Analysis of water seepage in a pavement system using the particulate approach

A particulate model has been developed to analyze the effects of transient and steady state seepage of water through a randomly-packed coarse-grained soil as an alternative to conventional seepage analysis based on continuum models. In this model, the soil skeleton and the pore water are volumetrically coupled in the transient and steady-state conditions. The concept of relative density has been used to define different compaction levels of the soil layers forming a pavement filter system and observe the seepage response to compaction. First, Monte–Carlo simulation is used to randomly pack discrete spherical particles from a specified particle size distribution (PSD) to achieve a desired relative density based on the theoretical minimum and maximum void ratios. Then, a water pressure gradient is applied across one two-layer unit to trigger water seepage. The interstitial pore water motion is idealized using Navier–Stokes (NS) equations with provision to incorporate the drag forces acting between the pore fluid and soil particles. The NS equations are discretized using finite differences and applied to discrete elements in a staggered, structured grid. The model predicted hydraulic conductivities are validated using widely used equations.Critical water velocities, hydraulic gradients and flow within the randomly-packed soil layers are identified under both steady state and transient conditions. Significantly critical transient conditions are observed prior to reaching the steady-state conditions. Moreover, any localized poorly-compacted areas are seen to be subjected to excessive hydraulic gradients and hence, higher likelihood of erosion. Since, the reported research effort involves modeling of the very properties that cause instability of earthen structures such as seepage induced piping, internal erosion and uplift in a particulate medium, it can be envisioned that the current results would provide insight into issues concerning the malfunction of earthen structures.