What are the unique advantages of pressure grouting soil pile compared with traditional cement-soil pile?

Compared with the traditional cement-soil pile, the pressure grouting soil pile does not depend on the original soil and groundwater.

Advantage analysis of cement mixing pile

Cement mixing pile is suitable for treating saturated soft clay from various sources, such as silt, muddy soil, silt, sandy soil, peat soil and cohesive soil with high water content and standard bearing capacity of foundation not greater than 120kPa. For peat soil or cohesive soil with low pH value and high organic matter content in groundwater, its applicability should be determined by experiments. The depth of reinforcement mainly depends on the power of mixer and foundation reaction. At present, the maximum reinforcement depth of cement mixing piles used in China can reach 30 m.

Cement mixing pile has a wide range of applications, mainly used to form composite foundation, supporting structure, impervious curtain and so on. 1) to form a composite foundation. The main purpose of forming composite foundation is to improve the bearing capacity and deformation characteristics of foundation. At present, cement mixing pile composite foundation is widely used in: (1) building (structure) foundation, such as civil residence, office building, factory building, pool, oil tank, etc. 10 floor below building (structure) foundation; (2) The foundation of large storage yards, such as steel works, cement works and large cargo works; (3) The foundation treatment of expressway and airport runways, such as the approach road foundation on both sides of expressway abutment and box culvert (passage), can adjust the differential settlement between subgrade and bridge pile foundation or box culvert (passage) foundation. 2) forming a supporting structure. Gravity retaining wall formed by cement mixing pile is often used to retain soil when excavating foundation pit on soft soil foundation. This kind of supporting structure is especially effective and economical when it is applied to shallow foundation pit with excavation depth of about 5 ~ 6 m. 3) forming an impervious curtain. Because the permeability coefficient of cement-soil reinforced by cement mixing pile is often much smaller than that of natural soil, it has better water-stopping and seepage-proof ability. In poor foundations such as muddy soil and sandy soil, cement mixing piles are often reinforced into continuous wall structures, which are used as anti-seepage and water-stop curtains. For example, in foundation pit excavation, bored piles or digging piles are often used to retain soil, and mixing piles are used behind the piles to form a continuous wall seepage-proof and water-stop curtain wall and form a composite supporting structure, which often has unexpected effects. In addition, when vacuum jacking treatment is carried out in sandy soil or muddy sandy soil, cement mixing piles are often used to spray mud or cement slurry along the peripheral boundary of the treatment area to form a closed curtain to improve the effect of vacuum preloading treatment.

Compared with other construction methods, cement mixing pile has the characteristics of short construction period, no pollution and low cost. This construction method has no vibration, no noise, no ground heave, no sewage discharge, no environmental pollution, no harmful influence on adjacent buildings, and has good comprehensive economic and social benefits.

There are many manufacturers of cement mixing pile machinery with high degree of mechanization in construction, with increasing mechanical models and improving performance. All kinds of deep mixing machines have their own advantages and are suitable for different geological conditions and engineering purposes. Not only the construction efficiency is improved, but also the bearing capacity or retaining capacity of the pile is greatly improved.

The stress and deformation of cement mixing pile mainly occur in the upper part of the pile body, and the stress and deformation in the lower part of the pile body are smaller. This bearing behavior of cement mixing pile can be summarized as follows: 1) Under the top load, the settlement of cement mixing pile is mainly caused by the compression of the pile body, while the compression of the upper part of the pile body is greater than that of the lower part, and it is almost zero at the pile end; 2) Because the upper part of the pile body is relatively large, all the friction resistance around the pile body is exerted on the upper part of the pile body, which is similar to the characteristics of pure friction pile. For some geological conditions, the mixing pile should have a critical pile length. When the pile length exceeds the critical pile length, the excess bearing capacity of the pile body is actually very small or even invalid.

The traditional cement-soil mixing pile is a foundation reinforcement method with good technical, economic and social benefits. Its theory and construction technology are gradually maturing, but there are also some problems: in engineering application, due to conservative design method, the replacement rate is as high as 40% ~ 80%, and the design strength of the pile is generally less than 0.6MPa. At the same time, due to insufficient investment in theoretical research, complete data of stress field and deformation field are not obtained, resulting in unsatisfactory design calculation method.

At the same time, in engineering practice, the performance and construction monitoring system of mixing machinery in China are relatively backward, such as the lack of monitoring devices for pile quality, and the need for manual monitoring for the phenomenon of blocking soil and breaking piles. In addition, the management link is weak, and the technical level and operation of the operators are not serious. Not only the construction technology needs to be further improved and improved, but also the quality inspection methods need to be strengthened and improved. ?

1. The construction technology of cement-soil mixing pile is divided into mud mixing method (hereinafter referred to as wet method) and powder mixing method (hereinafter referred to as dry method). It is suitable for treating silt, muddy soil, plain fill, soft plastic cohesive soil, loose-medium dense silt, slightly dense-medium dense silt, loose-slightly dense medium coarse sand, gravel sand, loess and other soil layers. It is not suitable for miscellaneous fill, hard plastic hard cohesive soil, dense sandy soil and soil layer with groundwater leakage that affects the quality of pile formation. When the natural water content of local foundation soil is less than 30% (loess water content is less than 25%) and more than 70%, dry method is not suitable. In winter construction in cold areas, the influence of negative temperature on treatment effect should be considered.

2. When using cement-soil mixing method to treat peat soil, acid soil with high organic matter content or PH value less than 4, clay with plasticity index greater than 25, or in corrosive environment and areas with no engineering experience, its applicability must be determined through field and indoor tests.

3. Cement-soil mixing method can adopt single-head, double-head, multi-head mixing or continuous tank mixing to form cement-soil and solid; Wet mixing can insert steel to form row piles (walls). Three-dimensional shapes can be divided into columns, walls, grids or blocks.

4. For the project of treating foundation by cement-soil mixing method, besides detailed geotechnical engineering investigation according to the current specifications, it is also necessary to find out PH value, organic matter content, underground obstacles and soft soil distribution, groundwater and its movement law.