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Flexible application of pile-row retaining structures for excavation support.

Release time:

2017-07-27

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Pile-supported retaining structures are foundation excavation support systems composed of various types of piles arranged in a row-like configuration. The most commonly used pile types are reinforced concrete bored piles and cast-in-place piles; other types include PCS retaining piles, PRC retaining piles, I-beam piles, or H-shaped steel piles.

Pile groups can be configured according to the project conditions. Cantilever support structures, anchor-supported support structures, internal bracing support structures, and bolt-supported support structures 。

Applicable conditions:

1. Suitable for excavation side walls with safety levels I, II, and III;

2. Cantilever structures are not recommended to exceed 5 meters in soft soil sites.

3. When the groundwater level is higher than the bottom of the excavation pit, it is advisable to adopt dewatering, pile walls with cutoff curtains, or underground continuous walls.

Pile wall support structure:

① Column-row pile retaining structure: When the slope soil is of good quality and the groundwater table is low, the soil arching effect can be utilized by employing sparsely arranged bored piles or drilled shafts as the retaining structure.

② Continuous pile support: In soft soils, soil arching often cannot be formed. Therefore, the supporting piles should be arranged in a continuous and closely spaced manner, with root piles or grouting for waterproofing provided between the piles. Alternatively, steel sheet piles or reinforced concrete sheet piles can also be used in a closely spaced configuration.

③ Combined Pile Wall Support: In soft soil areas with high groundwater levels, a combined system of bored cast-in-place piles and cement-mixing piles forming an impermeable wall can be adopted. For excavations with depths less than 6 meters, when gravity-type deep mixing piles cannot be used, closely spaced 600-mm bored piles can be employed, followed by root pile reinforcement behind the piles. Alternatively, precast concrete sheet piles or steel sheet piles can be driven into place, with grouting or additional mixing piles used for seepage control behind the sheet piles; a ring beam and supports should be provided at the top. For excavations with depths ranging from 6 to 10 meters, 800- to 1000-mm bored piles are commonly used, supplemented by deep-layer mixing piles or grouting for waterproofing, along with 2 to 3 support levels. For excavations deeper than 10 meters, either a diaphragm wall with supports or large-diameter 800- to 1000-mm bored piles combined with deep-layer mixing piles for waterproofing, accompanied by multiple support levels, can be employed.

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