Abstract：A method for calculating ground vertical displacements of double-layor elastic system due to shield tunneling was proposed combining the stiffness equivalent method with the Mindlin solution，which can simultaneously consider the unbalanced force at the tunnel face，the friction between the shield skin and the soil，the grouting pressure of the shield tail，the secondary grouting pressure，the additional load during tunnelling and the volume loss，and can also reflect the influence of the stiff difference of adjacent layers on ground displacements. The results show that the calculated ground vertical displacement induced by tunnelling in double-layer soil is different from that in single-layer soil while the overburden thickness is shallower，and close to the average value of the ground displacements calculated in soft and hard layers when the overburden thickness is getting deeper. It is also shown that the ground heave value first increases，then decreases and finally goes to zero with the secondary grouting ranging from the full face to the ungrouted zone and that the optimal grouting range is within the upper half. Comparisons between the ground vertical displacements of the field measurement and the theoretical calculation of Qinghuayuan Tunnel of the Jing-Zhang High Speed Railway indicate that the proposed double-layer model can describe the pattern of soil heave ahead of the tunnel face and settle-heave-stabilization behind of the tunnel face and that the calculated value of the ground vertical displacement by the model is much closer to the measured value than that calculated using single-layer model and the calculation error is reduced by 11.08%. The research results can provide a theoretical support for predicting ground vertical displacements caused by shield tunnelling both in single-layer soil and double-layer soil.
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2019, Vol. 38 
