Chenyang Zhao

Constitutive Parameter Adjustment for Mechanized Tunneling with Reference to Sub-system Effects

In this research, the effect of sub-system on model response for mechanized tunneling process has been taken into consideration. The main aim of this study is to modify the constitutive parameters in a way that the best agreement between numerical results and measurements is obtained. The sub-system includes supporting pressure at the face of the TBM, contraction along the TBM-shield and grouting pressure in the annular gap. The commercially available finite element code, PLAXIS is adopted to simulate the construction process. The soil behavior during the excavation is numerically reproduced by utilizing Hardening Soil model with small strain stiffness (HSsmall). The constitutive parameters are obtained via sensitivity and back analyses while they have been calibrated based on the real measurement of Western Scheldt tunnel in the Netherlands. Both local and global sensitivity analyses are used to distinguish which parameters are most influencing the soil deformation. Thereafter, the model validation is accomplished by applying different scenarios for face pressure distributions with respect to the slope of the tunnel. In addition, the effect of contraction factor is modified individually or coupled with the variation of grouting pressure. Evaluating the influence of the sub-system is conducted to assess its effects on the model responses and to seek the possibility to decrease the disagreement between the calculated displacement and real measured data.

Adequate Numerical Simulation of Tail Void Grouting for Tunneling in Saturated Soil

In this research, a 3D numerical simulations of tunneling in saturated soil are conducted. The tunnel shield and lining segments with different diameters are explicitly modeled during the progressive excavation. Special attention is paid to accurate simulation of the grout hydration in the tail void where a constitutive model that accounts for the time dependent stiffness is developed to describe the hardening behavior of grout mortar in the coupled hydro-mechanical analysis. Additionally, the effect of grouting pressure distribution along the lining segments is investigated as well. The results reveal that neglecting the evolution of stiffness may lead to underestimation of surface settlements. The results also indicated the insignificant impact of the shape of the annular gap on the soil deformations and lining forces.