How Do I Choose the Best Remedy for Piles?

Foundation treatment generally refers to engineering and technical measures taken to improve the bearing capacity of the foundation (soil or rock) supporting a building or to improve its deformation or permeability properties.

Ground treatment

(Engineering measures)

The problems faced by the foundation are mainly the following: 1) bearing capacity and stability problems; 2) compression and uneven settlement problems; 3) leakage problems; 4) liquefaction problems; 5) special problems of special soil. When natural foundations have one or more of the above five types of problems, foundation treatment measures are required to ensure the safety and normal use of the superstructure. Through ground treatment, one or more of the following purposes can be achieved.

(1) Improve the bearing capacity of foundation soil

Foundation treatment is mainly divided into: foundation engineering measures, geotechnical reinforcement measures.

Some projects do not change the engineering properties of the foundation, but only adopt foundation engineering measures; some projects also reinforce the soil and rock of the foundation at the same time to improve its engineering properties. The appropriate foundation form is selected, and the foundation that can meet the requirements without changing the engineering properties of the foundation is called a natural foundation; on the other hand, the reinforced foundation is called an artificial foundation. The design and construction quality of foundation treatment projects are directly related to the safety of the building. If improper treatment is used, engineering quality accidents often occur, and most of the remediation is difficult afterwards. Therefore, strict quality control and acceptance systems are required for foundation treatment to ensure project quality.

Commonly used foundation 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 pile expansion method, single liquid silicidation method and lye method.

1.Replacement cushion method

It is suitable for the treatment of shallow weak ground and uneven ground. Its main role is to improve the bearing capacity of the foundation, reduce the amount of settlement, accelerate the drainage and consolidation of weak soil layers, prevent frost heave and eliminate the expansion and contraction of expansive soil.

2. Dynamic compaction method

It is suitable for treating gravel soil, sandy soil, low-saturation silt and cohesive soil, collapsible loess, miscellaneous filling and plain filling. The dynamic compaction replacement method is suitable for projects with poorly controlled deformation on foundations such as high-saturation silt, soft-liquid cohesive soil, and its 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 increase the strength of the soil, reduce 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 vertical drainage method.

3.Sand gravel pile method

It is suitable for compacted loose sand, silt, cohesive soil, plain fill, miscellaneous fill and other foundations to improve the bearing capacity of the foundation and reduce compressibility. It can also be used to treat liquefiable foundation. For projects with poorly controlled deformation on saturated clay foundations, sandstone pile replacement treatment can also be used to make the sandstone piles and soft clay form a composite foundation, accelerate the drainage and consolidation of soft soil, and improve the bearing capacity of the foundation.

4.Vibration

There are two kinds of filler and no filler. Filling is commonly referred to as vibro-rock crushing. Vibration punching method is suitable for treating 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 20kPa, 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 mixing method

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 processing 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 needed, its applicability must be determined through tests. If the natural moisture content of the foundation is less than 30% (the moisture content of the loess is less than 25%), greater than 70%, or the pH value of the groundwater is less than 4, the method should not be used. 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 140kPa has certain difficulties.

6.

The determination of the foundation treatment plan can be carried out as follows:

1. Collect detailed engineering quality, hydrogeology, and foundation design materials.

2. According to the structure type, load size and use requirements, combining the factors such as topography, soil structure, soil condition, groundwater characteristics, surrounding environment and adjacent buildings, etc., several foundation treatment schemes to be considered are selected initially. In addition, when selecting a foundation treatment scheme, the combined effects of the superstructure, foundation and foundation should be considered at the same time; a combination of structural strengthening measures (such as setting ring beams and settlement joints) and foundation treatment should also be selected.

3. Carry out careful technical and economic analysis and comparison of the various foundation treatment schemes initially selected from the aspects of treatment effect, material source and consumption, equipment conditions, construction progress, and environmental impact. According to safety and reliability, convenient construction, that is, Economic rationality, etc., so as to adapt to local conditions and follow the best approach. It is worth noting that each method has certain scope, limitations and advantages and disadvantages. No solution is a panacea. When necessary, a comprehensive solution consisting of two or more foundation treatment methods can also be selected.

4. For the selected foundation treatment method, according to the importance of the building and the complexity of the site, corresponding field tests and experimental construction can be performed on a representative site, and the necessary tests are performed to verify the design parameters and Check the treatment effect. If the design requirements are not met, the cause should be found, measures taken, or the design modified to meet the design requirements.

5. The changes of the foundation soil layer are complex and changeable. Therefore, to determine the foundation treatment plan, experienced engineering and technical personnel must participate, and experts must be invited to design major projects. At present, there are some major projects. Due to the lack of experience and over-conservation in the design department, many schemes are often unreasonable and the waste is very serious, which must attract the attention of relevant leaders.

Shallow foundation

Shallow foundations are generally called foundations that have a small depth of burial and can be built by ordinary construction procedures such as trenching and drainage. It can enlarge the contact area between the building and the foundation and spread the upper load. Shallow foundations are: independent foundations (such as most column foundations); strip foundations (such as wall foundations); raft foundations (such as

Before foundation treatment

When using a soft soil layer as a holding layer, the following provisions can be implemented: 1) Silt and silty soil, it is better to use a better soil layer as a holding layer. When the overlying soil layer is thin, take measures to avoid construction Measures for disturbance of silt and silty soil; 2) flushing soil, construction waste, and stable industrial waste, which can be used as a support layer when uniformity and compactness are good; 3) for more organic matter content Miscellaneous fills such as household waste and industrial wastes that are erosive to the foundation should not be used as supporting layers without treatment. Local weak soil layers, dark ponds, dark trenches, etc. can be treated with foundation beams, soil replacement, pile foundation or other methods. When selecting the foundation treatment method, factors such as site engineering geology and hydrogeological conditions, building requirements for foundations, building structure type and foundation type, surrounding environment conditions, material supply conditions, and construction conditions should be comprehensively considered, and the technical and economic indicators should be compared and analyzed. After preference is adopted.

Foundation treatment design time

In the design of foundation treatment, the joint effects of the superstructure, foundation and foundation should be considered, and effective measures should be taken when necessary to strengthen the rigidity and strength of the superstructure to increase the building's ability to adapt to uneven deformation of the foundation. For the selected foundation treatment method, it is appropriate to select a representative site for corresponding field tests according to the design level of the foundation of the building, and perform necessary tests to check the design parameters and reinforcement effects, and provide relevant basis for construction quality inspection. .

After foundation treatment

For the treated foundation, when the base area and buried depth are determined according to the bearing capacity of the foundation and the characteristic value of the bearing capacity of the foundation needs to be corrected, the correction factor of the bearing capacity of the foundation width is set to zero, and the correction factor of the foundation bearing capacity of the foundation Take 1.0; when there is still a weak lower layer within the force range, the foundation bearing capacity of the weak lower layer should be checked. For buildings or structures subject to large horizontal loads or built on slopes, as well as steel oil tanks, storage yards, etc., the foundation stability calculation shall be performed after the foundation treatment. Structural engineers are required to provide load values for foundation bearing capacity calculation and foundation deformation calculation according to relevant codes; according to relevant codes and regional experience, the deformation of the foundation is based on the differences in building loads, the connection methods between buildings, and the construction sequence. The allowable value is reasonable for design requirements. After the foundation treatment, the foundation deformation of the building shall meet the requirements of the current relevant codes, and the settlement observation shall be performed during the construction. The necessary observations shall be continued during the use period to evaluate the foundation reinforcement effect and serve as the basis for use and maintenance. The design of the composite foundation should meet the requirements of bearing capacity and deformation of the building. When the foundation soil is special soil such as under-consolidated soil, expansive soil, collapsible loess, liquefiable soil, etc., the special properties of the soil should be considered in the design, and appropriate reinforcements and construction techniques should be selected. The characteristic value of the bearing capacity of the composite foundation shall be determined through on-site composite foundation load test, or the result of the load test of the reinforced body and the characteristic value of the bearing capacity of the surrounding soil shall be determined in combination with experience.