WO2022160712A1

WO2022160712A1 - Method for consolidating soft soil foundation by using industrial solid waste as main raw material

Info

Publication number: WO2022160712A1
Application number: PCT/CN2021/116000
Authority: WO
Inventors: 侯宜峰; 吴小刚; 谢胜华; 秦柯; 代永新; 朱君星; 唐恺; 赵蒙生; 曾学敏; 周玉新; 赵骏
Original assignee: 中钢集团马鞍山矿山研究总院股份有限公司; 华唯金属矿产资源高效循环利用国家工程研究中心有限公司; 中钢集团马鞍山矿院工程勘察设计有限公司
Priority date: 2021-01-27
Filing date: 2021-09-01
Publication date: 2022-08-04
Also published as: CN112921945A

Abstract

Disclosed is a method for consolidating a soft soil foundation by using industrial solid waste as a main raw material. The raw material of a soft soil curing agent comprises the following components in percentages by mass: 35.0-42.0% of carbonated steel slag, 22.0-27.0% of a slag powder, 6.0-10.0% of fly ash, 24.0-35.0% of cement, and 2.0-5.0% of lime, gypsum or a mixture of both in any ratio. When the total mass of soft soil, water and the soft soil curing agent is 100%, the mixing ratio of the soft soil curing agent is 12.0-20.0%; and according to the present invention, water is added at a water cement ratio of 0.45-0.55, and the mixture is stirred to prepare a soft soil curing agent slurry, which is injected into the soft soil foundation. According to the present invention, a cement curing agent is replaced with the carbonated steel slag, the slag powder and the fly ash, such that not only is the problem of the low utilization rate of industrial solid waste solved, and the consolidation cost of a mixing pile in the soft soil foundation is greatly lowered, but the treatment problem of the soft soil foundation in urban development and construction is also solved, and the present invention meets the requirements of "Technical Specifications for Consolidation Method of Mixing Pile in Soft Soil Foundation (YBJ225-91).

Description

A method for reinforcing soft soil foundation with industrial solid waste as main raw material

technical field

The invention relates to a method for reinforcing a soft soil foundation with industrial solid waste as the main raw material, and belongs to the technical field of soft soil foundation reinforcement.

Background technique

my country is a big steel producing country, and a large amount of steel slag is discharged every year. For a long time, the utilization rate of steel slag in my country has been low, but the amount of slag discharged every year is still increasing by tens of millions of tons. A large amount of steel slag is discarded and accumulated, and it is difficult to make full use of it. The important reason is that its composition contains a large amount of free oxides (f-CaO, f-MgO), and these free oxides easily react with water or steam to generate volume expansion (f-CaO , and f-MgO reaction expansion ratios are 98% and 148%, respectively), which makes it difficult for steel slag and tailings after steel slag disposal to be used in large-scale building materials, and the utilization rate of steel slag is low (less than 20%), and the stockpile is large. Long time (to be aged for more than 6 months).

The steel production process also emits a large amount of carbon dioxide, which is also a source of air pollution caused by industrial solid waste in my country. Therefore, using the carbonation reaction between calcium and magnesium components in steel slag and carbon dioxide to produce stable carbonate products can not only fix CO ₂ on a large scale, but also change the physical and chemical properties of steel slag. Carbonation of steel slag can not only use the by-product steel slag of the steel plant to fix its by-product waste gas CO ₂ , but also can significantly reduce the free oxides in the steel slag (f-CaO can be reduced to less than 1%), promote the utilization of steel slag, and realize waste treatment with waste. , recycling, has important social significance and engineering application research background.

In addition, my country is a country with a large population, and the population growth rate is relatively fast. In recent years, the development speed of my country's infrastructure construction has been greatly improved, and the demand for land is increasing. The amount of arable land in the country is also decreasing. This makes us focus on weak foundations, and it has far-reaching significance to make full use of these soft foundations. The soft soil has the characteristics of large natural water content, large plastic index, large natural void ratio, small weight and low permeability. It has high compressibility and poor strength, and cannot be directly used in engineering construction, foundation treatment, etc. It is necessary to take measures to treat the soft soil to improve the stability of the soft soil subgrade and the load bearing capacity.

There are many treatment methods for soft soil subgrade, and the classification is also different, including: sand cushion method, dynamic compaction method, replacement method, static drainage consolidation method, and gravel pile method. "Basic Construction" published in the 33rd issue of 2019, "Analysis of the application of soft soil foundation reinforcement treatment methods in road engineering" also introduced several commonly used soft soil foundation treatment methods, including: (1) Shallow layer treatment; (2) Drainage consolidation method treatment; (3) granular pile treatment; (4) reinforced soil pile treatment; (5) cement fly ash gravel pile (CFG) treatment. But in general, the most common way to solidify soft soil foundations is to add cement for mixing, and use a special mixing machine to spray cement into the soft soil for mixing, thereby strengthening the soft soil foundation. However, with the improvement of environmental protection requirements in the development of modern cities, the use of a large amount of cement as a curing agent has been unable to meet the needs of society.

SUMMARY OF THE INVENTION

The purpose of the present invention is to aim at the above-mentioned defects existing in the prior art, and to provide a method for reinforcing soft soil foundation with industrial solid waste as the main raw material, so as to solve the problem that a large amount of cement is used in the treatment of existing soft soil foundation, which cannot meet social demands and Scrap from steel plants is difficult to handle.

The present invention is a method for reinforcing soft soil foundation by using industrial solid waste as the main raw material. 27.0%, fly ash 6.0-10.0%, cement 24.0%-35.0%, lime, gypsum or any mixture of the two 2.0-5.0%; industrial solid waste carbonated steel slag, slag powder, fly ash account for soft soil 64.0 to 74.0% of the total amount of curing agent; according to the following process:

1) The amount of soft soil curing agent added

When the sum of the mass of soft soil, water and soft soil curing agent is 100%, the mixing ratio of soft soil curing agent is 12.0-22.0%;

2) Construction technology

(1) Preparation of soft soil curing agent slurry: Weigh carbonated steel slag, slag powder, fly ash, cement, lime and/or gypsum in a sample preparation bucket according to the proportions, mix them thoroughly, and then follow the steps of 0.45-0.55 water ash. The water-cement ratio is generally 0.5.

(2) Site leveling and staking: According to reliable benchmarking points and control pile positions, site leveling and staking are carried out.

(3) Drilling and spraying: The pile driver should be positioned accurately according to the designed pile position; the described pile driver adopts the mixing drill, start the mixing drill, and after the drill bit of the mixing drill drills down to the design depth, then rotate the drill bit in the opposite direction to lift the drill bit. While lifting, spray soft soil curing agent slurry into the borehole through the soft soil curing agent slurry sending device. The lifting speed of the drill bit of the mixing rig should not be greater than 0.8m/min; when the drill bit of the mixing drilling rig is lifted to the pile top elevation, turn off the soft soil curing. The agent slurry sending device is used, and the "drilling-lifting, spraying" is recirculated once until the construction of the pile is completed, and then the construction of the next pile is carried out; after the drill bit of the mixing drilling rig is drilled into 0.5 meters, the air compressor is turned on and the compressed air is sprayed. .

The design depth must enter the bearing layer ≥ 0.5m. The soft soil curing agent slurry sending device is a cement sending device in the prior art, and its rotational speed is not less than 50 rpm.

It should be noted that the soft soil curing agent slurry should be strictly filtered before sending, and generally two filtration processes are used. The prepared slurry shall not be segregated, and shall not be left for too long (not more than 2h), so as to avoid agglomeration in the slurry and damage to the pump body. Before pumping the slurry, the pipeline should be kept moist to facilitate slurry delivery.

(4) Cleaning and displacement: Before the pile driver is displaced, an appropriate amount of water should be poured into the collecting hopper of the pile driver, the slurry pump should be turned on, and the remaining slurry in all pipelines should be cleaned until the pipe body is clean, and the stirring rig’s The drill can be moved only after it has been cleaned;

(5) Sampling and testing: Sampling and testing the drill core to check whether the unconfined compressive strength of the pile body meets the requirements of "Technical Regulations for the Reinforcement Method of Mixed Pile on Soft Soil Foundation" (YBJ225-91), that is, the upper middle, The average value of the unconfined compressive strength of the lower part 28d is not less than 0.8MPa, and the minimum value is not less than 1/3 of the design strength.

The mass percentage content of each component in the soft soil curing agent raw material is preferably: carbonated steel slag 36.0%-41.0%, slag powder 23.0%-26.0%, fly ash 7.0-9.0%, cement 24.0%-31.0% %, lime, gypsum or a mixture of the two in any proportion of 3.0-4.0%; wherein industrial solid waste carbonated steel slag, slag powder and fly ash account for 66.0-73.0% of the total soft soil curing agent.

The carbonation steel slag needs to control the particle size, and the particle size is preferably below 2mm, and the finer the effect, the better the effect. Generally, the particle size below 1mm accounts for more than 80% of the mass.

Further, in the carbonated steel slag, it is preferable that the mass proportion of materials with a particle size of ≤1 mm is ≥80%; the cement is ordinary Portland cement of ≥42.5 grade.

Further, in step (3), the drill bit of the stirring drilling rig is drilled down to at least 0.5m of the bearing layer, and the rotational speed of the soft soil curing agent slurry sending device is not less than 50 rpm.

After adopting the above technical scheme, a method for reinforcing soft soil foundation with industrial solid waste as the main raw material of the present invention has the following beneficial effects:

(1) The use of carbonated steel slag, slag powder, fly ash and other industrial solid wastes instead of cement not only solves the problem of low utilization rate of solid waste in the metallurgical industry, but also greatly reduces the reinforcement cost of soft soil foundation mixing piles;

(2) Carbonated steel slag is used for soft soil foundation reinforcement for the first time. Carbonated steel slag is a stable carbonate product with low free oxide content and good stability;

(3) The bearing capacity of the soft soil foundation has been improved, and the unconfined compressive strength of the pile body can meet the requirements of "Technical Regulations for the Reinforcement Method of Soft Soil Foundation Mixing Pile" (YBJ225-91);

(4) The present invention has no vibration, no noise and no pollution to the environment during construction;

(5) There is no lateral extrusion on the soil, which reduces the dry shrinkage of the solidified soil compared with the consolidation of traditional cement, and has little impact on the adjacent buildings, which can maximize the use of the undisturbed soil and effectively improve the strength of the foundation;

(6) In the present invention, the soft soil solidifying agent slurry is sprayed into the depth of the soft soil foundation through a stirring drilling rig, so that a series of physical and chemical reactions are produced between the components in the soft soil solidifying agent slurry sprayed into the soft soil and the soft soil. reaction and synergistic effect, thereby significantly improving the strength of the reinforced soft soil foundation.

Detailed ways

In order to further describe the present invention, a method for reinforcing soft soil foundation with industrial solid waste as the main raw material of the present invention will be further described below with reference to the examples. However, the present invention is not limited to the examples.

The mass percentage content of each component in the soft soil curing agent raw material used in the present invention is: carbonated steel slag 35.0%-42.0%, slag powder 22.0%-27.0%, fly ash 6.0-10.0%, cement 24.0%-35.0% %, lime, gypsum or a mixture of the two in any proportion of 2.0 to 5.0%.

The carbonation steel slag needs to control the particle size, the particle size is preferably below 2mm, and the finer the effect, the better the cement is 42.5 grade ordinary Portland cement. The soft soil curing agent is prepared with dry materials, and the soft soil curing agent slurry is prepared according to the water-cement ratio of 0.5. The carbonated steel slag is mainly composed of iron oxides, calcium oxides, desulfurized gypsum, aluminum slag and a small amount of manganese oxides.

The method of the present invention is a method for reinforcing soft soil foundation with industrial solid waste as the main raw material and adopts the following techniques and steps to construct:

(1) Weigh carbonized steel slag, slag powder, fly ash and lime, gypsum or the mixture of the two and cement in the sample preparation bucket according to the proportion, mix them thoroughly, then add water according to the water-cement ratio of 0.5, and stir to make soft Soil stabilizer slurry.

(2) The construction shall be based on the reliable leveling point and control pile position, and the site shall be leveled and set out. The drilling rig shall be accurately positioned according to the designed pile position. Start the mixing drilling rig, start the air compressor after drilling 0.5 meters, spray compressed air, and drill to the design depth. Note that it is necessary to enter the bearing layer 0.5m, lift the drill to the designed reinforcement depth, rotate in reverse, spray soft soil curing agent slurry while lifting, the lifting speed of the drill should not be greater than 0.8m/min, and the speed of the cement sending device should not be less than 50 rpm /Minute;

(3) The drill bit is raised to the pile top elevation, and the cement sending device is closed, and the drilling is performed again to repeat step (2) until the construction of the pile is completed. The construction of the next pile is then carried out.

(4) Before the pile driver is displaced, an appropriate amount of water should be poured into the collecting hopper, the slurry pump should be turned on, and the remaining slurry in all pipelines should be cleaned until the pipe body is clean and the stirring head is cleaned before displacement.

(5) The soft soil curing agent slurry should be strictly filtered, and two filtering devices should be set up according to the diameter of the nozzle. The prepared slurry shall not be segregated, and shall not be left for too long (not more than 2h), so as to avoid agglomeration in the slurry and damage to the pump body. Before pumping the slurry, the pipeline should be kept moist to facilitate slurry delivery.

(6) Check whether the unconfined compressive strength of the pile body meets the requirements of the "Technical Regulations for the Reinforcement Method of Soft Soil Foundation Mixing Pile" (YBJ225-91), that is, the upper, middle and lower parts (divided by 1/3 of the pile length) are required to be free for 28d. The average value of the confining compressive strength is not less than 0.8MPa, and the minimum value is not less than 1/3 of the design strength.

Table 1 shows the proportions of each embodiment of the soft soil curing agent used in the method of the present invention, and Table 2 shows the unconfined compressive strength (MPa) results of the middle and lower 28d of the pile body of each embodiment after the soft soil foundation is reinforced. In the embodiment, the particle size of the carbonated steel slag needs to be controlled.

Table 1 Components and proportions of soft soil curing agent (%)

Table 2 The unconfined compressive strength (MPa) of the middle and lower part 28d of the pile body of Example 1-6

The experimental research and the results in Table 1 and Table 2 show that Examples 1 to 7 all meet the requirements of "Technical Regulations for Reinforcement Method of Stirred Pile on Soft Soil Foundation" (YBJ225-91) when testing the unconfined compressive strength of the pile body, namely The average value of the 28d unconfined compressive strength of the middle and lower parts of the pile body (divided by 1/3 of the pile length) is not less than 0.8MPa, and the minimum value is not less than 1/3 of the design strength. The soft soil curing agent of carbonated steel slag, slag powder and cement has achieved unexpected results in curing soft soil foundations.

The invention uses industrial solid wastes such as carbonated steel slag, slag powder, fly ash and the like to replace the cement curing agent, and the strength of the solidified pile body can meet the design requirements. It not only solves the problem of the utilization of solid waste in the metallurgical industry, but also solves the problem of the treatment of soft soil foundations in urban development and construction.

Claims

A method for reinforcing soft soil foundation with industrial solid waste as the main raw material, characterized in that the mass percentage of each component in the soft soil solidifying agent raw material is: carbonated steel slag 35.0%-42.0%, slag powder 22.0% %～27.0%, fly ash 6.0～10.0%, cement 24.0%～35.0%, lime, gypsum or any mixture of the two 2.0～5.0%; of which industrial solid waste carbonated steel slag, slag powder and fly ash account for 64.0 to 74.0% of the total amount of soft soil curing agent; according to the following process:

1) The amount of soft soil curing agent added

When the sum of the mass of soft soil, water and soft soil curing agent is 100%, the mixing ratio of soft soil curing agent is 12.0-22.0%;

2) Construction technology

(1) Preparation of soft soil curing agent slurry: Weigh carbonated steel slag, slag powder, fly ash, cement, lime and/or gypsum in a sample preparation bucket according to the proportions, mix them thoroughly, and then follow the steps of 0.45-0.55 water ash. Mix with water and stir to make soft soil curing agent slurry;

(2) Site leveling and staking: According to reliable benchmarking points and control pile positions, site leveling and staking are carried out;

(3) Drilling and spraying: The pile driver should be positioned accurately according to the designed pile position; the described pile driver adopts the mixing drill, start the mixing drill, and after the drill bit of the mixing drill drills down to the design depth, then rotate the drill bit in the opposite direction to lift the drill bit. While lifting, spray soft soil curing agent slurry into the borehole through the soft soil curing agent slurry sending device. The lifting speed of the drill bit of the mixing rig should not be greater than 0.8m/min; when the drill bit of the mixing drilling rig is lifted to the pile top elevation, turn off the soft soil curing. The agent slurry sending device is used, and the "drilling-lifting, spraying" is recycled once until the construction of the pile is completed, and then the construction of the next pile is carried out;

(4) Cleaning and displacement: Before the pile driver is displaced, an appropriate amount of water should be poured into the collecting hopper of the pile driver, the slurry pump should be turned on, and the remaining slurry in all pipelines should be cleaned until the pipe body is clean, and the stirring rig’s The drill can be moved only after it has been cleaned;

(5) Sampling and testing: Sampling and testing the drill core to check whether the unconfined compressive strength of the pile body meets the requirements of "Technical Regulations for the Reinforcement Method of Mixed Pile on Soft Soil Foundation" (YBJ225-91), that is, the upper middle, The average value of the unconfined compressive strength of the lower part 28d is not less than 0.8MPa, and the minimum value is not less than 1/3 of the design strength.
A method for reinforcing soft soil foundation with industrial solid waste as main raw material as claimed in claim 1, wherein the mass percentage of each component in the described soft soil solidifying agent raw material is: carbonated steel slag 36.0% ～41.0%, slag powder 23.0%～26.0%, fly ash 7.0～9.0%, cement 24.0%～31.0%, lime, gypsum or any mixture of the two 3.0～4.0%; Slag powder and fly ash account for 66.0-73.0% of the total soft soil curing agent.
A method for reinforcing soft soil foundations with industrial solid waste as the main raw material according to claim 1 or 2, characterized in that the particle size of the carbonated steel slag is less than or equal to 2 mm.
The method for reinforcing soft soil foundations with industrial solid waste as the main raw material according to claim 3, characterized in that: in the carbonated steel slag, the mass proportion of materials with particle size ≤ 1 mm is ≥ 80%; The cement is ≥42.5 grade ordinary Portland cement.
The method for reinforcing soft soil foundations with industrial solid waste as the main raw material according to claim 4, characterized in that: in step (3), the drill bit of the stirring drilling rig is drilled down to at least 0.5m of the bearing layer.
A method for reinforcing soft soil foundation with industrial solid waste as main raw material as claimed in claim 5, characterized in that: in step (3), the rotational speed of the soft soil curing agent slurry sending device is not less than 50 rpm.