Estimation of Drain Pipe Effects Using Electrical Prospecting and Unsaturated Soil/Water Coupled Analysis

Abstract

Elevation of the phreatic surface causes instability in earth structures. Therefore, drainage systems are important in constructing an earth structure. Drain pipes are a drainage system applicable even for an existing earth structure. However, it is difficult to estimate the effects of the drain pipe quantitatively, and design and construction of the drain pipe is conducted based on past experience. In this study of railway embankment with installed drain pipes, electrical prospecting of the phreatic surface and seepage analysis was conducted. In the seepage analysis, a ‘permeable boundary’ was newly applied to express the effects of the drain pipe for the existing unsaturated soil/water coupled analysis code. Consequently, the permeable boundary was validated for expressing the effects of the drain pipe. Preliminary seepage analysis on the installed drain pipe enabled us to design the optimum array and/or insertion length of the drain pipes.