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Abstract According to the construction of overlapping shield tunnel in soft soil area，four model tests have been carried out to simulate displacement and force variation rules of the existing tunnel due to the different construction orders and the different tunneling speeds. Experimental results indicate that：(1) In case of the upper tunnel first and the lower tunnel last，the lower tunnel construction leads to the longitudinal settlement of the upper tunnel. The circumferential internal force of tunnel segment of the upper tunnel generates deflection. The internal force in the arch bottom changes the most. (2) In case of the lower tunnel first and the upper tunnel last，the upper tunnel construction leads to the longitudinal uplift of the lower tunnel. The circumferential internal force of tunnel segment of the lower tunnel generates deflection. The internal force in the arch vault changes the most. (3) Regardless of the kind of construction orders，additional internal force along the longitudinal dimension will always be observed，with features of fluctuation and temporality. Comparing the influence of displacement and internal force on the existing tunnel induced by constructing overlapping tunnels，the lower tunnel first is better for the construction safety than the upper tunnel first. In the process of construction of overlapping shield tunnel，the additional deformation and force of the existing tunnel increase with the increase of tunnelling speed；and the impact range of tunnelling speed also increases. In this case，the tunnelling speed of the shield machine should be controlled in a proper range to avoid significant influence on the safety of adjacent existing tunnel structure.
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Received: 03 June 2013
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2013, Vol. 32 
