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.
2, in filling 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.
3. 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.
4. 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.
5, 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.
6, vibroflotation 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.
7. 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.
8, 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.
9, 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.
10, 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. At present, it has been successfully applied to the old city reconstruction projects in Beijing, Hebei and other places.
1 1, cement fly ash gravel pile (CFG pile) method
It 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.
12, 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.
13, lime-soil compaction pile method and soil compaction pile method
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.
14, column hammer punching pile 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.
15, 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.
Edit this paragraph II. Soft foundation treatment method
Soft foundation treatment methods can be divided into the following four categories according to their different principles and practices:
1, drainage consolidation method
Drainage consolidation method, also known as preloading method, includes surcharge preloading method, overload preloading method, vacuum preloading method, combined action of vacuum and surcharge method, groundwater level reduction method and electroosmosis method. By discharging the pore water in the soft clay foundation soil under preloading load, the soil can be consolidated, the pore volume in the soil can be reduced, and the strength of the soil can be improved, thus reducing the post-construction settlement of the foundation and improving the bearing capacity of the foundation.
2. Vibration density and compaction method
Vibration compaction compaction methods include surface in-situ compaction, dynamic compaction, vibration compaction, compaction, blasting compaction, soil piles and lime-soil piles. By taking certain measures, the deep soil is vibrated and compacted, so as to reduce the void ratio of foundation soil and improve its strength.
3, replacement and mixing method
Displacement mixing methods include cushion replacement method, vibroflotation replacement method, high-pressure jet grouting method, deep mixing method, cushion method and so on. Replacing part of soft soil in soft soil foundation with sand, gravel and other materials or mixing cement, lime or mortar in part of soft soil foundation to form solid, and forming composite foundation with unreinforced soil to improve foundation bearing capacity and reduce settlement.
4. Incremental method
There are many reinforcement methods, such as reinforced soil method, anchoring method, root pile method, low-strength concrete pile composite foundation method, reinforced concrete pile composite foundation method and so on. By burying solid geopolymers, ties and stressed steel bars in the soil layer, the bearing capacity of the foundation can be improved, the settlement can be reduced and the stability of the building can be maintained. The principle, application scope and engineering examples of the above methods can refer to the book Foundation Treatment Engineering Examples edited by Yin and Gong Xiaonan.
Edit the third paragraph. Other foundation treatment methods.
Other foundation treatment methods include: brick diaphragm wall foundation method, concrete diaphragm wall foundation method, single-layer or multi-layer stone diaphragm wall foundation method, mortar rubble diaphragm wall (retaining wall) foundation method and so on. I won't explain it here.
Edit the fourth paragraph. Principles of selecting basic scheme
When determining the foundation treatment scheme, according to different geological conditions, the bearing conditions of buildings (structures) and the cost comparison of various treatment schemes, choose the treatment method that can meet the requirements and has lower cost.
Treatment method of bad foundation
1. 1. 1 has many clay particles in physical properties, and its plasticity index Ip is generally greater than 17, which belongs to cohesive soil. Soft clay is mostly dark gray, dark green, smelly, contains organic matter, has a high water content, generally above 40%, and silt is also above 80%. The void ratio is generally 1.0 ~ 2.0, in which 1.0 ~ 1.5 is called silt, and when the void ratio is greater than 1.5, it is called silt. Because of its high clay content, high water content and large void ratio, its mechanical properties have corresponding characteristics-low strength, high compressibility, low permeability and high sensitivity. 1. 1.2 The strength of mechanical soft clay is extremely low, and the undrained strength is usually only 5 ~ 30 kPa, indicating that the basic value of bearing capacity is very low, generally not exceeding 70kPa, and some even only 20kPa. Soft clay, especially silt, is highly sensitive, which is also an important indicator different from ordinary clay. Soft clay has great compressibility. The compression coefficient is greater than 0.5MPa, up to 45MPa, and the compression index is about 0.35-0.75. Usually, soft clay layer belongs to normal consolidated soil or slightly overconsolidated soil, but some soil layers, especially newly deposited soil layers, may belong to underconsolidated soil. Low permeability coefficient is another important characteristic of soft clay, which is generally between10-5 ~10-8 cm/s. If the permeability coefficient is low, the consolidation rate is slow and the effective stress increases slowly, the settlement stability is slow and the foundation strength increases slowly. This feature is an important aspect that seriously restricts the foundation treatment method and treatment effect. 1. 1.3 Engineering characteristics Soft clay foundation has low bearing capacity and slow strength growth; It is easy to be deformed and uneven after installation; Large deformation rate and long stability time; It has the characteristics of low permeability, high thixotropy and rheology. Miscellaneous fill mainly appears in some old residential areas and industrial and mining areas, and it is the garbage soil left over or piled up by people's life and production activities. These garbage soils are generally divided into three categories: construction garbage soil, domestic garbage soil and industrial production garbage soil. It is difficult to describe different types of garbage soil and garbage soil piled at different times with unified strength index, compression index and permeability index. The main characteristics of miscellaneous fill are unplanned accumulation, complex composition, different properties, uneven thickness and poor regularity. Therefore, the same site shows obvious differences in compressibility and strength, which easily leads to uneven settlement and usually requires foundation treatment. Combined with the specific characteristics of the foundation soil of this project, the following measures were taken in the construction site: the shallow foundation was compacted by using the large tamping energy generated by the free fall of the heavy hammer, so that a relatively uniform hard shell layer was formed on its surface and a bearing layer with a certain thickness was obtained. Key points of construction: before construction, conduct tamping test to determine relevant technical parameters, such as the weight of tamping hammer, diameter of bottom surface and falling distance, final settlement, corresponding tamping times and total settlement; Before compaction, the elevation of tank bottom and pit bottom should be higher than the design elevation; When tamping, the water content of foundation soil should be controlled within the optimal water content range; Large-scale compaction should be carried out in sequence; When the basement elevation is different, it should be deep first and then shallow; After completion, the compacted topsoil shall be removed in time or the floating soil shall be compacted to the design elevation at the drop close to1m. Soil replacement cushion is a soft soil layer with a certain thickness dug out on an independent basis, and then filled with materials such as medium sand, coarse sand, gravel, gravel or pebbles and lime soil with stable performance and non-corrosiveness. Cushion should be compacted in layers, and the density of each layer after compaction should meet the design standards. Design of soil replacement cushion: The design of soil replacement cushion includes calculating the minimum width and thickness of cushion. In terms of cushion width, according to architectural experience, the top width of cushion is generally 200mm wider than the bottom width of foundation, and the bottom width of cushion is generally the same as the width of foundation. The thickness of the cushion should be determined according to the fact that the sum of the self-weight stress and additional stress of the soil acting on the bottom of the cushion is not greater than the bearing capacity of the soft soil layer, and the thickness should not be less than 500mm. During the foundation design of the workshop, according to the survey data, the foundation is a very thick soft clay layer with standard bearing capacity fk-80kN/m, gravity r= 17 kN/m3, IL= 1.00, and e= 1.00. It is understood that the independent foundation of the workshop bears the design value of superstructure load F- 155kN, the design indoor and outdoor height difference is 0.3m, and the buried depth of outdoor foundation is d = 0.80m As can be seen from the above data, the bearing capacity and deformation of the foundation can not meet the design requirements, and the soil cushion layer needs to be replaced. Cushion material is medium sand, and its bearing capacity design value is calculated according to f= 180kN/m (sand cushion density is controlled in medium density during construction), and the weight is taken as r =19.5kn/m. According to the formula 1 = b = [f/(f-yh)], the basement is determined. Where: 1, b- length and width of foundation bottom; F—— load design value of superstructure; F—— Bearing capacity of soil replacement cushion; 7- The average gravity of foundation and backfill soil is generally taken as r = 20kn/m; H—— Calculation height of foundation deadweight. After substituting the specific value, it is concluded that when using this formula to determine the thickness of cushion, a trial algorithm is needed, that is, a thickness is estimated in advance and then checked according to the above formula. If it does not meet the requirements, the thickness of cushion must be increased until it meets the requirements. In order to reduce the calculation workload, when designing the thickness of the soil replacement cushion of the machine room foundation, the calculation method of drawing is adopted: see the drawing of Building Foundation 1990.6438+00; 23 1。 First of all, according to the following formula, this project not only strengthens the design foundation, but also carries out the anti-deformation design of the structure itself according to the survey data in the construction design stage, so as to truly realize the idea of taking design as the center and combining prevention. Buildings often have certain rigidity because of their functional needs. There are two kinds of general industrial and civil buildings with relatively large stiffness. One is absolute stiffness, such as reinforced concrete silos and chimneys. The other is relatively rigid, such as multi-storey masonry buildings and multi-storey reinforced concrete frames. It has certain rigidity, but its strength is low, which is incompatible with rigidity and its tensile capacity is particularly weak. Therefore, when encountering soft soil foundation, the tensile strength of its key parts should be appropriately improved, which is beneficial to adjust the uneven settlement of some buildings by using the stiffness of buildings. In this project, columns and beams in key positions are reinforced by increasing the diameter of longitudinal reinforcement and densifying stirrups in the whole process, so as to increase the overall tensile strength of the building. 3.2 Setting Settlement Joints It is a common treatment measure to set settlement joints on buildings for soft foundations with large clay layer thickness, especially where there is a big difference in foundation compression. Settlement joints should be set according to the plane shape of the building, foundation soil, foundation type and load, generally in the following parts: ① the turning point of the building plane; (2) height difference or load difference; ③ Appropriate parts of masonry load-bearing structure or reinforced concrete frame structure with excessive length-height ratio; ④ Different building structures or foundation types; (5) The junction of houses built by stages. The settlement joint should be wide enough. When the building has two or three floors, the width of the settlement joint should be 50 ~ 80 mm. When the building has 4 to 5 floors, the width of the settlement joint is 80 ~ 120mm; when the building has more than 5 floors, the width of the settlement joint is not less than 120mm, which can be appropriately widened under special circumstances. Setting settlement joints in the above parts can greatly reduce uneven settlement joints caused by weak foundation soil. This project is a rectangular plane, because the length is more than 70 meters, so the settlement joint is set in the middle of the building with a width of 240 mm The building load not only causes the compression deformation of the soil layer under this building, but also causes the compression deformation of the soil layer in a certain range outside it due to the influence of foundation pressure diffusion. This deformation gradually decreases with the increase of distance. Due to the high compressibility of soft soil foundation, when two buildings are close, this additional uneven compression deformation is very large, which often causes the adjacent buildings to tilt or be damaged. If the stiffness and strength of the affected building are poor, the damage is mainly manifested as cracks; When the stiffness and strength are good, it indicates the inclination of the building. Reducing the dead weight can reduce the total settlement of the building, which is beneficial to the control of uneven settlement. It is also possible to reduce the dead weight in the part with large settlement predicted in advance, so as to directly adjust the uneven settlement. Because the weight of general masonry civil buildings accounts for a large proportion, if the weight of this part can be reduced by using light materials and changing the structural system, it will have obvious effect on controlling settlement. In this project, autoclaved concrete hollow block is used as masonry material, which not only plays the role of thermal insulation, but also reduces the weight of the building. High-rise buildings have sprung up, so the quality of foundation treatment directly affects the quality of the whole project. Reasonable and targeted soft foundation treatment and superstructure design can effectively reduce and eliminate the adverse effects of soft foundation on superstructure and ensure the engineering quality.