阅读说明：本技术 一种红黏土、水泥复合改良全风化千枚岩的方法 (Method for improving completely weathered phyllite by compounding red clay and cement ) 是由 赵秀绍 莫林利 饶江龙 付智涛 耿大新 王梓尧 陈子溪 石钰锋 于 2021-07-05 设计创作，主要内容包括：本申请涉及一种红黏土、水泥复合改良全风化千枚岩的方法,具体方法为在质量为m-(0)的全风化千枚岩中加入质量为m-(1)的干红黏土和质量为m-(2)的水泥进行复合改良,形成液限小于40%、碾压后路基面即时极限承载力的安全系数不低于2、沉降量小于15mm和地基系数K-(30)不低于130MPa/m的C组填料混合填料,所述混合填料中红黏土掺合比的范围为25.7%～60%,水泥掺合比的范围为3%～5%。本发明对普通铁路、高速铁路的要求提出了掺合比优选方案,可充分利用红黏土和全风化千枚岩两种特殊土,降低全风化千枚岩的液限和沉降量,提高极限承载力的安全系数和地基系数K-(30),将D组填料变为C组填料,满足路基各方面指标的要求。(The application relates to a method for compositely improving fully-weathered phyllite by red clay and cement, which is characterized in that the mass of the fully-weathered phyllite is m 0 Is added into fully weathered phyllite with mass m 1 Dry red clay and mass m 2 The cement is compositely improved to form a liquid limit less than 40%, a safety coefficient of the instant ultimate bearing capacity of the ground surface after rolling is not less than 2, a sedimentation amount is less than 15mm and a foundation coefficient K 30 The mixed filler of the C group filler is not lower than 130MPa/m, the blending ratio of red clay in the mixed filler ranges from 25.7% to 60%, and the blending ratio of cement in the mixed filler ranges from 3% to 5%. The invention provides a blending ratio optimization scheme for the requirements of ordinary railways and high-speed railways, can fully utilize two special soils of red clay and completely weathered phyllite, reduces the liquid limit and the settlement of the completely weathered phyllite, and improves the ultimate bearing capacitySafety factor and foundation coefficient of K 30 And D group of fillers are changed into C group of fillers, so that the requirements of various indexes of the roadbed are met.)

1. A method for improving fully weathered phyllite by compounding red clay and cement is characterized in that the phyllite is prepared by mixing and modifying red clay and cement₀Is added into fully weathered phyllite with mass m₁Dry red clay and mass m₂The cement is subjected to composite improvement, and m is recorded₁/(m₀+m₁) The blending ratio lambda of red clay is recorded as m₂/(m₀+m₁) The cement admixture ratio eta; the formed liquid limit is less than 40 percent, the safety coefficient of the limit bearing capacity is not less than 2, the sedimentation amount is less than 15mm and the foundation coefficient K₃₀The C group filler mixed filler is not lower than 130MPa/m, the blending ratio of red clay in the mixed filler ranges from 25.7% to 60%, and the blending ratio of cement in the mixed filler ranges from 3% to 5%.

2. The method for improving fully weathered phyllite by compounding red clay and cement according to claim 1, wherein the liquid limit w of the mixed filler is_LThe change rule of the red clay admixture ratio lambda and the cement admixture ratio eta meets the following formula:

η＝3％，w_L＝0.0016λ²-0.1858λ+38.407

η＝5％，w_L＝0.002λ²-0.2327λ+37.975

when the red clay admixture ratio is 40 percent and the cement admixture ratio is 3 percent, the liquid limit w of the mixed filler_LReduced to 33.8%; when the red clay admixture ratio is 60 percent and the cement admixture ratio is 5 percent, the liquid limit w of the mixed filler_LA minimum of 31.1% is reached.

3. The method of claim 1, wherein the red clay and cement composite modified fully weathered phyllite has a red clay admixture ratio of 40%, and a cement admixture ratio of 3%, the mixed filler has a safety factor of 2 in terms of immediate ultimate bearing capacity, the safety factor is increased to 4 after 28 days of curing, the settlement after construction of a 10m embankment is 10.36mm, and the foundation coefficient K is₃₀Is 166.6 MPa/m.

4. The method for improving fully weathered phyllite by compounding red clay and cement according to claim 1, wherein the water content of the mixed filler is 18%, and the compaction coefficient is 93%.

Technical Field

The application relates to the technical field of roadbed filler selection and improvement, in particular to a method for improving fully-weathered phyllite through red clay and cement compounding.

Background

The completely weathered phyllite has wide health in the northern part of Jiangxi province and the northwest part of Zhejiang, and has a great amount of distribution along the upper pithead cargo yard, branch engineering, nine-scene-stock railway, Mongolian railway Yueji section of coal transportation channel and Changjiu railway, and red clay is also attached along the railway.

(1) Problem of completely weathered phyllite as roadbed filling alone

When the completely weathered phyllite is used as roadbed filling, the liquid limit is as high as 43.3 percent, and the fully weathered phyllite is high liquid limit soil. According to TB 10001-2016 railway roadbed design specification, by adopting a 76g cone and a 10mm liquid limit standard, cohesive soil with the liquid limit of more than 40 percent is high liquid limit soil, is D group filler and is not suitable for railway roadbed filling. In a roadbed filling test section, completely weathered thousands of rock-soil are rolled, namely after 2 times of static pressure, 2 times of vibration and 2 times of static pressure, the compaction coefficient is generally not higher than 90%, the bearing capacity of a road base surface after compaction is low, a full-load transport filler automobile is easy to sink into the road base surface, and a half-load filler automobile is not sunk into the road base surface, but can pulverize the smoothly rolled road base surface to cause dust raising, so that the construction conditions of a construction site are deteriorated. In addition, the detection of the fully weathered phyllite roadbed through conventional rolling is difficult to meet the requirement of the compaction coefficient, and the foundation coefficient K₃₀The detection can not meet the requirement of 90MPa/m of the common railway and can not meet the requirement of 130MPa/m of a roadbed bed layer of the high-speed railway, so that the completely weathered phyllite is not suitable to be used as roadbed filling.

(2) Problems faced by red clay alone as roadbed filling

The red clay belongs to a special clay, and has the undesirable physical properties of high dispersibility, high porosity ratio, high natural water content, high liquid limit and the like, and is mainly characterized by high fracture property, high shrinkage and the like. The red clay has a liquid limit of 48.4 percent, belongs to high liquid limit clay, is D group filler, and is not suitable for railway roadbed filling. The red clay has the characteristics of high cohesive force and good water retention, and has good mechanical properties such as higher strength, lower compressibility and the like due to the cementing action of free iron oxide and aluminum, so that the red clay is often used as a better roadbed filler in Jiangxi areas. However, the red clay is easy to crack when dehydrated due to strong expansibility, the maximum cracking width is 2cm after being rolled in a Changbai goods yard, and the maximum cracking depth exceeds 1 m. When precipitation infiltrates into the cracks, the strength of the red clay can be seriously reduced, the red clay is easily argillized under the action of train load, and the bearing capacity is reduced, so that roadbed diseases such as ballast sacs, slurry-turning and mud-pumping are caused.

(3) The problem of improving the fully weathered phyllite by the conventional lime and cement

Lime and cement are commonly used for improving cohesive soil, when the fully weathered phyllite is improved, the strength improvement effect is not ideal, the roadbed surface is difficult to compact, the roadbed surface is rapidly pulverized under the repeated action of tires, and dust is often rolled in field construction, so that a loose soil layer is sandwiched between different rolled layers. Because the strength of the completely weathered phyllite improved by cement and lime is improved, the higher strength can be achieved by 1 day or even several days, the roadbed is continuously constructed, the instant bearing capacity of the rolled roadbed surface is not enough to support a filler-carrying automobile, automobile tires can sink into the roadbed surface, the roadbed surface can be rapidly damaged and pulverized, and the continuous construction of the railway roadbed is seriously influenced. Although the setting speed can be accelerated by increasing the dosage of cement and lime, the construction cost is increased.

(4) Problem of red clay alone improving completely weathered phyllite

The red clay modified fully-weathered phyllite can improve the instant bearing capacity of the fully-weathered phyllite, but the two kinds of special soil are special cohesive soil, the strength is remarkably reduced after the two kinds of special soil meet water, the settlement value after construction is large, and the long-term stability of a high-speed railway roadbed is not facilitated, so that the red clay modified fully-weathered phyllite alone is not suitable to be used as a high-speed railway roadbed filler.

A large amount of completely weathered phyllite and red clay are distributed along a plurality of railways in the Jiangxi province, and if the completely weathered phyllite and red clay are treated as abandoned parties, a large amount of cultivated land is occupied, so that the environmental problem is caused.

Disclosure of Invention

The invention aims to provide a method for improving fully-weathered phyllite by compounding red clay and cement, which can reduce the liquid limit and sedimentation amount of the fully-weathered phyllite, and improve the safety factor of the ultimate bearing capacity and the foundation coefficient K₃₀Changing D group filler into C group filler, overcoming the poor effect of improving the instant bearing capacity by traditional cement improvement and the settlement control and K of red clay improvement₃₀The improvement effect is not good, and the design index requirements of railways, especially high-speed railways can be met.

The technical scheme adopted by the invention is as follows: a method for improving fully weathered phyllite by compounding red clay and cement₀Is added into fully weathered phyllite with mass m₁Dry red clay and mass m₂The cement is subjected to composite improvement, and m is recorded₁/(m₀+m₁) The blending ratio lambda of red clay is recorded as m₂/(m₀+m₁) The cement admixture ratio eta; the formed liquid limit is less than 40 percent, the safety coefficient of the limit bearing capacity is not less than 2, the sedimentation amount is less than 15mm and the foundation coefficient K₃₀The C group filler mixed filler is not lower than 130MPa/m, the blending ratio of red clay in the mixed filler ranges from 25.7% to 60%, and the blending ratio of cement in the mixed filler ranges from 3% to 5%.

Further, the liquid limit w of the mixed filler_LThe change rule of the red clay admixture ratio lambda and the cement admixture ratio eta meets the following formula:

η＝3％，w_L＝0.0016λ²-0.1858λ+38.407

η＝5％，w_L＝0.002λ²-0.2327λ+37.975

the blending ratio of the red clay is 40 percent and the blending ratio of the cement isAt 3%, the liquid limit w of the mixed filler_LReduced to 33.8%; when the red clay admixture ratio is 60 percent and the cement admixture ratio is 5 percent, the liquid limit w of the mixed filler_LA minimum of 31.1% is reached.

Further, when the red clay admixture ratio is 40% and the cement admixture ratio is 3%, the safety coefficient of the instant ultimate bearing capacity of the mixed filler is 2, the safety coefficient is improved to 4 after 28 days of maintenance, the settlement after construction of a 10m high embankment is 10.36mm, and the foundation coefficient K is₃₀Is 166.6 MPa/m.

Further, the water content of the mixed filler is 18%, and the compaction coefficient is 93%.

The invention has the beneficial effects that:

(1) the liquid limit is reduced, so that the completely weathered phyllite becomes a usable filler; the liquid limit of the completely weathered thousand rock-soil is 43.3 percent, and the completely weathered thousand rock-soil is a D group filler according to the requirements of TB 10001-2016 railway roadbed design specification and is not suitable to be used as a roadbed filler; when the blending ratio of the red clay is 40%, the liquid limit is reduced to 38.2%, and after 3% of cement is added for compound improvement, the liquid limit value is reduced to 33.8%; when the red clay admixture ratio is 60 percent and the cement admixture ratio is 5 percent, the liquid limit w of the mixed filler_LReaching a minimum value of 31.1%; the mixed filler is C group filler, and the mixed filler after composite improvement becomes chemical improved filler, which can meet the filling of the foundation bed bottom layer and below of the common railway and the high-speed railway;

(2) the instant bearing capacity of the compacted road base surface is greatly improved; when the conventional improvement method adopts cement or lime to improve the completely weathered phyllite, the cement and the lime need a longer time for hardening, so that the improvement range of the bearing capacity is smaller: the calculated ultimate bearing capacity of the cement mixed with 3 percent for 28 days of curing is 438.1kPa, and the calculated ultimate bearing capacity of the cement mixed with 5 percent for 28 days of curing is 507.7kPa, which can not meet the requirement of the bearing capacity; when 40% of red clay and 3% of cement are adopted for improvement, the ultimate bearing capacity reaches 1498.8kPa after rolling, the ground pressure safety coefficient relative to a truck is not lower than 2, and the bearing capacity can be reached without maintaining time of the roadbed, so that the roadbed construction can be continuously carried out, and the construction period is greatly shortened;

(3) greatly improving the foundation coefficient K₃₀(ii) a The composite improvement is carried out by adopting 40 percent of red clay and 3 percent of cement, and the foundation coefficient K₃₀The requirement of 185.8MPa/m which is larger than 130MPa/m of the high-speed railway foundation bed bottom layer can be met, the filling of the high-speed railway foundation bed bottom layer and the following layers can be met, and the method is suitable for the filling of all the layers of the high-speed railway foundation bed removing surface layer;

(4) the compression modulus of the soil is greatly increased, the post-construction settlement is reduced, when the improvement is carried out by adopting 40% of red clay and 3% of cement, the settlement of the 10m embankment is 10.36mm, the control standard of 15mm of the high-speed railway is met, and a certain safety reserve amount is reserved.

(5) The influence of the abandoned party on the environment is reduced, and the method has great environmental benefit; for the traditional single filler filling method, the completely weathered phyllite is a D group filler, the detection is basically unqualified after filling and rolling, even if lime and a cement modifier are added for improvement, the improved filler is easy to loosen, rise dust and raise dust under the repeated action of a transport vehicle, so the phyllite weathered soil belongs to an unusable filler; after the improved method is adopted, the availability of the completely weathered phyllite reaches 50% -87% of the total fill quantity, the completely weathered phyllite can be largely consumed, the completely weathered phyllite can be fully utilized, and the improved mixed filler is divided into groups C, so that the requirement of roadbed design specifications is met, meanwhile, the influence of the weathered phyllite abandoned parties on the environment is reduced, the method can also be used for roadbed filling of high-speed railways, and the application range of the completely weathered phyllite is greatly expanded;

(6) the gradation is changed, and the compaction work can be reduced when the same compaction degree is achieved; the completely weathered phyllite is broken continuously in a rolling state, but still keeps the original phyllite structure, is in a plate shape or a long column shape, and is easy to form an overhead structure after being compacted, so the compacting is not suitable; the fully weathered phyllite has a grain size of 10-15 um in the length direction and a thickness of 0.5um generally; the particles are in surface-to-surface and angle-to-surface contact, so when the particles are compacted, an overhead structure is formed, and the particles are not suitable for compaction; the red clay particles are granular, the particle size of the red clay particles is usually 1-4 um, and the red clay particles can effectively fill gaps left by completely weathered phyllite, so that the gradation is improved, and the compactibility of soil is increased; after the overhead structure is changed into a compact structure, the contact points of particles are increased, so that the bearing performance is improved; after the cement is added, the cement is hydrolyzed to generate hard setting products such as set cement and the like, a reticular cementing structure is formed, and the compression modulus and the bearing performance of the soil are further improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 shows the liquid limit w after 28 days of curing with mixed filler_LA relation graph of red clay admixture ratio lambda and cement admixture ratio eta;

FIG. 2 shows the liquid limit w of the mixed packing_LAnd cement admixture ratio eta;

FIG. 3 shows the liquid limit w of the mixed packing_LA relation graph of the blending ratio lambda of the red clay;

FIG. 4 is a graph showing the relationship between the compressive modulus of a mixed filler and the cement admixture ratio eta;

FIG. 5 is a schematic diagram of a calculation model of ultimate bearing capacity of a filler-loaded automobile, wherein (a) is a schematic diagram of a basic model of ultimate bearing capacity of an automobile, (b) is a schematic diagram of Taylor ultimate bearing capacity model of ultimate bearing capacity of an automobile, and (c) is a schematic diagram of a bearing capacity model of a roadbed;

FIG. 6 is a graph showing the relationship between the ultimate bearing capacity of the mixed filler and the blending ratio λ of red clay;

FIG. 7 is a graph showing the relationship between the ultimate bearing capacity of the mixed filler and the cement admixture ratio eta;

FIG. 8 (a) shows the ground coefficient K of the mixed filler₃₀A finite element analysis model schematic diagram, wherein (b) is a settlement curve of the bearing plate;

FIG. 9 shows the ground coefficient K of the mixed filler₃₀And cement admixture ratio eta;

FIG. 10 is a ground coefficient K of the mixed filler₃₀A relation graph of the blending ratio lambda of the red clay;

FIG. 11 shows the foundation coefficient K when the cement admixture ratio is 3%₃₀Schematic diagram of the change rule along with the curing days;

fig. 12 shows (a) a scanning electron microscope picture of fully weathered phyllite, (b) a scanning electron microscope picture of fully weathered phyllite + red clay, and (c) a scanning electron microscope picture of the mixed filler obtained by the improved method according to the embodiment of the present invention.

The reference signs explain: 1-imaginary roadbed, 2-destruction surface, 3-roadbed, 4-wheel, 5-rigid loading plate, 6-roadbed soil cylinder model, 7-red clay, 8-completely weathered phyllite and 9-cement reaction product.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application belongs. The use of "first," "second," and similar terms in the description and claims of this patent application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.

As shown in figure 1, a method for compositely improving fully weathered phyllite by red clay and cement, wherein the mass of the fully weathered phyllite is m₀Is added into fully weathered phyllite with mass m₁Dry red clay and mass m₂The cement is subjected to composite improvement, and m is recorded₁/(m₀+m₁) The blending ratio lambda of red clay is recorded as m₂/(m₀+m₁) The cement admixture ratio eta; the formed liquid limit is less than 40 percent, the safety coefficient of the limit bearing capacity is not less than 2, the sedimentation amount is less than 15mm and the foundation coefficient K₃₀The C group filler mixed filler is not lower than 130MPa/m, the blending ratio of red clay in the mixed filler ranges from 25.7% to 60%, and the blending ratio of cement in the mixed filler ranges from 3% to 5%.

Liquid limit w of the mixed filler_LThe change rule of the red clay admixture ratio lambda and the cement admixture ratio eta meets the following formula:

η＝3％，w_L＝0.0016λ²-0.1858λ+38.407

η＝5％，w_L＝0.002λ²-0.2327λ+37.975

according to the fitting formula, when red clay is adopted to improve the fully weathered phyllite, the lambda is 23% -49%, and the liquid limit of soil is lower than 40%, so that the low liquid limit C group filler is obtained. When the cement and red clay are adopted to compositely improve the completely weathered phyllite, the liquid limit can meet the requirement.

When the red clay admixture ratio is 40 percent and the cement admixture ratio is 3 percent, the liquid limit w of the mixed filler_LReduced to 33.8%; when the red clay admixture ratio is 60 percent and the cement admixture ratio is 5 percent, the liquid limit w of the mixed filler_LA minimum of 31.1% is reached.

As shown in FIG. 12, the fully weathered phyllite 8 used in the embodiment of the present invention has a particle size of 10-15 um in the length direction, a thickness of 0.5um, and a particle size of 1-4 um in the red clay 7. The completely weathered phyllite 8 still keeps the original thousand-piece-shaped structure after being crushed, is in a sheet shape and a long column shape, is in point-point contact or point-surface contact after being compacted to form an overhead structure, is not easy to compact, has larger deformation after being stressed when meeting water, and therefore the compacted soil can not meet the standard requirements of railway subgrades. The gradation is obviously changed after the red clay 7 is added, the red clay 7 effectively fills the pores of the completely weathered phyllite 8, the multipoint contact is realized, and the bearing performance is greatly improved. However, the particles of the red clay 7 and the fully weathered phyllite 8 are fine soil, and have larger deformation after meeting water, so that the sedimentation is difficult to control. After 3% of cement is added, the generated cement reaction product 9 is a net-shaped hard coagulation product, pores left by the completely weathered phyllite 8 and the red clay 7 are further cemented, and the strength after meeting water is greatly improved, so that the post-construction settlement can be effectively controlled. And the cement is singly adopted for improvement, and the cement admixture is too little to fill and bond the pores of the completely weathered phyllite 8, so that the bearing performance is improved slightly. Therefore, the composite improvement scheme of doping the red clay 7 and the cement can meet the requirements of various indexes of the roadbed.

(I) liquid limit test and blending ratio optimization method

The liquid limit is an important basis for selecting the engineering filler of the railway roadbed, and according to TB 10001-2016 railway roadbed design specification, when the liquid limit is more than 40%, the filler is high liquid limit soil, is D group filler, and is not suitable to be used as a roadbed filler. The filler C with the liquid limit less than 40 percent can be used as the filler of other layers of the general speed railway except the surface layer of the foundation bed. When chemical improvement is adopted, if other control requirements can be met, the filler can be used for the filler of other layers of the surface layer of the high-speed railway except the foundation bed.

The quality m of completely weathered thousand rock-soil₀For reference, the mass of incorporation is m₁Dry red clay and mass m₂The cement of (1). Memory m₁/(m₀+m₁) The blending ratio lambda of the red clay is converted into percentage; memory m₂/(m₀+m₁) The cement admixture ratio eta is converted into percentage. The blending ratio of the red clay is 0 percent and represents the mass m of the red clay₁The quality m of completely weathered rock-soil₀The ratio of (A) to (B) is 0: 5, the blending ratio of the red clay is 20 percent and represents the mass m of the red clay₁The quality m of completely weathered rock-soil₀The ratio of (1): 4, the blending ratio of the red clay is 40 percent and represents the mass m of the red clay₁The quality m of completely weathered rock-soil₀The ratio of (A) to (B) is 2: 3, the blending ratio of the red clay is 60 percent and represents the mass m of the red clay₁The quality m of completely weathered rock-soil₀The ratio of (A) to (B) is 3: 2, the blending ratio of the red clay is 100 percent and represents the mass m of the red clay₁The quality m of completely weathered rock-soil₀The ratio of (A) to (B) is 5: 0.

in the embodiment of the invention, 2000g of dried and completely weathered phyllite, 1500g of dried red clay and 500g of cement are taken, and the liquid limit test is carried out according to the mixture ratio shown in the table 1. According to the specification of geotechnical engineering test for TB 10102-2018 railway engineering, a 76g cone is adopted in the test, and the depth of penetration of the cone tip into the soil is 10mm as the liquid limit standard of the soil.

TABLE 1 liquid limit test ratio

The test result is shown in figure 1, and the liquid limit w of the mixed filler can be obtained by fitting a plurality of function formulas_LThe change rule of the red clay admixture ratio lambda and the cement admixture ratio eta is shown in the formulas (1) to (3):

η＝0％，w_L＝-3×10^-5λ³+0.0064λ²-0.3404λ+44.806 (1)

η＝3％，w_L＝0.0016λ²-0.1858λ+38.407 (2)

η＝5％，w_L＝0.002λ²-0.2327λ+37.975 (3)

when the cement admixture ratio is 0%, the mixed soil meets the standard of the C-group filler when the red clay admixture ratio is 23-49%. When the cement admixture ratio is 3% or 5%, the standard of the C group filler is met, and the standard of chemical improvement is met, so that the mixed soil with improved cement is suitable for roadbed filling of high-speed railways. As can be seen from fig. 1, when the blending ratio of the red clay is 40%, the liquid limit value of the mixed filler is the lowest and the liquid limit value is lower than 40%, and the vicinity thereof can be taken as a preferable range.

As shown in fig. 2, when the cement admixture ratio is increased from 0% to 3%, the liquid limit value of the mixed filler is remarkably decreased, and when the cement admixture ratio is increased from 3% to 5%, the liquid limit value of the mixed filler is decreased to a small extent, so that when the mechanical properties are satisfied, it is preferable that the cement admixture ratio is 3%.

Consolidation test and sedimentation-based optimization method

In order to calculate the settlement of the filled embankment, a consolidation test is required, and the ingredients of the consolidation test are shown in the table 2. All the compacted soil samples adopt 18% of water content, namely the optimal water content. The dry density after compaction was 1.58g/cm3, i.e. the degree of compaction was 93%.

TABLE 2 ingredient table for consolidation test

The test results are shown in FIG. 3 and FIG. 4, the fully weathered phyllite compression modulus is 8.58MPa, and the consolidation pressure range is 100-200 MPa; the compression modulus is 9.63MPa when the modified clay is 40 percent red clay; the compressive modulus was 17.31MPa when modified with 3% cement. The improvement effect of the cement is superior to that of red clay in the aspect of improving the compression modulus.

As can be seen from fig. 3, the compressive modulus of the mixed filler increases with the increase of the blending ratio of the red clay, but the increase is not large, and even if the blending ratio increases to 60%, the compressive modulus increases only by 32%. As can be seen from fig. 4, the compression modulus of the mixed filler increases with the increase of the cement admixture ratio, and in the case where the fully weathered phyllite is blended with 3% cement, the compression modulus of the mixed filler increases by 130.0% with respect to the fully weathered phyllite. Obviously, the effect of adding cement on improving the compression modulus is far better than that of red clay. When the compressive modulus of the mixed filler is 3% relative to the cement admixture, the increase in the compression modulus is small or no increase as compared with 5% of the cement admixture, and therefore the cement admixture is preferably 3%.

After-construction settlement of the embankment is calculated by applying the post-construction load on the 10m roadbed and adopting a layering summation method, the calculation result is shown in Table 3, the settlement of the completely weathered phyllite is 28.39mm, the settlement of the completely weathered phyllite and 40% red clay is 25.15mm, and the reduction range of the settlement is not obvious. The settlement of the completely weathered phyllite and 3% cement is 13.99mm, which can meet the requirements, but the safe reserve is small. After the composite improvement scheme of completely weathered phyllite, 40% red clay and 3% cement is adopted, the sedimentation amount of the mixed filler is 10.36mm, and the mixed filler has considerable safe storage. The effect of the cement is superior to that of red clay in reducing the sedimentation amount.

TABLE 3 calculated post-construction settlement values for different blending protocols

(III) shear strength test and bearing capacity optimization-based method

The ultimate bearing capacity of the fully weathered phyllite compacted roadbed is only 222.5kPa, which is far lower than the most basic requirement of a lorry with 700kPa, when a transport filler automobile transports fillers thereon, the fully weathered phyllite compacted roadbed is easy to sink into the roadbed 3 or cause the damage of the compacted roadbed, so the fully weathered phyllite compacted roadbed is not suitable to be used as a temporary channel of the transport filler automobile.

The sample preparation method adopts the same proportion as that of the consolidation test, positive pressures of 50kPa, 100kPa, 150kPa and 200kPa are respectively adopted, and then Moore coulomb theory is adopted to obtain the shear strength index of the soil. The specific expression of the Moire coulomb theory is shown in formula (4):

wherein tau is the shear strength measured by a direct shear test, sigma is the positive pressure applied during the test,the internal friction angle of the soil, and c the cohesive force of the soil.

The subgrade is generally compacted in a layering mode, each layer is 30cm generally, each layer of a compacted roadbed surface is used as a temporary passing surface of a filler-carrying automobile, if the bearing capacity cannot meet the requirement, a sunken damage surface 2 can be formed, the automobile is sunk into the roadbed surface, and roadbed construction is affected.

In fig. 5, (a) and (b) show imaginary road surfaces 1 as imaginary planes for establishing a load-bearing model, and (c) show road surfaces 3 as actual road surfaces. From the basic model diagram of the ultimate bearing capacity of the automobile shown in (a) and the taylor ultimate bearing capacity model diagram of the ultimate bearing capacity of the automobile shown in (b) in fig. 5, formula (5) can be obtained:

wherein, P_uThe ultimate bearing capacity of a roadbed surface, b is the basic width of a Taylor ultimate bearing capacity calculation model, gamma is the volume weight of soil below the basis, and gamma is₀The weighted average volume weight of soil above the foundation, d the buried depth of the foundation and c the cohesive force of the soil; n is a radical of_γNq and Nc are angles of friction with the soilThe related bearing capacity coefficient is calculated by the following method:

considering that the wheel 4 is the surface directly acting on the road surface 3, the base burial depth d is 0, and therefore γ₀d is 0, i.e., the second term in formula (5) is 0. According to CJJ37-2012 specification of urban road engineering, as shown in fig. 5 (c), the action of the truck wheel 4 and the ground can be equivalent to a circle with a diameter D of 0.213m, so equation (5) can be modified to equation (9):

according to the 'CJJ 37-2012 urban road engineering design specification', the bearing capacity requirement of the truck on a road surface is determined to be 700kPa by BZZ-100 standard load, and the road surface is considered as a temporary passing surface, so that the conventional safety factor 3 of Taylor is not required, and the safety factor is sufficient only by taking 2. The limit bearing capacity of the roadbed surface can be calculated based on the lorry according to the formula (9), and the calculation results are shown in fig. 6 and 7, so that the red clay is better than cement in the aspect of improving the limit bearing capacity of the roadbed.

As shown in FIG. 6, the limit bearing capacity of the fully weathered phyllite is only 222.48kPa, which is less than the ground pressure of the truck-packed vehicle, so that the truck-packed vehicle can sink into the roadbed surface, and the roadbed surface is damaged. After 40% of red clay is doped into the completely weathered phyllite, the ultimate bearing capacity reaches 1498.88kPa, which is 2 times of the required load, so that the temporary passing requirement of the lorry can be met. The requirement can be met even if 40% red clay is doped without cement, and the improvement does not require curing time.

As shown in fig. 7, after 5% of cement is added into the fully weathered phyllite and the fully weathered phyllite is cured for 28 days, the ultimate bearing capacity is 507.66kPa, which still cannot meet the requirement, that is, the effect of improving the bearing capacity by using cement is not good, and the requirement of a filler-carrying automobile cannot be met.

Comparing fig. 6 and fig. 7, it can be seen that the effect of improving the ultimate bearing capacity of the red clay is far better than that of the cement. The method comprises the steps of selecting 40% of red clay and 3% of cement for composite improvement, and performing grinding to obtain an instant bearing capacity, wherein the bearing capacity provided for a filler-carrying automobile is 1498.9kPa, and the safety coefficient of the instant bearing capacity is 2; the ultimate bearing capacity is 2848.70kPa after 28 days of maintenance, the safety factor reaches 4, and the pavement surface can be ensured to be used as a temporary channel due to large safe storage. And it can be obtained by linear interpolation, when the cement admixture ratio is 3%, the red clay preferably has an admixture ratio of 25.7%.

Foundation coefficient K₃₀Value analysis method and method based on K₃₀Optimization methodMethod of

Coefficient of foundation K₃₀The value is through K₃₀The tester tests that a rigid bearing plate with the diameter of 30cm is placed on a roadbed surface, then the bearing plate is loaded in stages, the loading strength of each stage is 0.04MPa, and the average sedimentation of the bearing plate exceeds 1.25mm, and the sedimentation curve is obtained as shown in (b) in figure 8.

As shown in FIG. 8 (a), the foundation coefficient K was constructed using Midas finite element software₃₀The model adopts a roadbed soil cylindrical model 6 with the diameter of 3m and the height of 3m to prevent the influence of boundary effect on the middle load bearing plate, and a rigid load bearing plate 5 with the diameter of 30cm is arranged in the middle.

The foundation coefficient K of the roadbed can be calculated through the formula (10)₃₀：

Wherein p is the corresponding load when the settling amount s reaches 1.25 mm.

Applying graded load on the load bearing plate, wherein each grade of load is 0.04MPa, and the load settlement exceeds 1.25mm, and calculating the foundation coefficient K of different blended fillers according to a load-settlement curve of numerical analysis and a formula (9)₃₀The results are shown in FIGS. 9 and 10. When the compaction coefficient is 93 percent and the water content is 18 percent, the foundation coefficient K of the fully weathered phyllite compacted roadbed₃₀The pressure is 78.59MPa/m, is lower than the requirement of 89MPa/m below the foundation bed of the ordinary speed railway, and is lower than the requirement of the surface layer of the foundation bed of the high-speed railway of 130 MPa/m. Improved with 40% red clay, K₃₀The pressure is increased to 91.53MPa/m, the filling requirements of the foundation bed bottom layer and the layers below the foundation bed bottom layer of the ordinary speed railway can be met, but the requirements of the high-speed railway cannot be met. 3 percent of cement is adopted for improvement, and the foundation coefficient is K₃₀Is 109.18MPa/m, and can not meet the requirement of the high-speed railway bed bottom layer. In the improvement of foundation coefficient K₃₀In the aspect of value, the cement effect is superior to that of red clay, and after the cement is compositely improved by selecting 40 percent of red clay and 3 percent of cement, the foundation coefficient K₃₀Is 166.6 MPa/m.

As shown in FIG. 9, 3% or 5% of the total amount of the additive is addedCoefficient of cement foundation₃₀The requirement of the high-speed railway bed bottom layer is met: foundation coefficient K of foundation bed bottom layer₃₀The foundation coefficient K is required to be 130MPa/m and is below a foundation bed₃₀110MPa/m is required, but since 5% of the cement admixture causes waste, the cement admixture is preferably 3%.

As shown in FIG. 10, the foundation coefficient K of the fully weathered phyllite is increased even if more red clay is added₃₀Can only meet the requirement of 90MPa/m of the general-speed railway roadbed but can not meet the requirement of the high-speed railway roadbed. And the fully weathered phyllite and red clay mixed soil doped with 3 percent of cement has all foundation coefficients K₃₀All can meet the requirements. Considering the influence of the curing age, the foundation coefficient K is required to be within a short time₃₀The red clay blending ratio of the layer below the high-speed railway bedding foundation layer is preferably 40%, the red clay recommended blending ratio of the high-speed railway bedding foundation layer is preferably 60%, and the red clay blending ratio of the common-speed railway is preferably 20%.

In summary, the preferable range of the selection index of the railroad bed is shown in table 4:

TABLE 4 preferred range of railway roadbed selection index

As shown in Table 4, the liquid limit, bearing capacity, sedimentation amount and foundation coefficient K of the obtained mixed filler after the fully weathered phyllite is compositely improved by the method of the embodiment of the invention₃₀All indexes need to meet corresponding standard requirements. For a high-speed railway, compound improvement must be adopted, and the cement mixing amount is not less than 3%, the red clay mixing amount is not less than 25.7%, and the preferable scheme is a combination scheme of 3% cement and 40% red clay.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.