BEHAVIOR AND SIMULATION OF DEEP CEMENT MIXING (DCM) AND STIFFENED DEEP CEMENT MIXING (SDCM) PILES UNDER FULL SCALE LOADING

A new kind of Deep Cement Mixing (DCM) pile called Stiffened Deep Mixing Pile (SDCM) is introduced to mitigate the low flexural strength and unexpected failures of DCM piles. A jet grouting method with a jet pressure of 22 MPa, was utilized in the installation of DCM piles. The SDCM pile consists of a DCM pile with a precast reinforced concrete core pile inserted at its center. Pile and embankment load tests were conducted, and then the results of the field load tests were simulated by a 3D finite element method (FEM) to back-analyze and confirm the related design parameters. These parameters were then used further in numerical experiments. The field test results showed that the settlements and lateral movements of the SDCM pile using a prestressed concrete core pile with area ratio (A(core)/A(DCM)) of 0.17 and a length ratio of 0.85 was less than those of the DCM pile by 40% and 60%, respectively. Moreover, the SDCM pile foundation increased the bearing capacity by as much as 2.2 times. The average lateral pile capacity of the SDCM piles was 15 times higher than the DCM piles. A strength reduction factor of 0.40 was obtained at the concrete core and the DCM interface from the full scale pullout test. The behavior of both the DCM and SDCM piles was confirmed from the subsequent 3D FEM simulations. From the 3D FEM simulations, the length of the concrete core pile had more influence on the settlements of the SDCM pile than its cross-sectional area. However, both the length and cross-sectional area of concrete core pile affected the lateral resistance of the SDCM pile.