Effect Of Fine Soil Content On Physical And Mechanical Properties Of Mixed Coarse-and Fine-grained Soil

In this paper,the research object is mixed coarse-and fine-grained soil.A series of laboratory experiments were carried out under different fine soil contents to reveal the effect of fines content on the physical and mechanical properties of mixed coarse-and fine-grained soil.Through the compaction test of mixed coarse-and fine-grained soil with different grading,the experimental results showed that the compaction curves show three different forms with different fine-grained contents.Taking the maximum dry density as the evaluation index,two thresholds of the curves were found(FSC1 and FSC2),corresponding to the fine content of 40%and 85%respectively.Based on the maximum dry density and optimal moisture content measured by the compaction test,unconsolidated undrained shear tests under different fine-grained contents and confining pressures were carried out.The experimental results showed that the shear strength firstly increases with the increase of fine-grained content,and then decreases and then rises again.There are also two thresholds,corresponding to the compaction results:For the 1-2 mm grain soil,FSC1 is 40%and 50%respectively,and FSC2 is 85%at low confining pressures(100 and 200 kPa),while at high confining pressure(500 kPa),FSC1 is between 30%and 40%,and FSC2 is also 85%;For the 0.25-0.5mm grain soil,FSC1 is 40%and FSC2 is 85%at all three confining pressures.By measuring the moisture content of the sample which is at maximum dry density after different freeze-thaw cycles,the influence of the uneven distribution of fine-grained soil on moisture migration was determined:The more fine soil in the upper laye is,the larger the amount of water in the lower soil layer migrating to the upper layer is.And the greater the non-uniformity gap between the upper and lower soil samples is,the more obvious the water migration is.