Environmental temperature requirements for line slurry and mud maintenance maintenance: First of all, with the progress and development of modern social economy, my country's transportation network is becoming more and more complete. Railway construction is an important transportation construction project in my country. Quality is directly related to people's life safety and the level of regional economic exchanges. In the construction process, roadbed construction is an important basic project, which requires the construction unit to carry out construction based on a full inspection of the construction site environment. However, judging from the current railway operation situation, the phenomenon of roadbed slurry and mud occurs from time to time. Mainly This is because during operation, the railway will not only bear the weight of the railway track and the dynamic load of the rolling stock, but will also be invaded by water flow, wind and sand, rain and snow, severe cold, high temperature, etc. for a long time, as well as various adverse geological conditions and human factors. The impact will lead to changes in the roadbed structure, aggravate the occurrence of slurry and mud problems, and seriously threaten the safety of railway operations. Based on this, this article analyzes the mechanism of slurry and mud generation in railway subgrade and its influencing factors.

Keywords: railway subgrade; mechanism of slurry and mud; influencing factors

CLC number: U216.421 Document identification code: A

Date of receipt : 2020-04-23

About the author: Liu Xiangming (1970- ), male, senior engineer, undergraduate, research direction: construction engineering management.

Slurry is a type of mud that is formed after the base soil is soaked, softened or liquefied by surface water or groundwater. Under the action of the dynamic load of the train, it forms a gap along the track bed ballast and gushes out to the surface. Roadbed disease phenomenon. Once this phenomenon occurs, the technical status of the railway line will change drastically, reducing the operating quality of the line, and a large amount of manpower, physical and financial resources will be invested in subsequent maintenance work. However, due to the softening of the base bed and the hardening of the ballast, the track bed will be damaged. The overall elasticity of the railway roadbed is reduced, resulting in the repaired railway subgrade requiring more resources for later maintenance, which greatly increases the operating cost and poses greater safety risks. Therefore, it is necessary to conduct an in-depth analysis of the mechanism and influencing factors of the phenomenon of slurry and mud in railway subgrade, so that corresponding preventive measures can be taken to further improve the construction quality of railway subgrade.

1 Classification of railway subgrade mud and mud problems and analysis of their mechanisms

1.1 Classification of mud and mud diseases

1.1.1 Soil base surface mud problems

Grouting of soil base generally occurs in embankments and soil cuttings. There is no groundwater in this section or the groundwater is not well developed. This is mainly because the base bed of this section is clay and silty clay, which is not dense and has low strength. Characteristics: Once there is heavy rainfall, mud will enter the track bed due to the slurry under the action of live load. Therefore, this section will often see slurry during the rainy season or after spring thaw, and may even cause serious base subsidence problems [1] .

1.1.2 Rock base surface slurry

The occurrence of rock base surface slurry phenomenon is generally because the roadbed in this section is composed of muddy soft rock, so it is easy to cause The mud is turned under the action of rainwater, live load and track bed grinding. It is usually turned in the rainy season and stopped in the dry season.

1.1.3 Fissure spring muddying

Fifty spring muddying generally occurs in road cuttings or tunnels in mountainous and hilly areas. This road section is an area with relatively developed groundwater, and fissure water in the mud And soft rock weathering is formed under the action of suction, and is brought by pressure water to the base surface to pollute the track bed. Because the terrain of this section is low and the groundwater is well developed, muddying continues all year round, and is more serious in the rainy season.

1.2 Mechanism Analysis

Since the railway subgrade is easily affected by rainfall and groundwater, once surface water or groundwater penetrates into a specific foundation soil, under the action of live load, the pore water pressure Continuous changes will lead to overall softening phenomena such as mud and ballast sinking. The formation process of mud and mud mainly goes through three stages: mud extrusion and rise, combined action of backlog suction and mud and mud formation. The first is the extrusion rising stage. Generally, after the line has been running for a period of time, the load of the train causes the hydrophilic clay soil on the foundation bed or the easily weathered and hydrophilic soft rock to settle unevenly. If it encounters The rainy season will cause rainwater to seep into the machine tool and cause water accumulation. Under repeated action, the soil layer on the foundation bed will soften and form mud, and the mud will rise along the pores of the ballast. If continuous rainfall is severe, the phenomenon of mud and mud will be aggravated; The second is the mud extrusion and suction stage. After the first stage, the machine tool will form a hardened ballast layer due to drying and other factors, which will produce shrinkage cracks. At this time, the mud rises and is affected by two forces. One is the extrusion force. , the other is the suction force. The hardened layer pressurizes the closed mud, which increases the water pressure of the pore mud, and the train will also produce sharp suction during operation, which ultimately leads to the intensification of mud turning and mud turning; the third is mud turning and mud turning. In the formation stage, the mud is squeezed, pumped and raised repeatedly, making the ballast hardening more and more serious. The base bed switches back and forth between dry and wet, and more and more mud is produced, which continuously flows upward through the gaps in the hardening layer. , until the mud overflows the track bed, covers the sleepers, causes water accumulation in the track bed, and causes weeds to grow, seriously affecting the driving safety of the train [2].

2 The main influencing factors of railway subgrade muddying disease

2.1 Subgrade filler

The nature of subgrade filler determines the quality and difficulty of subgrade construction.

If the subgrade filler has good properties and reasonable gradation, the subgrade construction is easy, and the quality of the subgrade filling is easy to control and ensure. On the contrary, if the subgrade filler has poor properties and unreasonable gradation, the construction personnel need to take various measures according to the construction requirements during the subgrade construction process. Improvement measures should be taken to deal with it. Improper treatment will cause construction quality problems. Looking at the current phenomenon of slurry and mud that occurs during railway operation in my country, the general permeability coefficient range of soil base surfaces in frequently occurring areas is 1.05×10-5-9.5×10-7cm/s; the permeability coefficient range of stone base surfaces is It is 4.8×10-5-6.1×10-7cm/s; its mineral composition is mainly illite, montmorillonite or one of them, so it is also necessary to focus on effective improvement of these roadbed fillers. In addition, the strong frost heaving property of silty soil is also the main geology for mud and mud. When it contains more humus and easily soluble salts, the roadbed is more likely to form mud and mud.

2.2 Water

The essence of muddying and muddying in roadbed is the migration and phase change process of water in the subgrade. Therefore, water is also the main factor causing muddying and muddying disease. For the above-mentioned From the analysis of the types of mud and mud diseases, both surface water and groundwater can cause the occurrence of this disease. Surface water will penetrate into the soil of the roadbed through infiltration, greatly reducing the shear strength of the soil, causing many diseases to occur in the roadbed. , mud flooding is the most serious disease; groundwater increases the water content of the roadbed soil in clayey soil and argillaceous rocks, and long-term erosion of the roadbed, coupled with train loads and other external forces, will produce more serious bed mud flooding. Diseases such as mud formation [3].

2.3 Temperature

Temperature is one of the reasons for the mud and mud in the roadbed. Freezing damage is an important temperature factor that causes this phenomenon. It can be said that there is no certain freezing depth or freezing index. It is difficult to form frost heave and muddying of roadbed. Under the conditions of the same freezing depth or freezing index, the characteristics of the freezing speed and the temperature below 0℃ will affect the occurrence of mud turning. For example, in early winter, when the temperature changes alternately between cold and warm, the temperature will range from 0℃ to - If the temperature fluctuates between 5°C and 5°C for a long time, a large amount of water in the roadbed will accumulate very close to the road surface, causing serious mud and mud phenomena; for another example, the temperature will rise in spring, when it begins to thaw. During this period, the soil base will melt rapidly and the roadbed will become muddy and muddy. Based on the above situation, it is because water changes due to the influence of temperature, so compared to water, temperature is an indirect factor [4].

2.4 Train load

Train load is an external factor that causes the subgrade bed to turn mud and mud, mainly because the dynamic stress generated by the train load in the bed is very large, and its The roadbed is unevenly distributed in the forward direction and cross-sectional direction. If the roadbed is subjected to a large load force for a long time, the quality of the roadbed will decrease. Moreover, within a certain range of transportation volume, the transportation volume is related to the muddying and muddying disease of the roadbed. Produces an almost straight-line proportional relationship.

2.5 Defects of the track bed structure

The defects of the track bed structure refer to problems such as insufficient track bed thickness and track bed contamination and hardening. Insufficient track bed thickness will reduce the elasticity of the track bed and cause damage to the roadbed. Uneven force will cause the ballast to invade the road crown after being stressed, causing damage to the road crown surface. After the damage, there will be water accumulation in the center of the road, which will then turn into siltation. Finally, the roadbed will undergo plastic deformation due to the reduction in compaction strength. When After the train passes by, it will cause a certain load on the roadbed. At this time, the silt will be exposed to the surface due to the force, and the phenomenon of slurry and mud will appear. The pollution and hardening of the track bed are mainly due to the cleanliness, gradation and material of the ballast that are not up to standard, thus reducing the Due to its wear resistance and compression resistance, the ballast will be ground into powder when the train passes by. In addition, the carbon ash and other spoils generated after the freight train passes will mix with the powdered ballast, gradually causing the water permeability of the track bed to decrease. The formation of water and silt accumulation will lead to the occurrence of mud and mud.

3 Measures to prevent and control the slurry disease

3.1 Improve the track bed anti-fouling system, maintain it scientifically, and ensure the track bed is clean

Improving the track bed anti-fouling system can reduce track bed pollution For example, adding a protective net on the freight train carriage to prevent cinders from scattering on the track bed; or strengthening maintenance work, regularly treating the track bed, using a wheel screening system for cleaning, and ensuring the quality of the stone if additional stones are needed. .

3.2 Strengthen drainage measures and improve the drainage system

Good drainage can reduce water accumulation in the foundation bed, thereby reducing siltation and reducing the occurrence of mud and mud. For example, in Bury a perforated PVC plastic pipe under the subgrade bed and add a filter layer to eliminate accumulated water in the track bed; if the foot of the subgrade slope is lower than the outer road surface, it is necessary to add no less than 2 inches between the foot of the slope and the edge of the drainage ditch. % slope; for subgrades with high groundwater levels, the influence of groundwater on the subgrade can be reduced by deepening the side ditches on both sides.

3.3 Improving the soil quality of the foundation bed

Improving the soil quality of the foundation bed will also reduce the problem of grouting and mud. Generally, the shallow penetration grouting method is used to treat the foundation bed. In practice, In application, it is necessary to use Tem-106 polymer chemical material to improve the waterproofness and impact resistance of the subgrade surface layer. Tem-106 polymer chemical material will chemically react with the water in the soil and produce high elasticity and high toughness. slurry block, thereby further improving the strength of the foundation bed; in addition, the replacement method is also an important method to improve the soil quality of the foundation bed. Generally, coarse sand, medium sand, graded gravel or improved soil with artificial materials is used as the replacement material [5].

3.4 Reduce the impact of train dynamic load on the foundation bed

Renovate the track structure by adopting heavy rails, increasing the length of sleepers, thickening the thickness of the track bed, enlarging the sleepers and reducing the distance between sleepers. , so as to reduce the upward "pumping" force produced by the dynamic load on the mud, which can also greatly reduce the occurrence of mud turning and mud leaking.

3.5 Improve the temperature environment of diseased subgrade

Most areas in our country have distinct four seasons, especially railway projects in the northern region are extremely susceptible to the influence of temperature, so seasonal frozen soil During the construction of roadbed in areas prone to slurry and mud, attention should be paid to the construction of thermal insulation berms. For example, thermal insulation berms can be built at the foot of the subgrade slope. The surface of the berm can be insulated by mixing sand or EPS insulation boards; As the thaw begins in spring, green plants are planted on road sections prone to spring thaw to reduce the impact of temperature as much as possible.

4 Conclusion

The problem of mud and mud problems in railway subgrades seriously affects driving safety. Therefore, in the current construction of railway engineering projects, construction units are required to strengthen the control of mud and mud diseases. Attention should be paid to the problem. During construction, measures such as improving the anti-fouling system of the track bed, improving the drainage system, improving the soil quality of the foundation bed, reducing the impact of train dynamic loads on the foundation bed, and improving the temperature environment of the diseased roadbed should be taken to prevent the occurrence of slurry and mud. , for railway projects that have been completed and are in operation, maintenance work must be strengthened, and problems must be rectified in a timely manner once problems are discovered. Finally, the occurrence of mud and mud diseases can be avoided, which affects the driving safety of trains and ensure the healthy development of my country's railway industry