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Carbon dioxide (CO2) sequestration through CO2 enhanced oil recovery (EOR) in oil reservoirs is one way to reduce this gas in the atmosphere. Undesirable chemical reactions that occur during these operations can affect the reservoir structure and characteristics. In this study, the effect of CO2-water-rock interaction on the rock permeability alteration and final oil recovery has been evaluated experimentally during CO2 injection into a carbonate rock. The effect of flow rate, displacement type and pressure were investigated during CO2 EOR injection. Different scenarios of miscible/immiscible displacement, secondary/tertiary recovery has been evaluated for different levels of connate water salinity and injection rate. The results show that the severity of damage is directly related to the injection rate, however change in displacement type from miscible to immiscible reduce the intensity of chemical reactions in porous medium. Moreover, in the tertiary CO2 injection, the chemical reactions become more severe due to the higher water saturations. Interestingly, this growth in the level of chemical reactions has a negligible impact on permeability reduction, since the major volume of possible reactions occurs in coarse and high permeable pores. Results reveal that damage is more intense in the case of more saline water.

Highly inelastic nonlinear interaction of liquefied soil and underground RC ducts is computationally investigated in view of the structural damage. The required ductility is expected to be insensitive to the risk of liquefaction for normally deposited layers of soil, and the lesser ductility is acceptable for the case of highly liquefiable foundation similar to the seismic isolation. Although the structural nonlinearity has a fewer effect on the uplift of the underground ducts, the amount of main reinforcement may control the structural damage with the same efficiency for both drained and undrained soil deposits.

Liquefaction can significantly increase the deformation of soil around underground structures but at the same time, the stiffness and internal stress of soil are also dramatically reduced. Therefore, it is questionable that if it is really essential for the structure to accommodate all the free-field ground deformations as the conventional design approach currently requests. In the present study, a typical subway tunnel is subjected to earthquake excitations using dynamic Finite Element method coupled with soil and pore water considering the nonlinearity of both structure and soil foundation. The simulation is carried out in both drained and perfectly undrained conditions to clarify the effect of liquefaction on seismic response of the structures. The computational results imply that the required ductility of RC ducts can be moderated provided that the liquefaction risk is high. Furthermore, the effect of sheet piling on various types of tunnel damages such as uplift or shear deformation is also investigated. It is found that installation of sheet piles can cause the structure to suffer more damage due to the increase of relative stiffness between the structure and the soil.

Although seismic performance of large underground structures has been extensively studied recently, the focus of these researches is on the behavior of soil during earthquake motion, considering simple assumptions for the structure. The present study tries to have a more precise view towards the performance of large underground structures subjected to earthquake excitations. To achieve that aim, a typical subway tunnel is analyzed using dynamic Finite Element method coupled with soil and pore water. Both linear and nonlinear elements are used to model the underground structure. The computational results prove that nonlinearity of the structure should be considered to realize the accurate deformation and internal force response. Furthermore, the simulation is carried out in both drained and perfectly undrained conditions to clarify the effect of liquefaction on seismic response of the structures. It shows that ground liquefaction greatly deteriorates the soil skeleton stiffness and results in the reduced damage to RC structures even though large displacement of the ground is produced. It implies that the required ductility of RC ducts can be moderated provided that the liquefaction risk is high.