Method for modifying red clay by straw fiber composite ecological cement and application thereof

Abstract

The invention discloses a method for modifying red clay by straw fiber composite ecological cement and application thereof. The straw fiber composite ecological cement modified red clay is prepared from air-dried red clay, ecological cement, straw fiber and water. The method comprises the following steps: a, obtaining straw fiber, ecological cement and red clay raw materials; b, testing to obtain the optimal moisture content, specific gravity and liquid-plastic limit index of the red clay; c, setting a plurality of orthogonal test proportions; d, matching the proportioned dry materials, adding a proper amount of water, braising the materials for 24 hours, uniformly stirring one part of the materials to prepare a standard cutting ring sample, and uniformly stirring the other part of the materials for a planting test; and e, performing a direct shear test, a penetration test, a fracture analysis test, a soil-water characteristic curve test and a plant growth test on the cutting ring sample after the dry-wet cycle. According to the method, the shear strength, permeability resistance and water stability of the red clay can be improved, deformation and crack development of the red clay are effectively prevented, and the modified red clay obtained through the method can be applied to channel slope construction.

Description

Technical Field

[0001] The invention relates to the technical field of red clay water conservancy channel treatment, and in particular to a method for modifying red clay with straw fiber composite ecological cement and application thereof. Background Art

[0002] Red clay is a brownish-red or brownish-yellow highly plastic clay formed by lateritization geological action of weathered residual slope deposits of carbonate rocks under warm and humid tropical and subtropical climate conditions. Red clay poses many engineering risks in the fields of highways, railways, water conservancy and geotechnical engineering due to its swelling, shrinking and fissure properties.

[0003] Specifically, red clay shrinks and cracks when it dries, which not only increases the surface area for water evaporation, but also accelerates the evaporation of water in the deep soil. As the width and depth of the shrinkage cracks continue to expand, the soil structure is damaged, resulting in a decrease in its strength and stability. During heavy rainfall, the shrinkage cracks become fast channels for water migration, forming preferential flows, which accelerates the infiltration of water into the soil, further causing a sharp decrease in soil strength and slope stability, thereby inducing geological disasters such as landslides.

[0004] In my country, the key hydraulic structure of long-distance water diversion projects is the channel. Ensuring the safe operation of the water supply channel is crucial to alleviating the shortage of water resources and achieving efficient allocation of water resources. The safety of the channel is closely related to the water loss suffered during the water supply process. According to data, my country currently has nearly 4.5 million kilometers of various water transfer channels. However, the actual canal water utilization rate only accounts for 53% of the total water transfer. The main factor leading to channel leakage is the destruction of the channel structure, which in turn leads to the failure of the anti-seepage layer. Therefore, ensuring the integrity of the channel structure during the water supply process is the key to ensuring the water supply capacity of the channel.

[0005] It should be pointed out that when the water supply channel passes through the red clay area, it faces many problems; the characteristics of red clay include fissures, swelling and shrinkage, strength attenuation and over-consolidation, which reduce the stability of the channel. Due to the lack of an anti-seepage drainage system during construction, construction defects and material damage, the channel water seeps into the red clay, affecting the stability of the channel slope. Seasonal climate change exacerbates the dry-wet alternation and freeze-thaw cycle of the red clay, causing the red clay to crack and deteriorate its engineering properties, which in turn affects the safety of water supply. Therefore, it is often necessary to make certain improvements to the red clay in the area where the channel passes, so that the physical and mechanical properties of the red clay can be changed to meet the construction requirements.

[0006] Common methods for modifying red clay are mainly divided into two categories: physical modification and chemical modification; physical modification includes soil replacement, humidity regulation, mechanical compaction and other technologies. Chemical modification involves the use of curing materials to react chemically with red clay to improve its engineering properties, with the aim of reducing the water sensitivity of red clay and enhancing its mechanical properties. Among chemical modifications, lime, fly ash and cement are the most commonly used inorganic modifiers, but these modifiers also have some shortcomings. For example, the strength of soil improved by lime increases slowly, it is prone to shrinkage and cracking, and its water stability is poor, which will slow down the construction progress; cement-modified soil is limited by soil type, is prone to shrinkage and cracking, and it is difficult to ensure uniform mixing; the early strength of fly ash-modified soil is low, and its water stability is also not ideal. Summary of the invention

[0007] The purpose of the present invention is to provide a method for modifying red clay with straw fiber composite ecological cement and its application in view of the deficiencies in the prior art. The method for modifying red clay with straw fiber composite ecological cement can significantly improve the shear strength, anti-penetration performance and water stability of red clay through modification, thereby effectively preventing the deformation and crack development of red clay under various environments and loads; by applying the red clay modified with straw fiber composite ecological cement to channel slope construction, due to the improvement of the shear strength, anti-penetration performance and water stability of the improved red clay, that is, the modified red clay modified with straw fiber composite ecological cement can form a stable surface, so that the red clay water conservancy slope maintains a higher stability.

[0008] A method for modifying red clay with straw fiber composite ecological cement, the straw fiber composite ecological cement modified red clay comprising air-dried red clay, ecological cement, straw fiber and water;

[0009] The ecological cement accounts for 3%-5% of the total mass of the straw fiber composite ecological cement modified red clay, the straw fiber accounts for 0.5%-1% of the total mass of the straw fiber composite ecological cement modified red clay, and the mass of the air-dried red clay and water accounts for 94%-96.5% of the total mass of the straw fiber composite ecological cement modified red clay;

[0010] The straw fiber composite ecological cement modified red clay method comprises the following steps, specifically:

[0011] Step a, obtaining straw fiber, ecological cement, and red clay raw materials, and drying the straw fiber and the red clay raw materials, and obtaining air-dried red clay after the red clay raw materials are dried;

[0012] Step b: Conduct tests according to the requirements of the Geotechnical Test Method Standard (GB / T50123-2020) to obtain the optimal moisture content, specific gravity, and liquid and plastic limit indicators of red clay;

[0013] Step c, according to the sample preparation method described in the "Standard for Geotechnical Test Methods" (GB / T50123-2020), according to the optimal moisture content and the corresponding maximum dry density, within the range of the straw fiber and ecological cement ratio, set several orthogonal test ratios;

[0014] Step d, mix the dry materials in proportion, add appropriate amount of water and stew for 24 hours, stir a portion of them evenly to make standard ring knife samples, and cure them under standard curing conditions for 4 days; stir a portion of them evenly and use them for planting experiments;

[0015] Step e, subjecting the cured ring knife samples to dry-wet cycles, and subjecting the ring knife samples after the dry-wet cycles to direct shear tests, penetration tests, crack analysis tests, soil-water characteristic curve tests, and plant growth tests, so as to obtain the best ratio through test data analysis.

[0016] Wherein, in the step a, the straw fiber is dried at 70° C. for 24 hours, and the red clay raw material should be dried at 110° C. for 10 hours.

[0017] Wherein, in the step e, the dry cycle process is: after vacuuming for 4 hours, let it stand for 20 hours, and then put it in an oven and bake it at 50° C. for 48 hours, and repeat this process 5 times.

[0018] Wherein, the straw fiber is rice straw fiber, sugarcane straw fiber or corn straw fiber.

[0019] The straw fibers should satisfy the conditions that the fiber proportion is greater than 90% and the medulla proportion is less than 10%, and the fiber length in the straw fibers is less than or equal to 3 cm, and the proportion of fibers with a length of 1 cm-2 cm should be greater than 70%.

[0020] Wherein, the ecological cement is low-alkalinity sulphoaluminate cement, and the pH value of the ecological cement is between 10-10.6.

[0021] An application of straw fiber composite ecological cement modified red clay, wherein the straw fiber composite ecological cement modified red clay is obtained by the straw fiber composite ecological cement modified red clay method.

[0022] Among them, the application of the straw fiber composite ecological cement modified red clay includes the following construction steps:

[0023] Step 1: Construction preparation: determine the design requirements and construction plan for fill and slope protection, conduct measurement and survey, clean up the site, and ensure the safety of the construction area;

[0024] Step 2: Earth excavation: Carry out earth excavation according to the design requirements to ensure that the slope and height of the construction slope and the protection slope meet the design requirements;

[0025] Step 3: Preparation of improved materials: Calculate the total amount of straw fiber composite ecological cement modified red clay required for the filling section in advance, select a good site for drying, then transport the ecological cement and straw fiber to the site for use, fully stir the mix, and maintain for 4 days for use;

[0026] Step 4, filling and compacting straw fiber composite ecological cement modified red clay: according to the design requirements, select the well-maintained straw fiber composite ecological cement modified red clay for filling on the original soil layer; the filling should be compacted layer by layer, and the height of each layer should not exceed 30cm. Use a special geotechnical filling machine for compaction. After the filling is completed, a modified red clay compaction layer is formed;

[0027] Step 5: Channel lining construction: After compaction is completed, the channel concrete lining panel can be constructed, and after the panel construction is completed, the exposed slope surface on the upper part of the channel can be protected;

[0028] Step 6, protection of the upper slope of the channel: For the protection of the upper slope of the channel, first use anchor rods to fix the geocell to the filled slope surface, and then fill a sand cushion layer of a certain thickness. After the sand cushion layer is filled, fill it with uncompacted straw fiber composite ecological cement modified red clay. The proportion is obtained according to the straw fiber composite ecological cement modified red clay proportion growth test, and a modified red clay planting layer can be formed;

[0029] Step 7: Spraying grass seeds: After the modified red clay planting layer is paved, plant seeds can be spread.

[0030] Compared with the prior art, the present invention has the following beneficial effects, specifically:

[0031] 1. The method of modifying red clay with straw fiber composite ecological cement of the present invention uses straw fiber and ecological cement as the main admixtures to achieve soil reinforcement modification treatment of red clay; through this modification treatment, the shear strength, anti-permeability and water stability of red clay can be significantly improved, thereby effectively preventing the deformation and crack development of red clay under various environments and loads. The method of modifying red clay with straw fiber composite ecological cement not only improves the stability of red clay, but also provides a broader possibility for the application field of red clay, especially for engineering projects such as water conservancy slopes that have higher requirements for the anti-permeability and shear strength of fill;

[0032] 2. The two admixtures of the present invention not only solve the problems of slow strength growth, easy shrinkage and cracking, and poor water stability of soil improved by lime and fly ash, but also have little impact on the environment and plant growth; straw fiber can be turned into treasure and widely used in soil modification, with direct source and low cost, and can improve soil quality and provide nutrients required for plant growth; ecological cement is more environmentally friendly than ordinary cement, and the pH value of its modified soil is more suitable for the growth of slope protection plants. Ecological cement also has the characteristics of early strength and fast hardening, short maintenance cycle, which is conducive to shortening the construction period and reducing construction costs; the combined use of the two admixtures can effectively improve the barrenness of red clay, and can significantly improve the germination rate, growth and survival rate of common slope protection plants such as ryegrass and bahia grass, and has higher application value;

[0033] 3. By applying the straw fiber composite ecological cement modified red clay to the channel slope construction, the shear strength, anti-permeability and water stability of the improved red clay are improved, that is, the modified straw fiber composite ecological cement modified red clay can form a stable surface, so that the red clay water conservancy slope maintains a higher stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention is further described below with the aid of the accompanying drawings. However, the embodiments in the accompanying drawings do not constitute any limitation to the present invention.

[0035] Figure 1 This is a schematic diagram of the structure of straw fiber composite ecological cement modified red clay during water conservancy slope construction.

[0036] Figure 2 This is a schematic diagram of the structure of the upper part of the water conservancy slope when straw fiber composite ecological cement modified red clay is used in the construction of the water conservancy slope.

[0037] Figure 3 This is a comparison chart of pH of modified red clay at different eco-cement dosages.

[0038] Figure 4 This is a comparison chart of cracks in red clay modified by straw fiber composite ecological cement.

[0039] Figure 5 This is a comparison chart of the water curves of straw fiber composite ecological cement modified red clay.

[0040] Figure 6 This is the plant growth status of red clay modified by straw fiber composite ecological cement.

[0041] Figure 7 This is a comparison chart of shear strength.

[0042] exist Figure 1 and Figure 2 Included are:

[0043] 1-original soil layer; 2-improved red clay compaction layer; 3-channel concrete lining; 4-sand cushion layer; 5-improved red clay planting layer; 6-anchor rod; 7-geocell. DETAILED DESCRIPTION

[0044] The present invention is described below in conjunction with specific implementation methods.

[0045] In order to verify the performance of the improved red clay filler of the present invention, the following comparative test was set up:

[0046] The comparative example is red clay soil, which is set as Example 1;

[0047] Example 2: 0.5% straw fiber is used to improve red clay soil;

[0048] Example 3: 0.75% straw fiber is used to improve red clay soil;

[0049] Example 4: 1% straw fiber is used to improve red clay soil;

[0050] Example 5: 3% ecological cement is used to improve red clay soil;

[0051] Example 6: 4% ecological cement is used to improve red clay soil;

[0052] Example 7: 5% ecological cement is used to improve red clay soil;

[0053] Example 8: 0.5% straw fiber and 3% ecological cement were used to improve red clay soil;

[0054] Example 9: 0.5% straw fiber and 4% ecological cement were used to improve red clay soil;

[0055] Example 10: 0.5% straw fiber and 5% ecological cement were used to improve red clay soil;

[0056] Example 11: 0.75% straw fiber and 3% ecological cement were used to improve red clay soil;

[0057] Example 12: 0.75% straw fiber and 4% eco-cement were used to improve red clay soil;

[0058] Example 13: 0.75% straw fiber and 5% eco-cement were used to improve red clay soil;

[0059] Example 14: 1% straw fiber and 3% ecological cement were used to improve red clay soil;

[0060] Example 15: 1% straw fiber and 4% ecological cement were used to improve red clay soil;

[0061] Example 16: 1% straw fiber and 5% ecological cement are used to improve red clay soil.

[0062] Example 1: Take red clay from Wuxuan County, Laibin, Guangxi for use, use an oven to dry the obtained red clay for more than 10 hours at 105°C, use a crushing and screening integrated machine to screen and crush the red clay, and select a sieve of 1 mm or less; according to the "Standard for Geotechnical Test Methods" (GB / T50123-2020), perform a limit moisture content test and a compaction test on the mixed soil, and obtain the plastic limit ωp=29.7% and the optimal moisture content ωy=27.7% of the mixed soil; take 1000g Dried red clay requires 277g of water to mix with red clay. Considering the influence of factors such as evaporation during actual water distribution, the actual amount of water added is set to 285g. About 285g of water is evenly mixed into the red clay for 3 times. After simmering for 24 hours, mix evenly. Use a sample maker to make a standard ring knife soil sample, and cure the obtained soil sample under a standard curing environment for 4 days; subject the cured samples to a dry-wet cycle. The dry cycle is to evacuate for 4 hours, then let it stand for 20 hours, and then put it in an oven to bake at 50°C for 48 hours, and repeat this 5 times.

[0063] Example 2-4: Red clay from Wuxuan County, Laibin, Guangxi was prepared for use, and the obtained red clay was dried in an oven at 105° C. for more than 10 hours. The red clay was screened and crushed using a crushing and screening machine, and the screen was 1 mm or less. The straw fiber was dried at 70 ° C for 24 hours and then passed through a 2 mm standard sieve; according to the "Standard for Geotechnical Test Methods" (GB / T50123-2020), the mixed soil was subjected to a limit moisture content test and a compaction test, and the plastic limit ωp of the mixed soil was 29.7% and the optimal moisture content ωy was 27.7%; 1000g of dried red clay was taken, and the water required for the red clay was 1000*0.277=277g, the straw fiber required for Example 2 was 1277*0.5 / 100=6.4g, and the mass of dried red clay was 1000-6.4=993.6g, and the straw fiber required for Example 3 was 1277*0.75 / 100=9.6g, and the mass of dried red clay was 1000-9.6 =990.4g, the straw fiber required for Example 4 is 1277*1.0 / 100=12.8g, the mass of dried red clay is 1000-12.8=987.2g, the straw fiber obtained in Examples 2, 3 and 4 and the dried red clay are respectively mixed evenly, considering the influence of factors such as evaporation during actual water distribution, the actual amount of water added is set to 285g, about 285g of water is evenly added into the mixed improved soil for 3 times, and the material is stewed for 24h before mixing evenly, and a standard ring knife soil sample is made using a sample preparation device, and the obtained soil sample is cured for 4 days under a standard curing environment; the cured sample is subjected to a dry-wet cycle, and the dry cycle is to vacuum for 4h and then stand for 20h, and then put it in an oven and bake at 50°C for 48h, and this is repeated 5 times.

[0064] Example 5-7: Red clay from Wuxuan County, Laibin, Guangxi was prepared for use, and the obtained red clay was dried in an oven at 105° C. for more than 10 hours. The red clay was screened and crushed using a crushing and screening integrated machine, and the screen was selected to be 1 mm or less. Take a certain amount of ecological cement for standby; according to the "Standard for Geotechnical Test Methods" (GB / T50123-2020), the mixed soil is subjected to a limit moisture content test and a compaction test, and the plastic limit ωp of the mixed soil is obtained to be 29.7% and the optimal moisture content ωy is 27.7%; take 1000g of dried red clay, then the water required for the red clay is 1000*0.277=277g, the ecological cement required for Example 5 is 1277*3 / 100=38.3g, and the mass of dried red clay is 1000-38.3=961.7g, and the ecological cement required for Example 6 is 1277*4 / 100=51.1g, and the mass of dried red clay is 1000-51.1=948.9 g, the ecological cement required for Example 7 is 1277*5 / 100=63.9g, and the mass of dried red clay is 1000-63.9=936.1g. The ecological cement obtained in Examples 5, 6, and 7 and the dried red clay are respectively mixed evenly. Considering the influence of factors such as evaporation during actual water distribution, the actual amount of water added is set to 285g. About 285g of water is evenly added to the mixed improved soil for 3 times. After stewing for 24 hours, the mixture is mixed evenly. A sample preparation device is used to prepare a standard ring knife soil sample, and the obtained soil sample is cured for 4 days under a standard curing environment; the cured sample is subjected to a dry-wet cycle, and the dry cycle is to vacuum for 4 hours and then stand for 20 hours, and then put it in an oven and bake it at 50°C for 48 hours, and this is repeated 5 times.

[0065] Example 8-16: Take red clay from Wuxuan County, Laibin, Guangxi for use, use an oven to dry the red clay for more than 10 hours at 105°C, use a crushing and screening integrated machine to screen and crush the red clay, and select a sieve of 1mm or less. Take a certain amount of ecological cement for use; according to the "Standard for Geotechnical Test Methods" (GB / T50123-2020), perform a limit moisture content test and a compaction test on the mixed soil to obtain the plastic limit ωp=29.7% and the optimal moisture content ωy=27.7% of the mixed soil; take 1000g of dried red clay, then the water required to mix the red clay is 1000*0.277=277g, the straw fiber required for Example 8 is 1277*0.5 / 100=6.4g, the required ecological cement is 1277*3 / 100=38.3g, and the mass of dried red clay is 1000-6.4-38.3=9 55.3g, the ecological cement, straw fiber and dried red clay obtained in Example 8 are evenly mixed, considering the influence of factors such as evaporation during actual water distribution, the actual amount of water added is set to 285g, about 285g of water is evenly added into the mixed improved soil for 3 times, and the material is stewed for 24 hours before mixing evenly. A standard ring knife soil sample is made using a sample preparation device, and the obtained soil sample is cured for 4 days under a standard curing environment; Examples 9-16 are sampled according to the matching method described in Example 8; the cured samples are subjected to a dry-wet cycle, the dry cycle is to vacuum for 4 hours, then stand for 20 hours, and then put into an oven to bake at 50°C for 48 hours, and this is repeated 5 times.

[0066] After the dry-wet cycle was completed, Examples 1-16 were subjected to direct shear test, permeability test, soil-water curve test, plant growth test, crack analysis test and pH measurement test, and the best ratio was obtained through test data analysis.

[0067] The pH test was carried out on Example 1 and Examples 5, 6, 7 and ordinary cement with the same cement quality as Examples 5, 6, 7. The pH test results are as follows: Figure 3 As shown, it can be found that the pH value of Example 1 is 4.7 and is acidic, while the pH of the control group of ordinary cement is in the range of 9.4-10; the pH of the ecological cement group of Examples 5, 6, and 7 is between 7.3-8. As can be seen from Table 1, the pH value of ecological cement soil is more suitable for plant growth than ordinary cement. Ordinary cement will greatly change the pH value of red clay. The pH range of red clay improved by ordinary cement belongs to the medium-strong alkaline range. The pH of ecological cement improved soil at a 5% dosage is lower than that of ordinary cement improved soil at a 3% dosage. Compared with ordinary cement improved soil, the pH of ecological cement improved soil is reduced by an average of 22%.

[0068] Table 1 pH values ​​of soils for common slope protection plants

[0069]

[0070] The crack comparison test was carried out on Examples 1-16 respectively. Figure 4 The following is a comparison of the crack development of soil improved with different straw fiber composite eco-cement after 5 cycles. It can be seen from the figure that the crack development of Example 1 is the most obvious, forming two through cracks; the number and width of cracks in Examples 2, 3, and 4 are significantly lower than those in Example 1, indicating that straw fiber has a strong ability to inhibit the cracking of red clay; although the number of cracks in Examples 5 and 6 is less than that in Example 1, the crack width is basically the same as that in the examples, indicating that at a lower dosage of eco-cement, the crack inhibition effect on red clay cannot be achieved; no obvious cracks were observed in Example 7, and no obvious cracks were observed in Examples 8-16 either.

[0071] The electric quadruple direct shear apparatus was used to perform saturated direct shear tests on Examples 1-16 after 5 cycles. The cohesion and internal friction angle obtained are shown in Table 2 below. It can be seen from the table that the internal friction angle and cohesion of the red clay soil improved by straw fiber composite ecological cement are stronger than those of red clay soil, that is, Examples 8-16 are better than Example 1, among which Example 3 has the best effect, with the internal friction angle increased by about 40% and the cohesion increased by about 6.4 times. In addition, there are two situations in the red clay improved by ecological cement. Examples 5 and 6 only have a slight increase in the internal friction angle, and the cohesion is basically the same as that of Example 1, while Example 7 has a significant increase. In addition, for Examples 2, 3, and 4, that is, straw fiber improved red clay, its cohesion is even lower than that of red clay soil. Analyzing the reasons for the above phenomenon, for Examples 2, 3, and 4, straw fiber is a degradable material, and red clay soil is an acidic environment. Under 5 dry-wet cycles, the straw fiber is partially corroded, resulting in local defects in the improved soil, which makes it easier for stress concentration to cause damage. For Examples 5 and 6, it is because the amount of ecological cement added is too low at this dosage, and it cannot produce a fundamental effect on the improvement of the strength of red clay. Example 7 has a significant improvement effect. For Examples 8-16, the improvement effect is generally better than the improvement of the two materials alone. The reason is that the ecological cement can adjust the pH of the red clay to a weakly alkaline range. Studies have shown that straw fibers soaked in alkaline solutions have higher strength and better durability. In addition, since the strength of the straw fiber is improved, not only is the bonding effect between the straw fiber and the red clay enhanced, forming a good composite with the red clay, but also the problem of shrinkage and cracking that is prone to occur when the amount of ecological cement added is high is suppressed. Therefore, the synergistic improvement of the two materials makes the shear strength of Examples 8-16 better than that of the single improvement, among which the improvement effect of Example 13 is the most obvious. Figure 7 As shown, it is also far superior to red clay soil.

[0072] Table 2 is a comparison of the shear strength of red clay improved by different straw fiber composite eco-cement

[0073] Example 1 2 3 4 5 6 7 8 Cohesion(kPa) 3.5 2.6 2.77 2.94 3.47 3.60 12.26 4.53 Internal friction angle (rad) 0.09 0.12 0.14 0.15 0.13 0.13 0.11 0.13 Example 9 10 11 12 13 14 15 16 Cohesion(kPa) 5.95 14.21 6.3 12.3 24.65 13.08 17.38 16.87 Internal friction angle (rad) 0.14 0.13 0.14 0.11 0.13 0.11 0.103 0.103

[0074] The permeability test of Examples 1-16 was carried out using a TST-55 permeameter. The measured permeability coefficients are shown in Table 3 below. It can be found that the permeability coefficients of Examples 1, 5, 6, and 7 are all relatively large, 1-2 orders of magnitude higher than those of other Examples. The effect of ecological cement in improving the anti-seepage capacity of red clay is not ideal. Instead, it has a tendency to further increase with the increase of cement content. The reason is that during the compaction of cement soil, cement will solidify. The specific gravity of cement after solidification is slightly larger than that of soil particles, just like gravel in clay soil. The greater the cement content, the more gravel it contains after solidification, and the maximum dry density increases. Under the same dry density conditions, as the cement content increases, the relative compaction degree of the corresponding sample of cement soil decreases, the more voids between soil particles, and the permeability coefficient will increase. As for the permeability coefficients of Examples 2, 3, and 4, there is a significant reduction effect compared with Example 1, which is reduced by about one order of magnitude. The reason is that when the straw fiber content is 0.75%, the straw fiber has a weak attraction to the soil and cannot fill the internal pores. At this time, the properties of the red clay itself occupy a dominant position; as the fiber content increases, the bonding effect of the straw fiber and the red clay is enhanced, and a good complex is formed with the red clay, and its permeability decreases. For Examples 8-16, that is, when straw fiber and ecological cement are mixed, the anti-permeability coefficient is significantly reduced compared to Example 1, and the improvement effect after mixing is better than that of using it alone. With the increase of fiber content, the anti-permeability coefficient shows a trend of further reduction, and the effect of increasing the cement content leading to an increase in the permeability coefficient has been significantly weakened. Compared with Example 1, the permeability coefficient of Example 11 is reduced by about 70 times, about two orders of magnitude, and the anti-permeability performance is significantly improved.

[0075] Table 3 is a comparison of the permeability coefficients of red clay improved by different straw fiber composite ecological cement

[0076]

[0077] Note: The unit of permeability coefficient is 10-6cm / s.

[0078] The soil-water characteristic curves of Examples 1-16 after 5 dry-wet cycles were measured using a pressure membrane instrument and a saturated salt solution method. Due to too much data, only the examples with the best results in the direct shear and impermeability tests were analyzed. Figure 5It is a comparison diagram of the soil-water characteristic curve of Example 1 and Examples 3, 7, and 13. It can be seen from the figure that the initial saturated moisture content of the improved soil is higher than that of the plain soil, among which Example 13 is about 12.5% ​​higher than that of Example 1, indicating that the improved soil has better water holding capacity under the initial saturated state. With the increase of the suction value, the volumetric moisture content of the plain soil of Example 1 decreases significantly when the suction value is about 10kpa, while the volumetric moisture content decrease point of Examples 3, 7, and 13 moves significantly to the right, among which Example 13 only decreases at about 150kpa. In the high suction range of 10000kpa-100000kpa, the plain soil of Example 1 and the cement-improved soil of Example 7 still do not show obvious convergence of the curve, while Examples 3 and 13 show obvious convergence trends, indicating that the volumetric moisture content of the fiber-improved soil has stabilized at this time, and the volumetric moisture content of the plain soil and cement-improved soil is still decreasing. When straw fiber and ecological cement are mixed, the improved soil has both the high water holding range of cement-improved soil and the stability of fiber-improved soil. The reason for this is that the volume expansion and contraction caused by the dry-wet cycle effect will cause uneven stress distribution inside the soil. The improvement of red clay by straw fiber mainly utilizes the cellulose in the straw fiber to enhance the structural strength of the soil. These celluloses provide deformable space, which provides a buffer for the volume change of red clay, thereby releasing some stress. With the increase of straw fiber content, the deformable space inside the red clay is correspondingly expanded, so that the stress is more effectively released when the volume changes, and the degree of damage to the soil is further reduced. Therefore, under the influence of dry-wet cycles, red clay improved by straw fiber with different contents will show different soil-water characteristic curves. As for the improvement of red clay by ecological cement, the performance of red clay is enhanced by forming gel substances, which make the combination between soil particles tighter. In addition, the ionic components in ecological cement will also change the charge on the red clay mineral particles, thereby balancing some Coulomb forces. With the increase of the amount of ecological cement added, the connection between soil particles is strengthened, so that the improved red clay can show better soil-water stability after 5 dry-wet cycles.

[0079] Through the above test, it can be obtained that the shear strength parameters, permeability coefficient, and soil-water stability of Example 13 are comprehensively at the best effect, so a plant planting test is carried out on it. The selected examples are Examples 1, 3, 7, and 13, and the planted plants are ryegrass. Figure 6The growth effect comparison diagram of ryegrass with planting days of 7 days, 15 days and 29 days respectively shows that the growth effect of Example 13 is better than that of Example 1 on the 7th day of planting, while the growth effects of Examples 3 and 7 are not significant compared with Example 1. On the 15th day of planting, the growth effect of Example 1 is significantly atrophied compared with that on the 7th day, and is not as good as the growth effects of Examples 3, 7 and 13 in the same period. On the 29th day of planting, the ryegrass leaves in Example 1 have turned yellow and showed a trend of dying, while Examples 3, 7 and 13 still have good growth. The reason is that Example 1 has not been improved, its nutrients are few, the soil is poor and the water stability is poor, and it is impossible to provide water and nutrients for the growth of ryegrass for a long time, resulting in the death of ryegrass in Example 1 in the later stage. In Example 13, due to the addition of straw fiber and ecological cement, the straw fiber adds nutrients to the red clay, and the ecological cement improves the soil and water stability of the red clay, so Example 13 shows a better plant growth effect.

[0080] Based on the comparative analysis of the above embodiments 1-16, it can be seen that the method for modifying red clay with straw fiber composite ecological cement of the present invention has the following advantages, specifically:

[0081] Advantages 1. By using straw fiber and ecological cement as the main admixtures, the red clay can be reinforced and modified; through this modification, the shear strength, anti-permeability and water stability of the red clay can be significantly improved, thereby effectively preventing the deformation and crack development of the red clay under various environments and loads. The straw fiber composite ecological cement modified red clay method not only improves the stability of the red clay, but also provides a broader possibility for the application of red clay, especially for engineering projects such as water conservancy slopes that have higher requirements for the anti-permeability and shear strength of the fill;

[0082] Advantage 2. The two admixtures of the present invention not only solve the problems of slow strength growth, easy shrinkage and cracking, and poor water stability of soil improved by lime and fly ash, but also have little impact on the environment and plant growth; straw fiber can be turned into treasure and is widely used in modified soil. It has a direct source and low cost, and can improve soil quality and provide nutrients required for plant growth; ecological cement is more environmentally friendly than ordinary cement, and the pH value of its modified soil is more suitable for the growth of slope protection plants. Ecological cement also has the characteristics of early strength and fast hardening, and a short maintenance period, which is conducive to shortening the construction period and reducing construction costs; the combined use of the two admixtures can effectively improve the barrenness of red clay, and can significantly improve the germination rate, growth and survival rate of common slope protection plants such as ryegrass and bahia grass, and has higher application value.

[0083] The invention discloses an application of straw fiber composite ecological cement modified red clay, wherein the straw fiber composite ecological cement modified red clay is obtained by the straw fiber composite ecological cement modified red clay method.

[0084] Specifically, Figure 1 and Figure 2 As shown, the application of the straw fiber composite ecological cement modified red clay includes the following construction steps:

[0085] Step 1: Construction preparation: determine the design requirements and construction plan for fill and slope protection, conduct measurement and survey, clean up the site, and ensure the safety of the construction area;

[0086] Step 2: Earth excavation: Carry out earth excavation according to the design requirements to ensure that the slope and height of the construction slope and the protection slope meet the design requirements;

[0087] Step 3: Preparation of improved materials: Calculate the total amount of straw fiber composite ecological cement modified red clay required for the filling section in advance, select a good site for drying, then transport the ecological cement and straw fiber to the site for use, fully stir the mix, and maintain for 4 days for use;

[0088] Step 4, filling and compacting straw fiber composite ecological cement modified red clay: according to the design requirements, select the well-maintained straw fiber composite ecological cement modified red clay for filling on the original soil layer 1; the filling should be compacted layer by layer, and the height of each layer should not exceed 30 cm. Use a special geotechnical filling machine for compaction. After the filling is completed, the improved red clay compaction layer 2 is formed;

[0089] Step 5, channel lining construction: After compaction is completed, the channel concrete lining 3 panel construction can be carried out, and after the panel construction is completed, the exposed slope surface on the upper part of the channel is protected;

[0090] Step 6, protection of the upper slope of the channel: For the protection of the upper slope of the channel, first use the anchor rod 6 to fix the geocell 7 to the filled slope surface, and then fill a sand cushion layer 4 of a certain thickness. After the sand cushion layer 4 is filled, fill it with uncompacted straw fiber composite ecological cement modified red clay, the proportion of which is obtained according to the straw fiber composite ecological cement modified red clay proportion growth test, and form a modified red clay planting layer 5;

[0091] Step 7, spraying grass seeds: after the improved red clay planting layer 5 is paved, plant seeds can be sprayed.

[0092] The application of the straw fiber composite ecological cement modified red clay of the present invention uses the straw fiber composite ecological cement modified red clay in the construction method of the channel slope; wherein, the perforated geocell 7 has the characteristics of being customizable, easy to transport, easy to construct, and durable, and can form a stable structure with strong lateral restriction and large rigidity on the slope; the crushed stone layer, the improved compacted soil layer, and the slope protection plants can form a comprehensive drainage system: the introduction of the slope protection plants can effectively reduce the soil and water loss caused by the runoff of rainwater on the slope during the rainy season, and at the same time have a certain heat insulation function to reduce the adverse effects of dry-wet cycles on the slope; the introduction of the sand cushion layer is conducive to the rapid discharge of rainwater from the slope, which is conducive to preventing rainwater from further infiltrating and affecting the stability of the slope. The introduction of the improved soil compaction layer not only changes the poor engineering characteristics of red clay such as shrinkage and cracking, but also can form a stable surface due to the improvement of the shear strength, anti-permeability, and water stability of the red clay after the improvement, so that the red clay water conservancy slope can maintain a higher stability.

[0093] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, according to the concept of the present invention, there will be changes in the specific implementation methods and application scopes. The content of this specification should not be understood as limiting the present invention.

Claims

1. A method for modifying red clay with straw fiber composite ecological cement, characterized in that: The straw fiber composite ecological cement modified red clay comprises air-dried red clay, ecological cement, straw fiber and water; The ecological cement accounts for 3%-5% of the total mass of the straw fiber composite ecological cement modified red clay, the straw fiber accounts for 0.5%-1% of the total mass of the straw fiber composite ecological cement modified red clay, and the mass of the air-dried red clay and water accounts for 94%-96.5% of the total mass of the straw fiber composite ecological cement modified red clay; The straw fiber composite ecological cement modified red clay method comprises the following steps, specifically: Step a, obtaining straw fiber, ecological cement, and red clay raw materials, and drying the straw fiber and the red clay raw materials, and obtaining air-dried red clay after the red clay raw materials are dried; Step b: Conduct tests according to the requirements of the Geotechnical Test Method Standard (GB / T50123-2020) to obtain the optimal moisture content, specific gravity, and liquid and plastic limit indicators of red clay; Step c, according to the sample preparation method described in the "Standard for Geotechnical Test Methods" (GB / T50123-2020), according to the optimal moisture content and the corresponding maximum dry density, within the range of the straw fiber and ecological cement ratio, set several orthogonal test ratios; Step d, mix the dry materials in proportion, add appropriate amount of water and stew for 24 hours, stir a portion of them evenly to make standard ring knife samples, and cure them under standard curing conditions for 4 days; stir a portion of them evenly and use them for planting experiments; Step e, subjecting the cured ring knife samples to dry-wet cycles, and subjecting the ring knife samples after the dry-wet cycles to direct shear tests, penetration tests, crack analysis tests, soil-water characteristic curve tests, and plant growth tests, so as to obtain the best ratio through test data analysis.

2. The method for modifying red clay with straw fiber composite ecological cement according to claim 1, characterized in that: In the step a, the straw fiber is dried at 70° C. for 24 hours, and the red clay raw material is dried at 110° C. for 10 hours.

3. The method for modifying red clay with straw fiber composite ecological cement according to claim 1, characterized in that: In the step e, the dry cycle process is: after vacuuming for 4 hours, let it stand for 20 hours, and then put it in an oven at 50° C. for 48 hours, and repeat this process 5 times.

4. The method for modifying red clay with straw fiber composite ecological cement according to claim 1, characterized in that: The straw fiber is rice straw fiber, sugarcane straw fiber or corn straw fiber.

5. The method for modifying red clay with straw fiber composite ecological cement according to claim 1, characterized in that: The straw fiber should meet the conditions that the fiber proportion is greater than 90% and the medulla proportion is less than 10%, and the fiber length in the straw fiber is less than or equal to 3 cm, and the proportion of 1 cm-2 cm length fiber should be greater than 70%.

6. The method for modifying red clay with straw fiber composite ecological cement according to claim 1, characterized in that: The ecological cement is low-alkalinity sulphoaluminate cement, and the pH value of the ecological cement is between 10-10.

6.

7. An application of straw fiber composite ecological cement modified red clay, characterized by: The straw fiber composite ecological cement modified red clay is obtained by the straw fiber composite ecological cement modified red clay method according to any one of claims 1 to 6.

8. The application of straw fiber composite ecological cement modified red clay according to claim 7, characterized in that: The construction steps for application include: Step 1: Construction preparation: determine the design requirements and construction plan for fill and slope protection, conduct measurement and survey, clean up the site, and ensure the safety of the construction area; Step 2: Earth excavation: Carry out earth excavation according to the design requirements to ensure that the slope and height of the construction slope and the protection slope meet the design requirements; Step 3: Preparation of improved materials: Calculate the total amount of straw fiber composite ecological cement modified red clay required for the filling section in advance, select a good site for drying, then transport the ecological cement and straw fiber to the site for use, fully stir the mix, and maintain for 4 days for use; Step 4, filling and compacting straw fiber composite ecological cement modified red clay: according to the design requirements, select the well-maintained straw fiber composite ecological cement modified red clay for filling on the original soil layer (1); the filling should be compacted layer by layer, and the height of each layer should not exceed 30 cm. A special geotechnical filling machine is used for compaction. After the filling is completed, a modified red clay compaction layer (2) is formed; Step 5, channel lining construction: After compaction is completed, the channel concrete lining (3) panel construction can be carried out, and after the panel construction is completed, the exposed slope surface on the upper part of the channel is protected; Step 6, protection of the upper slope of the channel: For the protection of the upper slope of the channel, first use anchor rods (6) to fix the geocell (7) to the filled slope surface, and then fill a sand cushion layer (4) of a certain thickness. After the sand cushion layer (4) is filled, fill it with uncompacted straw fiber composite ecological cement modified red clay, the proportion of which is obtained according to the straw fiber composite ecological cement modified red clay proportion growth test, to form a modified red clay planting layer (5); Step 7, spraying grass seeds: after the improved red clay planting layer (5) is paved, plant seeds can be sprayed.

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