Assessing the impact of squeezing ground on TMB excavation
Document typeMinor thesis
Rights accessOpen Access
This study takes part in a major project that aims to provide a ready to use tool which will give information of squeezing phenomena to engineers and TBM designers in terms of: - Quantification of squeezing rates of the ground around the TBM - Quantification of squeezing pressures that build up against the TBM shield - Quantification of risks of jamming of the TBM - Assessment of technological measures to cope with squeezing conditions This project is conceived to carry out the following work: 1. Modeling of the process of shield TBM excavation through squeezing ground with FLAC 5.0 SP, for which the following parameters will be considered: Geometrical parameters - Diameter of the tunnel D: As it defines the geometry of the excavated tunnel - Overburden of the tunnel H: As the in-situ hydrostatic stress field will be directly linked to the overburden Initial conditions - In situ stresses: It will be calculated directly from the overburden (γ.H), as a hydrostatic stress field will be supposed Ground parameters These parameters are relative to the chosen rheological model or general creep model used to characterize squeezing phenomena. TBM parameters - Length of the shield L: The shield will be modeled as a perfectly rigid support - Over-coring of the cutter-head - Skin friction, depending on the operational state of the TBM (standstill or advancing) Construction parameters - Advancement rate of the TBM (case Normal Operation) - Standstill duration (case Exception) 2. Development of a visco-elastic model and implementation with FLAC. This will require formulating a mathematical expression for the hyperbolic creep law and the following programming with FLAC. In terms of FLAC commands, a user-defined constitutive model will be created. The formulation will be based on Phienwej’s et al study Time-Dependant Response of Tunnels Considering Creep Effect, 2007. 3. Step 1 and 2 will be merged and tested to guarantee the functionality of the designed excavation process when the surrounding ground is constituted by the hyperbolic creep law. 4. Parametric study of the variables that play a role in the process of shield TBM excavation through squeezing ground. If steps 1, 2 and 3 result successful, parametric study will be carried out to better understand the influence of the mentioned parameters, for both cases of Normal Operation and Exception, in the event of a shielded TBM excavating through squeezing ground. This will be made by means of the numerical analysis of a large number of cases where different values are assigned to the variables.