Analysis and Behaviour of Curved Retaining Walls in Black Cotton Soil using PLAXIS 3D

Abstract

In this research paper, the main focus is understanding the 3D finite element analysis and behaviour of non-circular curved retaining wall when compared to conventional straight retaining wall using black cotton soil. As retaining walls constructed in highly expansive soils, such as Black Cotton soil, frequently suffer from severe lateral displacement and structural instability. This study evaluates the reduction in lateral displacements and bending moments achieved by utilizing an arched geometry. Utilizing PLAXIS 3D software, numerical models were developed by diaphragm walls which help to simulate a 10m deep excavation. A curve-in-plan retaining wall is an alternative design to the traditional straight retaining wall, specifically intended for use in situations involving very deep excavations. It is found that such curved shape helps to reduce displacements when compared to straight retaining walls.

Introduction

This study investigates the behavior and performance of straight and curved embedded retaining walls in expansive Black Cotton soil using 3D finite element analysis (PLAXIS 3D). The research compares conventional straight cantilever retaining walls with curved diaphragm retaining walls to evaluate their structural stability and deformation characteristics.

Introduction

Retaining walls are structures designed to hold back soil where there is a sudden change in ground elevation. They resist the lateral earth pressure exerted by retained soil, which tends to cause sliding and overturning. Their stability depends on soil properties such as cohesion, internal friction angle, and wall movement. Retaining walls are widely used in highways, dams, railways, tunnels, harbors, mines, and other civil engineering projects.

The study focuses on two retaining wall types:

• Cantilever Embedded Retaining Wall: Resists overturning through passive earth pressure developed below the embedded depth. Proper design minimizes wall movement and protects nearby structures.
• Curved Retaining Wall: Uses arch action to distribute lateral soil pressure toward the ends of the wall, reducing horizontal deflection. Curved diaphragm walls have fewer joints, making them suitable for deep excavations in expansive soils.

Literature Review

Previous studies have highlighted the advantages of curved retaining walls and advanced numerical modeling:

• Chavan & Sharma (2017): Used PLAXIS 2D to analyze straight retaining walls in Black Cotton soil. Conventional walls showed poor stability due to swelling and shrinkage of expansive soil.
• Gilmore & Fuentes (2017): Demonstrated that curved retaining walls reduce horizontal displacement by 15–25% compared with straight walls because of arch action.
• Zhang & Zhang (2001): Proposed cantilever arched retaining walls, showing that arch-beam behavior reduces deformation and construction costs.
• Schweiger et al. (2009): Compared 2D and 3D finite element analyses and concluded that 3D modeling is essential for accurately predicting wall deformation and ground settlement in complex excavations.

Modeling Methodology

The research employs PLAXIS 3D to simulate straight and curved diaphragm retaining walls embedded in Black Cotton soil.

Soil Model

A 100 m × 100 m × 50 m soil domain is created with:

• Mohr-Coulomb constitutive model
• Drained soil behavior
• Black Cotton soil properties including:
  • Unit weight
  • Young's modulus
  • Poisson's ratio
  • Cohesion (30 kN/m²)
  • Friction angle (17°)

The groundwater table is placed at the bottom of the model to eliminate pore-water pressure effects.

Retaining Wall Geometry

Both wall types have:

• Length: 30 m
• Retained height: 10 m
• Embedded depth: 10 m

The curved wall is modeled as a parabolic arch with a 2 m rise.

Both wall geometries are extruded to form 20 m deep diaphragm walls.

Structural Components

The model includes:

• Diaphragm wall plates (1 m thick reinforced concrete)
• Capping beams along the wall top
• Steel props connecting opposite walls to improve excavation stability

Elastic material properties are assigned to each structural element based on stiffness, density, and moment of inertia.

Research Objective

The primary objective is to compare straight and curved retaining walls under identical soil and loading conditions to determine whether curved diaphragm walls can:

• Reduce lateral wall deflection.
• Improve overall stability.
• Minimize dependence on internal support systems.
• Perform better in expansive Black Cotton soil.

Conclusion

Based on 3D finite element analysis conducted in PLAXIS 3D, the following conclusion are found regarding the behaviour of retaining walls in expansive Black Cotton Soil. 1) Inefficiency of Straight Walls: Straight diaphragm walls are structurally inefficient in highly expansive soil as it suffer from severe displacement (up to 58.13mm). Which in practical applications require massive concrete thickness to prevent failure. 2) Superiority of Curved Geometry: After modifying the wall geometry to a non-circular curved or arch drastically improves structural stability and also capitalizes on 3D spatial soil structure interactions. 3) Displacement Reduction: The arched geometry successfully reduces the maximum lateral displacement by 25.71% (from 58.13mm to 43.18 mm), And also reduced the maximum bending moment by 4.17% (from 344.6 KN-m to 330.2 KN-m).

References

[1] Sandip M Chavan, Dr. Vijay Sharma, “Behaviour of Retaining Wall in Black Cotton Soil”, International Research Journal of Engineering and Technology (IRJET), Volume: 04 Issue: 07, July 2017, Pp: 780-784. [2] Daniel Gilmore, Raul Fuentes, “Predicting the behaviour of non-circular, curved-in-plan retaining walls using the trial load method”, 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul, 2017, Pp: 1987-1990. [3] Zhang, Y. P., & Zhang, T. Q., Behaviour Analysis of Cantilever Arched Retaining Structures in Foundation Pits,\" Journal of Zhejiang University (SCIENCE), Volume: 2, No. 3, Pp: 309-312. [4] H. F. Schweiger, F. Scharinger, & R. Lüftenegger, “3D finite element analysis of a deep excavation and comparison with in situ measurements” Geotechnical Aspects of Underground Construction in Soft Ground, Taylor & Francis Group, Pp: 193-199. [5] Plaxis 3D Connect Edition V20 | Tutotial Manual [6] Table 2: The Properties used for Black cotton soil, Source: Sandip M Chavan, Dr. Vijay Sharma, “Behaviour of Retaining Wall in Black Cotton Soil”, Pp:781 [7] Table 3: Dimensions of the wall, Source: Daniel Gilmore, Raul Fuentes, “Predicting the behaviour of non-circular, curved-in-plan retaining walls using the trial load method”, Pp: 1989 [8] Table 5,6: The Properties used for Diaphragm Wall, Capping Beam, Source: BS EN 1991-1-1:2002, The Concrete Society, [No date], Goh, 1993 and Richards and Powrie, 1994. [9] Table 7: The Properties used for Steel Prop, Source: EN 1993-1-1:2005, Geocentrix, 2004.

Copyright

Copyright © 2026 Aditya Raghuwanshi, Dr. Raghvendra Singh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.