During construction, the foundation should be promptly reinforced or improved to meet the requirements of the upper structure. Appropriate foundation treatment methods must be applied to ensure stability, enhance the bearing capacity of the foundation soil, minimize settlement or uneven settlement of the building, and reduce the collapsibility of collapsible loess while improving its resistance to liquefaction. The commonly used foundation treatment methods in construction are outlined below.
1. Dynamic Compaction Method
The dynamic compaction method involves lifting a heavy rammer with machinery to a specified height and then repeatedly dropping it to compact the foundation soil. This process forms a dense, hardened surface layer that increases soil strength, decreases compressibility, and reinforces the foundation. Additionally, it improves the soil’s resistance to vibration-induced liquefaction and eliminates soil collapsibility.
This method is typically used for deep reinforcement of cohesive soils, sandy soils, collapsible loess, miscellaneous fill, and layered fill soils that are slightly wet and located at least 0.8 meters above the groundwater level. During construction, seismic isolation measures—such as digging anti-seismic trenches deeper than the building’s foundation—should be implemented to reduce vibration and noise from dynamic compaction, minimizing its impact on nearby structures and facilities.
2. Sand and Gravel Pile Method
The sand and gravel pile method creates holes in weak foundation soils using vibration, impact, or water flushing. Sand, gravel, or crushed stone is then inserted into these holes to form large-diameter, dense piles composed of sand or gravel. These piles reinforce the foundation by increasing the bearing capacity and reducing soil compressibility.
This method is suitable for compacting loose sand, silt, cohesive soils, plain fill, and miscellaneous fill. It is also effective for treating liquefiable foundations. In projects where deformation control of prefabricated structures on saturated clay foundations is critical, sand and gravel piles can be used to replace soil and form a composite foundation. This accelerates drainage and consolidation of soft soils, ultimately strengthening the foundation.
3. Compaction Pile Method
The compaction pile method uses mechanical (manual or explosive) drilling, typically driving steel pipes into the soil with a hammer. These pipes laterally compact the surrounding soil to create pile holes. After removing the steel pipes, the holes are filled with a mixture of 20-30% plain soil or gray soil, which is compacted in layers. This process forms a composite foundation that supports the upper load and reinforces the foundation.
This technique is commonly applied to plain fill, mixed fill, and collapsible loess located above the groundwater level, with natural moisture content ranging from 12% to 25% and thickness between 5 to 15 meters. Treatment depth generally reaches 5 to 10 meters, with a required compactness of at least 0.95 during construction. When weak foundations have high moisture content, this method also effectively reinforces the foundation and eliminates loess collapsibility within the pile depth.
Article source: Architectural Technology Magazine
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