A method for jointly reducing the swelling property of phyllite soil by using red clay and lime

Abstract

This application relates to a method for jointly reducing the expansibility of phyllite soil by using red clay and lime. The specific steps are as follows: adding dry red clay with a mass of m1 and lime with a mass of m2 to completely weathered phyllite with a mass of m0 for composite improvement. Denote m1 / (m0 + m1) as the mixing ratio λ of red clay, and denote m2 / (m0 + m1) as the lime content η, to form a mixed filler with a free swell ratio lower than 4% and a swelling force not greater than 125 kPa. The range of the mixing ratio of red clay in the mixed filler is 40% - 60%, and the range of the lime content is 3% - 5%. By incorporating a certain proportion of red clay and lime into phyllite soil, the present invention forms a composite improved soil, greatly reducing the swelling force and free swell ratio, and enabling the compacted subgrade soil to have a certain degree of compactness, making the compacted subgrade not easily pulverized, reducing dust, reducing the dosage of lime by incorporating red clay, and at the same time disposing of this special soil of red clay, reducing engineering waste.

Description

Technical Field

[0001] This application relates to the technical field of selection and improvement of subgrade fillers, and specifically relates to a method for jointly reducing the expansibility of phyllite soil by using red clay and lime. Background Art

[0002] The phyllite soil distributed in the northern part of Jiangxi Province is often associated with red clay. The terrain where phyllite soil and red clay are distributed is low hills. Below the surface is 1 - 6 m thick red clay, and underlying it are tens of meters of phyllite soil. Some hills are distributed in interbedded layers. The free swelling ratio of phyllite soil is not high. According to the "Technical Code for Building in Expansive Soil Regions" (GB 50112 - 2013), it is judged as non - expansive soil. However, the measured expansion force of phyllite soil in Jiangxi reaches 700 kPa when the compaction degree is 95%, and the unloaded swelling ratio reaches 29.15%, which has exceeded the expansibility of "medium - expansive soil" in some literatures. When phyllite soil is used as a subgrade filler, expansibility problems may occur. For example, in a certain section of Jiangshan on the Shanghai - Kunming Line, the foundation is weathered phyllite. In order to form a certain - graded filler in a certain upper layer, a certain amount of phyllite soil was incorporated. As a result, during the operation period, the maximum uplift of the track reached 2.86 cm, causing the high - speed railway to slow down to 40 km / h for operation, and then a large amount of energy and cost were spent on treatment. In addition, the liquid limit of phyllite soil reaches 43.6%. According to the "Code for Design of Railway Subgrade" (TB 10001 - 2016), soil with a liquid limit greater than 40% is a high - liquid - limit Group D filler and is not suitable to be directly used as a subgrade filler.

[0003] Lime is commonly used in the filling of poor soil and is a traditional improvement filler. When using lime to improve phyllite soil, due to the low cohesion and lack of compactness of phyllite soil, the subgrade compaction is not good. It is easy to powder under sunlight, and when the self - unloading truck for transporting the filler walks on it, it is easy to form a loose soil layer and generate dust, causing a lot of inconvenience to the construction. In addition, when using lime to improve phyllite soil, its expansion force is large, that is, it can generate a large upward expansion force, which can cause the track to uplift and have a serious impact on railway operation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for jointly reducing the expansibility of phyllite soil by using red clay and lime. By incorporating a certain proportion of red clay and lime into phyllite soil to form a composite improved soil, the expansion force and unloaded swelling ratio are greatly reduced, and the compacted subgrade soil has a certain degree of compactness, making the compacted subgrade not easy to powder, reducing dust, reducing the amount of lime used by incorporating red clay, and at the same time disposing of this special soil of red clay and reducing engineering waste.

[0005] The technical solution adopted by the present invention is: a method for jointly reducing the expansibility of phyllite soil by using red clay and lime. The specific steps are to add a mass of m 0 of completely weathered phyllite soil with a mass of m1 The dry red clay and the lime with a mass of m 2 are compoundly improved. Denote m 1 / (m 0 +m 1 ) as the admixture ratio λ of the red clay, and denote m 2 / (m 0 +m 1 ) as the lime content η, to form a mixed filler with an unloaded expansion rate lower than 4% and an expansion force not greater than 125 kPa. The range of the admixture ratio of the red clay in the mixed filler is 40% - 60%, and the range of the lime content is 3% - 5%.

[0006] Furthermore, the variation rules of the expansion force P e of the mixed filler, the admixture ratio λ of the red clay, and the lime content η satisfy the following formula:

[0007] When η = 3%, P e = 0.077λ 2 - 8.9152λ + 363.39

[0008] When η = 5%, P e = 0.0642λ 2 - 7.0231λ + 291.52

[0009] When the admixture ratio of the red clay is 40% and the lime content is 3%, the unloaded expansion rate δ ep of the mixed filler drops to 3.25%, and the expansion force P e drops to 125 kPa; when the admixture ratio of the red clay is 60% and the lime content is 3%, the unloaded expansion rate δ ep of the mixed filler drops to 2.15%, and the expansion force P e drops to 100 kPa.

[0010] Furthermore, the unloaded expansion rate and the expansion force of the mixed filler are measured after curing for 28 days.

[0011] The beneficial effects of the present invention are as follows:

[0012] (1) By adding a certain proportion of red clay and lime to phyllite soil, a compound improved soil is formed, greatly reducing the expansion force and the unloaded expansion rate; compared with improving by adding lime alone, the red clay can provide initial cohesion, making the improved soil have better compactness, facilitating compaction accumulation, making the compacted roadbed not easy to pulverize, and reducing dust; at the same time, by adding red clay to reduce the amount of lime, consuming this special soil of red clay, the engineering waste can be reduced;

[0013] (2) When the improvement scheme of 40% red clay + 3% lime is adopted, the unloaded expansion rate is reduced to 3.25%, the decrease rate of the unloaded expansion rate is 25.9%, and the decrease rate is 88.8% of the unloaded expansion rate of phyllite; the swelling force is reduced to 125 kPa, the decrease rate of the swelling force relative to phyllite is 575 kPa, and the decrease rate is 82.1% of the swelling force of phyllite; when the improvement scheme of 60% red clay + 3% lime is adopted, the unloaded expansion rate is reduced to 2.15%, the decrease rate of the unloaded expansion rate is 27%, and the decrease rate is 92.6% of the unloaded expansion rate of phyllite; the swelling force is reduced to 100 kPa, the decrease rate of the swelling force is 600 kPa, and the decrease rate is 85.7% of the swelling force of phyllite; when compound improvement is adopted, the unloaded expansion rate can be reduced to less than 4%, which can meet the control requirements of expansive fillers;

[0014] (3) By adopting the method for reducing the expansibility of phyllite described in the present invention, the red clay and phyllite distributed in interbedded layers in northern Jiangxi can be fully utilized, the amount of waste rock and soil and water loss can be reduced, and important economic and social benefits can be obtained; due to the incorporation of red clay, at least 5% of the lime dosage can be saved compared with pure lime improvement, thereby reducing carbon emissions. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is the flowchart of the method of the embodiment of the present invention;

[0017] Figure 2 It is the variation law of the unloaded expansion rate δ ep with the mixing ratio λ of red clay;

[0018] Figure 3 It is the variation law of the unloaded expansion rate δ ep with the mixing ratio η of lime;

[0019] Figure 4 It is the variation law of the swelling force P e with the mixing ratio λ of red clay;

[0020] Figure 5 It is the variation law of the swelling force P e with the mixing ratio η of lime. Detailed Embodiments

[0021] To better understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0022] Unless otherwise defined, technical terms or scientific terms used herein shall have the ordinary meaning as understood by those of ordinary skill in the art to which this application pertains. The terms "first", "second", and similar terms used in the specification and claims of this patent application do not denote any order, quantity, or importance, but are merely used to distinguish different components. Similarly, terms such as "a" or "an" do not denote a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "coupled" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0023] As Figure 1 shown, a method for jointly reducing the expansibility of phyllite soil with red clay and lime, the specific steps are as follows:

[0024] S1: Add dry red clay with a mass of m 0 and lime with a mass of m 1 to the completely weathered phyllite with a mass of m 2 for composite improvement. Denote m 1 / (m 0 + m 1 ) as the admixture ratio λ of red clay, and denote m 2 / (m 0 + m 1 ) as the lime content η;

[0025] S2: After curing the improved filler with different admixture ratios λ of red clay and lime contents η for 28 days, conduct unloaded expansion rate and swelling force tests, and measure the unloaded expansion rate δ ep and swelling force P e of the improved filler;

[0026] S3: According to the test results of the unloaded expansion rate and swelling force, analyze and obtain the variation laws of the unloaded expansion rate δ ep , swelling force P e with the admixture ratio λ of red clay and the lime content η, and obtain an optimized joint improvement plan.

[0027] In the embodiments of the present invention, the admixture ratio λ of the red clay is 0, 20%, 40%, 60%, 80% and 100% respectively, where 0 is pure phyllite soil and 100% is pure red clay; the lime content η is 0, 3%, 5% and 8%, where 0 means no lime is added. Unloading expansion rate and swelling force tests are respectively carried out on the improved fillers with the above-mentioned admixture ratio λ of red clay and lime content η, and the experimental results as shown in Figures 2 to 5 can be obtained.

[0028] As shown in Figure 2 , when the lime content η is not 0, the unloading expansion rate δ ep decreases non-linearly with the increase of the admixture ratio λ of red clay. When the admixture ratio λ of red clay is less than 60%, the red clay has a more significant influence on the unloading expansion rate δ ep ; when the admixture ratio λ of red clay is greater than 60%, increasing the admixture ratio λ of red clay further has a negligible contribution to reducing the unloading expansion rate δ ep . Therefore, the admixture ratio λ of red clay should not be greater than 60%.

[0029] As shown in Figure 3 , the unloading expansion rate δ ep first decreases rapidly and then tends to be constant with the increase of the lime content η. When the change range of the lime content η is 0 - 3%, the unloading expansion rate δ ep decreases rapidly. When the admixture ratio λ of red clay is 0, 20%, 40%, 60%, 80% and 100% respectively, the values of the unloading expansion rate δ ep decrease by 19.55%, 18.25%, 17.15%, 15.0%, 11.8%, 8.35% respectively; when the change range of the lime content η is 3 - 5%, the corresponding values of the unloading expansion rate decrease by 2.0%, 1.8%, 0.8%, 0.35%, 0.2% and 0.15% respectively; when the change range of the lime content η is 5 - 8%, the corresponding values of the unloading expansion rate δ ep decrease by 2.85%, 0.45%, 0.4%, 0.35%, 0.3% and 0.25% respectively. By comparison, it is found that when the lime content η exceeds 3%, increasing the lime content η further has a very small contribution to reducing the unloading expansion rate δ ep , and increasing the lime content η will significantly increase the project cost. Therefore, the optimal lime content η is 3%.

[0030] As shown in Figure 4 , when the lime content η is 0, the swelling force P e decreases linearly with the increase of the admixture ratio λ of red clay, and the variation law satisfies the following formula:

[0031] P e = 672.62 - 5.6607λ

[0032] At this time, when using red clay alone to improve phyllite soil, there is no optimal mixing ratio of red clay.

[0033] When the lime content η is 3%, the variation law of the red clay mixing ratio λ and the lime content η satisfies the following formula:

[0034] P e = 0.077λ 2 - 8.9152λ + 363.39

[0035] When the lime content η is 5%, the variation law of the red clay mixing ratio λ and the lime content η satisfies the following formula:

[0036] P e = 0.0642λ 2 - 7.0231λ + 291.52

[0037] When the lime content η is 8%, the variation law of the red clay mixing ratio λ and the lime content η satisfies the following formula:

[0038] P e = 0.0485λ 2 - 5.2299λ + 227.23

[0039] According to the above formula, it can be seen that the swelling pressure P e reaches an extreme value when the red clay mixing ratio is about 55%. When the lime content is 3%, the extreme value of the swelling pressure P e is 107.5 kPa; when the lime content is 5%, the extreme value of the swelling pressure P e is 99.5 kPa, and when the lime content is 8%, the swelling pressure P e is 86.3 kPa. Therefore, the optimal mixing ratio of red clay is 55%.

[0040] As Figure 5 shown, when the red clay mixing ratio λ is 40% and 60%, the swelling pressure P e has little difference from the extreme value. Therefore, it can be determined that the optimal mixing ratio range of red clay can be controlled within 40% - 60%, and the swelling pressure P e range is 87.5 - 125 kPa. Figure 5 Overall, the swelling pressure P e decreases with the increase of the lime content η. When using lime alone to improve phyllite soil, when the lime content η is 3%, 5% and 8%, the swelling pressure P e is reduced to 375 kPa, 300 kPa and 255 kPa respectively. Therefore, using lime alone for improvement cannot achieve a good effect of reducing the swelling pressure.

[0041] From Figure 2It can be seen that when using red clay for single improvement, when the mixing ratio λ of red clay is 40% and 60%, the unloaded expansion rate δ ep decreases by 8.75% and 12.0% respectively compared with pure phyllite soil. When the mixing ratio λ of red clay is 40%, the unloaded expansion rate δ ep is 20.4%. When the mixing ratio λ of red clay is 60%, the unloaded expansion rate δ ep is 17.15%. From Figure 3 it can be seen that when using lime for single improvement, when the lime content η is 3%, the unloaded expansion rate δ ep decreases by 19.55% compared with pure phyllite soil. At this time, the unloaded expansion rate δ ep is 9.6%. When using a combination of 40% red clay and 3% lime for improvement, the unloaded expansion rate δ ep decreases by 25.9%. At this time, the unloaded expansion rate δ ep is 3.25%, which is 91.52% of the superposition value of the reduction in the unloaded expansion rate by using 40% red clay for single improvement and 3% lime for single improvement (i.e., 8.75% + 19.55% = 28.3%). When using a combination of 60% red clay and 3% lime for improvement, the unloaded expansion rate δ ep decreases by 27% compared with pure phyllite soil. At this time, the unloaded expansion rate δ ep is 2.15%, which is 85.56% of the superposition value of the reduction in the unloaded expansion rate by using 60% red clay for single improvement and 3% lime for single improvement (i.e., 12% + 19.55% = 31.55%).

[0042] From Figure 4 it can be seen that when using red clay for single improvement, when the mixing ratio λ of red clay is 40% and 60%, the swelling force P e decreases by 275 kPa and 375 kPa respectively compared with pure phyllite soil. When the mixing ratio λ of red clay is 40%, the swelling force P e is 425 kPa. When the mixing ratio λ of red clay is 60%, the swelling force P e is 325 kPa. From Figure 5 it can be seen that when using lime for single improvement, when the lime content η is 3%, the swelling force P e decreases by 325 kPa compared with pure phyllite soil. At this time, the swelling force P e is 375 kPa. When using a combination of 40% red clay and 3% lime for improvement, the swelling force P e decreases by 575 kPa compared with phyllite soil. At this time, the swelling force P eis 125 kPa, which is 95.83% of the superposition value of the reduced swelling force by separately improving with 40% red clay and separately improving with 3% lime (i.e., 325 + 275 = 600 kPa); when jointly improving with 60% red clay and 3% lime, the swelling force P e is reduced by 600 kPa relative to phyllite soil, and the swelling force P e at this time is 100 kPa, which is 85.71% of the superposition value of the reduced swelling force by separately improving with 60% red clay and separately improving with 3% lime (i.e., 325 + 375 = 700 kPa).

[0043] When applied to the engineering subgrade, considering that red clay and phyllite soil often coexist, their density and moisture content are similar. Therefore, the volume ratio of red clay to phyllite soil can be used to replace the mass ratio during on-site mixing. According to the experimental results of the embodiments of the present invention, when the range of the red clay admixture ratio λ is 40% - 60% and the range of the lime dosage η is 3% - 5%, after thorough mixing and then compaction, a mixture filler with a zero-load swelling rate δ ep lower than 4% (i.e., the limit value of the zero-load swelling rate δ ep in subgrade engineering) and a swelling force P e not greater than 125 kPa can be formed.

[0044] In the embodiments of the present invention, by adding a certain proportion of red clay and lime to phyllite soil to form a composite improved soil, the swelling force P e and the zero-load swelling rate δ ep are greatly reduced; compared with separately adding lime for improvement, red clay can provide initial cohesion, making the improved soil have better compactness, which is conducive to compaction accumulation, making the compacted subgrade not easy to powder and reducing dust; at the same time, by adding red clay to reduce the dosage of lime and consume this special soil of red clay, the engineering waste can be reduced. When jointly improving with 40% red clay and 3% lime, the effect of reducing the zero-load swelling rate δ ep and the swelling force P e is better than that of separately improving with 8% lime, which is equivalent to saving 5% of the lime dosage with 40% red clay. Therefore, the cost can be saved and the carbon emission during lime production can be reduced.

[0045] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for jointly reducing the expansibility of phyllite soil by using red clay and lime, characterized in that, the specific steps are as follows: S1: Add dried red clay with a mass of m 0 and lime with a mass of m 1 to the completely weathered phyllite with a mass of m 2 for composite improvement. Denote m 1 / (m 0 +m 1 ) as the admixture ratio λ of the red clay, and denote m 2 / (m 0 +m 1 ) as the lime content η; S2: After curing the improved filler with different mixing ratios λ of red clay and lime content η for 28 days, conduct the unloaded swelling rate and swelling force tests, and measure the unloaded swelling rate δep and swelling force Pe of the improved filler; S3: According to the test results of the unloaded swelling rate and swelling force, analyze and obtain the variation laws of the unloaded swelling rate δep and swelling force Pe with the red clay mixing ratio λ and lime content η, and obtain the optimized joint improvement plan; the specific optimization plan is to incorporate a combination of red clay and lime into the phyllite soil, where the red clay mixing ratio is 40%-60% and the lime content is 3%-5%; under these conditions, a composite filler with an unloaded swelling rate δep < 4% and a swelling force Pe ≤ 125 kPa is formed.

2. The method according to claim 1, characterized in that: The swelling force Pe, the admixture ratio λ of red clay, and the lime content η satisfy the following formula: When η = 3%, Pe = 0.077λ 2 - 8.9152λ + 363.39; when η = 5%, Pe = 0.0642λ 2 - 7.0231λ + 291.52.

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