What is Submerged Floating tunnel (SFT)?

Tunnel type with segments submerged in water floating by buoyancy
Provision of a linear route that can replace airplanes and ships
Not affected by weather above sea level
Can be constructed regardless of seabed depth  

Research target – shore connection
-Submerged floating tunnels and subsea bored tunnels have different confining conditions, relatively free and rigid
-Unbalance of displacement from two tunnels at shore connection can cause stress concentration
-Joint design for stability at shore connection is necessary


Main factors?
-Marine environmental factors: hydrostatic pressure, temperature, wave
-Ground environmental factors: geographic characteristics, ground properties, ground-tunnel interaction, earthquake
-Structural factors: tunnel shape, segment properties, joint stiffness, purpose of tunnel

Methods for analysis
-Theoretical analysis on tunnel behavior at shore connection
-Numerical simulation for analyze effect of each main factor
-Experimental test with small scale model for verification

Goals
-Understanding dynamic behavior of SFTs at shore connection
-Understanding Influence of main factors
-Design for tunnel construction at shore connection securing stability of tunnel and surrounding ground

Required design aspects
-Tunnel joint at shore connection
-Ground reinforcement on ground surrounding shore connection
-Construction method for shore connection
-Method for ground reinforcement


Numerical results for effect of joint design
-Numerical analysis for evaluating the effect of joint design at shore connection of SFT can be utilized in overall design of shore connection.
-Joint design is simulated in numerical software by adjusting the degree of freedom (DOF) of tunnel joint.
-Displacement and rotation are controlled by joint rigidity or stiffness.
-Interval of joint design application also affects the behavior of soil surrounding tunnel.
Numerical results for effect of ground reinforcement
-Ground reinforcement is simulated by numerical software to analyze the effect of grouting material.
-Grouting materials are clay (soft) and cement (hard).
-Stress concentration at shore connection is released with grouting.
-Ground displacement decreases with grouting application.
-Hard grouting material can cause stress concentration.