Simplified method for predicating consolidation settlement of soft ground improved by floating soil-cement column

A simplified method is presented for predicting consolidation settlement of soft ground improved by floating soil-cement column on the basis of double soil-layer consolidation theory. Combining the axisymmetric consolidation model and equal strain assumption, the governing equation was derived for the consolidation of clayey subsoil reinforced by soil-cement column. By modifying the boundary condition of the interface between the improved layer and underlying layer on seepage and pore-water pressure, the analytical solution of consolidation of soft ground improved by floating soil-cement column was developed under depth-dependent ramp load. The results of the parameter analysis of consolidation behavior show that the consolidation rate is closely related with the depth replacement ratio by the column and the permeability of upper layer. The influence of column-soil constrained modulus ratio and radius ratio of the influence zone to the column on consolidation is also affected by depth replacement ratio. The column-soil total stress ratio increases with time and approaches the final value accompanied with the dissipation of excess pore water pressure.

Analysis of 1D consolidation with non-Darcian flow described by exponent and threshold gradient

Numerous experiments have shown that the water flow in fine-grained soils can obey an exponential relationship at small gradients and a linear relationship when the hydraulic gradient exceeds a certain limit. Based on the non-Darcian flow described by exponent and threshold gradient, the theory of 1D consolidation is modified in this paper to consider a linear variation in the vertical total stress with depth and the effect of ramp loading. The numerical solutions were derived in detail by the finite difference method for excess pore water pressure and the average degree of consolidation. Finally, the influence of various parameters on consolidation behavior was investigated. The results show that the rate of consolidation is reduced when non-Darcian flow described by exponent and threshold gradient is adopted in the theory of 1D consolidation. As well the distribution of vertical total stress has a great influence on the dissipation of excess pore water pressure, either for pervious top and pervious bottom (PTPB) or for pervious top and impervious bottom (PTIB). For the case of PTIB, the distribution of vertical total stress in a foundation has a great influence on the rate of consolidation; however, for the case of PTPB, the rate of consolidation is independent of the distribution of vertical total stress. The rate of consolidation is dependent on the ratio of the thickness of a soil layer to the equivalent head of the final average vertical total stress; the greater the value of this ratio, the slower the rate of consolidation. Finally, an increase in construction time reduces the consolidation rate of a foundation. Thus, consolidation behavior of 1D consolidation with non-Darcian flow has been thoroughly acquainted in this paper.

Consolidation solution for composite foundation considering a time-and depth-dependent stress increment along with three distribution patterns of soil permeability

In actual engineering practice,the stress increment within a composite foundation caused by external loads may vary simultaneously with depth and time.In addition,column installation always leads to a decay of soil permeability towards the column.However,almost none of the consolidation theories for composite foundation comprehensively consider these factors until now.For this reason,a stress increment due to external loads changing simultaneously with time and depth was incorporated into the analysis,and three possible variation patterns of soil's horizontal permeability coefficient were considered to account for the detrimental influence of column installation.These three patterns included a constant distribution pattern(Pattern I),a linear distribution pattern(Pattern II),and a parabolic distribution pattern(Pattern III).Solutions were obtained for the average excess pore water pressures and the average degree of consolidation respectively.Then several special cases were discussed in detail based on the general solution obtained.Finally,comparisons were made,and the results show that the present solution is the most general rigorous solution in the literature,and it can be broken down into a number of previous solutions.The consolidation rate is accelerated with the increase in the value of the top to the bottom stress ratio.The consolidation rate calculated by the solution for Pattern I is less than that for Pattern II,which in turn is less than that for Pattern III.