Abstract
In this paper, a three-dimensional finite difference analysis is presented to investigate the interactive effects of sequential tunneling and the superstructure on the settlement profile of the ground. To simulate the practical sequential tunneling procedure, tunnel excavation is conducted in a step-by-step framework; tunnel excavation starts from the beginning of the model and is updated in a continuous manner, and the installation of the tunnel support system is done with a delay step compared to tunnel excavation. The numerical modeling accuracy is validated using the available analytical and numerical solutions for both two-dimensional and three-dimensional simplified cases. The well-validated modeling procedure is adopted to investigate effects of tunnel diameter, depth of tunneling, and number of superstructure stories on the profile of occurring settlements. Two cases of free-field and three-dimensional superstructural modeling are compared with regard to the effect of tunneling. In addition, the effect of tunneling advancement on the generation of excess structural forces and moments are studied as another important factor in the soil-tunneling-superstructure interaction problem. It is observed that, in the free-field case, with advancing the tunnel face, the longitudinal settlement profiles approach the steady-state condition and the maximum ground settlement tends to converge to a specific value, whereas as the tunnel passes under a structure, the settlement increases steadily as the tunnel progresses. There is a direct relationship between the depth and diameter of the tunnel and the settlement. In addition, the effect of the number of superstructure stories on the maximum settlement is more considerable compared to the free-field condition. According to the results, when the tunnel passes under 8-story and 12-story structures, the maximum settlement increases by 40% and 70%, respectively, compared to the free-field condition. It is also shown that tunneling-induced settlements result in the regeneration of structural forces.
Highlights
Due to the occurrence of settlements and settlement-induced displacements in surface structures, excavating tunnels in urban areas has always been of a great importance
Compared to the results obtained from the field, their transverse settlement profile was wider, and the maximum settlement value was increased in the vicinity of the superstructure
Jenck and Dias three-dimensionally studied the tunneling problem considering a structural frame as the superstructure; evaluating effects of the weight and the stiffness of the structure on the settlement profiles, they found that the stiffness of the structure plays an important role in the modeling accuracy. ey showed that the transverse settlement profile of the free field and the model with the consideration of the superstructure follow a relatively similar behavior [20]
Summary
Due to the occurrence of settlements and settlement-induced displacements in surface structures, excavating tunnels in urban areas has always been of a great importance. As there was not a common agreement between researchers on the suitable model size and the constitutive law, as the preliminary phase, a considerable number of numerical models with different sizes and governing constitutive laws were built, to evaluate the sensitivity of the settlement profile to these two factors In this regard, free-field analyses are carried out for a variety of model sizes; constitutive laws and longitudinal settlement profiles with the advancement of tunneling are calculated and analyzed for each of the studied cases as a basis for the selection of the proper size of the model and for the preliminary assessment of the selected constitutive law prior to its characterization (due to the large number of the studied cases, the results are not presented here). Generation of the excess internal structural forces and moments in the superstructure due to sequential tunneling is evaluated
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