Nowadays, the foundation of construction projects need to be compacted, which is inseparable from ramming. Small construction projects can be tamped with small electric rammer. Large construction projects usually have rigid indexes for the foundation, which need to be tamped to a certain extent before they are qualified. In this way, the rammer has certain index requirements, Therefore, we need to use dynamic compaction machine.
Dynamic compaction method is also called dynamic consolidation method. It is to use large crawler dynamic compaction machine to drop 8-30 tons of heavy hammer freely from 6-30 meters to tamp the soil strongly, rapidly improve the bearing capacity and compression modulus of the foundation, form a relatively uniform and dense foundation, and change the pore distribution of the foundation soil within a certain depth of the foundation.
Dynamic compaction method has been widely used in highway, railway, airport, nuclear power station, large industrial area, port reclamation and other foundation reinforcement projects. The utility model has the advantages of short construction period, good effect and low cost.
The dynamic compaction method is suitable for the treatment of gravel soil, sandy soil, silt and cohesive soil with low saturation, collapsible loess, plain fill and miscellaneous fill. Before dynamic compaction, one or several test areas should be selected on the representative site of the construction site for trial compaction or trial construction. The number of test areas should be determined according to the complexity of construction site, construction scale and building type.
Three different reinforcement mechanisms of dynamic compaction
1. Dynamic consolidation: when dynamic consolidation method is used to treat fine-grained saturated clay, its reinforcement mechanism is dynamic consolidation theory. During dynamic compaction, the huge impact energy produces a large stress wave in the soil, destroys the original structure of the soil, liquefies the soil locally and produces many cracks, increases the drainage channel, and makes the pore water escape smoothly. After the excess pore water pressure dissipates, the soil consolidates. Because of the thixotropy of the soft soil, the strength is restored（ Amway: thixotropy refers to the property that clay softens due to remolding and its strength decreases under the condition of constant moisture content. After softening, it hardens with the extension of standing time and its strength increases.)
2. Dynamic compaction: the dynamic compaction method is used to reinforce porous, coarse-grained and unsaturated clay based on the mechanism of dynamic compaction, that is, the impact dynamic load reduces the pores in the soil and makes the soil dense, so as to improve the strength of foundation soil. The compaction process of unsaturated soil is the process in which the gas phase (air) in soil is squeezed out, and the compaction deformation is mainly caused by the relative displacement of soil particles.
3. Dynamic replacement: dynamic replacement can be divided into integral replacement and pile replacement. Integral replacement uses dynamic compaction to squeeze the gravel into the silt, and its mechanism is similar to that of soil replacement cushion. Pile replacement is to fill gravel into soil by dynamic compaction, and part of gravel piles (or piers) are rammed into soft soil at intervals to form pile (pier) gravel piles (piers). Its mechanism is similar to that of gravel piles formed by vibroflotation method, forming composite foundation as a whole.