Abstract
Water leaking into metro segments is related directly to the presence of underground water. However, to date, the underground confined water channels formed by metro underpass reinforcement structures have not been considered as causes of the problem. In the present study, based on field investigations and geological data, confined water is identified as the source of segment leakage on Line 5 of Hangzhou Metro in China. It is then hypothesized that the problem stems from an underground confined water channel formed under the reinforced structure of the subway. Numerical simulations predict a settlement difference of 8–10 mm between the reinforcement area and the weak strata, and field monitoring data show this difference to be 8.62 mm. This consistency between the numerical simulations and the field measurements verifies the hypothesis. Finally, given the causes of underground confined water channels, corresponding technical measures such as piecewise secondary grouting are proposed to cut them off and avoid metro-segment leakage. The present research results contribute to the causes of and the laws governing the metro-segment leakage that occurs at subway stations and other reinforced structures.
Highlights
Water leaking into metro segments is related directly to the presence of underground water
Xu et al [3] used the finite element (FE) method to subject the seepage and stress fields of the surrounding rocks and structures to coupling analysis to obtain the distribution rules for the stress, displacement, and pore water pressure during construction; the results showed groundwater to be the direct source of the water flow causing tunnel leakage
Shin et al [11] used a numerical simulation method to build a two-dimension model and studied the coupled mechanical and hydraulic interaction between the segment lining and the surrounding ground; the results showed that hydraulic degradation leads to significant changes in pore water pressure and structural properties and accelerates leakage
Summary
To obtain the water pressure accurately, a pressure gauge with a range of 0–2.50 MPa was installed in the grouting hole and measured the water pressure as being 0.60 MPa. Based on geological prospecting data, the groundwater in this area is from the phreatic and confined water at the lower part of the station, so the phreatic or confined water is the main cause of the engineering problems. Having flowed along the UCWC to the formation above the problem zone, the confined water seeps down the boreholes and eventually into the tunnel segment to cause MSL.
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