Earth Retaining Structures Design

A retaining wall is a structure designed to resist the lateral pressure of soil or other materials, preventing them from sliding, collapsing, or eroding. These walls are typically used to support and stabilise slopes, prevent soil erosion, and manage changes in ground elevation, particularly in areas where a slope or embankment would otherwise be unstable. Atlas Engineering & Technology Group (AETG) can provide effective solutions, testing techniques and methods of analysis to meet clients needs in challenging and diverse environments. 

Key Functions of a Retaining Wall Design

  • Resisting Lateral Earth Pressure: A retaining wall resists the horizontal pressure exerted by the soil or material behind it, preventing it from sliding or falling.
  • Preventing Erosion: By stabilising the soil, retaining walls can reduce the risk of erosion caused by wind, water, or gravity.
  • Levelling Slopes: They can create level platforms or terraces on sloped terrain, making it more suitable for construction or landscaping.
  • Controlling Water Flow: In some cases, retaining walls can help manage water runoff or groundwater, reducing the risk of slope failure due to water saturation.

Types of Retaining Structures AETG Work With

  1. Gravity Retaining Walls: These rely on their weight to resist the pressure of the soil behind them. Made of heavy materials like concrete, stone, or brick, gravity walls do not require reinforcement or anchoring.
  2. Cantilevered Retaining Walls: These are made from reinforced concrete and use a cantilever design (a wall with a base slab and stem). They resist earth pressure by transferring the load to the base.
  3. Counterfort Walls: Similar to cantilevered walls but with counterforts (diagonal braces) added to the back of the wall for additional support. These are typically used for taller walls where additional reinforcement is needed.
  4. Anchored Retaining Walls: These walls are secured by cables or rods anchored into the ground or bedrock behind them. They are typically used for high walls or in locations where space is limited.
  5. Reinforced Soil Walls: These walls are constructed with layers of geogrids, geotextiles, or other reinforcing materials, along with the soil, to provide additional strength and stability.
  6. Modular Block Walls: Made from large, interlocking blocks of concrete or stone, modular walls are easy to construct and can be used for various landscaping or engineering projects.
  7. Gabion Walls: Made from wire mesh cages filled with rocks, stones, or other materials. The wire mesh cages (gabions) are stacked and connected together to form a flexible and durable structure.
  8. Soil Nail Wall: This technique used to reinforce and stabilize soil or rock masses, especially in situations where excavation or slope failure is a concern. It involves inserting steel rods or bars into the ground to provide lateral support and resist forces acting on the slope or soil mass.
  9. MSE Wall: Mechanically Stabilized Earth (MSE) walls are retaining structures made up of alternating layers of soil and reinforcement materials that are used to retain soil in applications where conventional gravity or cantilever retaining walls may not be feasible.

Considerations in Earth Retention Structures Design:

Soil Properties:

  • Cohesion (c): The internal force that holds soil particles together.
  • Angle of Internal Friction (φ): The resistance of soil to sliding along a failure plane.
  • Unit Weight of Soil (γ): The weight of the soil per unit volume, influencing the pressure exerted on the structure.
  • Pore Water Pressure: The water content within the soil that can influence the effective stress and stability.

Forces Acting on the Retaining Structure:

  • Active Earth Pressure: The pressure exerted by soil on the wall when the wall moves away from the soil (expansion of the soil mass).
  • Passive Earth Pressure: The pressure exerted by soil when the wall moves into the soil (compression of the soil mass).
  • Water Pressure: Any water build-up behind the retaining wall due to poor drainage or groundwater can add additional lateral load.
  • Seismic Forces: Earthquake-induced forces that can influence the stability of the structure, particularly in seismic zones.
  • Dead Loads: The weight of the wall itself and any additional loads (such as a structure or surcharge load) placed on top of the retaining wall.

Factor of Safety (FoS):

  • A safety factor is applied to ensure that the retaining structure can withstand the expected loads without failure. A typical factor of safety ranges from 1.5 to 2.0, depending on the type of structure, material, and loading conditions.

Why Choose AETG for Earth Retaining Structures Design?

The design of earth-retaining structures is a crucial aspect of geotechnical engineering, involving detailed analysis of the forces acting on the structure and the stability of the surrounding soil. By combining principles of structural design with soil mechanics, our engineers ensure that the retaining walls function safely and effectively and are constructed in accordance with Australian Standard AS4678. Different types of retaining walls offer various benefits depending on the application, height, and soil conditions, and the design must be customised to address the unique requirements of each project. Contact Atlas Engineering & Technology Group today to see how we can help with the needs of your project.

Successfully Completed Jobs by AETG to Date

✔ Proposed infrastructure Construction - Warf Rd, Melrose Park NSW

An excavation inspection report was prepared for the above mentioned site to assess the stability of a deep excavation and its need for shoring. The report evaluates the stability and structural integrity of excavations for proposed manholes C and D, which reached depths of 5.40 m and 6.50 m, respectively. Based on visual inspections, geological analysis, and client-provided documentation, the report concludes that the shoring systems are properly embedded into competent bedrock (Hawkesbury Sandstone and Ashfield Shale) and deemed safe for personnel entry, provided the load within the influence zone stays within design limits.

✔ Proposed Pavement Upgrade - Mulgoa Rd, Regentville NSW

The Excavation Inspection Report, prepared by AETG for Ferrycarrig Construction Pty Ltd, documents a geotechnical assessment conducted at Hatchinson Ave, Jamisontown, as part of the Mulgoa Road Upgrade project. The inspection evaluated the stability of a 3.0 m deep excavation within silty clay soils, concluding that the existing shoring and 1:1 benching were adequate for personnel entry. The report provides safety recommendations, including maintaining a 1.5 m buffer zone from excavation edges, minimising nearby vibrations, and retaining shoring supports. The findings are valid for up to two weeks post-inspection, subject to weather conditions and site changes.