Active earth pressure acting on retaining wall considering anisotropic seepage effect

Abstract

This paper presents a general solution for active earth pressure acting on a vertical retaining wall with a drainage system along the soil-structure interface. The backfill has a horizontal surface and is composed of cohesionless and fully saturated sand with anisotropic permeability along the vertical and horizontal directions. The extremely unfavourable seepage flow on the back of the retaining wall due to heavy rainfall or other causes will dramatically increase the active earth pressure acting on the retaining walls, increasing the probability of instability. In this paper, an analytical solution to the Laplace differential governing equation is presented for seepage problems considering anisotropic permeability based on Fourier series expansion method. A good correlation is observed between this and the seepage forces along a planar surface generated via finite element analysis. The active earth pressure is calculated using Coulomb's earth pressure theory based on the calculated pore water pressures. The obtained solutions can be degenerated into Coulomb's formula when no seepage exists in the backfill. A parametric study on the influence of the degree of anisotropy in seepage flow on the distribution of active earth pressure behind the wall is conducted by varying ratios of permeability coefficients in the vertical and horizontal directions, showing that anisotropic seepage flow has a prominent impact on active earth pressure distribution. Other factors such as effective internal friction angle of soils and soil/wall friction conditions are also considered.

Parametric Study of Sheet Pile Wall using ABAQUS

“…It is also observed that, for all the ases of an angle of friction corresponding to ϕ=26 0 , 30 0 , 36 0 , 40 0 and 46 0 both the active and passive earth pressure distribution result shows maximum value, at the base of the wall. A Similar trend of results was reported previously in the literature [21,23,24]. Many researchers have associated the reason for this behavior as large wall deflection in the higher elevation of the wall and restrained or a very smaller wall deflection in the bottom of the wall.…”

Reply to the discussion by Ganesh on “Analysis of passive earth pressure modification due to seepage flow effects”

“…Note that these assumptions have also been adopted for the analysis of passive earth pressure acting on retaining wall, e.g., Morrison and Ebeling (1995), Soubra and Macuh (2002), and Patki et al (2015). In particular, the same boundary conditions of seepage flow inside the backfill were also adopted in Barros (2006), Wang et al (2008), Santos and Barros (2015), and Hu et al (2017). Distribution of the normalized pressure head, h p /H, along a log-spiral failure surface is illustrated in Fig.…”

Analysis of passive earth pressure modification due to seepage flow effects

“…To investigate the effect of the anisotropy of seepage flow, the ratio of permeability coefficient ξ=(k y /k x ) 1/2 was introduced by Hu et al (2017), and the solution to the Laplace equation for anisotropic seepage can be then obtained as…”

“…Field measurements have shown that permeability values in the horizontal direction are multiples of those in the vertical direction; this can significantly affect the pore pressure distribution in the backfill behind the wall (Kenney 1963;Head 1988;Jeng et al 2001;Hazelton and Murphy 2007). By assuming that the horizontal axis coincides with the direction of the maximum permeability, Hu et al (2017) showed analytically that the anisotropic permeability of the backfill can significantly affect D r a f t the distribution of both the pore water pressure and the active earth pressure on retaining structures. However, studies of the passive earth pressure including anisotropic seepage flow are rarely considered and thus this aspect requires further investigation.…”