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Abstract When the pipe jacking has been put through sand foundation consolidated under expressway embankment loading，differential settlements will be produced in cross section and longitudinal direction of the embankment due to the ground disturbance and ground loss caused by pipe jacking construction. Field observation and analysis indicate that the index，whether the increment of the slope caused by differential settlement in cross or longitudinal direction less than 0.5% or not，can be used to control and predict the stability of the embankment dynamically during pipe jacking or water depression. It can prevent the road surface from cracking efficiently. Field experiment and measured law show that the settlement of the disturbance zone is advanced and instantaneous during pipe jacking construction，to sand ground layer，the area of the disturbance zone is larger than the value calculated according to soft soil theory. The disturbance zone is mainly in the range of 1 m beyond the pipe wall exine and expand based on this. The percentage to the compressibility increment of the soil above the pipe axis could be more than 50%，and the void ration can be larger than 35%，the strength is decreased plasticity index has been reduced in different degrees，all these lead to the reconsolidation of the soil in the disturbance zone，which brings forward the settlement of the embankment directly. Compression is the main characteristic of the soil under the pipe axis. When the pipe jacking is through sand soil layer，more attention should be paid to water depression during pipe jacking and open caisson construction which can bring disadvantage to expressway embankment.
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Received: 12 November 2008
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