Composite paste slurry suitable for pretreatment of pier pile foundation in karst area and preparation method and grouting method of composite paste slurry

Abstract

The invention discloses composite paste slurry suitable for pretreatment of a pier pile foundation in a karst area and a preparation method and a grouting method of the composite paste slurry, the composite paste slurry is based on the filling design of part of a karst cave but not the whole karst cave, cement, slurry, stone powder and a composite additive are prepared into semi-solid slurry with the slump of 5-10 cm, and the composite paste slurry has underwater anti-dispersion performance, the composite admixture is composed of a first admixture and a second admixture in a mass ratio of 1: 1; each cubic meter of the composite paste slurry comprises the following components by mass: 200 to 300 kg of cement, 550 to 780 kg of slurry and 820 to 1200 kg of stone powder, and the addition amount of the first additive and the second additive is 0.6 to 1% of the weight of the cement. The problems that when an existing pretreatment grouting technology is used for treating the karst problem of the bridge pier, the number of drilled holes is large, the reinforcing effect is common, cost is high, the environment is polluted, and adaptability to complex geology is insufficient are solved.

Description

Technical Field

[0001] The present invention relates to the technical fields of intercity rail transit and pre-treatment of bridge engineering pile foundations, and particularly relates to a composite paste for pre-treating pier pile foundations in karst areas, a preparation method thereof, and a grouting method thereof. Background Art

[0002] In intercity rail transit and bridge construction, when the pier foundation is located in a karst area, adverse geological phenomena such as karst caves, solution troughs, and solution grooves will cause difficulties such as ground collapse during pile foundation construction, difficulty in advancing the steel casing in place, and uncontrollable construction period costs. There will also be a serious situation of excessive concrete consumption during pile pouring, and even pose a serious threat to the stability of the pier. Traditional pile foundation pre-treatment mainly uses mortar and cement grouting, partially fills low-grade concrete and adds a large amount of quick-setting agents, etc. There are many limitations in the grouting materials and methods for dealing with pier karst problems:

[0003] (1) The slurry of the traditional grouting method has problems such as water bleeding and low stone formation rate, high leakage rate, and it is difficult to form a stable and effective filling body in the karst cavity, resulting in poor reinforcement effect;

[0004] (2) In a karst cave with rich groundwater, it will be diluted and washed by groundwater or under dynamic water conditions, resulting in the loss of the slurry, especially the cementitious material in the slurry, and a decrease in strength, affecting the grouting effect;

[0005] (3) Adding a quick-setting agent can make the grouting material coagulate quickly, but the cost is high, and the problem of pipe blockage frequently occurs, resulting in construction interruption. At the same time, there are also certain potential hazards in terms of durability.

[0006] (4) The existing grouting technology has poor adaptability to complex karst geological conditions, cannot accurately control the grouting range and grouting volume, and is prone to under-grouting or over-grouting.

[0007] Therefore, there is an urgent need for a new grouting technology to solve the problem of pre-treating pile foundations in pier karst areas, so as to improve the stability of the pier and the safety of bridge engineering, while reducing engineering costs and achieving the purpose of green environmental protection. Summary of the Invention

[0008] The purpose of the present invention is to provide a composite paste for pre-treating pier pile foundations in karst areas, a preparation method thereof, and a grouting method thereof. The composite paste is designed based on the filling of part rather than the whole karst cavity, and is composed of cement mixed with waste slurry and stone powder from construction sites, and then mixed with a composite admixture to form a semi-solid slurry with a slump of 5 - 10 cm, and has underwater anti-dispersion performance, which well solves the problems existing in the existing pre-treatment grouting technology for dealing with pier karst problems, such as a large number of drill holes, general reinforcement effect, high cost, environmental pollution, and insufficient adaptability to complex geology.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a composite paste applicable to the pre-treatment of pier pile foundations in karst areas. The composite paste is composed of cement, slurry, stone powder and a composite admixture. Among them, the composite admixture is composed of a first admixture and a second admixture with a mass ratio of 1:1; the mass ratio of each component per cubic meter of the composite paste is as follows: 200 kg - 300 kg of cement, 550 kg - 780 kg of slurry, and 820 kg - 1200 kg of stone powder. The addition amounts of the first admixture and the second admixture are both 0.6% - 1% of the weight of the cement. The specific ratio is determined through experiments according to the karst geological conditions (such as the size of the karst cave, the nature of the filling material, etc.) and engineering requirements to ensure that the composite paste has good comprehensive performance.

[0011] Further, the viscosity of the slurry is greater than 25 s, and the specific gravity is 1.2 g / cm 3 ~1.22 g / cm 3 .

[0012] Further, the slurry is selected from the yellow clay slurry prepared by stirring yellow clay powder and water, or the waste slurry prepared by diluting waste slurry with water or thickening it with mud powder.

[0013] Further, the waste slurry is at least one of the slurry for pile foundation pouring, the slurry from the sand washing plant, and the slurry from the slurry shield. Since these waste slurries are all slurries that need to be disposed of outside the construction site or require special treatment to prevent environmental pollution, the present invention realizes the reuse of resources by reusing these waste slurries.

[0014] Further, each cubic meter of the composite paste is composed of 300 kg of cement, 280 kg - 300 kg of yellow clay powder, 400 kg - 480 kg of water, 850 kg of stone powder, 3 kg of the first admixture, and 3 kg of the second admixture; or, each cubic meter of the composite paste is composed of 300 kg of cement, 550 kg - 620 kg of waste slurry, 820 kg - 880 kg of stone powder, 3 kg of the first admixture, and 3 kg of the second admixture.

[0015] Further, the cement is P.O42.5R ordinary Portland cement.

[0016] Further, the stone powder is the powder obtained by crushing or screening at least one of construction waste, muck from earth pressure balance shield, and waste powder from the stone yard; the average particle size of the stone powder is 0.5 mm - 3 mm, and the maximum particle size is less than 5 mm.

[0017] Further, the first admixture is the HY-1# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a powdery solid; the second admixture is the HY-2# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a liquid.

[0018] Second, the present invention provides a preparation method of the above-mentioned composite paste applicable to the pre-treatment of pier pile foundations in karst areas, including the following steps:

[0019] S1. Pretreatment of raw materials: Screen the stone powder and remove the coarse particles to ensure that the average particle size of the stone powder is 0.5 mm to 3 mm, and the maximum particle size is less than or equal to 5 mm.

[0020] S2. Stirring and mixing: According to the set mass ratio, first add the slurry and cement into the mixer and stir at a stirring speed of 1440 r / min for 1 min to 3 min to mix evenly into a semi-finished slurry; then pump the prepared semi-finished slurry to a flat-mouth forced mixer and add the stone powder, and stir at a stirring speed of 25 r / min for 1 min to 3 min to form a uniform paste; finally, add the composite admixture and continue to stir at a stirring speed of 25 r / min for 2 min to obtain a composite paste with stable performance.

[0021] Third, the present invention further provides a grouting method, using the above-mentioned composite paste applicable to the pre-treatment of pier pile foundations in karst areas for grouting, and the steps include:

[0022] (1) Arrangement of grouting holes: According to the exploration results of the karst area of the pier, a combination of geophysical prospecting and drilling is used to accurately determine the positions and scopes of karst caves and solution grooves, and grouting holes are arranged around the pier foundation. The depth of the grouting holes should penetrate the karst development layer and enter the stable bedrock by 1.0 m.

[0023] (2) Grouting sequence: Adopt the method of grouting by drilling in sequence. First, grout the peripheral grouting holes, and then gradually grout the middle grouting holes from the outside to the inside. And in each grouting hole, insert the grouting pipe to the bottom of the hole and adopt the backward grouting method to accurately grout section by section in the order from bottom to top.

[0024] (3) Control of grouting pressure and flow rate: During the grouting process of each grouting hole, at the initial grouting, adopt a grouting pressure of 0.5 MPa and a grouting flow rate of 10 cubic meters per hour to enable the composite paste to quickly fill part of the voids; as the grouting progresses, when the voids are gradually filled, the grouting pressure gradually increases to 0.8 MPa to 1.0 MPa, and the grouting flow rate correspondingly decreases to 6 cubic meters per hour; when the grouting pressure reaches the designed final pressure of 1.0 MPa to 1.5 MPa, end the grouting of the current interval lifting section, lift the grouting pipe upward, and wait for the slurry to initially solidify before grouting the next section until the grouting of the current grouting hole is completed.

[0025] The functions of the components in the composite paste of the present invention are as follows: Cement is used as the main gelling material and provides strength support. The slurry is selected from yellow clay slurry prepared by stirring yellow clay powder and water, or waste slurry prepared by diluting waste slurry with water or thickening it with mud powder, which can increase the viscosity and water retention of the slurry, prevent the slurry from settling and bleeding. The viscosity of the prepared slurry is greater than 25 s, and the specific gravity is 1.20 - 1.22. Stone powder can improve the workability and strength of the slurry, increase the solid content and volume of the grouting material, reduce costs, and improve the late strength. The maximum particle size is required to be less than 5 mm, and there are no requirements for strength and impurity content. The composite admixture is HY-1# admixture and HY-2# admixture produced by Hunan Hongyu Engineering Group Co., Ltd. Among them, after mechanically mixing cement, slurry, and stone powder, HY-1# admixture is used to suspend and thicken clay particles and then rapidly solidify to reduce the slump of the paste, so as to achieve early strength of the grouting material, basically no bleeding occurs, the setting time of the grouting material is controllable, and the slurry does not disperse and has erosion resistance under dynamic water conditions; HY-2# admixture can accelerate the cement gelling, make the grouting material rapidly lose fluidity, and reduce the slump of the grouting material to less than 10 cm.

[0026] Compared with the prior art, the present invention provides a composite paste applicable to the pre-treatment of bridge pier pile foundations in karst areas, its preparation method and grouting method, and has the following beneficial effects:

[0027] (1) Improve the reinforcement effect: Based on the filling design of part rather than the whole karst cave, the composite paste provided by the present invention is a semi-solid paste with a slump of 5 - 10 cm, which is improved by forced stirring and adding two different admixtures. It has underwater anti-dispersion performance, good workability, water retention and a high stone formation rate. It can form a stable and strong filling consolidation body in karst cavities, corrosion and fissures, effectively enhance the integrity of the bridge pier foundation and the surrounding rock mass, and significantly improve the bearing capacity and stability of the bridge pier.

[0028] (2) Adapt to complex geological conditions: The supporting grouting method provided by the present invention can well adapt to various complex karst geological conditions through scientific grouting hole arrangement, grouting sequence and precise pressure and flow control, realize the effective treatment of karst areas with different scales and forms, and improve the reliability and success rate of grouting construction.

[0029] (3) Reduce costs: The present invention rationally uses waste materials such as slurry shield, pile foundation pouring and sand washing plant waste slurry, stone yard waste powder, earth pressure balance shield muck, and construction waste as the main raw materials, and mixes in cement and other gelling materials and admixtures. On the premise of ensuring the grouting effect, it can reduce the cost of grouting materials and at the same time reduce the consumption of natural resources.

[0030] (4) Environmentally friendly and pollution-free: Most of the raw materials used in the composite paste material are waste materials, which are non-toxic and harmless. The resource recycling of waste materials not only consumes waste materials but also does not pollute the surrounding environment, meeting the requirements of green engineering construction. Specific implementation manners

[0031] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] The present invention will be further described in detail below through detailed embodiments.

[0033] Unless otherwise specified, the experimental methods used in the embodiments are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0034] The source information of the raw materials used in the embodiments of the present invention is as described below:

[0035] The cement is the P.O42.5R ordinary Portland cement produced by Yingde Conch Cement Co., Ltd. The stone powder is the powder obtained by crushing or screening the waste materials generated from on-site projects such as construction waste, muck from earth pressure balance shield tunneling, and waste powder from stone quarries, and the average particle size is required to be 0.5 mm to 3 mm, and the maximum particle size is less than or equal to 5 mm. The first admixture is the HY-1# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a powdery solid. The second admixture is the HY-2# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a liquid.

[0036] Example 1

[0037] This embodiment provides a composite paste applicable to the pre-treatment of bridge pier pile foundations in karst areas. Each cubic meter of the composite paste is composed of 300 kg of cement, 780 kg of slurry, 850 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is a yellow clay slurry with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm 3 prepared by stirring 300 kg of yellow clay powder and 480 kg of water with a high-speed pulp making machine.

[0038] The preparation method of the composite paste includes the following steps:

[0039] S1. Pretreatment of raw materials

[0040] Use a sieve sand machine to screen the stone powder and remove coarse particles to ensure that the average particle size of the stone powder is 0.5 mm to 3 mm and the maximum particle size is less than 5 mm; the cement should meet the corresponding national standards and there is no caking phenomenon; fully stir and screen the yellow clay mud powder to ensure its uniformity.

[0041] S2. Stir and mix

[0042] According to the set mass ratio, first add the slurry and cement into the mixer and stir at a stirring speed of 1440 r / min for 2 min to mix evenly into a semi-finished slurry; then pump the obtained semi-finished slurry to a flat-mouth forced mixer and add stone powder, and stir at a stirring speed of 25 r / min for 2 min to form a uniform slurry; finally, add the first admixture (HY-1# admixture) and the second admixture (HY-2# admixture), and continue to stir at a stirring speed of 25 r / min for 2 min to obtain a composite paste with stable performance.

[0043] The 7-day compressive strength of the composite paste provided in this embodiment is 3.5 MPa, and the 28-day compressive strength is 5.0 MPa.

[0044] Example 2

[0045] This embodiment provides a composite paste applicable to the pre-treatment of bridge pier pile foundations in karst areas. Each cubic meter of the composite paste consists of 300 kg of cement, 750 kg of slurry, 850 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is a yellow clay slurry with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm 3 prepared by stirring 300 kg of yellow clay mud powder and 450 kg of water.

[0046] The preparation method of the composite paste is the same as that in Example 1, so it will not be elaborated here.

[0047] The 7-day compressive strength of the composite paste provided in this embodiment is 3.8 MPa, and the 28-day compressive strength is 5.5 MPa.

[0048] Example 3

[0049] This embodiment provides a composite paste applicable to the pre-treatment of bridge pier pile foundations in karst areas. Each cubic meter of the composite paste consists of 300 kg of cement, 680 kg of slurry, 850 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is a yellow clay slurry with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm3 Yellow clay slurry

[0050] The preparation method of the composite paste is the same as that in Example 1, so it will not be elaborated here.

[0051] The 7-day compressive strength of the composite paste provided in this example is 4.0 MPa, and the 28-day compressive strength is 6.0 MPa.

[0052] Example 4

[0053] During the actual on-site construction process, in order to further save engineering materials and reduce the project cost to achieve the purpose of green environmental protection and turning waste into treasure, waste slurry generated from other working conditions can also be used in the implementation process. After adding water for dilution or adding mud powder for thickening, the obtained waste slurry can be used to replace the yellow clay slurry in Examples 1 to 3 for laboratory mix proportion tests and on-site implementation.

[0054] Specifically, this example provides a composite paste applicable to the pre-treatment of bridge pier pile foundations in karst areas. Each cubic meter of the composite paste consists of 300 kg of cement, 550 kg of slurry, 880 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is selected as the waste slurry with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm 3 obtained by diluting the pile foundation grouting slurry with water. The pile foundation grouting slurry is the waste slurry generated at the on-site construction site.

[0055] The preparation method of the composite paste includes the following steps:

[0056] S1. Pretreatment of raw materials

[0057] Use a sieve sand machine to screen the stone powder and remove coarse particles to ensure that the average particle size of the stone powder is 0.5 mm to 3 mm, and the maximum particle size is less than 5 mm; the cement should meet the corresponding national standards and there is no caking phenomenon.

[0058] S2. Stirring and mixing

[0059] According to the set mass ratio, first add the slurry and cement into the mixer and stir at a stirring speed of 1440 r / min for 2 min to mix evenly into a semi-finished slurry; then pump the obtained semi-finished slurry into a flat-mouth forced mixer and add stone powder, and stir at a stirring speed of 25 r / min for 2 min to form a uniform paste; finally, add the first admixture (HY-1# admixture) and the second admixture (HY-2# admixture), and continue to stir at a stirring speed of 25 r / min for 2 min to obtain a composite paste with stable performance.

[0060] The 7-day compressive strength of the composite paste provided in this embodiment is 3.5 MPa, and the 28-day compressive strength is 5.2 MPa.

[0061] Example 5

[0062] This embodiment provides a composite paste applicable to the pre-treatment of pier pile foundations in karst areas. Each cubic meter of the composite paste is composed of 300 kg of cement, 580 kg of slurry, 850 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is selected from the waste slurry material with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm 3 diluted with water from the slurry of a slurry shield. The slurry of the slurry shield is the waste slurry generated at the construction site.

[0063] The preparation method of the composite paste is the same as that in Example 4, so it will not be elaborated here.

[0064] The 7-day compressive strength of the composite paste provided in this embodiment is 3.4 MPa, and the 28-day compressive strength is 4.8 MPa.

[0065] Example 6

[0066] This embodiment provides a composite paste applicable to the pre-treatment of pier pile foundations in karst areas. Each cubic meter of the composite paste is composed of 300 kg of cement, 620 kg of slurry, 820 kg of stone powder, 3 kg of the first admixture (HY-1# admixture), and 3 kg of the second admixture (HY-2# admixture); among them, the slurry is selected from the waste slurry material with a viscosity greater than 25 s and a specific gravity of 1.2 g / cm 3 ~1.22 g / cm 3 thickened with mud powder from the slurry of a sand washing plant. The slurry of the sand washing plant is the waste slurry generated at the construction site. The mud powder can be yellow clay mud powder.

[0067] The preparation method of the composite paste is the same as that in Example 4, so it will not be elaborated here.

[0068] The 7-day compressive strength of the composite paste provided in this embodiment is 2.9 MPa, and the 28-day compressive strength is 4.4 MPa.

[0069] Example 7

[0070] This embodiment provides a grouting method, which uses any one of the composite pastes in Examples 1 to 6 to grout the pier pile foundations in karst areas. The steps include:

[0071] (1) Grouting hole arrangement: Based on the exploration results of the karst area of the bridge pier, a combination of geophysical prospecting and drilling is used to accurately determine the location and scope of karst caves and solution grooves. Eight grouting holes are arranged around the bridge pier foundation. For grouting holes with a pile diameter of 1.5 m, two drill holes are arranged, with a spacing of 1.5 m between the two drill holes and arranged along the pile circumference. The depth of the grouting hole should penetrate the karst development layer and enter the stable bedrock by 1.0 m.

[0072] (2) Grouting sequence: Considering the entire pile cap in combination with the geological exploration data as a whole, each pile adopts the method of grouting by drilling in sequence (the second-order holes play the role of checking and strengthening the grouting effect of densification), and there is no need to construct edge-sealing holes; first grout the peripheral grouting holes, and then gradually grout the middle grouting holes from the outside to the inside. In principle, each hole is drilled once. In each grouting hole, insert the grouting pipe to the bottom of the hole and adopt the backward grouting method (the grouting pipe is a smooth pipe and can only discharge slurry at the bottom of the pipe), and accurately grout the karst cave position section by section in the order from bottom to top.

[0073] (3) Control of grouting pressure and flow rate: During the grouting process of each grouting hole, at the initial grouting stage, a grouting pressure of 0.5 MPa and a grouting flow rate of 10 m³ / h are adopted to enable the composite paste slurry to quickly fill part of the cavity; as the grouting progresses, when the cavity is gradually filled, the grouting pressure gradually increases to 0.8 MPa, and the grouting flow rate correspondingly decreases to 6 m³ / h; when the grouting pressure reaches the designed final pressure of 1.0 MPa, end the grouting of this interval lifting section, lift the grouting pipe upward, and wait for the slurry to initially solidify before proceeding with the next section of grouting until the grouting of the current grouting hole is completed, and then perform hole-sealing grouting. The grouting pressure of the grouting holes at the middle pile position is 0.2 MPa greater than that at the outer pile position.

[0074] Through the preparation method and grouting method provided by the present invention for preparation and perfusion, it can solve the difficulties in the excavation of slurry and muck in urban rail transit, with high treatment costs, and fully utilize waste materials from the environmental protection aspect, achieving the transformation of waste into treasure; moreover, from a technical aspect, it can accurately pour each layer of karst cave. By adding composite admixtures for improvement, the slump of the new composite paste slurry can be controlled. At the same time, in cooperation with the mechanized slurry mixing equipment for the complete set of new composite paste slurry for continuous flow operation, the purpose of reducing production costs, improving the controllability and quality of pier karst grouting is finally achieved. After the pre-treatment of pier karst grouting, the pile-forming speed of subsequent processes such as rotary drilling (percussion) can be significantly increased, and the over-pouring of cast-in-place concrete can be effectively controlled, effectively improving the construction progress of the entire project and reducing construction costs, and ensuring the stability and safety of the pile foundation.

[0075] The above embodiments are only illustrative of the concept and technical solutions of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the relevant technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

[0076] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite paste applicable to the pre-treatment of pier pile foundations in karst areas, characterized in that, The composite paste is composed of cement, slurry, stone powder and a composite admixture. Among them, the composite admixture is composed of a first admixture and a second admixture with a mass ratio of 1:1; the mass ratio of each component per cubic meter of the composite paste is as follows: 200 kg - 300 kg of cement, 550 kg - 780 kg of slurry, and 820 kg - 1200 kg of stone powder. The addition amounts of the first admixture and the second admixture are both 0.6% - 1% of the weight of the cement.

2. The composite paste applicable to the pre-treatment of pier pile foundations in karst areas according to claim 1, wherein The viscosity of the mud is greater than 25 s, and the specific gravity is 1.2 g / cm 3 ~1.22 g / cm 3 .

3. The composite paste according to claim 1, which is applicable to the pre-treatment of pier pile foundations in karst areas, is characterized in that The slurry is selected from the yellow clay slurry prepared by stirring yellow clay powder and water, or the waste slurry prepared by diluting waste slurry with water or thickening it with mud powder.

4. The composite paste according to claim 3, which is applicable to the pre-treatment of pier pile foundations in karst areas, is characterized in that, The waste slurry is at least one of the slurry for pile foundation pouring, the slurry from the sand washing plant, and the slurry for slurry shield.

5. The composite paste according to claim 3, which is applicable to the pre-treatment of pier pile foundations in karst areas, is characterized in that Each cubic meter of the composite paste is composed of 300 kg of cement, 280 kg - 300 kg of yellow clay powder, 400 kg - 480 kg of water, 850 kg of stone powder, 3 kg of the first admixture, and 3 kg of the second admixture; or each cubic meter of the composite paste is composed of 300 kg of cement, 550 kg - 620 kg of waste slurry, 820 kg - 880 kg of stone powder, 3 kg of the first admixture, and 3 kg of the second admixture.

6. The composite paste according to claim 1, which is applicable to the pre-treatment of pier pile foundations in karst areas, is characterized in that, The cement is P.O42.5R ordinary Portland cement.

7. The composite paste applicable to the pre-treatment of pier pile foundations in karst areas according to claim 1, wherein The stone powder is the powder obtained by crushing or screening at least one of construction waste, muck from earth pressure balance shield, and waste powder from the stone yard; the average particle size of the stone powder is 0.5 mm - 3 mm, and the maximum particle size is less than 5 mm.

8. The composite paste according to claim 1, which is applicable to the pre-treatment of pier pile foundations in karst areas, is characterized in that The first admixture is the HY-1# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a powdery solid; the second admixture is the HY-2# admixture produced by Hunan Hongyu Engineering Group Co., Ltd., which is a liquid.

9. A preparation method of a composite paste applicable to pre-treatment of pier pile foundations in karst areas as claimed in any one of claims 1 to 8, characterized in that, It includes the following steps: S1. Pretreatment of raw materials: Screen the stone powder and remove the coarse particles to ensure that the average particle size of the stone powder is 0.5 mm - 3 mm, and the maximum particle size is less than or equal to 5 mm; S2. Stirring and mixing: According to the set mass ratio, first add the slurry and cement into the mixer and stir at a stirring speed of 1440 r / min for 1 min - 3 min to mix evenly into a semi-finished slurry; then pump the prepared semi-finished slurry to a flat-mouth forced mixer and add the stone powder, and stir at a stirring speed of 25 r / min for 1 min - 3 min to form a uniform paste; finally, add the composite admixture and continue to stir at a stirring speed of 25 r / min for 2 min to obtain a composite paste with stable performance.

10. A grouting method, characterized in that, Grouting is carried out using the composite paste according to any one of claims 1 - 8 applicable to the pretreatment of pier pile foundations in karst areas. The steps include: (1) Arrangement of grouting holes: According to the exploration results of the karst area of the pier, a combination of geophysical exploration and drilling is used to accurately determine the positions and scopes of karst caves and solution grooves, and grouting holes are arranged around the pier foundation. The depth of the grouting holes should penetrate the karst development layer and enter the stable bedrock by 1.0 m; (2) Grouting sequence: Adopt the method of grouting by sequential drilling. First, grout the peripheral grouting holes, and then gradually grout the middle grouting holes from the outside to the inside. And in each grouting hole, insert the grouting pipe to the bottom of the hole and adopt the backward grouting method, and carry out precise grouting section by section in the order from bottom to top; (3) Control of grouting pressure and flow rate: During the grouting process of each grouting hole, at the initial grouting, adopt a grouting pressure of 0.5 MPa and a grouting flow rate of 10 m³ / h to enable the composite paste to quickly fill part of the voids; As the grouting progresses, when the voids are gradually filled, the grouting pressure gradually increases to 0.8 MPa - 1.0 MPa, and the grouting flow rate correspondingly decreases to 6 m³ / h; When the grouting pressure reaches the designed final pressure of 1.0 MPa - 1.5 MPa, end the grouting of this interval lifting section, lift the grouting pipe upward, and wait for the slurry to initially solidify before carrying out the next section of grouting until the grouting of the current grouting hole is completed.