Cushion replacement method: suitable for the treatment of shallow soft foundation and uneven foundation. Its main function is to improve the bearing capacity of foundation, reduce settlement, accelerate the drainage consolidation of soft soil layer, prevent frost heave and eliminate the expansion and contraction of expansive soil. Dynamic compaction method: it is suitable for treating gravel soil, sandy soil, silt, cohesive soil, collapsible loess, miscellaneous fill and plain fill with low saturation. Dynamic compaction replacement method: it is suitable for projects with poor deformation control on foundations such as high saturated silt and soft plastic cohesive soil. Before design, its applicability and treatment effect must be determined through field tests. Dynamic compaction method and dynamic compaction replacement method are mainly used to improve soil strength, reduce compressibility, improve soil anti-vibration liquefaction ability and eliminate soil collapsibility. Saturated cohesive soil should be combined with surcharge preloading and vertical drainage.
Sand-gravel pile method: it is suitable for tamping loose sand, silt, cohesive soil, plain fill, miscellaneous fill and other foundations, improving foundation bearing capacity and reducing compressibility, and can also be used to treat liquefiable foundations. For projects with lax deformation control on saturated clay foundation, sand-gravel piles can also be used for replacement treatment, so that sand-gravel piles and soft clay can form a composite foundation, accelerate drainage consolidation of soft soil and improve foundation bearing capacity. Vibro-impact method: there are two kinds of packing and no packing. Filling soil is usually called vibro-replacement gravel pile method. The vibroflotation method is suitable for treating foundations such as sandy soil, silt, silty clay, plain fill and miscellaneous fill. For the treatment of cohesive soil and saturated loess foundation with undrained shear strength not less than 20kPa, its applicability should be determined by field test before construction. Vibration compaction without filler is suitable for treating medium-coarse sand foundation with clay content not exceeding 10%. Vibro-replacement gravel pile is mainly used to improve the bearing capacity of foundation and reduce the settlement of foundation, and can also be used to improve the sliding stability of soil slope or the shear strength of soil.
Cement-soil mixing method: it is divided into slurry deep mixing method (wet method for short) and powder jet mixing method (dry method for short). Cement-soil mixing method is suitable for treating normal consolidated silt and silt, cohesive soil, silt, saturated loess, plain fill and saturated loose sand without flowing groundwater. It is not suitable for treating peat soil, clay with plasticity index greater than 25, foundation with corrosive groundwater and high organic matter content. If it needs to be adopted, its applicability must be determined through experiments. This method is not suitable when the natural water content of foundation is less than 30% (loess water content is less than 25%), more than 70% or the pH value of groundwater is less than 4. Continuous overlapping cement mixing piles can be used as waterproof curtain for foundation pit. Because of its mixing ability, it is difficult to apply this method in cohesive soil and silt foundation with foundation bearing capacity greater than 140kPa.
High-pressure jet grouting method: it is suitable for treating silt, muddy soil, cohesive soil, silt, sandy soil, artificial fill and gravel soil foundation. When the soil foundation contains a large number of large-size stones, a large number of plant roots or high organic matter, its applicability should be determined according to the field test results. It is not suitable for the situation that the groundwater velocity is too high and the shotcrete cannot solidify around the grouting casing. High-pressure jet grouting pile has a deep treatment depth, which can be used not only for foundation reinforcement, but also as a waterproof curtain for deep foundation pit or dam. At present, the maximum treatment depth has exceeded 30m.
Preloading method: it is suitable for treating saturated cohesive soil foundation such as silt, muddy soil and fill. According to the preloading method, it is divided into surcharge preloading method and vacuum preloading method. The surcharge preloading is divided into plastic drainage belt or sand drain foundation surcharge preloading and natural foundation surcharge preloading. When the thickness of soft soil layer is less than 4m, the natural foundation surcharge preloading method can be used; When the thickness of soft soil exceeds 4m, vertical drainage preloading methods such as plastic drainage belt and sand drain should be adopted. For vacuum preloading engineering, drainage wells must be set in the foundation. Preloading method is mainly used to solve the settlement and stability of foundation. Compacted cement-soil pile method: it is suitable for treating silt, plain fill, miscellaneous fill, cohesive soil and other foundations above groundwater level.