Improvement of expansive soil filling material for subgrade of Nanning-Guangzhou passenger dedicated line

There are more than 55 kilometers subgrade in NGZQ-5 section of Nanning-Guangzhou high-speed railway passenger dedicated line. A large number of filling material along the construction section is high expansive clay soil, and it must be improved by physical or chemical methods. The liquid and plastic limits, expansibility, mechanical strength and water stability of expansive soil is studied. The results of the experiment show that the filling material is high liquid limit and expansive soil, and it can not meet the requirements of high speed railway subgrade. The free expansion rate of expansive soils improved by cement or gravel is reduced, the water stability is improved considerably, and the mechanical strength is enhanced. cement content. And it is qualified filling material if cement content is more than 5%, or gravel content is more than 55%. Further research show that the physical method of mixing gravel is more appropriate and economical. The improved method recommended by testing study is applied successfully in the construction of subgrade in NGZQ-5 section of Nanning-Guangzhou high-speed railway. It is demonstrated to be a fast and economy improved method.