An observation of groundwater behavior has been made around a tunnel during its excavation to investigate the phenomenon of erosion and collapse caused by groundwater in Neogene Pliocenean unconsolidated sandstone.
The observed data showed that the behavior of groundwater is affected by the impervious and continuous layer, and that the vertical flow is dominant in the near field of group-well and the approximation of horizontal uniform flow does not give good results.
Using Theis' unstable well theory and the observed drawdown heads, several sets of hydrogeological constants for the aquifer were obtained by direct search solution. These values corresponded with those obtained by discharge test, and no major change in these values obtained during excavation, in spite of multi-layered geological structure.
The predicted drawdown heads for unsteady state conditions corresponded well with measured data.