Abstract:

The thaw settlement occurs in cross passage of a metro in Nanjing constructed by freezing method during operation period. The causes for the thaw settlement, i. e. soft ground, irrational procedure connection and insufficient thaw settlement grouting, are analyzed in terms of ground characteristics, construction technology and environment factors. The thaw treating principle and technology of splittingcompaction grouting are adopted to reinforce the surrounding ground of cross passage, and grouting effect monitoring points are arranged within construction influencing scope. The results show that: 1) The thaw settlement can be effectively controlled by supplemented ground drainage on the basis of splittingcompaction grouting. 2) The settlement of cross passage during grouting can be divided into 3 phases, i. e. fast slowing down period, low slowing down period and stable period; the settlement rates and drainage volumes of every period are distinctive. 3）The maximum rising height of upline and downline of separated tunnels is 31.2 mm and 29.8 mm respectively; and the settlement of cross passage 342 days after grouting is less than 1 mm which indicates the rationality and feasibility of the grouting method.

Key words: metro, cross passage, soft soil, freezing method, thaw settlement, grouting reinforcement