Abstract: The accurate prediction of penetration resistance is crucial for the successful application of bucket foundations. The undrained shear strength (s_u) obtained from the direct simple shear (DSS) tests is a key soil parameter in bucket installation design. The DSS tests consider the stress state of the soil under K₀ consolidation, the rotation of principal stresses and the actual engineering plane strain state, which corresponds to the loading conditions of the soil during installation of suction bucket. This study summarizes the calculation methods for bucket penetration resistance in clay and analyzes the characteristics of various methods. To address the issue of determination of soil strength, the coastal soil is subjected to consolidated undrained triaxial shear tests using a single shear apparatus. The influences of dry density (ρ_d), effective normal stress (σ_v') and overconsolidation ratio (OCR) on s_u are explored, and the reasons for the differences in values of s_u are analyzed. Finally, three prediction methods for s_u based on the critical state theory, strength index and SHANSEP are proposed. The research findings provide a basis for determining soil parameters in calculation of foundations penetration resistance of bucket in clayey soils.