Application	PLAXIS 2D
Version	PLAXIS 2D 2024.1 and later
Date created	22 October 2024
Date modified	22 October 2024
Original author	Richard WITASSE - Principal Application Engineer
Keywords	PLAXIS 2D, Soil improvement, Stone columns, Consolidation, Embankment

 

Stone columns are a ground improvement technique used in geotechnical engineering. They involve creating vertical columns of compacted stone or gravel in the soil. These columns enhance the load-bearing capacity of the soil, reduce settlement, and improve drainage.

Ideally, the modelling of embankment with stone columns should be performed in PLAXIS 3D as it provides a more accurate representation of the complex interactions between the stone columns and the surrounding soil leading to better predictions of settlement, load-bearing capacity, and overall performance. Despite the advantages of 3D analysis, many engineers still rely on 2D analyses as it is generally simpler and faster to set up and run compared to 3D analyses and are less expensive in terms of both software and computational resources. This makes it more accessible, especially for smaller projects or firms with limited budgets.

This exercise concerns the analysis of a 6 m high embankment constructed and stabilized with 10 m long stone columns with a diameter of 0.8 m installed in a square pattern installed at 2.5 m spacing. The subsoil consists of three soft layers. On top a 2.0 m peat layer overlays an 8 m soft clay layers and a stiff dense sand layer underlies the two top soft formations and extends to a depth of 15 m below the ground surface (see Figure 1).

 

The 2D plane strain analysis of stone column implies a representation of their geometry as strip elements the thickness of which must be set such as to provide a similar behaviour as in their real effective 3D group configuration. In this context, a companion exercise entitled “Calibration of a Plane Strain Unit Cell Model for the Analysis of Stone Columns Reinforcement” deals with the calibration of a unit cell plane strain model, the purpose of which is to match the results of a reference axisymmetric model. This calibration process enables the definition of the equivalent stone column strip thickness and the reduced vertical permeability values for the peat and soft clay layers to be used in the 2D plane strain embankment model.