Method for improving dispersive soil by using cement and fly ash
By using cement and fly ash as modifiers, dispersible soil is improved, and the adverse impact of traditional modifiers on the environment and high cost problems are solved, and the effects of improving soil strength, reducing dispersion and reducing costs are achieved.
Patent Information
- Application Number
- CN202510171182.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-17
- Publication Date
- 2025-04-15
AI Technical Summary
In the prior art, when improving dispersible soil, the use of traditional admixtures such as lime may have adverse effects on the environment, and are costly and difficult to effectively reduce soil dispersion and improve soil strength.
Cement and fly ash are used as modifiers, and are added to dispersible soil through different proportional components designs to control the optimal moisture content and maximum dry density of the soil sample, and the dispersion and mechanical properties are identified through multiple experiments to obtain the optimal modifier ratio.
Effectively enhance soil strength, reduce dispersion, maintain soil pH balance, reduce modifier costs, reduce sewage discharge, and is environmentally friendly, suitable for large-scale engineering applications.
Smart Images
Figure CN119822714A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of dispersible clay modification in water conservancy projects, and in particular relates to a method for improving dispersible soil by utilizing cement and fly ash. Background Art
[0002] Dispersible soil is a special kind of widely distributed clay soil, which has poor anti-penetration ability and is sensitive to water. Under certain conditions, the clay particles contained in the soil are suspended in the water and easily washed away by rainwater or seepage, causing damage. Therefore, when it is used in engineering projects such as transportation, geotechnical engineering, and water conservancy projects, which will change the water content of dispersed soil, it will cause irreversible damage such as erosion, pipe bursts, landslides, and dam breaches with reservoirs, channels, and other projects that are directly or indirectly in contact with dispersed soil, thus causing serious engineering accidents.
[0003] There are methods for improving and strengthening dispersed soil at home and abroad, such as: et al. explored the improvement effects of different types of fly ash on dispersed soil and determined that Class C fly ash is more effective than Class F fly ash in stabilizing dispersed soil ( H, M, Seyrek E, et al. Comparison of the effect of using class Cand Ffly ash on the stabilization of dispersive soils), Zhu Yanbao, Chen Wei, etc. adopted the "lime + fly ash" modification treatment scheme, which provided a theoretical basis and scientific guidance for the management and engineering application of dispersed soils (Zhu Yanbao, Yu Zhongli, Zheng Jian, et al. Experimental study on the modification treatment of dispersed soils in western Jilin and Chen Wei, Teng Hao, Fu Shu. Study on the implementation plan of dispersed soil modification treatment.), but the above methods have the following disadvantages: the modification research of dispersed soils mostly adopts the method of adding traditional admixtures such as lime. However, in large-scale projects, if a large amount of lime is not properly treated and discharged into the environment, it may have an adverse effect on the surrounding soil and water. Summary of the invention
[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for improving dispersed soil using cement and fly ash. According to different dispersed soils, adding different amounts of fly ash can effectively enhance soil strength, reduce soil dispersibility, maintain soil pH balance, reduce modifier costs and reduce pollution.
[0005] In order to achieve the above object, the technical solution adopted by the present invention is:
[0006] A method for improving dispersive soil by using cement and fly ash comprises the following steps:
[0007] Step 1: obtaining original dispersed soil at the sampling site, and then crushing, grinding, air-drying and sieving the original dispersed soil in sequence, and taking the sieve-off as dispersed soil to be treated; at the same time, designing a modifier with cement and fly ash as components according to different proportions;
[0008] Step 2: According to GB / T 50123-2019 "Standard for Geotechnical Test Methods", the maximum dry density and optimal moisture content of the target area soil are measured by compaction test, the liquid and plastic limits of the soil are measured by limit moisture content test, and modifiers with different proportions are added to the undersize to control the optimal moisture content and maximum dry density of the soil sample;
[0009] Step 3: According to T / CECS1337-2023 "Standard for Test Methods of Unsaturated Soils" and ASTM D4647 and ASTMD6572, the dispersibility of the original dispersible soil in step 1 is comprehensively identified through three tests: pinhole test, fragment test, and mud ball test;
[0010] Step 4: According to the physical property index of the original dispersible soil measured in step 2 and the dispersibility result identified in step 3, the modifiers with different proportions prepared in step 1 are added to the sieve and water is added for improvement, and then the dispersibility of the improved soil is identified according to the method in step 3 to obtain the best modifier ratio;
[0011] Step 5. Comprehensively identify the dispersibility of the improved soil in step 4 through three tests: pinhole test, fragment test, and mud ball test; test the mechanical properties of the improved soil through consolidation compression test, triaxial shear test, and permeability test (GB / T50123-2019 "Standard for Geotechnical Test Methods"); if the tested improved soil eliminates the dispersibility of the soil sample and the mechanical properties meet the requirements of the construction unit, proceed to step 6, otherwise return to step 4 and increase the content of the modifier;
[0012] Step 6: Use the best modifier ratio identified in step 5 to improve the soil under the sieve, and then fill the improved soil back into the foundation of the sampling address in step 1, and compact it to its original state with a convex block.
[0013] The specific steps of step one are as follows: air-drying the original dispersed soil, crushing it with a small wooden hammer and passing it through a sieve of less than 2 mm for later use; drying the fly ash and passing it through a sieve of less than 0.5 mm for later use; and measuring the moisture content of the test soil and fly ash by the drying method one day before mixing the soil.
[0014] The percentage of each component of the modifier added to the dispersed soil to be treated in step 1 is: cement content is 1% to 4%, fly ash content is 1% to 4%, and the added water is the optimal moisture content of the dispersed soil to be treated.
[0015] The original dispersed soil in step 1 is high Na + The content of dispersed soil, the percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 3% to 4%, fly ash: 1% to 2%, and the content of water added is the optimal moisture content of the improved soil after adding the modifier.
[0016] The original dispersed soil described in step 1 is alkaline dispersed soil with a pH value of ≥ 9.8. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 1%, acid fly ash: 3% to 4%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier; the acid fly ash is a silicate (such as silicon dioxide) or an aluminate (such as aluminum dioxide).
[0017] The original dispersed soil described in step 1 contains montmorillonite in an amount not less than 11% of the total content. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 2% to 3%, acid fly ash: 2% to 3%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier.
[0018] The main components of cement in the modifier of the present invention include calcium oxide CaO, magnesium oxide MgO and aluminum oxide Al2O3, the main components of fly ash are aluminum oxide Al2O3 and silicon dioxide SiO2. The cement and fly ash are combined to form a joint modifier, and the improvement mechanism of the dispersible soil is as follows:
[0019] (1) In the early stage, the combined modifier can quickly fill the pores inside the dispersed soil, especially dividing the large pores in the soil into multiple tiny pores, thereby significantly improving the filling efficiency. This process not only effectively reduces the total volume of soil pores, but also significantly enhances the density and stability of the soil. In addition, by optimizing pore filling, the surface roughness of soil particles can be improved, further improving the mechanical properties of the soil.
[0020] (2) The dispersibility of soil is closely related to the percentage of exchangeable sodium ions. The percentage of exchangeable sodium ions of dispersed soil is significantly higher than that of non-dispersed soil. As the dosage of fly ash increases, the exchangeable sodium ion content of the soil gradually decreases. Therefore, after adding fly ash to the dispersed soil, the high-valent cations carried on the surface of the fly ash particles can be adsorbed and exchanged with Na, so that the dispersed soil particles gradually form larger aggregates. In addition, the cementing substances produced by the hydrolysis and hydration of fly ash can promote a stronger connection between soil aggregates and fill the pores between soil particles, so that the soil is transformed from dispersed soil to non-dispersed soil, the compressibility of the soil is significantly reduced, and the anti-permeability characteristics are significantly enhanced.
[0021] (3) As the fly ash hydrolysis reaction deepens, a large amount of Ca is easily precipitated during the reaction. 2+ When it exceeds the amount required for ion exchange, it reacts chemically with SiO2 and Al2O3 that make up the clay minerals in an alkaline environment:
[0022] SiO2+Ca(OH)2+nH2O→CaO·SiO2·(n+1)H2O
[0023] AI2O3+Ca(OH)2+nH2O→CaO·AI2O3·(n+1)H2O
[0024] Since dispersed soil is alkaline, the hydrolysis products of fly ash can react with SiO2 and Al2O3 in the soil to form stable crystalline compounds that are insoluble in water, and gradually harden in water and air, reducing the compressibility of the modified soil.
[0025] Therefore, in the later stage of ion exchange, silica gel and aluminum gel formed by diffusion in the soil further react with fly ash to form calcium silicate hydrate and calcium chlorate hydrate, forming a relatively strong protective film around the dispersed soil clay particles, which increases the strength of the modified soil. The rate of the hardening reaction is related to the mineral composition in the dispersed soil and the active CaO content in the fly ash.
[0026] Compared with the prior art, the present invention has the following beneficial effects:
[0027] 1. Compared with the traditional method of using modifiers to improve dispersed soil, the present invention uses cement and fly ash to improve dispersed soil. Cement has the advantages of improving the stability of dispersed soil, enhancing its impermeability, frost resistance and impact resistance, which is of great significance to the protection of the surrounding environment; fly ash has the ability to improve the arableness of soil, improve acidic soil and saline-alkali soil, increase soil temperature, improve soil water retention capacity, and can be recycled to realize the reuse of energy resources.
[0028] 2. The fly ash used in the present invention is more environmentally friendly. Fly ash is industrial waste left over from industrial construction and is also a relatively cheap admixture. Most of it is disposed of by landfill. Using it as a soil modifier can reduce the cost of building materials, effectively save and recycle resources, and actively promote the realization of sustainable development goals.
[0029] 3. Excessive use of traditional curing agents can easily lead to soil compaction, calcification, increased alkalinity, and reduced soil ventilation, which is not conducive to vegetation survival and subsequent engineering construction. The modifier of the present invention effectively maintains the balance of soil pH by adjusting the composition, and significantly improves the condition of soil embrittlement.
[0030] 4. The improved dispersed soil obtained by the present invention has significantly improved soil strength. The compression resistance, compression resistance or permeability tests all show that the modifier of the present invention has a good effect on improving soil strength. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Figure 1 The process flow chart of an embodiment of the present invention.
[0032] Figure 2 It is a particle size distribution curve diagram of the original dispersed soil of an embodiment of the present invention.
[0033] Figure 3 This is a graph showing the pinhole test results of some samples obtained after the original dispersed soil was solidified and improved by a series of modifiers in the examples of the present invention.
[0034] Figure 4 This is a graph showing the test results of some sample fragments obtained after a series of modifiers were used to solidify and improve the original dispersed soil in the examples of the present invention.
[0035] Figure 5 This is a diagram showing the mud ball test results of some samples obtained after the original dispersed soil was solidified and improved by a series of modifiers in the examples of the present invention.
[0036] Figure 6 This is a diagram showing the comprehensive evaluation results of the dispersibility test after a series of modifiers were used to solidify and improve the original dispersible soil in the embodiments of the present invention.
[0037] Figure 7 This is a graph showing the strength results of soil samples after a series of modifiers were used to solidify and improve the original dispersed soil in an embodiment of the present invention.
[0038] Figure 8 This is a diagram showing the compression characteristics of soil samples after a series of modifiers have been used to solidify and improve the original dispersed soil in an embodiment of the present invention.
[0039] Fig. 9 This is a graph of the permeability coefficient of soil samples after a series of modifiers are used to solidify and improve the improved soil in an embodiment of the present invention. DETAILED DESCRIPTION
[0040] The technical solution of the present invention is further described in detail below through embodiments and drawings.
[0041] Embodiment 1, as Figure 1 As shown, a method for improving dispersed soil using cement and fly ash comprises the following steps:
[0042] Step 1, obtaining the original dispersed soil at the sampling address, and then crushing and grinding the original dispersed soil with a small wooden hammer, naturally air-drying and passing through 0.5mm and 2mm hole sieves in turn, and taking the sieve under as the dispersed soil to be treated; the moisture content of the original dispersed soil is measured to be 14.2% by the drying method; at the same time, the modifier is designed with cement and fly ash as components according to different proportions;
[0043] Step 2: According to GB / T 50123-2019 "Standard for Geotechnical Test Methods", the physical properties of the original dispersed soil in step 1 are determined by compaction test, limit moisture content test, and particle analysis test, including moisture content, density, particle size distribution, plastic limit, and liquid limit; and modifiers with different proportions of components are added to the sieve to control the optimal moisture content and maximum dry density of the soil sample;
[0044] Step 3: According to T / CECS1337-2023 "Standard for Test Methods of Unsaturated Soils" and ASTM D4647 and ASTMD6572, the dispersibility of the original dispersible soil in step 1 is comprehensively identified through pinhole test, fragment test and mud ball test;
[0045] Step 4: According to the physical property index of the original dispersible soil measured in step 2 and the dispersibility result identified in step 3, the modifiers of different proportions prepared in step 1 are respectively added to the sieve under the 2 mm hole sieve and mixed thoroughly, and water is added, mixed manually until uniform, tightly wrapped with plastic film, and stored in a sealed bag to obtain improved soil; then the dispersibility of the improved soil is identified according to the method in step 3, i.e., pinhole test, mud ball test and fragment test, and the improvement effect of different proportions of cement and fly ash on the original dispersible soil is obtained and compared, and the best modifier ratio is obtained; the mechanical properties of the improved soil are tested by consolidation compression test, triaxial shear test and permeability test;
[0046] Step 5, repeat step 3, solidify and improve the dispersed soil to be treated, and use 95% compaction degree to make a sample of the improved soil prepared after solidification and improvement for the pinhole test and mud ball test in step 3. After the pinhole test, the moisture content is kept at the liquid limit and the mud ball with a diameter of 15 mm is made as the sample for the mud ball test. The sample for the fragment test is the same as the sample for the pinhole test, and the result with the strongest dispersion in the pinhole test, mud ball test and fragment test is used as the comprehensive judgment standard; after testing, the tested soil sample has eliminated the dispersion of the soil sample and the mechanical properties meet the requirements of the construction unit, and further proceed to step 6;
[0047] Step 6: Use the best modifier ratio identified in step 5 to improve the soil under the sieve, and then fill the improved soil back into the foundation of the sampling address in step 1, and compact it to its original state with a convex block.
[0048] Step 1 of this embodiment is specifically as follows: air-dry the original dispersed soil, crush it with a small wooden hammer and sieve it below 2 mm for later use; dry the fly ash and sieve it below 0.5 mm for later use; and measure the moisture content of the test soil and fly ash by the drying method one day before mixing the soil.
[0049] The percentage of each component of the modifier added to the dispersed soil to be treated in step 1 is: cement content is 1% to 4%, fly ash content is 1% to 4%, and the added water is the optimal moisture content of the dispersed soil to be treated.
[0050] The original dispersed soil in step 1 is high Na + The content of dispersed soil, the percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 3% to 4%, fly ash: 1% to 2%, and the content of water added is the optimal moisture content of the improved soil after adding the modifier.
[0051] The original dispersed soil described in step 1 is an alkaline dispersed soil with a pH value of ≥ 9.8. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 1%, acid fly ash: 3% to 4%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier; the acid fly ash is a silicate (such as silicon dioxide) or an aluminate (such as aluminum dioxide).
[0052] The original dispersed soil described in step 1 contains montmorillonite in an amount not less than 11% of the total content. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 2% to 3%, acid fly ash: 2% to 3%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier.
[0053] Step 2 of this embodiment is specifically as follows:
[0054] Compaction test: The optimal moisture content and maximum dry density of the original dispersed soil (the test object is the original dispersed soil under the sieve of 2mm hole sieve) were measured using SJL-1 standard portable compactor. The compaction power per unit volume was 592.2kJ / m 3 The results show that the optimal moisture content of the original dispersed soil is 14.2%, and the maximum dry density is 1.71 g˙cm -3 ;
[0055] Limit moisture content test: The limit moisture content of the original dispersed soil (the test object is the original dispersed soil under the 0.5mm hole sieve) is measured by using the liquid-plastic limit combined determination method and a digital soil liquid-plastic limit combined determination instrument. Three samples are taken for determination and the average value is taken. The results show that the liquid limit (wl) of the original dispersed soil is 26.4%, the plastic limit (wp) is 15%, and the plasticity index (lp) is 11.4.
[0056] Particle analysis test: Use a laser particle size analyzer to measure the particle size composition and corresponding content of the original dispersed soil (the measurement object is the original dispersed soil that passes through a 0.5mm hole sieve). The results are as follows: Figure 2 As shown, from Figure 2 It can be seen that the clay content in the original dispersed soil is 6.47%, the silt content is 65.72%, and the sand content is 27.81%).
[0057] Step 3 of this embodiment is specifically as follows:
[0058] Pinhole test: Use a pinhole test device to add water to the original dispersed soil sample (the treatment object is the original dispersed soil under the sieve of 2mm hole sieve) to make it close to the optimal moisture content (±2%). The amount of water added is calculated by formula (1);
[0059]
[0060] In formula (1): m w —Amount of water added, g; m—mass of soil sample, g; w0—moisture content of soil sample, %; w—optimal moisture content, %;
[0061] The soil sample after adding water was tightly wrapped with plastic film and placed in a container for 24 hours. Then the soil sample after 24 hours was weighed and compacted in multiple times. The layers were roughened and each layer was compacted with a hammer to more than 95% of the maximum dry density. The total height of the soil sample after compaction was 38.1 mm.
[0062] Push the small cone into the center of the compacted soil sample into the water, take a 1mm diameter hard steel wire through the small cone and penetrate the entire soil sample, rotate the hard steel wire to make the soil sample pinhole clean and unobstructed, and wax the surface of the soil sample into the water, and do not allow wax oil to flow into the pinhole to block the aperture;
[0063] Assemble the pinhole test device, connect the water inlet to the rubber tube, and adjust the water head height to let the soil sample flow through under different water heads (50mm, 180mm, 380mm and 1020mm) in turn, and observe and record the water flow rate per minute, the color of the water in the measuring cylinder, and the changes in the pinhole of the soil sample;
[0064] After the test, disassemble the pinhole test device, take out the soil sample from the cylinder of the pinhole test device, cut the soil sample to check the pinhole size, and use a ruler to measure the hole size. According to the pinhole test judgment standard in Table 1, judge the dispersibility of the original dispersible soil;
[0065] Table 1
[0066]
[0067] Block test: The naturally air-dried, unscreened, dispersed soil was loaded into a mold to prepare a block. A 1 cm 3 The soil block was used as the sample, and the fragment test device was used to conduct the fragment test; the sample was carefully picked up with tweezers and placed in a beaker containing 250 mL of deionized water, and the disintegration rate and crushing phenomenon of the debris in the sample were observed, and the dispersion and disintegration of the sample at 1 hour and 6 hours were recorded. If the dispersibility level of the soil block changed significantly after 6 hours, the 6-hour result was used as the judgment result; the judgment standard of dispersibility soil as shown in Table 2 was determined according to ASTM D6572 standard and "Dispersibility Soil Research", and the dispersibility of the original dispersibility soil was judged;
[0068] Table 2
[0069]
[0070]
[0071] Mud ball test: Based on the ASTM D6572 standard and the fragment test in the "Dispersible Soil Research", the mud ball test device was used to add deionized water to the soil sample that passed through the 2mm hole sieve of the original dispersed soil to keep its water content near the liquid limit to obtain the sample. The sample was rolled into a mud ball with a diameter of about 15mm and a smooth surface. Then, the mud ball was carefully placed in the center of a beaker containing 200mL of deionized water with tweezers. The dispersion of the mud ball in the water and the turbidity of the water in the beaker were observed, and the disintegration of the mud ball in the water after 1h and 6h was recorded, and the image was retained to record the test data; the criteria for the determination of dispersed soil corresponding to the fragment test are shown in Table 3;
[0072] Table 3
[0073]
[0074]
[0075] Through the pinhole test, fragment test and mud ball test, it is comprehensively judged that the original soil sample in step one is a typical dispersed soil.
[0076] Step 4 of this embodiment is specifically as follows: In this embodiment, CxFy is used to represent that the modifier components are added to the dispersed soil to be treated, including cement with a mass fraction of x% and fly ash with a mass fraction of y%, and the values of x% are 0%, 1%, 2%, 3%, and 4%, respectively; the values of y% are 0%, 1%, 2%, 3%, and 4%, respectively; and a cylindrical soil sample of 50×38.1 mm is prepared by static pressure method;
[0077] After the original soil is improved with the best modifier ratio in step 4, the improved soil is returned to the foundation of the sampling address in step 1 and compacted to the original state with a convex block roller.
[0078] Step 5 of this embodiment is specifically as follows:
[0079] Dispersion test of original dispersible soil after solidification and improvement:
[0080] (1) Pinhole test results: Based on the pinhole test results of the sample Figure 3 It can be seen that when the modifier component is COF0, that is, the cement and fly ash dosages are both 0, the sample is placed under a water head of 50 mm and continuously flows through the pinhole test device for 5 minutes, and the final flow rate reaches 1.1 mL / s. After the test, it is observed that the water in the measuring cylinder is turbid. The sample is taken out and cut, and the results show that the sample pore diameter exceeds 2 times the diameter of the steel needle. According to the dispersion criterion of the pinhole test, the sample is classified as dispersed soil, which confirms that the original soil sample used in this embodiment belongs to dispersed soil;
[0081] When the cement and fly ash content in the modifier component was 1% and 1% respectively, the sample was placed under a water head of 50 mm and flowed through the pinhole test device for 5 minutes, and the flow rate was controlled to reach 1.0 mL / s. After the end, it was observed that the water in the measuring cylinder was turbid. The sample was taken out and cut. The results showed that the pore diameter of the sample was more than 2.5 times the diameter of the steel needle. According to the dispersion criterion of the pinhole test, the sample was classified as dispersed soil.
[0082] When the cement and fly ash content in the modifier component was 2% and 1% respectively, the sample was placed under a water head of 180 mm and flowed through the pinhole test device for 5 minutes. The most controlled flow rate was 1.3 ml / s. After the test, it was observed that the water in the measuring cylinder was slightly turbid. The sample was taken out and cut. The results showed that the pore size of the sample exceeded the diameter of the steel needle by 1.3 to 1.7 times. According to the dispersion criterion of the pinhole test, the sample was classified as transitional soil.
[0083] When the cement and fly ash content in the modifier component was 4% and 1% respectively, the sample was placed under a water head of 1020 mm and flowed through the pinhole test device for 5 minutes, with a flow rate of 1.4 ml / s. After the test, it was observed that the water in the measuring cylinder was clear. The sample was taken out and cut, and the results showed that the sample pore size was equal to the diameter of the steel needle. According to the dispersion criterion of the pinhole test, the soil sample was classified as non-dispersible soil.
[0084] (2) Piece test results: Based on the piece test results of the sample Figure 4It can be seen that when the modifier component is C0F0, that is, the cement and fly ash content is 0, the soil sample quickly disintegrates in the water, appears scattered at the bottom of the container, and floats around the water surface in a "cloudy" turbidity. According to the standard for identifying dispersed soils in the fragment test, the soil sample is identified as dispersed soil;
[0085] When the cement and fly ash content in the modifier component is 1% and 1% respectively, the sample disintegrates. Compared with the phenomenon of the initial dispersible soil in the container, the disintegration is relatively light. According to the dispersibility judgment standard of the fragment test, the sample is classified as dispersible soil.
[0086] When the cement and fly ash content in the modifier components is 2% and 1% respectively, a slight, visible colloidal suspension is produced near or around the surface of the soil block, and the water is slightly turbid. According to the dispersion judgment standard of the fragment test, the sample is classified as transitional soil;
[0087] When the cement and fly ash content in the modifier component is 3% and 1% respectively, the sample does not disintegrate after contact with water or there is no turbidity after disintegration, and the water is clear and transparent. According to the dispersibility judgment standard of the fragment test, the sample is classified as non-dispersible soil;
[0088] (3) Mud ball test results: Based on the mud ball test results of the sample Figure 5 It can be seen that when the modifier component is C0F0, that is, the cement and fly ash content is 0, the mud ball disintegrates quickly, the soil-water interface is completely blurred, and a large amount of cloudy precipitation is produced at the bottom of the glass container. According to the dispersion criterion of the mud ball test, the sample is classified as dispersed soil;
[0089] When the cement and fly ash content in the modifier component was 1% and 1% respectively, the soil-water interface was blurred and a large amount of cloudy precipitation was produced at the bottom of the glass container. According to the dispersion criterion of the mud ball test, the sample was classified as dispersive soil.
[0090] When the cement and fly ash content in the modifier component is 2% and 1% respectively, there is slightly visible turbid water produced by the suspension of colloid particles around the surface of the mud ball, and the soil-water interface can be vaguely observed. According to the dispersion judgment standard of the mud ball test, the soil sample is classified as transitional soil.
[0091] When the cement and fly ash content in the modifier components is 3% and 1% respectively, the mud ball disintegrates very slowly when in contact with water, and the soil-water interface is clear. According to the dispersion judgment standard of the mud ball test, the soil sample is classified as non-dispersible soil.
[0092] Figure 6 This is a comprehensive evaluation result of the dispersion test of a series of modifiers on the improved soil after solidification in this embodiment. Figure 6It can be seen that under different cement and fly ash dosages, with the increase of the combined modifier dosage, the dispersibility of the soil sample shows a trend of "dispersibility-transitional-non-dispersibility", which indicates that the combined modifier significantly inhibits the dispersibility of the soil sample, and when the cement dosage in the modifier exceeds 2% and the fly ash parameter exceeds 2%, the solidification effect is better; comprehensively judging, 2% cement and 2% fly ash are the best modifier ratio.
[0093] Mechanical properties test of original dispersed soil after solidification and improvement:
[0094] The main goal of improving natural soil is to improve its load resistance, including the load bearing capacity of buildings, foundations and hydraulic structures, and to enhance its resistance to overload, climate change and natural disasters such as earthquakes and landslides. Consolidation compression test, triaxial shear test and permeability test were used to test the strength of soil samples after the original dispersed soil was solidified and improved by a series of modifiers in the embodiments of the present invention. The results are as follows: Figure 7 As shown, from Figure 7 It can be seen that improving the compaction degree is beneficial to the interaction between the combined modifier and soil particles, promoting the reaction, thereby further improving the strength. This shows that the dispersed soil improved by the modifier of the present invention has a good load resistance capacity for buildings, foundations and hydraulic structures, and enhances its resistance to overload, climate change and natural disasters such as earthquakes and landslides.
[0095] The compressibility of soil refers to the property of soil to reduce its volume under the action of external forces. Figure 8 The compression characteristic diagram of the soil sample after the original dispersed soil is solidified and improved by the combined modifier in the embodiment of the present invention is shown in FIG. Figure 8 It can be seen that under the same compaction degree, with the increase of cement and fly ash content, the compression coefficient generally shows a downward trend, indicating that the addition of cement and fly ash in the modifier can effectively improve the compression performance of the soil and make its deformation under load smaller.
[0096] The pores between soil solid particles are interconnected, and water flows through these pores driven by pressure difference or energy difference. This phenomenon is called seepage. The characteristic that describes the seepage capacity of soil is called permeability, which is usually measured by the permeability coefficient. Fig. 9 The permeability coefficient diagram of the soil sample after a series of modifiers are used to solidify and improve the original dispersed soil in the embodiment of the present invention. Fig. 9 It can be seen that the modifier has a good effect in improving the permeability characteristics of the soil. With the increase of cement and fly ash content, the permeability coefficient generally shows a decreasing trend. Therefore, the permeability performance of the soil can be optimized by reasonably adjusting the content of the modifier.
[0097] In order to ensure that the solidified dispersed soil can achieve the best effect, in step 6 of this embodiment, each time the improved soil is backfilled, the backfill depth should be 0.5m. When the soil strength is stable, another layer of soil is applied thereon, and this is repeated until the backfill reaches the designed depth.
[0098] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.
Claims
1. A method for improving dispersed soil using cement and fly ash, characterized in that: The following steps are involved: Step 1: obtaining original dispersed soil at the sampling site, and then crushing, grinding, air-drying and sieving the original dispersed soil in sequence, and taking the sieve-off as dispersed soil to be treated; at the same time, designing a modifier with cement and fly ash as components according to different proportions; Step 2: According to GB / T 50123-2019 "Standard for Geotechnical Test Methods", the maximum dry density and optimal moisture content of the target area soil are measured by compaction test, the liquid and plastic limits of the soil are measured by limit moisture content test, and modifiers with different proportions are added to the undersize to control the optimal moisture content and maximum dry density of the soil sample; Step 3: According to T / CECS1337-2023 "Standard for Test Methods of Unsaturated Soils" and ASTM D4647 and ASTMD6572, the dispersibility of the original dispersible soil in step 1 is comprehensively identified through three tests: pinhole test, fragment test, and mud ball test; Step 4: According to the physical property index of the original dispersible soil measured in step 2 and the dispersibility result identified in step 3, the modifiers with different proportions prepared in step 1 are added to the sieve and water is added for improvement, and then the dispersibility of the improved soil is identified according to the method in step 3 to obtain the best modifier ratio; Step 5. Comprehensively identify the dispersibility of the improved soil in step 4 through three tests: pinhole test, fragment test, and mud ball test; test the mechanical properties of the improved soil through consolidation compression test, triaxial shear test, and permeability test (GB / T 50123-2019 "Standard for Geotechnical Test Methods"); if the tested improved soil eliminates the dispersibility of the soil sample and the mechanical properties meet the requirements of the construction unit, proceed to step 6, otherwise return to step 4 and increase the content of the modifier; Step 6: Use the best modifier ratio identified in step 5 to improve the soil under the sieve, and then fill the improved soil back into the foundation of the sampling address in step 1, and compact it to its original state with a convex block.
2. The method according to claim 1, characterized in that In step 1, the original dispersed soil is air-dried, crushed with a small wooden hammer and sieved with a diameter of less than 2 mm for later use; the fly ash is dried and sieved with a diameter of less than 0.5 mm for later use; one day before soil mixing, the moisture content of the test soil and fly ash is measured by the drying method.
3. The method according to claim 1, characterized in that The percentage of each component of the modifier added to the dispersed soil to be treated in step 1 is: cement content is 1% to 4%, fly ash content is 1% to 4%, and the added water is the optimal moisture content of the dispersed soil to be treated.
4. The method according to claim 1, characterized in that: The original dispersible soil in step 1 is high Na + The content of dispersed soil, the percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 3% to 4%, fly ash: 1% to 2%, and the content of water added is the optimal moisture content of the improved soil after adding the modifier.
5. The method according to claim 1, characterized in that The original dispersed soil described in step 1 is alkaline dispersed soil with a pH value of ≥ 9.
8. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 1%, acid fly ash: 3% to 4%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier; the acid fly ash is silicate or aluminate.
6. The method according to claim 1, characterized in that The original dispersed soil described in step 1 contains montmorillonite in an amount not less than 11% of the total content. The percentage of each component of the modifier added to the dispersed soil to be treated in step 4 is: cement: 2% to 3%, acid fly ash: 2% to 3%, the modified soil sample is kept neutral, and the content of water added is the optimal moisture content of the modified soil after adding the modifier.