Method of soil solidification

Abstract

The application discloses a soil solidification method and belongs to the field of road engineering. The solidification method comprises the following steps: S1, performing particle size analysis on undisturbed soil to determine the weight proportion of gravelly soil, sandy soil, fine-grained soil and clay soil; S2, determining the adding amount of gravelly soil additive, sandy soil additive, fine-grained soil additive and clay soil additive, so that the weight proportion of gravelly soil, sandy soil, fine-grained soil and clay soil in the solidification system reaches (0.1-2.0):(1.0-5.0):(82.0-86.0):(10.0-15.0); and S3, mixing the gravelly soil, sandy soil, fine-grained soil and clay soil in proportion, mixing the mixture with an appropriate amount of liquid material, and uniformly mixing the mixture, and then standing or compression molding to complete soil solidification, wherein the liquid material is a calcium hydroxide solution. Compared with the prior art, the soil solidification method can form a soil solidification system with good later strength and water stability, and can be widely applied to the field of road base and cushion paving.

Description

Technical Field

[0001] This invention relates to the field of road engineering, and specifically provides a soil solidification method. Background Technology

[0002] Soil is classified into various types based on its inherent characteristics. Furthermore, even within the same type, the composition of soil varies significantly across different regions, leading to instability and difficulty in full utilization. For example, many soils possess an inorganic double-layer structure, exhibiting certain gelling properties. However, when exposed to mineral-containing water, this structure ionizes, disrupting the double-layer structure and halting the gelation reaction, resulting in the formation of flocculent matter. Additionally, silt, saline soil, and loess are all fine-grained soils. The lack of a skeletal structure and capillary action greatly restrict soil strength formation, and the strength of dry soil gradually diminishes under repeated capillary action.

[0003] Cement and lime are the most common inorganic curing materials in road engineering. However, their practical application has two significant drawbacks. First, while traditional hydration-based gelation curing methods achieve high early strength, the relatively low dosage prevents the gel products from effectively forming a network structure. Under the influence of temperature and humidity changes, this structure is prone to damage, with soil particles redistributing within the cured soil, resulting in insufficient durability. Second, gel materials are mainly based on alkali activation and cement hydration. Under capillary water and ion diffusion mechanisms, additives migrate to the surrounding area over time, causing uneven distribution of internal strength and the diffusion of certain alkaline and heavy metal elements, which can damage the environment. Third, inorganic curing materials are rigid materials, exhibiting significant physical phenomena such as thermal expansion and contraction. The volume changes of rigid materials inevitably lead to numerous cracks, making them highly susceptible to shear failure in practical engineering applications.

[0004] While existing organic curing materials can avoid the problem of numerous cracks easily generated by rigid materials to some extent, their strength is only about one-third that of inorganic materials. Furthermore, the cost of organic materials is dozens of times higher than that of inorganic materials, and their cost and strength greatly restrict their promotion in engineering applications. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a soil solidification method that can form a soil solidification system with good long-term strength and water stability.

[0006] The original soil described in this invention can be any type of engineering soil in the prior art, such as saline soil, silt, loess sand, and fine-grained soil.

[0007] The technical solution adopted by this invention to solve its technical problem is: a soil consolidation method, characterized by including:

[0008] S1. Perform particle size analysis on the undisturbed soil (soil to be solidified without any grinding treatment) to determine the weight ratio of gravelly soil, sandy soil, fine-grained soil and clay soil in the undisturbed soil;

[0009] S2. Determine the addition amounts of gravel-like admixtures, sand-like admixtures, fine-particle admixtures, and clay admixtures, so that the weight ratio of gravel-like admixtures, sand-like admixtures, fine-particle admixtures, and clay admixtures in the solidification system reaches (0.1-2.0):(1.0-5.0):(82.0-86.0):(10.0-15.0).

[0010] The gravel has a particle size of 2mm-60mm and is composed of gravel admixtures and gravel soil.

[0011] The particle size of the sand-like material is 0.075mm-2mm, excluding 2mm, and the sand-like material is composed of sand-like admixtures and sand-like soil.

[0012] The fine particles have a particle size of 0.005mm-0.075mm, excluding 0.075mm, and are composed of fine particle admixtures and fine-grained soil.

[0013] The clay particles have a particle size of less than 0.005 mm and are composed of clay admixtures and clay soil.

[0014] S3. Gravel, sand, fine particles, and clay particles are mixed in proportion and mixed evenly with an appropriate amount of liquid material. The mixture is then left to stand or pressed into shape to complete soil solidification. The liquid material is a calcium hydroxide solution.

[0015] As a preferred option, when determining the amount of admixture to be added in step S2, the material with the highest content in the soil can be used as a benchmark, and it can be considered that the material of that grade does not need to be added. The amount of admixture to be added for other grades can be calculated based on the mass of the material of that grade.

[0016] As a preferred embodiment, the weight ratio of gravel-like particles, sand-like particles, fine particles, and clay particles in the solidification system is (0.5-1.5):(1.0-3.0):(84.0-86.0):(11.0-13.0).

[0017] As a preferred option, the amount of liquid material added is 4-12% of the weight of the solidified system (gravel-like, sand-like, fine-grained, clay-like), and the specific amount can be determined based on the liquid and plastic limits of the soil.

[0018] Preferably, the liquid material is a mixture of saturated calcium hydroxide and water in a weight ratio of 1:(0.5-1.5). If the calcium hydroxide is added to the powder and it is too saturated, the powder will be mixed in half, resulting in uneven reaction of the soil mixture and easy local expansion and cracking. If the calcium hydroxide content is too low, the material reaction will be incomplete, affecting the final strength. The weight ratio of saturated calcium hydroxide to water is particularly preferred to be 1:(0.8-1.2).

[0019] Preferably, step S3 includes:

[0020] S31. Gravel, sand, fine particles, and clay particles are mixed in proportion and stirred at a speed of 100-400 rpm (particularly preferably 200-300 rpm) until uniformly mixed to obtain a solid mixture. The stirring time is preferably 4-6 min.

[0021] S32. Add liquid material to the solid mixture in proportion, and stir evenly at a speed of 300-600 rpm (particularly preferably 400-500 rpm), with a stirring time preferably 10-20 min;

[0022] S33. Reduce the speed to 50-150 rpm (preferably 80-100 rpm) and continue stirring for 3-10 minutes.

[0023] Preferably, the gravel-like admixture includes mullite and / or wollastonite. When mullite and wollastonite work together, their mass ratio is preferably 1:(0.5-1.5).

[0024] Preferably, the sand-like admixture includes calcium chloride and / or ceramic particles. When calcium chloride and ceramic particles are used together, the preferred mass ratio is 1:(3-7).

[0025] Preferably, the fine-particle admixture includes sodium bicarbonate and / or quicklime. When sodium bicarbonate and quicklime work together, their mass ratio is preferably 1:(0.5-1.5).

[0026] Preferably, the clay admixture includes silica fume, nano-fly ash, and / or nano-montmorillonite. When silica fume, nano-fly ash, and nano-montmorillonite are used together, the preferred mass ratio of the three is 1:(0.5-1.5):(3-7).

[0027] Preferably, if the mixture after low-speed mixing in step S33 is dark brown and sticky in flakes, it can be left to stand and mold; if the mixture is light-colored and can only be molded by hand, it is recommended to use a hydraulic press to compact and mold it.

[0028] If the clay content in the original soil is greater than 15% (e.g., silt, or silt in some alluvial plains), the clay content cannot be eliminated and can only be increased, making the solidification method of this invention unsuitable.

[0029] Extensive research by the applicant has revealed that the clay content and soil gradation in a solidified soil system significantly influence the soil's later-stage strength; a smoother gradation results in higher mixture strength. Based on this, the applicant proposes the soil solidification method described in this invention. Compared to existing technologies, this solidification method offers the following significant advantages:

[0030] (i) It is not limited to a single soil type and has a certain degree of universality. Users can adjust it according to the particle size classification in the soil.

[0031] (II) The cured system obtained by the method of this invention firstly possesses a certain self-healing ability. As time goes by, the internal particle interlocking structure will be further strengthened, ensuring that even if surface cracks occur, the cracks will not extend inward. Secondly, the graded curing method does not conflict with traditional inorganic curing methods. The early strength of the material can be supplemented by changing the composition of the liquid material. For example, an appropriate amount of water glass can be added to the liquid material to improve the early strength of the cured system.

[0032] (III) Through actual experimental comparison, it can be found that the thermal shrinkage and drying shrinkage coefficients of the solidification system obtained by the method of the present invention are significantly lower than those of traditional inorganic solidified soil materials.

[0033] (iv) The solidified soil specimen of the present invention has good water resistance; the early strength increase is slower than that of cement, and the compressive strength can reach 2-4 MPa after 7 days of molding.

[0034] The results show that for general soils, the strength of soil specimens cured by the graded theory after soaking in water is higher than that of dry-compressed soil, and the water stability is greater than 1. However, the strength loss of most cement-based cured soil specimens after soaking in water is around 50-80%. For special soil types, although the strength of graded theory-cured soil undergoes some loss after soaking, it is still significantly better than that of traditional inorganic curing methods. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the present invention.

[0036] Unless otherwise specified, the content of each ingredient used below is a percentage by mass.

[0037] Example 1

[0038] Undiscovered soil: Sandy, low-liquid-limit silty soil.

[0039] 1. Adding raw materials:

[0040] Gravel admixture: Mullite and wollastonite in a mass ratio of 1:1, with a particle size of 2mm-60mm.

[0041] Sand-like admixture: calcium chloride and ceramic particles in a mass ratio of 1:5, with a particle size of 0.075mm-2mm (excluding 2mm).

[0042] Fine-grained admixture: sodium bicarbonate and quicklime in a mass ratio of 1:1, with a particle size of 0.005mm-0.075mm (excluding 0.075mm).

[0043] Clay admixture: silica fume, nano fly ash, and fine montmorillonite in a mass ratio of 1:1:5, with a particle size of less than 0.005 mm.

[0044] 2. Curing method:

[0045] S1. Particle size analysis of the undisturbed soil reveals its particle size range, as detailed in Table 1.

[0046] Table 1. Particle size distribution of undisturbed soil

[0047]

[0048] Note: The margin of the measured value represents stones and other impurities contained in the original soil.

[0049] In this embodiment, the fine-grained soil content of the original soil is greater than the target mix proportion. When calculating, the amount of other particle sizes to be added is estimated based on the weight of the fine-grained soil. For example, 100g of this type of silt has a fine-grained soil mass of 87.56g. Then the amount of gravel admixture to be added is 87.56 / 85*1=1.03g. Similarly, the amount of sand admixture to be added is 87.56 / 85*(2-0.69)=1.35g, and the amount of clay admixture to be added is 87.56 / 85*(12-11.56)=0.45g.

[0050] S3. Mix the various admixtures with the original soil to be solidified in proportion, and stir at a speed of 300 rpm until the mixture is uniform (stirring time is 5 min) to obtain a solid mixture;

[0051] S4. Add calcium hydroxide solution at 10% of the mass of solid mixture and stir evenly at 500 rpm (stirring time is 15 min). The calcium hydroxide solution is made by mixing saturated calcium hydroxide and water in a 1:1 weight ratio.

[0052] S5. Reduce the speed to 100 rpm and continue stirring for 5 minutes;

[0053] S6. After standing for 1 hour, the sample is pressed into shape using a press to obtain the test sample of Example 1.

[0054]

Example 2

[0055] Original soil: Collapsible loess.

[0056] The raw materials and curing methods were the same as in Example 1, and the test sample for Example 2 was prepared.

[0057]

Example 3

[0058] Original soil: saline soil.

[0059] The raw materials and curing methods were the same as in Example 1, and the test sample for Example 3 was prepared.

[0060] [Test Example]

[0061] The samples of each embodiment and the cement-cured specimens were tested using the unconfined compressive strength (UCS) method. The mechanical properties of the cured soil specimens were characterized by measuring their unconfined compressive strength under static pressure.

[0062] Among them, the preparation of cement-cured test specimens: 425 cement (8% admixture) was used to cure sandy low liquid limit silt, collapsible loess and saline soil respectively to prepare cement-cured test specimens.

[0063] The test is divided into two types: dry pressing without lateral confinement and standard immersion without lateral confinement. Dry pressing refers to bagging and curing at room temperature, and the test can be performed after the target age is reached. Immersion strength refers to the test result after immersion in water for 12 hours based on the current age.

[0064] The test results are shown in Tables 2, 3 and 4.

[0065] Table 2 Comparison of silt solidification results in Example 1

[0066]

[0067] Table 3 Comparison results of solidification of collapsible loess in Example 2

[0068]

[0069] Table 4 Comparison of solidification results of saline soil in Example 3

[0070]

[0071] Comparison of experimental results reveals significant differences in the curing effect of the same curing agent on different soil types. The gradation theory curing method, due to the presence of water-soluble solid particles such as calcium chloride, provides beneficial calcium ions to the cured soil mixture after immersion in water. The resulting tetrahedral structure with calcium as its core effectively enhances the final molding strength of the soil mixture. However, for the curing of special soil types (see Table 4), the gradation theory immersion strength still shows a significant decrease. This is mainly because the soil itself has a high salt content. After immersion, under the influence of capillary action, salt precipitates to the surface of the mixture, affecting the particle distribution in the gradation theory and causing uneven aggregate structure distribution, thus affecting the molding strength after immersion.

[0072] For general fine-grained soils such as silt and loess, the gradation theory solidification method has obvious advantages and higher material strength stability. However, for special fine-grained soils such as saline soils, the advantages of the gradation solidification theory are not obvious, but the water immersion strength can still meet the requirements of the current soil subgrade specifications, which has certain significance for promotion.

[0073] Compared to traditional cement-based solidification materials, experimental results show that cement-based materials suffer significant strength loss after immersion in water. However, the solidified soil specimens based on the gradation theory show almost no difference in strength between the immersion and non-immersion states. This indicates that using the gradation theory for soil solidification can effectively fill the tiny pores between soil particles, effectively preventing capillary water flow. The denser internal structure provides higher mechanical strength and prevents water erosion. Even if a small amount of free water appears inside, the dense internal structure can effectively prevent the water from entraining the soil particles, thus achieving a reinforcement and waterproofing effect.

[0074] The embodiments described above are merely preferred embodiments of the present invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the technical solutions of the present invention should be included within the protection scope of the present invention.

Claims

1. A soil consolidation method, characterized in that, include: S1. Perform particle size analysis on the undisturbed soil to determine the weight ratio of gravelly soil, sandy soil, fine-grained soil and clay soil in the undisturbed soil. S2. Determine the addition amounts of gravel-like admixtures, sand-like admixtures, fine-particle admixtures, and clay admixtures, so that the weight ratio of gravel-like admixtures, sand-like admixtures, fine-particle admixtures, and clay admixtures in the solidification system reaches (0.1-2.0):(1.0-5.0):(82.0-86.0):(10.0-15.0). The gravel has a particle size of 2mm-60mm and is composed of gravel admixtures and gravel soil. The gravel admixtures include mullite and / or wollastonite. The particle size of the sand-like material is 0.075mm-2mm, excluding 2mm. The sand-like material is composed of sand-like admixtures and sand-like soil. The sand-like admixtures include calcium chloride and / or ceramic particles. The fine particles have a particle size of 0.005mm-0.075mm, excluding 0.075mm. The fine particles are composed of fine-particle admixtures and fine-particle soil-like materials. The fine-particle admixtures include sodium bicarbonate and / or slaked lime. The clay particles have a particle size of less than 0.005 mm and are composed of clay admixtures and clay soil. The clay admixtures include silica fume, nano-fly ash and / or nano-montmorillonite. S3. Gravel, sand, fine particles, and clay particles are mixed in a certain proportion and then mixed evenly with an appropriate amount of liquid material. The mixture is then allowed to stand or pressed into shape to complete soil solidification. The material mixing process includes the following steps: S31. Gravel, sand, fine particles, and clay particles are mixed in proportion and stirred at a speed of 100-400 rpm until uniformly mixed to obtain a solid mixture; S32. Add liquid material to the solid mixture in proportion and stir evenly at a speed of 300-600 rpm. The liquid material is a mixture of saturated calcium hydroxide and water in a weight ratio of 1:(0.5-1.5), and the amount of liquid material added is 4-12% of the weight of the solidified system. S33. Reduce the speed to 50-150 rpm and continue stirring for 3-10 minutes.

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