The sleeve-valve-pipe grouting technique was applied to strengthening the saturated sandy gravel stratum, which is the load-bearing stratum for the foundation project of the Pingnan Third Bridge, the largest span (575 m) CTST (concrete-filled steel tube) arch bridge under construction in the world. Shallow plate load test and large-scale shear test were carried out to check the bearing capacity of the reinforced sandy gravel stratum and the friction coefficient of the contact surface between concrete and reinforced sandy gravel stratum. The purpose of the tests was to verify the effectiveness of sleeve-valve-pipe construction technique for strengthening the saturated sandy gravel stratum. Results indicated that the grouting had greatly improved the carrying capacity and frictional cofficient of the sandy gravel stratum. The research findings offer important reference for the construction of long span bridge foundation in Xijiang River Basin under similar geological conditions, and hopefully provide basis for the optimization design and construction of such foundation form.