Road properties of completely weathered phyllite composite improved soil

In order to make full use of completely weathered phyllite as subgrade filler, the combined improvement schemes were designed, in which red clay blending ratio was 0, 20%, 40%, 60%, and 100%, respectively, and cement content is 0, 3%, and 5%, respectively. The tests of boundary moisture content, shear strength and unconfined compression of the improved soil were carried out, and the road performances of the improved soil were analyzed. The test results of the improved soil show that the liquid limit of the improved soil is lower than 40% when cement content is 3% or 5%, and all improved soils comply with the liquid limit control requirement of the design of railway earth structure (less than 40%). The cohesion of the improved soil increases with the increase of red clay blending ratio and cement content. The internal friction angle of the improved soil increases first and then decreases with the increase of red clay blending ratio, and increases with the increase of cement content. But both shear indexes increase slightly when cement content is more than 3%. The calculation results of ultimate bearing capacity of the improved completely weathered phyllite subgrade show that the ultimate bearing capacity of the subgrade with 5% cement is only 725.3 kPa, and the value of the subgrade with 40% red clay is 2 198.3 kPa, being 2.34 and 7.10 times that of the completely weathered phyllite subgrade, respectively. Therefore, the improvement effect of red clay is better than that of cement. Analysis results show that the rational mixing scheme is that red clay blending ratio is 40% and cement content is 3%. Under the scheme, when the curing age is 28 days, the calculated value of the ultimate bearing capacity of the improved completely weathered phyllite subgrade is 4 247.7 kPa, and the liquid limit of the improved completely weathered phyllite is 32.7%. Microscopic mechanism analysis results show that red clay particles are smaller than fully weathered phyllite particles. When red clay blending ratio is greater than 40%, red clay can surround the point-to-point contact of phyllite particles, and increase the contact points and contact area, which greatly improves the ultimate bearing capacity of the improved soil subgrade. The test results of unconfined compressive strength show that the 7-day unconfined compressive strength of the improved soil in the optimized scheme is 487.25 kPa, which meets the requirement of the design of railway earth structure. 2 tabs, 17 figs, 30 refs.