The embankment, embankment and embankment base shall be compacted according to the specified requirements. Subgrade compaction is a key process to ensure the strength and stability of subgrade, and it is also a heavy task in subgrade construction. Therefore, roadbed compaction should be organized according to the pressure test results of the test section to ensure quality, improve efficiency and reduce costs.
The effect of roadbed compaction is affected by many factors, mainly including the nature of the soil, the compaction method, and the strength (stiffness) of the foundation or underlying layer. In order to make compaction work economically and effectively, compaction machinery should be reasonably selected according to the type of soil, compaction requirements, mechanical properties and site conditions to control the thickness and humidity of the compacted soil and determine the corresponding compaction Number of passes and operation rules, and check the compaction quality in layers
At present, there are many types of compaction machinery. According to the principle of action, they can basically be divided into three categories: static grinding, tamping and vibration. The working characteristics and use occasions of the machine should be considered when selecting the machine. The static roller compactor relies on its own quality, and its compaction capacity is reflected in the relative layer thickness by linear load, rolling times and compaction speed. The compaction thickness does not exceed 25cm, and the rolling speed is 2-4km/h. It takes 8-10 times of rolling to meet the requirements; while the vibratory roller acts on the soil through the impact force generated by the high-frequency vibration of the vibrating wheel, forcing changes in the arrangement of the particles in the soil, causing small particles to penetrate into the pores of the large particles, Achieve compaction effect. Due to the large excitation force, the compaction thickness of the vibratory roller can reach 50-60cm, and the compaction thickness of some heavy-duty vibratory rollers above 20t can even exceed Im, and the compaction speed is 4-6km/h. The compactness required by the standard can be achieved by pressing 4-6 times, and the construction efficiency is 2^-3 times that of the static roller compactor. In order to effectively improve the construction progress, vibratory rollers should be considered in some areas with longer high-cold periods and shorter construction seasons; and static roller rollers should be used for construction on mountain roads or work sites with loose mountain soil, because of the excitement generated by vibratory rollers. Vibration force can easily cause mountain collapse and landslide, and construction accidents can adversely affect construction progress. Tamping compaction machinery uses the impact of the tamping tool to compact materials when it is dropped multiple times, including rammers, ramming plates, and tamping machines. The impact force generated by the rammer on the ground surface is much greater than the static pressure, and it can be transmitted to a deeper place. The compaction effect is also good, and it is suitable for various types of soil.
Subgrade compaction is mostly done by rolling machines (various road rollers), and compaction machines are often used where road rollers cannot be compacted. Generally speaking, heavy-duty compaction machinery, due to its large compaction capacity (self weight, line pressure, drop distance, amplitude and frequency, etc.), has good compaction effects, high productivity, small unit compaction power, and low cost; but it is easy to cause Soil damage or damage to adjacent structures. Therefore, compaction machinery is often used in conjunction to ensure the quality of the project and give full play to the effectiveness of the machinery.
(2) Laying thickness and compaction times
After many times of compaction, the soil particles are tightly arranged, the internal friction and cohesive force continue to increase, and sufficient shear strength is formed to resist the compressive stress and no longer deform (that is, no longer compact).
When the number of compaction passes> n0, increasing the number of compaction passes has no effect, and the degree of compaction cannot be increased. Note: If n>10, the standard is not met, you must consider: increase the tonnage of the roller, change the compaction method, and reduce the thickness of the fill.
At the beginning, the soil layer is relatively loose (loose pavement), and its bearing capacity is weak. If a greater compaction strength is used, it will cause greater shear flow deformation, which will destroy the soil structure. Therefore, light pressure (stabilization) should be started at the beginning to make the loose material have a certain strength and bearing capacity.
Then, increase the compaction strength (heavy pressure) to gradually reach the required compactness. The compaction strength cannot be increased, otherwise the solid particles may be broken and the original gradation may be destroyed. Basic principles of compaction: slow pressure -> fast pressure; light pressure -> heavy pressure; static pressure -> vibration pressure.
