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Professional Guide to Dewatering Well Sealing: Best Practices for Construction Sites

Introduction

Proper sealing of dewatering wells is critical to ensure structural integrity and waterproofing in construction projects. This guide outlines the step-by-step process for effective dewatering well sealing, following the “inside-out” principle for optimal results.

Key Principles of Dewatering Well Sealing

  • “Inside-Out” Approach: Seal wells starting from the center before moving to peripheral ones.
  • Pre-Sealing Water Level Control: Maximize dewatering around the target well to minimize internal water pressure before sealing.
  • Final Well Caution: Exercise extra care when sealing the last remaining wells.

Step-by-Step Sealing Process

1. Dewatering System Design

  • Analyze engineering drawings and geological conditions to design an efficient dewatering system.
  • For localized deep areas (e.g., elevator pits, sumps), place wells centrally or nearby for maximum efficiency.
  • Position wells in areas with thinner waterproof slabs to simplify sealing and reduce costs.
  • Avoid interference with structural elements (piles, columns, shear walls, foundation beams).

2. Dewatering Well Construction

  • Install wells and initiate dewatering operations.

3. Excavation Precautions

  • Protect well openings with composite bamboo plywood to prevent soil ingress.
  • Reserve 300mm of soil around wells for manual excavation to avoid mechanical damage.

4. Waterproof Steel Sleeve Fabrication

  • Use Φ325×8 hot-rolled seamless steel pipes (height ≥ combined slab & footing thickness).
  • Fabricate waterproofing external rings (≥6mm steel, OD ≥525mm) and weld at sleeve mid-height.
  • Weld internal flange bolts and base reinforcement (4xФ20x150mm rebars).

5. Sleeve Installation

  • Fix the sleeve centrally over the well before footing concrete placement.

6. Waterproofing Membrane Application

  • Extend the membrane up to the sleeve’s external ring, sealed with waterproof mastic.

7. Slab Construction

  • Install additional rebar around sleeves per design specifications.

8. Well, Backfilling

  • Phase dewatering shutdown:
    1. Stop interior dewatering first.
    2. Seal interior wells.
    3. Stop exterior dewatering.
  • Backfill with graded gravel (base) and dry Portland cement (upper 2m).

9. Flange Sealing

  • Install 10mm rubber gaskets and tighten bolts crosswise for airtight compression.

10. Concrete Placement

  • Fill sleeve with high-grade dry concrete (one class above slab mix) and compact thoroughly.

11. Curing Protocol

  • Secondary compaction before the initial set.
  • Cure with plastic sheeting and felt (≥14 days) to minimize shrinkage.

Conclusion

Adhering to this methodical sealing process ensures long-term waterproofing performance and structural stability. Always align sequencing and timing with real-time site monitoring and design requirements.

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