Evaluation of Deformation Characteristics of Soil Ground against Ground Cave-in Caused by Damaged Pipe using Generalized Interpolation Material Point Method (GIMP)

Abstract

As the number of ground cave-in occurred in Seoul and the social costs associated with the ground cave-ins are increasing, the ground cave-ins are in the spotlight as one of the major ground hazards which can be occurred in urban area. Most of the ground cave-ins occurred in urban area is mainly due to damaged sewer pipe. If there is a crack on a sewer pipe, water flows out of the crack when the damaged sewer pipe is filled with water. After that, water flows into the crack with soil around the sewer pipe. As this process repeating, a cavity is formed near the sewer pipe and this can finally lead to a ground cave-in. When unsaturated ground becomes saturated due to water discharged from a sewer pipe, shear strength of soil decreases and it makes a cavity unstable. In this study, model tests and numerical analysis are performed to investigate the effect of decrease in shear strength of soil induced by the saturation of ground on the formation of a ground cave-in. Unlike model tests which performed by repeating water inflow and outflow, the process of water leakage from the model ground was skipped to investigate the effect of reduction in shear strength of soil and to exclude the effect of seepage force during water leakage. Problems involving large deformation such as a ground cave-in are not properly solved using the finite element method (FEM) as a result of mesh related problems. Generalized interpolation material point method (GIMP) in which the body is discretized into finite number of material points was used in this study as an alternative to FEM. Though there are differences between the model test and numerical simulation caused by boundary conditions, incomplete saturation, and exclusion of seepage analysis, similar ground deformation characteristics are observed in the model test and numerical simulation