Design and Construction Standards - Tualatin Valley Water District

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Section 2Trench Excavation and Backfill2.1 Types of Allowed Backfill2.2 Materialsa. Class A backfill – compacted native material1. Class A backfill requires District approval and shall only be considered for use inunpaved areas.b. Class B backfill – compacted crushed rock granular material1. Class B backfill shall be used in all paved areas.c. Refer to Standard Detail 10.a. Class A Backfill – compacted native material1. The District may require a geotechnical engineering investigation of the suitabilityof native materials for use in trench backfill.2. Class A backfill material shall be free of organic material, wood, rocks larger than6 inches in any dimension, and other debris.3. The moisture content of Class A backfill material shall be no more than 5% aboveoptimum during backfill placement and compaction.b. Class B Backfill – compacted crushed rock granular material1. Class B backfill material shall be crushed rock meeting the requirements of ODOTStandard Specifications Section 00641 and Section 02630.2. Designated sizes shall be 1”-0” or ¾”-0” with no more than 5% passing theNo. 200 sieve (wet analysis).c. Bedding and Pipe Zone Material1. Bedding and pipe zone material shall be Class B backfill material.d. Foundation Stabilization Material1. Foundation stabilization material shall be 2 1/2"-0” crushed rock meeting therequirements of ODOT Standard Specifications Section 00641 and Section 02630,or other material as approved by the Inspector.TVWD Water System Standards June 2012 Page 2-1
Trench Excavation and Backfill Section 22.3 Pavement, Curb, and Sidewalk Removala. Prior to excavation of the trenches, cut all pavements, curbs, and sidewalks,regardless of the thickness, with a pavement saw or other approved pavementcutter.b. The width of the pavement cut shall be at least equal to the required width of thetrench at ground surface. The city, county, or state agency responsible for thestreet may require T-cutting or additional pavement milling prior to re-surfacing.c. Removed pavement and concrete materials shall be hauled from the site to berecycled and not used for trench backfill.2.4 Trench Width, Base, and Gradea. The width of trenches in which pipe is to be laid shall be 12 inches greater thanthe nominal diameter of the pipe or 24 inches minimum, unless otherwiseapproved by the District Engineer.b. Grade the full width of the bottom of the trench where the pipe is to be laid;additional excavation to accommodate pipe bells shall be required. The trenchbottom shall be level across the width and on a uniform grade between gradebreaks along the length of the trench.2.5 Shoring, Sheeting, and Bracing of Trenchesa. Trench safety, including but not limited to shoring and bracing design, shall bethe responsibility of the contractor.b. Erect, maintain, and remove shoring, sheeting and bracing as required by themost stringent of all applicable laws, codes, and ordinances.c. Where sheeting and bracing are used, increase trench widths accordingly by thethickness of the sheeting. Keep sheeting in place until the pipe has been placedand backfilled at the pipe zone.d. Shoring and sheeting shall be removed as backfilling progresses in a mannerthat will not damage the pipe or permit voids in the backfill.e. Foundation Stabilization1. When the existing material in the bottom of the trench is unsuitable for supportingthe pipe, excavate below the flow line of the pipe. If firm, native material is notpresent within three feet below the bottom of the pipe zone, contact the Inspectorfor further guidance on foundation stabilization.2. Backfill the trench to the bottom of the pipe zone with approved material andcompact.2.6 Location of Excavated Materialsa. During trench excavation, place the excavated material within the constructioneasement or specified working area so that the excavated material does notobstruct any private or publicly traveled roadways.TVWD Water System Standards June 2012 Page 2-2
Page 1 and 2: Design andConstruction StandardsDel
Page 3 and 4: Table of ContentsList of TablesList
Page 5 and 6: Water System Design and Constructio
Page 17: Water System Design and Constructio
Page 21 and 22: Trench Excavation and Backfill Sect
Page 23 and 24: Water Mains Section 3Section 3Water
Page 25 and 26: Water Mains Section 33.2 Materials3
Page 27 and 28: Water Mains Section 3ii.iii.f. Flan
Page 29 and 30: Water Mains Section 33. Casing seal
Page 31 and 32: Water Mains Section 3ii.iii.c. Tapp
Page 33 and 34: Water Mains Section 3v. Measure the
Page 35 and 36: Water Mains Section 35. Operate all
Page 37 and 38: Valves and Valve Boxes Section 44.2
Page 39 and 40: Valves and Valve Boxes Section 44.
Page 41 and 42: Fire Hydrants Section 5Section 5Fir
Page 43 and 44: Water Service Connections Section 6
Page 49 and 50: Precast Concrete Vaults Section 74.
Page 51 and 52: Section 8Backflow Prevention Genera
Page 53 and 54: Backflow Prevention General Require
Page 59: Standard DetailsTVWD Water System S

Design and Construction Standards - Tualatin Valley Water District

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