepare calculations/drawings for the following:

- Erosion control - Retention/detention basins - Outflow structures - Emergency spillways - Earth dams Practice 670 210 1150 Publication Date 20Sep95 Page 3 of 21 FLUOR DANIEL

STORM DRAINAGE

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HYDROLOGY ANALYSIS

Technical Release 55 (TR-55)

Technical Release 55, Urban Hydrology for Small Watersheds, presents simplified procedures to calculate storm runoff volume, peak rate of discharge, hydrographs, and storage volumes required for floodwater reservoirs. These procedures are applicable in small watersheds, especially urbanizing watersheds, in the United States.

The model described in TR-55 begins with a rainfall amount uniformly imposed on the watershed over a specified time distribution. Mass rainfall is converted to mass runoff by using a runoff CN (curve number). CN is based on soils, plant cover, amount of impervious areas, interception, and surface storage. Runoff is then transformed into a hydrograph by using unit hydrograph theory and routing procedures that depend on runoff travel time through segments of the watershed.

Use peak discharge method for up to 2,000 acres of drainage area. Use tabular method for up to 20 square miles of drainage area.

In TR-20, the use of TC (Time of Concentration) permits this method for any size watershed within the scope of the curves or tables, while in TR-55, the procedure is limited to a homogeneous watershed. The approximate storage routing curves are generalizations derived from TR-20 routings.

Use TR-20 if the watershed is very complex or a higher degree of accuracy is required. Use TR-20 if TT (travel time) is greater than 3 hours and time of concentration TC is greater than 2 hours and a drainage area of individual subareas differ by a factor of 5 or more. Refer to Civil Engineering software, quick TR-55, and TR-20 for computer application.

Synthetic Unit Hydrograph Method (Chapter 16, Pages 16-1 To 16-26)

Over the past 2 decades, the federal, state, county, and local agencies have made numerous hydrologic investigations of drainage basins using synthetic unit hydrograph methodology. The synthetic unit hydrograph method should be used on larger drainage areas.

Rational Method

The rational method is 1 of the most widely used techniques for estimating peak runoffs, and is applicable to most of the drainage problems encountered on Fluor Daniel projects.

The rational formula is Q = CIA where

Q = Peak runoff, cfs

C = Coefficient of runoff, the rate of direct runoff to rainfall

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I = Rainfall intensity, inches per hour, corresponding to the time of concentration

A = Tributary area, acres

The rational method is commonly used for determining peak discharge from relatively small drainage areas up to 200 acres.

HYDROLOGY DESIGN CRITERIA

Normally, design for a storm frequency of 10 years for projects, unless otherwise specified by the client.

Check for storm frequency of 50 years to estimate the consequences of flooding the site. For major structures such as culvert under public highway, use a storm frequency of 50 years.

Design major flood control channels and major lift stations for a storm frequency of 100 years.

Stormwater runoff from tank farms is normally not included in the design. Stormwater is impounded within the dikes and released after the peak stormwater runoff has passed. Design containment storage within containment areas for a storm frequency of 10 years, 24-hour storm for projects, unless otherwise specified by the client.

Ponding at inlets should be less than 3 inches for a frequency of 25 years storm.

RATIONAL METHOD Rational Formula

The rational formula is Q = CIA. On a topographic plan of the drainage area, draw the drainage system and block off the subareas draining into the system.

Determine A, the area of each subarea in acres.

Coefficient Of Runoff

The coefficient of runoff is intended to account for the many factors which influence peak flow rate. The coefficient of runoff primarily depends on the rainfall intensity, soil type and cover, percentage of impervious area, and antecedent moisture condition.

Determine the coefficient of runoff C, for appropriate class of ground surface from the following table. If more than 1 class of ground surfaces fall in 1 tributary drainage area, use a composite coefficient of runoff value.

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Coefficient of Runoff C

Roofs 1.00

Pavements

Concrete 1.00

Asphalt 1.00

Oiled Compacted Soil 0.80

Compacted Gravel 0.70

Compacted Impervious Soil 0.60

Natural Bare Soil 0.60

Uncompacted Gravel 0.50

Compacted Sand Soil 0.40

Natural Soil, Grass Cover 0.40

Uncompacted Soil 0.20

Lawns 0.20

Composite coefficient of runoff C:

A1C1+A2C2+A3C3+ −−−−AnCn A1+A2+A3+An

where

A1 A2 A3 ---- An = Areas in acres of different class of surfaces C1 C2 C3 ---- Cn = Corresponding coefficient of runoff

Time Of Concentration

If rain were to fall continuously at a constant rate and be uniformly distributed over an impervious surface, the rate of runoff from that surface would reach a maximum rate equivalent to the rate of rainfall. The time required to reach the maximum or equilibrium runoff rate is defined as the time of concentration.

The time of concentration depends upon the length of the flow path, the slope, soil cover, and the type of development.

Determine the initial time of concentration using the nomograph on Attachment 01. Use a minimum time of concentration of 5 minutes for paved areas and a minimum time of concentration of 10 minutes for unpaved areas.

Precipitation

The various precipitation amounts during specified time periods at recording stations are analyzed using common models of probability distributions.

A number of alternative statistical distributions such as Log Pearson Type III, Pearson Type III, Two-Parameter Lognormal, Three-Parameter Lognormal, and Weibull, Type I, Extreme Value are used in flood hazard analysis.

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Intensity Duration Curves

Use the intensity duration curves available from federal, state, county or local agencies for the project location. If such curves are not available, construct these curves using Weather Bureau Technical Paper Number 40 (Continental United States); 42 (Puerto Rico and Virginia Islands); 43 (Hawaiian Islands); 47 and 52 (Alaska); or NOAA Atlas, Precipitation - Frequency Atlas of the United States, published by the National Weather Service.

For constructing the curves, given only 1 or 2 points, use the following conversion factors based on 30 minutes as 1.00: Duration in Minutes Factor Duration in Minutes Factor 5 2.22 40 0.80 10 1.71 50 0.70 15 1.44 60 0.60 20 1.25 90 0.50 30 1.00 120 0.40

To go from 1 curve to another, use the following factors based on the 50 year maximum rainfall as 1.000:

1 year 0.428 25 years 0.898

2 years 0.455 50 years 1.000

5 years 0.659 100 years 1.108

10 years 0.762

Rainfall intensity duration curves for more than 100 years can be constructed using rainfall data for periods of 2, 5, 10, 25, 50, and 100 years; and time periods of 20 minutes, 60 minutes, 2 hours, 3 hours, 6 hours, 12 hours; and 24 hours using the following formula: _ _

Xji = Xi + Kj Si Xi where

j = Return period in years

i = Specific storm duration in minutes, hours or days Xji = Precipitation in inches for return period j and duration i Xi = Mean maximum annual storm for duration i

Kj = Frequency factor (in standard deviations) for a return period of j years Si = Standard deviation of maximum annual storm for duration i

For more detailed procedures using this formula, refer to "Analysis of Data," Pages 7 to 25 of Rainfall Depth Duration Frequency for California, Department of Water Resources, State of California, November 1982.

A sample set of curves is shown in the sample problems in this practice.

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Using the initial time of concentration, determine "I" intensity of rainfall in inches per hour from the intensity duration curve for the plant's geographical location using the proper yearly rainfall frequency.

Compute Q = CIA.

Refer to sample problems in this practice.

Travel Time

Determine the size of the channel or pipe required to carry Q on the slope of the drain. Determine the velocity of flow.

Measure the length of flow to the point of inflow of the next subarea downstream. Compute the time of flow for this reach and add it to the initial time of concentration for the first area to determine a new time of concentration.

Calculate Q for second subarea, using the new time of concentration and continue in similar fashion until a junction with a lateral channel is reached.

Start at the upper end of the lateral and carry its Q to the junction with the main channel.

Storm Runoff At Junction

Compute the Q at the junction.

Tributary area with longer time of concentration

Tributary area with shorter time of concentration

QA QB

TA TB

IA IB

Peak Q cfs (cubic feet per second), time of concentration in minutes, rainfall intensity in inches/hour. If TA = TB then Qp = QA + QB TP = TA = TB If QA > QB then Qp = QA + QBIA IB TP = TA If QA< QB then Qp = QB + QAIB IA TP = TB Qp = Peak Q at junction

Tp = Peak time of concentration at junction

If more than 2 tributary areas are contributing at 1 junction, combine 2 areas at a time and proceed similarly until tributary areas are combined.

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DITCHES AND CHANNELS Capacity

The capacity of ditches and channels will be calculated using the Manning's equation:

Q= 1.486_n r2/3_s1/2_A where:

Q = Capacity in cfs

A = Cross sectional area of flow in square feet

r = Hydraulic radius = Area of flow in feet

Wetted perimeter s = Slope of energy grade line in foot per foot

n = Roughness coefficient

Values of roughness coefficient n for ditches and channels Lined ditches and channels

n = 0.014 for poured concrete

n = 0.016 for shotcrete (gunite)

n = 0.014 for asphalt

n = 0.035 for medium weight rip rap

n = 0.025 for crushed rock

n = 0.030 for grass

Unlined ditches and channels

n = 0.020 for very fine sand, silt or loam

n = 0.025 for sand and gravel

n = 0.030 for coarse gravel

Values of n for other surfaces can be found in Session 7, Pages 7-17 of King and Brater, Handbook of Hydraulics, McGraw-Hill Book Company, New York; and Chapter 5, Pages 110 to 113 of Chow, Ven Te, Open-Channel Hydraulics, McGraw-Hill Book Company, New York, 1959.

Ditches and channels should be designed with the top of the walls at or below the adjacent ground to allow interception of surface flows.

The minimum velocity of flow should be 2.0 feet per second in order to prevent the settling of solids, if there is possibility of solids flowing in the ditches and channels.

Velocities in unlined ditches and channels must be limited to prevent cutting or erosion of the ditch or channel bottom or sides. Permissible channel velocities for various types of soil can be found in Session 7, Pages 7-19 of King and Brater, Handbook of Hydraulics,

McGraw-Hill Book Company, New York; and Chapter 7, Page 165 of Chow, Ven Te, Open-Channel Hydraulics, McGraw-Hill Book Company, New York, 1959. If the mean velocity exceeds that permissible for that particular kind of soil, the channel should be protected with some type of lining.

Freeboard or additional wall heights are to be added above the calculated water surface. For ditches and channels with capacities to 50 cfs, add 1.0 feet.

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For ditches and channels with capacities from 50 cfs to 200 cfs, add 1.5 feet.

For ditches and channels with more than 200 cfs capacities, refer to Chapter 7, Pages 159 and 160, of Chow, Ven Te, Open-Channel Hydraulics, McGraw-Hill Book Company, New York, 1959.

For curved alignments, add freeboards above the superelevated water surface.

It is desirable to provide a depth greater than critical. If not possible, an energy dissipator may be required at the end of the ditch section.

Linings

Ditches and channels with a flow velocity that exceeds permissible velocity will be lined. Lining of ditches and channels will be poured concrete, gunite, asphalt, crushed rock, riprap, or other type of slope protection.

For design procedure of riprap design, refer to Chapter 3, Pages III-137 to III-150 of Virginia Erosion and Sediment Control Handbook, Virginia Department of Conservation and Recreation Division of Soil and Water Conservation, 1980.

GRAVITY STORM SEWER SYSTEM Capacity

The capacity of a gravity storm sewer system will be calculated using the Manning's equation. Refer to sections covering Ditches and Channels in this practice.

Closed storm sewers should be deigned to flow full for the design storm, unless otherwise specified by the Client.

The gravity storm sewer system will be designed in such a manner that at the maximum design flow, the water level in the most remote catch basin of the system or subsystem is a minimum of 6 inches below top of grating. The controlling elevation at a junction of a main, lateral, or sublateral for calculating the hydraulic gradeline upstream will be the hydraulic grade elevation of the main or lateral at the point or the soffit elevation of the pipe, whichever is greater.

Values of Manning's n for closed sewers are as follows:

Pipe Material n

Polyvinyl chloride pipe 0.010

Steel 0.011

Ductile iron 0.013

Cast iron 0.013

Cement lined pipe 0.015

Concrete pipe 0.013

Vitrified clay pipe 0.013 Fiberglass reinforced plastic 0.010 Corrugated metal pipe 0.024

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The preferred slope for sewer lines will be approximately 0.01 foot (1/8 of an inch) per foot. The minimum slope will be approximately 0.005 foot (1/16 of an inch) per foot but may be decreased, if necessary, provided the required minimum velocity is maintained to avoid disposition of solids.

The minimum pipe size for branch lines will be 4-inch diameter and 8-inch diameter for catch basin outlet pipes.

The minimum velocity for closed storm sewers should be 2.0 feet per second to prevent the settling of solids.

For concrete sewers where high velocity flow is continuous and grit erosion is expected to be a problem, use a maximum velocity of about 10 feet per second.

The alignment chart in Attachment 02 can be used for the solution of Manning's equation for circular pipes flowing full.

The graph in Attachment 03 is used for the solution of problems involving sewers flowing only partly filled. The following procedure is used for finding the hydraulic elements of the pipes.

Compute the ratio of q/Q for each line. Find the ratio of h/D and v/V.

From the ratio h/D, calculate h. From the ratio v/V, calculate v.

q = Actual flow, cfs

Q = Quantity if pipe flowing full, cfs h = Actual depth of flow, feet D = Inside diameter of pipe, feet

v = Actual velocity, fps (feet per second) V = Velocity if pipe were flowing full, fps

Losses

Manhole losses will be calculated from the following:

hmh=0.05  _2gv2  to0.75  _2gv2  

depending upon the inlet and outlet pipe size, elevation and design. Bend losses will be calculated from the following equations:

hb=Kb  v2 2g    where Kb=2.0_ δ 90  

where δ = Central angle of bend in degrees.

Bend losses should be included for closed conduits; those flowing partially full as well as those flowing full.

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CULVERTS

Drainage culverts are normally corrugated metal pipe, reinforced concrete pipe, or reinforced concrete box as necessary to meet the requirements for stormwater drainage flow, truck loads, and depth of fill above the culvert.

Culverts under roads will be designed to support the earth pressures on the culvert and the maximum wheel load that will be imposed over it through its design life, plus the applicable impact, as defined in AASHTO (American Association of State Highway and Traffic Officials) Standard specifications for Highway Bridges. In the absence of construction or maintenance vehicles with a greater wheel load, the culvert will be designed to support a wheel load of 16,000 pounds (HS-20 loading). Minimum cover over culverts will be 12-inches for circular corrugated metal pipe, and 18-inches for reinforced concrete pipe, and corrugated metal pipe arches.

The minimum size of culvert will be 12-inch diameter for lengths of 30 feet or less and 18-inch diameter for lengths over 30 feet.

Where installation of multiple culverts is required, the minimum clear distance between pipes will be as follows:

Pipe Diameter Minimum Clear Distance

12 inch to 24 inch 27 inch to 72 inch 78 inch to 120 inch 12 inches 1/2 diameter 36 inches

Culverts will have a slope that will provide a minimum velocity of 2.0 fps. Culverts will be sized to pass the 10-year storm flow with unsubmerged inlet. However, the culvert will be checked for the 50-year storm with ponding at the entrance not to exceed the top of the road subgrade.

In designing any culvert larger than a 36-inch diameter single-barrel pipe (for example, arch and oval pipe, multiple-barrel culverts, concrete box), design features such as headwalls, endwalls, transition structures, and energy dissipators will be selected strictly on the basis of culvert performance and be economically justified.

Procedure for determining culvert size:

List the design data. Refer to sample problems in this practice. Estimate first trial size.

Find headwater depth.

Inlet Control: Using Attachments 04, 05, or 06, determine HW/D using the appropriate entrance scale. Convert HW/D to HW (headwater) by multiplying by D (pipe diameter) in feet.

Outlet Control: Using Attachment 07, 08, or 09, determine H (head) in feet using the appropriate value for k(e) as given in the following table:

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Entrance Loss Coefficients Type of Entrance

Coefficient k(e) Concrete Pipe

Projecting from fill, socket end (groove end) 0.2

Projecting from fill, square cut end 0.5

Headwall or beadwall and wingwalls Socket end of pipe (groove end) Square end

Round radius (radius - 1/2 D)

0.2 0.5 0.2

End section conforming to fill slope 0.5

Corrugated Metal Pipe

Projecting from fill (no beadwall) 0.9

Headwall or beadwall and wingwalls, square edge 0.5

Beveled to conform to fill slope 0.7

Flared end section (available from manufacturer) 0.5

Beadwall, rounded edge 0.1

Solve for HW in the following equation:

HW=H+ho−SoL

For TW (tailwater) elevation equal to or greater than the top of the culvert at the outlet, set ho equal to TW.

For TW elevation less than the top of the culvert at the outlet, use the following equation or TW, whichever is greater, where dc, the critical depth in feet, is determined from

Attachment 10 or 11.

ho=dc+D

2

Compare the headwaters for both inlet and outlet control. The higher headwater governs and indicates the flow existing under the given conditions for the trial size selected. Select culvert size which keeps headwater depth below allowable limit.

STORMWATER DETENTION AND RETENTION BASINS Flood Control Detention Basin

The primary function of the flood control detention basin is to store the storm runoff during peak flood and reduce the peak discharge.

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The flood control detention basin is generally the least expensive and most reliable measure. It can be designed to fit a wide variety of sites and can accommodate multiple outlet

spillways to control multifrequency outflow.

Measures other than flood control detention basins may be preferred in some locations. Any device selected, however, should be assessed as to its function, maintenance needs, and impact.

Design flood control detention basins for 50 years storm frequency.

For flood control detention basin storage volume requirement calculations procedure, for up to 2,000 acres of drainage area, refer to Chapter 6 Storage Volume for Detention Basins, Pages 6-1 to 6-11 of Urban Hydrology for Small Watersheds, TR-55, United States Department of Agriculture, Soil Conservation Service, January 1975, or use local drainage manual, if available.

Stormwater Retention Basin

Regulations require management of storm runoff from industrial plant sites so as not to discharge toxic or hazardous pollutants to receiving waters.

The purpose of stormwater retention basins is to store the stormwater during periods of storm runoff and release it at a lower rate to the treatment process.

Retention pond and storage basin capacities will be determined based on the total

accumulated stormwater runoff from the design storm frequency for duration of 24 hours. A minimum freeboard of 12 inches will be provided on top of water surface.

Lining for ponds and basins will be as recommended in the Geotechnical Investigation Report or as required by process and environmental criteria for the project.

Sediment Control Basin

Erosion and sediment control measures are required during construction to prevent surface storm water runoff pollution into stream channels and water bodies.

The sediment control basin is required to collect and store sediment or debris from affected areas.

The sediment control basin collects and holds stormwater runoff to allow suspended sediment to settle out.

Design sediment control basins for 10-year storm frequency, unless regulatory agencies dictate otherwise.

The surface area of the sediment basin at the height of the rim of the riser pipe is calculated by using the following formula:

A= KQ Vs

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where

A = Basin surface area square feet

Q = Storm runoff cfs

K = 1.2

Vs = 0.00096 ft/sec settling velocity for a 0.02 millimeter particle size. Particles greater than or equal to the 0.02 millimeter particle size are to be retained in the basin.

The sediment storage volume is 75 cu yd per acre of disturbed construction area. The settling zone will be a minimum of 2 feet deep.

The combined capacities of the riser pipe and spillway are designed to be sufficient to pass the peak rate of storm runoff of a 10-year storm frequency.

The sediment control basin will need to be periodically cleaned out to restore the basin to its original designed volume capacity.

A concentric antivortex device and trash rack should be provided on top of the riser pipe. A concrete base of sufficient weight to prevent flotation of the riser is attached to the riser pipe with a watertight connection.

Stone riprap protection should be provided on the spillway to reduce erosion of the spillway dike.

A protection fence should be provided around the sediment control basin for safety. The sediment control basin may be used after construction as a permanent stormwater management basin.

For sediment control basin design requirements and procedure, refer to Chapter 3, Pages III-59 to III-88 of Virginia Erosion and Sediment Control Handbook, Virginia Department of Conservation and Recreation Division of Soil and Water Conservation, 1980.

STORM DRAINAGE SOFTWARE

(AVAILABLE IN IRVINE)

1. Advanced Designer Series Civil Soft

Storm Plus

Storm Drain Analysis Program

Storm Plus is based on the original computer program F0515P and was developed in April 1979. This program was written for use by the Los Angeles County Flood Control District or by its contractors on district projects.

This program computes and plots uniform and nonuniform steady flow water surface profiles and pressure gradients in open channels or closed conduits with irregular or regular sections. The flow in a system may alternate between super critical, subcritical, or pressure flow in any sequence. The program will also analyze natural river channels

STORM DRAINAGE