Field test on treating settlement by grouting for soft soil composite subgrade of high speed railway

Field tests were carried through on treating settlement by full-face grouting and layered grouting for soft soil composite subgrade of certain in-service high speed railway in Yangtze Delta area to study subgrade lifting law caused by grouting. The results indicate that the differential deformation between the up line and down line can be reduced when symmetrical and uniform grouting is adopted on both sides of subgrade. The pore water pressure of foundation soil rises along with subgrade uplift due to grouting, while the excess pore water pressure dissipates gradually along with the fallback of subgrade uplift after the end of grouting. The deformation of concrete support layer is bell-shaped parabola bulge and the grouting in adjacent holes produces additive effect in a short time. There is a key soil layer in layered grouting. The deformation of concrete support layer becomes significant when grouting in the key layer. Accordingly, the disturbance of key layer must be controlled as possible in practical grouting construction. Layered grouting causes more stable subgrade uplift and smaller excess pore water pressure, and the grouting effect is ideal. © 2015, Chinese Academy of Railway Sciences. All right reserved.