Modification method of medium expansive soil

Abstract

The invention relates to a method for modifying medium expansive soil, and belongs to the technical field of highway engineering. The method comprises the following steps: determining a design mass mixing ratio, converting the design mass mixing ratio into a construction mass mixing ratio, mixing raw materials to obtain a batch, crushing / mixing the batch to obtain a mixture, stacking the mixture for modification to obtain a modified material, namely the modified medium expansive soil, and performing moisture content and secondary compaction test on the modified medium expansive soil to obtain the medium expansive soil. And the water content of the modified expansive soil is adjusted to a construction water content control range, so that the modified expansive soil meets the requirements of building a highway subgrade. According to the method, ecological damage, resource waste and environment pollution are avoided, meanwhile, the cost is reduced, the modification speed of the medium expansive soil is greatly increased, and the construction water content control range and the compaction degree calculation standard of the modified medium expansive soil used for building the highway subgrade are scientifically determined.

Description

Technical Field

[0001] The invention relates to the technical field of highway engineering, and in particular to a method for modifying medium expansive soil. Background Art

[0002] Expansive soil is widely distributed in my country, such as Guangxi, Yunnan, Henan, Hubei, Sichuan, Shaanxi, Hebei, Anhui, Jiangsu and other places, with different distribution ranges. With the rapid development of my country's economy, highway construction has also developed rapidly for decades and will continue to develop rapidly. In highway construction, it is inevitable to encounter expansive soil road construction materials. Expansive soil is a high-plastic clay soil rich in hydrophilic minerals (montmorillonite, illite and kaolin) with obvious water absorption expansion and water loss shrinkage. It has the characteristics of water absorption expansion, water loss shrinkage, repeated expansion and contraction deformation, water-immersion bearing capacity attenuation, and shrinkage crack development. It is extremely unstable in nature, often causing uneven vertical or horizontal expansion and contraction of highways, causing displacement, cracking, tilting and even destruction, and it is not easy to repair and is very harmful. In order to ensure the stability of the roadbed and the flatness of the road surface for a long time to achieve the purpose of safe and comfortable driving, the engineering problems caused by expansive soil must be solved. According to the expansion property, it can be divided into weak expansive soil (40%≤ )、Medium expansive soil(60%≤ )、Strong expansive soil( ≥90%) three categories.

[0003] (JTG F10-2006) "Technical Specifications for Highway Roadbed Construction" stipulates that weak expansive soil can be used directly to build the roadbed; strong expansive soil cannot be used to build the roadbed; medium expansive soil can be used to build the roadbed after modification.

[0004] At present, the modification methods of expansive soil for highway roadbed construction include: using one, two, or three of fly ash, lime, and cement for modification. The disadvantages of using lime and cement for modification are high cost, and the production of lime and cement destroys the ecology, wastes resources, and causes serious pollution; the disadvantage of using only fly ash for modification is that the modification speed is too slow, generally requiring more than 15 days. In addition, when designing the material mix ratio, the initial unmodified mixture is used for compaction test, and the material mix ratio is calculated based on the test results to prepare modified expansive soil. After that, the prepared modified expansive soil is directly used for roadbed construction without adjusting the moisture content, and the maximum dry density obtained from the above compaction test is used as the basis for calculating the compaction degree of the roadbed. This is wrong, and the result is often distortion of the compaction test data, resulting in misjudgment of the compaction quality of the roadbed. Summary of the invention

[0005] The invention provides a method for modifying medium expansive soil, which aims to overcome the drawbacks of the prior art, reduce costs, accelerate the modification speed of the medium expansive soil while avoiding ecological damage, waste of resources and environmental pollution, and scientifically determine the construction moisture content control range and compaction degree calculation basis of the modified medium expansive soil used for roadbed construction.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for modifying medium expansive soil comprises the following steps:

[0008] Step 1: Determine the design quality mix ratio

[0009] Determine the mass ratio of medium expansive soil: fly ash: waste tire fiber: papermaking wastewater soluble matter: water, where medium expansive soil, fly ash, papermaking wastewater soluble matter and waste tire fiber are all dry material masses, and this mass ratio is called the design mass mix ratio, referred to as the design mix ratio, and papermaking wastewater soluble matter is referred to as soluble matter;

[0010] Step 2: Convert the design quality mix ratio into the construction quality mix ratio

[0011] The medium expansive soil, fly ash and waste tire fiber used in the construction process all contain a certain amount of water. According to their moisture content, soluble matter content and design mix ratio, they are converted into the mass ratio of wet medium expansive soil: wet fly ash: wet waste tire fiber: papermaking wastewater: water. This mass ratio is called the construction quality mix ratio, or construction mix ratio for short.

[0012] Step 3: Raw material matching

[0013] According to the construction mix ratio, wet medium expansive soil, wet fly ash and wet waste tire fiber are mixed, and this material is called mixed material; papermaking wastewater and water are mixed, and this material is called mixed water;

[0014] Step 4: Crushing / mixing of batch materials

[0015] Add the batch material into the crusher for crushing and mixing. Add mixed water according to the construction mix ratio by sprinkling at the discharge point. The resulting material is called the mixed material of the batch material, or simply the mixed material. The diameter of the agglomerate contained in the mixed material is ≤3cm.

[0016] Step 5: Modification of mixed material stacking

[0017] The mixed materials are piled for modification and covered with plastic film to prevent water from evaporating and other water from entering;

[0018] The stacking modification time is longer than the modification period of the mixing material, that is, to ensure that the free expansion rate is less than 60% after stacking modification. The mixture at this time is called modified medium expansive soil; the modification period of the mixing material is referred to as the modification period, which refers to the time from the completion of mixing of the mixing material to the time when the free expansion rate is less than 60%; in engineering practice, the modification period of each pile is calculated from the end time of the stacking of the mixing material;

[0019] Step 6: Second compaction test to adjust the moisture content of the modified expansive soil

[0020] According to (T 0801-2009) "Water Content Test Method (Drying Method)", the test was carried out to detect the moisture content of the modified expansive soil. ; Use modified medium expansive soil and conduct tests according to (T 0804-1994) "Compaction test method for inorganic binder stabilized materials" to obtain the maximum dry density and optimum moisture content ; Moisture content , Optimum moisture content And compaction assessment standards As the basis for adjusting the moisture content of expansive soil in modification, the maximum dry density As a calculation of compaction degree for roadbed construction benchmark.

[0021] The chemical composition, properties and moisture content of the modified expansive soil and the mixed material (the mixture that did not undergo chemical reaction at the beginning, that is, the mixture used in the first compaction test) have changed greatly. and maximum dry density , Optimum moisture content and optimum moisture content , and their moisture content and dry density relationship curves will be different. Therefore, before the modified expansive soil is used for roadbed construction, a compaction test must be carried out to determine its maximum dry density. and optimum moisture content , instead of using the maximum dry density of the mixture and optimum moisture content .

[0022] The study found that: (1) The moisture content of the modified expansive soil (that is ), the reason is that in the process of modifying the medium expansive soil, part of the water participates in the chemical reaction to form larger molecular hydrated compounds; in addition, the water absorption capacity of the medium expansive soil decreases after modification, so will also be less than , and the water content in the modified expansive soil Whether adjustments are necessary remains to be determined. (2) < The reasons are as follows: first, during the modification process of the medium expansive soil, larger molecular hydrate compounds are formed, which increases the mass per unit volume; second, < , that is, reaching the maximum dry density The water requirement (the density of water is smaller than that of compacted solid) is reduced; thirdly, the modifier particles and their chemical reaction products fill the internal voids of the expansive soil. (3) The calculation formula for compaction degree is: , at dry density In case of confirmation, Reducing the compaction rate may result in the appearance that the test data is qualified even though the compaction degree is actually unqualified. < ,so It cannot be used as a basis for calculating the compaction degree of roadbed construction.

[0023] The method for adjusting the moisture content of modified medium expansive soil is: using modified medium expansive soil, according to (T 0804-1994) "Compaction Test Method for Inorganic Binder Stabilized Materials" to test, and obtain the relationship curve between the moisture content and dry density of modified medium expansive soil, such as Figure 1 As shown; then according to the compaction evaluation standard Draw a horizontal line to intersect the relationship curve between moisture content and dry density of the modified expansive soil at two points, and draw vertical lines through the left and right intersection points to intersect the horizontal axis at and .if ≤ ≤ , then the modified medium expansive soil can be used to directly build the roadbed; if the moisture content < ,or > , then it is necessary to adjust the moisture content of the expansive soil in the modification The adjusted moisture content is recorded as , adjusting the moisture content of expansive soil during modification is a common technology and will not be elaborated here.

[0024] Adjusted moisture content That is, the moisture content of the modified expansive soil during roadbed construction. ≤ ≤ (This range is called the construction moisture content control range), the compaction degree can reach the evaluation standard , so if It is not within the construction moisture content control range and must be adjusted within the range.

[0025] The modified expansive soil can only be used for roadbed construction after its moisture content is adjusted to within the construction moisture content control range, and the compaction degree is calculate.

[0026] Furthermore, the designed mix ratio in step 1 is medium expansive soil: fly ash: waste tire fiber: soluble matter: water = 100: 10-30: 0.1-0.6: 0.3-2: 0-20.

[0027] Furthermore, the moisture content of the wet expansive soil and wet fly ash is ≤5%.

[0028] Furthermore, the wet fly ash refers to the fine ash collected from the flue gas after coal combustion, and is the main solid waste discharged from coal-fired power plants.

[0029] Furthermore, the wet waste tire fiber is the fiber produced during the processing of waste tire rubber powder, and its moisture content is 0.3%-1%.

[0030] Furthermore, the papermaking wastewater is wastewater generated in the pulping and papermaking process, and the papermaking wastewater needs to be clarified, wherein the content of insoluble organic matter is less than 0.1%.

[0031] Furthermore, the quality of the fly ash and water meets the requirements of (JTG / T F20-2015) "Technical Specifications for Highway Pavement Base Construction".

[0032] Further, the method for determining the designed mix ratio and the modification period is:

[0033] 1) First compaction test

[0034] Medium expansive soil is calculated as 100. Based on technology, economy, construction period, climate and experience, the amount of fly ash, soluble matter and waste tire fiber is selected within the dosage range. According to (T 0804-1994) "Compaction Test Method for Inorganic Binder Stabilized Materials", a compaction test is carried out to obtain the maximum dry density. and optimum moisture content ; The material used in the first compaction test is called mixed material, which is the mixed material before modification;

[0035] 2) Calculate the initial mix ratio

[0036] According to the dosage of medium expansive soil, fly ash, soluble matter and waste tire fiber, and the compaction test results, the preliminary design quality mix ratio is calculated, which is referred to as the initial design mix ratio, namely: medium expansive soil: fly ash: waste tire fiber: soluble matter: water;

[0037] 3) Free expansion rate test

[0038] Pass T 0124-1993 free expansion rate test and obtain free expansion rate and modification period n;

[0039] 4) Determine the design mix ratio

[0040] If the modification period n is within expectations, the above-mentioned initial mix ratio can be used as the design mix ratio; otherwise, adjust the material dosage and re-test.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. Compared with the prior art using lime and / or cement modification, the present invention does not use lime and / or cement, which can reduce costs and avoid the production of lime and / or cement from damaging the ecology, wasting resources, and causing serious pollution.

[0043] 2. The characteristics of expansive soil are swelling when wet and cracking when dry. The present invention uses waste tire fibers, which have a reinforcement effect and have a significant effect on limiting swelling and shrinkage, improving the strength, plate properties and durability of the constructed roadbed, especially having an outstanding anti-crack effect.

[0044] 3. The modification speed of the present invention is fast, and the modification period is generally about 3 days, which is equivalent to or even higher than the modification speed using lime and / or cement, and is much faster than the modification speed using fly ash alone.

[0045] 4. The present invention realizes that all the modified materials used are industrial wastes under the condition of fast modification speed, and the amount used is large, and the environmental protection effect is more significant.

[0046] 5. The present invention has found that the moisture content, optimum moisture content and maximum dry density of the mixed material (mixture before modification) and the modified expansive soil (mixture after modification), as well as the composition and moisture content-dry density relationship curve have changed greatly. That is to say, the mixture is no longer the same material before and after modification. The prior art only conducted a compaction test on the mixed material (mixture before modification), and then directly used the modified expansive soil (mixture after modification) to build the roadbed. This practice of treating the mixtures before and after modification as the same is wrong. For this reason, the present invention is designed to conduct a second compaction test on the modified expansive soil (mixture after modification), and use the test results to guide the construction, so that the modification method is scientific and reasonable, and the errors in the prior art are corrected. In addition, in the prior art, the modified expansive soil (mixture after modification) is directly used to build the roadbed, but its moisture content may be < ,or > , or The moisture content of the modified expansive soil may not be within the control range of the construction moisture content, and the compaction degree may not meet the evaluation standard. Therefore, there are errors in the prior art. The present invention uses the modified expansive soil (modified mixture) to conduct a second compaction test, and adjusts the moisture content of the modified expansive soil to ≤ ≤ , so that the compaction can reach the assessment standard, and the compaction is Calculation overcomes the problem of using compaction degree in existing technology Calculation errors avoid false images in compaction test data and eliminate misjudgment of the compaction quality of roadbed construction.

[0047] 6. The roadbed constructed by the present invention has high strength, and the long-term strength can reach more than 0.5MPa. In addition, the plate has good body properties and outstanding anti-crack performance. Therefore, it has a variety of uses, not only for roadbed construction, but also for roadbed treatment, soft soil foundation treatment, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the relationship curve between moisture content and dry density of modified expansive soil. DETAILED DESCRIPTION

[0049] The technical solutions and effects of the present invention are further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0050] Example 1

[0051] Conditions of this example: free expansion rate of medium expansive soil =75%, the modification period is required to be no more than 5 days, the compaction evaluation standard =95%, the roadbed is built in sunny weather in summer.

[0052] A method for modifying medium expansive soil comprises the following steps:

[0053] 1. Construction Preparation

[0054] 1. Determine the design mix ratio

[0055] 1) First compaction test to determine the initial mix ratio

[0056] The medium expansive soil is calculated as 100, and the amount of fly ash, soluble matter and waste tire fiber is selected within the amount range to form a solid material mass mix ratio according to technology, economy, construction period, climate and experience. The solid material mass mix ratio selected in this embodiment is: medium expansive soil: fly ash: soluble matter: waste tire fiber = 100: 20: 0.7: 0.3.

[0057] Soluble matter refers to the soluble matter in papermaking wastewater, the main component of which is caustic soda. The preparation method is to weigh a certain amount of papermaking wastewater, filter out the insoluble organic matter in the papermaking wastewater, and then heat it to evaporate all the water to obtain the soluble matter. The soluble matter content can be obtained by weighing and calculating. In this embodiment, the soluble matter content is 4%.

[0058] According to (T 0804-1994) "Compaction Test Method for Inorganic Binder Stabilized Materials", the compaction test was carried out. The test results of this embodiment are: Maximum dry density =1.65g / cm 3 ; Optimum moisture content =20%.

[0059] According to the optimum moisture content = 20% of the initial design mix ratio, then the water dosage x in the initial design mix ratio is calculated as:

[0060]

[0061] Right now:

[0062] Calculation shows: x≈30.3.

[0063] The initial mix ratio of this embodiment is: medium expansive soil: fly ash: soluble matter: waste tire fiber: water = 100: 20: 0.7: 0.3: 30.3.

[0064] 2) Free expansion rate test

[0065] According to the initial mix ratio of expansive soil: fly ash: soluble matter: waste tire fiber: water = 100: 20: 0.7: 0.3: 30.3, mix evenly, and cover the modified material with plastic cloth. Then use the modified mixture to test according to (T 0124-1993) "Free Expansion Rate Test" to obtain the free expansion rate. This test is performed once every 1 day (24 hours) and the results are , , ,…… , until <60%, where n is the modification period in days (d).

[0066] The free expansion rate test results of this embodiment are: =71%, =66%, =58%<60%; then n=3d.

[0067] 3) Determine the design mix ratio

[0068] The modification period is 3 days, which is within the requirements. The above initial mix ratio can be used as the design mix ratio, that is, the design mix ratio is: medium expansive soil: fly ash: soluble matter: waste tire fiber: water = 100: 20: 0.7: 0.3: 30.3.

[0069] 2. Convert the design mix ratio into the construction mix ratio

[0070] According to (T 0801-2009) "Test Method for Moisture Content (Drying Method)", the moisture content of wet expansive soil, wet fly ash and wet waste tire fiber was measured, and the results were 2%, 3% and 0.5% respectively. The design mix ratio of expansive soil: fly ash: soluble matter: waste tire fiber: water = 100: 20: 0.7: 0.3: 30.3 is converted into the construction mix ratio of wet expansive soil: wet fly ash: papermaking wastewater: wet waste tire fiber: water ≈ 102: 20.6: 17.5: 0.3: 10.9.

[0071] 3. Second compaction test

[0072] According to (T 0801-2009) "Water Content Test Method (Drying Method)", the test was carried out to detect the moisture content of the modified expansive soil. ; Use modified medium expansive soil and conduct tests according to (T 0804-1994) "Compaction test method for inorganic binder stabilized materials", draw the relationship curve between moisture content and dry density of modified medium expansive soil, and get the maximum dry density and optimum moisture content , and then through the compaction evaluation standard Draw a horizontal line to intersect the moisture content and dry density relationship curve of the modified expansive soil at two points, and draw a vertical line through the left and right intersection points to intersect the horizontal axis to obtain and According to the moisture content , Optimum moisture content , and Adjust the moisture content of the modified expansive soil. ≤ ≤ When the water content of the modified medium expansive soil does not need to be adjusted, the modified medium expansive soil can be used directly to build the roadbed; when < ,or > When the moisture content of the expansive soil in the modification needs to be adjusted ,make ≤ ≤ ( The closer to the optimal moisture content The better), then it can be used to build the roadbed. Maximum dry density It is used as the basis for calculating the compaction degree k when constructing roadbed.

[0073] The test results of this embodiment are:

[0074] Moisture content =14%;

[0075] Optimum moisture content =12.2%, maximum dry density =1.68g / cm 3 ;

[0076] Compaction evaluation standard =95%, =10.8%, =13.4%.

[0077] The results of the two compaction tests show that: (1) moisture content , Optimum moisture content , maximum dry density The optimum moisture content (That is, moisture content ), maximum dry density Compared with the previous tests, there have been significant changes; (2) The relationship curves between moisture content and dry density of the two compaction tests are different, and the control range of construction moisture content is also different; (3) =14%> =13.4%, then the moisture content of the expansive soil in the modification needs to be adjusted This embodiment adopts the method of drying. Reduce to ,conform to =10.8%≤ ≤ =13.4%, so far the modified expansive soil is prepared, and can be used to build roadbed, which is a common technology, and will not be described here. The above situation shows the necessity of the second compaction test and the scientific rationality of the present invention, and also shows that there are errors in the prior art.

[0078] 2. Construction

[0079] 1. Raw material matching

[0080] Use a batching machine to mix the wet medium expansive soil, wet fly ash and wet waste tire fiber in accordance with the construction mix ratio of wet medium expansive soil: wet fly ash: wet waste tire fiber = 102: 20.6: 0.3 to obtain the construction mix ratio batch material; according to the construction mix ratio of papermaking wastewater: water = 17.5: 10.9, mix the papermaking wastewater with water to obtain mixed water.

[0081] 2. Crushing / mixing of batch materials

[0082] Add the batch material to the crusher for crushing and mixing, and use the rain spraying method at the discharge point to add mixing water according to the usage ratio determined by the construction mix ratio batch material: mixing water, and the resulting mixture is the construction mix ratio mixing material. Among them: construction mix ratio batch material: mixing water = (wet expansive soil + wet fly ash + wet waste tire fiber) : (papermaking wastewater + water) = 122.9: 28.4.

[0083] The crusher adopts a hammer crusher, and is equipped with a screen with an aperture of 3 cm and a return system. Materials with a diameter of ≤3 cm become mixing materials, and materials with a diameter of >3 cm are returned to the crusher through the return system for re-crushing / mixing.

[0084] 3. Modify the construction mix ratio and adjust the moisture content

[0085] The construction mix is ​​piled up for modification and covered with plastic film to prevent water volatilization and other water from entering. The stacking modification time is longer than the modification period of the mix for 3 days to ensure that its free expansion rate is less than 60% after stacking modification, and the modified expansive soil must be air-dried (when constructing the roadbed in sunny weather in summer, the modified expansive soil must go through processes such as shipping, paving, leveling and rolling, and part of the water will evaporate. Air-drying is also a natural process accompanying the construction, so under normal circumstances, it is necessary to have a slightly higher water content) to make its water content meet the requirements. =10.8%≤ ≤ =13.4%, which meets the requirements for highway subgrade construction, that is, the preparation of modified expansive soil is completed and can be used for road subgrade construction, and the maximum dry density =1.68g / cm 3 Calculate the degree of compaction.

[0086] In addition, the construction mix ratio can be adjusted to make the modified expansive soil Directly within the construction moisture content control range, for > When the water evaporates slowly, or < It is appropriate to build roadbed under such circumstances.

[0087] The method of adjusting the moisture content is a common technique and will not be described in detail here.

[0088] Studies have shown that the modified medium expansive soil will continue to be modified after the roadbed is built, and its long-term free expansion rate will become very small, and its crack resistance is also very outstanding. Therefore, the modified medium expansive soil of the present invention is a good road construction material.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for modifying medium expansive soil, characterized in that: The following steps are involved: Step 1: Determine the design quality mix ratio Determine the mass ratio of medium expansive soil: fly ash: waste tire fiber: papermaking wastewater soluble matter: water, where the medium expansive soil, fly ash, papermaking wastewater soluble matter and waste tire fiber are all dry material masses; Step 2: Convert the design quality mix ratio into the construction quality mix ratio The medium expansive soil, fly ash and waste tire fiber used in the construction process all contain a certain amount of water. According to their moisture content, soluble matter content and designed mass mix ratio, they are converted into the mass ratio of wet medium expansive soil: wet fly ash: wet waste tire fiber: papermaking wastewater: water; Step 3: Raw material matching According to the construction mix ratio, wet medium expansive soil, wet fly ash and wet waste tire fiber are mixed, and this material is called mixed material; papermaking wastewater and water are mixed, and this material is called mixed water; Step 4: Crushing / mixing of batch materials Add the batch material into the crusher for crushing and mixing. Add mixed water according to the construction mix ratio by sprinkling at the discharge point. The resulting material is called the mixed material of the batch material, or simply the mixed material. The diameter of the agglomerate contained in the mixed material is ≤3cm. Step 5: Modification of mixed material stacking The mixed materials are piled for modification and covered with plastic film to prevent water from evaporating and other water from entering; The stacking modification time is longer than the modification period of the mixing material, that is, to ensure that the free expansion rate is less than 60% after stacking modification. The mixture at this time is called modified medium expansive soil; the modification period of the mixing material is referred to as the modification period, which refers to the time from the completion of mixing of the mixing material to the time when the free expansion rate is less than 60%; in engineering practice, the modification period of each pile is calculated from the end time of the stacking of the mixing material; Step 6: Second compaction test to adjust the moisture content of the modified expansive soil According to T 0801-2009 moisture content test method (drying method), the test was carried out to detect the moisture content of the modified expansive soil. ; Use modified medium expansive soil and conduct the test according to T 0804-1994 Inorganic binder stabilized material compaction test method to obtain the maximum dry density and optimum moisture content ; Moisture content , Optimum moisture content And compaction assessment standards As the basis for adjusting the moisture content of expansive soil in modification, the maximum dry density As a calculation of compaction degree for roadbed construction benchmark.

2. The method for modifying medium expansive soil according to claim 1, characterized in that: The designed mix ratio in step 1 is medium expansive soil: fly ash: waste tire fiber: papermaking wastewater soluble matter: water = 100: 10-30: 0.1-0.6: 0.3-2: 0-20.

3. The method for modifying medium expansive soil according to claim 2, characterized in that: The moisture content of the wet expansive soil and wet fly ash is ≤5%.

4. The method for modifying medium expansive soil according to claim 3, characterized in that: The wet fly ash refers to the fine ash collected from the flue gas after coal combustion, and is the main solid waste discharged from coal-fired power plants.

5. The method for modifying medium expansive soil according to claim 2, characterized in that: The wet waste tire fiber is the fiber produced in the process of processing waste tire rubber powder, and its moisture content is 0.3%-1%.

6. The method for modifying medium expansive soil according to claim 2, characterized in that: The papermaking wastewater is wastewater generated in the process of pulping and papermaking. The papermaking wastewater needs to be clarified and the content of insoluble organic matter is less than 0.1%.

7. The method for modifying medium expansive soil according to claim 1, characterized in that: The quality of the fly ash and water meets the requirements of JTG / T F20-2015 Technical Specifications for Highway Pavement Base Construction.

8. The method for modifying medium expansive soil according to claim 1, characterized in that: The method for determining the designed mix ratio and the modification period is: 1) First compaction test Medium expansive soil is calculated as 100. Based on technology, economy, construction period, climate and experience, the amount of fly ash, soluble matter and waste tire fiber is selected within the dosage range. According to T 0804-1994 Inorganic binder stabilized material compaction test method, a compaction test is carried out to obtain the maximum dry density. and optimum moisture content ; The material used in the first compaction test is called mixed material, which is the mixed material before modification; 2) Calculate the initial mix ratio The initial mix ratio is calculated based on the amount of medium expansive soil, fly ash, soluble matter and waste tire fiber and the compaction test results: medium expansive soil: fly ash: waste tire fiber: soluble matter: water; 3) Free expansion rate test Pass T 0124-1993 free expansion rate test and obtain free expansion rate and modification period n; 4) Determine the design mix ratio If the modification period n is within expectations, the above-mentioned initial mix ratio can be used as the design mix ratio; otherwise, adjust the material dosage and re-test.

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