Foundation for Two-Story Prefabricated Houses

The design and construction of foundations for two-story prefabricated houses should be based on geological conditions, load requirements, and regulatory standards. Common solutions and key points are as follows:

I. Foundation Type Selection

1. Strip Foundation: Suitable for ordinary geological conditions (e.g., silty clay, dense sand), with relatively low costs. Construction steps include foundation layout, trenching (approximately 1 meter deep), preparation of the bedding layer (commonly using tri-mix soil), and stone or brick masonry (blue stone or 37-wall). Reinforcement is recommended using 10 or 12 rebar, with a width of about 40 centimeters and a height of 30-40 centimeters. If the characteristic value of the foundation bearing capacity fak ≥ 120 kPa (e.g., silty clay foundation), a reinforced concrete strip foundation can be used, with a total length of 86 meters, a width of 1.2 meters, a buried depth of 1.5 meters, a concrete strength grade of C30, and HRB400-grade rebar.
2. Isolated Foundation: Suitable for areas with poor geological conditions (e.g., shallow water layers, loose sand), requiring excavation to the rock layer (about 2 meters deep) to enhance stability. A geological survey must be conducted before construction to determine the depth and reinforcement measures (e.g., reinforcement for loose sand).

II. Foundation Depth Reference

The foundation depth should be adjusted according to soil type:

• Rock Foundation: 0.5-1 meter;
• Dense Sand: 1.5-2 meters; Loose Sand: 2-2.5 meters (requires reinforcement);
• Soft Clay: 2-3 meters; Hard Clay: 1.5-2 meters.
  For complex geological conditions (e.g., soft clay or shallow water layers), a professional institution should be commissioned to conduct a geological survey to ensure foundation stability.

III. Precautions for the Use of Prefabricated Components

1. Prefabricated Slabs: Cost about half as much as cast-in-place slabs but have a service life of about 50 years and poor seismic resistance and integrity. If prefabricated slabs are used, ensure the structural integrity of the caps, ground beams, columns, and ring beams, and that the rebar configuration meets safety requirements (e.g., rebar ratio, anchorage length).
2. Cast-in-Place Slabs Preferred: When economically feasible, it is recommended to prioritize cast-in-place slabs, which can significantly improve the house's load-bearing capacity, seismic resistance, and durability, especially in areas with poor geological conditions or high load requirements.

IV. Construction and Acceptance Requirements

1. Before construction, a specialized plan should be prepared, specifying material standards (e.g., cement using P·O 42.5 grade, sand with a mud content ≤ 3%) and equipment configuration (e.g., excavators, concrete mixers).
2. During construction, strictly follow the design drawings and regulatory requirements, focusing on controlling the quality of concrete pouring, rebar spacing, and foundation depth.
3. After completion, a professional institution should be commissioned to conduct acceptance tests to ensure that indicators such as foundation bearing capacity and settlement meet standards.