Influence of Subway Construction on Groundwater Environment in Downtown Area of Chengdu

Located at the southeast of the Minjiang alluvial-proluvial fan, the downtown area of Chengdu mainly composed of sand gravel layer. Now Chengdu has 8 subway lines operated; in the next 10 years, more than 34 routes will be constructed. Metro Line 7 forming a transfer relationship with multiple urban MRTS and urban commuter radiation built completly in downtown area, with depth of subway station 1.73-11.3 m, and the depth of interval tunnel 6.47-28.01 m. In order to study how the groundwater will be influenced, 3 3d groundwater numerical models in different scales have been constructed using FeFlow software, the results illustrated regional groundwater seepage field and local seepage field.

Baed on 1 regional model (417 km2 for downtown Chengdu ) and 2 models of typical underground space (Taipingyuan station and Yipintianxia station), at the same time with the basic geology and hydrogeology Analysis, shows that:

(1) The influence of metro line 7 on the seepage field is relatively limited in regional scale, and the change of groundwater level is very little(4-10cm) at several typical observation points; in the long-term, the raising of groundwater level will decrease gradually.

(2) Comparing the simulation results of Taipingyuan station and Yipintianxia station shows the impact of subway construction on the groundwater environment in the downtown Chengdu. In the big view, from northwest to southeast, the phenomenon of underground water interception or raising in subway stations decrease gradually, this is owing to the influence of aquifer thickness, groundwater flow direction and the direction of underground station structure.

(3) As the main body or long section of the underground structure is coincide with the groundwater flow direction, the cross-section blocking the groundwater is minimized, so its influence on the groundwater seepage field is not notable even with development of the underground space, this is also help avoiding the floatation effect on the building foundation due to the raising of the groundwater flow.