## 6 Conclusions  
In general, the offshore structures constructed or to be constructed in active seismic regions are susceptible to liquefaction. During the 6 February 2023 Turkiye Earthquakes, the problem of liquefaction was encountered in the Iskenderun Port. For this reason, it is important to investigate the ground failures sourced from earthquakes in offshore structures to be built in seismically active regions. In this study, a case study is presented that is a typical example for these structures. The main conclusions obtained from the study can be highlighted as follows:  
1. For geotechnical site characterization, a total of 10 offshore geotechnical boreholes were drilled and detailed seismic reflection profiles were obtained. The detailed stratigraphic sections and their geotechnical parameters of the seabed sediments were obtained. The seabed stratigraphy and their geotechnical parameters are generally homogenous. This feature of the project site decreases the geotechnical uncertainty. 2. The seabed sediments in the project area are susceptible to liquefaction. As a result of liquefaction analysis, the factor of safety was calculated as 0.04-0.29 for natural conditions. For ground improvement methods, the jet grout column construction was considered. The targeted uniaxial compressive strength of the jet grout columns was 3 MPa, and the pattern of the columns was designed as 2 m \(\times\) 2 m. When considering this design, the minimum factor of safety was obtained as 1.01. 3. In the first stage of the jet grout construction works, various trial columns were constructed, and the optimum jet parameters were determined. Injection pressure, withdrawal speed, and amount of cement were determined as 420 bar, 40 cm/min, and 2200 kg, respectively. The minimum and maximum uniaxial compressive strength values of the core specimens obtained from the jet columns were found to be 2.71 MPa-4.51 MPa. As a result, the improved parameters considered in the design were achieved. 4. Determination of jet grout dimensions constructed in a terrestrial environment is relatively easy when compared to jet grout dimensions constructed in an offshore environment. For this reason, new applicable approaches for this purpose are necessary. Hence, in the study, a new procedure for the determination of jet grout dimensions constructed in an offshore environment is introduced. 5. The methodology is based on the shallow seismic reflection method. The whole area is measured by seismic method while the site is in virgin conditions. The measurement results are assessed together with the data obtained from the offshore boreholes. After this stage, jet grout columns are constructed, and seismic measurements are obtained again. The jet grout dimensions are determined by employing the shallow reflection method. The results are checked by boreholes and observed by the divers visually and it is determined that the results are satisfactory. 6. While the quality control of jet grouts can be carried out on a certain number of columns with conventional methods, the dimensions of all columns can be controlled with the method proposed in this study. In addition, the method is non-destructive on the columns, it is easier, and faster to apply. 7. The most important limitation of the method proposed herein is that the strength parameters of the jet columns cannot be obtained directly. For this purpose, core samples must be obtained from test columns and a limited number of control drillings. 8. The methodology is introduced by employing one project. Depending on the development of technology and increase in the number of projects, the method can be advanced, and the reliability of the method can be increased. 9. In a numerical analysis, the larger vertical deformation values are determined for unimproved ground, while the vertical deformation values calculated for mitigated ground are significantly reduced. The finite element analysis results obviously show the importance of soil improvement against liquefaction.