The common piling methods for foundation treatment are divided into deep dynamic compaction in holes, cushion replacement, dynamic compaction, gravel pile method, vibroflotation method, cement-soil mixing method, high-pressure jet grouting method, preloading method, rammed cement-soil pile method, cement fly ash gravel pile method, lime pile method, lime soil compaction pile method, soil compaction pile method, column hammer compaction pile method, single liquid silicification method and alkali liquor method.
Deep dynamic compaction in hole
The new patented technology of deep dynamic compaction (DDC) in hole foundation treatment (patent number ZL921KLOC-0/4452.0) is to first form a hole in the foundation, drive a dynamic compaction hammer into the hole, and then carry out dynamic compaction while adding materials or layering fillers. Deep dynamic compaction (DDC) technology in holes won the highest award-Eureka Gold Award at the 52nd Eureka World Invention Expo, which is the only gold award of China's foundation treatment technology in the world so far.
The difference between DDC technology and other technologies is that it introduces dynamic compaction into deep foundation through tunnel, and uses special-shaped heavy hammer to stratify the filler in the hole from bottom to top for deep dynamic compaction with high kinetic energy, overpressure and strong compaction, so that the filler in the hole can be consolidated vertically and the soil around the pile can be consolidated horizontally. According to different soil conditions, different technologies are adopted to make the pile body in the shape of beads, enlarged heads and trays. High deformation modulus, small settlement deformation, not affected by groundwater. The depth of foundation treatment can reach more than 30 meters.
Deep dynamic compaction (DDC) in holes has a wide range of applications, which can be used to treat thick miscellaneous fill, collapsible loess, soft soil, liquefied soil, weathered rock, expansive soil and red clay, as well as various complex and difficult foundations such as underground civil air defense fortifications, ancient tombs, karst soil caves and uneven hardness of hard interlayer. According to different geological conditions and design requirements, this technology can use local materials, such as building ballast soil, industrial non-toxic waste, plain soil, sand, gravel, sand pebbles, fly ash, stone-mixed soil, lime soil, concrete and so on. , making all kinds of DDC piles. Greatly reduce the engineering cost, the construction quality is easy to control, the ground vibration is small, the construction noise is low and the construction speed is fast; The diameter of pile is 0.6~3.0m, and the treatment area of single pile is 1.0 ~ 14.0m2, which is not limited by seasons and can absorb a large amount of construction waste at the same time, and can be used for the construction of urban areas or residential areas where dangerous buildings are rebuilt.
Replacement cushion 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, silty soil, cohesive soil, collapsible loess, miscellaneous fill and plain fill with low saturation.
Dynamic compaction replacement method
It is suitable for projects with lax deformation control on high saturated silt, soft plastic cohesive soil and other foundations, and its applicability and treatment effect must be determined through field tests before design. 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.
gravel pile method
It is suitable for compacting loose sand, silt, cohesive soil, plain fill, miscellaneous fill and other foundations, improving foundation bearing capacity and reducing compressibility, and can also be used for treating 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.
Vibration 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 anti-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. Dry 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 foundations 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.
Tamping cement-soil pile method
It is suitable for treating silt, plain fill, miscellaneous fill, cohesive soil and other foundations above the groundwater level. This method has the advantages of short construction period, low cost, civilized construction and easy cost control, and has been successfully applied to the old city reconstruction projects in Beijing, Hebei and other places.
Cement fly ash gravel pile method
Cement fly ash gravel pile (CFG pile) method is suitable for self-weight consolidation treatment of cohesive soil, silt, sandy soil and plain fill. The applicability of muddy soil should be determined according to regional experience or field test. A cushion with a certain thickness should be set between the foundation and the top of the pile to ensure that the pile and soil share the load and form a composite foundation. This method is suitable for strip foundation, independent foundation, box foundation and raft foundation, and can be used to improve the bearing capacity of foundation and reduce deformation. For the liquefiable foundation, the multi-pile composite foundation of gravel pile and cement fly ash gravel pile can be used to eliminate the liquefaction of foundation soil and improve the bearing capacity.
Lime pile method
It is suitable for treating saturated cohesive soil, silt, muddy soil, miscellaneous fill and plain fill. When it is used in the soil layer above the groundwater level, the strength of the pile can be improved by reducing the amount of quicklime and increasing the water content of the admixture. This method is not suitable for underwater sand.
Lime soil and soil extrusion
It is suitable for treating collapsible loess, plain fill, miscellaneous fill and other foundations above the groundwater level, and the treatment depth is 5 ~ 15m. When it is used to eliminate the collapsibility of foundation soil, the soil squeezing pile method should be adopted; When it is used to improve the bearing capacity of foundation soil or enhance its water stability, lime-soil compaction pile method should be adopted; This method is not applicable when the water content of local foundation soil is more than 24% and the saturation is more than 65%. The effects of lime-soil compaction pile method and soil compaction pile method in eliminating soil collapsibility and reducing permeability are basically the same, and the bearing capacity and water stability of soil compaction pile method are not as good as those of lime-soil compaction pile method.
Column hammer punching pile expansion method
It is suitable for treating miscellaneous fill, silt, cohesive soil, plain fill and loess. For saturated soft soil below groundwater level, its applicability should be determined through field tests. The depth of foundation treatment should not exceed 6m.
Single liquid silicification method and alkali solution method
It is suitable for treating collapsible loess and other foundations with permeability coefficient of 0. 1 ~ 2m/d above groundwater level. In the site of self-weight collapsible loess, the applicability of alkali liquor method should be determined through experiments for grade II collapsible loess foundation.
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