BEHAVIOR OF STRESSES AND DEFORMATIONS FOR SOIL SURROUNDING TBM TUNNEL BY FINITE ELEMENT SIMULATION

Abstract

ABSTRACT The increasing investment for the underground space such as the construction of the tunneling will part of the infrastructure development and exploitation of this space which becomes fundamental base in the development of large cities. In an urban environment, the tunneling induced ground loss is an essential matter to estimate ground movement during the excavation process. Therefore, an attempt has been made to study the settlement and behavior of stresses through tunnels construction by tunnel boring machine method (TBM)and their influences on the adjacent structures. In this research study is carried out to predict of the behavior of the stresses and ground movement effect of applying a tunnel boring machine during the excavation process. A numerical model is built and developed to a tunnel project within the governorate of Diyala. For this purpose, two profiles of soil investigations are brought the first from Al-Shareef Al- Jadeed bridge project and second for new buildings of Diyala University project. The main objective of this research is to study the behavior of stresses and determine the settlement in the area of study using a finite element method and to assess and the determination of extent the impact of a distance to move the mechanism of the drilling and advance into the soil. The model is run as three dimensional in both drained to sandy soil and undrained of clay soil of states with applied Mohr-Coulomb model. Results are presented in terms of stress-depth curves. Those stresses are the vertical and horizontal, total and effective in addition to the pore water pressure. The changes in state of stresses compared to the insite soil are put into consideration. Three vertical sections are chosen to study the TBM tunneling effects on surrounding soil. The first section (x=0) runs through center of the tunnel. Second section is located near lateral edge of the tunnel, while the third section is chosen more or less far II from the tunnel edge. The advance of TBM is reflected by stages through one to five. It is believed that the mentioned details of the analysis will provide full vision of stress change in the soil profile. The strains induced by the boring process are presented in different and simple methods. These methods reflected the soil movement and surface settlement of soil. The deflected shape of the tunnel is shown as well. Through running an axisymmetric FE analysis, calculation results revealed mat large changes in stresses take place in zones of soil near the tunnel boundaries. In other words, the close-near by soil is mostly affected by tunneling. These stress changes reduce as proceeded farther away from tunnel horizontally and seams to reach a to negligible values for distances above 12m away tunnel edge. All changes in the state of stress compared to the in-site soil depend on soil profile in site. The FE results also revealed that soil change in stress is more pronounced in the zone above tunnel than under it. It is believed that surrounding confinement plays a major role to that. The deflected soil shape shows that there is a vertical depression in the tunnel associated with lateral bulge. Maximum surface settlement recoded is 20mm in the upper soil region over tunnel which belongs the Al-Shareef Al-Jadeed bridge project and level off as gelling away horizontally from tunnel center. Upon proceeding with drilling, soil movement vectors seem to run towards the tunnel. As in the case of stresses, it is maximum in zones near tunnel. And last but not least, this study provides soil engineering a good guide and through understanding how to avoid places of heavy engineering facilities upon passing by TBM tunnel near or under these structures. Every soil site has its own profile and should run a full FE analysis but the general trend of behavior is through to the same