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Abstract
Seepage is ubiquitous during tunneling in areas with high groundwater tables. The ground settlement trough on a single tunnel is well described by Peck’s formula, but it cannot reflect the settlement caused by seepage. In this paper, assuming that the groundwater inside and outside the tunnel is a one-dimensional steady-state seepage condition, the groundwater seepage and drainage model of the tunnel was established. Based on the model and the principle of groundwater dynamics, the seepage flow calculation formula was derived, and the dewatering funnel curve equation of the groundwater level surface of a tunnel aquifer was obtained. A case study of a tunnel project in Gansu Province was carried out, and the influence of seepage on the effective stress of the stratum around the tunnel and the calculation of ground settlement caused by seepage were analyzed. The results show that seepage makes the effective stress of the upper soil layer of the tunnel increase, which leads to an increase in ground deformation; when the groundwater level of the tunnel is greatly lowered, the seepage has a significant influence on the vertical deformation of the stratum.
Highlights
When a tunnel is excavated in areas with shallow groundwater levels, groundwater seepage will occur because of the effect of the water head difference inside and outside of the tunnel
The results show that seepage makes the effective stress of the upper soil layer of the tunnel increase, which leads to an increase in ground deformation; when the groundwater level of the tunnel is greatly lowered, the seepage has a significant influence on the vertical deformation of the stratum
There is no lining after the tunnel is excavated, and the drainage is similar to the pumping of large-diameter and stability calculation, it is very important to determine the drawdown value of the groundwater level and the scope of the dewatering funnel
Summary
When a tunnel is excavated in areas with shallow groundwater levels, groundwater seepage will occur because of the effect of the water head difference inside and outside of the tunnel. Attewell and Farmer (1974) [4], O’Reilly and News (1982) [5], Sagaseta (1987) [6], Rankin (1988) [7], Mair et al (1993) [8], Loganathan and Poulos (1998) [9], Lee et al (1999) [10], and Marshall et al (2012) [11] revised the calculation coefficient of the surface subsidence trough by considering factors such as tunnel depth and tunnel diameter, and popularized it These methods were established without considering the influence of seepage and consolidation. In view of this, based on the steady-state seepage condition, the calculation formula of tunnel seepage was derived, and the dewatering funnel curve equation of the tunnel aquifer groundwater level was obtained. The influence of seepage on the effective stress of the stratum around the cavern, as well as the calculation of the ground settlement caused by it, were analyzed
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