gravity utilities - college of engineering

GRAVITY UTILITIES

CET-2030 Construction Graphics

• Sanitary Sewers: Collect & convey wastewater• Storm Sewers: Collect & convey storm runoff• Underdrains: Collect & convey ground water

Types of Gravity Utilities

• Have sloping pipes (for fluid to flow)• Have a connection to the atmosphere

GRAVITY UTILITIES


• Location (Horizontally): Dimension or station /offset

• Size & Slope: Label on the plans

• Depths (Invert Elevations): On plan, schedule or profile

Plans require specifying:

SANITARY SEWER DESIGN


Average Daily Flow = OEPA Estimated Flow x Units

Peak Factor x Average Daily Flow x 24Peak Daily Flow = ---------------------------------------------------

Runoff PeriodRunoff period approximates the interval into which all the flow will normally occur

Ohio EPA Standard Flows & Factors



Ohio EPA Flows: Based on Land Use



Ohio EPA Flows: Pipe Sizing



Practice Design Problem

Determine the pipe size and required minimum slope for a 700 student Junior/Senior High School complex.

STORM SEWER DESIGN


• Requires knowledge of drainage basin • Area• Ground Cover• Slopes

• Requires knowledge of local rainfall characteristics

• Beyond scope of this class and thus covered in CET-3220

GRAVITY SEWER SYSTEMS


Consist of Sloped Pipes & Structures (MH’s & CB’s) at Proper Locations

• Storm structures (CB’s) located at low points to handle surface flows graded to inlet

• Sanitary structures (MH’s) located at high points to limit clean water infiltration

It is ILLEGAL to drain storm runoff and other clean water into a Sanitary sewer!!!!



• Storm & Sanitary structures maximum 400’ apart on straight runs (for access)

• Locate structures in changes in:

• Elevation • Pipe size• Pipe Slope• Direction• & at pipe intersections

• Locate in easily accessible areas out of traffic

• Out of foundation zone of influence along buildings



Minimum Depths •48” Minimum Cover on Sanitary Sewers (for freezing)•Storm Sewer Minimums

•9” Cover below bottom of pavement base•12” below unpaved ground•2’ cover at structures (CB’s & MH’s) for constructability

12” Cover

9” Cover



Anatomy of a Structure



Plan & Profile Views • Pipe callout includes length, size, type and slope• Pipe length measured Center to Center of structure• Slope arrow in plan shows direction of flow (downhill)

MATCHING TOPS


Outlet pipe top should be no higher than the lowest inlet pipe top

• Tops matched, bigger outlet lower

• Outlet invert and top lower then inlet invert and top

• Inverts match but bigger outlet top is HIGHER than inlet top

OK

OK

NOT OK!

SANITARY DROP MANHOLES


• Required when inlet is 2’ or more higher than the outlet

• Drop connection accommodates low flows allowing personnel access to structure

• Expensive to install

• Avoid by dropping pipes at previous outlet

STANDARD INVERT NOTATION


A standard notation is used to identify pipes and corresponding IE’s at a structure

• Pipes are identified by the direction you look to see them if you are standing on the structure

• Pipes in CB above would be labelled as:Inlets: 12” W, 10” N, 8” SOutlet: 18” E

Flow direction is not considered when labeling pipes!!!

STANDARD NOTATION


What do you think?Do tops match? Are they set ok?

MH STRUCTURE SIZING


Manhole walls must be structurally sound after pipe openings are made

Minimum inside diameters are required to provide the wall area depending on angle and size of pipes

Up to Up to

It’s good design practice to keep pipes deflections at 90° or less deflection angle to avoid structure wall problems

MH STRUCTURE SIZING


What do you think?

gravity utilities - college of engineering

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