CN115521094A - Preparation method and construction process of improved expansive soil - Google Patents

Abstract

The invention discloses a preparation method and a construction process of improved expansive soil, wherein the method comprises the following steps: based on the total weight of the improved expansive soil as 100 percent, 6 to 11.5 percent of phosphate tailings, 10 to 17.5 percent of weathered sand, 0.1 to 0.5 percent of basalt fiber, 15 to 20 percent of water and 50.7 to 68.7 percent of expansive soil are mixed and stirred uniformly to obtain the improved expansive soil. The problem that the expansive soil expands when meeting water and loses water and contracts is effectively solved, the effect that industrial waste residues which are difficult to dispose are used as additives is achieved on the premise that the expansion rate is improved and the strength of the improved soil is guaranteed, and the advantages of environmental protection, economy and short construction period are achieved. The modified expansive soil is used as a backfill material, and has lighter weight and better stability compared with the original expansive soil.

Description

Preparation method and construction process of improved expansive soil

Technical Field

The invention belongs to the technical field of geotechnical engineering, and particularly relates to a preparation method and a construction process of improved expansive soil.

Background

Expansive soil is also called as expansive soil, and has strong hydrophilicity because the soil body contains more minerals such as montmorillonite, illite and the like. The expansive soil is widely distributed all over the world, and according to related investigation, the expansive soil is mainly distributed in China, east China, xinjiang areas and the like. The expansive soil is easy to be soaked in water and wet, the volume is expanded, the water loss is dry, and the body is shrunk, so that the pile foundation is easy to transversely and longitudinally lift or structurally shear in the repeated process, and the building is cracked and the concrete column of the building is structurally damaged. Aiming at roadbed engineering, the expansive soil is easy to cause pavement cracks due to repeated swelling and shrinkage caused by water absorption and water loss, and threatens safety.

At present, the common modes of expansive soil subgrade side slope and foundation treatment are soil replacement, soil quality improvement, pre-soaking, reinforcement and the like. The soil body replacement mode directly and effectively reduces the content of montmorillonite, thereby achieving the purpose of reducing the swelling and shrinking characteristics. The soil improvement is divided into a physical chemical biological method for treating the expansive soil, for example, a certain proportion of lime is doped into the expansive soil, and cement and the like are subjected to physical chemical reaction with the expansive soil through a newly added material, so that the permeability and the expansibility of the expansive soil are reduced. The reinforcement adopts geotextile, geogrid and reinforced fiber to carry out special treatment on the expansive soil so as to achieve the purpose of enhancing the toughness of the expansive soil. However, the engineering quantity of soil body replacement is huge, a large amount of waste expansive soil is generated and needs to be disposed, the method is slightly deficient in consideration of economic conditions, and some methods in soil body improvement easily cause uneven soil body structures, so that cracking diseases are generated in the construction process. Although the reinforced earth after reinforcement has better toughness, the reinforced earth has the defect of poorer dispersibility.

In order to solve the problems, CN 109536175A discloses a swelling soil improver, its preparation and application, and a method for improving swelling soil using the same, wherein coarse coal gangue particles are doped into swelling soil, negative charges on the surface of swelling soil particles can adsorb surrounding cations, thereby reducing the thickness of the water film adsorbed on the surface of the swelling soil particles, increasing the mutual attraction between the water films of the swelling soil particles, enabling the swelling soil particles to approach, closing the gaps between the swelling soil particles, reducing the water absorption and swelling properties of the swelling soil, enhancing the strength of the swelling soil fine particles, and inhibiting the swelling and shrinking properties of the swelling soil. Although the shear resistance and the expansion and contraction performance of the expansive soil are improved, the preparation process of the used material is complex and the operation is complex.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides the preparation method of the improved expansive soil and the construction process thereof, which not only effectively solve the problem that the expansive soil expands when meeting water and loses water and shrinks, but also achieve the effect of using industrial waste residues which are difficult to dispose as additives on the premise of improving the expansion rate and ensuring the strength of the improved soil, and achieve the advantages of environmental protection, economy and short construction period. The modified expansive soil is used as a backfill material, and has lighter weight and better stability compared with the original expansive soil.

To achieve the above objects, according to an aspect of the present invention, there is provided an improved expansive soil preparation method, including:

taking the total weight of the improved expansive soil as 100%, mixing and stirring 6% -11.5% of phosphate tailings, 10% -17.5% of weathered sand, 0.1% -0.5% of basalt fiber, 15% -20% of water and 50.7% -68.7% of expansive soil uniformly to obtain the improved expansive soil.

Further, the mixing and stirring uniformly specifically comprises:

step 1: mixing 50.7-68.7% of expansive soil, 6-11.5% of phosphate tailings and 15-20% of water by taking the total weight of the improved expansive soil as 100% to obtain slurry;

step 2: 10 to 17.5 percent of weathered sand and 0.1 to 0.5 percent of basalt fiber which are calculated by taking the total weight of the improved expansive soil as 100 percent are added into the slurry which is stirred to be continuously and uniformly stirred to form the improved expansive soil.

Further, the content of the basalt fibers is 0.3 percent based on 100 percent of the total weight of the modified bentonite.

Further, the basalt fiber is bundle monofilament, the diameter of the monofilament is 13 mu m, and the density is 2605kg/m ³ Average length of 6mm, ultimate elongation of 3.5%, melting point 1250 ℃.

Further, the chemical composition of the phosphate tailings comprises: fe ₂ O ₃ 、Al ₂ O ₃ 、P ₂ O ₅ 、CaO、MgO、SiO ₂ 。

Further, P in the chemical composition of the phosphate tailings ₂ O ₅ The content of CaO is 35%, and the content of MgO is 15%.

Further, the heterogeneous coefficient Cu of the weathered sand is 2.79, the natural water content is 13.54%, the specific gravity of a coarse grain group of 2mm-0.5mm is 10.8%, the specific gravity of a medium grain group of 0.5mm-0.25mm is 22.1%, the specific gravity of a fine grain group of 0.25mm-0.075mm is 65.9%, the mud content is not more than 5%, and the sand equivalent is not less than 60%.

According to a second aspect of the present invention, there is provided an improved expansive soil which is characterized by being prepared by the method for preparing the improved expansive soil.

According to a third aspect of the present invention, there is provided a construction process for improving expansive soil, comprising the steps of:

(1) Mixing 50.7-68.7% of expansive soil, 6-11.5% of phosphorus tailings and 15-20% of water by taking the total weight of the improved expansive soil as 100% to obtain slurry;

(2) Adding 10-17.5% of weathered sand and 0.3% of basalt fiber into the slurry after the mixing, and continuously and uniformly stirring to form improved expansive soil;

(3) Carrying out layered filling on the mixed improved expansive soil;

(4) The improved expansive soil is compacted in layers, and water is sprayed to maintain for at least 3 days before each layer is compacted.

Further, in order to ensure that the roadbed can be fully compacted, the widening is not less than 50cm on two sides of the roadbed during filling, and the loose paving thickness of each layer is not more than 30cm.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. the preparation method of the improved expansive soil not only effectively solves the problem that the expansive soil expands when meeting water and loses water and contracts, but also has the effect of utilizing industrial waste residues which are difficult to dispose as additives on the premise of improving the expansion rate and ensuring the strength of the improved soil, and has the advantages of environmental protection, economy and short construction period. The improved expansive soil is used as a backfill material, and has lighter weight and better stability compared with the original expansive soil.

2. The preparation method of the improved expansive soil provided by the invention has the advantages that the industrial slag waste such as the phosphorus tailings is subjected to waste utilization to generate economic benefit conversion, the particle size is changed due to ion exchange between the phosphorus tailings and the inside of soil, so that a certain optimization effect is realized on the shear strength of the expansive soil, and the water stability is improved.

3. According to the preparation method of the improved expansive soil, the basalt fibers in the phosphate tailing weathered sand-basalt fiber improved expansive soil play a role in drawing and bonding, and the oblique section strength of a soil body is effectively enhanced. The method is equivalent to the soil body reinforcement principle, and is more convenient and quicker to construct and shorter in period. The improved soil is simple and convenient to prepare, and the phosphorus tailings are used, so that the waste utilization is in line with the concept of green and economy.

4. According to the preparation method of the improved expansive soil, the phosphorus tailings weathered sand-basalt fiber improved expansive soil follows the principle of local materials, the excavated expansive soil is added with the modifier for improvement, and the modifier is recycled, so that the improved expansive soil has better economical efficiency. And the no-load expansion rate of the expansive soil is effectively reduced, and the shear strength is improved.

Drawings

FIG. 1 is a diagram of a phosphorus tailing entity used in the present invention;

FIG. 2 is a pictorial view of basalt fiber used in the present invention;

FIG. 3 is a diagram of a weathered sand object used in the present invention;

FIG. 4 is a schematic view showing the change of the no-load expansion ratio of the modified expansive soil under different weathered sand mixing amounts according to the present invention;

FIG. 5 is a graph illustrating stress-strain curves for different sand loadings at a net confining pressure of 50kPa in accordance with the present invention;

FIG. 6 is a graph illustrating stress-strain curves for different sand loadings at a net confining pressure of 100kPa in accordance with the present invention;

FIG. 7 is a graph illustrating stress-strain curves for different sand loadings at a net confining pressure of 200kPa in accordance with the present invention;

FIG. 8 is a diagram of an exemplary embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The raw material components used in the following examples are all commercially available raw materials.

The invention provides a preparation method of phosphorus tailings weathered sand-basalt fiber improved expansive soil, which comprises the following steps:

based on the total weight of the improved expansive soil as 100 percent, 6 to 11.5 percent of phosphate tailings, 10 to 17.5 percent of weathered sand, 0.3 percent of basalt fiber, 15 to 20 percent of water and 50.7 to 68.7 percent of expansive soil are mixed and stirred uniformly to obtain the improved expansive soil.

Preferably, the modified bentonite is prepared by any mixing method, and for the sake of brief explanation, the following examples adopt a preferred preparation method, that is:

step 1: mixing the expansive soil, the phosphate tailings and water according to the proportion to obtain slurry;

and 2, step: adding the weathered sand and the basalt fiber in the proportion into the mixed slurry, and continuously and uniformly stirring to form improved expansive soil;

by adopting the technical scheme, the phosphate tailings and the expansive soil have ion exchange reaction, and the expansive soil contains Na ⁺ 、K ⁺ Equivalent low-valent cations and Ca contained in phosphate tailings ²⁺ 、Mg ²⁺ The exchange of high valence cations leads to the formation of aggregates of finer soil particles in the expansive soil, so that the effective internal friction angle of the soil particles is increased. The hard coagulation reaction between the phosphate tailings and the expansive soil can generate calcium silicate hydrate colloid, and the colloid is attached to soil particles, so that the contact area between the particles is increased, the friction force between the particles is increased, and the shear strength of the expansive soil is improved.

Optionally, the phosphate tailings are industrial waste residues generated after the phosphate concentrate is mined, and the main chemical component of the phosphate tailings is Fe ₂ O ₃ 、Al ₂ O ₃ 、P ₂ O ₅ 、CaO、MgO、SiO ₂ . Wherein P is ₂ O ₅ The CaO content was about 35%, and the MgO content was about 15%.

Optionally, efflorescence sand non-uniformity coefficient C _u 2.79 percent, the natural water content is 13.54 percent, the specific gravity of 2mm-0.5mm of coarse grain group is 10.8 percent, the specific gravity of 0.5mm-0.25mm of medium grain group is 22.1 percent, the specific gravity of 0.25mm-0.075mm of fine grain group is 65.9 percent, the cleaning is not needed, no impurities exist, the mud content is not more than 5 percent, and the sand equivalent is not less than 60 percent.

The weathering sand with a certain content is added into the expansive soil to reduce the expansion rate. Because the swelling and shrinkage of weathered sand can be almost ignored and the surfaces of the particles are rough, the effective internal friction angle of the soil body is increased after the two particles are uniformly mixed, so that the friction resistance is greater than the friction force between the plain soil particles, and the effects of inhibiting expansion and improving the shear strength are achieved.

Optionally, the basalt fibers are bundled monofilaments having a diameter of 13 μm and a density of 2605kg/m ³ Average length of 6mm, ultimate elongation of 3.5%, melting point 1250 ℃.

The basalt fiber is in a regular porous bundle-shaped structure, is degraded and then is integrated with soil, and the material is environment-friendly and pollution-free. When the basalt fibers are added into the expansive soil, the friction force between the fibers and the soil particles is further increased, and meanwhile, the tensile force between the soil particles is increased by adding the fibers, so that the damage of the oblique section is more effectively resisted. The addition of the basalt fibers simultaneously plays a role of reinforcement in the soil body, so that the strength of the soil body is further enhanced.

Example 1

Taking 6 percent of phosphate tailings, 17.5 percent of water, 66.2 percent of expansive soil, 0.3 percent of basalt fiber and 17.5 percent of weathered sand by taking the total weight of the improved expansive soil as 100 percent; mixing the expansive soil, the phosphate tailings and water according to the proportion to obtain slurry; and adding the weathered sand and the basalt fiber in the proportion into the mixed slurry, and continuously and uniformly stirring to obtain the improved expansive soil.

Example 2

The cement mortar consists of 6 percent of phosphate tailings, 17.5 percent of water, 63.7 percent of expansive soil, 0.3 percent of basalt fiber and 12.5 percent of weathered sand. The starting materials and preparation were the same as in example 1.

Example 3

Taking 6 percent of phosphate tailings, 17.5 percent of water, 61.2 percent of expansive soil, 0.3 percent of basalt fiber and 15 percent of weathered sand based on the total weight of the improved expansive soil as 100 percent. The starting materials and preparation were the same as in example 1.

Example 4

Taking 6 percent of phosphate tailings, 17.5 percent of water, 58.7 percent of expansive soil, 0.3 percent of basalt fiber and 17.5 percent of weathered sand based on the total weight of the improved expansive soil as 100 percent. The starting materials and preparation were the same as in example 1.

Comparative example 1

Taking 0% of phosphate tailings, 17.5% of water, 82.5% of expansive soil, 0% of basalt fiber and 0% of weathered sand by taking the total weight of the improved expansive soil as 100%. The starting materials and preparation were the same as in example 1.

Example 5

Taking 7.5 percent of phosphate tailings, 17.5 percent of water, 59.7 percent of expansive soil, 0.3 percent of basalt fiber and 15 percent of weathered sand by taking the total weight of the improved expansive soil as 100 percent. The starting materials and preparation were the same as in example 1.

Example 6

Based on the total weight of the improved expansive soil being 100%, 9% of phosphate tailings, 17.5% of water, 58.2% of expansive soil, 0.3% of basalt fiber and 15% of weathered sand are taken. The starting materials and preparation were the same as in example 1.

Example 7

Based on the total weight of the improved expansive soil being 100%, 11.5% of phosphate tailings, 17.5% of water, 55.7% of expansive soil, 0.3% of basalt fiber and 15% of weathered sand are taken. The starting materials and preparation were the same as in example 1.

Comparative example 2

Taking 0% of phosphate tailings, 17.5% of water, 67.2% of expansive soil, 0.3% of basalt fiber and 15% of weathered sand based on the total weight of the improved expansive soil as 100%. The starting materials and preparation were the same as in example 1.

The apparatus for the shear strength test of the improved soil sample adopts a GDS unsaturated soil triaxial apparatus provided by Europe and America geodetic apparatus China Co., ltd, and the GDS unsaturated soil triaxial test system UNSAT is produced in the United kingdom and is sold as GDS instruments and the type is UNSAT.

Compaction test: the soil sample is placed in an oven at 105-110 ℃ for drying for 24h, taken out and cooled to a constant temperature, repeatedly crushed by a crusher until the soil sample can pass through a 2mm sieve, and compaction tests are carried out according to different material mixing amounts in the embodiment by taking the soil test method standard (GB/T50123-1999) as a standard, so as to achieve the purpose of obtaining the maximum dry density and the optimal water content under different sand mixing amounts.

No load expansion test: fully stirring the above embodiments to uniformly mix, selecting the optimal water content measured by a compaction test, selecting the maximum dry density of the optimal water content, controlling the dry density of the optimal water content to configure a soil sample, putting the configured soil sample into a sealing bag, standing for 24 hours, then putting the soil sample into a tool changing sample with the diameter of 61.8mm and the height of 20mm, putting the sample into an expansion instrument, filling water to submerge the sample, and recording expansion data every 2 hours until the difference range is within 0.01mm to be considered as stable in expansion. The test data were averaged two by two.

Unsaturated soil triaxial shear test: three groups of samples with different ambient pressures of 50kPa, 100kPa and 200kPa are arranged, the optimal water content obtained by the compaction test is selected to carry out air extraction saturation and a shear test on the samples with different material mixing amounts, and the shear strength test of unsaturated soil is divided into three stages: (1) substrate suction balancing; (2) isostatic consolidation; (3) 3 stages of uniform shearing, wherein the former two test stages take the condition that the volume change of the back pressure water is less than 0.02 percent of the volume of the sample as the stage finishing standard; the shear rate was 0.005mm/min and the test was terminated by a shear to axial strain of 20%.

The no-load expansion ratio and the shear strength improvement obtained by modifying the expansive soil according to the mixture ratio of the examples 1 to 4 are shown in the table 1:

TABLE 1 improved expansive soil no-load expansion rate and shear strength test under different weathered sand proportions

As shown in table 1 and fig. 4-7, the weathered sand improves the shear strength of the expansive soil to a certain extent and has an inhibition effect on expansion, and when the amount of the weathered sand is 15%, the shear strength of the improved expansive soil is optimal and tends to increase first and then decrease, because the pores between soil particles increase with the increase of the amount of the weathered sand, and the weathered sand cannot provide a cohesive effect, so that the cohesive force of the soil is reduced, and the shear strength is reduced accordingly.

The no-load expansion rate and shear strength improvement obtained by modifying the expansive soil according to the formulation of examples 4 to 7 and comparative example 2 are shown in table 2:

TABLE 2 improved expansive soil no-load expansion rate and shear strength test under different phosphorus tailings proportions

The invention also provides a construction process for improving the expansive soil, which comprises the following steps:

(1) Mixing 50.7-68.7% of expansive soil, 6-11.5% of phosphorus tailings and 15-20% of water according to the proportion to obtain slurry, wherein the total weight of the improved expansive soil is 100%;

(2) Adding 10-17.5% of weathered sand and 0.3% of basalt fiber into the slurry after the mixing, and continuously and uniformly stirring to form improved expansive soil;

(3) Carrying out layered filling on the mixed improved expansive soil;

preferably, in order to ensure that the roadbed can be fully compacted, the widening is not less than 50cm on two sides of the roadbed during filling, and the loose pavement thickness of each layer is not more than 30cm;

(4) The improved expansive soil is compacted in layers, and water is sprayed to maintain for 3 days before each layer is compacted.

In order to make the construction process more clear and definite, the construction process is specifically described by combining with specific engineering practices (as shown in fig. 8):

example 8

(1) Excavating expansive soil on side slope or roadbed

(2) And (3) mixing 9% of the phosphate tailings, 58.2% of the expansive soil and 17.5% of water by taking the total weight of the improved expansive soil as 100%, putting the mixture into a stirrer, and uniformly stirring until most uniform particles appear, and stopping stirring.

(3) Adding 0.3% of basalt fiber and 15% of weathered sand into the mixed particles and continuously mixing until the particles are uniformly distributed to form the phosphate-tailing weathered sand-basalt modified expansive soil, wherein the total weight of the modified expansive soil is 100%.

(4) And backfilling the improved expansive soil to the excavated part to form the phosphate tailing weathered sand-basalt improved expansive soil slope or roadbed.

(5) And (3) performing layered filling on the improved expansive soil after mixing to ensure that the roadbed can be fully compacted, widening the two sides of the roadbed during filling to be not less than 50cm, and paving each layer of loose soil to be not more than 30cm.

(6) And (5) carrying out watering maintenance for 3 days after the compaction is finished.

It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.

Claims (10)

1. The preparation method of the improved expansive soil is characterized by comprising the following steps:

based on the total weight of the improved expansive soil as 100 percent, 6 to 11.5 percent of phosphate tailings, 10 to 17.5 percent of weathered sand, 0.1 to 0.5 percent of basalt fiber, 15 to 20 percent of water and 50.7 to 68.7 percent of expansive soil are mixed and stirred uniformly to obtain the improved expansive soil.

2. The method for preparing improved expansive soil according to claim 1, wherein the mixing and stirring uniformly comprises: :

step 1: mixing 50.7-68.7% of expansive soil, 6-11.5% of phosphate tailings and 15-20% of water by taking the total weight of the improved expansive soil as 100% to obtain slurry;

step 2: adding 10-17.5% of weathered sand and 0.1-0.5% of basalt fiber into the slurry which is mixed and stirred to form the improved expansive soil, wherein the total weight of the improved expansive soil is 100%.

3. The method for preparing the improved expansive soil according to any one of claims 1 or 2, wherein the basalt fiber is 0.3% by weight based on 100% by weight of the total weight of the improved expansive soil.

4. The method for preparing improved expansive soil according to claim 3, wherein the basalt fiber is bundled monofilament with a diameter of 13 μm and a density of 2605kg/m ³ Average length of 6mm, ultimate elongation of 3.5%, melting point 1250 ℃.

5. The method for preparing improved bentonite according to any one of claims 1 or 2, wherein the chemical composition of the phosphate tailings comprises: fe ₂ O ₃ 、Al ₂ O ₃ 、P ₂ O ₅ 、CaO、MgO、SiO ₂ 。

6. The method for preparing the improved bentonite according to claim 3, wherein P in the chemical composition of the phosphorus tailings ₂ O ₅ The content of CaO is 35%, and the content of MgO is 15%.

7. The method for preparing the improved expansive soil according to any one of claims 1 or 2, wherein the non-uniformity coefficient Cu of the weathered sand is 2.79, the natural water content is 13.54%, the specific gravity of 2mm-0.5mm of a coarse grain group is 10.8%, the specific gravity of 0.5mm-0.25mm of a medium grain group is 22.1%, the specific gravity of 0.25mm-0.075mm of a fine grain group is 65.9%, the mud content is not more than 5%, and the sand equivalent is not less than 60%.

8. An improved expansive soil prepared by the method of any one of claims 1 to 7.

9. The construction process for improving the expansive soil is characterized by comprising the following steps of:

(1) Mixing 50.7-68.7% of expansive soil, 6-11.5% of phosphorus tailings and 15-20% of water by taking the total weight of the improved expansive soil as 100% to obtain slurry;

(2) Adding 10-17.5% of weathered sand and 0.3% of basalt fiber into the slurry after the mixing, and continuously and uniformly stirring to form improved expansive soil;

(3) Carrying out layered filling on the mixed improved expansive soil;

(4) The improved expansive soil is compacted in layers, and water is sprayed to maintain for at least 3 days before each layer is compacted.

10. The process of claim 9, wherein the roadbed is widened by not less than 50cm at the two sides during filling and the loose pavement thickness of each layer is not more than 30cm.

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