Soil conditioning test for EPB shield tunneling in slate stratum in the Changsha region

Serious abrasion of cutters and unsmooth soil occurred when EPB shield tunneling in the slightly weathered slate stratum of Changsha Metro Line 4 was performed. The mineral compositions, structural and physical properties of slate were obtained by XRD, SEM and laboratory mechanical test. The improvement effect of soil under different parameters was examined by laboratory slump test, and accurate, reasonable conditioning parameters after validating practicability in construction site were discussed. The results show that the slate is rich in quartz, feldspar and its lithology is dense, and may causes high abrasiveness. Besides, the conditioning soil by bentonite mud and foaming agent is of strong practicality as well as remarkable effect. The laboratory slump test of soil condition indicates that the best slump of value conditioning soil by bentonite mud is between 19 and 22 cm, and mud concentration is 14%~15%, mud injection ratio is 14%~17% and water injection of each segment is 5~7 m³; the best slump value of conditioning soil by foaming agent is between 19 and 21 cm, and foam concentration is 4%~6%, foaming agent injection ratio is about 10% and water injection of each segment is 8~10 m³.