CN115368063A - Bagasse fiber composite low-alkali cement modified expansive soil and construction method of bagasse fiber composite low-alkali cement modified expansive soil applied to side slope - Google Patents
Bagasse fiber composite low-alkali cement modified expansive soil and construction method of bagasse fiber composite low-alkali cement modified expansive soil applied to side slope Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D17/00—Excavations; Bordering of excavations; Making embankments
- E02D17/20—Securing of slopes or inclines
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/74—Means for anchoring structural elements or bulkheads
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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Abstract
The modified expansive soil comprises air-dried expansive soil, low-alkali cement, bagasse fibers and water, wherein the low-alkali cement accounts for 6-8% of the mass of the dried expansive soil, the bagasse fibers account 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 mixed soil and the optimal water content. The construction method of applying the modified expansive soil to the side slope is characterized in that the perforated geocell is used as a framework, graded broken stones are filled in the framework, the modified expansive soil is paved and compacted to form a modified soil layer, and finally a mixture of the foreign soil and the slope protection grass seeds is sprayed to form the foreign soil layer. The modified expansive soil can obviously improve the compressive strength and the shear strength of the expansive soil, inhibit the expansion deformation and the crack development of the expansive soil, has small influence on the environment and the 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 integral rigidity and stability of the side slope and standardize the construction steps of the modified soil of the side slope.
Description
Technical Field
The invention belongs to the field of geological disaster treatment and geotechnical engineering, and particularly relates to bagasse fiber composite low-alkali cement modified expansive soil and a construction method for applying the same to a side slope.
Background
Expansive soil is a special soil which absorbs water to expand and loses water to shrink, and is also called as 'cancer soil' due to the intractable and serious problems of the expansive soil. The expansion and shrinkage property, the crack property and the hyperconcentration property of the expansive soil cause great potential safety hazards to artificial buildings built on the expansive soil.
At present, for the problem of expansive soil slope treatment, a tamping method, a soil changing method, a wet maintaining method, a rigid support, a flexible support, a physical and chemical improvement method and the like are commonly used. According to engineering practice, the tamping method has very limited treatment effect on medium and strong expansive soil; the soil changing method has the problems of high soil transporting cost, waste soil accumulation and the like; the wet-keeping method is usually combined with other treatment modes to work together, the effect is good, and the construction is complex; due to the huge expansive force of the expansive soil, the common rigid supporting effect is not considerable; the scholars adopt flexible supports such as geotextile bags, which can buffer the expansion force and weaken the expansion deformation, but have the problems of difficult construction and later maintenanceAnd the problems of complexity and the like. For the physical and chemical modification method, the existing engineering uses two materials of lime and cement, and cations such as Ca in hydration products of the two materials 2+ Can replace and adsorb ions to reduce the content of hydrophilic minerals, ca, in the clay 2+ 、OH - The gelled component formed by the reaction of the gelled component and the clay mineral after penetrating into the soil body can play a role in bridging soil particles and blocking gaps of the soil particles, so that the liquid limit is reduced, and the shear strength of the soil body is increased; the strength and the crack resistance of the expansive soil are successfully improved by doping the expansive soil with nano graphite powder, shell powder, steel slag, lignin fiber, basalt fiber, polypropylene fiber, polyethylene fiber, sawdust fiber and the like by a learner; the disadvantages are that: (1) the common cement modified soil is strongly alkaline and has large influence on the environment, (2) most fibers in the existing research have high cost and are not beneficial to engineering practice, (3) the common modified soil construction method of the existing expansive soil side slope adopts mechanical rough polishing modified soil according to the thickness of a required modified soil layer, then the modified soil is repeatedly rolled to preset compactness by a vibration compactor, and finally the side slope is accurately leveled manually, so that the problems of complicated construction steps, low integral stability of the side slope, remarkable side slope seepage, incapability of ecological slope protection and the like exist.
CN101423353B discloses a method for improving expansive soil by using waste foundry sand and a construction method thereof, which provides an improvement method for changing waste into valuable, but the problems of (1) too large proportion of modified admixture, low economic benefit, poor blending uniformity, (2) general improvement effect on the strength of expansive soil, (3) unclear construction scheme and incapability of ensuring the overall stability and seepage of side slope exist. The patent application of CN102352622A discloses a method for improving expansive soil by alkaline residue and a construction method, which play an important role in the development of the field of expansive soil improvement treatment, but have the following problems: (1) The proportion of the modified admixture is too large, the economic benefit is low, and the mixing uniformity is poor; (2) ecological environmental protection problems are not considered; (3) The alkaline residue obtaining way is single, and the obtaining difficulty changes greatly along with the change of project positions; (4) The construction scheme can not ensure the integral stability and seepage of the side slope. The patent of CN103233458B discloses an expansive soil improved by waste straw ash and marble ash, its preparation method and application in construction, disclosing an economical expansive soil modifying admixture, effectively improving the mechanical properties of expansive soil, and carefully describing the construction method of modified soil, but the following disadvantages exist: (1) the proportion of the modified admixture is large, and the economic benefit is low; (2) ecological environmental protection problems are not considered; (3) the maintenance time of the modified soil is short before construction; and (4) the construction process is complicated. CN103882855B discloses a cement modification and filling construction method for expansive soil, which makes contributions to the construction research of cement modified soil by combining with the actual construction process, but has the following problems: (1) The optimal cement mixing amount measurement standard is single and the mixing material proportion is not determined; (2) ecological environmental protection problems are not considered; (3) curing time of the modified soil is not specified.
Disclosure of Invention
The invention aims to solve the technical problems that the modified expansive soil doping cost is high and ecological protection is not facilitated by the current physical and chemical method, and the like, and provides bagasse fiber composite low-alkali cement modified expansive soil and a construction method thereof applied to a side slope, wherein the compressive strength and the shear strength of the expansive soil can be obviously improved; the swelling deformation and crack development of the expansive soil can be effectively inhibited; the doping material has little influence on the environment and the plant growth, and can realize green slope protection; the integral rigidity and stability of the side slope can be effectively enhanced, and the construction steps of the modified soil of the side slope are normalized.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the bagasse fiber composite low-alkali cement modified expansive soil comprises air-dried expansive soil, low-alkali cement, bagasse fibers and water, wherein the low-alkali cement accounts for 6-8% of the mass of the dried expansive soil, the bagasse fibers account for 0.5-0.9% of the mass of the dried expansive soil, and the dried expansive soil is the expansive soil dried by the air-dried expansive soil in a 105 ℃ oven for 24 hours.
According to the scheme, the mass 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 : adding water to the mixed soil to reach the desired water contentThe soil mixture is prepared by uniformly mixing air-dried expansive soil, low-alkali cement and bagasse fibers;
m 1 : the quality of the air-dried expansive soil in the mixed soil;
ω 0 : air-drying the initial water content of the expansive soil;
ω 2 : expected water content of the mixed soil at omega y -ω p Within range, ω y 、ω p Respectively determining the optimal water content and the plastic limit after a boundary water content test and a compaction test are carried out on the mixed soil.
According to the scheme, 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％。
According to the scheme, the diameters of the bagasse fibers are smaller than 2mm, wherein the bagasse fibers with the 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.
The invention also provides a preparation method of the bagasse fiber composite low-alkali cement modified expansive soil, which comprises the following steps:
s1, taking a plurality of air-dried expansive soil, crushing, sieving by using a 2mm standard sieve, drying bagasse fibers at 70 ℃ for 24 hours, sieving by using a 2mm standard sieve, and weighing m 1 The screened air-dried expansive soil is tested to have the initial water content of omega 0 Weighing the required low-alkali cement and bagasse fibers according to the mass ratio, wherein the mass ratio of the low-alkali cement to the bagasse fibers (admixture) is specific to the drying expansive soil, the drying expansive soil is the expansive soil obtained by drying the air-dried expansive soil in a 105 ℃ oven for 24 hours, and the mass of the drying expansive soil is m 1 ÷(1+ω 0 ) The low-alkali cement accounts for 6-8% of the weight of the dried expansive soil, and the bagasse fiber accounts for 0.5-0.9% of the weight of the dried expansive soil; uniformly mixing the air-dried expansive soil, the low-alkali cement and the bagasse fibers according to a dry mixing method and an external mixing method to form mixed soil;
s2, according to road soil engineering test regulation (JTG 3430-2020), making a limit on the mixed soilWater content test and compaction test to determine the plastic limit omega of the mixed soil p And optimum water cut omega y ；
S3, calculating the expected water content omega of the mixed soil obtained in the step S1 2 To omega y -ω p Mass m of water to be added 0 Mass m of said water to be added 0 Equal to the product of the mass of the dried expansive soil in the mixed soil multiplied by the expected water content omega of the mixed soil 2 Minus the initial water content omega of the air-dried expansive soil 0 A 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, adding water with corresponding mass into the mixed soil obtained in the step S1, uniformly mixing to form a soil sample, and curing the obtained soil sample for 3 days to obtain the modified expansive soil.
According to the scheme, 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.
According to the scheme, when water is mixed and stirred in the step S4, water is uniformly added for at least 3 times to reduce the agglomeration of soil particles; the obtained soil sample curing environment is as follows: the temperature is 20 +/-1 ℃, and the air humidity is 98%.
The invention also provides a construction method for applying the bagasse fiber composite low-alkali cement modified expansive soil to a side slope, which comprises the following steps:
1) Cleaning and leveling the side slope;
2) Using a geocell with a positioning anchor rod anchoring hole as a framework, and filling graded broken stones inwards;
3) Paving the modified expansive soil on the framework and the graded broken stones, and enabling the modified expansive soil to reach the required compaction degree by using a vibratory compactor to form a modified soil layer;
4) And uniformly spraying a mixture of the foreign soil and the grass seeds for slope protection by using the guniting device to form a foreign soil layer, thereby finishing construction.
According to the scheme, the geocell is made of high-density polyethylene, the height of the geocell is 200mm, the welding distance is 800mm, and the thickness of the geocell is 1.5mm.
According to the scheme, the thickness of the modified soil layer is 12-16 cm, and the thickness of the removed soil layer is 9-11 cm.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the bagasse fiber composite low-alkali cement modified expansive soil, the bagasse fibers and the low-alkali cement are used as the expansive soil reinforcement modified admixture, an effective method is provided for physical and chemical modification of the expansive soil, the compressive strength and the shear strength of the expansive soil can be obviously improved, and the expansion-shrinkage deformation and crack development of the expansive soil can be effectively inhibited;
2. the admixture has little influence on the environment and the plant growth, wherein, the bagasse fiber has: (1) the waste is changed into valuable, a large amount of bagasse produced by sugar mills is randomly piled as waste, even fire is caused for many times, resources are wasted, and meanwhile, serious environmental pollution is caused, so that the application of the bagasse to modified expansive soil is equivalent to the consumption of waste to improve engineering cancers; (2) the sources are wide and direct, the sugar factories are widely distributed, and the bagasse can be used as the direct waste of the sugar factories and can be used for modifying the expansive soil without carrying out complex secondary treatment on the bagasse; (3) the price is low, the bagasse is used as the waste material of the sugar refinery and is usually disposed at will or burned, and the acquisition cost is low; (4) the bagasse fibers are doped with expansive soil to act on the side slope, can be used as flexible connection among soil particles at the early stage, play roles in controlling cracking, increasing soil strength and reducing harmomegathus, can be gradually strengthened along with the root system of the slope protection grass at the middle stage, can provide nutrient substances for the growth of the slope protection grass by degradation of the bagasse fibers, and can play a role in flexibly connecting the soil particles after the root system of the slope protection grass grows at the later stage; the low-alkali cement has the characteristic of being more friendly to the ecology than ordinary cement, and the review of the literature shows that the pH value of the common slope protection grass such as tall fescue, evergreen, bluegrass and elymus is in a range of 4.6-8.7, while the pH value of the modified soil doped with 7% of the ordinary cement is 12.9 and the pH value of the modified soil doped with 7% of the low-alkali cement is 8.5 according to agricultural industry standards (NY/T1377-2007), so that the low-alkali cement modified soil is more suitable for the growth of the slope protection grass in an acid-alkali environment obviously;
3. the preparation method of the bagasse fiber composite low-alkali cement modified expansive soil is simple to operate, has high fault-tolerant rate, and can be widely applied to the preparation of similar modified soil;
4. the existing slope construction scheme has the problems of complex operation, poor integral stability, seepage and the like, and the modified soil provided by the invention is applied to the slope construction method, so that the slope modified soil construction steps can be standardized, and the construction is simplified; the geocell with the holes has the characteristics of customization, easy transportation, good construction, wear resistance, stable chemical performance and the like, and can ensure that the side slope forms a stable structure body with strong lateral limitation and large rigidity; the gravel layer, the modified soil layer, the soil dressing layer and the slope protection grass can effectively solve the seepage problem of slope water;
5. the method can realize green protection of the side slope, provides a new idea for the problems of cracking and instability of the shallow layer of the expansive soil side slope, particularly can directly excavate expansive soil on a construction site to manufacture modified expansive soil, and has the characteristics of local materials, simple construction and green protection.
Drawings
FIG. 1 is a flow chart of the preparation of the bagasse fiber composite low-alkali cement modified expansive soil;
FIG. 2 is a graph showing the crack comparison of the low-alkali cement modified expansive soil with different amounts of bagasse fiber mixed with plain soil after 7 dry-wet cycles in example 7 of the present invention;
FIG. 3 is an electron microscope scanning microscopic view of the bagasse fiber composite low-alkali cement modified expansive soil after 7 dry-wet cycles of the doping amount ratio in example 2 of the present invention;
FIG. 4 is a layout view of the expansive soil slope construction structure of the present invention;
in the figure: 1-modifying a soil layer; 2-grass seeds of slope protection; 3-non-expansive alien soil; 4-side slope; 5-graded broken stone; 6-geocell; 7-positioning the anchor rod.
Detailed Description
The following further describes embodiments of the present invention with reference to the accompanying drawings.
The bagasse fiber composite low-alkali cement modified expansive soil comprises air-dried expansive soil, low-alkali cement, bagasse fibers and water, wherein the low-alkali cement accounts for 6-8% of the mass of the dried expansive soil, the bagasse fibers account for 0.5-0.9% of the mass of the dried expansive soil, and the dried expansive soil is an expanded soil prepared by drying the air-dried expansive soil in a 105 ℃ oven for 24 hoursAnd (5) expanding soil. The low-alkali cement is called low-alkalinity sulphoaluminate cement (L.SAC 42.5) and is provided by the cement company Limited of the electrification group, and the components and the proportions thereof are respectively as follows: 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 percent. The bagasse fibers are obtained from a certain sugar mill in Guangxi Nanning, the diameters of the sieved bagasse fibers are smaller than 2mm, and the bagasse fibers with the 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.
As shown in fig. 1, the preparation method of the bagasse fiber composite low-alkali cement modified expansive soil comprises the following steps:
s1, taking a plurality of air-dried expansive soil, crushing, sieving by using a 2mm standard sieve, drying bagasse fibers at 70 ℃ for 24 hours, sieving by using a 2mm standard sieve, and weighing m 1 The screened air-dried expansive soil is tested to have the initial water content of omega 0 Weighing the required low-alkali cement and bagasse fibers according to the mass ratio, wherein the mass ratio of the low-alkali cement to the bagasse fibers (admixture) is specific to the drying expansive soil, the drying expansive soil is the expansive soil obtained by drying the air-dried expansive soil in a 105 ℃ oven for 24 hours, and the mass of the drying 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 the air-dried expansive soil, the low-alkali cement and the bagasse fibers according to a dry mixing method and an external mixing method to form mixed soil;
s2, according to road soil engineering test regulation (JTG 3430-2020), performing a limit water content test and a compaction test on the mixed soil, and determining the plastic limit omega of the mixed soil p And optimum water cut omega y (ii) a The limit water content test adopts a liquid-plastic limit combined tester, and the compaction test adopts a light manual compaction tester;
s3, calculating the expected water content omega of the mixed soil obtained in the step S1 2 To omega y -ω p (ω 2 At omega y -ω p In range) mass m of water to be added 0 Mass m of said water to be added 0 Equal to the product of the mass of the dried expansive soil in the mixed soil multiplied by the expected water content omega of the mixed soil 2 Subtracting the initial water content omega of the air-dried expansive soil 0 A 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, adding water with the corresponding mass into the mixed soil obtained in the step S1, uniformly adding the water for at least 3 times to uniformly mix the water and the mixed soil to form a soil sample, and maintaining the soil sample for 3 days at the temperature of 20 +/-1 ℃ and the air humidity of 98% to obtain the modified expansive soil.
As shown in figure 4, the construction method of the bagasse fiber composite low-alkali cement modified expansive soil applied to the side slope comprises the following steps:
1) Cleaning and leveling the side slope 4;
2) The geocell 6 with holes anchored by a positioning anchor rod 7 is used as a framework, the type of the geocell 6 is TGLG-HDPE-200-800-1.5, the material is high-density polyethylene, the height is 200mm, the welding distance is 800mm, the thickness is 1.5mm, and graded broken stones 5 are filled inwards;
3) Laying modified expansive soil on the geocell 6 and the graded broken stones 5, and enabling the modified expansive soil to reach the required compaction degree by using a vibratory compactor to form a modified soil layer 1 with the thickness of 12-16 cm;
4) The mixture of the non-expansive foreign soil 3 and the grass seeds 2 (such as tall fescue) is uniformly sprayed by a guniting device to form a foreign soil layer with the thickness of about 9-11 cm, and then the construction is finished.
The invention is further described below with reference to three examples.
Example 1:
1. taking the air-dried expansive soil of Guangxi Nanning buffalo for later use, crushing the expansive soil, sieving the crushed expansive soil by a standard sieve of 2mm, and drying the bagasse fiber at 70 ℃ for 24 hours and then sieving the dried bagasse fiber by the standard sieve of 2 mm; weighing the expansive soil, the low-alkali cement and the bagasse fibers which need to be sieved and air-dried according to the mass ratio, and uniformly mixing by adopting a dry-blending and external-doping method; measuring the initial water content of the air-dried expansive soil to be 3.1%, weighing 1500g of the air-dried expansive soil, wherein the low-alkali cement accounts for 6% of the mass of the dried expansive soil, and thus weighing 1500/(1 + 3.1%), 6% =87.3g of the low-alkali cement for later use; the bagasse fiber accounts for 0.5% of the weight of the dried expansive soil, so 1500/(1 + 3.1%) + 0.5% =7.3g bagasse fiber is weighed for standby;
2. according to the highway soil engineering test regulation (JTG 3430-2020), performing a limit water content test and a light compaction test on the mixed soil to obtain the plastic limit omega of the mixed soil p =22.6% and optimum water content ω y ＝22.0％；
3. Calculating the mass of water required to be added for enabling the expected water content of the mixed soil (the admixture expansive soil) obtained in the step 1 to reach 22.0-22.6% to be 275-284 g;
4. uniformly mixing 280g of water into the mixed soil for 3 times, uniformly mixing to form a soil sample, and curing the obtained soil sample at the temperature of 20 +/-1 ℃ and the humidity of 98% for 3 days to obtain the modified expansive soil;
5. side slope construction: (1) cleaning and leveling the side slope 4; (2) anchoring a geocell 6 with holes by using a positioning anchor rod 7 as a framework, and filling graded broken stones 5 inwards; (3) laying modified expansive soil on the soil and using a vibration compactor to achieve the required compaction degree to form a modified soil layer 1 with the thickness of about 15 cm; (4) and uniformly spraying a mixture of the non-expansive foreign soil 3 and the grass seeds 2 to form a foreign soil layer with the thickness of about 10cm by using a guniting device, and finishing construction.
The improvement effect is as follows: according to the highway geotechnical test specification (JTG 3430-2020), a direct shear test, an unconfined compressive strength test, a non-load expansion rate test and a shrinkage test are carried out on the modified soil; carrying out image processing on a photo taken after seven dry-wet cycles of the modified soil cutting ring sample by using PACS (particles and cracks analysis system) software and Adobe Photoshop software developed by doctor Liuchun, university of Nanjing, so as to obtain the fracture rate; the pH value of the modified soil was measured according to agricultural industry Standard (NY/T1377-2007). To obtain: compared with the plain soil, the cohesive force of the expansive soil improved by compounding 6% of low-alkali cement and 0.5% of bagasse fiber is increased by 128.77%, the friction angle is increased by 42.86%, the unconfined compressive strength is increased by 110.19%, the load-free expansion rate is reduced by 19.21%, the linear shrinkage rate is reduced by 21.88%, the crack rate of a seven-time dry-wet cycle circular cutter sample is reduced by 69.23%, the pH value of the modified soil is 8.3, and compared with the pH value of 12.6 of common cement under the same mixing amount, the pH value of the modified soil is reduced by 34.13%. In conclusion, the modified soil is excellent in property, green and environment-friendly, and provides an effective method for treating the common expansive soil problem.
Example 2:
1. taking the air-dried expansive soil of Guangxi Nanning buffalo for later use, crushing the expansive soil, sieving the crushed expansive soil by a standard sieve of 2mm, and drying the bagasse fiber at 70 ℃ for 24 hours and then sieving the dried bagasse fiber by the standard sieve of 2 mm; weighing the air-dried soil, the low-alkali cement and the bagasse fibers to be sieved according to the mass ratio, and uniformly mixing by adopting a dry blending and external mixing method; measuring the initial water content of the air-dried expansive soil to be 3.1%, weighing 1500g of the air-dried expansive soil, wherein the low-alkali cement accounts for 7% of the mass of the dried expansive soil, and weighing 1500/(1 + 3.1%) + 7% =101.8g of the low-alkali cement for later use; the bagasse fiber accounts for 0.7% of the weight of the dried expansive soil, so 1500/(1 + 3.1%) +0.7% =10.2g bagasse fiber is weighed for standby;
2. according to the road geotechnical test specification (JTG 3430-2020), performing limit water content test and light compaction test on the mixed soil to obtain the plastic limit omega of the mixed soil p =22.9% and optimum water content ω y ＝21.2％；
3. Calculating the mass of the water required to be added for enabling the expected water content of the mixed soil obtained in the step 1 to reach 21.2-22.9% to be 263-288 g;
4. uniformly mixing 275g of water into the mixed soil for 3 times, uniformly mixing to form a soil sample, and curing the obtained soil sample at the temperature of 20 +/-1 ℃ and the humidity of 98% for 3 days to obtain modified expansive soil;
5. side slope construction: (1) cleaning and leveling the side slope 4; (2) anchoring a geocell 6 with holes by using a positioning anchor rod 7 as a framework, and filling graded broken stones 5 inwards; (3) laying modified expansive soil on the soil and compacting the soil to a required degree by using a vibration compactor to form a modified soil layer 1 with the thickness of about 15 cm; (4) and uniformly spraying a mixture of the non-expansive foreign soil 3 and the grass seeds 2 to form a foreign soil layer with the thickness of about 10cm by using a guniting device, and finishing construction.
The improvement effect is as follows: according to the highway geotechnical test specification (JTG 3430-2020), a direct shear test, an unconfined compressive strength test, a non-load expansion rate test and a shrinkage test are carried out on the modified soil; carrying out image processing on a photo taken after seven dry-wet cycles of the modified soil cutting ring sample by using PACS (particles and cracks analysis system) software and Adobe Photoshop software developed by doctor Liuchun, university of Nanjing, so as to obtain the fracture rate; the pH value of the modified soil was measured according to agricultural industry Standard (NY/T1377-2007). To obtain: compared with plain soil, the cohesive force of the modified expansive soil improved by compounding 7% low-alkali cement with 0.7% bagasse fiber is increased by 227.94%, the friction angle is increased by 51.02%, the unconfined compressive strength is increased by 128.14%, the unloaded expansion rate is reduced by 19.77%, the linear shrinkage rate is reduced by 37.50%, the crack rate of a seven-time dry-wet cycle annular cutter sample is reduced by 75.00%, the pH value of the modified soil is 8.5, and compared with the pH value of 12.9 of common cement under the same mixing amount, the pH value of the modified expansive soil is reduced by 34.11%.
Example 3:
1. taking the air-dried expansive soil of Guangxi Nanning buffalo for later use, crushing the expansive soil, sieving the crushed expansive soil by a standard sieve of 2mm, and drying the bagasse fiber at 70 ℃ for 24 hours and then sieving the dried bagasse fiber by the standard sieve of 2 mm; weighing the required screened air-dried soil, the low-alkali cement and the bagasse fibers according to the mass ratio, and uniformly mixing by adopting a dry-blending and external-doping method. Measuring the initial water content of the air-dried soil to be 3.1%, weighing 1500g of air-dried expansive soil, wherein the low-alkali cement accounts for 8% of the mass of the dried expansive soil, and weighing 1500/(1 + 3.1%) + 8% =116.4g of low-alkali cement for later use; the bagasse fiber accounts for 0.9% of the weight of the dried expansive soil, so 1500/(1 + 3.1%) + 0.9% =13.1g bagasse fiber is weighed for standby;
2. according to the highway soil engineering test regulation (JTG 3430-2020), performing a limit water content test and a light compaction test on the mixed soil to obtain the plastic limit omega of the mixed soil p =21.7% and optimum water content ω y ＝20.0％；
3. Calculating the mass of the water required for enabling the expected water content of the mixed soil obtained in the step 1 to reach 20.0-21.7% to be 246-271 g;
4. uniformly mixing 258g of water into the mixed soil for 3 times, uniformly mixing to form a soil sample, and curing the obtained soil sample at the temperature of 20 +/-1 ℃ and the humidity of 98% for 3 days to obtain the modified expansive soil;
5. side slope construction: (1) cleaning and leveling the side slope 4; (2) anchoring the geocell 6 with the hole by using a positioning anchor rod 7 as a framework, and filling graded broken stones 5 into the geocell; (3) laying modified expansive soil on the soil and compacting the soil to a required degree by using a vibration compactor to form a modified soil layer 1 with the thickness of about 15 cm; (4) and uniformly spraying a mixture of the non-expansive alien soil 3 and the grass seeds 2 by using a guniting device to form an alien soil layer with the thickness of about 10cm, and finishing construction.
The improvement effect is as follows: according to highway geotechnical test regulation (JTG 3430-2020), direct shear test, unconfined compressive strength test, no-load expansion rate test and shrinkage test are carried out on the modified soil; carrying out image processing on a photo taken after seven dry-wet cycles of the modified soil cutting ring sample by using PACS (particles and cracks analysis system) software and Adobe Photoshop software developed by doctor Liuchun, university of Nanjing, so as to obtain the fracture rate; the pH value of the modified soil was measured according to agricultural industry Standard (NY/T1377-2007). To obtain: compared with plain soil, the cohesive force of the modified expansive soil improved by compounding 8% of low-alkali cement with 0.9% of bagasse fiber is increased by 314.13%, the friction angle is increased by 51.02%, the unconfined compressive strength is increased by 146.88%, the no-load expansion rate is reduced by 20.90%, the linear shrinkage rate is reduced by 56.25%, the crack rate of a seven-time dry-wet cycle annular cutter sample is reduced by 82.69%, the pH value of the modified soil is 8.7, and compared with the pH value of 13.1 of common cement under the same mixing amount, the pH value of the modified expansive soil is reduced by 33.59%.
TABLE 1 comparison of the physical Properties of expansive soils at different admixture ratios
FIG. 2 is a graph showing the crack comparison of the low-alkali cement modified expansive soil with the composite low-alkali cement of the plain soil and the bagasse fibers with different contents after 7 dry and wet cycles of the example of the invention; FIG. 3 is an electron microscope scanning microscopic view of the bagasse fiber composite low-alkali cement modified expansive soil after 7 dry-wet cycles of the doping amount ratio in example 2 of the present invention; the physical property pair ratios of the expansive soil are shown in table 1.
As can be seen from Table 1, the low-alkali cement composite bagasse fiber is doped into the expansive soil, and the physical properties of the expansive soil are changed to a large extent, and the water content is seen from the limit: the liquid limit, plastic limit and optimal water content generally show a trend of decreasing with the increase of the doping amount of the low-alkali cement and the bagasse fiber, and the two main reasons are as follows: (1) produced by hydration of cementCa 2+ Will have a replacement reaction with part of the adsorbed mineral cations and promote the agglomeration of soil particles, thereby improving the water absorption performance and water stability of the soil body; (2) after the low-alkali cement and the bagasse fibers are added, soil body gradation becomes better, compaction performance is better, and plasticity becomes smaller. From the strength point of view: the cohesive force and the unconfined compressive strength of the soil body are obviously enhanced along with the increase of the proportion of the admixture, because: (1) ca in cement hydration products 2+ Ca left after the exchange with low-valence ions in clay minerals is finished 2+ Will continue to react with partial substances in the clay mineral to generate crystal CaO & Al which is not dissolved in water 2 O 3 ·(n+1)H 2 O， CaO·SiO 2 ·(n+1)H 2 O; (2) ca (OH) in cement hydration products 2 Can be mixed with CO in air 2 Reaction to form water-insoluble CaCO 3 The products of the two reactions enable the sheet structure and the pores on the surface of the expansive soil to be bonded by the gelled substance, so that the connection strength between soil particles is increased, the distance between the soil particles is reduced, the agglomeration of the soil body is promoted, and the strength is effectively enhanced by enhancing the bonding between the soil particles and the water stability; (3) the bagasse fibers are bridged among the soil particles, and the tensile and shear resistant effects of the bagasse fibers can effectively increase the strength of the soil body and prevent the development of cracks, so that the strength of the soil body is increased. From the perspective of the collapsible property: as can be seen from the microscopic image of the electron microscope in FIG. 3, most of the soil particles in the plain soil are in a layered structure, and the soil particles are connected in a surface-to-surface manner, so that the distance between the soil particles is easy to increase after multiple dry and wet cycles. As can be seen from Table 1, the no-load expansion rate and the linear shrinkage rate are both obviously reduced along with the increase of the proportion of the admixture, which is mainly because (1) the gelled substance enhances the connection effect among the soil grains and reduces the distance between the soil grains; (2) the soil body particles are wrapped by the gelled substance, so that the contact chance of minerals with strong water sensitivity and water is effectively reduced, and the cementing power of the gelled substance can bear a part of expansion force, so that the expansion and contraction characteristics of the soil body are improved; (3) the bagasse fibers can directly resist the action of soil body force by strengthening the connection among soil particles, and can also inhibit the expansion and contraction deformation of the soil body. From the aspect of crack development: as shown in FIG. 2 and the data in Table 1, the fracture development of the expansive soil increases with the proportion of the admixtureIs significantly inhibited as a result of the interaction of the low alkali cement with the bagasse fibres. In view of the PH: the pH value of the low-alkali cement doped soil is far lower than that of common cement doped soil.
In conclusion, the low-alkali cement and the bagasse fibers have good physical and chemical modification effects on the expansive soil, and all indexes of the expansive soil are improved along with the increase of the proportion of the admixture. But taking into account the following points: (1) common slope grass is suitable for growing in an acid-base environment of 4.6-8.7; (2) the price of the low-alkali cement with the same specification is about 11.9 percent higher than that of the common cement; (3) too much bagasse fiber can cause fiber agglomeration; (4) the strength increase of the second admixture scheme and the third admixture scheme is not significant. Finally, the optimal admixture ratio of 7 percent of low-alkali cement and 0.7 percent of bagasse fiber is determined.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and are merely exemplary embodiments of the present invention, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered in 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 dried by the air-dried expansive soil in an oven at 105 ℃ for 24 hours.
2. The bagasse fiber composite low alkali cement modified expansive soil according to claim 1, wherein the mass of 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 mixed soil is prepared from air-dried expansive soil, low-alkali cement and bagasseMixing the fibers uniformly;
m 1 : the quality of the air-dried expansive soil in the mixed soil;
ω 0 : air-drying the initial water content of the expansive soil;
ω 2 : desired water content of the mixed soil at omega y -ω p Within range, ω y 、ω p Respectively determining the optimal water content and the plastic limit after a boundary water content test and a compaction test are carried out on the mixed soil.
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 bagasse fibers are all smaller than 2mm in diameter, and wherein 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 preparation method of the bagasse fiber composite low-alkali cement modified expansive soil as defined in any one of claims 1 to 4, which is characterized by comprising the following steps:
s1, taking a plurality of air-dried expansive soil, crushing the air-dried expansive soil, sieving the crushed expansive soil by using a 2mm standard sieve, drying bagasse fibers at 70 ℃ for 24 hours, sieving the bagasse fibers by using the 2mm standard sieve, and weighing the bagasse fibers with mass m 1 Measuring the initial water content of the air-dried expansive soil to be omega 0 Weighing the required 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 specific to the dried expansive soil, the dried expansive soil is the expansive soil dried by air in an oven at 105 ℃ for 24 hours, and the mass of the dried expansive soil is m 1 ÷(1+ω 0 ) The low-alkali cement accounts for 6-8% of the weight of the dried expansive soil, and the bagasseThe fiber accounts for 0.5 to 0.9 percent of the mass of the dried expansive soil; uniformly mixing the air-dried expansive soil, the low-alkali cement and the bagasse fibers according to a dry mixing method and an external mixing method to form mixed soil;
s2, according to road soil engineering test regulation (JTG 3430-2020), performing a limit water content test and a compaction test on the mixed soil, and determining the plastic limit omega of the mixed soil p And optimum water cut omega y ；
S3, calculating the expected water content omega of the mixed soil obtained in the step S1 2 To omega y -ω p Mass m of water to be added 0 Mass m of said water to be added 0 Equal to the product of the mass of the dried expansive soil in the mixed soil multiplied by the expected water content omega of the mixed soil 2 Subtracting the initial water content omega of the air-dried expansive soil 0 A 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, adding water with corresponding mass into the mixed soil obtained in the step S1, uniformly mixing to form a soil sample, and curing the obtained soil sample for 3 days to obtain the modified expansive soil.
6. The preparation method of the bagasse fiber composite low-alkali cement modified expansive soil according to claim 5, wherein the limit water content test in the step S2 adopts a liquid-plastic limit joint determinator, and the compaction test adopts a light manual compaction tester.
7. The method for preparing the bagasse fiber composite low-alkali cement modified expansive soil according to claim 5, wherein when the water is blended and mixed in the step S4, the water is uniformly added in at least 3 times in order to reduce the agglomeration of soil particles; the obtained soil sample curing environment is as follows: the temperature is 20 +/-1 ℃, and the air humidity is 98%.
8. A construction method for applying the bagasse fiber composite low-alkali cement modified expansive soil to a side slope, which is characterized by comprising the following steps:
1) Cleaning and leveling the side slope;
2) Using a geocell with a positioning anchor rod anchoring hole as a framework, and filling graded broken stones into the geocell;
3) Paving the modified expansive soil on the framework and the graded broken stones, and enabling the modified expansive soil to reach the required compaction degree by using a vibratory compactor to form a modified soil layer;
4) And uniformly spraying a mixture of the foreign soil and the grass seeds for slope protection by using the guniting device to form a foreign soil layer, thereby finishing construction.
9. The construction method of applying the bagasse fiber composite low-alkali cement modified expansive soil to a side slope according to claim 8, wherein the geocell is made of high-density polyethylene, is 200mm in height, is 800mm in welding distance and is 1.5mm in thickness.
10. The construction method of applying the bagasse fiber composite low-alkali cement modified expansive soil to the side slope according to claim 8, characterized in that the thickness of the modified soil layer is 12 cm-16 cm, and the thickness of the removed soil layer is 9-11 cm.
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