CN115368063B - Bagasse fiber composite low-alkali cement modified expansive soil and construction method for applying same to side slope - Google Patents

Abstract

The bagasse fiber composite low-alkali cement modified expansive soil comprises air-dried expansive soil, low-alkali cement, bagasse fiber and water, wherein the low-alkali cement accounts for 6% -8% of the mass of the dried expansive soil, the bagasse fiber accounts for 0.5% -0.9% of the mass of the dried expansive soil, and the mass of the water is determined by the plastic limit of the mixing soil and the optimal water content. The construction method of the modified expansive soil applied to the side slope takes a Kong Tugong grid chamber as a framework, graded broken stones are filled in the framework, the modified expansive soil is paved on the framework and compacted to form a modified soil layer, and finally, the mixture of the alien soil and the slope protection grass seeds is sprayed to form the alien soil layer. The modified expansive soil disclosed by the invention can obviously improve the compressive strength and the shear strength of the expansive soil, inhibit the expansion and contraction deformation and crack development of the expansive soil, has little influence on the environment and plant growth, and can realize green slope protection; the construction method of the modified expansive soil applied to the side slope can effectively enhance the overall rigidity and stability of the side slope and normalize the construction steps of the side slope modified soil.

Description

A kind of bagasse fiber composite low-alkali cement modified expansive soil and its application in slope construction work method

technical field

The invention belongs to the fields of geological disaster treatment and geotechnical engineering, and in particular relates to a bagasse fiber-composite low-alkali cement modified expansive soil and a construction method applied to slopes.

Background technique

Expansive soil is a special soil that swells when it absorbs water and shrinks when it loses water. Due to the stubbornness and seriousness of the problem of expansive soil, it is also called "cancer soil". The expansion and contraction, fissure and over-consolidation of expansive soil make artificial buildings built on it a huge safety hazard.

At present, for the treatment of expansive soil slopes, commonly used methods include compaction method, soil replacement method, moisture retention method, rigid support, flexible support, and physical and chemical improvement methods. According to engineering practice, the tamping method has very limited treatment effects on medium and strong expansive soils; the soil replacement method has problems such as high cost of soil transportation and accumulation of waste soil; the moisturizing method is often combined with other treatment methods to work together, the effect is good, and the construction is more complicated; Due to the huge expansion force of expansive soil, the effect of common rigid support is not appreciable; some scholars use flexible support such as geotechnical woven bags, which can buffer the expansion force and weaken the effect of expansion deformation, but there are construction difficulties, Later maintenance is cumbersome and other issues. As far as physical and chemical modification methods are concerned, lime and cement are two materials that are relatively mature in engineering. The cations in the hydration products of the two, such as Ca ²⁺ , can replace adsorbed ions to reduce the content of hydrophilic minerals in clay. After Ca ²⁺ , OH ^- permeate into the soil, the gel component formed by the reaction with clay minerals can play a role in bridging soil particles and blocking the gap between soil particles, thereby reducing the liquid limit and increasing the shear strength of the soil; Scholars have used nano-graphite powder, shell powder, steel slag, lignin fiber, basalt fiber, polypropylene fiber, polyethylene fiber and wood chip fiber to successfully improve the strength and crack inhibition performance of expansive soil; the disadvantages are: ① Ordinary cement The modified soil is strongly alkaline and has a great impact on the environment. ② Most of the fibers in the existing research have high cost, which is not conducive to engineering practice. ③ Currently, the common modified soil construction method for expansive soil slopes is to modify The thickness of the soil layer is modified by rough mechanical throwing, followed by repeated rolling with a vibratory compactor to a predetermined compaction degree, and finally the slope is precisely leveled manually. The construction steps are cumbersome, the overall stability of the slope is not strong, and the seepage of the slope Significant and impossible to achieve ecological slope protection and other issues.

The patent of CN101423353B discloses a method and construction method for improving expansive soil with waste foundry sand. This patent proposes an improvement method for turning waste into treasure, but there are (1) the proportion of modified admixture is too large, and the economic benefit is low , the mixing uniformity is poor, (2) the improvement effect on the strength of expansive soil is general, (3) the construction plan is not clear and the overall stability and seepage of the slope cannot be guaranteed. The patent application of CN102352622A discloses a method and construction method for improving expansive soil with alkali slag, which has played an important role in the development of the field of expansive soil modification and treatment, but there are the following problems: (1) The proportion of modified admixtures If it is too large, the economic benefit is low, and the mixing uniformity is poor; (2) ecological and environmental protection issues are not considered; (3) the acquisition method of alkali slag is single, and the difficulty of obtaining alkali slag varies greatly with the change of project location; (4) the construction plan cannot guarantee the slope Overall stability and seepage etc. The patent of CN103233458B discloses an expansive soil improved with waste straw ash and marble ash and its preparation method and application in construction, revealing an economical modified admixture of expansive soil, and effectively improving the expansive soil mechanical properties, and described the construction method of modified soil in detail, but there are the following deficiencies: (1) the proportion of modified admixture is relatively large, and the economic benefit is low; (2) ecological and environmental protection issues are not considered; (3) the modification before construction The maintenance time of soil is short; (4) The construction process is cumbersome. The patent of CN103882855B discloses a kind of expansive soil cement modification and filling construction method. This patent combines the actual construction process and contributes to the construction research of cement modified soil, but there are the following problems: (1) optimal cement content The measurement standard is single and the proportion of additives is not specified; (2) ecological and environmental protection issues are not considered; (3) the curing time of modified soil is not specified.

Contents of the invention

The technical problem to be solved by the present invention is to provide a kind of bagasse fiber composite low-alkali cement modified expansive soil and its application in slopes in view of the current physical and chemical method modified expansive soil, which is expensive and unfavorable for ecological protection. The construction method, which can significantly improve the compressive strength and shear strength of expansive soil; can effectively inhibit the expansion and contraction deformation and crack development of expansive soil; the admixture has little impact on the environment and plant growth, and can realize green slope protection; can effectively strengthen the edge The overall stiffness and stability of the slope, and standardize the construction steps of slope modified soil.

The technical scheme that the present invention adopts for solving the problems of the technologies described above is:

A bagasse fiber composite low-alkali cement modified expansive soil, comprising air-dried expansive soil, low-alkali cement, bagasse fiber and water, wherein the low-alkali cement accounts for 6%-8% of the mass of the dried expansive soil, and the bagasse The fibers account for 0.5%-0.9% of the mass of the dried expansive soil, and the dried expansive soil is air-dried expansive soil dried in an oven at 105° C. for 24 hours.

According to the above scheme, the quality of the water is calculated according to the following formula;

m ₀ ＝m ₁ ÷(1+ω ₀ )×(ω ₂ -ω ₀ )

In the formula, m ₀ : the mass of water to be added to the mixed soil to reach the desired moisture content, and the mixed soil is uniformly mixed with air-dried expansive soil, low-alkali cement and bagasse fiber;

m ₁ : the mass of air-dried expansive soil in the mixed soil;

ω ₀ : initial moisture content of air-dried expansive soil;

ω ₂ : Expected moisture content of the mixed soil. Within the range of ω _y -ω _p , ω _y and ω _p are the optimal moisture content and plastic limit determined after the limit moisture content test and compaction test of the mixed soil, respectively.

According to the above plan, the components and proportions of the low-alkali cement are: LOSS 0.33%, SiO ₂ 9.94%, AL ₂ O ₃ 29.38%, Fe ₂ O ₃ 3.16%, CaO 43.56%, MgO 2.76%, SO ₃ 9.62%, TiO ₂ 1.25%.

According to the above scheme, the diameters of the bagasse fibers are all less than 2mm, and the bagasse fibers with a length of 0-8mm, 8-15mm, and 15-20mm respectively account for 77.4%, 22.1%, and 0.5% of the total mass of the bagasse fibers.

The present invention also provides a method for preparing the above-mentioned bagasse fiber composite low-alkali cement modified expansive soil, comprising the following steps:

S1. Take some air-dried expansive soil, pass it through a 2mm standard sieve after crushing, pass the bagasse fiber through a 2mm standard sieve after drying at 70°C for 24 hours, weigh _m1 of the sieved air-dried expansive soil, and measure the initial water content of the air-dried expansive soil The ratio is ω ₀ , and the required low-alkali cement and bagasse fiber are weighed according to the mass ratio. The mass ratio of low-alkali cement and bagasse fiber (admixture) is for the drying expansive soil, and the drying expansive soil is air-dried expansive soil The expansive soil dried in an oven at 105°C for 24 hours, the quality of the dried expansive soil is m ₁ ÷ (1+ω ₀ ), the low-alkali cement accounts for 6%-8% of the mass of the dried expansive soil, and the bagasse fiber It accounts for 0.5%-0.9% of the mass of the dried expansive soil; the air-dried expansive soil, low-alkali cement and bagasse fiber are evenly mixed according to the dry mixing method and the external mixing method to form a mixed soil;

S2. According to the "Highway Geotechnical Test Regulations" (JTG 3430-2020), do limit water content test and compaction test on the mixed soil to determine the plastic limit ω _p and optimal water content ω _y of the mixed soil;

S3. Calculate the mass m ₀ that needs to be added water to make the expected moisture content ω ₂ of the mixed soil obtained in step S1 reach ω _y -ω _p , and the mass m ₀ that needs to be added water is equal to the mass of the dried expansive soil in the mixed soil multiplied by the mixed soil The difference between the desired moisture content of soil ω ₂ minus the initial moisture content of air-dried expansive soil ω ₀ , that is, m ₀ =m ₁ ÷ (1+ω ₀ )×(ω ₂ -ω ₀ );

S4. According to the calculation result of step S3, add the corresponding mass of water into the mixed soil obtained in step S1, mix evenly to form a soil sample, and perform 3-day curing on the obtained soil sample to obtain the modified expansive soil.

According to the above scheme, the limit moisture content test in the step S2 uses a combined liquid-plastic limit tester, and the compaction test uses a light manual compactor.

According to the above scheme, when mixing with water in the step S4, in order to reduce the agglomeration of soil particles, water is evenly added in at least 3 times; the obtained soil sample maintenance environment is: temperature 20 ± 1 ° C, air humidity 98%.

The present invention also proposes a construction method for applying the above-mentioned bagasse fiber composite low-alkali cement modified expansive soil to a slope, comprising the following steps:

1) Cleaning and leveling the slope;

2) Use positioning anchors to anchor the geocell with holes as the skeleton, and fill the inside with graded gravel;

3) Laying the modified expansive soil on the skeleton and graded crushed stone and using a vibratory compactor to make the modified expansive soil reach the required degree of compaction to form a modified soil layer;

4) Use the spraying device to evenly spray the mixture of guest soil and slope protection grass seeds to form a guest soil layer, and the construction is completed.

According to the above scheme, the material of the geocell is high-density polyethylene, the height is 200mm, the welding distance is 800mm, and the thickness is 1.5mm.

According to the above scheme, the thickness of the modified soil layer is 12cm-16cm, and the thickness of the modified soil layer is 9-11cm.

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

1. The bagasse fiber composite low-alkali cement modified expansive soil of the present invention adopts bagasse fiber and low-alkali cement as an admixture for reinforcement and modification of expansive soil, which provides an effective method for physical and chemical modification of expansive soil, which can significantly improve The compressive strength and shear strength of expansive soil can effectively inhibit the expansion and contraction deformation and crack development of expansive soil;

2. The additives have little impact on the environment and plant growth. Among them, bagasse fiber has: ①Turn waste into treasure. A large amount of bagasse produced by sugar factories every year is piled up randomly as waste, and even causes fires many times, wasting resources. At the same time, it also caused serious environmental pollution, so using bagasse to modify expansive soil is equivalent to consuming waste to improve engineering cancer; ②The source is extensive and direct, and sugar factories are widely distributed, and bagasse is used as a direct source of sugar factory waste, which can be used to modify expansive soil without complex secondary treatment; ③ low price, bagasse as sugar factory waste is often disposed of at will or incinerated, low cost of acquisition; ④ excellent properties, bagasse fiber Add expansive soil to act on the slope. In the early stage, it can be used as a flexible connection between soil particles, which can control cracks, increase soil strength and reduce expansion and contraction. In the middle stage, following the gradual reinforcement of slope protection grass root system, bagasse fiber The degradation of grass can provide nutrients for the growth of slope protection grass, and the root system of slope protection grass grows in the later stage, which not only plays the role of flexible connection with soil particles; compared with ordinary cement, low-alkali cement is more ecologically friendly. According to literature review, common slope protection grass such as high The suitable growth pH range of fescue, Four Seasons Green, Bluegrass and Elymus is 4.6-8.7, and according to the "Agricultural Industry Standard" (NY/T1377-2007), the pH value of the modified soil mixed with 7% ordinary cement is 12.9, the PH value of the modified soil mixed with 7% low-alkali cement is 8.5, obviously the acid-base environment of the low-alkali cement modified soil is more suitable for the growth of slope protection grass;

3. The preparation method of bagasse fiber composite low-alkali cement modified expansive soil is simple to operate and has a high fault tolerance rate, and can be widely used in the production of similar modified soils;

4. The existing slope construction scheme has problems such as complicated operation, poor overall stability, and seepage. The construction method of the modified soil in the present invention can standardize the construction steps of the modified soil of the slope and simplify the construction; Geocells have the characteristics of customization, easy transportation, good construction, wear resistance, stable chemical properties, etc., and can make the slope form a stable structure with strong lateral restrictions and high rigidity; crushed stone layer, modified soil layer , soil layer and slope protection grass can effectively solve the seepage problem of slope water;

5. It can realize the green protection of the slope, and provide new ideas for the shallow cracking and instability of the expansive soil slope. In particular, it can directly excavate the expansive soil on the construction site to make modified expansive soil, which has the advantages of local materials, simple construction, Features of green protection.

Description of drawings

Fig. 1 is the preparation flowchart of bagasse fiber composite low-alkali cement modified expansive soil of the present invention;

Fig. 2 is a comparison diagram of cracks between plain soil and different content bagasse fiber composite low-alkali cement modified expansive soil after 7 dry-wet cycles in the embodiment of the present invention;

Fig. 3 is the scanning electron microscopic view of the bagasse fiber composite low-alkali cement modified expansive soil after 7 times of dry-wet cycles in the dosage ratio of Example 2 of the present invention;

Fig. 4 is the structural layout diagram of expansive soil slope construction of the present invention;

In the figure: 1-modified soil layer; 2-slope protection grass seeds; 3-non-expansive guest soil; 4-side slope; 5-graded gravel; 6-geocell; 7-positioning anchor.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

The bagasse fiber composite low-alkali cement modified expansive soil of the present invention comprises air-dried expansive soil, low-alkali cement, bagasse fiber and water, wherein the low-alkali cement accounts for 6%-8% of the mass of the dried expansive soil, The bagasse fiber accounts for 0.5%-0.9% of the mass of the dried expansive soil, and the dried expansive soil is air-dried expansive soil dried in an oven at 105° C. for 24 hours. The full name of low-alkali cement is low-alkalinity sulfoaluminate cement (L.SAC 42.5), which is provided by Dengdian Group Cement Co., Ltd. Its components and proportions are: LOSS 0.33%, SiO ₂ 9.94%, AL ₂ O ₃ 29.38%, Fe ₂ O ₃ 3.16%, CaO 43.56%, MgO 2.76%, SO ₃ 9.62%, TiO ₂ 1.25%. The bagasse fiber is taken from a sugar factory in Nanning, Guangxi. The diameter of the bagasse fiber after sieving is less than 2mm, and the bagasse fiber with a length of 0-8mm, 8-15mm, and 15-20mm accounts for 77.4% and 22.1% of the total mass of bagasse fiber respectively. , 0.5%.

As shown in Figure 1, the preparation method of bagasse fiber composite low-alkali cement modified expansive soil of the present invention comprises the steps:

S1. Take some air-dried expansive soil, pass it through a 2mm standard sieve after crushing, pass the bagasse fiber through a 2mm standard sieve after drying at 70°C for 24 hours, weigh _m1 of the sieved air-dried expansive soil, and measure the initial water content of the air-dried expansive soil The ratio is ω ₀ , and the required low-alkali cement and bagasse fiber are weighed according to the mass ratio. The mass ratio of low-alkali cement and bagasse fiber (admixture) is for the drying expansive soil, and the drying expansive soil is air-dried expansive soil The expansive soil dried in an oven at 105°C for 24 hours, the quality of the dried expansive soil is m ₁ ÷ (1+ω ₀ ), the low-alkali cement accounts for 6%-8% of the mass of the dried expansive soil, and the bagasse fiber It accounts for 0.5%-0.9% of the mass of the dried expansive soil; the air-dried expansive soil, low-alkali cement and bagasse fiber are evenly mixed according to the dry mixing method and the external mixing method to form a mixed soil;

S2. According to the "Highway Soil Test Regulations" (JTG 3430-2020), do limit moisture content test and compaction test on the mixed soil to determine the plastic limit ω _p and optimal water content ω _y of the mixed soil; limit moisture content test A liquid-plastic limit combined measuring instrument is used, and a light manual compaction instrument is used for the compaction test;

S3. Calculate the mass m 0 that needs to be added to make the expected water content ω ₂ of the mixed soil obtained in step S1 reach ω _y -ω _p (ω ₂ is within the range of ω _y -ω _p ), and the mass _{m 0 that} needs to be added water is equal to the mixed soil The mass of the dried expansive soil in the composite is multiplied by the expected moisture content of the mixed soil ω ₂ minus the difference between the initial moisture content of the air-dried expansive soil ω ₀ , that is, m ₀ =m ₁ ÷(1+ω ₀ )×(ω ₂ - ω ₀ );

S4, according to the calculation result of step S3, mix the water of the corresponding quality into the mixed soil obtained in step S1, in order to reduce the soil particles from agglomerating, add water evenly in at least 3 times, mix evenly to form a soil sample, and analyze the obtained soil sample in The modified expansive soil can be obtained by curing for 3 days at a temperature of 20(±1)°C and an air humidity of 98%.

As shown in Figure 4, the construction method of the bagasse fiber composite low-alkali cement modified expansive soil of the present invention applied to the slope comprises the following steps:

1) cleaning and leveling the slope 4;

2) Use the positioning anchor rod 7 to anchor the geocell 6 with holes as the skeleton. The model of the geocell 6 is TGLG-HDPE-200-800-1.5, the material is high-density polyethylene, the height is 200mm, and the welding distance is 800mm. The thickness is 1.5mm, and it is filled with graded gravel 5;

3) Lay the modified expansive soil on the geocell 6 and the graded gravel 5, and use a vibratory compactor to make the modified expansive soil reach the required degree of compaction, forming a modified soil layer 1 with a thickness of about 12-16 cm ;

4) Use a spraying device to evenly spray the mixture of non-expanding guest soil 3 and slope protection grass seeds 2 (such as tall fescue) to form a guest soil layer with a thickness of about 9-11 cm, and the construction is completed.

The content of the present invention will be further described below in conjunction with three embodiments.

Example 1:

1. Take the air-dried expansive soil from Buffalo in Nanning, Guangxi for use, pass through a 2mm standard sieve after crushing, and pass the bagasse fiber through a 2mm standard sieve after drying at 70°C for 24 hours; weigh the required sieved air-dried expansive soil, low-alkali cement and The bagasse fiber is mixed evenly by dry blending and external mixing method; the initial moisture content of the air-dried expansive soil is 3.1%, and 1500g of air-dried expansive soil is taken by weighing, and the low-alkali cement accounts for 6% of the quality of the dried expansive soil, so 1500/( 1+3.1%)*6%=87.3g low-alkali cement for later use; bagasse fiber accounts for 0.5% of the dry expansive soil quality, so take 1500/(1+3.1%)*0.5%=7.3g bagasse fiber for later use;

2. According to the "Highway Soil Test Regulations" (JTG 3430-2020), the limit moisture content test and light compaction test are carried out on the mixed soil, and the plastic limit ω _p = 22.6% and the optimal moisture content ω _y = 22.0%;

3. Calculation makes the expected moisture content of the mixed soil (admixture expansive soil) obtained in step 1 reach 22.0%-22.6%, and the quality that needs to add water is between 275g-284g;

4. Mix about 280g of water into the mixed soil three times evenly, mix evenly to form a soil sample, and maintain the obtained soil sample for 3 days at a temperature of 20(±1)°C and a humidity of 98% to obtain the modified soil. Expansive Soil;

5. Slope construction: ①Clean and level the slope 4; ②Anchor the geocell 6 with holes with positioning anchor 7 as a skeleton, and fill the inside with graded gravel 5; ③Pay modified expansion on it soil and use a vibrating compactor to achieve the required degree of compaction to form a modified soil layer 1 with a thickness of about 15 cm; ④Use a spraying device to evenly spray the mixture of non-expandable guest soil 3 and slope protection grass seeds 2 to form a thickness of about 10 cm The guest soil layer, that is, the construction is completed.

Improvement effect: According to the "Highway Soil Test Regulations" (JTG 3430-2020), the modified soil was subjected to direct shear test, unconfined compressive strength test, unloaded expansion rate test, and shrinkage test; The PACS (particles and cracks analysis system) software and Adobe Photoshop software developed by the doctor performed image processing on the photos taken after seven dry-wet cycles of the modified soil ring sample to obtain the crack rate; according to the "Agricultural Industry Standard" (NY/T1377 -2007) measured the pH value of the modified soil. It is concluded that the cohesion of expansive soil improved by 6% low-alkali cement and 0.5% bagasse fiber is 128.77% higher than that of plain soil, the friction angle is 42.86% higher, and the unconfined compressive strength is 110.19% higher. The load expansion rate is reduced by 19.21%, the linear shrinkage rate is reduced by 21.88%, the ring knife-like crack rate is reduced by 69.23% after seven dry-wet cycles, and the pH value of the modified soil is 8.3. 34.13%. In summary, the modified soil has excellent properties and is green and environmentally friendly, and it provides an effective method for the treatment of common expansive soil problems.

Example 2:

1. Take the air-dried expansive soil from Buffalo in Nanning, Guangxi for use, pass through a 2mm standard sieve after crushing, and pass the bagasse fiber through a 2mm standard sieve after drying at 70°C for 24 hours; weigh the required sieved air-dried soil, low-alkali cement and bagasse according to the mass ratio The fibers are mixed evenly by dry blending and external mixing method; the initial moisture content of the air-dried expansive soil is 3.1%, and 1500g of air-dried expansive soil is taken by weighing, and the low-alkali cement accounts for 7% of the dry expansive soil quality, so 1500/(1 +3.1%)*7%=101.8g low-alkali cement for subsequent use; bagasse fiber accounts for 0.7% of the dry expansive soil quality, so take by weighing 1500/(1+3.1%)*0.7%=10.2g bagasse fiber for subsequent use;

2. According to the "Highway Soil Test Regulations" (JTG 3430-2020), the limit moisture content test and light compaction test are carried out on the mixed soil, and the plastic limit ω _p = 22.9% and the optimal moisture content ω _y = 21.2%;

3. Calculate the expected moisture content of the mixed soil obtained in step 1 to reach 21.2%-22.9%, and the quality of adding water is between 263g-288g;

4. Mix about 275g of water into the mixed soil three times, mix evenly to form a soil sample, and maintain the obtained soil sample for 3 days at a temperature of 20(±1)°C and a humidity of 98% to obtain the modified soil Expansive Soil;

5. Slope construction: ①Clean and level the slope 4; ②Anchor the geocell 6 with holes with positioning anchor 7 as a skeleton, and fill the inside with graded gravel 5; ③Pay modified expansion on it soil and use a vibrating compactor to achieve the required degree of compaction to form a modified soil layer 1 with a thickness of about 15 cm; ④Use a spraying device to evenly spray the mixture of non-expandable guest soil 3 and slope protection grass seeds 2 to form a thickness of about 10 cm The guest soil layer, that is, the construction is completed.

Improvement effect: According to the "Highway Soil Engineering Test Regulations" (JTG 3430-2020), the modified soil was subjected to direct shear test, unconfined compressive strength test, unloaded expansion rate test, and shrinkage test; with the help of Dr. Liu Chun from Nanjing University The developed PACS (particles and cracks analysis system) software and Adobe Photoshop software were used to image-process the photos taken after seven dry-wet cycles of the modified soil ring sample to obtain the crack rate; according to the "Agricultural Industry Standard" (NY/T1377- 2007) measured the pH value of the modified soil. It is concluded that the cohesion of the modified expansive soil improved by 7% low-alkali cement compounded with 0.7% bagasse fiber is 227.94% higher than that of plain soil, the friction angle is increased by 51.02%, and the unconfined compressive strength is increased by 128.14%. , the no-load expansion rate decreased by 19.77%, the linear shrinkage rate decreased by 37.50%, the seven-time dry-wet cycle ring knife-like crack rate decreased by 75.00%, the pH value of the modified soil was 8.5, and the pH value of the ordinary cement was 12.9 in the same amount. A reduction of 34.11%.

Example 3:

1. Take the air-dried expansive soil from Buffalo in Nanning, Guangxi for use, pass through a 2mm standard sieve after crushing, and pass the bagasse fiber through a 2mm standard sieve after drying at 70°C for 24 hours; weigh the required sieved air-dried soil, low-alkali cement and bagasse according to the mass ratio The fibers are mixed evenly by dry blending and external blending. The initial moisture content of the air-dried soil is 3.1%. Weigh 1500g of air-dried expansive soil. Low-alkali cement accounts for 8% of the mass of the dried expansive soil. Therefore, weigh 1500/(1+3.1%)*8%=116.4g of low-alkali cement Standby; bagasse fibers account for 0.9% of the dry expansive soil quality, so take 1500/(1+3.1%)*0.9%=13.1g bagasse fibers for use;

2. According to the "Highway Geotechnical Test Regulations" (JTG 3430-2020), the limit moisture content test and light compaction test are carried out on the mixed soil, and the plastic limit ω _p = 21.7% and the optimal moisture content ω _y = 20.0%;

3. Calculate the mass of water needed to add water between 246g-271g so that the expected moisture content of the mixed soil obtained in step 1 reaches 20.0%-21.7%;

4. Mix about 258g of water into the mixed soil three times evenly, mix evenly to form a soil sample, and maintain the obtained soil sample for 3 days at a temperature of 20(±1)°C and a humidity of 98% to obtain the modified soil. Expansive Soil;

5. Slope construction: ①Clean and level the slope 4; ②Anchor the geocell 6 with holes with positioning anchor 7 as a skeleton, and fill the inside with graded gravel 5; ③Pay modified expansion on it soil and use a vibrating compactor to achieve the required degree of compaction to form a modified soil layer 1 with a thickness of about 15 cm; ④Use a spraying device to evenly spray the mixture of non-expandable guest soil 3 and slope protection grass seeds 2 to form a thickness of about 10 cm The guest soil layer, that is, the construction is completed.

Improvement effect: According to the "Highway Soil Engineering Test Regulations" (JTG 3430-2020), the modified soil was subjected to direct shear test, unconfined compressive strength test, unloaded expansion rate test, and shrinkage test; with the help of Dr. Liu Chun from Nanjing University The developed PACS (particles and cracks analysis system) software and Adobe Photoshop software were used to image-process the photos taken after seven dry-wet cycles of the modified soil ring sample to obtain the crack rate; according to the "Agricultural Industry Standard" (NY/T1377- 2007) measured the pH value of the modified soil. It is concluded that the cohesion of the modified expansive soil improved by 8% low-alkali cement compounded with 0.9% bagasse fiber is 314.13% higher than that of plain soil, the friction angle is increased by 51.02%, and the unconfined compressive strength is increased by 146.88%. , the no-load expansion rate decreased by 20.90%, the linear shrinkage rate decreased by 56.25%, the seven-time dry-wet cycle ring knife-like crack rate decreased by 82.69%, the pH value of the modified soil was 8.7, and the pH value of the ordinary cement was 13.1 in the same amount. A reduction of 33.59%.

Table 1 Comparison of physical properties of expansive soil with different admixture ratios

Fig. 2 is a comparison chart of plain soil and different dosages of bagasse fiber composite low-alkali cement modified expansive soil cracks after 7 dry-wet cycles in Example 2 of the present invention; Fig. 3 is a ratio of 7 dry-wet cycles in Example 2 of the present invention Electron microscope scanning micrograph of bagasse fiber composite low-alkali cement modified expansive soil; comparison of physical properties of expansive soil with different admixture ratios is shown in Table 1.

It can be seen from Table 1 that the addition of low-alkali cement composite bagasse fibers has a large degree of change in the physical properties of expansive soil. From the perspective of critical moisture content: the liquid limit, plastic limit and optimal moisture content generally present There are two main reasons for the decreasing trend with the increase of the content of low-alkali cement and bagasse fiber: ① Ca ²⁺ produced by cement hydration will undergo a replacement reaction with some adsorbed mineral cations, and at the same time promote the agglomeration of soil particles, thereby improving The water absorption performance and water stability of the soil are improved; ② After adding low-alkali cement and bagasse fiber, the soil gradation becomes better, the compaction performance is better, and the plasticity becomes smaller. From the perspective of strength: the cohesion and unconfined compressive strength of the soil are significantly enhanced with the increase of the proportion of admixtures. This is because: ① Ca ²⁺ in cement hydration products and clay minerals After the low-valent ion exchange is completed, the remaining Ca ²⁺ will continue to chemically react with some substances in the clay minerals to form water-insoluble crystals CaO·Al ₂ O ₃ ·(n+1)H ₂ O, CaO·SiO ₂ ·(n+1)H ₂ O; ②Ca(OH) ₂ in the cement hydration product can react with CO ₂ in the air to form water-insoluble CaCO ₃ , the products of these two reactions make the surface of expansive soil The flaky structure and pores are bonded by cementitious substances, which increases the connection strength between soil particles and reduces the distance between soil particles, promotes the agglomeration of soil, and effectively enhances the bonding and water stability between soil particles. Strength; ③The bagasse fibers are bridged between soil particles, and its tensile and shearing effects can effectively increase the strength of the soil while preventing the development of cracks, thereby increasing the strength of the soil. From the point of view of expansion and contraction: From the microscopic image scanned by electron microscope in Figure 3, it can be seen that most of the soil particles in the plain soil have a layered structure, and the soil particles are mostly connected in the form of surface-to-surface. After many times of drying and wetting cycles, the distance between soil particles It's easy to get big. It can be seen from Table 1 that both the no-load expansion rate and the linear shrinkage rate decrease significantly with the increase of the proportion of additives, which is mainly because (1) the cementitious material enhances the connection between soil particles and reduces the distance between soil particles ;②Soil particles are wrapped by cementitious substances, which effectively reduces the chance of water-sensitive minerals in contact with water, and the cementation force of the cementitious substances can also bear part of the expansion force, so that the expansion and contraction characteristics of the soil are improved;③ The bagasse fiber directly resists the force between the soil by strengthening the connection between the soil particles, and can also inhibit the expansion and contraction deformation of the soil. From the perspective of crack development: From the data in Figure 2 and Table 1, it can be seen that the crack development of expansive soil is obviously suppressed with the increase of the proportion of admixture, which is also the result of the joint action of low-alkali cement and bagasse fiber. From the perspective of pH value: the pH value of low-alkali cement admixture soil is much lower than that of ordinary cement admixture soil.

In summary, low-alkali cement and bagasse fiber have a good physical and chemical modification effect on expansive soil. With the increase of the proportion of admixtures, all the indicators of expansive soil are improved. But consider the following points: ①The acid-base environment suitable for the growth of common slope protection grass is usually between 4.6-8.7; ②The price of low-alkali cement of the same specification is about 11.9% more expensive than ordinary cement; ③Too many bagasse fibers will lead to fiber agglomeration ; ④ The strength increase of the second and third admixture schemes is not obvious. Finally, 7% low-alkali cement + 0.7% bagasse fiber was determined to be the best admixture ratio.

The above-mentioned embodiment is only to illustrate the technical conception and characteristics of the present invention, and is only an embodiment of the present invention. Limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. The bagasse fiber composite low-alkali cement modified expansive soil is characterized by comprising air-dried expansive soil, low-alkali cement, bagasse fiber and water, wherein the low-alkali cement accounts for 6% -8% of the mass of the dried expansive soil, the bagasse fiber accounts for 0.5% -0.9% of the mass of the dried expansive soil, and the dried expansive soil is the expansive soil which is dried in an oven at 105 ℃ for 24 hours.

2. The bagasse fiber composite low-alkali cement modified bentonite according to claim 1, wherein the mass of water is calculated according to the formula;

m ₀ ＝m ₁ ÷(1+ω ₀ )×(ω ₂ -ω ₀ )

wherein m is ₀ : the mixing soil reaches the expected water content and is prepared by uniformly mixing air-dried expansive soil, low-alkali cement and bagasse fibers;

m ₁ : the mass of the air-dried expansive soil in the mixed soil;

ω ₀ : air-drying the initial water content of the expansive soil;

ω ₂ : the expected water content of the mixed soil is omega _y -ω _p Within a range omega _y 、ω _p And respectively carrying out a limit water content test and a compaction test on the mixed soil to determine the optimal water content and the plastic limit.

3. The bagasse fiber composite low-alkali cement modified expansive soil according to claim 1, wherein the low-alkali cement comprises the following components in percentage by weight: LOSS 0.33%, siO ₂ 9.94％、AL ₂ O ₃ 29.38％、Fe ₂ O ₃ 3.16％、CaO 43.56％、MgO 2.76％、SO ₃ 9.62％、TiO ₂ 1.25％。

4. The bagasse fiber composite low-alkali cement modified expansive soil according to claim 1, wherein the diameters of the bagasse fibers are smaller than 2mm, and the bagasse fibers with lengths of 0-8mm, 8-15mm and 15-20mm respectively account for 77.4%, 22.1% and 0.5% of the total mass of the bagasse fibers.

5. A method for preparing the bagasse fiber composite low-alkaline cement modified expansive soil according to any one of claims 1 to 4, comprising the following steps:

s1, taking a plurality of air-dried expansive soil, crushing, sieving with a 2mm standard sieve, drying bagasse fibers at 70 ℃ for 24 hours, sieving with the 2mm standard sieve, and weighing the mass of m ₁ The sieved air-dried expansive soil is measured to have the initial water content of omega ₀ Weighing the low-alkali cement and bagasse fibers according to the mass ratio, wherein the mass ratio of the low-alkali cement to the bagasse fibers is the mass ratio of the low-alkali cement to the bagasse fibers to the dry expansive soil, the dry expansive soil is the expansive soil obtained by drying the air-dried expansive soil in a drying oven at 105 ℃ for 24 hours, and the mass of the dry expansive soil is m ₁ ÷(1+ω ₀ ) The low-alkali cement accounts for 6-8% of the mass of the dried expansive soil, and the bagasse fiber accounts for 0.5-0.9% of the mass of the dried expansive soil; uniformly mixing air-dried expansive soil, low-alkali cement and bagasse fibers according to a dry mixing method and an external mixing method to form mixed soil;

s2, performing limit water content test and compaction test on the mixed soil according to JTG 3430-2020 of Highway geotechnical test procedure to determine the plastic limit omega of the mixed soil _p Optimum water content omega _y ；

S3, calculating to enable the expected water content omega of the mixing soil obtained in the step S1 ₂ Up to omega _y -ω _p Mass m of water to be added ₀ The mass m of the water to be added ₀ Equal to the mass of the dried and expanded soil in the blended soil multiplied by the expected water content omega of the blended soil ₂ Subtracting the initial water content omega of the air-dried expansive soil ₀ The difference of (i.e. m) ₀ ＝m ₁ ÷(1+ω ₀ )×(ω ₂ -ω ₀ )；

And S4, according to the calculation result of the step S3, water with corresponding mass is mixed into the mixed soil obtained in the step S1, the mixture is uniformly mixed to form a soil sample, and the obtained soil sample is cured for 3 days, so that the modified expansive soil is obtained.

6. The method for preparing bagasse fiber composite low-alkaline cement modified expansive soil according to claim 5, wherein the limit water content test in the step S2 adopts a liquid-plastic limit combined tester, and the compaction test adopts a light manual compaction tester.

7. The method for preparing bagasse fiber composite low-alkaline cement modified expansive soil according to claim 5, wherein water is added uniformly for at least 3 times in order to reduce agglomeration of soil particles when water is added in step S4; the maintenance environment of the obtained soil sample is as follows: the temperature is 20+/-1 ℃ and the air humidity is 98 percent.

8. A construction method of applying the bagasse fiber composite low-alkaline cement modified expansive soil according to any one of claims 1 to 4 to a side slope, comprising the following steps:

1) Cleaning and leveling the side slope;

2) Using a positioning anchor rod to anchor the geocell with the hole as a framework, and filling graded broken stone inwards;

3) Paving the modified expansive soil on the framework and the graded broken stone, and enabling the modified expansive soil to reach the required compactness by utilizing a vibrating compactor to form a modified soil layer;

4) And uniformly spraying the mixture of the soil and the slope protection grass seeds by using a slurry spraying device to form a soil covering layer, thus finishing the construction.

9. The construction method of the bagasse fiber composite low-alkaline cement modified expansive soil applied to the side slope according to claim 8, wherein the geocell is made of high-density polyethylene, the height is 200mm, the welding distance is 800mm, and the thickness is 1.5mm.

10. The construction method of the bagasse fiber composite low-alkaline cement modified expansive soil applied to the side slope according to claim 8, wherein the thickness of the modified soil layer is 12 cm-16 cm, and the thickness of the foreign soil layer is 9 cm-11 cm.