Construction Process and Technical Requirements for Capping Beam (Guide Beam)

1.1 Construction Process

The construction of the capping beam involves several critical steps to ensure structural integrity and compliance with design specifications.

1.2 Material Requirements

1.2.1 Concrete

• Grade: C30 commercial ready-mix concrete is used for the capping beam.

1.2.2 Reinforcement Steel

• Steel bars must meet design specifications in material and forming dimensions.

1.2.3 Formwork

1. Side Formwork: Prefabricated steel templates ensure smooth, clean, and deformation-free surfaces for easy demolding.

2. Reinforcement: Side formwork is secured using 10cm × 10cm wooden beams and 42mm diameter steel pipes with necessary fittings to ensure stability.

1.3 Key Construction Steps

1.3.1 Survey and Layout

• A professional survey engineer marks the capping beam alignment using the exchange method.

• After verification by on-site technicians, rebar binding proceeds.

• Once formwork is erected, the capping beam elevation is checked and marked inside the template.

1.3.2 Earthwork Excavation

• Excavation begins only after all supporting piles are completed and concrete reaches 75% of design strength.

• Method: Mechanical excavation with manual assistance to prevent damage to pile reinforcement.

• Soil is excavated 10cm above the capping beam base, followed by manual leveling to avoid soil disturbance.

• The final excavation depth is 5cm below the beam base, and excavated soil is transported to designated areas.

1.3.3 Pile Head Removal

• After exposing pile heads, manual jackhammers remove excess concrete and slurry up to the beam base level.

• Strict elevation control prevents damage to the underlying pile structure.

• Waste concrete is reused for backfilling, leaving a 30 cm-wide drainage trench beside the slope toe.

1.3.4 Base Leveling

• After excavation, a 5 cm-thick M10 mortar layer levels the base.

• Once hardened, template alignment lines are marked for precise formwork installation.

1.3.5 Reinforcement Works

1) General Requirements

• All steel bars must have factory certifications and pass lab tests before use.

• Surface must be free of oil, rust, or contaminants.

• Straightening is done via winch, with ≤2% elongation for Grade I and ≤1% for Grade II steel.

• Welding standards:

  • Double-sided weld ≥5d, single-sided ≥10d (d = bar diameter).

  • Electrodes: E43 for Grade I (stirrups), E50 for Grade II.

• Spacing rule: No more than 50% of bars may have joints within a 35d (≥500mm) zone.

2) Rebar Processing

• Cutting and bending follow design specs, with labeled storage to prevent mix-ups.

• Tolerances:

  • Main bars: ±10mm in length.

  • Stirrups: ±5mm in dimensions.

  • Bent bars: ±20mm.

3) Installation & Binding

• Clean and straighten pile-exposed bars before binding.

• Key rules:

  • Stirrups must be perpendicular to the main bars, with overlaps staggered.

  • Binding wires secure all intersections (100% for single-leg stirrups).

  • Spacers maintain concrete cover thickness.

• Allowable deviations:

  • Main bar spacing: ±10mm.

  • Layer spacing: ±10mm.

  • Stirrup spacing: ±10mm.

  • Cover thickness: ±5mm.

4) Embedded Parts & Openings

• Install steel plates, monitoring points, etc., per design, with reinforced fixing to prevent displacement during concreting.

1.3.6 Formwork Engineering

1) Construction Method

• Base: Plastic sheeting.

• Sides: 30×15cm steel forms with cup-lock scaffolding support.

• Bracing: Multi-layer steel pipe struts ensure dimensional accuracy.

2) Quality Control

• Templates must maintain precise geometry and alignment.

• Clean surfaces before concreting to enhance finish quality.

• Monitor for deformation during pouring and adjust immediately.

3) End Formwork

• Reinforced using longitudinal bars as tie rods or wedge anchors to resist concrete pressure.

4) Demolding

• Forms are removed after concrete reaches sufficient strength (timing depends on ambient temperature).

• Post-demolding, curing continues until compliance with standards.

1.3.7 Concrete Pouring

1. Pre-Pour Checks: Remove debris, pump out water, and inspect formwork.

2. Pour Length: Minimum 30m per batch to ensure continuity.

3. Compaction:

   • Use Ø35mm vibrators for dense zones.

   • Secondary vibration at pile-beam junctions prevents cracks.

   • Vibration time: ≥30 sec per point in a 50 cm-spaced grid.

4. Finishing:

   • Initial leveling with wood floats, final troweling after setting.

   • Workers use plywood walkways to avoid footprints.

5. Curing: Minimum 14 days of water curing (or insulation in cold weather).