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Introduction of railway subgrade construction scheme?
What is the current railway subgrade construction scheme in China? The following is the railway subgrade construction scheme compiled by Zhong Da Consulting Company for reference.

Adopt the principle of overall arrangement by sections and sections, and organize the construction according to "three stages, four sections and eight processes"; According to the design requirements, in the special construction site, the methods of shoulder wall, cut-off wall and cut-off pile plate retaining wall are adopted for subgrade reinforcement and protection construction.

Before and during the construction, fully consider the influence of rain, and prepare for rain, water and flood prevention to reduce the influence of rain on the construction.

Earthwork allocation should be balanced, economical and reasonable based on the principle of "moving, digging and filling, taking soil nearby, reasonable transportation and standardizing soil abandonment".

Before embankment filling, choose the mechanical type according to different fillers, measure the degree of compaction in time during the filling process, and constantly adjust the process parameters to ensure the degree of compaction of embankment body, especially the transition section. Make a shape, a good one.

Subgrade earthwork is constructed by machinery, and difficult sections are constructed manually with small machines. Excavators, loaders, graders, rollers, bulldozers, dump trucks and other mechanical equipment are mainly used for supporting construction.

Special site sections should be constructed in time to ensure that the construction is carried out in a safe and orderly state.

Standardized and programmed construction operations. The earthwork filling of subgrade adopts the technology of "three stages, four sections and eight processes" to organize the construction.

Three stages: preparation stage, construction stage and acceptance stage;

Four sections: filling area, leveling area, rolling area and testing area;

Eight procedures: construction preparation → basement treatment → layered filling → sprinkling and drying → paving and leveling → rolling and tamping → inspection and visa → subgrade shaping.

In the construction of stone cutting, the overburden is stripped first, and then the blasting construction is carried out.

In order to ensure the quality, weak blasting is the main method, and presplitting blasting is used for the slope.

When widening the existing subgrade, the slope should be brushed along the temporary excavation line and the basement should be treated: before earthwork operation, the slope should be brushed to remove weeds and sundries on the slope surface, and then the basement of the widened section should be treated according to the design requirements, that is, the sandy loess of the original basement should be excavated with an excavator, replaced with pseudo-ginseng lime soil, filled in layers, compacted with a heavy roller, and the compaction degree should be detected with a nuclear densimeter and a K30 load plate. After it is qualified, the widening operation should be started.

Construction method

road embankment

Construction preparation:

Check the design documents, jointly measure the leveling points, retest the control points and encrypt the control points. Restore the center line and survey the boundary markers of the land.

According to the designed soil-taking position, the filler test is carried out to determine the maximum dry density and optimum water content of the filler.

Investigate the operation of existing lines, subgrade conditions and the location of underground pipelines within the construction scope.

Get in touch with the operation department to discuss related matters.

Actively cooperate with local government departments, do a good job in land acquisition and demolition, and build temporary access roads and construction access roads.

A section of subgrade with gentle terrain and satisfying bearing capacity is selected as the test site of earthwork filling process.

Earthwork filling process test:

In order to obtain the parameters of earthwork filling, before the formal construction of embankment, the earthwork filling process test is carried out, and the test section is selected in the double-track bypass section.

Test purpose: Through the on-site earthwork filling process test, determine the suitable materials for subgrade filling, select the appropriate rolling machinery, and determine the relationship between construction water content, rolling times and compaction degree, so as to guide embankment construction.

Test preparation: Test the filler according to the Geotechnical Test Method for Railway Engineering (TBJ 102-96), and get the maximum dry density and optimum water content.

Prepare complete testing instruments and tools, that is, nuclear density meter and sand filling equipment.

For the subgrade determined as the test section, the basement treatment shall be carried out in advance.

Test implementation: transport the selected filler to the prepared test section, level it with bulldozer, control the virtual paving thickness at 25cm, and make the surface smooth. Four continuous sections with a length of 50 meters were laid in the experimental section, and the water content of each section was controlled by drying or sprinkling water to keep different values.

After the filling is completed, it will be rolled by the selected machinery. The roller vibrates after static pressure twice, and the running speed is controlled below 4km/h .. The compactness and water content of each vibrating pressure and each section should be tested. When the detected degree of compaction no longer increases, stop rolling, and then carry out a layer of filling process test, the method is the same as the first layer.

Through the analysis of the test data of two layers, the reasonable water content range of construction control is determined, that is, the upper and lower limit values, and the rolling times of different compaction degrees.

General lot basement treatment:

Before embankment construction, investigate the soil quality and natural environment of the basement within the filling range and deal with it in combination with the design. If it is not specified in the design, the corresponding method shall be adopted according to the actual situation.

The transverse slope is less than 1: 10, and the foundation soil is dense. After the original surface turf is removed, the embankment can be directly filled.

When the cross slope is steeper than 1: 10, in order to ensure the stability of the slope width, the original ground is dug into steps, and the width of the steps is not less than 1 m..

When the in-situ surface layer is cultivated land or loose soil, it should be treated separately according to the thickness of loose soil. When the thickness is less than 0.3m, the in-situ surface shall be rolled to achieve the specified degree of compaction. When the scarification thickness is greater than 0.3m, the scarification shall be excavated, then backfilled and compacted by layers.

In case of paddy fields, ponds or soil with excessive water content, pre-drainage, dredging and replacement should be adopted for treatment.

In addition to the above, there will be other situations. When the design is not clear, report it to the design unit in time and treat it equally with the research.

Foundation treatment in special sections:

Digging and tamping: when the water content of the original basement is high, the original soil should be dug thoroughly and dried to reach the optimal water content, and then the bearing capacity of the basement should be improved by mechanical compaction.

Cement-soil compaction pile: Pile-forming test should be conducted before construction, and at least two piles should be used to determine the construction experience and parameters.

Cement-soil compaction piles are drilled by sidetracking or Luoyang shovel.

According to the selected proportion, mechanical stirring is carried out on site.

Put the mixed material into the hole three times, and the thickness of each layer of loose material is about 65cm.

Each layer of packing is tamped with an olive hammer. Even if the material is dense, the bed will be compacted horizontally and vertically; The top surface of the third floor is tamped with a flat hammer to ensure that the top surface of the pile is flush with the foundation bed.

After tamping the pile top, gradually fill the ballast into the casing, and lift the casing upward while filling until the casing is completely pulled out and the orifice is filled.

The treated foundation adopts standard penetration and static cone penetration to detect the quality of piles. After foundation reinforcement, the bearing capacity of composite foundation shall not be less than 170KPa.

During the construction, the construction organization should be well organized to ensure that the cement completes the mixing of soil and cement, the filling and compaction of piles within the initial setting time.

Laying geogrids: Choose geogrids according to the quality and specifications required by the design. When laying, the surface of the soil layer should be smooth without hard protrusions, and the laying edges should be measured in sequence.

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