1. Introduction
Retaining walls are critical elements in basement construction, exposed to soil pressure, groundwater, and hydrostatic head. Waterproofing solutions vary depending on whether the positive side of the wall (soil-facing surface) is accessible for application or not.
- Confined Retaining Walls
- Occur where the wall is cast directly against soil support systems (e.g., diaphragm walls, shore piles, contiguous piles).
- The positive side (soil side) is not accessible after casting, so waterproofing must be pre-applied before concreting.
- Systems must bond integrally with fresh concrete to avoid lateral water migration.
- Typical solution: HDPE pre-applied bonded membranes, PVC compartmentalized systems.
- Unconfined Retaining Walls
- Found in open excavations, where the soil-facing side of the wall remains accessible after construction.
- Waterproofing is applied externally on the positive side after the wall has cured.
- Multiple membrane systems are possible, with protection boards/drainage layers to manage soil & backfill pressure.
- Typical solution: SBS modified bitumen membranes, spray-applied PU membranes, crystalline coatings.
Retaining walls in basements require robust waterproofing due to constant exposure to soil, groundwater, and hydrostatic head. Selection depends on:
- Soil report
- Groundwater table
- Soil type
- Space for execution on positive side
2. Area of Waterproofing
- Positive Side → applied directly on soil-facing side (preferred).
- Negative Side → inner face application, used in repairs or as supplementary system.
3. Types of Retaining Wall Waterproofing
- Confined Walls → positive side inaccessible (shore piles, diaphragm walls).
- Unconfined Walls → positive side accessible (open excavation).
4. Confined Retaining Walls
Recommended: HDPE Pre-applied bonded membranes, PVC compartmentalized sheets.
Property | HDPE Membrane (Fully Bonded) | Read More |
Suitability | Confined areas (shore piles, diaphragm walls) |
Documents:
Decision Guide
- Confined retaining walls (positive side inaccessible): Prefer pre-applied fully bonded HDPE or PVC compartment systems to prevent lateral migration.
- Unconfined retaining walls (positive side accessible): Use SBS or PU systems with protection board; ensure drainage and soil-side protection.
- Negative-side only scenarios: Consider injection grouting to stop active ingress, then apply breathable cementitious as supplementary treatment.
5. Video Masterclass
Conix Masterclass: Basements - Retaining Walls Waterproofing — Coming Soon
Disclaimer
Conix is an industry initiative & a neutral resource, compiled from industry references and best practices. It is not brand-specific. Always cross-check with project requirements and local codes before finalizing specifications.
