Simulation of a tunnel excavation at shallow depth (Ohio River Bridge)


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Industries 
Client Name 
VINCI
Location 
United States
Software Used 
Project Description 

The behavior, during excavation, of a shallow tunnel cutting densely fractured limestones and dolomites raised concerns. The tunnel is called "Drumanar tunnel‘ and located in Louisville, in Southern Indiana. The model geometry is shown on Figure 1.

Itasca's Role 
  • Analysis of in‐situ geometry data, including block size distribution and fracture orientation. Building of an equivalent 2D DFN (Discrete Fracture Network) model.
  • Numerical modeling using UDEC, accounting for the blocky nature of the medium using the 2D DFN (Figure 2) and simulating the excavation sequence, with structural support installation.
  • Parametric analysis, accounting for variability, along the tunnel path, of the various rock layer thicknesses and the rock quality (good, moderate and poor).
Project Results 
  • Rock displacement is mainly dominated by rock quality: the case with poor joint properties shows noticeable rock displacement.
  • Surface settlements remain in the same order as those measured at the crown, as expected for a shallow excavation (Figure 3).
  • The maximum loads on the liner take place mostly in segments located near the intersection between the vertical wall and the raft. Additional reinforcement must be considered in these places.
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