Application of ground improvement methods in tunnels constructed in problematic soils

Within the scope of this study, three soil profiles with different geological characteristics were selected by considering adverse conditions in order to represent the soil-structure interaction as realistically as possible. The excavation of a horseshoeshaped tunnel constructed using the NATM method was modeled and analyzed in the defined loose sand-silt and soft clay soil profiles using Plaxis 2D software. As ground improvement methods, area-wide jet grouting and subsequently applied anchorage systems were evaluated. The jet grout application notably reduced vertical deformations, particularly in the lower half. However, the anchorage system applied after jet grouting did not provide a significant contribution to vertical deformations within the scope of static analyses and was determined to potentially have a negative impact on structural efficiency. In the dynamic analyses, no collapse occurred under the Mw 6.93 Loma Prieta earthquake. Therefore, additional analyses for lower-magnitude earthquakes were deemed unnecessary.