Foundation Preparation for Single-Story Prefabricated Houses
Foundation preparation for single-story prefabricated houses requires special attention to soil investigation, excavation depth, cushion layer construction, ground beam specifications, and foundation moisture-proofing. Details are as follows:
Soil Investigation: The soil on rural homesteads is complex and diverse, potentially including filled-in ponds, soft mud, mixed sand and loose soil, among others. Before starting construction, a soil investigation must be carried out to determine the type of foundation based on the investigation results. For example, for soft soil foundations, replacement can be used to substitute the soft soil with higher-strength materials; if the soil conditions are poor, raft foundations or pile foundations can be considered to ensure the stability of the foundation.
Excavation Depth: The excavation depth should be based on reaching the hard soil layer (old soil) and entering it by 20 centimeters. Under normal terrain conditions, the old soil layer is commonly found at a depth of about 1 to 1.5 meters. When excavating the foundation pit, ensure that the bottom soil layer is uniform. If there is soft soil locally, it needs to be replaced and compacted; when encountering groundwater, timely drainage is required to prevent water accumulation in the foundation pit from affecting construction quality. After the foundation pit is excavated, it should not be exposed to the sun or rain for a long time. Construction should proceed to the next step as soon as it passes inspection.
Cushion Layer Construction: At the bottom of the treated and compacted foundation trench, a 10-centimeter-thick cushion layer of C15 or C20 plain concrete needs to be poured. The cushion layer provides a flat working surface, facilitating the subsequent binding of steel reinforcement cages and the installation of formwork; it also isolates the foundation from the soil layer, preventing soil from mixing into the foundation concrete; and protects the steel reinforcement from ground moisture erosion, making the foundation force more evenly distributed.
Ground Beam Specifications: The ground beam is the 'belt' between the foundation and the wall, serving to connect the entire foundation into a whole and prevent wall cracking due to uneven settlement. The cross-sectional width of the ground beam should not be less than the wall thickness, the cross-sectional height should not be less than 24 centimeters, there should be no fewer than 4 longitudinal steel bars, the diameter of the steel bars should not be less than 12 millimeters, and the diameter of the stirrups should not be less than 6 millimeters.
Foundation Moisture-Proofing: Moisture-proofing can be achieved by laying a moisture-proof membrane or constructing a prefabricated board elevated layer. When laying a moisture-proof membrane, after backfilling and compacting the foundation, first lay a layer of fine sand and gravel, compact and level it, then lay a layer of high-density polyethylene film (such as PE film or geotextile) with a thickness of more than 0.15 millimeters, and finally pour a 10-centimeter-thick concrete cushion layer or floor on the moisture-proof membrane. When constructing a prefabricated board elevated layer, after pouring the ground beam, control the backfill height at a distance of 30 to 50 centimeters from the ground, compact the backfill, and leave a cavity between the foundation and the first-floor ground, allowing underground moisture to rise into the cavity and dissipate.
