As urban areas expand, the demand for resilient infrastructure has sparked a surge in the planning and development of roads, rail networks, and ports. This growth also drives the implementation of ground improvement techniques essential for sustainable, large-scale construction on challenging terrains like soft, unstable subsoil and fractured rock masses.
At the forefront of these advancements, Tetra Tech Coffey’s Senior Principal, Dr. Ching Dai, joined industry leaders at the 5th International Conference on Transportation Geotechnics (ICTG2024) in Sydney. Presenting his paper, “Evaluating the Necessity of Sliding Mechanisms in Trapezoidal MSE Wall Design,” Ching contributed to discussions on optimising design methodologies for more efficient, stable infrastructure solutions.
Here Ching shares his latest innovative extension to the state of practice in transportation geotechnics.
About the research
The paper addresses a specific geotechnical design challenge: determining whether a sliding mechanism is necessary for trapezoidal Mechanically Stabilised Earth (MSE) walls, especially in contexts where traditional MSE wall designs would require extensive vertical excavation.
The study explores replacing traditional rectangular MSE wall reinforcements with trapezoidal ones to optimize construction efficiency and cost, especially when such walls are constructed in front of slopes or existing walls. While conventional design standards generally require sliding mechanisms, the clarity around their necessity for trapezoidal configurations is limited, prompting this research.
Using finite element analysis, the study examined the lateral earth pressures on trapezoidal MSE walls and assessed the factor of safety (FOS) for sliding stability. The findings suggest that trapezoidal walls may naturally exhibit high sliding stability, potentially making sliding mechanisms redundant. Design charts were developed to help engineers assess the need for sliding mechanisms under different conditions, such as varying friction angles and trapezoidal wall slopes.
A practical application of this design was tested on a highway embankment widening project showing that the trapezoidal MSE wall-maintained stability without a sliding mechanism. Stability was validated through construction monitoring, highlighting that trapezoidal MSE walls might achieve adequate stability against lateral forces, offering a cost-effective and constructible solution for similar infrastructure projects.
How does this address the design challenge?
The primary design challenge addressed here is the uncertainty in applying sliding mechanisms to trapezoidal MSE walls. Standard guidelines do not explicitly address trapezoidal wall geometry, leading designers to adopt conventional sliding checks by default. This study challenges this approach by providing evidence that sliding mechanisms may not be essential for trapezoidal MSE walls, depending on specific site conditions. This insight could influence future standards, making trapezoidal MSE wall designs more widely applicable without compromising stability.
What are some of the core challenges your research is addressing?
A sliding mechanism is traditionally considered necessary for trapezoidal MSE walls due to concerns about lateral earth pressure, which can cause horizontal displacement if not adequately resisted. Here’s why this becomes a consideration, particularly when vertical excavation is involved:
Lateral Earth Pressure and Stability: MSE walls retain soil, which exerts lateral pressure. In conventional, rectangular MSE walls, this pressure is resisted by friction between the base and the foundation, along with the wall’s own weight. Sliding mechanisms are incorporated as a safety measure to prevent lateral movement, which could undermine the stability of the wall.
Geometric Influence of Trapezoidal Walls: Trapezoidal MSE walls, with sloping reinforcement, differ from rectangular walls in that they lack the uniform resistance profile of a vertical, rectangular cut. This irregular geometry might redistribute lateral forces differently, potentially reducing the resistance against sliding. For this reason, designers often default to including sliding mechanisms, as this aspect is not always thoroughly addressed in conventional guidelines.
Reducing risk of horizontal movement: Without a sliding mechanism, there’s a perceived risk that trapezoidal MSE walls could shift under pressure if the friction at the base and the weight aren’t sufficient to counteract lateral earth pressures. Adding a sliding mechanism or at least performing sliding checks is traditionally viewed as a way to minimize this risk, especially in areas with poor soil conditions or where additional lateral support is needed.
Under certain conditions (e.g., high base friction and specific wall slopes), trapezoidal MSE walls may inherently resist sliding well enough that these mechanisms aren’t always required. However, the conventional inclusion of sliding mechanisms remains a cautious approach to ensure stability across diverse site conditions.
For more information in relation to this technical paper, contact the author.
Connect with Ching Dai | Senior Principal, Tetra Tech Coffey at [email protected]
About the event
ICTG2024 served as a pivotal gathering, drawing together experts dedicated to advancing sustainable, technology-driven solutions for urban transport infrastructure. The event highlighted the global challenges of transportation infrastructure and underscored the innovative paths forward in geotechnical engineering. Vist the event website 5th ICTG (2024) | 20-22 November 2024