Analysis of passive earth pressure modification due to seepage flow effects

Abstract

Using an assumed vertical retaining wall with a drainage system along the soil–structure interface, this paper analyses the effect of anisotropic seepage flow on the development of passive earth pressure. Extremely unfavourable seepage flow inside the backfill, perhaps due to heavy rainfall, will dramatically increase active earth pressure while reducing passive earth pressure, thus increasing the probability of instability of the retaining structure. A trial and error analysis based on limit equilibrium is applied to identify the optimum failure surface. The flow field is computed using Fourier series expansion, and the effective reaction force along the curved failure surface is obtained by solving a modified Kötter equation considering the effect of seepage flow. This approach correlates well with other existing results. For small values of both the internal friction angle and interface friction angle, the failure surface can be appropriately simplified with a planar approximation. A parametric study indicates that the degree of anisotropic seepage flow affects the resulting passive earth pressure. In addition, incremental increases in the effective friction angle and interface friction angle both lead to an increase in passive earth pressure.

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

“…Therefore, the impermeable layer at y = 0 was adopted instead of the lower impermeable layer. Bearing all of these considerations in mind, the boundary conditions applied in Hu et al (2018) are valid and applicable in engineering practice.…”

“…For the cases of larger values of effective internal friction angle of the soil, , and soil-wall interface friction angle, ␦, the dis-cusser speculates that the curved failure surface would extend below the heel of the retaining wall. Fortunately, such a scenario would not happen during passive failure following the iterative procedure presented in Hu et al (2018). Through a few attempts by the iterative procedure, several curved surfaces (characterized by two angles v and cr ) can be obtained within a prescribed tolerance, which is set as 0.1% of the mean value of P p obtained using eqs.…”

“…It is worth noting that a simplified procedure considering the planar failure surface was also presented in Hu et al (2018), to validate and optimize the complex implementation procedure used in the curved failure surface. The analytical solution to the distribution of the effective reactive pressure, p=, and pore-water pressure, u, along the planar failure surface can be directly obtained by solving the Laplace equation and the modified Kötter (1903) equation.…”

“…We would like to thank the discusser (Ganesh 2019) for his interest and comments on our recent paper (Hu et al 2018), which addressed primarily the detrimental effects of anisotropic seepage flow on passive earth pressure acting on a retaining wall, when the more realistic curved failure surface in the backfill is assumed in the calculations. The main issues raised by the discusser include (i) clarification of the boundary conditions, (ii) determination of the curved failure surface, and (iii) applications of the proposed method.…”

Buoyancy Force Acting on Underground Structures considering Seepage of Confined Water

“…Seepage leads to a change in the force acting on underground structures because of the change in the pore pressure. The complex foundation-soil-water interaction behaviour is not fully understood [17][18][19][20][21][22][23][24]. Studies on the effect of seepage on the buoyancy force acting on underground structures are limited.…”