【Daily Topic】【Civil Engineering Version 20160524】

The main factors affecting the quality of compaction are (　ABD　). A. Compaction work　　 B. Moisture content of soil　 C. Workability of soil　 D. Thickness of each layer of soil applied

　　The quality of soil compaction is related to many factors, among which the main influencing factors are: compaction work, the moisture content of the soil, and the thickness of each layer of soil applied. 　　1. Influence of compaction work: The unit weight of the compacted fill is related to the work applied to it by the compaction machinery. The relationship between the unit weight of soil and the work required is shown in Figure 1-50. When the moisture content of the soil remains constant, its unit weight increases sharply at the beginning of compaction. As it approaches the maximum unit weight of the soil, although the compaction work increases significantly, the unit weight of the soil does not change. In actual construction, the appropriate number of compaction passes should be determined for different types of soil, based on the selected compaction machinery and the required degree of density. Furthermore, loosening the soil should not be done by using heavy rolling machinery directly, as this will cause significant irregularities in the soil layer and result in low efficiency. The relationship between soil density and compaction effort. 2. The impact of moisture content: Under the same compaction effort, the moisture content of the fill material has a direct effect on the quality of compaction. Softer soil is difficult to compact due to the greater friction between the soil particles. When the soil has an appropriate moisture content, water acts as a lubricant, reducing the friction between soil particles and thus facilitating compaction. Every type of soil has its optimal moisture content. At this moisture content, when the soil is compacted using the same amount of compaction energy, the resulting unit weight is maximum (Figure 1-52). The optimal moisture content ω0p of various soils and the maximum dry unit weight they can achieve can be determined through compaction tests. During construction, the difference between the moisture content of the soil and its optimal moisture content can be kept within the range of -4% to +2%. 　　The influence of soil moisture content on its compaction quality 3. The influence of soil layer thickness: Under the action of compaction forces, the compressive stress decreases gradually with increasing depth; the depth over which this effect is observed depends on factors such as the compaction machinery used, the properties of the soil, and its moisture content. The thickness of the soil layer applied should be less than the effective working depth of the compaction machinery, and the optimal thickness of the soil layer should also be taken into account. If it is laid too thickly, many compactions are required to achieve the desired density; if it is laid too thinly, the total number of mechanical compactions must be increased. The optimal soil covering thickness should enable the soil to be compacted with minimal mechanical power consumption.

A、Compaction work　　 B、Soil moisture content　D、Thickness of each layer of soil applied

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A. Compaction work　　 B. Moisture content of soil　 C. Workability of soil