Constructing a basement in urban or congested areas often requires innovative techniques to ensure safety and stability, especially when excavation is deep or adjacent properties are close by. One effective method is using shore piles along with inclined anchors to support the excavation and retain earth pressure. This blog explains the step-by-step process of constructing a basement using this system.
1. What Are Shore Piles and Inclined Anchors?
Shore Piles are temporary or permanent retaining elements installed vertically along the excavation boundary. They provide lateral support to prevent soil collapse.
Inclined Anchors (also called tieback anchors) are steel tendons or rods inserted at an angle into the soil or rock behind the retaining system. They provide additional support by anchoring into stable strata, effectively resisting lateral loads.
2. Step-by-Step Basement Construction Process
Step 1: Site Survey and Soil Investigation
- Conduct a detailed topographical and geotechnical survey.
- Determine soil strata, water table level, and load-bearing capacity.
- Identify nearby structures that may be affected by excavation.
Step 2: Design of Retention System
- Based on soil data, design the shore pile spacing, diameter, and depth.
- Design inclined anchors’ angle, depth, and tension force required.
- Consider construction loadings, surcharge from adjacent buildings, and groundwater pressure.
Step 3: Installation of Shore Piles
- Use techniques such as rotary drilling, bored piling, or driven piles.
- Install piles along the excavation boundary at pre-defined spacing.
- Allow piles to cure (if concrete) and achieve the required strength.
Step 4: Initial Excavation and Anchor Drilling
- Start excavation in layers (benching), typically 1.5 to 2 meters at a time.
- After each layer, drill inclined holes behind the shore pile wall.
- Insert high-tensile steel anchors and grout them into position.
Step 5: Anchor Tensioning
- After the grout has set, apply tension to the anchors using hydraulic jacks.
- Lock the anchors against the waler beam (steel or concrete), which distributes the anchor force to the pile wall.
- Repeat excavation and anchor installation layer by layer.
Step 6: Dewatering and Waterproofing
- Control groundwater using sump pumps, well points, or recharge wells.
- Apply basement waterproofing (membranes or coatings) to internal surfaces.
- Install drainage systems to prevent water accumulation behind the retaining wall.
Step 7: Basement Raft and Retaining Wall Construction
- Lay the basement raft slab over compacted and waterproofed subgrade.
- Construct RCC retaining walls along the pile face, integrating them with the raft and intermediate slabs.
- Ensure construction joints are properly sealed.
Step 8: Removal or Retention of Anchors (if temporary)
- If the anchors are temporary, they may be released or cut off after the full basement structure is completed and self-supporting.
- Permanent anchors are usually grouted and left in place.
3. Advantages of Shore Piles and Inclined Anchors
- Suitable for deep basements in confined areas.
- Minimizes risk to adjacent structures.
- Allows controlled excavation and better working space.
- Anchors reduce pile size and spacing requirements by sharing lateral loads.
4. Key Considerations for Success
- Ensure anchors are tested for load-bearing capacity.
- Monitor ground movement and structure settlement during construction.
- Maintain proper sequencing between excavation, anchoring, and slab casting.
- Comply with local building codes and safety norms.
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