03. Basements - Retaining Walls

03. Basements - Retaining Walls

System Manual
Unconfined_01. BOQ with Specs, Checklists_Basement-Retaining Walls.xlsxConfined_01. BOQ with Specs, Checklists_Basement-Retaining Walls - Copy.xlsx

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:

  1. Soil report
  2. Groundwater table
  3. Soil type
  4. 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)
HDPE Membrane Waterproofing

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

SpecX Masterclass: Basements - Retaining Walls Waterproofing — Coming Soon

Disclaimer

SpecX 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.