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Soil Nailing Wall, Bored Piles, Tieback Anchors & Foundation Waterproofing Guide

1. Soil Nailing Wall

Technical Specifications:

  • Nail Length: 0.5–1.2 times excavation depth

  • Spacing: 1–2 m

  • Inclination Angle: 5°–20° from horizontal

  • Reinforcement: HRB335 or HRB400 steel bars (Ø16–32 mm)

  • Drill Hole Diameter: 70–120 mm

  • Grout Strength: ≥ M10

  • Shotcrete Face: ≥ C20 concrete, ≥ 20 mm rebar cover

Construction Sequence:

  1. Slope trimming → 2. Drilling → 3. Nail installation → 4. Grouting → 5. Mesh & reinforcement binding → 6. Shotcrete application

Key Requirements:

  • Groundwater must be controlled before construction

  • Shotcrete machine range: ≥100m horizontal, ≥30m vertical

  • Air compressor: ≥9 m³/min flow rate, >0.5 MPa pressure

  • Delivery hose pressure rating: ≥0.8 MPa

2. Bored Piles

Technical Specifications:

  • Cantilever Piles: Minimum Ø600 mm

  • Capping Beam: Width ≥ pile diameter, height ≥400 mm (≥C20 concrete)

  • Vertical Tolerance: ≤0.5% deviation

  • Positioning Tolerance: ≤50 mm

Construction Sequence:

  1. Drilling → 2. Rebar cage installation → 3. Concrete pouring → 4. Capping beam construction

Reinforcement Details:

  • Stiffening hoops: Welded to main bars

  • Spiral ties: Wire-tied to main bars

3. Tieback Anchors

Applications:

  • Combined with soldier piles or soil nailing systems

Construction Sequence:

  1. Drilling → 2. Tendon installation → 3. Grouting → 4. Curing → 5. Anchorage assembly → 6. Stressing

Quality Controls:

  • Position Tolerance: ≤100 mm

  • Inclination Tolerance: ≤3%

  • Grout Strength: ≥15 MPa (75% design strength before stressing)

Load Transfer:

Anchors connect to piles via steel wale beams for force distribution.

4. Internal Bracing Systems

Structural Options:

  • Steel Bracing:

    • Connections: Welded or high-strength bolted

    • Wale beam joints: Within 1/3 of the span from supports

    • Pile interface: ≥C20 fine concrete infill

    • Stiffener plates are required at connection nodes

  • Concrete Bracing:

    • Minimum concrete grade: C20

    • Monolithic casting within each plane

    • Rigid corner connections

Critical Notes:

  • Install load-transfer elements before bracing removal

  • Custom engineering is required for geometry, sections, and connections

5. Earthwork Excavation

Planning Requirements:

  1. Excavation Drawings must show:

    • Cut/fill lines, footing locations, elevation markers

    • Deep excavation zones with upper/lower level indicators

  2. Phased Excavation (Soil Nailing Applications):

    • Example: 2 major phases + 6 sub-phases

    • Initial: 3 sub-phase cuts → Central bulk excavation

    • Followed by bottom-up excavation (300 mm soil left for manual trimming)

Winter Work Precautions:

  • Prevent subgrade freezing using loose soil or insulating covers

Waterproofing Systems

1. Concrete Waterproofing (Basement Slab & Walls)

Material Specifications:

  • Cement: ≥32.5 MPa

  • Aggregates:

    • Sand: Medium grade, ≤3% silt, ≤1% clay lumps (non-alkali reactive)

    • Gravel: 5–40 mm, ≤1% silt, ≤0.5% clay lumps

Admixtures:

  • Fly ash (≥Grade II, ≤20% content)

  • Silica fume (dosage by testing)

  • Permitted additives: Water reducers, expansion agents, crystalline materials

Waterproofing Methods:

A. Membrane Waterproofing

  • Base Slab: Empty-spread or spot-bonded application

  • Walls: Full-bonded application

  • Lap Joints: ≥10 mm overlap, staggered seams (1/3–1/2 width offset)

  • Corners: 500 mm reinforcement layer, 45°/135° fillets

B. Crystalline Coating

  • Pre-wet surfaces 15 minutes before application

  • Application: 50°–60° trowel angle, 0.8 mm total thickness

  • Cure: Immediate water spray after initial set

C. Polyurethane Coating

  • Weak Points: Additional layer at joints/pipes

  • Thickness: 1.2–2.0 mm (2 coats)

  • Masonry Tie-ins: Remove 2 brick courses for lap joints

2. Post-Construction Joint Waterproofing

  • Install the interior membrane protection layer first

  • Waterstop steel plates centered in the wall thickness

3. Exterior Waterproofing at Grade

  • Termination Point: 150 mm above finish grade

  • Sealing: Metal flashing + sealant (200 mm nail spacing)

  • Expansion Joint: 30 mm gap filled with elastic sealant

This technical guide complies with industry standards for foundation support systems and waterproofing best practices. Proper implementation ensures structural integrity and long-term water resistance.

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