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Adjustments to existing Manholes

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Manhole adjustments are required when the existing finish level is incorrect due to changes in site conditions. This could mean:
1️⃣ Lowering the manhole if it is too high.
2️⃣ Raising the manhole if more fill is planned for the area.

While this may sound simple, adjusting an existing manhole can sometimes be more expensive than building a new one due to the complexity of modifications, material waste, and additional structural work.

1. Raising an Existing Manhole

🔹 Standard Issue

  • Manholes like DTC-2203 (DN1050) and DTC-2200 (DN1200) have a tapered top section.
  • If a manhole needs to be raised by 1 meter, the taper section cannot simply be extended.

🔹 Solution & Process

  • Step 1: Cut off the tapered section of the existing manhole.
  • Step 2: Pour a 1-meter-high extension to raise the height.
  • Step 3: Reinstall a new tapered section on top.

🔹 Additional Cost Considerations

✅ Cutting & Demolition Costs – Removing the tapered section properly.
✅ Formwork & Setup – New formwork for the 1-meter extension.
✅ Concrete Pouring – Extra concrete volume required.
✅ Concrete Testing – To ensure compliance with Sydney Water specifications.
✅ New Lid Allowance – If the existing lid no longer fits or is damaged.
✅ Disposal of Cut-Off Section –

  • The removed piece cannot be reused.
  • It needs to be broken down into smaller pieces for transport.
  • Tipper & Tip Fees must be included in the estimate.
  • Tip fees for general waste are higher than for clean concrete, so confirming disposal costs is crucial.

🔹 Additional Consideration for DN1200 (DTC-2200) Manholes

  • These contain steel reinforcement cages inside the concrete.
  • Cutting and modifying the steel cage is much more time-consuming than cutting plain concrete.
  • Labor, cutting tools, and setup time increase significantly.
Talk to Estimator

2. Lowering an Existing Manhole

🔹 Standard Issue

The manhole finish level is too high and needs to be lowered.

🔹 Solution & Process

  • Step 1: Cut the manhole down to the required height.
  • Step 2: Reinstall the lid or pour a new transition section if required.

🔹 Additional Cost Considerations

✅ Cutting & Demolition Costs – Cutting reinforced concrete is labor-intensive.
✅ Disposal of Cut-Off Section – Needs tipping allowance for general waste.
✅ Adjusting Internal Benching – If we cut the manhole too low, internal benching may need to be reconstructed.
✅ New Lid Allowance – If the cut affects the lid compatibility.
✅ Manhole Sealing – If the existing joints are compromised, grouting or sealing work may be required.

3. Key Estimating Factors for Manhole Adjustments

✔ Site Inspection is Crucial

Depth, reinforcement, liner presence, and structural impact must be checked on-site.

✔ Cutting & Demolition Needs to be Priced Separately

Cutting through steel-reinforced concrete is much harder than standard concrete.

✔ Liner Extensions Must Be Accounted For

If a corrosion-resistant liner is present, it must be extended properly.

✔ Concrete Testing Costs

If additional concrete is poured, Sydney Water may require strength testing.

✔ Disposal Costs Can Be Significant

  • If the cut-off section cannot go to a concrete recycler, general waste tipping fees apply.
  • Confirm disposal costs with the tip before finalizing the estimate.

✔ Allow for Additional Backfilling & Compaction Testing

  • If soil is disturbed while working, backfill material and geotechnical testing may be required.

Accurate Estimating = Preventing Unexpected Costs

Estimating manhole adjustments requires a detailed breakdown of:
✅ Cutting & demolition
✅ Disposal & tip fees
✅ Concrete, steel, and liner adjustments
✅ Formwork & pouring costs
✅ New lid allowance & internal benching work

📧 Contact WSE Sydney for expert estimating:
📧 tenders@watersewerestimatingsydney.com.au
📞 +61 451 404 645

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