Soil Steel Structures – No backfill

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Soil Steel Structures – No backfill. Soil Steel Structures – Compacted backfill. Soil Steel Structures – Backfill Comparison. Loose Backfill. No Backfill. Compacted Backfill. De-Watering. Dam and Pump. Diversion Channel. Material Storage. Material Marking. Material Handling. Excavation. - PowerPoint PPT Presentation

Text of Soil Steel Structures – No backfill

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Soil Steel Structures No backfillCulverts Installation1Steel culverts are soil-steel structures:Without compacted backfill, they will not carry the loadThe culvert will buckle and fail if not supportedSoil Steel Structures Compacted backfillCulverts Installation2Steel culverts are soil-steel structures:With compacted backfill, the soil will prevent bucklingSoil Steel Structures Backfill Comparison

No BackfillLoose BackfillCompacted BackfillCulverts Installation3Demonstration in Lab using steel can:1 no backfill deformation at 7kg, failure at 28kg2 loose backfill 15% deformation at 200kg, approaching failure3 compacted backfill no deformation at 200kg

Dam and PumpDiversion ChannelDe-WateringCulverts InstallationMaterial Storage

Culverts InstallationPrepare storage area on site for pipe material and granular backfillStore plates concave upOnly stack on plates of same curvature

5Material Marking

Culverts InstallationMark one edge of platesMark visible on outside only ensures correct lapping


Material HandlingCulverts InstallationWhen picking up plates, attach sling to one side only maintain shapeImproper handling dents, scratches in galvanized coating, tears in bolt holes7

ExcavationCulverts InstallationRemove unsuitable material as per plansMonitor alignment and elevation as excavation proceedsDewater if underlying ground is wet (sump/pump, vertical sand drains with well points)


Base PreparationCulverts InstallationGeotextile used to stabilize soft foundationsTypically woven geotextile (stronger, less flexible) for stabilizationAdd cushion layer of crush granular on top of geotextile to minimu=ize puncturing by equipment9Base Preparation

Culverts InstallationCompacted Pitrun as base materialUse perforated pipes running full length to handle groundwaterCompact to 95% Proctor density, sheepsfoot roller, max. 150mm layers10Clay Seals

Culverts InstallationClay seals, extending into base, at both endsPrevents water movement through backfill that may result in loss of fine material11

Bed PreparationSmall Pipe Flat BedLarge Pipe Pre-shape BedCulverts InstallationSmall pipe flat bed, loose surface of uncompacted gravel (150mm), ensure contact between corrugations and baseLarge pipe use form to pre-shape loose gravel (150mm) minimize rotation, reduce pipe deflections, ensure uniform contact, 12


Culverts InstallationCamber longitudinal pre-shapingUse in high fill casesPredict settlement and build in, so linear slope results in time13

Assembly - FloorCulverts InstallationPreferable to start at d/s end (laps away from flow)All bottom plates connected and aligned before attaching side plates14Correct Seam LappingIncorrect Seam LappingAssembly - Seams

Culverts InstallationSeams bolt in valley should be nearest to edgeMore ductile, less potential for cracking15

Assembly Side Plates

Culverts InstallationSide plates, roof plates, and bevel ends can be pre-assembled off to the side while the floor plates are being assembledSide plates are attached to the floor alternating side to side to minimize spiralling from eccentric loads

16Assembly Roof PlatesCheck DimensionsControl Shape

Culverts InstallationRoof plates are then addedAfter 2 complete rings check dimensionsControl shape with cable stays and/or scaffolding17CSP Pipe Assembly

Culverts InstallationCSP Pipe comes as complete ringsThey are lifted off the truck, not rolledAssemble using steel band couplersBottom half of coupler is placed before next section of pipeComplete pipe is laid out before top halves of couplers are bolted to bottom halves18

Prepare for BackfillCulverts InstallationMark limits of fill on pipe with spray paintNote clay/gravel limitsFill height limits ensure symmetrical fill placed on both sides19Backfill - Haunch

Culverts InstallationHaunch tight area between bed and sidewallsCritical to structural integrity of pipeFilled with crush granular, small handheld compaction equipmentIf high pressure water jetting, need appropriate nozzle pressure and application pattern20Backfill - Haunch

Culverts InstallationAll corrugations filled21Backfill - Sides

Culverts InstallationAbove haunches still use small equipment (minimize stresses on pipe)Spread and compact in 150mm layersKeep balanced (within 300mm) on both sides avoid distortion, rolling)Move equipment parallel to the pipe22Backfill Clay Seal

Culverts InstallationClay Seal backfill concurrent with rest of backfillLarge equipment (Sheepsfoot roller) required for clay23Backfill Top of Culvert

Culverts InstallationNear the crown, move perpendicular to the pipeNo large equipment should be above the pipe until substantial; cover is in place24Backfill Frozen ConditionsStockpileMobile Asphalt Plant

Culverts InstallationTo be avoidedIf to be done:Stockpile prior to freezing, use one area of stockpile at a time, avoid frozen skinGranular material should be dry, can use mbile asphalt plantIce and snow to be removed from compaction zoneCompact quickly, scarify surface if more than one day between placement and compaction25Concrete End Treatment

Culverts InstallationConcrete End Treatment larger pipes, u/s and d/sLow volume of concrete, but detailed formworkComponents:Cutoff wall below invertSloping shouldersHeadwallPurpose:Reinforce bevel endsResist uplift forcesPrevent piping26Cutoff Wall Before Backfill

Culverts InstallationIf cutoff wall built before backfill, advantages are:No re-excavationMinimize volume of concreteAllows formwork to be re-usedConfines backfill27Cutoff Wall After Backfill Reinforcing SteelFormwork

Culverts InstallationAfter Backfill:Excavate (sump/pump to keep dryReinforcing Steel and shear connectorsPlace forms brace to handle pressureConcrete poured, 24 hours to cure before stripping forms28Shoulders and HeadwallShouldersHeadwall

Culverts InstallationHand excavate for sloping shouldersDrill holes for anchor bolts, place rebar, build formsForms and concrete are done contiguously for shoulders and headwallAllow 24 hours for curing before stripping forms29Rock Protection

Culverts InstallationTrim banks for rock placementTop of rock should be flush with the sloping shoulders (or bevel end if no concrete end treatment)Rock is underlain with non-woven geotextile (can stretch)Rock has already been tested for durabilityRock is placed with a backhoe caution adjacent to concrete end treatment30