The stiffened deep cement mixing (SDCM) pile is a composite pile composed of the deep cement mixing (DCM) pile and an inner precast core pile. The excellent bearing performance of the SDCM pile that has been successfully witnessed in engineering practice is attributed to the double-layer load transfer mechanism, which effectively transfer the load from the stiffened core to the cemented soil and further to the adjacent soil. The mechanical properties of SDCM piles with stiffened cores that using large-size prestressed high-strength concrete (PHC) piles are rarely studied. This study aims to explore the bearing performance and failure behavior of the SDCM pile with a large-size PHC pile as stiffened core. The relationship between load and settlement as well as the distribution and development of axial force and lateral resistance was studied through field full-scale tests. The effects of the volume ratio, size, and concrete stiffness of the core pile, and the strength of cemented soil on the axial bearing capacity of SDCM piles were explored through the verified three-dimensional numerical model. The load transfer and failure modes at the internal and external interfaces of SDCM piles with different pile lengths were analyzed. Results show that the length of the core pile (Lcore) is a key factor for the bearing capacity of the SDCM pile. The bearing capacity of SDCM pile increases by 57.90% and 46.67% with Lcore increasing by 45% when cemented soil strength (qu, DCM) is 150 MPa and 300 MPa, respectively. The influence of qu, DCM and concrete stiffness on the bearing capacity of the SDCM pile is gradually significant with the increase of Lcore. The ultimate bearing capacity increases by 4.3% for every 100% increase in cemented soil strength at the optimal pile length. With the increase of Lcore, the investigated pile exhibits three failure modes, including the failure of pile end soil and cemented soil, the failure of pile top soil and core pile end soil, and the failure of pile top soil. The results of this study provide reference for the application of SDCM piles with large-size PHC piles as stiffened cores in the engineering field.

Liquefaction can lead to structural failure as it reduces the bearing capacity of building foundations. This phenomenon occurs in saturated sandy soils where pore water pressure increases, significantly decreasing effective soil stress. Evaluating the axial and lateral bearing capacity of bored piles affected by liquefaction is crucial to ensure the stability and performance of foundation systems. This study focuses on assessing the capabilities of bored piles in the Governor's Office of Sulawesi Barat Province, which are influenced by liquefaction phenomena. The empirical approach applied the O'Neill and Reese 1989 method, while the numerical approach used RS Pile. The calculation results revealed decreased axial bearing capacity under liquefaction conditions. In non-liquefaction, PC. 4 can withstand up to 24946 kN, with displacements of 0.94 cm (x), 0.39 cm (y), and 1.12 cm in settlement. In liquefaction, it decreases to 2876.78 kN, with displacements of 1.32 cm (x), 0.86 cm (y), and 1.68 cm in settlement. In non-liquefaction, PC.3 can withstand up to 17407.93 kN with displacements of 0.02 cm (x), 0.04 cm (y), and 0.06 cm in settlement. In liquefaction, it decreases to 1713.05 kN, with displacements of 0.02 cm (x), 0.05 cm (y), and 0.07 cm in settlement.