Abstract: Based on the deformation law of a station yard with subgrade disease, supplementary geological exploration and analysis are performed. A program of karst foundation strengthening is developed as follows. ①Strengthen karst foundation and soil on the top surface of bed rock through grouting. ②Strengthen the original composite foundation through high-pressure jet grouting. ③Strengthen the cushion layer and the soil layer 3-5 m above it by low-pressure grouting. ④ Strengthen karst foundation by the grouting curtain in the side of subgrade. ⑤Build a monitor system to estimate the strengthen effect. The calculation settlement and bearing capacity characteristic value of the strengthened subgrade is 12.4 mm and 455 kPa respectively, which can satisfy the design requirement of the subgrade. And the monitoring results show that the deformation of subgrade trends to be slower after the strengthening of karst foundation and soil on the top surface of bed rock; and the deformation presents wholeness with a sharply reduced deformation rate after the accomplishment of jet grouting piles and the reinforced area by low-pressure grouting. Six months after the reinforcement, the deformation trends to be steady, which certifies the validity and availability of the strengthening program.

Key words: railway station subgrade, karst diseases, reinforcement and strengthening, effect assessment