What are the construction techniques for railway subgrade reinforcement and waterproofing?

Recently, with the continuous acceleration of railway construction in China, the networks of conventional and high-speed railways have been continuously improved. As the core load-bearing structure of railway lines, the roadbed directly affects the safety, stability, and comfort of railway operation. The railway subgrade is subjected to the repeated effects of train loads for a long time, and is also affected by natural factors such as precipitation, groundwater, and geological conditions, which can easily lead to subgrade settlement, slope collapse, erosion and other diseases. In severe cases, it can affect the normal passage of trains and even cause safety accidents. The reinforcement and waterproofing construction technology of railway subgrade, as the core means of preventing subgrade diseases and ensuring subgrade quality, directly determines the service life and operational safety of railway subgrade based on its application level.

The construction technology of railway subgrade reinforcement and waterproofing is a systematic construction technology system. The core is to improve the bearing capacity and stability of the subgrade through scientific reinforcement methods, and reduce the erosion and damage of the subgrade by water through reasonable waterproofing and drainage measures. The two complement and work together to ensure the long-term stability of the railway subgrade. Industry experts suggest that railway subgrade construction should follow the principle of "prevention first, combination of prevention and control, and adaptation to local conditions". Based on the geological conditions, hydrological environment, and railway grade of the subgrade, targeted reinforcement and drainage technologies should be selected to ensure construction quality meets regulatory requirements and prevent subgrade diseases from the source.

The railway subgrade reinforcement technology is mainly used to improve the bearing capacity, deformation resistance, and stability of the subgrade, and is suitable for scenarios such as soft foundation, high slope, and subgrade settlement. Common reinforcement technologies include replacement reinforcement method, compaction reinforcement method, pile reinforcement method, and geosynthetic material reinforcement method, each of which has its specific scope of application and construction points.

The replacement and reinforcement method is a widely used and technically mature foundation method in railway subgrade reinforcement, suitable for reinforcing subgrade bases with low bearing capacity such as soft soil layers and miscellaneous fill soils. This technology excavates the poor soil layer within a certain depth range of the roadbed base and replaces it with high-quality filling materials with high strength, good stability, and strong permeability, such as graded sand and gravel, lime soil, plain concrete, etc. After layered rolling and compaction, a reinforcement layer that meets the requirements is formed, thereby improving the bearing capacity of the roadbed base and reducing roadbed settlement. In the construction of a certain ordinary speed railway subgrade, in response to the problem of insufficient bearing capacity of the base silty soil, the construction unit adopted the method of replacing graded sand and gravel for reinforcement, with a replacement depth controlled at 1.2 meters. After rolling and compacting, the bearing capacity of the subgrade was significantly improved, effectively avoiding the hidden danger of subgrade settlement in the later stage.

The compaction reinforcement method is mainly used for shallow roadbed reinforcement, which reduces soil porosity, increases soil compactness, and improves the deformation resistance and stability of the roadbed through mechanical or manual compaction. The commonly used methods include heavy hammer compaction and dynamic compaction. Heavy hammer compaction is suitable for reinforcing shallow silty soil, silty soil and other roadbeds. The compaction depth is generally 1.5-3.0 meters, and the construction is convenient and the cost is moderate; The dynamic compaction method is suitable for reinforcing deep soft foundations. The impact force generated by the free fall of a large heavy hammer from a high place makes the deep soil compact, greatly improving the bearing capacity of the roadbed. It is suitable for scenarios such as high-speed railway roadbeds that require high bearing capacity. Before construction, it is necessary to conduct a trial compaction to determine a reasonable number of compaction times, compaction spacing, and compaction depth to ensure the reinforcement effect.

The pile reinforcement method is suitable for scenarios such as deep soft foundations and high fill roadbeds. By setting piles in the roadbed and sharing the load with the roadbed soil, the stability and bearing capacity of the roadbed are improved. Common types of piles include CFG piles, cement soil mixing piles, gravel piles, etc. CFG piles (cement fly ash gravel piles) have the characteristics of high bearing capacity, convenient construction, and good economy, and are widely used in high-speed railway subgrade reinforcement. By mixing cement, fly ash, gravel and other materials and pouring them into piles, a composite foundation is formed with the subgrade soil, effectively reducing subgrade settlement; Cement soil mixing piles are suitable for reinforcing soft soil foundations. By using mixing machinery to evenly mix cement with roadbed soil, cement soil piles are formed to enhance the overall integrity and stability of the roadbed.

Geosynthetic material reinforcement method is a new reinforcement technology widely used in recent years. It mainly uses materials such as geogrids, geotextiles, and geomembranes, which are laid inside or on the surface of the roadbed. Through the tensile and shear properties of the materials, the overall integrity and deformation resistance of the roadbed are enhanced, while also playing an auxiliary role in filtering and drainage. Geogrid is commonly used for reinforcing roadbed slopes and overall roadbed reinforcement. When laid in roadbed fill, it can effectively constrain the deformation of the fill and improve the bearing capacity of the roadbed; Geotextile is mainly used for roadbed filtration to prevent the loss of roadbed soil particles and protect the roadbed structure.

Compared with reinforcement technology, the construction technology of railway subgrade waterproofing and drainage is equally crucial. Water is one of the main factors causing subgrade diseases. Rainwater erosion and groundwater immersion can cause softening of subgrade soil, decrease in bearing capacity, and subsequently lead to problems such as subgrade settlement and slope collapse. Railway subgrade waterproofing and drainage technology is mainly divided into two categories: surface waterproofing and drainage, and underground waterproofing and drainage, covering multiple aspects such as drainage systems and waterproofing facilities. The core is to timely discharge surface water and groundwater within the subgrade range to avoid water erosion of the subgrade.

Ground waterproofing and drainage technology is mainly used to remove surface water from the roadbed surface. Common measures include roadbed slope drainage, roadbed top drainage, and surrounding drainage systems. The drainage of roadbed slopes is mainly achieved by setting up facilities such as slope rapids and drainage ditches to quickly discharge rainwater on the slope surface, preventing rainwater from washing the slope and causing slope collapse; The drainage on the top surface of the roadbed is achieved by setting up road arches and drainage ditches to ensure that there is no accumulated water on the top surface of the roadbed and to prevent rainwater from seeping into the interior of the roadbed; The drainage around the roadbed is achieved by setting up side ditches, intercepting ditches, etc., to intercept surface water around the roadbed and prevent it from flowing into the roadbed area. In the construction of a railway in a certain mountainous area, the construction unit combined the characteristics of concentrated precipitation and steep slopes in the mountainous area to set up rapid flow channels and drainage ditches on the roadbed slopes, and set up interception ditches around the roadbed to effectively discharge surface water and prevent slope erosion and roadbed softening problems.

Underground waterproofing and drainage technology is mainly used to remove groundwater inside the roadbed, lower the groundwater level, and avoid groundwater soaking the roadbed. Common measures include infiltration ditches, infiltration wells, blind ditches, and waterproof isolation layers. Infiltration trenches and wells are mainly used to remove underground water, by setting permeable materials inside the roadbed to collect groundwater and discharge it out of the roadbed; Blind ditches are suitable for internal drainage of roadbeds. By laying permeable materials such as gravel and pebbles, underground drainage channels are formed to discharge the seepage inside the roadbed; The waterproof isolation layer is used to prevent groundwater from seeping into the top surface of the roadbed. Commonly used materials such as geomembranes and waterproof rolls are laid on the top surface of the roadbed to form a closed waterproof barrier, which is suitable for roadbed areas with high groundwater levels.

The reporter learned that quality control of railway subgrade reinforcement and waterproofing construction is particularly important. Construction units need to strictly follow industry standards, conduct geological surveys before construction, control construction processes during construction, and conduct post construction effect testing. Before construction, it is necessary to clarify the geological conditions and hydrological environment of the roadbed through geological drilling, hydrological monitoring, and other methods, providing a basis for the selection of reinforcement and waterproofing technologies; During the construction process, it is necessary to strengthen the control of material quality and construction technology, such as the proportion of reinforcement materials, compaction parameters, size and slope of drainage facilities, all of which must meet the design requirements; After the construction is completed, it is necessary to test the effectiveness of roadbed reinforcement and the drainage capacity of the drainage system to ensure compliance with regulatory requirements and provide guarantees for the long-term safe operation of the railway.

Industry experts say that with the development of high-speed and heavy-duty railway construction, the requirements for roadbed reinforcement and waterproofing construction technology are constantly increasing. In recent years, the application of new materials and construction equipment, such as high-strength geosynthetic materials, intelligent compaction equipment, and automated drainage systems, has further improved construction efficiency and quality. In the future, we will further promote the refinement and intelligent development of railway subgrade reinforcement and waterproofing and drainage technology, combine BIM technology and intelligent monitoring methods, optimize construction processes, improve technical standards, and provide strong support for the high-quality construction of railway engineering in China, helping to create a safe, efficient, and durable railway transportation network.