Chapter 2 - Full-Scale Tests on Stiffened Deep Cement Mixing Piles Including Three-Dimensional Finite Element Simulation

Abstract

The stiffened deep cement mixing (SDCM) pile employs a precast concrete pile inserted at the center of the DCM pile. A series of full-scale tests involving SDCM and DCM piles under axial compression, lateral, pullout, and embankment loads were performed. The ultimate bearing capacities of two DCM piles have significant differences, confirming the low quality that commonly occurs on DCM piles, resulting in their low bearing capacity. The length of the concrete core pile affected both the ultimate bearing capacity and settlement, whereas its sectional area had a negligible effect. The DCM piles failed by pile body failure. The SDCM pile with a length ratio of 0.85 failed by soil failure. Thus, the effective length ratio of the SDCM pile should be larger than 0.85. The average lateral ultimate bearing capacities of SDCM piles with area ratio of 0.11 and length ratios of 0.54 and 0.85 could be improved by 11 times compared to those of DCM piles. The average lateral ultimate bearing capacities of SDCM piles with area ratio of 0.17 and length ratios of 0.54 and 0.85 could be improved by 15 times compared to those of DCM piles. Thus, the sectional area of the concrete core pile affected both the lateral ultimate bearing capacity and displacement. The SDCM pile with area ratio and length ratio of 0.17 and 0.85, respectively, effectively reduced the settlement and lateral movement induced by the embankment loading compared to the DCM pile, with a settlement reduction of 40% less than that of the DCM pile. The lateral movement in SDCM piles was 60% less than that in the DCM pile. The lateral movement:settlement ratio can be reduced in SDCM piles, especially in the surrounding clay, by as much as 50%. Three-dimensional finite element simulation of the results of full-scale embankment showed that the length of concrete core pile significantly affected the settlement of the SDCM pile. The effective length of the concrete core pile should be greater than 6m, corresponding to the length ratio of 0.85. Both the length and the sectional area of the concrete core pile affected the lateral movement of the SDCM pile under embankment loading.