Study Of The Effect Of Dry-wet Cycles On Engineering Behavior Of Improved-Soil

The high-speed railway subgrade-filling should have better engineering properties. However, it is difficult to find the subgrade-filling satisfying the engineering demands along the railway. The improved subgrade-filling can be used for the subgrade engineering. It is found that the environment change will result to the degradation of the subgrade-filling properties and subgrade to failure finally. According to these analysises, the following researches have been done in this paper.First, a lot of experiments were done to investigate the effect of environment changes on the strength of cement-soils. The results show that the strength degradation of the improved cement silty clay is higher than that of the improved cement silt, and the strength degradation tend to stability with the increase of the number of dry-wet cycles. The clay grain content is the main factor affecting the strengh variation of cement-soils by analyzing degradation mechanism. Therefore, the conclusion can be deduced, which is the strength degradation can be improved by properly reducing the clay content in silty clays. It is verified using tests and results show that the deformation and cracks resulting from the dry shrinkage and the wet dilatation can be reduced if proper coarse grains are added into silty clays. As a result, the strength of the improved cement silty clay can be increased after dry-wet cycles. But the optimal adding ratio exists for a silty clay.Second, the engineering characteristic of lime improved soils were further studied, and effects of curing ages,lime-soil ratios and water contents on the compressive strength and the shear wave velocity were researched. The correlation between elastic wave velocity and strength is analyzed. The results show that shear wave velocity is a better parameter describing strength change than the compressive wave velocity.