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Discussion on construction technology of silt subgrade filling?
In highway subgrade construction, the key point is the selection of subgrade filler. Generally speaking, the choice of filler and construction technology are often quite different. Combined with the concrete construction example of highway subgrade, it is suggested to discuss the concrete construction technology of fine sand as subgrade filler.

1 project overview

This project is a highway construction project. The total earthwork of this project reaches 1.46 million cubic meters. According to the design requirements, the subgrade of this project is filled with aeolian sand. Aeolian sand is widely distributed in the project area. The concrete construction technology of filling subgrade with fine sand is introduced below.

Construction technology of filling subgrade with 2 powder fine sand

2. 1 construction process

Fine sand filling construction is carried out in this project, and the specific construction process is: construction preparation → excavation and transportation, filling → paving and leveling → rolling → compactness detection → surface water replenishment and rolling → next construction.

2.2 construction points

(1) Construction preparation. Before the formal filling construction, the center line should be set out on the subgrade according to the requirements of design drawings. In general, a pile is set every 20m. Then, anchor piles are driven at appropriate positions on both sides of the subgrade. Then, according to the elevation of the top surface of each filling layer, the sideline of each layer of fine sand filling is released. The released padding edge needs to be positioned with bamboo poles. In general, a bamboo pole is set every 20m. Clear marks need to be set on bamboo poles. The length of the bamboo pole used is generally about 60cm. (2) Virtual paving thickness. Generally speaking, the compaction technology of fine sand is obviously different from the traditional subgrade filling technology. Generally speaking, the water sedimentation method is used for the compaction of fine sand. If the traditional rolling technology is used to compact fine sand, the effect is not obvious. After the process test in the construction site, if the water content of fine sand meets the requirements, the compactness of fine sand can also meet the relevant requirements, and it only needs to be rolled by a roller for 2 ~ 3 times. If the roller is used for excessive rolling, it will have adverse effects and cause problems such as loose fine sand.

(3) elevation control. At the construction site, the original elevation is taken as the original elevation after the original ground is compacted. After the construction of fine sand, the loss of surface moisture will lead to the problem of loose surface of fine sand, so it is meaningless to detect the elevation of each layer of fine sand after the completion of filling construction. In general, the elevation and filling thickness need to be detected once every five layers of silt are filled, and the deviation of subgrade centerline needs to be detected. If deviations are found, they need to be corrected. (4) Control the amount of soil. The amount of filler required for each filling section should be determined by comprehensively considering the virtual paving thickness, average width and length of each layer. Then, according to the transport capacity of the hauling vehicles, the number of vehicles required for the filling construction of each road section is determined.

(5) soil. This project uses large-tonnage dump trucks to transport fine sand. Dump trucks purchased at the construction site should be of the same model as far as possible. When the dump truck transports fine sand to the construction site, it can be unloaded according to the determined spacing and the number of vehicles. When unloading fine sand, water should be sprayed in time. In the process of fine sand transportation, traffic organization and command should be carried out reasonably to avoid traffic congestion. (6) Leveling and watering. Fine sand should be leveled when it is discharged to the construction site. In the process of leveling, the method of leveling soil side by side should be adopted, which can effectively control the thickness of virtual paving. First, bulldoze the fine sand. In the process of rough leveling, attention should be paid to timely watering and wetting. In the process of leveling, in order to control the virtual paving thickness, the method of hanging lines should be adopted. This can effectively ensure that the sideline is straight and the slope is consistent. In the process of watering and wetting, special attention should be paid to the adequacy of water sources; When the first layer of silty fine sand is watered, the method of layered and divided watering should be adopted to avoid adverse effects on subgrade caused by too much watering at one time; Water should be completely uniform.

(7) Rolling. When the fine sand is watered to meet the water content requirements, a grader can be used for fine leveling. Then the fine sand is rolled by vibratory roller, and the static pressure method is adopted. This project should be rolled from outside to inside and from low to high. Roller tracks should be staggered by half a wheel width. Generally, it needs to be rolled twice. If there are obvious wheel tracks on the subgrade, the roller should be used to quickly roll the large row of shafts 1 time to eliminate the wheel tracks. (8) Other requirements. In order to effectively ensure the compactness of silt subgrade, especially the compactness of silt at the edge of embankment, each side of subgrade should exceed the design width of embankment, and the width of the excess part is generally controlled at 30cm. At the same time, water the silt in advance to keep it moist. Water evenly. (9) Compaction degree detection. Compared with traditional subgrade filler, fine sand can not achieve good results by using heavy standard compaction method. Its testing principle is quite different from the field construction technology. It is generally believed that the relative density method is used to detect the standard dry bulk density of fine sand. According to the relevant engineering practice experience, we can know that this is a practical method in the construction site.

3 key factor control

(1) Water content control. In fine silt, the water content is closely related to the compactness of filler. If the water content of fine silt is too small and the interior is loose, the relative displacement of soil particles is not easy, and the compactness can not meet the specification requirements. If the water content is too large, free water will appear in the gaps between soil particles, which will affect the compaction effect of soil. Therefore, in the construction of fine sand filling, the key point should be to control the sprinkler problem. If the water spray is uneven, it will lead to the problem of insufficient compaction of fine sand. (2) Fine silt oozes water. When the silt subgrade is filled to a certain height, part of the water in it will gradually seep out of the slope, causing the toe of the slope to collapse. Therefore, in the process of sprinkling water, the sprinkling amount of fine sand should be strictly controlled. At the same time, appropriate drainage measures should be taken to protect the subgrade slope and the toe of the service road. (3) Selection of machinery and related control parameters. In the rolling construction of this project, heavy vibratory roller and YCT25 impact roller are selected according to the specific conditions of the project. According to the rolling condition of this project, the silt surface is usually in a loose state of 3 cm ~ 5 cm, and the silt at a depth of 5 cm ~ 15 cm can meet the requirements of the specification for compactness. In order to ensure the compaction effect, after determining the compaction machinery, the compaction thickness and edge should also be determined according to the specific conditions of the project. As shown in table 1, it is a comparison table of compaction thickness and rolling times selected by soil analysis and machinery.

4 conclusion

The construction of subgrade filler is one of the important links in subgrade construction, and its construction quality directly affects the quality of subgrade. Combined with a highway construction project, it is pointed out that there is a lot of aeolian sand around the project, so aeolian sand is used to fill the subgrade. The implementation effect of this project shows that using aeolian sand to fill subgrade can effectively save materials and speed up the construction progress.

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