Prefabricated House Foundation

The construction of a prefabricated house foundation should follow these key steps and specifications:

1. Geological Survey and Design Adaptation
Before construction, conduct a detailed geological survey of the site. Analyze soil layer distribution by excavating test pits with a depth of ≥1.5 meters, focusing on identifying unfavorable soil layers such as soft soil and silt. The foundation bearing layer should be selected as stable old soil with a characteristic bearing capacity of ≥120 kPa, and the burial depth should meet regional requirements: ≥0.5 meters in southern regions and exceeding the frost line by 0.2 meters in northern frozen soil areas. If the groundwater level is higher than the designed foundation elevation, drainage ditches and collection wells should be installed for dewatering to prevent groundwater infiltration from affecting foundation stability during construction.

2. Material Preparation and Quality Control

• Sand and Gravel: Use well-graded medium-coarse sand (silt content ≤3%) and crushed stone with a particle size of 5-30 mm (crushing value ≤20%), mixed in a 3:7 ratio to ensure foundation material strength.
• Cement: Select P·O42.5 ordinary Portland cement with an initial setting time of ≥45 minutes and a final setting time of ≤600 minutes to prevent material failure due to construction interruptions.
• Reinforcing Steel: Use HRB400E grade reinforcing steel for foundation ring beams, with a diameter of ≥12 mm, a yield strength of ≥400 MPa, and no cracks or rust on the surface to ensure structural tensile performance.
• Masonry Units: Use MU10 grade fired common bricks with a compressive strength of ≥10 MPa and a water absorption rate of ≤15% to ensure a stable connection between the wall and foundation.

3. Foundation Treatment Methods

• Compaction Method: Repeatedly compact the soil layer using a pneumatic hammer or heavy roller to increase soil density to meet bearing capacity standards.
• Soil Replacement Method: Replace loose soil with higher-density materials (such as sand and gravel), suitable for areas with shallow soft soil layers.
• Piling Method: Insert reinforced concrete piles into soft soil layers to enhance foundation stability through friction between the piles and soil, suitable for areas with complex geological conditions.

4. Foundation Pit Excavation and Support

• Surveying and Setting Out: Set out the foundation pit excavation line according to the building axis and install reference stakes to control the axis, with an allowable deviation of ±5 mm.
• Layered Excavation: Switch to manual clearing when mechanical excavation reaches 20 cm above the foundation base to avoid disturbing the undisturbed soil; the slope coefficient should be determined based on soil type (e.g., 1:0.5 for clay and 1:1.5 for sand).
• Slope Support: Adopt a composite system of "sloping + soil nailing wall" with a slope ratio of 1:1.25, two-stage sloping, and a platform width of 1.5 meters to prevent slope collapse during excavation.

5. Foundation Compaction Treatment
Use a frog hammer to compact the plain soil in layers, with a virtual铺厚度 of 250 mm per layer and a compaction coefficient of ≥0.94 to ensure uniform and dense foundation and avoid future settlement.

6. Damp-Proofing Treatment

• Laying Damp-Proof Membrane: Lay fine sand and crushed stone on the surface of high-density polyethylene film (PE film or geotextile) and compact it for leveling, then pour a concrete垫层 to block ground moisture.
• Prefabricated Slab Elevated Floor: Leave a 30-50 cm cavity between the foundation and the ground to allow moisture to dissipate and prevent dampness on the first-floor ground.