Commonly used methods to deal with wet subsidence loess foundation are, plain soil pile squeeze dense method, water immersion treatment. It can be selected according to the conditions of foundation wet subsidence type, grade, and requirements of structures.

Gray soil or plain soil bedding

Dig out or dig to the expected depth all the wet subsidence soil layer below the foundation, and then backfill with gray soil (three parts of lime and seven parts of soil) or plain soil (clay soil dug out on the spot) compacted in layers, the thickness of the bedding layer and the size of the calculation method is the same as that of the gravel bedding layer, and the pressure diffusion angle φ adopts 30 ° for the gray soil, and adopts 22 ° for the plain soil. The thickness of bedding layer is generally 1.0~3.0 m. It eliminates the wet subsidence of soil within the range of bedding layer, and reduces or avoids the wet subsidence generated by the additional stress of foundation gene, such as digging out the part of σh + γh ≥Phs in the holding layer of the foundation, and adopting the bedding layer, it can eliminate the wet subsidence of the non-self-weight of the foundation. It is easy to construct and effective, and is a commonly used method for shallow wet subsidence treatment or partial treatment of foundations. Construction must ensure the quality of the project, the backfill of gray soil, plain soil layer, should control its water content and large dry density, otherwise it will not achieve the expected results.

Heavy hammer tamping and strong tamping method

Heavy hammer tamping method can eliminate the shallow layer of wet subsidence, such as with 15~40kN heavy hammer, fall height 2.5~4.5m, in the case of water content, can eliminate the wet subsidence in the soil layer in the depth of 1.0~1.5m. Strong tamping method according to the domestic use of records, in the hammer weight of 100 ~ 200kN, free fall height of 10 ~ 20m, hammering two times, can eliminate the wet subsidence of soil layer within the range of 4 ~ 6m.

Both methods should be carried out beforehand on-site tamping test, in order to determine to achieve the desired treatment effect (a certain depth of the elimination of wet subsidence) necessary for the tamping point, the number of hammer blows, tamping volume, etc., in order to guide the construction, quality assurance.

Lime soil or ash squeeze pile

Use pile driving, drilling or explosive expansion methods to form holes in the soil, and then use lime soil or mix lime and fly ash to fill the pile holes in layers (a few are also used in plain soil), and destroy the loose and large hole structure of loess foundation by compacting method, so as to eliminate or alleviate the wet subsidence of the foundation. This method is suitable for eliminating the wet subsidence of foundation soil within 5~10m depth. The effect of compact pile depends on the degree of soil being compacted, the pile diameter and pile distance should be determined by test in the field, and the dry density of foundation soil at the edge of compacted range should be more than 16.0kN/m3. When using compact pile to treat wet subsidence loess foundation, waterproofing measures should be taken on the surface layer of foundation (e.g. surface tamping, etc.).

Pre-soaking treatment

Self-weight wet subsidence loess foundation utilizes its self-weight wet subsidence property, and can be fully soaked in water before the structure is built, so that it will be wet subsidence under self-weight, and then built. Practice has proved that this can eliminate several meters below the surface of the loess outside of the self-weight wet subsidence, the surface of the soil layer within a few meters is often due to the pressure is low and still have wet subsidence, have to be dealt with again. In addition, consideration should also be given to the effects of cracking and subsidence that may occur on the nearby ground surface after pre-soaking.