Three-dimensional numerical investigation on lateral movement and factor of safety of slopes stabilized with deep cement mixing column rows

Deep cement mixing (DCM) column rows have been widely used to increase the stability of excavated slopes in soft clay. However, large lateral movements are encountered frequently and lead to the loss of slope serviceability. This paper investigates the parameters that affect the lateral movements and factors of safety (FS) of an excavated slope stabilized by DCM columns in soft Bangkok clay. The considered parameters are the penetration depth (Pr), the spacing (Sr), improvement area ratio (ar), and the elastic modulus (Er) of the DCM column row. The three dimensional finite element method (FEM) was used for the analyses, and the initial calibration was based on the results of full-scale field tests. The DCM column rows behave as long piles with a fixation condition when Pr/H > 3.5, where H is the excavation depth. For a close spacing of DCM column rows of Sr/D ≤ 2 where D is the column diameter, the DCM column rows and soil in between move by approximately the same amount, which is considered effective in terms of soil arching. The improvement area ratio (ar) was found to be the dominant parameter, controlling the lateral movement and FS. FS of greater than 2 was found when ar was greater than 0.19. For ar greater than 0.19, the variation in stiffness of DCM column, possibly due to non-uniformity of mixing cement and in-situ clay, insignificantly affects FS of the excavated slopes. This ascertains the stability of the excavated slopes at various sections. A unique relationship between maximum lateral movement and FS of the excavated slope in soft Bangkok clay exists for all parametric studies. This relationship can be used to examine the stability of the excavated slope from the measured field lateral movement during and after the end of construction.