Impact of reinforced core on performance and failure behavior of stiffened deep cement mixing piles

The behavior up to failure of stiffened deep cement mixing (SDCM) piles under axial compression is discussed on the basis of finite element simulation and laboratory small-scale model tests. The numerical investigation by means of axial pile load test simulation was carried out using the calibrated parameters and soil profile and properties from previous field tests. The results reveal that the effectiveness of a reinforced core for increasing the ultimate load of the SDCM piles and the associated failure mode mainly depend on the core dimension, core volume ratio and the strength of the deep cement mixing (DCM) socket, whereas the core stiffness has a significant effect only for the case of a relatively long core. These results imply that the core material could potentially be a cheaper, less stiff construction material. For a constant volume of reinforced core, the SDCM piles with a more slender core provide higher ultimate loads and less settlement, particularly at high core-volume ratios. Reduced-scale models were tested under normal gravity to verify the numerical findings. Good agreement was found between the simulation and test results on the influence of the core shape and material on the load-carrying behavior and failure modes of SDCM piles. A series of numerical analyses were extended to establish a guideline for recommending an appropriate size of the core in SDCM piles and to discuss the failure modes with respect to the length of the core. From the developed charts and given strength of DCM socket, the suitable core length and cross sectional dimension can be systematically chosen with known expected failure mode.