Improved expansive soil as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of expansive soil, and particularly relates to improved expansive soil as well as a preparation method and application thereof. The invention relates to improved expansive soil, which is prepared from the following components in percentage by mass: 0.6 to 1.2 percent of biopolymer, 3 to 7 percent of plant ash, 0 to 2 percent of plant matrix and the balance of expansive soil to be improved. By doping the biopolymer, the plant ash and the plant matrix, the physical and mechanical properties of the expansive soil can be improved from four aspects of filling and bonding effects, ion exchange effects, reinforcement effects and fertility increasing effects, and the purposes of reducing the expansive potential of a soil body, inhibiting fracture development and strength attenuation of the soil body and facilitating plant growth are achieved. The plant ash and the plant matrix are used for improving the expansive soil, the environmental pollution challenge caused by poor treatment of agricultural waste is solved, waste is turned into wealth, and great economic benefits and social benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of expansive soil, and in particular relates to improved expansive soil and a preparation method and application thereof. Background Art

[0003] At present, the main methods for improving the poor engineering properties of expansive soil include replacement method, flexible reinforcement, lime cement and ion curing agent improvement, but these methods are time-consuming and economically expensive, or easily cause environmental pollution, which is not conducive to subsequent ecological restoration. Therefore, it is very necessary to seek a low-cost, environmentally friendly method that can improve the poor engineering properties of expansive soil.

[0004] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0005] The object of the present invention is to provide an improved expansive soil and a preparation method and application thereof, so as to solve the problem that the existing methods for improving expansive soil in the background technology do not have good engineering properties.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The first object of the present invention is to provide an improved expansive soil, which is prepared from the following components by mass percentage: 0.6-1.2% biopolymer, 3-7% wood ash, 0-2% plant matrix and the balance of the expansive soil to be improved.

[0008] Preferably, the biopolymer is selected from one of xanthan gum, guar gum and gum arabic.

[0009] Preferably, the particle size of the wood ash is 10-80 mesh, and its main components include silicon dioxide, potassium phosphate, calcium carbonate, calcium oxide, phosphorus pentoxide and potassium oxide, and their mass percentages are: 20-30%, 15-25%, 10-15%, 5-10%, 5-10% and 5-10% respectively.

[0010] Preferably, the plant matrix comprises three parts, namely, unrotten plant fibers, partially rotten plant fibers and completely rotten plant fibers, with the mass percentages being 40-50%, 30-40% and 20-30% respectively; wherein the length of the plant fibers is 1-3 cm and the width is 0.1-0.2 mm; the plant fibers are taken from agricultural waste, such as straw fibers, coconut fibers and bagasse fibers; the completely rotten plant fibers, partially rotten plant fibers and unrotten plant fibers provide nutrients for the early, middle and late stages of plant growth respectively.

[0011] In this technical solution, the improvement principle of expansive soil is as follows:

[0012] (1) Filling and bonding. When xanthan gum is dissolved in water, it forms a viscous colloid. On the one hand, it fills the pores between soil particles, changes the internal pore structure of the soil, reduces the migration rate of water in the soil, and improves the water retention of expansive soil. On the other hand, the carboxyl (-COOH) group and hydroxyl (-OH) group contained in xanthan gum form a stable spatial network structure with clay minerals through electrostatic bonding or hydrogen bonding, and use its own tensile strength to limit the deformation of surrounding soil particles, effectively improving the connection between soil particles. The stronger the connection between soil particles, the greater the tensile strength, and the more difficult it is to produce cracks.

[0013] (2) Ion exchange. The high-valent cations (such as calcium ions and magnesium ions) in wood ash replace the hydrophilic low-valent cations (such as potassium ions and sodium ions) on the surface of clay particles, reducing the sensitivity of clay particles to water, thereby releasing the bound water bound in the adsorption layer and diffusion layer, reducing the thickness of the hydration film on the surface of soil particles, and inhibiting the development of cracks. The smaller the thickness of the hydration film on the surface of clay particles, the greater the connection force between particles and the higher the shear strength of the soil. With the further diffusion of high-valent cations, the low-valent hydrophilic cations between the crystal layers of clay minerals are also replaced, making it difficult for water molecules to form crystal layers, thereby reducing the expansion of the clay minerals themselves.

[0014] (3) Reinforcement effect. The unrotten plant fibers in the plant matrix intertwine and entangle with each other in the expansive soil to form a three-dimensional spatial reinforcement structure. When the expansive soil expands and contracts, the plant fibers constrain the deformation of the expansive soil through the reinforcement structure, increase the overall stability of the soil, and thus improve the physical and mechanical properties of the expansive soil.

[0015] (4) Fertilizing effect. The decayed plant fibers in the plant matrix contain a certain amount of organic matter and humus, and the wood ash contains nutrients such as nitrogen, phosphorus and potassium, which can effectively improve the fertility of the expansive soil and meet the long-term growth needs of slope protection plants.

[0016] A second object of the present invention is to provide a method for preparing the improved expansive soil, comprising the following steps:

[0017] S1. Weigh each component by mass percentage, mix them evenly, and obtain a mixed soil;

[0018] S2. Determine the optimum moisture content and maximum dry density of the mixed soil according to the light compaction test in the Highway Geotechnical Test Code (JTG 3430-2020);

[0019] S3. Add water to the mixed soil according to the optimal moisture content, stir evenly and seal under natural conditions for 3-4 days to obtain the improved expansive soil.

[0020] More specifically, when the expansive soil is weak expansive soil, the amount of the plant ash is 3-5%; when the expansive soil is medium or strong expansive soil, the amount of the plant ash is 5-7%.

[0021] The third object of the present invention is to provide the application of the improved expansive soil in expansive soil slope engineering or roadbed filling engineering.

[0022] More specifically, when the improved expansive soil is used in an expansive slope project, the amount of the plant matrix is ​​1-2%; when the improved expansive soil is used in a roadbed filling project, the amount of the plant matrix is ​​0%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The biopolymer, plant fiber and wood ash of the present invention have the advantages of being natural, harmless, renewable, widely available and easy to construct. After being mixed with soil, they can quickly improve the physical, chemical and mechanical properties of expansive soil from four aspects, namely, filling and bonding, ion exchange, reinforcement and fertilization, thereby achieving the purpose of reducing the expansion potential of the soil, inhibiting the development of soil cracks, improving the shear strength of the soil and promoting plant growth.

[0025] (2) The plant matrix used in the present invention is derived from agricultural and forestry waste, and the wood ash used is derived from power plants that use agricultural waste as raw materials. Using the plant matrix and wood ash to improve expansive soil helps to solve the environmental pollution challenges caused by poor disposal of agricultural waste, turning waste into treasure, and has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the effect diagram of the slope engineering construction structure;

[0027] Description of main reference numerals:

[0028] 1. Plain expansive soil; 2. Improved expansive soil; 3. Slope protection plants; 4. Drainage ditch. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solution of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In the embodiments, the plant substrate only needs to meet the requirements of “Organic substrate for greening” (LY / T 1970—2011).

[0031] Example 1: Roadbed Engineering

[0032] 1000kg of improved expansive soil (free expansion rate before improvement is 62%) is prepared for roadbed engineering. The specific method is as follows:

[0033] S1. Weigh the following ingredients by mass percentage: 1% xanthan gum, 0% plant matrix, 5% wood ash and 94% expansive soil, i.e., 10kg biopolymer, 0kg plant matrix, 50kg Guangxi Zhuang Fang Yuan brand wood ash and 940kg Guangxi Ningming area expansive soil; mix the weighed ingredients to obtain a mixed soil;

[0034] S2. According to the Highway Geotechnical Test Code (JTG 3430-2020), a light compaction test was conducted on the mixed soil to determine that the optimal moisture content of the mixed soil was 21.58% and the maximum density was 1.67g / cm 3 ;

[0035] S3. Weigh 202.85kg of water according to the optimal moisture content of 21.58% and add it to the mixed soil, stir evenly, and seal for 3-4d to obtain the improved expansive soil;

[0036] S4. The improved expansive soil is transported to the site, evenly paved, and the paving thickness is 30cm;

[0037] S5. Use a roller to quickly roll and accurately level the soil, with a soil compaction degree of more than 98%.

[0038] Basic physical tests were conducted on untreated expansive soil (plain expansive soil) samples and expansive soil samples (improved expansive soil) treated by the method of this embodiment. The results are shown in Table 1.

[0039] Table 1 Physical and mechanical properties of plain expansive soil and improved expansive soil

[0040]

[0041] As shown in Table 1, the engineering properties of the improved expansive soil have been significantly improved: the free expansion rate has decreased by 50%, and the cohesion and internal friction angle have increased by 67.36% and 23.32% respectively. The free expansion rate of the plain expansive soil is 62%, and the free expansion rate of the improved expansive soil with 1% xanthan gum and 5% plant ash is only 31%, which meets the requirement of the Technical Specifications for Highway Subgrade Construction that the expansion rate of the improved expansive soil is less than 40%.

[0042] Example 2: Slope Engineering

[0043] Prepare 1000kg of improved expansive soil (the free expansion rate before improvement is 62%) for slope engineering. The specific method is as follows:

[0044] S1. Weigh the following ingredients by mass percentage: 1% xanthan gum, 1.5% plant matrix, 5% wood ash and 92.5% expansive soil, i.e. 10kg biopolymer, 15kg plant matrix, 50kg Shandong Yuanli Bio-branded wood ash and 925kg expansive soil in Nanning, Guangxi; mix the above ingredients evenly to obtain a first mixed soil;

[0045] S2. According to the Highway Geotechnical Test Code (JTG 3430-2020), a light compaction test was conducted on the mixed soil to determine that the optimal moisture content of the mixed soil was 21.78% and the maximum density was 1.64 g / cm 3 ;

[0046] S3. According to the optimum moisture content of 21.78%, 201.47kg of water was weighed and added to the first mixed soil, stirred evenly, and sealed for 3-4d to obtain the first improved expansive soil;

[0047] S4. Adding plant grass seeds suitable for the local growth environment to the improved expansive soil and stirring evenly to obtain a second improved expansive soil; wherein the plant grass seeds include fibrous root plants such as Bermuda grass, tall fescue, white grass and ryegrass, and the vertical length of the root system is less than 30cm;

[0048] The saturated permeability coefficient of the second improved expansive soil sample is less than 10 -7 cm / s, after 10 dry-wet cycles, the crack rate is less than 2.6%, the maximum crack width is less than 1 cm, the cohesion is greater than 40 kPa, and the internal friction angle is greater than 18°;

[0049] S5. The second improved expansive soil is transported to the site and compacted on the surface of the expansive soil slope with a compaction degree of 90% and a thickness of 30 cm; wherein the expansive soil slope and the second improved expansive soil are connected in a "tooth" shape (such as Figure 1 As shown), the compactness between the slope and the second improved expansive soil layer is improved;

[0050] S6. Provide sufficient water before and after the grass seeds germinate, and the plant survival rate will reach over 95%.

[0051] The synergistic effect of plants and the second improved expansive soil can play a role in preventing seepage and retaining moisture, making the moisture inside the expansive soil slope fluctuate around the optimal moisture content with a fluctuation range of less than 5%, eliminating the expansion and contraction deformation and strength degradation caused by alternating sunny and rainy weather. Figure 1 shown.

[0052] In summary, the biopolymer, plant fiber and wood ash of the present invention have the advantages of being natural and harmless, renewable, widely available and convenient to construct. After being mixed with soil, they can quickly improve the physical, chemical and mechanical properties of expansive soil from four aspects, namely, filling and bonding, ion exchange, reinforcement and fertilization, so as to reduce the expansion potential of soil, inhibit the development of soil cracks, improve the shear strength of soil and facilitate plant growth.

[0053] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. An improved expansive soil, characterized in that: The improved expansive soil is prepared from the following ingredients by mass percentage: 0.6-1.2% biopolymer, 3-7% wood ash, 0-2% plant matrix and the balance of the expansive soil to be improved.

2. The improved expansive soil according to claim 1, characterized in that: The biopolymer is selected from one of xanthan gum, guar gum and gum arabic.

3. The improved expansive soil according to claim 1, characterized in that: The particle size of the plant ash is 10-80 meshes, and its main components include silicon dioxide, potassium phosphate, calcium carbonate, calcium oxide, phosphorus pentoxide and potassium oxide, and the mass percentages thereof are 20-30%, 15-25%, 10-15%, 5-10%, 5-10% and 5-10% respectively.

4. The improved expansive soil according to claim 1, characterized in that: The plant matrix comprises unrotten plant fibers, partially rotten plant fibers and completely rotten plant fibers, with the mass percentages being 40-50%, 30-40% and 20-30% respectively; wherein the length of the plant fibers is 1-3 cm and the width is 0.1-0.2 mm.

5. A method for preparing the improved expansive soil according to claim 1, characterized in that: The following steps are involved: S1. Weigh each component by mass percentage, mix them evenly, and obtain a mixed soil; S2. Determine the optimum moisture content and maximum dry density of the mixed soil according to a light compaction test; S3. Add water to the mixed soil according to the optimal moisture content, stir evenly and seal under natural conditions for 3-4 days to obtain the improved expansive soil.

6. The preparation method according to claim 5, characterized in that: When the expansive soil is weak expansive soil, the amount of the plant ash is 3-5%; when the expansive soil is medium or strong expansive soil, the amount of the plant ash is 5-7%.

7. Use of the improved expansive soil according to claim 1 in expansive soil slope engineering or roadbed filling engineering.

8. The use according to claim 7, characterized in that: When the improved expansive soil is used in an expansive slope project, the amount of the plant matrix is ​​1-2%; when the improved expansive soil is used in a roadbed filling project, the amount of the plant matrix is ​​0%.

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