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Longitudinal Deformation of Deep Shield Tunnels Caused by Upper Load Reduction
Jinlei Zheng1, Shaohui He1, Yiming Li1
1School of Civil Engineering, Beijing Jiaotong University, Beijing 100083, China.
Materials (Basel, Switzerland)
|July 2, 2021
Summary
A new double-sided elastic foundation beam model accurately predicts shield tunnel uplift caused by nearby excavations. This method improves upon traditional models by accounting for ground arch effects, leading to more reliable deformation calculations for geotechnical engineers.
Area of Science:
- Geotechnical Engineering
- Tunnel Engineering
- Structural Mechanics
Background:
- Above-crossing excavations pose a risk of uplift damage to existing shield tunnels.
- Current methods, like the single-sided elastic foundation beam model, overestimate uplift in deep tunnels due to ignoring the ground arch effect.
- Accurate deformation calculation is crucial for geotechnical engineers to mitigate risks associated with tunnel construction.
Purpose of the Study:
- To propose a novel partial missing double-sided elastic foundation beam model for shield tunnels.
- To develop and validate a more accurate method for calculating shield tunnel deformation under above-crossing excavations.
- To address the overestimation of uplift by traditional models by incorporating two-sided foundation reactions.
Main Methods:
- Developed a partial missing double-sided elastic foundation beam model with double Winkler foundation springs, treating the tunnel as an Euler-Bernoulli beam.
- Employed a two-stage analysis: calculating vertical unloading stress using Mindlin's solution and then solving beam deformation via the finite difference method.
- Validated the model using two engineering case studies.
Main Results:
- The proposed model demonstrates superior accuracy in predicting maximum uplift values compared to traditional methods, showing good agreement with observational data.
- The model effectively accounts for the two-sided foundation reaction forces resulting from the ground arch effect in deep tunnels.
- Calculated longitudinal influence ranges were found to be larger than actual measurements due to segment staggering, a factor noted in both models.
Conclusions:
- The partial missing double-sided elastic foundation beam model offers a more precise approach to calculating shield tunnel uplift and deformation.
- This improved model is essential for geotechnical engineers to ensure the safety and stability of tunnels affected by adjacent construction activities.
- Further refinement may be needed to fully capture the longitudinal impact considering factors like segment staggering.
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