Key parameter design method of alkali slag cement lime soil for pavement base based on environmental protection requirements

Abstract

The present invention discloses a method for designing key parameters of alkali slag cement lime soil for road base based on environmental protection requirements, comprising the following steps: alkali slag raw material processing and moisture content testing; selecting cement, lime, and plain soil materials; determining the natural moisture content of plain soil materials; designing an orthogonal test plan for preparing road base materials with alkali slag cement lime soil; calculating the mass ratio of road base materials with alkali slag cement lime soil; performing performance testing of road base materials with alkali slag cement lime soil; and selecting the alkali slag cement lime soil ratio with the lowest material cost under the premise of meeting technical indicators. It can be seen from the above structure that the method for designing key parameters of alkali slag cement lime soil for road base based on environmental protection requirements of the present invention specifically selects the mix ratio of alkali slag cement lime soil and key parameters of alkali slag according to the soil quality corresponding to different road projects and the different requirements of the road base to be built, so as to optimize and reduce the cost of road base materials under the premise of achieving the mechanical properties of the road base and environmental protection requirements.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering, and in particular to a key parameter design method of alkali slag cement lime soil of a road base based on environmental protection requirements. Background Art

[0002] As a basic chemical raw material, soda ash is widely used in various industries such as construction, chemical industry, and agriculture. The main method of making alkali is the ammonia-soda method, which will discharge a large amount of solid waste alkali slag during the process. According to statistics, for every ton of soda ash produced, about 300-600kg of alkali slag is discharged, and the annual discharge is as high as 7.8 to 10 million tons. The traditional ground discharge method of alkali slag occupies a large amount of land resources, and the utilization rate is less than 15%. In addition, due to the high chloride ion characteristics of SR, harmful components will pollute the soil and groundwater, and there is a potential for pollution, which will harm the ecological environment. Therefore, from the perspective of environmental protection and land resource utilization, scientific and environmentally friendly treatment of solid waste alkali slag has become a difficult problem faced by salt chemical companies.

[0003] In recent years, scholars at home and abroad have been committed to the research on the resource utilization of solid waste alkali slag. The main methods include using the alkalinity of alkali slag to improve acidic soil, using alkali slag as a solidifying agent to solidify silt, using alkali slag and other materials to make engineering soil for backfilling materials, using alkali slag as an admixture to partially replace fly ash to prepare building materials, and using alkali slag as a modifier to improve and solidify the land. The above-mentioned research methods for the utilization of alkali slag consume alkali slag to a certain extent, but due to the low strength of the alkali slag itself and the rich Cl-, the project has alkali efflux and steel corrosion. As a result, conventional alkali slag treatment methods are difficult to simultaneously meet the project's requirements for bearing capacity, environmental protection and other aspects. How to scale up and resource-based utilization of solid waste alkali slag is an urgent issue.

[0004] If alkali slag is directly used as a road filling material, due to its high water content, strong hydrophilicity, poor water stability and large porosity, the engineering effect of using it alone as an engineering filler is not ideal, and the engineering value of using it as a filler is low. At present, in the field of road engineering, some engineering and technical personnel use alkali slag, soil and lime to prepare alkali slag lime soil, mainly judging the feasibility and effect of alkali slag road use based on material strength, but do not consider the chloride ion content of alkali slag lime soil and its impact on the environment; there is currently no case of using alkali slag as an additive to cement lime soil as a road base material. This patent proposes a key parameter design method for alkali slag cement lime soil for road base based on environmental protection requirements. According to the soil quality of the area where the road is constructed and the corresponding alkali slag in different states, the key parameters of alkali slag cement lime soil are designed and optimized from an environmental protection perspective, taking into account the mechanical properties while taking into account the environmental protection characteristics of the material, so as to consider the environmental protection performance of the material based on the dual perspectives of the mechanical properties and environmental protection performance of the material, and meet the technical performance. Consider, thereby optimizing the material mix ratio and key parameters. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for designing key parameters of alkali slag cement lime soil for road base based on environmental protection requirements, so that according to the different soil types of the road base under construction and the alkali slag in different states, and the mechanical performance requirements and environmental protection requirements of the road base construction, the mix ratio of alkali slag cement lime soil that meets the above requirements can be designed, and the key parameters of the alkali slag cement lime soil can be designed and optimized, taking into account both the mechanical properties and the environmental protection characteristics of the material.

[0006] The technical solution adopted by the present invention is:

[0007] The key parameter design method of alkali slag cement lime soil for pavement base based on environmental protection requirements includes the following steps:

[0008] 1) Take samples of cement, lime and soil materials used to build the road base and test the natural moisture content of the soil materials. Cement and lime are selected according to the materials listed in the construction procurement list;

[0009] 2) Test the storage conditions under the same storage conditions and storage t 1 ~t n The moisture content of the alkali residue material under n different storage times corresponds to K1~Kn, respectively. 1 ~t n The time increases successively;

[0010] 3) The alkali residue retrieved from the alkali plant is dried and then ground and crushed, and then sieved through multiple standard sieves to obtain alkali residue particles of M sizes, and the sieved alkali residue particles of M sizes are divided into n parts and then water is added to each part, so that the moisture content of each size of the alkali residue particles reaches K1~Kn respectively;

[0011] 4) Use the external admixture method to replace part or all of the lime components in cement lime soil with an equal amount of solid waste alkali slag to obtain alkali slag cement lime soil with a moisture content of w%, and set three influencing factors, namely: alkali slag dosage, alkali slag particle size and alkali slag moisture content. Each influencing factor is designed with M levels of variation. Using the characteristics of orthogonal experiment, L P (M 3 ) Orthogonal test plan table, and design the orthogonal test plan for the P group mix ratio;

[0012] 5) Calculate the amount of water required for each test mix according to the target moisture content w% of the alkali slag cement lime soil, and calculate the dry density of each group of test mix samples;

[0013] 6) According to the dry density of each test mix ratio sample obtained in step 5) and the target moisture content of alkali slag cement lime soil, prepare the alkali slag lime stabilized soil specimens of unconfined compressive strength of alkali slag cement lime soil in accordance with the "Testing Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009), and calculate the representative value of the 7-day unconfined compressive strength of the alkali slag lime stabilized soil specimens of each test mix ratio with reference to the "Technical Specifications for Highway Pavement Base Construction" (JTG F20-2015), and select the test mix ratio whose strength meets the standard requirements;

[0014] 7) The alkali slag cement lime soil component of the test mix ratio selected in step 6) is used to prepare the slag cement lime soil filtrate according to the "Highway Geotechnical Test Code" (JTG340-2020) and the pH value of the filtrate is determined, and the test mix ratio with a pH in the range of 6 to 8.5 is selected according to the "Agricultural Irrigation Water Quality Standard" (GB 5084-2021) and the "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T 31962-2015);

[0015] 8) Measure the chloride content in each test mix group selected in step 7) according to the determination method of soluble salt chloride in the "Highway Geotechnical Test Code" (JTG340-2020), and select the alkali slag cement lime soil test mix that meets the requirements according to the provisions of chloride in the basic control items of farmland irrigation water quality in the "Farmland Irrigation Water Quality Standard" (GB 5084-2021).

[0016] A further improvement of the present invention is that in the step 1), the bare soil material of the test section is stored in a ventilated place, ground and crushed by a grinder after natural drying, sieved with a standard sieve to remove particles with a particle size greater than 10 mm, and the natural moisture content of the bare soil material is measured after drying.

[0017] A further improvement of the present invention is that in step 2), the t 1 Represents the alkali residue that has just left the factory and has not been stored. n Represents alkali slag that has been stored for half a year.

[0018] A further improvement of the present invention is that in step 3), the particle size of the alkali residue particles is less than 10 mm.

[0019] A further improvement of the present invention is that in the step 4), the mass ratio of cement, lime and soil in the reference group is lime: cement: soil = x: y: 100, and the mass ratio of alkali slag cement, lime and soil in the test group is: (alkali slag + lime): cement: soil = x: y: 100. The alkali slag lime has M groups of alkali slag dosages at different levels, and the mass ratio of cement and soil in each group remains unchanged. The content of alkali slag in each group is 0, x / (M-1), 2x / (M-1), ..., (M-3)x / (M-1), (M-2)x / (M-1) and x, respectively, and the corresponding content of lime in each group is x, (M-2)x / (M-1), (M-3)x / (M-1), ... 2x / (M-1), x / (M-1) and 0, respectively.

[0020] A further improvement of the present invention is that in the step 5), a light or heavy compaction test is performed according to the type of the raw soil material and in accordance with the "Test Procedure for Stabilized Materials of Inorganic Binders for Highway Engineering" (JTG E51-2009), so as to calculate the dry density of the samples of each test mix group.

[0021] A further improvement of the present invention is that in the step 7), the alkali slag lime stabilized soil specimen of the test mix ratio selected in step 6) is crushed, dried and passed through a standard sieve with a particle size of 0.15 mm, the sieved particles are placed in a container, and deionized water is added according to a water-soil ratio of 5:1, and then fully mixed by shaking to form a suspension, and then the clear filtrate obtained by filtering is the alkali slag cement lime filtrate, and finally the pH value of the alkali slag cement lime soil filtrate is measured by a pH meter.

[0022] A further improvement of the present invention is that in step 8), the chloride in the alkali residue cement lime filtrate is determined by silver nitrate titration, and Cl - (mg / L) ≤350 mg / L of alkali slag cement lime soil test mix ratio.

[0023] A further improvement of the present invention is to take 25 mL of the filtrate and place it in a conical flask, add methyl orange indicator, and add 0.02 mol / L NaHCO 3 Solution, until the solution pH is about 7, add 5-6 drops of potassium chromate indicator, and titrate with silver nitrate solution. When the titration reaches the end point, a brick-red silver chromate precipitate is generated;

[0024] Calculate the chloride content according to the following formula:

[0025] ;

[0026] ;

[0027] Where:

[0028] —Concentration of silver nitrate standard solution, unit: mol / L;

[0029] —Volume of silver nitrate solution used for titration, unit: mL;

[0030] —Dry soil mass of the volume of leachate taken during analysis, unit: g;

[0031] 0.0355—Molar mass of chloride ion, unit: g / mmol.

[0032] A further improvement of the present invention is that 9) the alkali slag cement lime soil mix ratio with the best economic benefit is selected from the alkali slag cement lime soil test mix ratios selected in step 8).

[0033] The beneficial effects of the present invention are:

[0034] First, the key parameter design method of alkali slag cement lime soil for road base based on environmental protection requirements of the present invention can specifically select the component ratio of alkali slag cement lime soil according to the soil quality corresponding to different roadbed projects and the different requirements of the roadbed to be built, so as to maximize the amount of alkali slag replacing lime and minimize the cost of road base materials while meeting the mechanical properties and environmental protection requirements of the roadbed.

[0035] Second, the key parameter design method of alkali slag cement lime soil for road base based on environmental protection requirements of the present invention, the present invention applies alkali slag, an industrial waste residue, to roadbed materials, reducing the impact of alkali slag on the environment; different proportions are adopted according to the grade of the highway to be built, and the appropriate proportion is selected by changing the amount of alkali slag used, so that its engineering performance meets the economic and strength expectations.

[0036] Third, the key parameter design method of the road base alkali slag cement lime soil based on environmental protection requirements of the present invention is to design the key parameters of the road base alkali slag cement lime soil by adjusting the pH value and chloride Cl - The determination of alkali residue and the selection of appropriate alkali residue cement lime soil ratio based on environmental protection have realized the recycling of alkali residue waste and reduced the various impacts of traditional alkali residue discharge on soil and environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the test result table of natural moisture content of bare soil material.

[0038] Figure 2 is an orthogonal factor level table.

[0039] Figure 3 This is the orthogonal test plan table for the alkali slag cement lime soil test group.

[0040] Figure 4This is the test plan table for the proportion of alkali slag cement lime soil materials.

[0041] Figure 5 This is the 7-day unconfined compressive strength test result table of alkali slag lime soil samples.

[0042] Figure 6 This is the pH value measurement result table of alkali residue cement lime soil filtrate.

[0043] Figure 7 For alkali residue cement lime soil material Cl - Dissolution test results table. Implementation

[0044] The key parameter design method of alkali slag cement lime soil for pavement base based on environmental protection requirements includes the following steps:

[0045] Alkali slag material treatment and moisture content testing

[0046] After the alkali residue is sampled from the alkali plant, the alkali residue material is transported to the laboratory and placed in a drying box for drying. The dried alkali residue is ground and crushed with a ceramic grinder, and sieved with 0.15mm, 1.18mm, 2.36mm, and 4.75mm standard round hole sieves; finally, the dried alkali residue is treated with water, and the moisture content of the alkali residue of each particle size is controlled to be 0%, 43.60%, 64.58%, and 85.38% respectively, which is used to simulate four different storage states of alkali residue.

[0047] Cement, lime and soil material selection

[0048] Cement is purchased according to grade requirements. 32.5 Portland cement; lime is purchased as finished dry anhydrous slaked lime according to grade requirements. Raw soil materials are sampled from different locations of the roadbed pits in the test section. The materials are transported to the laboratory for preliminary manual crushing and then placed in a ventilated place for natural storage; the initially crushed raw soil materials are sieved with a standard sieve.

[0049] Determination of natural moisture content of raw soil materials

[0050] Six samples of the sieved soil material were randomly taken and placed in different aluminum boxes, which were numbered 1 to 6. The weight was measured with an electronic scale, and then the samples were moved to a drying oven and dried at 100°C for 12 hours. The baked aluminum boxes were taken out and the weight was measured again with an electronic scale, so that the average value was determined as the natural moisture content of the soil material. The test results are shown in Figure 1 .

[0051] Design of orthogonal test scheme for preparing road base material with alkali residue cement lime soil

[0052] Taking the cement lime soil used for the road base of the test section as the reference group, the ratio of cement: lime: soil = 3:9:100, an orthogonal experiment was designed to explore the effects of the three factors of alkali slag dosage, alkali slag particle size, and alkali slag moisture content on the strength and environmental performance of alkali slag cement lime soil. The orthogonal factor level table is shown in Figure 2. Figure 2 ; 16 groups of alkali slag cement lime soil test groups with different test factor levels, L 16 (4 3 )Orthogonal test plan table see Figure 3 .

[0053] Test plan for preparing road base materials with alkali residue cement lime soil

[0054] Calculate the mass ratio of materials according to the orthogonal scheme, see Figure 4 The moisture content of the S1~S16 test group was designed to be 18.5%, and the mass of each material required to make the unconfined compressive strength specimens of alkali slag cement lime soil was calculated by the external admixture method.

[0055] Performance test of road base material prepared by alkali residue cement lime soil

[0056] Mechanical properties test

[0057] Use an electronic balance to weigh the alkali residue, cement, lime and soil required for each test. Use a measuring cylinder to weigh enough water and pour it into a spray pot, spray it into the mixture and mix it well. After mixing evenly, put it into a plastic bag, seal it, and soak it in the prepared water to suffocate it.

[0058] Use a brush to apply a thin layer of lubricating oil on the inner wall of the cylindrical test mold and the contact surfaces of the upper and lower pads. Place the lower pad on the bottom of the test mold and leave it exposed 2cm, then pour the mixture after the suffocation time has arrived into the test mold in 3 times, then place the upper pad in the test mold, and also leave it exposed 2cm.

[0059] Place the test mold on the base of the press so that the upper chassis of the press contacts the upper pad of the test mold, start the press, and control the pressurization rate to 1mm / min. When the upper and lower pads are all pressed into the test mold, stop pressurizing, maintain the pressed state for 2 minutes, then release the pressure, remove the test mold, and place the pressed test mold on the demolding machine for demolding.

[0060] Weigh the mass m of the specimen with an electronic scale, accurate to 1g, and measure the height h of the specimen with a vernier caliper. Measure three times and take the average value, accurate to 0.1mm. If it meets the requirements, it is a qualified specimen. Otherwise, remake the specimen. After the specimen is removed from the test mold and weighed, it should be immediately placed in a curing box for curing. The conditions are a temperature of 20±1℃, a humidity of 95%, and a curing time of 7d. On the last day of the curing period, immerse the specimen in water with a water depth exceeding 2.5cm above the top surface of the specimen (weigh the mass of the specimen before placing it in water). During the curing period, the mass loss of the specimen should meet the requirement that the small specimen should not exceed 1g. If the mass loss does not meet the requirements, the specimen will be scrapped.

[0061] Take the specimen that has been immersed in water for a day and night out of the water, use a soft old cloth to absorb the visible free water on the surface of the specimen and weigh the mass m of the specimen. Use a vernier caliper to measure the height h of the specimen to an accuracy of 0.1 mm, otherwise make a new specimen.

[0062] Place the specimen on the lifting platform of the pavement material strength tester and conduct a compression test. During the test, the deformation of the specimen should increase at a constant rate and maintain a rate of 1mm / min. The maximum pressure P (kN) when the specimen is destroyed should be recorded.

[0063] The 7-day unconfined compressive strength of the alkali-slag lime soil samples of group S1~S16 was calculated according to the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009). The mechanical properties test data can be found in Figure 5 .

[0064] The test results show that the maximum compressive strength of alkali slag cement lime soil can reach 8.35 MPa and the minimum is 5.90 MPa. Combined with the provisions of 4.2.4 in the "Technical Specifications for Highway Pavement Base Construction" (JTG / T F20-2015), it can be seen that the compressive strength of the alkali slag cement lime soil ratio designed by the present invention meets the requirements of the base of expressways and first-class highways.

[0065] Environmental performance test

[0066] Prepare a 5:1 water-soil ratio leachate according to the Highway Geotechnical Test Code (JTG340-2020). Dry the test group materials that meet the strength requirements and are crushed by drying, pass through a 0.15mm round hole sieve, and place them in a 250mL conical flask after sieving. Add 100mL of deionized water and shake vigorously for 3 minutes. Fold the filter paper and place it in the funnel, slowly pour out the suspended soil slurry, and collect the clear filtrate for later use.

[0067] The pH value of the filtrate of alkali slag cement lime soil is measured by a pH meter. Figure 6 shown.

[0068] According to the pH measurement results, the pH of alkali slag cement lime soil meets the pH limit of 5.5~8.5 in the "Agricultural Irrigation Water Quality Standard" (GB5084-2021) and the pH limit of 6~9 in the "Water Quality Standard for Sewage Discharge into Urban Sewers" (GB / T 31962-2015). The experimental groups are: S11, S12, S13, S14, S15, and S16.

[0069] There is a slight deviation between the pH requirement for irrigation water in the "Water Quality Standard for Farmland Irrigation" and the pH requirement for sewage in the "Water Quality Standard for Sewage Discharge into Urban Sewers". The alkali slag cement lime soil corresponding to the filtrate of alkali slag cement lime soil that meets the pH requirements of both the "Water Quality Standard for Farmland Irrigation" and the "Water Quality Standard for Sewage Discharge into Urban Sewers" fully meets the environmental protection requirements. That is, the alkali slag cement lime soil whose filtrate meets the pH requirements of the "Water Quality Standard for Farmland Irrigation" and the "Water Quality Standard for Sewage Discharge into Urban Sewers" can be used in urban and rural roadbeds, and has a very wide range of applications.

[0070] According to the determination method of soluble salt chloride in the "Highway Geotechnical Test Code" (JTG340-2020), the chloride of alkali slag cement lime soil in groups S11, S12, S13, S14, S15 and S16 was determined by silver nitrate titration. The specific steps are as follows:

[0071] Take 25 mL of the filtrate and place it in a conical flask, add methyl orange indicator, and use a rubber dropper to drop 0.02 mol / L NaHCO 3 solution until the pH value of the solution is about 7, add 5 to 6 drops of potassium chromate indicator, and titrate with silver nitrate solution. When the titration reaches the end point, a brick-red silver chromate precipitate is generated.

[0072] Calculate the chloride content according to the following formula:

[0073] ;

[0074] ;

[0075] Where:

[0076] —Concentration of silver nitrate standard solution, unit: mol / L;

[0077] —Volume of silver nitrate solution used for titration, unit: mL;

[0078] —Dry soil mass of the volume of leachate taken during analysis, unit: g;

[0079] 0.0355—Molar mass of chloride ion, unit: g / mmol.

[0080] Alkali slag cement lime soil material Cl - The dissolution test results are shown in Figure 7 .

[0081] According to the "Farmland Irrigation Water Quality Standard" (GB5084-2021), chloride (as Cl - It is stipulated in the plan that Cl - (mg / L) ≤350 mg / L. Select the Cl that meets the requirements of the standard - The experimental groups with limit values ​​are: S13, S15, and S16.

[0082] The Cl content of irrigation water in the "Farmland Irrigation Water Quality Standard" is - There are requirements, but the "Water Quality Standard for Sewage Discharge into Urban Sewers" does not require Cl in sewage. - There are requirements, so the alkali slag cement lime soil corresponding to the filtrate of alkali slag cement lime soil that meets the pH requirements of the "Farmland Irrigation Water Quality Standard" fully meets the urban sewage discharge standards, that is, the alkali slag cement lime soil filtrate that meets the pH requirements of the "Farmland Irrigation Water Quality Standard" can also be used in urban and rural roadbeds, further ensuring the environmental protection effect of the constructed roadbed in daily use, and further reflecting that the application range of alkali slag cement lime soil is very wide.

[0083] After screening step by step according to the above steps, there are three experimental groups that meet the standards: S13, S15, and S16. The material ratios of these three experimental groups are the same, all of which are alkali slag: cement: lime: soil = 9:3:0:100. However, the alkali slag treatment is different, that is, the particle size of S13 alkali slag is 0.15mm, and the alkali slag moisture content is 85.38%; the particle size of S15 alkali slag is 2.36mm, and the alkali slag moisture content is 43.60%; the particle size of S16 alkali slag is 4.75mm, and the alkali slag moisture content is 0%. According to the best economic benefit, the smaller the alkali slag particle size, the higher the crushing cost; the smaller the alkali slag moisture content, the higher the processing cost. When considering the moisture content and crushed particle size, the moisture content processing cost is preferably considered. It is difficult and costly to dry the alkali slag to 0% moisture content, while the cost difference between processing the alkali slag particle size to 2.36mm and 4.75mm is relatively small. Finally, the S15 experimental group was selected as the final key parameters, that is, the alkali slag dosage was 9%, the alkali slag particle size was 2.36mm, and the alkali slag moisture content was 43.60%.

[0084] Based on the above selection, the alkali slag cement lime soil ratio with the lowest material cost is selected.

[0085] The present invention adds an appropriate amount of solid waste alkali slag to the original cement lime soil, based on the strength and environmental performance of the road base alkali slag cement lime soil, specifically through the design of key parameters, based on the unconfined compressive strength index and environmental performance index, according to the 7-day unconfined compressive strength, pH value, chloride Cl - Content screening selects the ratio of alkali slag cement lime soil, making alkali slag cement lime soil have a wider application. Its ratio design method is to use alkali slag to replace the lime content in cement lime soil, converting alkali slag into road additive materials, thereby improving the performance of alkali slag road use.

Claims

1. The key parameter design method of alkali slag cement lime soil for road base based on environmental protection requirements is characterized by The following steps are involved: 1) Take samples of cement, lime and soil materials used for the test section pavement base and test the natural moisture content of the soil materials. Cement and lime are selected according to the conventional materials listed in the construction procurement list; 2) Test the storage conditions under the same storage conditions, storage t1~t n The moisture content of the alkali residue material under n different storage times corresponds to K1~Kn, and the moisture content of the alkali residue material under n different storage times corresponds to K1~Kn, respectively. n The time increases successively; the t1 represents the fresh alkali slag that has just left the factory and has not been stored, the t n It represents the alkali residue that has been stored for half a year and its properties have stabilized; 3) The fresh alkali residue taken from the alkali plant is dried and then ground and crushed, and then sieved through multiple standard sieves to obtain alkali residue particles of M particle sizes, and the sieved alkali residue particles of M particle sizes are divided into n parts and then water is added to each part, so that the moisture content of each particle size of the alkali residue particles reaches K1~Kn respectively; 4) Use the external admixture method to replace part or all of the lime components in cement lime soil with an equal amount of solid waste alkali slag to obtain alkali slag cement lime soil with a moisture content of w%, and set three influencing factors, namely: alkali slag dosage, alkali slag particle size and alkali slag moisture content. Each influencing factor is designed with M levels of variation. Using the characteristics of orthogonal experiment, L P (M 3 ) Orthogonal test plan table, and design the orthogonal test plan for the P group mix ratio; 5) Calculate the amount of water required for each test mix according to the target moisture content w% of the alkali slag cement lime soil, and calculate the dry density of each group of test mix samples; 6) According to the dry density of each test mix sample obtained in step 5) and the target moisture content of alkali slag cement lime soil, prepare the unconfined compressive strength specimens of alkali slag cement lime soil in accordance with the "Testing Procedures for Inorganic Binder Stabilized Materials for Highway Engineering", and calculate the representative value of the 7-day unconfined compressive strength of the alkali slag lime stabilized soil specimens of each test mix with reference to the "Technical Specifications for Highway Pavement Base Construction", and select the test mix whose strength meets the standard requirements; 7) The alkali slag cement lime soil component of the test mix ratio selected in step 6) is used to prepare the slag cement lime soil filtrate according to the "Highway Geotechnical Test Code" and the pH value of the filtrate is measured, and the test mix ratio with a pH in the range of 6 to 8.5 is selected according to the "Agricultural Irrigation Water Quality Standard" and the "Water Quality Standard for Sewage Discharged into Urban Sewers"; 8) Measure the chloride content in each test mix group selected in step 7) according to the determination method of soluble salt chloride in the "Highway Geotechnical Test Procedures", and select the alkali slag cement lime soil test mix that meets the requirements according to the provisions of chloride in the basic control items of farmland irrigation water quality in the "Farmland Irrigation Water Quality Standards".

2. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In the step 1), the soil material of the test section is stored in a ventilated place, ground and crushed by a grinder after natural drying, sieved with a standard sieve to remove particles with a particle size greater than 10 mm, and the natural moisture content of the soil material is measured after drying.

3. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In the step 3), the particle size of the alkali residue particles is less than 10 mm.

4. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In the step 4), the cement lime soil of the test section that originally did not contain alkali slag is regarded as a reference group, the dry mass ratio of cement lime soil materials in the reference group is lime: cement: soil = x: y: 100, and the dry mass ratio of alkali slag cement lime soil materials in the test group is: (alkali slag + lime): cement: soil = x: y:

100. The alkali slag lime has M groups of different levels of alkali slag dosage, and the mass ratio of cement and soil in each group remains unchanged. The content of alkali slag in each group is 0, x / (M-1), 2x / (M-1), ..., (M-3)x / (M-1), (M-2)x / (M-1) and x, and the corresponding content of lime in each group is x, (M-2)x / (M-1), (M-3)x / (M-1), ... 2x / (M-1), x / (M-1) and 0, respectively.

5. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In the step 5), a light or heavy compaction test is performed according to the type of the base soil material and in accordance with the Testing Procedures for Stabilized Materials with Inorganic Binders for Highway Engineering, combined with the particle group characteristics of the base soil, so as to calculate the dry density of the samples of each test mix group.

6. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In the step 7), the alkali slag lime stabilized soil specimen of the test mix ratio selected in step 6) is crushed, dried and passed through a standard sieve with a particle size of 0.15 mm, the sieved particles are placed in a container, and deionized water is added according to a water-soil ratio of 5:1, and then fully mixed by shaking to form a suspension, and then the clear filtrate obtained by filtering is the alkali slag cement lime soil filtrate, and finally the pH value of the alkali slag cement lime soil filtrate is measured by a pH meter.

7. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: In step 8), the chloride in the alkali residue cement lime filtrate is determined by silver nitrate titration, and Cl - Test mix ratio of alkali slag cement lime soil ≤350 mg / L.

8. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 7, characterized in that: Take 25 mL of the filtrate and place it in a conical flask, add methyl orange indicator, and use a rubber dropper to add NaHCO3 solution until the solution pH is about 7, then add 5-6 drops of potassium chromate indicator and titrate with silver nitrate solution. When the titration reaches the end point, a brick-red silver chromate precipitate is generated. Calculate the chloride content according to the following formula: ; ； Where: —Concentration of silver nitrate standard solution, unit: mol / L; —Volume of silver nitrate solution used for titration, unit: mL; —Dry soil mass of the volume of leachate taken during analysis, unit: g; 0.0355—Molar mass of chloride ion, unit: g / mmol.

9. The key parameter design method of road base alkali slag cement lime soil based on environmental protection requirements as claimed in claim 1, characterized in that: 9) Select the alkali slag cement lime soil mix ratio with the best economic benefit from the alkali slag cement lime soil test mix ratios selected in step 8).

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