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, Rigid Inclusions, Embedded beam, Consolidation, Embankment

 

Rigid inclusions are a ground improvement technique used to enhance the bearing capacity and reduce the settlement of weak, compressible soils. This method involves installing high-modulus columns, typically made of concrete or grout, into the ground. These columns are significantly stiffer than the surrounding soil and help distribute loads more effectively.

Ideally, the modelling of embankment with rigid inclusions should be performed in PLAXIS 3D which provides the most realistic representation of the geometry and load/stress distribution between inclusions and soil. 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 deals with the 2D analysis of an 8 m high embankment constructed and stabilized with 8 m long rigid inclusions with a diameter of 0.38 m installed in a square pattern installed at 1.9 m spacing. The subsoil consists of three soft layers (1.5 m peat layer in between a 2.5 m and a 2 m alluvium layers). A stiff dense sand layer underlies the three top soft formations and extends to a depth of 20 m below the ground surface (see Figure 1).

 

The 2D analysis of slender elements like rigid inclusions requires the use of 2D embedded beam elements. The special interface elements used with embedded beams enhance the modelling of soil-structure interaction, capturing both skin resistance and foot resistance more accurately providing a more realistic simulation. Although the analysis is in 2D, embedded beams can somewhat account for 3D effects, but this requires the calibration of 2D embedded beam interface elements to obtain a realistic distribution of axial force within the inclusions.

In this context, a companion exercise entitled “Calibration of an Embedded Beam for the 2D Plane Strain Analysis of an Embankment with Rigid Inclusions” is provided first. It deals with the calibration of the embedded beam material parameters in a unit cell plane strain model until perfectly matching the results of a reference axisymmetric mode in which the rigid inclusions have been modelled as solid elements. The calibrated parameters will be used in the framework of this 2D analysis.