The embankment, embankment bed 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 economical and effective, 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 be basically divided into three categories: static rolling, tamping and vibration. When choosing a machine, the working characteristics and use occasion of the machine should be considered. The static roller compactor relies on its own quality to reflect its compaction ability 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 generated by the high-frequency vibration of the vibrating wheel, forcing the arrangement of the particles in the soil to change, and the small particles infiltrate 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 where the high and cold time is longer and the construction season is short; and the static roller roller should be used for construction in mountainous roads or work sites with loose mountain soil. This is due to the excitement generated by the vibration roller. Vibration forces can easily cause mountain collapse and landslides, and construction accidents can adversely affect construction progress. Tamping compaction machinery uses the impact of a rammer to compact materials when it is dropped multiple times, including rammers, ramming plates, and tamping machines. The impact force of 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 effect, high productivity, small unit compaction work, 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. Table 1-4 lists the use occasions of various compaction machines for reference
Note: ①The symbol A in the table represents applicable, B represents available when no suitable machinery is available, and C represents not applicable;
②The type of soil is divided according to the provisions of the "Highway Geotechnical Test Regulations" (JTJ051-93), among which huge stones are included;
③The self-propelled road roller (roller) is suitable for compaction of general embankment and road bed replacement, etc., and runs in a straight line
④Sheep foot (bump, strip) roller should be used in conjunction with smooth roller.
The scope of application of various types of rollers to compact various materials
(2) Laying thickness and compaction times
After many times of compaction, the soil particles are tightly arranged, the internal friction and cohesion are continuously increased, and sufficient shear strength is formed to resist the effect of 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.
