Simulation of Stone Column Ground Improvement (Comparison between Axisymmetric and Plane Strain)

Maryam Gaber,Anuar Kasa,Norinah Abdul-Rahman,Jamal Alsharef

doi:10.3844/ajeassp.2018.129.137

Abstract

Most of the numerical studies on stone columns are based on the unit cell concept. However, the impact of interactions between adjacent columns and between the columns and the surrounding soil has not been investigated thoroughly. In this study, the finite element software, PLAXIS-2D-V8.2, was used to simulate a stone column as a unit cell and as a plane strain model in order to specify the difference between the performances of each model. The key factors that were investigated included the diameter and c/c spacing of the stone columns, friction angle of the stone column material and undrained cohesion of the soft soil. The emphasis of this parametric study was on the settlement improvement factor and excess pore water pressure, since these are critical to the design of stone columns. The main findings of this study were that in the plane strain model, the settlement improvement factor ranged between 2.2 and 3.2, which means that the settlement was improved more than twice. Meanwhile, in the unit cell concept, the settlement improvement factor did not exceed 1.53. The results of the settlement improvement were compared with the theoretical solutions that are commonly used for studies into the behaviour of stone columns. The unit cell model showed a lower peak value of excess pore water pressure than the plane strain model.

Highlights

Ground improvement techniques have been used in many difficult foundation sites throughout the world to increase the bearing capacity, reduce the settlement, improve the slope stability and to resist liquefaction
According to Dheerendra Babu et al (2013), there are five main numerical approaches to the modelling of stone columns: (i) The axisymmetric model, which is a “unit cell” comprised of only one column and the surrounding soil (Balaam and Booker, 1981); (ii) the plane strain model, where the cylindrical columns are modelled as stone trenches, which are used extensively under long loads, such as embankments (Van Impe and De Beer, 1983); (iii) the axial symmetry technique, where stone rings are modelled instead of cylindrical columns in order to simulate the columns under circular loads such as tanks
The current study focused on the impact of the selected model on the behaviour of stone columns by a direct comparison between the unit cell and plane strain approaches

Summary

Introduction

Ground improvement techniques have been used in many difficult foundation sites throughout the world to increase the bearing capacity, reduce the settlement, improve the slope stability and to resist liquefaction. The study focused on some factors that impacted both the Settlement Improvement Factor (SIF) and excess pore water pressure in the unit cell and plane strain models.

Results

Conclusion