Common ground treatment methods are: replacement cushion method, dynamic compaction method, gravel pile method, vibrating method, cement soil mixing method, high pressure jet grouting method, pre-compression method, compacted cement soil pile method, cement fine coal Grey crushed stone pile method, lime pile method, lime soil compaction pile method and soil compaction pile method, column hammer piling method, single liquid silicidation method and lye method.
1. The replacement padding method is suitable for the treatment of shallow weak foundations and uneven foundations. Its main role is to improve the bearing capacity of the foundation, reduce the amount of settlement, accelerate the drainage consolidation of weak soil layers, prevent frost heave and eliminate the expansion and contraction of expansive soil.
2. The dynamic compaction method is suitable for treating gravel soil, sandy soil, low-saturation silt and cohesive soil, collapsible loess, miscellaneous filling soil and plain filling soil. The dynamic compaction replacement method is suitable for projects with poorly controlled deformation on foundations such as high-saturation silt, soft-liquid cohesive soil, etc. The applicability and treatment effect must be determined by field tests before design. The dynamic compaction method and the dynamic compaction replacement method are mainly used to improve the strength of the soil, reduce the compressibility, improve the ability of the soil to resist vibration and liquefaction, and eliminate the collapsibility of the soil. The saturated cohesive soil should be used in combination with the preloading method and the vertical drainage method.
3. The gravel pile method is suitable for compacting loose sand, silt, cohesive soil, plain filling, and miscellaneous filling. It can improve the bearing capacity of the foundation and reduce the compressibility. It can also be used to treat liquefiable foundations. For projects with poorly controlled deformation on saturated clay foundations, sand-gravel piles can also be used to replace sand-gravel piles and soft clay to form a composite foundation, which can accelerate the drainage and consolidation of soft soil and improve the bearing capacity of the foundation.
4. Vibration method is divided into two kinds with and without filler. Filling is commonly referred to as vibro-rock crushing. Vibration punching method is suitable for the treatment of foundations such as sand, silt, silty clay, plain and miscellaneous fill. For cohesive soil and saturated loess foundation with undrained shear strength of not less than 20kbra, its applicability should be determined by field tests before construction. Vibration densification without filler is suitable for treating medium and coarse sand foundations with a clay content of not more than 10%. Vibration and crushed stone piles are mainly used to improve the bearing capacity of the foundation and reduce the settlement of the foundation. It can also be used to improve the sliding stability of the soil slope or the shear strength of the soil.
5. Cement soil stirring method is divided into deep slurry stirring method (wet method for short) and powder spraying method (for dry method). The cement soil mixing method is suitable for the treatment of normally consolidated silt and silty soil, cohesive soil, silt soil, saturated loess, plain fill soil and saturated loose sand soil without flowing groundwater. It is not suitable for treating peat soil, clay with plasticity index greater than 25, and groundwater with corrosive and high organic matter content. If it is required to be used, its applicability must be determined through tests. If the natural moisture content of the foundation is less than 30% (loess moisture content is less than 25%), greater than 70%, or the groundwater brH value is less than 4, it should not be used in the method. Continuously overlapping cement mixing piles can be used as a water-proof curtain for foundation pits. Due to the limitation of its mixing ability, the application of this method to cohesive soils and silt foundations with a foundation bearing capacity greater than 140kbra is difficult.
6. High-pressure jet grouting method is suitable for treating silt, silty soil, cohesive soil, silt soil, sandy soil, artificial filling and gravel ground. When the foundation contains more large-diameter block stones, a lot of plant rhizomes or higher organic matter, its applicability should be determined according to the results of field tests. It is not suitable for situations where the groundwater flow speed is too large and the sprayed slurry cannot solidify around the grouting casing. The high-pressure rotary jet grouting pile has a large processing depth. In addition to ground reinforcement, it can also be used as a water-proof curtain for deep foundation pits or dams. At present, the maximum processing depth has exceeded 30m.
7. Preloading method is suitable for treating saturated cohesive soil foundation such as silt, silty soil, backfill soil. Divided into preloading method and vacuum preloading method according to the preloading method. Preloading preloading is divided into plastic drainage belt or sand well foundation preloading and natural foundation preloading. When the thickness of soft soil layer is less than 4m, natural foundation pile preloading method can be used for treatment. When the thickness of soft soil layer exceeds 4m, vertical drainage preloading method such as plastic drainage belt and sand well should be used. For vacuum preloading projects, drainage shafts must be installed in the foundation. Preloading method is mainly used to solve the problems of settlement and stability of the foundation.
8. The compacted cement soil pile method is suitable for the treatment of silty soil, plain filling soil, miscellaneous filling soil, cohesive soil and other foundations above the groundwater level. This method has a short construction period, low construction cost, civilized construction, and easy cost control. It is currently used in many projects in the old urban districts in Beijing and Hebei.
9. Cement fly ash gravel pile (CFG pile) method is suitable for treating cohesive soil, silt soil, sandy soil, and plain filled soil which has been consolidated by weight. The applicability of silty soil should be determined based on regional experience or field tests. A certain thickness of cushion should be set between the foundation and the pile top to ensure that the pile and soil jointly bear the load to form a composite foundation. The method is applicable to strip foundations, independent foundations, box foundations, and raft foundations, and can be used to improve the bearing capacity of the foundation and reduce deformation. For liquefiable foundations, multi-pile composite foundations of crushed stone piles and cement fly ash crushed stone piles can be used to achieve the purpose of eliminating liquefaction of the soil and improving bearing capacity.
10. The lime pile method is suitable for treating foundations such as saturated cohesive soil, silt, silty soil, miscellaneous fill and plain fill. When it is used in the soil layer above the groundwater level, the method of reducing the amount of quicklime and increasing the water content of the admixture can be adopted to improve the strength of the pile body. This method does not apply to sandy soils under groundwater.
11.The lime soil compacted pile method and the soil compacted pile method are suitable for the treatment of foundations such as collapsible loess, plain fills and miscellaneous fills above the groundwater level, and the treatment depth is 5 ~ 15m. When used to eliminate foundation soil When it is collapsible, the soil compaction pile method should be adopted; when it is used to improve the bearing capacity of the foundation soil or enhance its water stability, the lime soil compaction pile method should be used; the local foundation soil has a water content greater than 24% and is saturated When the degree is greater than 65%, this method is not suitable. The lime soil compacted pile method and the soil compacted pile method are basically the same in terms of eliminating the collapsibility of the soil and reducing the permeability. The soil compacted pile method has a lower bearing capacity and water stability than the lime soil compacted pile method.
12. The column hammer piling method is suitable for the treatment of foundations such as miscellaneous fill, silt, cohesive soil, plain fill and loess. The applicability of saturated soft soil layers below the groundwater level should be determined by field tests. The depth of foundation treatment should not exceed 6m.
13. The single-liquid silicidation method and the lye solution method are suitable for treating collapsible loess and other foundations with a permeability coefficient of 0.1 to 2 m / d above the groundwater level. In the case of self-weight collapsible loess sites, the applicability of the lye method should be determined by tests on a class II collapsible foundation.
14. When determining the foundation treatment plan, it is advisable to choose different methods for comparison and selection. For composite foundation, the choice of scheme is to improve the quality of the bearing capacity according to different soil properties and design requirements, and to choose a suitable pile forming process and reinforcement material.
