Consolidation analysis of soft soil improved with short deep mixed columns and long prefabricated vertical drains (PVDs)

Abstract

Soft soils may pose many challenges to construction of roadway embankments, such as low bearing capacity, excessive settlement, and slope instability. A combined method involving the use of deep mixed (DM) columns and prefabricated vertical drains (PVDs) was proposed to reinforce the soft soils. In the application of the combined method, the DM column is usually shorter than the PVD. To obtain an analytical solution of the composite foundation with short DM columns and long PVDs, the drainage system was converted into a cylindrical drain wall with equivalent properties, and only the radial drainage was considered. An axi-symmetric unit cell was established and the solution of average degree of consolidation was derived. The analytical solution was verified by comparisons with the results computed by three-dimensional finite element analyses. A parametric study was conducted to investigate the influence of diameter of DM column, moduli of DM column and soft soil, permeability of DM column, soft soil and smear zone, and improvement depth of DM column on the soil consolidation and some recommendations were proposed for its practical application. Based on the proposed solution a design chart was developed which can be used to easily obtain the degree of consolidation for soft soil improved by the combined method. The proposed design method was applied to a case history of an embankment on soft soil with short DM columns and long PVDs. Good agreement was found between the predicted average degree of consolidation and the field data.

Consolidation calculation of a foundation partially penetrated by concrete‐cored gravel (CCG) columns

“…The consolidation process of a composite foundation can be determined in terms of excess pore water pressure and settlement 25 . The consolidation processes derived from the proposed solution and measured settlements are compared herein.…”

“…The matrix Equation ( 27) for 𝑎 1𝑖 and 𝑏 2𝑖 is obtained by integrating the conditions ⑦ and ⑧ into Equations ( 23)− (25).…”

Stability Assessment of Embankment on Soft Soil Improved with Prefabricated Vertical Drains Using Empirical and Limit Equilibrium Approaches

“…In recent years, there has been an increasing interest among researchers in settlement predicting [10], simulating the behaviour [11] and developing analytical solutions [12] of the embankment with PVDs. Factors found to be influencing embankment stability with PVDs have been explored in several studies [13]- [15].…”

Analytical models for consolidation of combined composite ground improved by impervious columns and vertical drains

“…A number of methodologies, including the field tests, numerical simulations and analytical methods, have been developed to study the consolidation process associated with this new combined technique abovementioned. Compared with direct field measurements and numerical simulations, analytical approaches are more popular, because analytical solutions are relatively accurate and straightforward for end‐users.…”

“…However, the area of the impervious column was not deducted from the area of influence zone of the vertical drain, which may cause a large discrepancy, especially when the columns were of large diameters. Zhang et al (2015) obtained an analytical solution for composite foundation with short DM columns and long PVDs by converting the drainage system into a cylindrical drain wall with no consideration of well resistance. Moreover, the disturbance effect of the DM columns was not taken into account as well.…”