Abstract: One of the main practical difficulties attended with tunnel construction is related to underground water. Uncontrolled water behavior may cause extra loads on the lining, mechanical instability, and unfavorable environmental problems. Estimating underground water inflow rate to the tunnels is a complex skill. The common calculation methods are: empirical methods, analytical solutions, numerical solutions based on the equivalent continuous porous media. In this research the rate of underground water inflow to the Tabriz metro first line tunnel has been investigated by numerical finite difference method using FLAC2D software. Comparing results of Heuer analytical method and numerical simulation showed good agreement with each other. Fully coupled and one-way coupled hydro mechanical states as well as water-free conditions in the soil around the tunnel are used in numerical models and these models have been applied to evaluate the loading value on the tunnel support system. Results showed that the fully coupled hydro mechanical analysis estimated more axial forces, moments and shear forces in linings, so this type of analysis is more conservative and reliable method for design of tunnel lining system. As sensitivity analysis, inflow water rates into the tunnel were evaluated in different soil permeability, underground water levels and depths of the tunnel. Result demonstrated that water level in constant depth of the tunnel is more sensitive factor for water inflow rate to the tunnel in comparison of other parameters investigated in the sensitivity analysis.
Abstract: Groundwater inflow to the tunnels is one of the most
important problems in tunneling operation. The objective of this
study is the investigation of model dimension effects on tunnel inflow
assessment in discontinuous rock masses using numerical modeling.
In the numerical simulation, the model dimension has an important
role in prediction of water inflow rate. When the model dimension is
very small, due to low distance to the tunnel border, the model
boundary conditions affect the estimated amount of groundwater flow
into the tunnel and results show a very high inflow to tunnel. Hence,
in this study, the two-dimensional universal distinct element code
(UDEC) used and the impact of different model parameters, such as
tunnel radius, joint spacing, horizontal and vertical model domain
extent has been evaluated. Results show that the model domain extent
is a function of the most significant parameters, which are tunnel
radius and joint spacing.