Construction method of stiffness composite pile in collapsible loess

Abstract

The invention discloses a construction method of a stiffness composite pile in collapsible loess. The construction method comprises the steps that cement-soil stirring is conducted on the collapsible loess; cement-soil stirring is conducted on the collapsible loess; spraying water and liquid for pre-collapsing, wherein the spraying liquid is one or more of alkali liquid, water glass, calcium chloride solution and sodium hydroxide; high-pressure powder spraying and air injection are performed; the cement soil body is in a plastic state through stirring and softening, the cement soil body is squeezed and compacted through layer-by-layer back pressure of the spiral blades, then a dry hard state is formed through full-length re-spraying, re-stirring, back pressure and secondary compacting, meanwhile, the soil body around the pile is squeezed and compacted, and the side friction resistance is further increased; the ultra-high-strength pipe pile is pressed by overloading, a dry and hard cement soil body is forcibly dragged and downwards pre-sheared by a high-pressure pile value, and meanwhile, the soil body around the pile is transversely squeezed and expanded. The treatment effect is good, and the side friction resistance and the end bearing capacity are remarkably enhanced.

Description

Technical Field

[0001] The invention relates to a construction method of a rigid composite pile in collapsible loess. Background Art

[0002] The main strategies for building foundation treatment in collapsible loess areas include replacement cushion method, DDC pile method, heavy hammer compaction method and chemical method. The replacement cushion method is a mainstream treatment method for this type of foundation. Since its relatively weak geology cannot meet the requirements of construction, soil layer replacement is required, that is, sand and gravel with higher strength and density materials replace the original soil layer within the standard range to achieve the purpose of foundation treatment. However, it should be emphasized that the replacement cushion method is not suitable for vibration load foundations, which determines that its application has certain limitations, and its applicable foundation types are mainly concentrated in collapsible soil, plain fill soil, frost heaving soil, etc.

[0003] The layered filling of DDC pile method is realized by drilling. At present, sand, gravel, concrete blocks, soil, etc. are mostly used, and a heavy hammer of a certain weight is used to implement the impact operation to improve the performance of the foundation. When facing complex strata, composite materials should be selected for the consideration of the integrity of the pile body. In short, the backfill material of the soft soil layer is determined to be concrete blocks, and other soil layers are general materials to form a more ideal reinforcement performance. The advantages of this method are concentrated in a wider range of applications, less restrictions during construction, and can effectively eliminate the collapsibility of the foundation itself, so that the stiffness and bearing capacity of the foundation meet the standards. In addition, it is mainly composed of inorganic solids such as sand, gravel, and soil as backfill materials, which saves the processing of raw materials and has good economy.

[0004] The heavy hammer compaction method is widely used in foundation treatment technology and is quite effective in the treatment of collapsible loess foundation. Since it was introduced to China in the 1950s, its application has been concentrated on the treatment of collapsible loess foundation in North China and Northwest China. In principle, the heavy hammer compaction method is to achieve the effect of effectively compacting the foundation by lifting the special rammer to the standard height and then dropping it. It has many characteristics such as economy and convenience, and its construction effect in construction projects has been recognized by the industry. At this stage, the weight of the rammer is about 2~3t, and the operating height is between 4~6m. After repeated hammering of the foundation, its stability is greatly improved, and the collapsibility is greatly weakened or eliminated. With the help of this method, the occurrence of foundation settlement and deformation during construction can be effectively avoided, especially the influence of factors such as weakening water and pressure. Overall, it has a more significant application advantage. The strong compaction method is also a type of heavy hammer compaction method. Since it was introduced into my country in 1978, it has gradually developed into a mainstream technology in the field of foundation treatment of construction projects. Combined with the application practice of this method, its advantages and disadvantages are analyzed. In terms of advantages, it is capable of handling many types of bases such as miscellaneous fill, sand and gravel, especially for the reinforcement of domestic garbage and large pieces of gravel that are quite difficult to handle. In terms of disadvantages, when facing a clay foundation with a high degree of saturation, it is usually impossible to achieve a good effect, and the same is true for the treatment of silty soil. Precisely because of this, in actual construction, the combination with the foundation properties should be emphasized. When it comes to the fill reinforcement link, in order to avoid the occurrence of uneven foundation bearing capacity, it is necessary to pay enough attention to the control of the backfill composition. When introducing the dynamic compaction method to treat collapsible loess foundations, two conditions usually need to be met, one is above the groundwater level, and the other is that the saturation Sr is less than 60%.

[0005] Chemical methods are divided into silicification, liquid reduction, pre-immersion, etc. The mechanism of silicification is to reduce the content of water and air in the stratum by injecting chemical solvents, and to form an integral structure of the foundation under the action of cementation, thereby achieving reinforcement. There are many types of silicification methods, representative of which are pressure double liquid, pressure single liquid, pressure mixing and electric silicification. Among them, the use of different chemical solvents is the difference between double liquid and single liquid. The former is mostly calcium chloride solution, and the latter is glass water. The reaction of these solutions with calcium salts in the foundation can achieve the effect of significantly strengthening the foundation. In general, silicification methods have many types and a wide range of applications, and can be reasonably selected according to the needs of the project, but it should be emphasized that when asphalt, grease, etc. are infiltrated into the foundation, these substances can weaken the degree of contact between the solvent and the foundation, so silicification is not suitable. The alkali solution method shows good stability when treating collapsible loess foundations. The mechanism of this method is to allow the heated alkali solution to flow to the deep layer of the foundation to form calcium aluminate complexes. This type of substance is not only insoluble in water, but also has very high strength. Summary of the invention

[0006] The purpose of the invention is to provide a construction method for a rigid composite pile in collapsible loess with good treatment effect and strong bearing capacity.

[0007] The technical solution of the present invention is: A construction method for a rigid composite pile in collapsible loess, characterized by comprising: mixing the collapsible loess with cement soil; spraying water or liquid for pre-wetting, with a pressure of 25 MPa, wherein the liquid is one or more of alkali solution, water glass, calcium chloride solution, and sodium hydroxide; and spraying powder and air, with a pressure of 1.2 MPa; The cement soil is softened by stirring and put into a plastic state, and then the spiral blades are used to squeeze and expand the soil layer by layer to form a large-diameter cement soil in a dense plastic state; then the whole length is sprayed, stirred, and back-pressed to form a dry and hard state for the second time, and at the same time, the soil around the pile is squeezed and expanded to further increase the side friction resistance; Ultra-high-strength pipe piles are pressed in with overload at regular intervals, and the dry and hard cement soil is pre-sheared by forcibly pulling it downward with a high pile pressure value of 1000~6000kN. At the same time, the soil around the pile is compacted and expanded laterally. The pressure value increases with depth until the bearing capacity of the bearing layer at the pile end reaches the limit value.

[0008] A pile force sensor and a temperature and humidity sensor that communicate with an external analysis system are installed at the end of the ultra-high-strength pipe pile, or a pile force display device is directly installed on the pile driver, which can quickly and efficiently perform geophysical exploration, perception, quantitative measurement, analysis, and judgment of the reinforcement effect.

[0009] The present invention has good treatment effect, and the side friction resistance and end bearing capacity are significantly enhanced.

[0010] The present invention will be further described below in conjunction with the embodiments. DETAILED DESCRIPTION

[0011] A construction method for a rigid composite pile in collapsible loess, characterized by comprising: mixing the collapsible loess with cement soil; spraying water or liquid for pre-wetting, with a pressure of 25 MPa, wherein the liquid is one or more of alkali solution, water glass, calcium chloride solution, and sodium hydroxide; and performing high-pressure powder spraying and jetting, with a pressure of 1.2 MPa; The cement soil is softened by stirring and put into a plastic state, and then the spiral blades are used to squeeze and expand the soil layer by layer to form a large-diameter cement soil in a dense plastic state; then the whole length is sprayed, stirred, and back-pressed to form a dry and hard state for the second time, and at the same time, the soil around the pile is squeezed and expanded to further increase the side friction resistance; Ultra-high-strength pipe piles are pressed in with overload at regular intervals, and the dry and hard cement soil is pre-sheared by forcibly pulling it downward with a relatively high pile pressure value of 1000~6000kN. At the same time, the soil around the pile is compacted and expanded laterally. The pressure value increases with depth until the bearing capacity of the bearing layer at the pile end reaches the limit value (such as 9000kN).

[0012] A pile force sensor and a temperature and humidity sensor that communicate with an external analysis system are installed at the end of the ultra-high-strength pipe pile, or a pile force display device is directly installed on the pile driver, which can quickly and efficiently perform geophysical exploration, perception, quantitative measurement, analysis, and judgment of the reinforcement effect.

Claims

1. A construction method for rigid composite piles in collapsible loess, characterized by: include: Mixing cement soil on collapsible loess; Spraying water or liquid for pre-wetting, with a pressure of 25Mpa, wherein the liquid is one or more of alkali solution, water glass, calcium chloride solution, and sodium hydroxide; and spraying powder or air with a pressure of 1.2Mpa; The cement soil is softened by stirring and put into a plastic state, and then the spiral blades are used to squeeze and expand the soil layer by layer to form a large-diameter cement soil in a dense plastic state; then the whole length is sprayed, stirred, and back-pressed to form a dry and hard state for the second time, and at the same time, the soil around the pile is squeezed and expanded to further increase the side friction resistance; Ultra-high-strength pipe piles are pressed in with overload at regular intervals, and the dry and hard cement soil is pre-sheared by forcibly pulling it downward with a high pile pressure value of 1000~6000kN. At the same time, the soil around the pile is compacted and expanded laterally. The pressure value increases with depth until the bearing capacity of the bearing layer at the pile end reaches the limit value.

2. The method for constructing rigid composite piles in collapsible loess according to claim 1, characterized in that: The pile ends of ultra-high-strength pipe piles are equipped with pile driving force sensors and temperature and humidity sensors that communicate with external analysis systems, or the pile driving force display device is directly installed on the pile driver, which can quickly and efficiently perform geophysical exploration, perception, quantitative measurement, analysis, and judgment of the reinforcement effect.