SEM and NATM Tunnels
The sequential excavation method (SEM method) is a common method for the construction of tunnels in rock soil layers. This section presents the construction stages that are typically followed in the design of SEM and NATM tunnels, and how such tunnels can be simulated in our shoring design software DeepEX. SEM tunnels can be analyzed with the DeepEX Finite Element Analysis engine DeepFEM, which can be aquired as an additional module and works within the DeeEX superior interactive interface, expanding the software capabilities.
Figure: A SEM Tunnel Simulated in DeepEx Software
SEMTunnels - Typical Construction Stages
The excavation and tunnel construction sequence corresponds to 7 individual stages as illustrated in the following Figure.
Figure: SEM Tunnel Front and Side View - Typical Construction Stages
Stage 0: The green field conditions of the site prior to the tunnel construction initiation.
Stage 1: Excavation of the upper part of the top heading takes place. A support core is left intact. 3D arching effects are considered through partial deactivation of the soil region.
Stage 2: The tunnel crown is supported by a shotcrete lining. The support core is excavated. 3D arching effects are considered through partial deactivation of the soil region.
Stage 3: A temporary lining is constructed at the bottom of the so far excavated section. The specific stage corresponds further away from the excavating face where true plain strain conditions are valid.
Stage 4: Excavation of the bench part of the tunnel section. 3D arching effects are considered through partial deactivation of the soil region.
Stage 5: Excavation of the invert part of the tunnel section. 3D arching effects are considered through partial deactivation of the soil region.
Stage 6: Construction of the remaining lining sections (left, right wall and invert). The specific stage corresponds further away from the bench excavation location where true plain strain conditions are valid.
Figure: SEM Tunnel - Typical Construction Stages in DeepEX Software
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