Mingha Bluff culvert install 5

Threading on of six rebars through the culvert.

The last metre requires carefully executed hydraulic pressure.

Mixing the concrete for the two wing wall’s reinforced joints.

The concrete mix is delivered to the top of the culvert in an excavator bucket.

As with the culvert sections, the wing walls are pre-levelled when shackled to the crane lifting harness.

The first rebar is tensioned.

Fitting the rebar tensioning kit to the second rebar.

The excavator boom affords safe and efficient movement and capture of the heavyweight hydraulic tensioning components.

The tension is taken up by hand tightening the rebar lock nuts.

The hydraulic tensioning machine is well armoured.

Many hands assist the work proceeding at speed in tight spaces at the floor of the culvert.

The wing walls are first bolted to affix to the culvert’s downstream end.

Joining the wing walls quickly and safely is a coordinated team effort aided by a pair of pneumatic drills.

Eastside galvanised steel boxing affixed, ready to receive concrete.

Affixing westside boxing.

Concreting the steel reinforced wing wall joints.

Affixing the wing wall’s temporary prop.

9:00–10:43 pm, completion of culvert installation

Immediately after the final upstream section of culvert was placed at 9:10 pm, the 6 x high-tension steel threaded rebars were completely pushed through the 10.5m culvert. The multi-thread 80 ton post-tensioning of the culvert was executed using a Hydraulic Steel Rebar Tensioner. The task of tensioning the first tierod got underway just before 9:30 pm.

While 80 ton of tension is applied to the high-tensile steel threaded rebar by a hydraulic tensioner, the tension is taken up by manually tightening the rebar lock nut. The multiple rebar threads are tightened in a sequence around the culvert, akin to refitting a wheel when fixing a flat tyre.

Placement and affixing of the two downstream wing walls

Craning the downstream eastern wing wall into position.

At the same time as the multi-threads were being post-tensioned, the balance of the TruLine crew completed the placement, joining and reinforced concreting in place of the two wing walls at the northern end of the culvert. This task got underway at 9:28 pm and was completed with the affixing of the two wing wall’s temporary prop at 10:45 pm. This event marked the end of the culvert install task.

The penultimate task. Filling the western wing wall joint boxing with concrete the old fashioned way.

Backfilling

After a 30 minute smoko, including a generous slap-up barbecue accompanied by lashings of hot food delivered to the site, backfilling the trench got underway. The trench was filled evenly on each side up to the level of the top of the culvert, care was taken to not disturb the box culvert alignment. Fill was done in well-compacted layers of AP65 with the layers not exceeding 30cm.

The compacted haunching extended 1m either side of the culvert at the invert, and this fanned out progressively wider as the fill came up to 1.2m over the the 2.4m square box culvert.

Then to finish 600mm of railway ballast was laid up to the rail level, at which point the trench was completely backfilled. The backfill was matched to existing ground condtions and extended out to the end of the North Side wing walls.

The box culvert installation job was complete when the rail was lifted, levelled and reinstated.