Hole Digging in Prefabricated Slab Houses

Extreme caution must be exercised when digging holes in prefabricated slab houses, and professional standards must be followed, as failure to do so may lead to structural safety hazards.

1. Characteristics of Holes and Original Design Logic

The original holes in prefabricated slabs typically have a diameter of 8 centimeters and are spaced 3 centimeters apart horizontally and vertically. Their design purpose is to reduce the weight of the floor slab and avoid critical load-bearing areas (such as the ends of the slab, the very center, and the positions of steel bars). The distribution of these holes has been optimized through structural calculations, and adding or enlarging holes randomly may disrupt the original load-bearing balance, leading to localized stress concentration.

2. Principles for Selecting Hole-Digging Locations

1. Avoid Load Concentration Areas: The middle of the floor slab or areas with larger spans are the main load-bearing points, and digging holes here will significantly weaken the structural load-bearing capacity.
2. Prioritize Proximity to Load-Bearing Components: Areas around beams, columns, or load-bearing walls have lower loads, and the risk of digging holes here is relatively lower. For example, digging holes within one-third of the span near walls has a smaller impact on the overall structure.

3. Specifications for Hole Size and Shape

1. Size Limitations: Small-sized (diameter or side length ≤ 15 centimeters) circular or square holes have a smaller impact on the structure; large-sized (such as those exceeding one-third of the slab thickness) or irregularly shaped holes may lead to stress concentration or insufficient floor slab stiffness.
2. Shape Optimization: Circular holes are better at dispersing stress and reducing the risk of cracking compared to square holes; if square holes are required, the corners should be rounded.

4. Professional Evaluation and Reinforcement Measures

1. Structural Engineer Evaluation: Before digging holes, a qualified engineer must confirm the distribution of steel bars, the thickness of the floor slab, and any existing damage, and calculate the changes in load-bearing after hole digging through structural mechanics analysis. For example, it is necessary to detect the positions of prestressed tendons to avoid cutting critical steel bars.
2. Reinforcement Methods:
   • Whole Slab Removal Method: If the hole is large, it is recommended to remove the entire prefabricated slab and replace it with cast-in-place concrete to ensure structural continuity.
   • Local Reinforcement: For small holes, the load-bearing capacity can be improved by increasing the cross-section at the top of the slab (such as pouring a composite layer) or pasting carbon fiber sheets at the bottom of the slab.

5. Risks of Unauthorized Hole Digging

Unauthorized hole digging may cut prestressed tendons or main steel bars, leading to ceiling deformation, cracks, or even collapse. For example, cutting a single Φ8 steel bar may reduce the load-bearing capacity of the floor slab by more than 30%. In addition, the repair cost after unauthorized operations is usually 3-5 times that of professional design costs, and it is difficult to fully restore structural safety.

Conclusion: Hole digging in prefabricated slab houses must be based on structural safety, strictly following professional evaluation, standardized construction, and reinforcement principles to avoid greater losses.