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Culvert Pipes and Storm Sewers The Trench 2. Pipe “Template" Pipe Must be Placed in a Trench Bedding the Pipe 4. Pipe Joints 5. Backfill Material and Compaction 6. Pipe Cover and Avoiding Damage. Culvert Pipes and Storm Sewers Types What to Look For Concrete
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Culvert Pipes and Storm Sewers • The Trench • 2. Pipe “Template" • Pipe Must be Placed in a Trench • Bedding the Pipe • 4. Pipe Joints • 5. Backfill Material and Compaction • 6. Pipe Cover and Avoiding Damage
Culvert Pipes and Storm Sewers Types What to Look For Concrete Cracks, Out of Round, Chips, Exposed Reinforcement, Required Markings Metal (Galvanized Steel or Aluminum) Dents, Rust, Out of Round, Coating Damage, Scratches, Required Markings PVC & Composites Required Markings, Strength such as Schedule 40
The Trench • What to Look For • 2. Correct Grade Line • How Wide? • Placing in a Trench
What to Look For • Generally, No Soil Borings or Information • Soil Borings May Have Been Taken for Some Larger Pipes. • 2. Foundation Inspection • Basically the Same as Embankment Compaction. Use a Rod or Bar Steel to Probe the Trench Bottom. • Something Doesn’t Look Right • Muck, Buried Topsoil, Logs, etc. • May Need to Over Excavate and Place Suitable Material (Extra Pay)
The Trench Grade Line • Does it Flow? Is the Flow Line Straight? • Don’t Pond Water in the Pipe. • Camber • Some culvert pipes placed under embankments may require a cambered grade. • The portion of the pipe under the roadbed supports a greater load than the ends. To compensate for additional settlement, a camber or slight convex curve, is specified by the engineer and built into the grade line of the culvert. • Camber is Used When Soil Beneath the Pipe is Expected to Consolidate or Compact.
The Trench Width • Is There a Specific Specification? • Standard Specification 520.3.2.1 (3) “Trench width shall not exceed the pipes outside width by more than 36 inches.” • Wide Enough to Compact Backfill with Equipment • Generally 18 inches between the pipe and trench side is enough. • Any Restrictions? • Utility in the way. Other structures such as footings, walls or piling.
The Trench Width Shallow to Medium Depth Culvert & Sewer Pipe Trench
The Trench Width Medium to Deep Depth Culvert & Sewer Pipe Trench
Pipes Trench in Bed Rock • How Wide? • Usually 1.5 Times the Outside Diameter of the Pipe. • But Allow for Compaction Equipment. • How Deep? • Generally 6” Deeper Than the Bottom of the Pipe. • Don’t Pay for Rock Excavation Greater Than the Standard Trench Width and Depth Just Because the Contractor Over Excavated.
Culvert Pipe Template Earth bed shaped or trimmed to give full support for at least 1/10 outside diameter of circular pipes. Labor Intensive. Not Used Much Anymore.
Placing in a Trench • Don’t Build Grade Around Pipe • Contractor is Required to Build Grade to 1 Foot Above Top of Pipe. • Then Trench is Cut and Pipe Placed.
Bedding the Pipe • Bedding Specification • 520.3.2.1(6) Backfill with granular backfill as modified in 209.2.1.
Bedding the Pipe (2) For backfill for trench excavation, use a maximum size of any gravel, stone, or other broken or fragmented material so that 100 percent passes a 6-inch sieve, not less than 85 percent by weight passes a 3-inch sieve, and not less than 25 percent by weight passes a No. 4 sieve. For bedding under a culvert pipe, use granular backfill that consists substantially of sand with all particles retained on a one inch sieve removed.
Culvert Pipe Joints • Anything Special Required • Locking, Gasket, Fabric or Masonry • 3. Joint Ties • 4. Filling the Holes
Special Culvert Pipe Joints • Tie all Joints • Usually if unusual stress is predicted. • Infiltration • Pipe is in a contaminated area or placed in industrial byproducts.
Different Types of Joint Fillers • Anything Special Required • Locking (metal pipe) • Gasket • Fabric • Masonry (concrete pipe)
Culvert Pipe Joints • Make Sure They are Clean. • Gaskets Should Fit Properly. • 3. Fabric Should Extend all Around Pipe. • Glue, Tar or Mud the Entire Bell. • Make Sure Pipe is Square at Joints.
Filling the Lift Holes • Use Concrete of Other Approved Filler. • 2. If Precast Filler (Cone) is Used, Mud Prior to Inserting.
Backfill Material & Compaction • What is Required? • 2. Compacting the “Spring Line” • 3. Lifts • 4. Compaction of Lifts • 5. Avoiding a Frost Heave
Backfill Requirements Standard Specification 520.3.4.1 Public Highway Culverts (1) Backfill permanent pipe culvert installations under any public highway with selected material from excavation that is free of large lumps, clods, or rock. If the contract or engineer specifies, backfill with granular backfill conforming to 209.2. If granular backfill contains 3-inch or larger rocks, place so that the rocks do not contact the pipe during compaction.
Compacting the Spring Line • What is It? • 2. May Require Hand Methods
Lifts of Backfill Material Standard Specification 520.3.4.1 2) Place backfill in the trench over the top of the earth, granular foundation, or bed. Carefully place and thoroughly ram, tamp, or vibrate around the pipe in layers no greater than 6 inches deep, to the top of the pipe. Compact the entire length of each layer before placing the next layer. (3) Place and compact backfill material above the pipe in layers no more than 12 inches deep, to the top of the trench. Compact to the same degree as the material next to the trench.
Culvert Pipe Backfill Lifts Earth Support Bedding Details for Storm Sewer & Culvert Pipes
Culvert Pipe Backfill Lifts Granular Supported Bedding Details for Storm Sewers & Culvert Pipes
Nuclear Gauge in a Trench Nuclear gauge may give false readings in a trench. Gauge must be recalibrated (standard count) in the trench prior to taking a soils density test.
Avoiding a Frost Heave • What is the Nature of the Back Fill? • 2. Transitioning to the Grade Line (Blue Top)
Pipe Cover & Avoiding Damage • Types and Strength of Pipes • 2. Minimum Cover • 3. A Utility is in the Way • 4. Avoid Damage During Construction
Types & Strength of Pipes • Type III, IV, etc. • Pipe Strength Numbers Usually Scratched on Pipe. • Example Type III has One Row of Steel Mesh Type IV has Two Rows of Mesh. Type IV Used Under Railroads or Where Cover May Be an Issue. • Elliptical or Squash Pipes. • Gives More Cover But Not as Strong. Manufacture Pipe Specifications May Require More Cover Than an Equal Capacity Round Pipe. • Composites • Becoming More Common. Check Manufactures Specifications to Determine if Pipe Meets DOT Specifications. Also Some Local Governments May Not Allow Substitutions.
Minimum Pipe Cover • Usually a Manufacturer's Specification. • 2. Substituting an Elliptical to Gain Cover May Not Help Because They Require More Cover. • What if I Can’t get Required Cover? • A Stronger Pipe May Be Required. This Could Require a Contract Change Order.
A Utility is in My Way • Is the Utility in the Wrong Place? • Check With Utility Coordinator. Utility Might Not be Able to be Moved. • Contact Utility About Minimum Clearances. • Can Pipe Be Place On Top of Utility? • Can I Move the Pipe to Another Location? • Maybe, But What Problems Will That Bring About? • Document Findings and Decisions. • Usually Found in an Urban Situation. • Storm Sewer Line Crosses a Utility. • Sometime the Utility Cannot be Moved.
Pipe Cover & Avoiding Damage Standard Specification 520.3.4.1 4) Immediately after backfilling, cushion the installation as necessary by placing compacted earth embankment over the pipe for at least the trench width. Provide 2 feet or more cover, including backfill depth, above the pipe. Maintain this cushion during subsequent construction operations.
Avoid Damage During Construction • Pipe is Under Most Stress Prior to Pavement • 2. Two Foot Minimum Cover is Usually Enough • 3. Hauling With Scrapers or Trucking Across With Off Road Trucks Will Require More Than 2 Feet of Cover.
Culvert Pipes and Storm Sewers The Trench only needs to be wide enough to “fit” the pipe in. Start placing pipes at the inlet end and proceed to the discharge. You can use native materials to bed a pipe. Storm sewers and culvert pipes require the same specified backfill material. If cover over a pipe is an issue an equal capacity elliptical or “squash pipe” can be substituted.