One method of soil stabilization for potentially liquefiable sites is the use of a system of vertical drains to dissipate the excess pore water pressure generated by earthquake loading, thus avoiding liquefaction. Performance assessments for these systems require the estimation of vertical drain spacing such that a maximum threshold level of excess pore pressure ratio is not exceeded. FEQDrain can be used to analyze three dimensional pore pressure generation and dissipation in layered sand deposits with geocomposite vertical drains for liquefaction mitigation. FEQDrain has four different modes in which to analyze a problem. Option 1 considers the performance of a soil profile without any ground improvement (i.e. no drain is installed). Pore pressure generated by the earthquake can only migrate in a vertical direction. Option 2 examines soil layers with a perfect drain that dissipates any pore pressure that reaches it. Option 3 examines soil layers with a drain, but with constant values of vertical and horizontal hydraulic conductivity within the drain. Option 4 examines soil layers with a drain with properties guiding the nonlinear resistance that water will feel as it flows into and through the drain. This option can also include the presence of a reservoir to collect water rising through the drain.
